Altering Conversion and Product Selectivity of Dry Reforming of Methane in a Dielectric Barrier Discharge by Changing the Dielectric Packing Material

We studied the influence of dense, spherical packing materials, with different chemical compositions, on the dry reforming of methane (DRM) in a dielectric barrier discharge (DBD) reactor. Although not catalytically activated, a vast effect on the conversion and product selectivity could already be observed, an influence which is often neglected when catalytically activated plasma packing materials are being studied. The α-Al2O3 packing material of 2.0–2.24 mm size yields the highest total conversion (28%), as well as CO2 (23%) and CH4 (33%) conversion and a high product fraction towards CO (~70%) and ethane (~14%), together with an enhanced CO/H2 ratio of 9 in a 4.5 mm gap DBD at 60 W and 23 kHz. γ-Al2O3 is only slightly less active in total conversion (22%) but is even more selective in products formed than α-Al2O3. BaTiO3 produces substantially more oxygenated products than the other packing materials but is the least selective in product fractions and has a clear negative impact on CO2 conversion upon addition of CH4. Interestingly, when comparing to pure CO2 splitting and when evaluating differences in products formed, significantly different trends are obtained for the packing materials, indicating a complex impact of the presence of CH4 and the specific nature of the packing materials on the DRM process.


Introduction
An increasing energy and resource demand from a growing population and the impact it has on the environment, necessitate enhancing the share of renewable energy and replacing (part of the) fossil fuels, by recycling waste streams. These challenges have given the incentive for new methodologies that allow converting (two) greenhouse gasses (CO 2 and CH 4 ) into value added chemicals (like syngas, basic chemicals) and fuels [1,2].
Although syngas (CO and H 2 ) can be obtained in a two-step process, where hydrogen is added to CO-originating from CO 2 splitting into CO and O 2 -it is much more efficient to produce it directly through dry reforming of methane (DRM) in a one-step process, with the possibility of directly forming higher hydrocarbons [3,4]. A recent study suggests that, together with the Fischer-Tropsch process, DRM is economically the most promising method for CO 2 conversion [5]. Indeed, when executing thermal DRM, a conversion of 100% can be reached (accompanied by an energy efficiency of 60%) or a maximum energy efficiency of 70% (of the thermal thermodynamic optimum for syngas formation), coinciding with a conversion of 83% [1]. These high values for conversion and energy efficiency are a definite advantage of thermal DRM but require a high temperature (900-1200 K) and a catalyst. 1 fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh

•
For the non-packed reactor at 192 mL/min, the order is: eth • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphe > propane (formaldehyde in case of BaTiO3). Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  , T gas CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) bu fractions. Indeed, although the CO fraction is similar, a obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the d Furthermore, the BaTiO3 packing with smallest bead s substantial fraction of formaldehyde and produces overa including higher amounts of DME, compared to the other m When looking more closely to the results, four differen account the four largest component fractions (excluding CO

•
For the non-packed reactor at 50 mL/min and all α-A propane > ethyne.
• For the non-packed reactor at 192 mL/min, the order is • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 s > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much small the packing material and size, as detailed in Table 4.
, P do not only see differences in conversion (cf. Figure 5 and Table 3), cau CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also interest fractions. Indeed, although the CO fraction is similar, a larger fraction obtained for the γ-Al2O3 packing, while the fractions of ethyne and formaldehyde, DME and methanol do not even reach the detection limits Furthermore, the BaTiO3 packing with smallest bead size is the only substantial fraction of formaldehyde and produces overall relatively m including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can be account the four largest component fractions (excluding CO, which is alw

•
For the non-packed reactor at 192 mL/min, the order is: ethane > H2 > • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spheres, the or > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, show clear the packing material and size, as detailed in Table 4. Conversion same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh
• For the non-packed reactor at 192 mL/min, the order is: eth • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphe > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w
• For the non-packed reactor at 192 mL/min, the order is: eth • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphe > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4. Conversion impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The αor γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh
• For the non-packed reactor at 192 mL/min, the order is: eth • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphe > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.

when power
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 s propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: ethan • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphere > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4. and discharge length but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 th impact on the product fractions. Moreover, in case of BaTi have a clear impact, while this is much less visible for Zr fractions of ethyne are envisioned, the smallest size of the The αor γ-Al2O3 packing seems to produce the highest C same time producing substantially less dehydrogenated hy When comparing the different types of Al2O3 support do not only see differences in conversion (cf. Figure 5 and CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) bu fractions. Indeed, although the CO fraction is similar, a obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the d Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces over including higher amounts of DME, compared to the other When looking more closely to the results, four differen account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α-A propane > ethyne.
• For the non-packed reactor at 192 mL/min, the order is • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smal the packing material and size, as detailed in Table 4.
Cokes: small on inner electrode 13% [43] 4.5, 3.5, 2.5 or 2 60 50 17.67 26.5 kHz 72 Conversion roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formati but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The αor γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a large obtained for the γ-Al2O3 packing, while the fractions of et formaldehyde, DME and methanol do not even reach the detect Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh
• For the non-packed reactor at 192 mL/min, the order is: etha • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spher > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.   Conversion also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 ove roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons. Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a large obtained for the γ-Al2O3 packing, while the fractions of et formaldehyde, DME and methanol do not even reach the detect Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rel including higher amounts of DME, compared to the other mater When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.

when # contact points
Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially o H (originating from CH4) preferentially takes part in the forma but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and Ta CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a lar obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions ( Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4. , void space volumes materials, the relative amount of CO versus higher hydroc Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes an to above 9, which is quite striking, because the ratio of CH4 o roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that t impact on the product fractions. Moreover, in case of BaTiO3 have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the Si The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydr When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other ma When looking more closely to the results, four different tr account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller the packing material and size, as detailed in Table 4. and bead/gap size ratio and for the non-packed reactors. Moreover, by altering th materials, the relative amount of CO versus higher hy Indeed, the CO product fraction can vary from about 53 also the obtained CO/H2 ratio for the different sphere size to above 9, which is quite striking, because the ratio of C roughly 1 and 2. It indicates that the majority of C (especi H (originating from CH4) preferentially takes part in the f but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 t impact on the product fractions. Moreover, in case of BaT have a clear impact, while this is much less visible for Z fractions of ethyne are envisioned, the smallest size of th The αor γ-Al2O3 packing seems to produce the highest C same time producing substantially less dehydrogenated h When comparing the different types of Al2O3 suppo do not only see differences in conversion (cf. Figure 5 an CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) b fractions. Indeed, although the CO fraction is similar, obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces ove including higher amounts of DME, compared to the othe When looking more closely to the results, four differe account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order • For the smallest ZrO2 and BaTiO3 spheres and all SiO > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much sm the packing material and size, as detailed in Table 4.  Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydrocar Indeed, the CO product fraction can vary from about 53% up t also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 ove roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The αor γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a large obtained for the γ-Al2O3 packing, while the fractions of et formaldehyde, DME and methanol do not even reach the detect Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rel including higher amounts of DME, compared to the other mater When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4. when # contact points extent determined by the flow rate, although the ratio of CH4 o Table 3). Mainly the formation of CO, ethane, ethyne, DME (D to be affected by this. This can be attributed to different for explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the la and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroc Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially o H (originating from CH4) preferentially takes part in the forma but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and Ta  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a lar obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 192 mL/min, the order is: et • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.
, void space volumes general observation for the non-packed reactor. Indeed, it see extent determined by the flow rate, although the ratio of CH4 o Table 3). Mainly the formation of CO, ethane, ethyne, DME (D to be affected by this. This can be attributed to different fo explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the la and for the non-packed reactors. Moreover, by altering the flo materials, the relative amount of CO versus higher hydroc Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes an to above 9, which is quite striking, because the ratio of CH4 o roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that t impact on the product fractions. Moreover, in case of BaTiO3 have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the Si The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydr When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other ma When looking more closely to the results, four different tr account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller the packing material and size, as detailed in Table 4. and bead/gap size ratio general observation for the non-packed reactor. Indeed, i extent determined by the flow rate, although the ratio of C Table 3). Mainly the formation of CO, ethane, ethyne, DM to be affected by this. This can be attributed to differen explained in the Discussion section, because the different Table 4 and Figure 7 clearly show that CO is always t and for the non-packed reactors. Moreover, by altering th materials, the relative amount of CO versus higher hy Indeed, the CO product fraction can vary from about 53 also the obtained CO/H2 ratio for the different sphere size to above 9, which is quite striking, because the ratio of C roughly 1 and 2. It indicates that the majority of C (especi H (originating from CH4) preferentially takes part in the f but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 t impact on the product fractions. Moreover, in case of BaT have a clear impact, while this is much less visible for Z fractions of ethyne are envisioned, the smallest size of th The αor γ-Al2O3 packing seems to produce the highest C same time producing substantially less dehydrogenated h When comparing the different types of Al2O3 suppo do not only see differences in conversion (cf. Figure 5 an CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) b fractions. Indeed, although the CO fraction is similar, obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces ove including higher amounts of DME, compared to the othe When looking more closely to the results, four differe account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order • For the smallest ZrO2 and BaTiO3 spheres and all SiO > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much sm the packing material and size, as detailed in Table 4.  Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.
conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a lar obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 192 mL/min, the order is: et • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.
conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other ma When looking more closely to the results, four different tr account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller the packing material and size, as detailed in Table 4. and bead/gap size ratio do not only see differences in conversion (cf. Figure 5 an CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) b fractions. Indeed, although the CO fraction is similar, obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces ove including higher amounts of DME, compared to the othe When looking more closely to the results, four differe account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order • For the smallest ZrO2 and BaTiO3 spheres and all SiO > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much sm the packing material and size, as detailed in Table 4. have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The αor γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tab  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a large obtained for the γ-Al2O3 packing, while the fractions of et formaldehyde, DME and methanol do not even reach the detect Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rel including higher amounts of DME, compared to the other mater When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh
• For the non-packed reactor at 192 mL/min, the order is: etha • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spher > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.
when # contact points have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and Ta  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a lar obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w
• For the non-packed reactor at 192 mL/min, the order is: et • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.
, void space volumes impact on the product fractions. Moreover, in case of BaTiO3 have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the Si The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydr When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other ma When looking more closely to the results, four different tr account the four largest component fractions (excluding CO,
• For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller the packing material and size, as detailed in Table 4. and bead/gap size ratio Furthermore, it is clear from Table 4 and Figure 7 t impact on the product fractions. Moreover, in case of BaT have a clear impact, while this is much less visible for Z fractions of ethyne are envisioned, the smallest size of th The αor γ-Al2O3 packing seems to produce the highest C same time producing substantially less dehydrogenated h When comparing the different types of Al2O3 suppo do not only see differences in conversion (cf. Figure 5 an CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) b fractions. Indeed, although the CO fraction is similar, obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces ove including higher amounts of DME, compared to the othe When looking more closely to the results, four differe account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α propane > ethyne.
• For the non-packed reactor at 192 mL/min, the order • For the smallest ZrO2 and BaTiO3 spheres and all SiO > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much sm the packing material and size, as detailed in Table 4.
. Impact of the packing material (chemistry and physical), also influenced by setup 19% α-Al 2 O 3 Beads 1.25-2.24 mm Conversion to above 9, which is quite striking, because the ratio of CH4 ove roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3  an  have a clear impact, while this is much less visible for ZrO2  an  fractions of ethyne are envisioned, the smallest size of the SiO2 The αor γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a large obtained for the γ-Al2O3 packing, while the fractions of et formaldehyde, DME and methanol do not even reach the detect Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rel including higher amounts of DME, compared to the other mater When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh
• For the non-packed reactor at 192 mL/min, the order is: etha • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spher > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.
when # contact points also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially o H (originating from CH4) preferentially takes part in the forma but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and Ta CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a lar obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w
• For the non-packed reactor at 192 mL/min, the order is: et • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.

, void space volumes
Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes an to above 9, which is quite striking, because the ratio of CH4 o roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that t impact on the product fractions. Moreover, in case of BaTiO3 have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the Si The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydr When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other ma When looking more closely to the results, four different tr account the four largest component fractions (excluding CO,
• For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller the packing material and size, as detailed in Table 4. and bead/gap size ratio materials, the relative amount of CO versus higher hy Indeed, the CO product fraction can vary from about 53 also the obtained CO/H2 ratio for the different sphere size to above 9, which is quite striking, because the ratio of C roughly 1 and 2. It indicates that the majority of C (especi H (originating from CH4) preferentially takes part in the f but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 t impact on the product fractions. Moreover, in case of BaT have a clear impact, while this is much less visible for Z fractions of ethyne are envisioned, the smallest size of th The α-or γ-Al2O3 packing seems to produce the highest C same time producing substantially less dehydrogenated h When comparing the different types of Al2O3 suppo do not only see differences in conversion (cf. Figure 5 an CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) b fractions. Indeed, although the CO fraction is similar, obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces ove including higher amounts of DME, compared to the othe When looking more closely to the results, four differe account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α propane > ethyne.
• For the non-packed reactor at 192 mL/min, the order • For the smallest ZrO2 and BaTiO3 spheres and all SiO > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much sm the packing material and size, as detailed in Table 4. to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydrocar Indeed, the CO product fraction can vary from about 53% up t also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 ove roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a large obtained for the γ-Al2O3 packing, while the fractions of et formaldehyde, DME and methanol do not even reach the detect Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rel including higher amounts of DME, compared to the other mater When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, wh
• For the non-packed reactor at 192 mL/min, the order is: etha • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spher > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.  Table 3). Mainly the formation of CO, ethane, ethyne, DME (D to be affected by this. This can be attributed to different for explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the la and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroc Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially o H (originating from CH4) preferentially takes part in the forma but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and Ta CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a lar obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w
• For the non-packed reactor at 192 mL/min, the order is: et • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.
, void space volumes extent determined by the flow rate, although the ratio of CH4 o Table 3). Mainly the formation of CO, ethane, ethyne, DME (D to be affected by this. This can be attributed to different fo explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the la and for the non-packed reactors. Moreover, by altering the flo materials, the relative amount of CO versus higher hydroc Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes an to above 9, which is quite striking, because the ratio of CH4 o roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that t impact on the product fractions. Moreover, in case of BaTiO3 have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the Si The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydr When comparing the different types of Al2O3 supports (n do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but a fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other ma When looking more closely to the results, four different tr account the four largest component fractions (excluding CO,
• For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sph > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller the packing material and size, as detailed in Table 4. and bead/gap size ratio general observation for the non-packed reactor. Indeed, i extent determined by the flow rate, although the ratio of C Table 3). Mainly the formation of CO, ethane, ethyne, DM to be affected by this. This can be attributed to differen explained in the Discussion section, because the different Table 4 and Figure 7 clearly show that CO is always t and for the non-packed reactors. Moreover, by altering th materials, the relative amount of CO versus higher hy Indeed, the CO product fraction can vary from about 53 also the obtained CO/H2 ratio for the different sphere size to above 9, which is quite striking, because the ratio of C roughly 1 and 2. It indicates that the majority of C (especi H (originating from CH4) preferentially takes part in the f but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 t impact on the product fractions. Moreover, in case of BaT have a clear impact, while this is much less visible for Z fractions of ethyne are envisioned, the smallest size of th The α-or γ-Al2O3 packing seems to produce the highest C same time producing substantially less dehydrogenated h When comparing the different types of Al2O3 suppo do not only see differences in conversion (cf. Figure 5 an CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) b fractions. Indeed, although the CO fraction is similar, obtained for the γ-Al2O3 packing, while the fractions formaldehyde, DME and methanol do not even reach the Furthermore, the BaTiO3 packing with smallest bead substantial fraction of formaldehyde and produces ove including higher amounts of DME, compared to the othe When looking more closely to the results, four differe account the four largest component fractions (excluding C

•
For the non-packed reactor at 50 mL/min and all α propane > ethyne.
• For the non-packed reactor at 192 mL/min, the order • For the smallest ZrO2 and BaTiO3 spheres and all SiO > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much sm the packing material and size, as detailed in Table 4.  do not only see differences in conversion (cf. Figure 5 and Ta CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but al fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.  When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Ta CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but al fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O propane > ethyne. Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.
, P fractions of ethyne are envisioned, the smallest size of the SiO2 spher The αor γ-Al2O3 packing seems to produce the highest CO/H2 ratios same time producing substantially less dehydrogenated hydrocarbon When comparing the different types of Al2O3 supports (non-poro do not only see differences in conversion (cf. Figure 5 and Table 3), CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also inter fractions. Indeed, although the CO fraction is similar, a larger frac obtained for the γ-Al2O3 packing, while the fractions of ethyne formaldehyde, DME and methanol do not even reach the detection lim Furthermore, the BaTiO3 packing with smallest bead size is the o substantial fraction of formaldehyde and produces overall relativel including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can account the four largest component fractions ( Also the oxygenated fractions, which are much smaller, show c the packing material and size, as detailed in Table 4.  Conversion but also for higher hydrocarbons. Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Ta  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but al fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.

γ-Al2O3
Beads 20-40 mesh silica gel < α-Al2O3 < quartz ≈ γ-Al2O3 < 16% , P roughly 1 and 2. It indicates that the majority of C (especially of CO2) i H (originating from CH4) preferentially takes part in the formation of m but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the type impact on the product fractions. Moreover, in case of BaTiO3 and SiO have a clear impact, while this is much less visible for ZrO2 and α-A fractions of ethyne are envisioned, the smallest size of the SiO2 spher The αor γ-Al2O3 packing seems to produce the highest CO/H2 ratios same time producing substantially less dehydrogenated hydrocarbon When comparing the different types of Al2O3 supports (non-poro do not only see differences in conversion (cf. Figure 5 and Table 3), CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also inter fractions. Indeed, although the CO fraction is similar, a larger frac obtained for the γ-Al2O3 packing, while the fractions of ethyne formaldehyde, DME and methanol do not even reach the detection lim Furthermore, the BaTiO3 packing with smallest bead size is the o substantial fraction of formaldehyde and produces overall relativel including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can account the four largest component fractions (excluding CO, which is Also the oxygenated fractions, which are much smaller, show c the packing material and size, as detailed in Table 4.   and for the non-packed reactors. Moreover, by altering the fl materials, the relative amount of CO versus higher hydro Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes a to above 9, which is quite striking, because the ratio of CH4 roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that impact on the product fractions. Moreover, in case of BaTiO have a clear impact, while this is much less visible for ZrO fractions of ethyne are envisioned, the smallest size of the S The α-or γ-Al2O3 packing seems to produce the highest CO same time producing substantially less dehydrogenated hyd When comparing the different types of Al2O3 supports ( do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the de Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other m When looking more closely to the results, four different account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 50 mL/min and all α-Al propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sp > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smalle the packing material and size, as detailed in Table 4.   Table 3). Mainly the formation of CO, ethane, ethyne, DME (Di to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially o H (originating from CH4) preferentially takes part in the forma but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Ta  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but al fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O propane > ethyne. Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.
when pellet size extent determined by the flow rate, although the ratio of CH4 Table 3). Mainly the formation of CO, ethane, ethyne, DME (D to be affected by this. This can be attributed to different fo explained in the Discussion section, because the different flo Table 4 and Figure 7 clearly show that CO is always the l and for the non-packed reactors. Moreover, by altering the flo materials, the relative amount of CO versus higher hydro Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes an to above 9, which is quite striking, because the ratio of CH4 roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that impact on the product fractions. Moreover, in case of BaTiO3 have a clear impact, while this is much less visible for ZrO2 fractions of ethyne are envisioned, the smallest size of the S The α-or γ-Al2O3 packing seems to produce the highest CO/ same time producing substantially less dehydrogenated hyd When comparing the different types of Al2O3 supports ( do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the det Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other m When looking more closely to the results, four different t account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 50 mL/min and all α-Al propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sp > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smalle the packing material and size, as detailed in Table 4   do not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materia When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whic

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 s propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: ethan • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphere > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sho the packing material and size, as detailed in Table 4.

After activation: conversion
The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O propane > ethyne. Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  Packing: CO 2 conversion Furthermore, it is clear from Table 4 and Figure 7 that the t impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 ra same time producing substantially less dehydrogenated hydrocar When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materia When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whic Also the oxygenated fractions, which are much smaller, sho the packing material and size, as detailed in Table 4. . After activation: conversion H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  Packing: CO 2 conversion Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formation but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the t impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 ra same time producing substantially less dehydrogenated hydrocar When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materia When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whic Also the oxygenated fractions, which are much smaller, sho the packing material and size, as detailed in Table 4.    Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  Packing: CO 2 conversion extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dime to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow rat Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow ra materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formation but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the t impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 ra same time producing substantially less dehydrogenated hydrocar When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materia When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whic Also the oxygenated fractions, which are much smaller, sho the packing material and size, as detailed in Table 4.

After activation: conversion
Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  Before going into more detail on differences for the different general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dime to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow rat Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow ra materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formation but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the t impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 ra same time producing substantially less dehydrogenated hydrocar When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materia When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whic Also the oxygenated fractions, which are much smaller, sho the packing material and size, as detailed in Table 4.

After activation: conversion
Catalysts 2019, 9, x FOR PEER REVIEW Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The αor γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.   When comparing the different types of Al2O3 supports ( do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the de Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other m When looking more closely to the results, four different account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 50 mL/min and all α-Al propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sp > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smalle the packing material and size, as detailed in Table 4.  impact on the product fractions. Moreover, in case of BaTiO have a clear impact, while this is much less visible for ZrO fractions of ethyne are envisioned, the smallest size of the S The αor γ-Al2O3 packing seems to produce the highest CO same time producing substantially less dehydrogenated hyd When comparing the different types of Al2O3 supports ( do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the de Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other m When looking more closely to the results, four different account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 50 mL/min and all α-Al propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sp > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smalle the packing material and size, as detailed in Table 4.  to above 9, which is quite striking, because the ratio of CH4 roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that impact on the product fractions. Moreover, in case of BaTiO have a clear impact, while this is much less visible for ZrO fractions of ethyne are envisioned, the smallest size of the S The αor γ-Al2O3 packing seems to produce the highest CO same time producing substantially less dehydrogenated hyd When comparing the different types of Al2O3 supports ( do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the de Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other m When looking more closely to the results, four different account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 50 mL/min and all α-Al propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sp > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smalle the packing material and size, as detailed in Table 4.    Figure 7 clearly show that CO is always the and for the non-packed reactors. Moreover, by altering the fl materials, the relative amount of CO versus higher hydro Indeed, the CO product fraction can vary from about 53% u also the obtained CO/H2 ratio for the different sphere sizes a to above 9, which is quite striking, because the ratio of CH4 roughly 1 and 2. It indicates that the majority of C (especially H (originating from CH4) preferentially takes part in the form but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that impact on the product fractions. Moreover, in case of BaTiO have a clear impact, while this is much less visible for ZrO fractions of ethyne are envisioned, the smallest size of the S The αor γ-Al2O3 packing seems to produce the highest CO same time producing substantially less dehydrogenated hyd When comparing the different types of Al2O3 supports ( do not only see differences in conversion (cf. Figure 5 and T CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but fractions. Indeed, although the CO fraction is similar, a la obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the de Furthermore, the BaTiO3 packing with smallest bead siz substantial fraction of formaldehyde and produces overall including higher amounts of DME, compared to the other m When looking more closely to the results, four different account the four largest component fractions (excluding CO,

•
For the non-packed reactor at 50 mL/min and all α-Al propane > ethyne.
• For the non-packed reactor at 192 mL/min, the order is: e • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sp > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smalle the packing material and size, as detailed in Table 4.  general observation for the non-packed reactor. Indeed, it seems that th extent determined by the flow rate, although the ratio of CH4 over CO2 c Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dimethylet to be affected by this. This can be attributed to different formation ra explained in the Discussion section, because the different flow rate yield Table 4 and Figure 7 clearly show that CO is always the largest frac and for the non-packed reactors. Moreover, by altering the flow rate (no materials, the relative amount of CO versus higher hydrocarbons or Indeed, the CO product fraction can vary from about 53% up to 72%. also the obtained CO/H2 ratio for the different sphere sizes and materia to above 9, which is quite striking, because the ratio of CH4 over CO2 c roughly 1 and 2. It indicates that the majority of C (especially of CO2) is H (originating from CH4) preferentially takes part in the formation of m but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the type of impact on the product fractions. Moreover, in case of BaTiO3 and SiO2, have a clear impact, while this is much less visible for ZrO2 and α-Al2 fractions of ethyne are envisioned, the smallest size of the SiO2 spheres The αor γ-Al2O3 packing seems to produce the highest CO/H2 ratios (s same time producing substantially less dehydrogenated hydrocarbons When comparing the different types of Al2O3 supports (non-porou do not only see differences in conversion (cf. Figure 5 and Table 3), ca CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also intere fractions. Indeed, although the CO fraction is similar, a larger fracti obtained for the γ-Al2O3 packing, while the fractions of ethyne a formaldehyde, DME and methanol do not even reach the detection limi Furthermore, the BaTiO3 packing with smallest bead size is the on substantial fraction of formaldehyde and produces overall relatively including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can b account the four largest component fractions (excluding CO, which is a

•
For the non-packed reactor at 192 mL/min, the order is: ethane > H2 • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spheres, the o > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, show cle the packing material and size, as detailed in Table 4.
general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tabl CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detecti Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 s propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: ethan • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphere > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4 Before going into more detail on differences for the different packi general observation for the non-packed reactor. Indeed, it seems that th extent determined by the flow rate, although the ratio of CH4 over CO2 c Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dimethylet to be affected by this. This can be attributed to different formation ra explained in the Discussion section, because the different flow rate yield Table 4 and Figure 7 clearly show that CO is always the largest frac and for the non-packed reactors. Moreover, by altering the flow rate (no materials, the relative amount of CO versus higher hydrocarbons or Indeed, the CO product fraction can vary from about 53% up to 72%. also the obtained CO/H2 ratio for the different sphere sizes and materia to above 9, which is quite striking, because the ratio of CH4 over CO2 c roughly 1 and 2. It indicates that the majority of C (especially of CO2) is H (originating from CH4) preferentially takes part in the formation of m but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the type of impact on the product fractions. Moreover, in case of BaTiO3 and SiO2, have a clear impact, while this is much less visible for ZrO2 and α-Al2 fractions of ethyne are envisioned, the smallest size of the SiO2 spheres The αor γ-Al2O3 packing seems to produce the highest CO/H2 ratios (s same time producing substantially less dehydrogenated hydrocarbons When comparing the different types of Al2O3 supports (non-porou do not only see differences in conversion (cf. Figure 5 and Table 3), ca CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also intere fractions. Indeed, although the CO fraction is similar, a larger fracti obtained for the γ-Al2O3 packing, while the fractions of ethyne a formaldehyde, DME and methanol do not even reach the detection limi Furthermore, the BaTiO3 packing with smallest bead size is the on substantial fraction of formaldehyde and produces overall relatively including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can b account the four largest component fractions (excluding CO, which is a

•
For the non-packed reactor at 192 mL/min, the order is: ethane > H2 • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spheres, the o > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, show cle the packing material and size, as detailed in Table 4.

= C 2
Catalysts 2019, 9, x FOR PEER REVIEW Before going into more detail on differences for the differen general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tabl CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detecti Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 s propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: ethan • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphere > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.  Before going into more detail on differences for the different packi general observation for the non-packed reactor. Indeed, it seems that th extent determined by the flow rate, although the ratio of CH4 over CO2 c Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dimethylet to be affected by this. This can be attributed to different formation ra explained in the Discussion section, because the different flow rate yield Table 4 and Figure 7 clearly show that CO is always the largest frac and for the non-packed reactors. Moreover, by altering the flow rate (no materials, the relative amount of CO versus higher hydrocarbons or Indeed, the CO product fraction can vary from about 53% up to 72%. also the obtained CO/H2 ratio for the different sphere sizes and materia to above 9, which is quite striking, because the ratio of CH4 over CO2 c roughly 1 and 2. It indicates that the majority of C (especially of CO2) is H (originating from CH4) preferentially takes part in the formation of m but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the type of impact on the product fractions. Moreover, in case of BaTiO3 and SiO2, have a clear impact, while this is much less visible for ZrO2 and α-Al2 fractions of ethyne are envisioned, the smallest size of the SiO2 spheres The αor γ-Al2O3 packing seems to produce the highest CO/H2 ratios (s same time producing substantially less dehydrogenated hydrocarbons When comparing the different types of Al2O3 supports (non-porou do not only see differences in conversion (cf. Figure 5 and Table 3), ca CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also intere fractions. Indeed, although the CO fraction is similar, a larger fracti obtained for the γ-Al2O3 packing, while the fractions of ethyne a formaldehyde, DME and methanol do not even reach the detection limi Furthermore, the BaTiO3 packing with smallest bead size is the on substantial fraction of formaldehyde and produces overall relatively including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can b account the four largest component fractions (excluding CO, which is a

•
For the non-packed reactor at 192 mL/min, the order is: ethane > H2 • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spheres, the o > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, show cle the packing material and size, as detailed in Table 4.

= C 2
Catalysts 2019, 9, x FOR PEER REVIEW Before going into more detail on differences for the differen general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The αor γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (non do not only see differences in conversion (cf. Figure 5 and Tabl CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detecti Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 s propane > ethyne.

•
For the non-packed reactor at 192 mL/min, the order is: ethan • For the smallest ZrO2 and BaTiO3 spheres and all SiO2 sphere > propane (formaldehyde in case of BaTiO3).

•
For the two largest BaTiO3 spheres and the intermediate Z ethyne ≊ H2 > propane > ethene.
Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.   When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 propane > ethyne. Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 propane > ethyne. Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  H (originating from CH4) preferentially takes part in the formati but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ove roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formati but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.   Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydrocar Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ove roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the formati but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 an fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.  Packing: conversion extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4. , selectivity general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow r Table 4 and Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4 Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.

, selectivity
Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow r Table 4 and Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 propane > ethyne. Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4 Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.

, selectivity
Catalysts 2019, 9, x FOR PEER REVIEW Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow r Table 4 and Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.

, selectivity
Catalysts 2019, 9, x FOR PEER REVIEW Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow r Table 4 and Figure 7 clearly show that CO is always the larg and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 an have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO2 The α-or γ-Al2O3 packing seems to produce the highest CO/H2 same time producing substantially less dehydrogenated hydroc When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size i substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tren account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4. 88% CH 4 , 78% CO 2  Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The α-or γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4.   Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The α-or γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4 Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The α-or γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4 general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dime to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The α-or γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4 Before going into more detail on differences for the differen general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dime to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The α-or γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4 Before going into more detail on differences for the differen general observation for the non-packed reactor. Indeed, it seems extent determined by the flow rate, although the ratio of CH4 over Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dime to be affected by this. This can be attributed to different forma explained in the Discussion section, because the different flow ra Table 4 and Figure 7 clearly show that CO is always the large and for the non-packed reactors. Moreover, by altering the flow r materials, the relative amount of CO versus higher hydrocarb Indeed, the CO product fraction can vary from about 53% up to also the obtained CO/H2 ratio for the different sphere sizes and m to above 9, which is quite striking, because the ratio of CH4 over roughly 1 and 2. It indicates that the majority of C (especially of C H (originating from CH4) preferentially takes part in the formatio but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the impact on the product fractions. Moreover, in case of BaTiO3 and have a clear impact, while this is much less visible for ZrO2 and fractions of ethyne are envisioned, the smallest size of the SiO2 s The α-or γ-Al2O3 packing seems to produce the highest CO/H2 r same time producing substantially less dehydrogenated hydroca When comparing the different types of Al2O3 supports (nondo not only see differences in conversion (cf. Figure 5 and Table  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also fractions. Indeed, although the CO fraction is similar, a larger obtained for the γ-Al2O3 packing, while the fractions of eth formaldehyde, DME and methanol do not even reach the detectio Furthermore, the BaTiO3 packing with smallest bead size is substantial fraction of formaldehyde and produces overall rela including higher amounts of DME, compared to the other materi When looking more closely to the results, four different trend account the four largest component fractions (excluding CO, whi

•
For the non-packed reactor at 50 mL/min and all α-Al2O3 s propane > ethyne. Also the oxygenated fractions, which are much smaller, sh the packing material and size, as detailed in Table 4     also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons. Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w

•
For the non-packed reactor at 50 mL/min and all α-Al2O propane > ethyne. Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4. , yields CO and H 2 materials, the relative amount of CO versus higher hydrocarbons Indeed, the CO product fraction can vary from about 53% up to 72 also the obtained CO/H2 ratio for the different sphere sizes and mate to above 9, which is quite striking, because the ratio of CH4 over CO roughly 1 and 2. It indicates that the majority of C (especially of CO2 H (originating from CH4) preferentially takes part in the formation o but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the typ impact on the product fractions. Moreover, in case of BaTiO3 and SiO have a clear impact, while this is much less visible for ZrO2 and αfractions of ethyne are envisioned, the smallest size of the SiO2 sphe The α-or γ-Al2O3 packing seems to produce the highest CO/H2 ratio same time producing substantially less dehydrogenated hydrocarbo When comparing the different types of Al2O3 supports (non-po do not only see differences in conversion (cf. Figure 5 and Table 3) conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also int fractions. Indeed, although the CO fraction is similar, a larger fra obtained for the γ-Al2O3 packing, while the fractions of ethyne formaldehyde, DME and methanol do not even reach the detection l Furthermore, the BaTiO3 packing with smallest bead size is the substantial fraction of formaldehyde and produces overall relativ including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends c account the four largest component fractions (excluding CO, which i Also the oxygenated fractions, which are much smaller, show the packing material and size, as detailed in Table 4 Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w  Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4. , yields CO and H 2 to be affected by this. This can be attributed to different formation explained in the Discussion section, because the different flow rate y Table 4 and Figure 7 clearly show that CO is always the largest f and for the non-packed reactors. Moreover, by altering the flow rate materials, the relative amount of CO versus higher hydrocarbons Indeed, the CO product fraction can vary from about 53% up to 72 also the obtained CO/H2 ratio for the different sphere sizes and mate to above 9, which is quite striking, because the ratio of CH4 over CO roughly 1 and 2. It indicates that the majority of C (especially of CO2 H (originating from CH4) preferentially takes part in the formation o but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the typ impact on the product fractions. Moreover, in case of BaTiO3 and Si have a clear impact, while this is much less visible for ZrO2 and α fractions of ethyne are envisioned, the smallest size of the SiO2 sph The α-or γ-Al2O3 packing seems to produce the highest CO/H2 ratio same time producing substantially less dehydrogenated hydrocarbo When comparing the different types of Al2O3 supports (non-po do not only see differences in conversion (cf. Figure 5 and Table 3) conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also int fractions. Indeed, although the CO fraction is similar, a larger fr obtained for the γ-Al2O3 packing, while the fractions of ethyn formaldehyde, DME and methanol do not even reach the detection l Furthermore, the BaTiO3 packing with smallest bead size is the substantial fraction of formaldehyde and produces overall relativ including higher amounts of DME, compared to the other materials When looking more closely to the results, four different trends c account the four largest component fractions (excluding CO, which • For the non-packed reactor at 50 mL/min and all α-Al2O3 sph propane > ethyne.  Also the oxygenated fractions, which are much smaller, show the packing material and size, as detailed in Table 4 general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.

, yields CO and H 2
Before going into more detail on differences for the different pa general observation for the non-packed reactor. Indeed, it seems tha extent determined by the flow rate, although the ratio of CH4 over CO Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dimeth to be affected by this. This can be attributed to different formation explained in the Discussion section, because the different flow rate y Table 4 and Figure 7 clearly show that CO is always the largest f and for the non-packed reactors. Moreover, by altering the flow rate materials, the relative amount of CO versus higher hydrocarbons Indeed, the CO product fraction can vary from about 53% up to 72 also the obtained CO/H2 ratio for the different sphere sizes and mate to above 9, which is quite striking, because the ratio of CH4 over CO roughly 1 and 2. It indicates that the majority of C (especially of CO2 H (originating from CH4) preferentially takes part in the formation o but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the typ impact on the product fractions. Moreover, in case of BaTiO3 and Si have a clear impact, while this is much less visible for ZrO2 and α fractions of ethyne are envisioned, the smallest size of the SiO2 sph The α-or γ-Al2O3 packing seems to produce the highest CO/H2 ratio same time producing substantially less dehydrogenated hydrocarbo When comparing the different types of Al2O3 supports (non-po do not only see differences in conversion (cf. Figure 5 and Table 3) CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also int fractions. Indeed, although the CO fraction is similar, a larger fr obtained for the γ-Al2O3 packing, while the fractions of ethyn formaldehyde, DME and methanol do not even reach the detection l Furthermore, the BaTiO3 packing with smallest bead size is the substantial fraction of formaldehyde and produces overall relativ including higher amounts of DME, compared to the other materials When looking more closely to the results, four different trends c account the four largest component fractions (excluding CO, which Also the oxygenated fractions, which are much smaller, show the packing material and size, as detailed in Table 4 Before going into more detail on differences for the differe general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dim to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially of H (originating from CH4) preferentially takes part in the format but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Tab CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but als fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of e formaldehyde, DME and methanol do not even reach the detec Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall re including higher amounts of DME, compared to the other mate When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, s the packing material and size, as detailed in Table 4.

, yields CO and H 2
Catalysts 2019, 9, x FOR PEER REVIEW Before going into more detail on differences for the different pa general observation for the non-packed reactor. Indeed, it seems tha extent determined by the flow rate, although the ratio of CH4 over CO Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dimeth to be affected by this. This can be attributed to different formation explained in the Discussion section, because the different flow rate y Table 4 and Figure 7 clearly show that CO is always the largest f and for the non-packed reactors. Moreover, by altering the flow rate materials, the relative amount of CO versus higher hydrocarbons Indeed, the CO product fraction can vary from about 53% up to 72 also the obtained CO/H2 ratio for the different sphere sizes and mate to above 9, which is quite striking, because the ratio of CH4 over CO roughly 1 and 2. It indicates that the majority of C (especially of CO2 H (originating from CH4) preferentially takes part in the formation o but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the typ impact on the product fractions. Moreover, in case of BaTiO3 and Si have a clear impact, while this is much less visible for ZrO2 and α fractions of ethyne are envisioned, the smallest size of the SiO2 sph The α-or γ-Al2O3 packing seems to produce the highest CO/H2 ratio same time producing substantially less dehydrogenated hydrocarbo When comparing the different types of Al2O3 supports (non-po do not only see differences in conversion (cf. Figure 5 and Table 3) conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also int fractions. Indeed, although the CO fraction is similar, a larger fr obtained for the γ-Al2O3 packing, while the fractions of ethyn formaldehyde, DME and methanol do not even reach the detection l Furthermore, the BaTiO3 packing with smallest bead size is the substantial fraction of formaldehyde and produces overall relativ including higher amounts of DME, compared to the other materials When looking more closely to the results, four different trends c account the four largest component fractions (excluding CO, which • For the non-packed reactor at 50 mL/min and all α-Al2O3 sph propane > ethyne. Also the oxygenated fractions, which are much smaller, show the packing material and size, as detailed in Table 4    Before going into more detail on differences for the differ general observation for the non-packed reactor. Indeed, it seem extent determined by the flow rate, although the ratio of CH4 ov Table 3). Mainly the formation of CO, ethane, ethyne, DME (Di to be affected by this. This can be attributed to different form explained in the Discussion section, because the different flow Table 4 and Figure 7 clearly show that CO is always the lar and for the non-packed reactors. Moreover, by altering the flow materials, the relative amount of CO versus higher hydroca Indeed, the CO product fraction can vary from about 53% up also the obtained CO/H2 ratio for the different sphere sizes and to above 9, which is quite striking, because the ratio of CH4 ov roughly 1 and 2. It indicates that the majority of C (especially o H (originating from CH4) preferentially takes part in the forma but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that th impact on the product fractions. Moreover, in case of BaTiO3 a have a clear impact, while this is much less visible for ZrO2 a fractions of ethyne are envisioned, the smallest size of the SiO The α-or γ-Al2O3 packing seems to produce the highest CO/H same time producing substantially less dehydrogenated hydro When comparing the different types of Al2O3 supports (no do not only see differences in conversion (cf. Figure 5 and Ta  CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but al fractions. Indeed, although the CO fraction is similar, a larg obtained for the γ-Al2O3 packing, while the fractions of formaldehyde, DME and methanol do not even reach the dete Furthermore, the BaTiO3 packing with smallest bead size substantial fraction of formaldehyde and produces overall r including higher amounts of DME, compared to the other mat When looking more closely to the results, four different tre account the four largest component fractions (excluding CO, w Also the oxygenated fractions, which are much smaller, the packing material and size, as detailed in Table 4.

CO 2 Conversion in DRM and Comparison with CO 2 Splitting
The influence of four different packing materials (SiO 2 , ZrO 2 , α-Al 2 O 3 and BaTiO 3 ) and three different sphere sizes (1.25-1.4; 1.6-1.8 and 2.0-2.24 mm diameter) on the CO 2 , CH 4 and total conversion is displayed in Figures 1-3, respectively. Figure 1 shows the CO 2 conversion in DRM, compared to the conversion that we obtained before for pure CO 2 splitting [32], evidencing a clear impact of the presence of CH 4 . Figure S1 in the Supplementary Materials shows all data on conversion (CO 2− , CH 4− and total conversion) combined in one graph, for comparison.

CH4 and Total Conversion
The first observation to be made from Figure 2 is that the CH4 conversion is always higher than the CO2 conversion, which is logical, since the dissociation energy of a C-H bond in CH4 is 412 kJ/mol, while it is 743 kJ/mol for a C=O bond in CO2 [47].
Comparing again to the non-packed reactor, it can be seen that in contrast to the CO2 conversion, none of the packing materials allow a better conversion at the same flow rate. However, with the exception of BaTiO3, all materials do perform better than the non-packed reactor at the same residence time. BaTiO3 again performs worse than the non-packed reactor, even at the same residence time. The same trend is seen for the total conversion ( Figure 3).
When comparing the results for the different bead sizes and materials, we can make the following observations: Similar to the CO2 conversion, BaTiO3 performs worst and α-Al2O3 performs best, for the four materials tested. Although the bead size had little impact on CO2 conversion in case of ZrO2, increasing the ZrO2 bead size has a positive effect on the CH4 conversion. On the other hand, the upward trend in conversion of CO2 with increasing bead size of SiO2 is much less pronounced for CH4 conversion, showing even a slight drop for the largest SiO2 bead size. Finally, also for α-Al2O3 the dependence of bead size is somewhat different for CH4 and CO2 conversion. In Table 3, we list   To interpret the above results, we compare to modelling results obtained by Snoeckx et al. [46], keeping in mind the differences between their work and this work (70 W and 35 kHz in a non-packed reactor, versus 62 W and 23.5 kHz in both non-packed and packed bed reactors, respectively). The conversion of both CO2 and CH4 as a function of residence time, as predicted by the model, is plotted in Figure 4. In our work, the residence time is kept constant at 5.52 s, for which the model predicts a CO2 and CH4 conversion of 4.6 and 9.2%, respectively. We obtained 8.1% and 15.8% conversion for CO2 and CH4, respectively, in the non-packed reactor, while the packed bed reactor (with 2.0-2.24 mm α-Al2O3) can reach 22.5% (CO2) and 32.8% (CH4) conversion. Note that our obtained values in the non-packed reactor are almost a factor 2 higher than the calculated values but it is not possible to make an exact comparison, due to the different conditions (cf. above) and geometry. Moreover, the exact calculated values are subject to uncertainties, due to uncertainties in the reaction rate coefficients [48,49]. Hence, they should be interpreted merely based on trends. It is clear, however, that the packed bed reactor can improve the conversion of both CO2 and CH4 with more than a factor two, at the same residence time. Moreover, the data clearly exhibits that the CH4 conversion is always higher than the CO2 conversion, both in the model and in the experiments (both for non-packed and packed reactor). In addition, the model predicts that the CH4 conversion is typically twice as high as the CO2 conversion, in good agreement with our results for the non-packed reactor, while the packed bed reactors reveal a ratio of CH4/CO2 conversion varying between 1.5 and 2.2, with the exception of the largest SiO2 beads, where the ratio is only 1.2 (see Table 3), indicating a vast impact of the packing materials on the conversion process. The underlying reasons for these differences in conversion are difficult to link to specific material properties, as the materials diverge in many properties and there is no direct (linear) correlation in the trends in properties that coincide with the trends in conversions (see material characteristics in the Supplementary Materials). Hence, more research will be needed, using materials that are modified, in a controlled way, in specific material properties that are expected to pay  The CO 2 conversion in DRM shows that, when comparing the packed bed reactor to the non-packed reactor, only the largest α-Al 2 O 3 spheres achieve a higher CO 2 conversion than the non-packed reactor at the same flow rate. This indicates that only in this case, the positive influence of the packing compensates for the volume loss (and thus lower residence time) caused by introducing the packing. SiO 2 , ZrO 2 , α-Al 2 O 3 (with the smaller bead sizes) and γ-Al 2 O 3 do not reach this CO 2 conversion but still surmount the CO 2 conversion for the non-packed reactor at the same residence time. In the case of BaTiO 3 , a negative effect of the packing is observed, even at the same residence time. Furthermore, a clear impact of the size of the packing materials can be observed, although the effect itself depends on the type of material. The order in which the materials perform is BaTiO 3 < ZrO 2 < SiO 2 < α-Al 2 O 3 , although SiO 2 only performs better than ZrO 2 for the largest bead size. When looking at the effect of bead size, only SiO 2 and α-Al 2 O 3 show a significantly increased conversion for the largest bead size, in comparison to the other bead sizes. In case of BaTiO 3 and ZrO 2 , no significant impact of the bead size can be seen.
Interesting differences can be observed when comparing the CO 2 conversion in DRM with pure CO 2 splitting obtained in our previous experiments [32]. It is important to clarify that the total flow rate (and thus the residence time) is kept constant for CO 2 splitting and DRM but with DRM, the concentration of CO 2 is halved, as it has been 'diluted' with 50% CH 4 . Diluting with another gas can influence the conversion, even when the diluting gas does not actively participate in the reactions [45]. Indeed, Ramakers et al. have shown that the absolute conversion increases (from 5% to 41%) with a decreasing percentage (from 100 to 5% in argon) of CO 2 [45]. In a 50/50 CO 2 /Ar mixture, the rise in conversion of CO 2 is around a factor 1.6, compared to pure CO 2 splitting. Note, however, that the effective CO 2 conversion drops upon dilution with argon, because there is less CO 2 in the mixture. Our experiments clearly reveal that the absolute CO 2 conversion is also higher for DRM than for CO 2 splitting, with the exception of BaTiO 3 and 2.0-2.24 mm ZrO 2 packing. Indeed, in the non-packed reactor at 50 mL/min and 192 mL/min (straight lines in Figure 1), the conversion is (on average) a factor 1.8 and 1.5 higher in case of DRM, indicating that CH 4 aids the conversion of CO 2 . This is confirmed by computer simulations for DRM in a non-packed DBD reactor, where the CO 2 conversion was largely determined by collision with CH 2 radicals [46], originating from CH 4 dissociation.
For DRM in the packed reactor, the CO 2 conversion is always higher when using SiO 2 and α-Al 2 O 3 packing materials than for pure CO 2 splitting. However, the enhancement of the CO 2 conversion due to CH 4 depends on the size of the spherical packing material and is more significant for α-Al 2 O 3 than for SiO 2 , except for the bead size of 1.6-1.8 mm. For ZrO 2 , a complex and striking behaviour depending on the bead size is observed: the conversion drops for DRM for the 2.0-2.4 mm bead size, while it is enhanced (even by a factor 3.3) for the 1.6-1.8 mm beads and to a lesser extent also for the 1.25-1.4 mm beads. Finally, CH 4 has a clearly negative effect in case of the 2.0-2.24 mm beads of BaTiO 3 , while the conversion is (more or less) equal for CO 2 splitting and DRM for the other BaTiO 3 bead sizes. Last but not least, although BaTiO 3 in general performs best for CO 2 splitting, compared to the other packing materials, it yields the worst results for DRM.

CH 4 and Total Conversion
The first observation to be made from Figure 2 is that the CH 4 conversion is always higher than the CO 2 conversion, which is logical, since the dissociation energy of a C-H bond in CH 4 is 412 kJ/mol, while it is 743 kJ/mol for a C=O bond in CO 2 [47].
Comparing again to the non-packed reactor, it can be seen that in contrast to the CO 2 conversion, none of the packing materials allow a better conversion at the same flow rate. However, with the exception of BaTiO 3 , all materials do perform better than the non-packed reactor at the same residence time. BaTiO 3 again performs worse than the non-packed reactor, even at the same residence time. The same trend is seen for the total conversion ( Figure 3).
When comparing the results for the different bead sizes and materials, we can make the following observations: Similar to the CO 2 conversion, BaTiO 3 performs worst and α-Al 2 O 3 performs best, for the four materials tested. Although the bead size had little impact on CO 2 conversion in case of ZrO 2 , increasing the ZrO 2 bead size has a positive effect on the CH 4 conversion. On the other hand, the upward trend in conversion of CO 2 with increasing bead size of SiO 2 is much less pronounced for CH 4 conversion, showing even a slight drop for the largest SiO 2 bead size. Finally, also for α-Al 2 O 3 the dependence of bead size is somewhat different for CH 4 and CO 2 conversion. In Table 3, we list the CH 4 /CO 2 conversion ratios for all packing materials and sizes. To interpret the above results, we compare to modelling results obtained by Snoeckx et al. [46], keeping in mind the differences between their work and this work (70 W and 35 kHz in a non-packed reactor, versus 62 W and 23.5 kHz in both non-packed and packed bed reactors, respectively). The conversion of both CO 2 and CH 4 as a function of residence time, as predicted by the model, is plotted in Figure 4. In our work, the residence time is kept constant at 5.52 s, for which the model predicts a CO 2 and CH 4 conversion of 4.6 and 9.2%, respectively. We obtained 8.1% and 15.8% conversion for CO 2 and CH 4 , respectively, in the non-packed reactor, while the packed bed reactor (with 2.0-2.24 mm α-Al 2 O 3 ) can reach 22.5% (CO 2 ) and 32.8% (CH 4 ) conversion. Note that our obtained values in the non-packed reactor are almost a factor 2 higher than the calculated values but it is not possible to make an exact comparison, due to the different conditions (cf. above) and geometry. Moreover, the exact calculated values are subject to uncertainties, due to uncertainties in the reaction rate coefficients [48,49]. Hence, they should be interpreted merely based on trends. It is clear, however, that the packed bed reactor can improve the conversion of both CO 2 and CH 4 with more than a factor two, at the same residence time. . Calculated CH4 and CO2 conversion as a function of residence time in a non-packed DBD reactor, adopted from modelling. Adopted with permission from ref. [46]. Copyright 2018 American Chemical Society.

Comparison Studies α/γ-Al2O3
To obtain more insight in the effect of material parameters, we made a comparison between α-Al2O3 and γ-Al2O3 spheres of 2.0-2.24 mm. The CO2, CH4 and total conversion are depicted in Figure  5.
The CO2 conversion appears a factor 1.7 higher for the α-Al2O3 spheres than for the γ-Al2O3 spheres (i.e., 22.5% vs. 13.4%), while the CH4 conversion is only a factor 1.05 higher (i.e., 32.8% vs. 31.2%). The total conversion is a factor 1.24 higher for α-Al2O3 (i.e., 27.7% vs. 22.3%). These results show a clear impact of the bead material properties and/or surface area on conversion, possibly due to a higher BET-surface, a difference in crystallinity, acidity, higher porosity and/or total open pore volume of the γ-Al2O3, as shown in the Supplementary Materials (Table S1). However, to understand the underlying reasons for this effect, more detailed (operando) surface experiments would be needed, which are outside the scope of this paper. In conclusion, these differences show the importance of indicating as much as possible the material properties of packing materials applied, something that is not systematically done in the majority of the plasma catalysis papers. . Calculated CH 4 and CO 2 conversion as a function of residence time in a non-packed DBD reactor, adopted from modelling. Adopted with permission from ref. [46]. Copyright 2018 American Chemical Society.
Moreover, the data clearly exhibits that the CH 4 conversion is always higher than the CO 2 conversion, both in the model and in the experiments (both for non-packed and packed reactor). In addition, the model predicts that the CH 4 conversion is typically twice as high as the CO 2 conversion, in good agreement with our results for the non-packed reactor, while the packed bed reactors reveal a ratio of CH 4 /CO 2 conversion varying between 1.5 and 2.2, with the exception of the largest SiO 2 beads, where the ratio is only 1.2 (see Table 3), indicating a vast impact of the packing materials on the conversion process. The underlying reasons for these differences in conversion are difficult to link to specific material properties, as the materials diverge in many properties and there is no direct (linear) correlation in the trends in properties that coincide with the trends in conversions (see material characteristics in the Supplementary Materials). Hence, more research will be needed, using materials that are modified, in a controlled way, in specific material properties that are expected to play a key role.

Comparison Studies α/γ-Al 2 O 3
To obtain more insight in the effect of material parameters, we made a comparison between α-Al 2 O 3 and γ-Al 2 O 3 spheres of 2.0-2.24 mm. The CO 2 , CH 4 and total conversion are depicted in Figure 5.
The CO 2 conversion appears a factor 1.7 higher for the α-Al 2 O 3 spheres than for the γ-Al 2 O 3 spheres (i.e., 22.5% vs. 13.4%), while the CH 4 conversion is only a factor 1.05 higher (i.e., 32.8% vs. 31.2%). The total conversion is a factor 1.24 higher for α-Al 2 O 3 (i.e., 27.7% vs. 22.3%). These results show a clear impact of the bead material properties and/or surface area on conversion, possibly due to a higher BET-surface, a difference in crystallinity, acidity, higher porosity and/or total open pore volume of the γ-Al 2 O 3 , as shown in the Supplementary Materials (Table S1). However, to understand the underlying reasons for this effect, more detailed (operando) surface experiments would be needed, which are outside the scope of this paper. In conclusion, these differences show the importance of indicating as much as possible the material properties of packing materials applied, something that is not systematically done in the majority of the plasma catalysis papers.

Carbon, Hydrogen and Oxygen Balances
To determine whether all products have been identified by the GC (Gas Chromatograph), we present the mass balances for carbon, hydrogen and oxygen in Figure 6. Important to note here is that part of the deficit is possibly caused by the gas expansion, as explained above (see materials and methods). As can be seen, the carbon, hydrogen and oxygen balances seldom reach 100%. The largest deficit (between 20% and 30% loss of product) is in the hydrogen balance of the non-packed reactor at 50 mL/min, as well as for the BaTiO3 spheres of 1.6-1.8 mm, the α-Al2O3 spheres of 1.2-1.4 mm and the ZrO2 spheres of 2.0-2.4 mm. In all other cases, less than 20% product remains unaccounted for. Moreover, the oxygen and carbon balances reach much higher values: close to 90% (and even up to 95%) and thus less than 10% loss. It thus suggests that mainly products with more than one hydrogen atom are not taken into account in the converted products. We presume that mostly the formation of H2O and the sum of less abundant (oxygenated) hydrocarbons, that were not calibrated on the GC, lie at the basis of these incomplete balances. Indeed, the deficit in the hydrogen balance is for the majority of the experiments double of the deficit in the oxygen balance, suggesting the formation of H2O. An example of a chromatogram, showing the number (and type) of products that have not been calibrated and accounted for in the mass balances, is shown in Supplementary Materials (Figure S15). In addition, also coke deposition could be at the basis of carbon losses. When looking at the Raman measurements (see Supplementary Materials; Figures S16-S23), it is clear that SiO2 and to a limited extent also α-Al2O3 and ZrO2 suffer from coking at the sphere's surface, unlike the γ-Al2O3 and BaTiO3 spheres. To visually show the amount of cokes deposited on the spheres, photos are added in the Supplementary Materials ( Figure S24).
More detailed carbon, hydrogen and oxygen balances (with the contribution of the different components identified and calibrated by the GC) are shown in the Supplementary Materials ( Figures  S25-S27 for the carbon balance, Figures S28-S30 for the hydrogen balance and Figures S31-S33 for the oxygen balance). They allow a clear view on all identified products in the treated gas stream, as well as their relative contribution to the total converted products. From these balances, clear differences in product fractions also become apparent when comparing different packing materials. These are discussed in more detail in the following part.

Carbon, Hydrogen and Oxygen Balances
To determine whether all products have been identified by the GC (Gas Chromatograph), we present the mass balances for carbon, hydrogen and oxygen in Figure 6. Important to note here is that part of the deficit is possibly caused by the gas expansion, as explained above (see materials and methods). As can be seen, the carbon, hydrogen and oxygen balances seldom reach 100%. The largest deficit (between 20% and 30% loss of product) is in the hydrogen balance of the non-packed reactor at 50 mL/min, as well as for the BaTiO 3 spheres of 1.6-1.8 mm, the α-Al 2 O 3 spheres of 1.2-1.4 mm and the ZrO 2 spheres of 2.0-2.4 mm. In all other cases, less than 20% product remains unaccounted for. Moreover, the oxygen and carbon balances reach much higher values: close to 90% (and even up to 95%) and thus less than 10% loss. It thus suggests that mainly products with more than one hydrogen atom are not taken into account in the converted products. We presume that mostly the formation of H 2 O and the sum of less abundant (oxygenated) hydrocarbons, that were not calibrated on the GC, lie at the basis of these incomplete balances. Indeed, the deficit in the hydrogen balance is for the majority of the experiments double of the deficit in the oxygen balance, suggesting the formation of H 2 O. An example of a chromatogram, showing the number (and type) of products that have not been calibrated and accounted for in the mass balances, is shown in Supplementary Materials (Figure S15). In addition, also coke deposition could be at the basis of carbon losses. When looking at the Raman measurements (see Supplementary Materials; Figures S16-S23), it is clear that SiO 2 and to a limited extent also α-Al 2 O 3 and ZrO 2 suffer from coking at the sphere's surface, unlike the γ-Al 2 O 3 and BaTiO 3 spheres. To visually show the amount of cokes deposited on the spheres, photos are added in the Supplementary Materials ( Figure S24). Figure 6. Carbon, Hydrogen and oxygen balance for different sphere sizes and materials, as well as the non-packed reactor.

Product Fractions
As explained in the materials and methods section, the calculation of selectivities and balances induces an uncertainty, caused by the gas expansion. Therefore, we calculated the product fractions in this work (see Equation (4)), as these values only show the relative contribution of each product in the total identified product mixture, which is not subject to the gas expansion. The product fractions are plotted in Figure 7, to provide a general overview and are also listed in Table 4, to better compare the trends, based on quantitative data.   Figures S31-S33 for the oxygen balance). They allow a clear view on all identified products in the treated gas stream, as well as their relative contribution to the total converted products. From these balances, clear differences in product fractions also become apparent when comparing different packing materials. These are discussed in more detail in the following part.

Product Fractions
As explained in the materials and methods section, the calculation of selectivities and balances induces an uncertainty, caused by the gas expansion. Therefore, we calculated the product fractions in this work (see Equation (4)), as these values only show the relative contribution of each product in the total identified product mixture, which is not subject to the gas expansion. The product fractions are plotted in Figure 7, to provide a general overview and are also listed in Table 4, to better compare the trends, based on quantitative data.
As explained in the materials and methods section, the calculation of selectivities and balances induces an uncertainty, caused by the gas expansion. Therefore, we calculated the product fractions in this work (see Equation (4)), as these values only show the relative contribution of each product in the total identified product mixture, which is not subject to the gas expansion. The product fractions are plotted in Figure 7, to provide a general overview and are also listed in Table 4, to better compare the trends, based on quantitative data.  Before going into more detail on differences for the different packing materials, we can make a general observation for the non-packed reactor. Indeed, it seems that the product fraction is to some extent determined by the flow rate, although the ratio of CH 4 over CO 2 conversion is very similar (see Table 3). Mainly the formation of CO, ethane, ethyne, DME (Dimethylether) and formaldehyde seem to be affected by this. This can be attributed to different formation rates of different products, as explained in the Discussion section, because the different flow rate yields a different residence time. Table 4 and Figure 7 clearly show that CO is always the largest fraction, for all packing materials and for the non-packed reactors. Moreover, by altering the flow rate (non-packed reactor) or packing materials, the relative amount of CO versus higher hydrocarbons or oxygenates can be altered. Indeed, the CO product fraction can vary from about 53% up to 72%. Therefore, we list in Table 3 also the obtained CO/H 2 ratio for the different sphere sizes and materials. This value ranges from 4.7 to above 9, which is quite striking, because the ratio of CH 4 over CO 2 conversion is always between roughly 1 and 2. It indicates that the majority of C (especially of CO 2 ) is converted into CO, while the H (originating from CH 4 ) preferentially takes part in the formation of many products, not only for H 2 but also for higher hydrocarbons.
Furthermore, it is clear from Table 4 and Figure 7 that the type of packing material has a vast impact on the product fractions. Moreover, in case of BaTiO 3 and SiO 2 , also the sphere size seems to have a clear impact, while this is much less visible for ZrO 2 and α-Al 2 O 3 . For example, when high fractions of ethyne are envisioned, the smallest size of the SiO 2 spheres seems to be the best choice. The αor γ-Al 2 O 3 packing seems to produce the highest CO/H 2 ratios (see also Table 3), while at the same time producing substantially less dehydrogenated hydrocarbons (ethene and ethyne).
When comparing the different types of Al 2 O 3 supports (non-porous αand porous γ-Al 2 O 3 ), we do not only see differences in conversion (cf. Figure 5 and Table 3), causing a large discrepancy in CH 4 /CO 2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also interesting changes in the product fractions. Indeed, although the CO fraction is similar, a larger fraction of ethane and ethanol is obtained for the γ-Al 2 O 3 packing, while the fractions of ethyne and propane are lower and formaldehyde, DME and methanol do not even reach the detection limits. Furthermore, the BaTiO 3 packing with smallest bead size is the only material able to produce a substantial fraction of formaldehyde and produces overall relatively more oxygenated products, including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can be observed when taking into account the four largest component fractions (excluding CO, which is always the largest fraction):

•
For the non-packed reactor at 50 mL/min and all α-Al 2 O 3 spheres, the order is: ethane > H 2 > propane > ethyne.

•
For the smallest ZrO 2 and BaTiO 3 spheres and all SiO 2 spheres, the order is: ethyne CH4/CO2 conversion ratio (i.e., 1.5 vs. 2. fractions. Indeed, although the CO frac obtained for the γ-Al2O3 packing, wh formaldehyde, DME and methanol do no Furthermore, the BaTiO3 packing w substantial fraction of formaldehyde an including higher amounts of DME, comp When looking more closely to the re account the four largest component fract same time producing substantially less dehydrogenated hydrocarbons (ethene and ethyne). When comparing the different types of Al2O3 supports (non-porous α-and porous γ-Al2O3), we do not only see differences in conversion (cf. Figure 5 and Table 3), causing a large discrepancy in CH4/CO2 conversion ratio (i.e., 1.5 vs. 2.3, respectively) but also interesting changes in the product fractions. Indeed, although the CO fraction is similar, a larger fraction of ethane and ethanol is obtained for the γ-Al2O3 packing, while the fractions of ethyne and propane are lower and formaldehyde, DME and methanol do not even reach the detection limits.
Furthermore, the BaTiO3 packing with smallest bead size is the only material able to produce a substantial fraction of formaldehyde and produces overall relatively more oxygenated products, including higher amounts of DME, compared to the other materials.
When looking more closely to the results, four different trends can be observed when taking into account the four largest component fractions (excluding CO, which is always the largest fraction): • For the non-packed reactor at 50 mL/min and all α-Al2O3 spheres, the order is: ethane > H2 > propane > ethyne.
• For the smallest ZrO2 and BaTiO3 spheres and all SiO2 spheres, the order is: ethyne ≊ ethane > H2 > propane (formaldehyde in case of BaTiO3).
Also the oxygenated fractions, which are much smaller, show clear differences depending on the packing material and size, as detailed in Table 4.
Also the oxygenated fractions, which are much smaller, show clear differences depending on the packing material and size, as detailed in Table 4.

Discussion
The results of the non-packed reactor show an interesting way of tuning product fractions. By reducing the residence time (higher flow rate), the ratio of CO 2 /CH 4 conversion is similar but the fraction of the products can be altered. Indeed, shorter residence times seem to produce less CO and more oxygenates, hinting towards a kinetic effect that will determine the product fractions. Indeed, model calculations predict that the rates of formation of different products are different [50]: some products rise quickly, while others rise more slowly as a function of time or go over a maximum, because they are converted into another product. Hence, depending on the residence time (and thus flow rate), the product fractions can be altered.
Not only the residence time in the plasma/reactor has an influence on the conversion and product fractions but also the residence time of species in contact with the packing material's surfaces. Indeed, according to the Sabatier principle, the residence time and binding energy between the adsorbing molecule and the surface should be long/strong enough for conversion to take place, while the residence time and binding energy between the products and the surface should be short/weak, so that the product can easily desorb. However, in case of plasma-assisted conversion, also many other underlying mechanisms, both physical and chemical, that take place simultaneously, can influence the reactions (both partial chemical equilibrium and kinetics) and thus conversion and product distribution.
Indeed, based on the results, also packing materials clearly influence the plasma chemistry, as can be deduced from the different CO 2 /CH 4 conversion ratios and product fractions. The difference in the CO 2 /CH 4 conversion ratio can be caused by many factors, such as differences in discharge type, the number and transferred energy of the streamers, the streamer propagation, electric field enhancement, electron temperature difference, surface adsorption effects and so forth. We present the electrical characteristics for the different sphere sizes and materials in the Supplementary Materials but they do not reveal clear trends that can explain the observed differences in conversion ratios. Probably it is a combination of different effects. Similarly, no clear correlation can be made to the material properties (also presented in the Supplementary Materials). Indeed, all these differences influence the CO 2 and CH 4 conversion and thus the resulting products formed, due to differences in gain and loss reactions. In our previous work for pure CO 2 splitting, we could correlate the impact of bead size and material to differences in number of contact points, size of void spaces and to some extent the dielectric constant of the material but it could not explain all data, so other underlying mechanisms must be present as well [32]. Even though we expect differences induced by changes in the discharge mode and discharge properties, due to the differences in for example, dielectric constants of the packing materials, the data extracted from the electrical characterisation (Supplementary Materials:  Table S2) display no straightforward correlation to the observed differences in CO 2 /CH 4 conversion.
Nevertheless, not all differences in discharge behaviour can be measured. For example, modelling has revealed important differences in streamer propagation and/or streamer versus surface discharge behaviour, positive restrikes and local discharges, for packed bed reactors, depending on the dielectric constant of the packing material [51]. Moreover, the same modelling study showed that the impact of the discharge mode will be different for different chemical species and thus its impact on CO 2 and CH 4 conversion, as well as on the intermediate species and products, might vary, resulting in the observed differences in CO 2 /CH 4 conversion and product distribution. This complex interplay induced by the packing is too complex to postulate the underlying mechanisms for the observed differences in the data [51] and requires much more extended research, focused on materials with systematically altered properties, as well as extensive modelling.
Furthermore, some packing materials, such as Al 2 O 3 , behave superior to the others, both in case of CO 2 and CH 4 conversion, indicating that the observed results are not only related to the dielectric constant and its effects on the electrical properties of the plasma. Indeed, otherwise, BaTiO 3 (which has the highest dielectric constant) would provide the best results, which is clearly not the case. Moreover, if the results would only be correlated to the dielectric constant of the material, αand γ-Al 2 O 3 , both having the same dielectric constant, would yield the same conversion. This indicates that other effects, like for example, the surface area and/or the surface acidity, may lie at the base of this difference. Nevertheless, the fact that BaTiO 3 performs worse than the other materials can also be correlated to some extent to the electrical properties, because Wang et al. predicted by modelling that materials with higher dielectric constant constrain the discharge to the contact points of the packing materials. They suggested that this can limit surface activation due to a lower surface area in contact with the discharge [51]. On the other hand, materials with a higher dielectric constant result in a higher electric field enhancement, which will also be beneficial for CO 2 and CH 4 conversion [52,53]. Hence, these are opposite effects and this could explain why Al 2 O 3 is a superior material, having an "intermediate" dielectric constant of 9, while BaTiO 3 (with a dielectric constant of~4000 [54]) is performing worse. It should be noted that BaTiO 3 gave the best results in pure CO 2 splitting, indicating that the effect of electric field enhancement was in that case more important than the effect of the surface discharges. The role of surface discharge behaviour on CH 4 conversion (and vice versa) thus seems important, although this is only a hypothesis.
Other literature reports also support this careful hypothesis, suggesting a difference in behaviour of CH 4 and CO 2 conversion. Indeed, Snoeckx et al. predicted by modelling that CO 2 is not only converted during the microdischarge filaments in a DBD reactor but is also able to react further in the afterglow (both in between filaments as well as post-plasma), whereas CH 4 is mainly converted during the filaments and is being formed again (by recombination of reaction products) in the afterglow [46]. Nevertheless, the effect of different packing materials and sizes on the CH 4 /CO 2 conversion ratios might be more complicated, as a result of several other mechanisms as well, so it is not possible to explain all differences in detail. Thus, due to the complex and intertwined nature of the chemistry and physical effects at play, extensive modelling would be needed to confirm or reject this first hypothesis as part of the possible underlying mechanisms.
In addition to the above possible mechanisms, also other interesting hypotheses can be made, based on the surprising result of the difference in performance of BaTiO 3 in DRM versus pure CO 2 splitting.
Based on the results of pure CO 2 splitting, it is possible that BaTiO 3 strongly promotes the equilibrium of CO 2 splitting towards CO and O. In combination with a high CH 4 conversion (CH 4 /CO 2 conversion ratio of 2), which results in a high fraction of H atoms, the O atoms might recombine with H atoms into OH. The latter can further react towards oxygenated components (explaining the higher fractions of oxygenates in the presence of BaTiO 3 ), as well as towards H 2 O (and possibly HO 2 and H 2 O 2 ). The trapping of O atoms into OH radicals and H 2 O, when small amounts of CH 4 are added to CO 2 streams, has been predicted by modelling [55]. In the latter paper, it was described as a positive effect, because it allowed easier separation of the produced gas mixture but the study was only applied for a few % of CH 4 addition to CO 2 . Due to the high performance of BaTiO 3 towards CO 2 splitting, as demonstrated in our previous work [32], a much higher concentration of OH radicals might be present here, engaging in other (more negative) reactions, lowering the conversion. Indeed, recent modelling studies of CH 4 /O 2 mixtures have indicated a preferential formation of H 2 O from OH radicals [50]. These H 2 O molecules will promote the back reaction of CO into CO 2 , as suggested based on CO 2 /H 2 O models [56]. This can explain the lower CO 2 conversion in DRM for a BaTiO 3 packing, compared to pure CO 2 splitting. We cannot measure H 2 O with our GC but the deficits in the oxygen and hydrogen balance (see Figure 6) suggest that indeed a large amount of H 2 O might be formed. However, more research is needed to verify the above hypotheses. Note that the high amounts of OH radicals can not only cause back reactions of CO into CO 2 but can also explain the higher oxygenate content in case of the BaTiO 3 packing, compared to the other materials. It is thus advised, when aiming for a suitable catalyst for plasma-based DRM, to search for a material that benefits the reaction of OH towards CHO or further towards CH 3 O 2 instead of towards H 2 O. The different reaction pathways mentioned in this reasoning, are shown in the Supplementary Materials (Figures S34-S36).
Nevertheless, the above reasoning is only a first hypothesis, as other materials exhibiting a lower CO 2 conversion in case of DRM versus pure CO 2 splitting (i.e., ZrO 2 with bead size of 2.0-2.24 mm) do not result in a higher fraction of oxygenated products. This might be due to a difference in kinetics between the back reaction of H 2 O with CO 2 versus oxygenate formation. However, much more experimental and modelling work is needed to substantiate this hypothesis.
Finally, the CH 4 conversion is always higher than the CO 2 conversion, due to the lower C-H bond dissociation energy compared to C=O bond dissociation energy, for all packing materials and sphere sizes. However, the CH 4 /CO 2 conversion ratio varies from 1.2 to 2.3 (see Table 3), so the difference is more pronounced for some materials than for others. This suggests that for those packing materials with a lower CH 4 /CO 2 conversion ratio (e.g., 1.25-1.4 mm α-Al 2 O 3 and BaTiO 3 and 2.0-2.24 mm SiO 2 and α-Al 2 O 3 ; see Table 3), the situation is more complicated, for example, a back reaction or an impact on the kinetics of CH 4 conversion or CO 2 conversion is taking place.

Materials and Methods
We applied the same setup as described in our previous work [32]. It comprises two concentric electrodes: a grounded inner electrode made of stainless steel and the live outer electrode (10 cm) consisting of a stainless steel mesh, wrapped around the dielectric barrier. The dielectric barrier forms the reactor tube that encloses the gap with the inner electrode and is made of Al 2 O 3 . The gap is confined between the inner electrode (8 mm outer diameter) and the dielectric barrier (inner diameter 17 mm, thickness 2.4 mm), resulting in a gap size of 4.5 mm. In this gap, we inserted the spherical dielectric packing material. The packing spans the full discharge volume with a length of 10 cm (the outer electrode length). To prevent the spherical packing from shifting, the beads were secured with glass wool at both ends of the discharge zone. The high voltage was supplied by a generator, a transformer and a power supply (AFS GmbH, Horgau, Germany). The voltage was measured with a high voltage probe (Tektronix P6015A, Beaverton, OR, USA), while the current was measured with a Rogowski coil (Pearson 4100, London, UK) and the condenser (10 nF) measures the charge. The electrical signals were recorded with an oscilloscope (PicoScope 6402 A, Tyler, TX, USA).
Plotting Q versus U results in Q-U Lissajous figures, giving insight in the electrical characteristics. Analysing the Lissajous data and the oscillograms with Matlab yields six different data. The plasma power is calculated by multiplying the measured current and voltage. The burning voltage (U bur ) and peak-to-peak voltage (U pp ) are calculated from the Lissajous graphs. Furthermore, the root-mean-square current (I RMS ), number of micro discharges per period and displaced charge per micro discharge are extracted from the oscillograms. More information about how these data are obtained from the Lissajous plots and oscillograms can be found in ref. [32,57]. The data are summarised in Table S2 of the Supplementary Materials. All packing materials result in a lower burning voltage, which has already been observed before [58], as well as more micro discharges per period and a larger root-mean-square current.
The reaction conditions and packing materials tested in this work are listed in Table 5. Five different spherical packing materials were used in this work, that is, SiO 2 (SiLiBeads, Warmensteinach, Germany), Y-stabilised ZrO 2 (SiLiBeads, Warmensteinach, Germany), BaTiO 3 (Catal, Sheffield, UK), γ-Al 2 O 3 (BASF) and α-Al 2 O 3 (in-house formulated by droplet coagulation at VITO (Vlaamse Instelling voor Technologisch Onderzoek-Flemish institute for technological research), with the α-Al 2 O 3 being purchased from Almatis, Rotterdam, The Netherlands [32]). The different physical and chemical characteristics of each material are reported in the Supplementary Materials: Table S1 and Section 1 ( Figures S2-S14 and Table S4). The stability of the materials is also discussed in the Supplementary Materials. (Section 2, Figures S16-S24), which focuses on coking resistance.
The gas feed flow rates for both CO 2 and CH 4 are regulated with thermal mass flow controllers (Bronkhorst, Ruurlo, The Netherlands) and the outlet gas is analysed with a custom made online gas chromatograph (Trace GC 1310, Interscience, Bretèche, France). The GC is equipped with a TCD (thermal conductivity detector) and an FID (flame ionization detector) with a methanizer. The separation of the gasses is accomplished with four columns: a Molsieve 5A, 2 RT-Q-bonds and a RTX-f column.
The experiments are carried out as follows: the reactor is always packed with fresh packing. A vibration step is applied during packing to ensure dense packing of the reactor and uniform void spaces. Subsequently, the gas is flushed through the reactor for 10 min, followed by a blanc (i.e., without plasma) measurement, consisting of four consecutive GC measurements and electrical measurements, confirming the feed concentration CO 2,in and CH 4,in (a constant CO 2 /CH 4 ratio of 1/1 is applied in this study). Then, the plasma is ignited and stabilised for a duration of 40 min, followed by four consecutive GC and electrical measurements. This plasma measurement is repeated three times, each time with fresh packing. This way, the uncertainties introduced by packing the reactor are included in the final result. The error bars on the data-points below are thus based on the 12 measurements executed as explained above.
Based on the peak areas of the GC chromatogram obtained from the plasma measurements (CO 2,out and CH 4,out ) and the blanc measurement, the conversions for CO 2 and CH 4 are calculated (Equations (1) and (2)). The total conversion is calculated using the fractions of both gasses in the inlet gas flow (in our case, both 50%; Equation (3)).
X CO 2 = CO 2,in − CO 2,out CO 2,in * 100% (1) X Total = X CO 2 + X CH 4 2 As explained in our previous work [32], the conversion of gasses into a larger number of molecules leads to an expansion of the volume of the gas, causing a pressure increase. As the GC depressurizes the gas to 1 bar upon sampling (sample loop volume of 100 µL), some converted volume could thus be lost upon depressurizing, relative to the blanc experiment executed at a constant pressure of 1 bar. The formation of higher hydrocarbons, on the other hand, would lead to an increase in density. The extent of conversion, the type of products formed (density) and the product distribution, thus determine the extent of pressure increase and thus the possible loss of converted gas upon sampling. For CO 2 splitting, this can be easily accounted for, as demonstrated in refs. [32,45,57,59,60]. However, for DRM, it is nearly impossible to take this into account, because a plethora of products can be formed, which are not a priori known or can even not all be identified in the GC. Yet, it is still important to know that this process can play a role and expansion of the gas can influence (slightly overestimate) the conversions. More details about the extent of its impact on the obtained results can be found in the work of Pinhão et al. [59]. As it does not only affect the conversions but also the way to calculate the product selectivities, we report the data as relative fractions of products to the total of identified products. Indeed, these product fractions are not affected by the gas expansion. The relative product fractions are defined as follows (shown for H 2 as example): For information of the reader, the yields and selectivities (albeit with the uncertainties due to the gas expansion) are also calculated and shown in the Supplementary Materials (Tables S5 and S6).
The SEI (specific energy input) is defined as SEI ( kJ L ) = Plasma power (kW) Total gas f low rate ( L min ) * 60 ( s min ) The total gas flow rate is the sum of the flow rates of CO 2 and CH 4 . For all experiments in the packed bed reactor, this value is 50 mL/min, while in the non-packed reactor, we use a flow rate of 50 mL/min or 192 mL/min. Indeed, the experiments with a non-packed reactor at 50 mL/min provide comparison with the packed bed reactor at equal flow rate, while the experiments at 192 mL/min compare at the same residence time. This way, the reduction in the reactor volume caused by the addition of the packing (estimated as 74% volume, independent of the packing size [61]), is accounted for.
The plasma power in the above formula is the power generated in the plasma reactor, calculated based on the measured voltage and current and not the power that is set on the power supply (typically there is a power loss of~40%, from 100 Watt to 60 Watt). The analysis of the obtained Lissajous data gives a more correct value of the actual power that is supplied to the plasma (see Supplementary Materials: Table S2).

Conclusions
The aim of this research was to study the influence of different packing materials on the conversion and product fractions formed in the dry reforming of CH 4 in a packed bed DBD reactor and to compare this to our previous work on CO 2 splitting.
For this purpose, five different packing materials in three different sizes, that were not explicitly activated with catalytically active elements but could be catalytic in nature, were compared. The following conclusions can be drawn: The highest CO 2 , CH 4 and total conversion obtained in the packed bed reactor was 22.5%, 32.8% and 27.7%, respectively, for α-Al 2 O 3 spheres with a diameter of 2.0-2.24 mm. In the non-packed reactor at equal flow rate, the CH 4 and total conversion yielded still higher values of 37.3% and 28.5%, respectively, due to the longer residence time. Analysis of the packing materials before and after plasma confirmed that most of the packing materials have a high resistance to coking, although SiO 2 showed clear D and G bands.
It was clearly evidenced that the type and size of packing materials cannot only influence the overall conversion but also the CH 4 /CO 2 conversion ratio and the product fractions, even without being activated with catalytic elements. This emphasizes the importance of studying all essential aspects of a catalyst in case of plasma catalysis, including the non-catalytically activated support material.
Depending on the packing material applied, very high CO/H 2 ratios can be obtained, hinting to mechanisms where the H atoms (originating from CH 4 ) are mainly involved in the formation of hydrocarbons or oxygenated products, rather than into H 2 .
By studying two types of Al 2 O 3 (α and γ), with the same dielectric constant, we can conclude that apart from differences in electrical characteristics and discharge behaviour, other materials chemistry or structural (e.g., porosity) related features have a vast impact on product formation, leading to a very different product distribution, in case of α-Al 2 O 3 versus γ-Al 2 O 3 . It has to be noted that γ-Al 2 O 3 results in the highest product selectivity (higher than α-Al 2 O 3 ), with no detectable fractions of oxygenated products, except for a 10-fold higher ethanol formation (fraction of 3%), in combination with a high CO content (~70%), the latter being similar to α-Al 2 O 3 .
Another interesting observation was the discrepancy between the high CO 2 conversion of BaTiO 3 for CO 2 splitting, in contrast to the low CO 2 conversion in case of DRM. A possible explanation for this was put forward, based on models that hint towards the recombination of O and H atoms into OH and possibly enhanced back reactions. However, further studies, including both extensive modelling and plasma catalysis with materials with systematically altered properties, are required to confirm the complicated interplay of the different mechanisms.
In general, we can conclude that, even without a catalytic activation, the packing material already has a vast effect on the conversions and product fractions. This indicates the importance of studying all materials aspects in case of plasma catalysis, including the non-activated packing materials. Furthermore, it shows that more research is needed, combining extensive modelling with material research, to unravel the mechanisms at play. Finally, it exemplifies the tremendous future opportunities to create catalysts with true synergy in packing material and active element, that can significantly impact both conversion and selective production of chemicals, allowing to steer DRM to different types of products, ranging from oxygenates to higher hydrocarbons in a one-step process, making plasma-catalytic DRM competitive with thermal DRM in the future.
Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4344/9/1/51/s1. Figure S1: UV-DR spectra of SiO 2 before (blue graph) and after (red graph) plasma exposure (milled spheres). Figure S2: UV-DR spectra for ZrO 2 before (blue graph) and after (red graph) plasma exposure (milled spheres). Figure S3: UV-DR spectra for BaTiO 3 before (blue graph) and after (red graph) plasma exposure (milled spheres). Figure S4: Nitrogen Sorption for SiO 2 . Figure S5: Nitrogen Sorption for ZrO 2 . Figure S6: Nitrogen Sorption for α-Al 2 O 3 . Figure S7: Nitrogen Sorption for γ-Al 2 O 3 . Figure S8: Nitrogen Sorption for BaTiO 3 . Figure S9: Hg-porosimetry for SiO 2 . Figure S10: Hg-porosimetry for ZrO 2 . Figure S11: Hg-porosimetry α-Al 2 O 3 . Figure S12: Hg-porosimetry γ-Al 2 O 3 . Figure S13: Hg-porosimetry BaTiO 3 . Figure S14: Raman spectrum for SiO 2 , before and after plasma exposure. Figure S15: Raman spectrum for ZrO 2 , before and after plasma exposure. Figure S16: Raman spectrum for α-Al 2 O 3 , before and after plasma exposure. For both spheres (before and after plasma), 2 spectra are recorded: one with 90% of the light filtered out and one with 99% of the light filtered out. Figure S17: Zoomed-in (at coking regions) Raman spectrum for α-Al 2 O 3 , before and after plasma exposure. For both spheres (before and after plasma), 2 spectra are recorded: one with 90% of the light filtered out and one with 99% of the light filtered out. Figure S18: Raman spectrum for γ-Al 2 O 3 , before and after plasma exposure. Figure S19: Zoomed-in (at coking regions) Raman spectrum for γ-Al 2 O 3 , before and after plasma exposure. Figure S20: Raman spectrum for BaTiO 3 , before and after plasma exposure. Figure S21: Zoomed-in (at coking regions) Raman spectrum for BaTiO 3 , before and after plasma exposure. Figure S22: visual image of the spheres before and after plasma treatment. Figure S23: CO 2 , CH 4 and total conversion for different sphere sizes and materials, compared to the results for the non-packed reactor, at the same flow rate (50 mL/min) and at the same residence time (5.52 s; flow rate of 192 mL/min). Figure S24: Part of a gas chromatogram obtained in this work, zoomed in on the baseline. Figure S25: Total carbon balance for different sphere sizes and materials. Figure S26: Detailed carbon balance for different sphere sizes and materials, without CO 2 and CH 4 contribution. Figure S27: Normalized carbon balance for different sphere sizes and materials, without CO 2 and CH 4 contribution. Figure S28: Total hydrogen balance for different sphere sizes and materials. Figure S29: Detailed hydrogen balance for different sphere sizes and materials, without CH 4 contribution. Figure S30: Normalized hydrogen balance for different sphere sizes and materials, without CH 4 contribution. Figure S31: Total oxygen balance for different sphere sizes and materials. Figure S32: Detailed oxygen balance for different sphere sizes and materials, without CO 2 contribution. Figure S33: Normalized oxygen balance for different sphere sizes and materials, without CO 2 contribution. Figure S34: Reaction scheme to illustrate the main pathways for the conversions of CH 4 and O 2 and their interactions. Adopted with permission from ref. [17]. Copyright 2018 American Chemical Society. Figure S35: Reaction scheme to illustrate the main pathways for dry reforming of methane. Adopted with permission from ref. [17]. Copyright 2018 American Chemical Society. Figure S36: Reaction scheme to illustrate the main pathways for the conversions of CO 2 and H 2 O and their interactions. Adopted with permission from ref. [18]. Copyright 2018 Wiley-VCH. Table S1: Electrical characterisation for all experiments. Table S2: Physical and chemical characteristics of the packing materials. Table S3: Specifics of the equipment for all characterization techniques. Table S4: SEM-EDX measurements for all spheres before and after plasma, measured at 3 points per sphere. Table S5: Identified products, ranked in decreasing order of their yields, for the different packing materials and the non-packed reactor. The components highlighted are present for more than 1%, the others for more than 100 ppm. Table S6: Product selectivities (%) for the different packing materials and sizes and for the non-packed reactor. The highest selectivities for each component are highlighted.

Funding:
The authors acknowledge financial support from the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT Flanders) for I. Michielsen (IWT-141093), from an IOF-SBO project from the University of Antwerp, from the Fund for Scientific Research (FWO; grant number: G.0254.14 N) and from the European Fund for Regional Development through the cross-border collaborative Interreg V program Flanders-the Netherlands (project EnOp).