Synthesis of Alcohols and Alkanes from CO and H 2 over MoS 2 / γ-Al 2 O 3 Catalyst in a Packed Bed with Continuous Flow

Effects of reaction conditions on the production of alcohols (AOHs) and alkanes (Alk) from CO and H2, which can be obtained from the gasification of biomass, using a molybdenum sulfide (MoS2)-based catalyst of MoS2/γ-Al2O3 were studied. A high-pressure fixed packed bed (HPFPB) was employed to carry out the reaction. The results indicate that the conversion of CO (XCO) and specific production rates of alcohol (SPRAOH) and alkane (SPRAlk) are highly depended on temperature (T). In T = 423–573 K, maximum yield of alcohols (YAOH) and SPRAOH occur at T = 523 K. In the meantime, well performance gives the selectivity of ethanol (SEtOH) of 52.0 C%. For the studies on varying H2/CO mole ratio (MH/C) from 1 to 4 at 523 K, the appropriate MH/C to produce EtOH is 2, giving higher ratios of SPRAOH/SPRAlk and YAOH/YAlk than those with other MH/C. As for varying the total gas flow rates (QG) of 300, 450, 600 to 900 cm 3 min −1 tested at T = 523 K and MH/C = 2, the lower QG provides longer reaction time (or gaseous retention time, tR) thus OPEN ACCESS Energies 2012, 5 4148 offering higher XCO, however lower productivity. For setting pressure (PST) = 225–540 psi, a supply of higher pressure is equivalent to providing a larger amount of reactants into the reaction system, this thus suggests the use of higher PST should give both higher XCO and productivity. The assessment of the above results indicates that the MoS2/γ-Al2O3 catalyst favors the production of alcohols over alkanes, especially for ethanol. The information obtained is useful for the proper utilization of biomass derived gases of CO and H2.


Introduction
The energy crisis has been an issue of great concern in recent years.With the continued climbing crude oil price, utilization of alternative energy has become more and more essential.The use of biomass, such as agriculture residues and woody waste, to provide energy and chemicals is receiving increasing interest because these resources can supplement the existing supplies of raw energy materials while have less net environmental impact [1][2][3][4][5][6].Thus, bio-energy has the potential to provide a significant share of the projected renewable energy requirement in the future.As an example, ethanol (EtOH) has been broadly utilized as a good additive for enhancing the gasoline octane value and burning efficiency [1,7].
In the hydrogenation of synthesis gas (syngas), previous studies have shown that ethanol can be produced from syngas over many metal-containing catalysts, broadly classified into four categories.These include Rh-based catalysts [8], modified high-temperature and low-temperature methanol synthesis catalysts based on ZnO/Cr 2 O 3 and Cu/ZnO/Al 2 O 3 [9], respectively, modified Fischer-Tropsch catalysts based on Co, Fe and Ru [10], and non-sulfide [11] and sulfide Mo-based catalysts [12][13][14].Among these catalysts, molybdenum sulfide (MoS 2 ) catalysts have attracted much interest because of their higher selectivity to alcohols and excellent resistance to poisoning from sulfur in the feed gas [15][16][17][18][19].Previous studies also examined the effects of support on the Mo-based catalyst, indicating that the microstructures of MoS 2 clusters on Al 2 O 3 supports strongly affect the interaction between Mo oxide and alumina.The interaction is related to the high dispersion of Mo oxide, which leads to highly active structures [16,18].
In previous studies [2], various reaction conditions were also tested for the applications of different catalysts in order to demonstrate the feasibility for the hydrogenation of CO.Inoue et al. [20] studied the applicability of Rh catalyst reporting the activation energy result and indicating that the selectivity of methane increases at higher temperatures.Hu et al. [21] in a study concerning Rh catalyst described the mechanism of methane formation and pointed out that the reaction is very sensitive to temperature.Thus, the formation of methane becomes dominant at higher temperatures.
Besides the temperature factor, the H 2 /CO feed ratio is also a key adjustable variable affecting the conversion of syngas to ethanol or higher alcohols.Mazzocchia et al. [22] and Egbebi and Spivey [23] examined the effect of increasing H 2 /CO ratio (M H/C ) on the formation of both EtOH and methane, showing that the selectivity for ethanol on Rh-based catalysts actually increases with increasing H 2 /CO ratio.Moreover, the H 2 /CO can be adjusted to maximize S EtOH and restrain methane formation.It is noted that methane is also a thermodynamically favorable product.However, its economical value is less than alcohols.The major formation reactions of ethanol and methane are as follows: ΔH 0 298 = −253.6kJ mol −1 and ΔG 0 298 = −221.1 kJ mol −1 of ethanol.
ΔH 0 298 = −205.9kJ mol −1 and ΔG 0 298 = −141.9kJ mol −1 of methane.The competition of the above reactions and other side reactions of hydrogenation of CO thus greatly affects the selectivities of products by the heats and free energies of the associated reactions.
Hu et al. [21] also reported the roles of gas hourly space velocity (GHSV) as well as temperature, revealing that a lower GHSV results in higher EtOH, while a lower temperature gives less methane.As for the effect of system pressure, Spivey and Egbebi [1] indicated that an increasing pressure increases the equilibrium concentration of EtOH from the hydrogenation of CO following Le Chatelier's Principle.
In the hydrogenation of CO, molybdenum-based catalysts which have been also commonly used in the hydrogenation of petroleum have attracted much attention, especially alkali-modified catalysts.However, reports on the effects of operation conditions on the system performance employing MoS 2 /γ-Al 2 O 3 catalyst, which can be easily made, have been scarce.Thus, in this study, the hydrogenation of CO over MoS 2 /γ-Al 2 O 3 catalysts was practiced under various system conditions and examined concerning the production of alcohols and other hydrocarbons (HCs).The proper conditions to produce more alcohols, especially EtOH, with less methane were emphasized.Comparisons with the results using other catalyst were made to assess the corresponding effectiveness of hydrogenation of CO over various catalysts.

Preparation of Catalysts
Mo-based catalysts were prepared employing the wet impregnation method.The catalyst support is γ-Al 2 O 3 pellets (55.5 Å average pore diameter, 4 mm spherical pellet, 4-12 mesh), supplied by BDH Chemicals Ltd. (Poole, UK).It possesses a Brunauer-Emmett-Teller (BET) surface area of 280.46 m 2 g −1 .The γ-Al 2 O 3 support was pre-calcined in air at 900 °C to avoid any structural changes during the following high-temperature calcination for the preparation of catalyst.About 50 g dried γ-Al 2 O 3 was impregnated with 100 mL of 5 wt.% aqueous solution of ammonium heptamolybdate [(NH 4 ) 6 Mo 7 O 24 •4H 2 O], supplied by J.T. Baker (Phillipsburg, NJ, USA).The pH of the solution was controlled at 2.0 by adding nitric acid so as to avoid the overloading of the molybdenum.After being dried at 105 °C for 24 h, the sample was calcined at 500 °C for 6 h.The catalyst at this stage was denoted as Mo X O Y /γ-Al 2 O 3 .The resulted Mo X O Y /γ-Al 2 O 3 was further reduced and sulfurized in the mixed gas stream of H 2 S/H 2 with volume ratio of 5/95 at 673 K for 2 h to produce MoS 2 /γ-Al 2 O 3 catalyst.The molybdenum content in the final sample is about 34 mg g −1 .The above preparation procedures of catalyst are common, and the method is widely used because of its effectiveness.

Characterization of Catalysts
X-ray powder diffraction (XRD) patterns of the tested catalysts were obtained on a Rigaku TTRAX III powder diffractometer (Sendagaya, Shibuya-Ku, Tokyo, Japan) installing with the X-ray source of 18 kW rotating anode Cu target operated at wave length of 1.5456 Å, current of 20 mA and two theta from 20.020 to 110.000 deg using 4.0 deg min −1 of scanning speed.Scanning electron microscopy (SEM) images were carried out using JEOL JSM-7600F field emission scanning electron microscope (Akishima, Tokyo, Japan).The specific surface area (S BET ) was estimated by the BET equation using the data measured employing Micromeritics ASAP2020-physisorption analyzer (Norcross, GA, USA).The pore radius distribution and the mesopore analyses were obtained from the adsorption branch of the isotherm using the Barrett-Joyner-Halenda (BJH) method.The bulk particle density (ρ P ) and true density (ρ S ) (He displacement method) of catalysts were measured using Micromeritics AccuPyc II 1340 Pycnometer (Norcross, GA, USA).

Hydrogenation of CO
The experimental high-pressure fixed packed bed (HPFPB) system was set up as shown in Figure 1.CO and H 2 with purities of 0.9995 and 0.9995 were supplied by Ching-Fong Co. (Taipei, Taiwan).The syngas was provided from CO and H 2 cylinders with the mole ratio adjusted by mass flow controllers (MFCs) (Brooks 5850E Series, Hatfield, Philadelphia, PA, USA).Concentration of gas mixture was measured at pre-sampling port after the pre-mix chamber while before the HPFPB to confirm the steady inlet concentration.A 3/8 inch single-tube reactor packed with catalysts and spherical glass beads was vertically set and used in this study.For the pressure control, a regulator was installed for maintaining the system pressure and adjusting the output flow rate.The polar organic products such as alcohols and acids were collected by the absorption along with condensation using de-ionized (DI) water (4 °C) in a condenser.Fresh catalyst and DI water were used for each run.Before the outlet gas from the packed bed flowed into the condenser, the gas was by passed and the instantaneous concentrations were measured at different subsequent times to ensure achieving the steady state.After reaching the steady state in the packed bed reactor, the gas was then introduced into the condenser.The unabsorbed and uncondensed gas was also examined for checking the steady state.Moreover, at the steady state, the cumulative concentrations of liquid samples measured over a period of time increased linearly with time, further assuring achieving the steady state.The linear slope can be used to obtain the steady production rate (PR) of liquid product.Data at the steady state were thus used to compute the information needed.

Figure 1. Schematic diagram of apparatus for the hydrogenation of CO.
The HPFPB system was operated under the conditions with the H 2 /CO mole ratio = 1-4, total gas flow rate of syngas (Q G ) = 300-900 cm 3 min −1 , temperature (T) = 423-573 K, mass of catalyst (m S ) = 25 g, and setting pressure (P ST ) = 225-540 psi (reading at 298 K).The base conditions were as follows unless otherwise specified: H 2 /CO ratio M H/C = 2, mass flow rates of H 2 and CO (dm H2 /dt and dm CO /dt) of 1.07 and 7.50 g h −1 , P ST = 450 psi (30.6 atm) (reading at 298 K), m S = 25 g, Q G = 300 cm 3 min −1 and gas hourly space velocity GHSV = 1020 h −1 .
The conversion of CO is computed according to the following equation: where N j = number of carbon atoms in carbon-containing product j; M j = mole of carbon-containing product j other than CO; M CO,f = mole of carbon monoxide in feed; M CO,p = mole of carbon monoxide in product stream.The selectivity of product j is based on the total number of carbon atoms in the products and it therefore defined as: The yield of product j is also based on the total number of carbon atoms in the products and is defined as:

Analyses of Liquid and Gaseous Samples
The analysis of gaseous organic compounds was performed using gas chromatography/flame ionization detector (GC/FID, 6890 GC, Agilent Technologies, Santa Clara, CA, USA) with an AB-5 column (30 m × 0.53 mm × 5.00 μm, Abel Industries, Pitt Meadows, BC, Canada).A purge-and-trap sample concentrator (Model 4560, OI Analytical, College Station, TX, USA) was used to purify and inject the liquid samples into GC/FID for analysis.For the calibration of GC/FID, the standards of C 1 -C 4 alcohols (99.9%) and C 1 -C 6 alkanes (99.9%) employed were obtained from Accustandard Inc. (New Haven, CT, USA) and Sigma-Aldrich Inc. (Shanghai, China), respectively.
The gaseous products of CO, CO 2 and H 2 were analyzed by two separate chromatography/thermal conductivity detector analyzers (GC/TCD, 8900 GC, China Chromatography Co., Taipei, Taiwan).The GCs are installed with the same packed columns (60/80 Carbonxen-1000, 15 ft × 1/8 in SS, Sigma-Aldrich, Saint Louis, MO, USA).Different carrier gases of helium (He) for the analyses of CO and CO 2 and argon (Ar) for that of H 2 were respectively used.For the calibration of GC/TCD, the standards of CO and CO 2 (99.995%) and H 2 (99.995%) used were supplied by Ching-Fong Co.Standard errors (σ n−1 ) of data were computed to indicate the level of precision.For example, the σ n−1 of X CO and PR HC are about 2.6% and 4.3%.

Properties and Characteristics of Catalysts
The XRD patterns of MoS 2 /γ-Al 2 O 3 samples are shown in Figure 2. The peaks denoted with solid triangles (▼) at 2θ = 32.85°,39.85°, 49.66°, 58.57°, 60.05° and 66.67° match the polygonal structure of MoS 2 (JCPDS No. 17-0744) in accordance with the characteristic peaks reported by Berdinsky et al. [24].However, they also additionally noted 2θ at 28.86° and 43.99° for the MoS 2 nano-powder examined [24].The SEM micrograph of sample in Figure 3a (magnification = 200×) indicates crystalline part of MoS 2 (noted by white ○), and non-crystalline part of MoS 2 and surface of γ-Al 2 O 3 (denoted by white ∆).The enlargement of ∆ with magnification of 5000× is displayed in Figure 3b.The crystalline part of MoS 2 consists of polygonal particles which may exhibit lamellar structure as also noted by Ye et al. [25].However, small clusters appear on the surface as shown in Figure 3b.The MoS 2 crystallite size estimated using Figure 3a is about 128 μm × 128 μm × 24 μm.More accurate size may be calculated by using Scherrer formula from XRD diffraction information.Moreover, further examination of the morphology properties using selected area electron diffraction in transmission electron microscopy may provide more clear identification of the structures of crystalline and non-crystalline MoS 2 .The BET surface areas S BET and other particle properties of Al 2 O 3 support and MoS 2 /γ-Al 2 O 3 catalyst are listed in Table 1.It can be seen that the BET surface areas of Al 2 O 3 and MoS 2 /γ-Al 2 O 3 prepared with concentration of ammonium heptamolybdate solution (C Mo ) = 10 wt.% are 280.5 and 210.4 m 2 g −1 , respectively.The average pore size of 55.5 Å of Al 2 O 3 is smaller than that of 74.7 Å of MoS 2 /γ-Al 2 O 3 .Thus the doping of MoS 2 enlarges the pore during preparation of catalyst, however, which in turn reduces the S BET .Further accordingly, the porosity (ε P ) increases to 0.550 while bulk particle density ρ P decreases to 1.23 g cm −3 for MoS 2 /γ-Al 2 O 3 after doping of MoS 2 .The increase of true density or solid density ρ S to 3.21 g cm −3 is due to the addition of MoS 2 .onγ-Al 2 O 3 .The particle size of MoS 2 /γ-Al 2 O 3 is about 4-5 mm with average diameter of 4.09 mm which is only slightly larger than that of γ-Al 2 O 3 .ofabout 4 mm.
In the above, the XRD and SEM results confirm that the MoS 2 was successfully adopted on the Al 2 O 3 support, ensuring the possession of activity by the MoS 2 which promotes the restructuring of CO via hydrogenation.The S BET results of the catalyst indicate that a large portion of internal surface was retained, providing essential active sites for the adsorption and reactions.

Effect of Temperature T on the Catalytic Performance of MoS
Table 2 illustrates the CO hydrogenation performances over MoS 2 /γ-Al 2 O 3 catalysts at various temperatures (from 423 to 573 K).It can be seen that the conversion of CO (X CO ) increases monotonously with the increasing temperature.At 573 K, the highest X CO and the specific production rate (SPR) of hydrocarbons (HCs) are 8.2% and 16.1 mg h −1 g cat −1 , respectively.However, a comparison of the yields of alkanes (Y Alk ) and alcohols (Y AOH ) shows that Y Alk is greatly higher than Y AOH at 573 K. Thus, when using MoS 2 /γ-Al 2 O 3 as the catalyst for the hydrogenation of CO, it is better to control the temperature around 523 K in order to harvest more AOH products.The influences of temperature on the selectivities of HC products (S HC ) and specific production rates SPR of HCs over MoS 2 /γ-Al 2 O 3 catalysts are shown in Figure 4.The selectivities of ethanol (S EtOH ) exhibits the highest proportion of whole distribution at each T of 423, 473 and 523 K.However, at T = 573, S EtOH decreases while that of methane (S CH4 ) increases over S EtOH .Note that C 2 + alkanes denote C 2 -C 4 alkanes, for which the selectivities (S C2+Alk ) also increase as the temperature increases.The increase of T not only changes the selectivities, but also enhances the conversion.In order to assess the roles of temperature and conversion on the selectivities, comparison of the results at T = 523 K and 573 K is made.These two different temperatures result in about the same conversions of 8.1-8.2,indicating that the changes of selectivities are mainly associated with higher temperature.g P ST = 29.6 atm (3.0 Mpa), H 2 /CO = 2, SV = 27,000 mL g −1 h −1 , m S = 0.3 g (~0.6 mL), Rh/Mn = 1 [26].
The comparison between SPR Alk and SPR AOH , shows that higher temperatures are favorable for the formation of alkanes, especially for CH 4 .Further, a unique peak value of SPR AOH of 7.9 mg h −1 g cat −1 appears at T = 523 K that may indicate the optimal reaction temperature for higher AOH products rich in EtOH.Moreover, at T = 523 K, the higher production of alcohol products also restrains the amount of alkanes formed.
In a previous study concerning the effect of various temperatures over Rh-Mn/SiO 2 catalyst [26], the results indicated that the increasing temperature improves the X CO , SPR Alk , and SPR AOH .Besides, there is also a peak value of S EtOH at T = 573 K which is also a selectable temperature for producing EtOH as the target compound.The performance of MoS 2 /γ-Al 2 O 3 catalyst of this study is not as good as that of Rh-Mn/SiO 2 catalyst.However, the former catalyst is much cheaper than the latter one.The maximum S EtOH of this study is 54% compared to 67% of Luo et al. [26], 4.8% of Egbebi and Spivey [23], 56.1% of Hu et al. [21] and 35.7% of Haider et al. [27].

Effect of H 2 /CO Ratio M H/C on the Catalytic Performance
Although the ratio of H 2 and CO from biomass gasification is no more than 2, however, excess H 2 may be added for the adjustment of CO to produce more valuable products if feasible.Thus, the characteristics of production at 523 K using MoS 2 /γ-Al 2 O 3 catalysts with different M H/C are presented in Table 3.It shows a slight increase of X CO from 7.6 to 8.3% as the M H/C increases from 1 to 4. However, for the consideration of the relative proportion of AOH to Alk products, the M H/C of 2 gives higher ratios of SPR AOH /SPR Alk and Y AOH /Y Alk than other M H/C .This is consistent with the stoichiometric mole ratio of H 2 to CO of the synthesis reaction 2CO + 4H 2 → C 2 H 5 OH + H 2 O, favoring the formation of ethanol.
As for the selectivities of HC products at various M H/C , Figure 5 indicates that sum of selectivities of total AOH products are obviously higher than that of total alkane products, for which S EtOH is dominant.The results illustrate that MoS 2 /γ-Al 2 O 3 is an alcohol favorite catalyst, particularly for EtOH.The favor of formation of AOH holds for other M H/C values of 1, 3 and 4 examined.Note that there is an increase of C 2 + Alk at M H/C = 1 due to the lack of H 2 for promoting the formation of other HCs.Thus, M H/C of 2 is proper for alcohol synthesis because of its high S AOH , S EtOH and SPR AOH .
In a previous study as listed in Table 3, Egbebi and Spivey [23] showed a higher M H/C at 3 gives a higher S CH4 while a lower S EtOH using alkane favorite catalyst of Rh-Mn-Li/TiO 2 , which favors the reaction of CO + 3H 2 → CH 4 + H 2 O.Although the MoS 2 /γ-Al 2 O 3 catalyst employed in the present study does not favor the formation of CH 4 but ethanol, an increase of M H/C indeed slightly enhances its formation, consisting with the trend reported by Egbebi and Spivey [23].Reaction conditions: T = 523 K; other conditions are as specified in Table 2; b-f.As specified in Table 2; g.T = 543 K, P ST = 19.7 atm (20 bar), Q G = 220 mL min −1 , Rh/Mn/Li = 1/0.1/0.55 [23].

Effect of Total Gas Flow Rates Q G on the Catalytic Performance
Table 4 illustrates the CO hydrogenation performances under the conditions of T = 523 K and H 2 /CO = 2 with various Q G MoS 2 /γ-Al 2 O 3 catalysts.The X CO significantly reduces from 8.1 to 4.1% as Q G increases from 300 to 900 mL min −1 because of the decrease in reaction time (or gaseous retention time, t R ) with increasing Q G .For the same reason, the Y Alk and Y AOH also exhibit decreasing trends with increasing Q G .However, the SPRs of alcohol and HCs rising trends from 7.9 to 18.0 mg h −1 g cat −1 and 13.2 to 30.0 mg h −1 g cat −1 , respectively, as Q G increases.This is because more reactants are supplied with higher Q G .For efficient utilization of reactants aiming at synthesizing AOH with higher X CO and Y AOH , a lower Q G may meet the needs, but this is accompanied by a reduction in reactor productivity.The above said trend is also consistent with the findings of Hu et al. [21] concerning the effect of various GHSV and indicating that a lower GHSV improves the X CO over Rh-Mn/SiO 2 catalyst.Figure 6 further compares the S AOH , S Alk and X CO at various Q G for the case using MoS 2 /γ-Al 2 O 3 catalyst.It indicates the domination of S EtOH over others.Moreover, the effect of Q G on X CO is more vigorous than on S AOH and S Alk .Combined evaluation of the role of Q G on X CO as well as the aforementioned Y AOH suggests the use of lower Q G .
Noting that the volume of catalysts divided by Q G is equal to the 1/GHSV which represents the reaction time, the variation of X CO with 1/GHSV was examined for elucidating the global reaction kinetics.Kinetics in the form of d[CO]/dt = −k n [CO] n were then tested for the reaction order n = 0, 1 and 2 with the following linear equations: The correlation coefficients r 2 are 0.938, 0.945 and 0.951, respectively, for n = 0, 1 and 2. The fittings are re-plotted as 1 − X CO vs. 1/GHSV as shown in Figure 7.The data for short 1/GHSV, say 3.5 s, are essentially linear and well fitted by the said three kinetic models as illustrated in Figure 7a, revealing negligible differences.However, the aforementioned three models exhibit differences which increase with increasing reaction time as indicated in Figure 7b.Further study on the mass transfer effect and the mechanism of the hydrogenation of CO, which may involve rather complicated reactions, on the reaction system would be helpful for establishing and confirming the proper kinetic model.Reaction conditions: T = 523 K; other conditions are as specified in Table 2; b-f.As specified in Table 2;

Effect of System Pressures P ST on the Catalytic Performance
Table 5 illustrates the performances of hydrogenation of CO at various P ST (from 255 to 540 psi) over MoS 2 /γ-Al 2 O 3 catalyst.It can be seen that X CO increases monotonously with increasing pressure.At 540 psi, the highest X CO and SPR HCs are obtained, with values of 9.6% and 15.8 mg h −1 g cat −1 , respectively.In addition, the SPR and Y also rise for alkanes as well as alcohol with increasing system pressure.A supply of higher pressure is equivalent to provide a larger amount of reactants into the reaction system, thus enhancing the reactions.Focusing on the SPR and Y of both Alk and AOH, it can be seen that an increasing pressure does not significantly change the relative proportions between the AOH and Alk, giving SPR AOH /SPR Alk of about 1.91-2.08 and Y AOH /Y Alk of about 2.18-2.52.Production of Alk as well as of AOH increases with pressure.Figure 8 shows the variations of S HCs and X CO with P ST .Reaction conditions: T = 523 K; other conditions are as specified in Table 2; b-f.As specified in Table 2; g.T = 543 K, H 2 /CO = 1, Q G = 20 mL min −1 , m s = 2.65 g, weight hourly space velocity (WHSV) = 8,000 cm 3 h −1 g cat −1 [27].

Figure 6 .
Figure 6.S AOH , S Alk and X CO using MoS 2 /γ-Al 2 O 3 catalyst at different total gas flow rates (Q G ) at T = 523 K.

Figure 8 .
Figure 8. S AOH , S Alk and X CO using MoS 2 /γ-Al 2 O 3 catalysts at different system pressures (P = P ST ) at T = 523 K. )

Table 2 .
Performance of hydrogenation of CO over MoS 2 /γ-Al 2 O 3 catalyst at various temperatures a .

Table 3 .
Performances of hydrogenation of CO over MoS 2 /γ-Al 2 O 3 catalysts at various H 2 /CO a . a.

Table 4 .
Performances of hydrogenation of CO over MoS 2 /γ-Al 2 O 3 catalysts at various gas flow rates a .

SPR Alk SPR AOH Y Alk Y AOH S CH4 S C2+Alk S MeOH S EtOH S PrOH S BuOH S OtHC e
a.

Table 5 .
Performances of hydrogenation of CO over MoS 2 /γ-Al 2 O 3 catalysts at various pressure a . a.