Transformation of Furfural-Acetone Condensation Adduct over Mo/SBA-15 Catalysts under Atmospheric Pressure
Round 1
Reviewer 1 Report
In this article, Teles et al, prepared a series of catalysts, molybdenum supported on SBA-15 doped with different acid/oxophilic species (Zr, Fe and Al) and used in the transformation of furfural-acetone condensation adduct into hydro-deoxygenated products. The authors claim that carrying out the reaction under gas phase is the novelty of the work. But, advantages of gas-phase reaction is not described. Include a paragraph describing the advantages of gas phase reaction. In the catalyst characterization, Mo, Zr, Al and Fe contents were measured in Elemental analysis for few samples. It is unclear why the elemental analysis was not performed for the materials Zr-SBA, Fe-SBA and Al-SBA? Also, the results and discussion section starts with the catalyst characterization. There are no discussion on the synthesis of the catalysts. For the many of the abbreviations, the explanation is not provided in the very first occurrence of the abbreviations. For example, W/F is introduced in the line number 192. Same with the abbreviation TOS.The explanation for. W/F is given in line # 400. It should be explained in the place where it is first introduced. The authors can provide the details of quantification of product distribution as a footnote in Table 3. The developed catalyst are shown to mediate the transformation of furfural-acetone condensation adduct. As the main focus of the article is the production of Safety from the sustainable resources, the energy content of the liquid samples collected form the reactor need to be compared with the SAF.
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Author Response
Answers to the remarks of Reviewer 1 (Manuscript ID: catalysts-2552729)
Comment:
In this article, Teles et al, prepared a series of catalysts, molybdenum supported on SBA-15 doped with different acid/oxophilic species (Zr, Fe and Al) and used in the transformation of furfural-acetone condensation adduct into hydro-deoxygenated products. The authors claim that carrying out the reaction under gas phase is the novelty of the work. But, advantages of gas-phase reaction is not described. Include a paragraph describing the advantages of gas phase reaction.
Answer:
As requested by the reviewer, a new paragraph was included in the introduction (p. 2): “The development of such process under gas phase is highly desired due to the several advantages such as the easy scalability at industrial level, easy separation and regeneration of the catalyst, and carbon coverage can be mitigated in flow fixed-bed reaction by controlling the operating parameters [18]. Besides that, operating at atmospheric pressure the consumption of hydrogen is limited, ideal for the production of FAS”.
A new reference (18) was added in the revised manuscript:
18 Sirous-Rezaei, P.; Jae, J.; Ha, J-M.; Ko, C.H.; Kim, J.M.; Jeon, J-K.; Park, Y-K. Mild hydrodeoxygenation of phenolic lignin model compounds over a FeReOx/ZrO2 catalyst: zirconia and rhenium as efficient dehydration promoters. Green Chem. 2018, 20, 1472-1483
Comment:
In the catalyst characterization, Mo, Zr, Al and Fe contents were measured in Elemental analysis for few samples. It is unclear why the elemental analysis was not performed for the materials Zr-SBA, Fe-SBA and Al-SBA?
Answer:
The analysis of all bare supports modified by Zr, Fe or Al were done and are now given in the Table 1. A new sentence was added in the revised manuscript (p. 10): “the desired content of each element (Al, Zr or Fe) being to 4.0 wt%.”
Comment:
Also, the results and discussion section starts with the catalyst characterization. There are no discussion on the synthesis of the catalysts.
Answer:
A new paragraph (p. 2-3) have been included in the beginning of results and discussion section in order to explain the methods used for the preparation of catalysts and thus, introduce the discussion of materials properties: “A set of molybdenum supported on silica type SBA-15 and functionalized SBA-15 with different species (Zr, Fe and Al) has been prepared. The functionalized supports were prepared through different methods proposed in the literature in order to achieve a good homogeneity and dispersion of the dopants into the support [21,22]. In the case of Fe-SBA and Zr-SBA, simpler and effective methods were used, melting infiltration and incipient wetness impregnation respectively [21]. A pH-adjusting method was used to prepare the Al-SBA material, in an attempt to incorporate aluminium atoms in the silica framework while maintaining the ordered mesostructure [22].”Two new references (21 and 22) were added in the revised manuscript:
21 Yoon, B.S.; Kim, K-J.; Cho, E.H.; Park, H-R.; Roh, H-S.; Ko, C.H. Enhanced Fe-Cr dispersion on mesoporous silica support using surfactant-assisted melt-infiltration for the water-gas shift reaction in waste-to-hydrogen processes. Int. J. Hydrog. Energy, 2023, 48, 24894-24903.
22 Wu, S.; Han, Y.; Zou, Y-C.; Song, J-W.; Zhao, L.; Di, Y.; Liu, S-Z.; Xiao, F-S. Synthesis of heteroatom substituted SBA-15 by the “pH-adjusting” method. Chem. Mater. 2004, 16, 486-492
Comment:
For the many of the abbreviations, the explanation is not provided in the very first occurrence of the abbreviations. For example, W/F is introduced in the line number 192. Same with the abbreviation TOS. The explanation for. W/F is given in line # 400. It should be explained in the place where it is first introduced.
Answer:
In the revised version, all abbreviations were clearly explained.The W/F ratio represents the contact time which is expressed by the ratio between the weight of the catalyst (in g) and the molar flow of the reactant (in mol h-1). The sentence p.7 of the revised version was corrected as followed: “The conversion and product distribution obtained after 30 min on stream are presented on Table 3. Mo/SBA and Mo/Fe-SBA showed similar conversion at the same contact time (W/F = 73 mmol g-1 h-1), which is defined as the ratio between the catalyst weight (in g) and the molar flow of the reactant (in mol h-1).TOS is the abbreviation of time on Stream. As requested by the Reviewer, the caption of Table 3 was corrected and the text of the revised version p.8.
Comment:
The authors can provide the details of quantification of product distribution as a footnote in Table 3.
Answer:
As requested by the Reviewer, footnotes were given below Table 3:
a: the total conversion of FAc was calculated using equation 1 given in the experimental part.
b: the percentage molar of each product obtained was calculated using the equation 2 given in the experimental part.
Comment:
The developed catalyst are shown to mediate the transformation of furfural-acetone condensation adduct. As the main focus of the article is the production of Safety from the sustainable resources, the energy content of the liquid samples collected form the reactor need to be compared with the SAF.
Answer:
As indicated in the introduction part, it is very important to find new sources to improve SAF feedstocks in order to replace hydrocarbons derived from fossil sources by deoxygenated molecules coming from biomass. Unfortunately, the experimental conditions used in our study did not allow total deoxygenation of the model molecule (FAc) used in this study. Nevertheless, our results have enabled us to understand how this molecule can be transformed under mild conditions (300 °C under atmospheric pressure). A new sentence was added p. 6 of the revised manuscript: “Thus, all products obtained were not fully deoxygenated and cannot be blended directly in SAF, this feedstock mainly containing deoxygenated products. In order to favor the full deoxygenation of FAc, more severe experimental conditions (pressure and/or temperature) have to be used.”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors Teles et al, reported their work on titled, Transformation of furfural-acetone condensation adduct over Mo/SBA-15 catalysts under atmospheric pressure. Although, this work contains some results, the organization and interpretation of the result should be enhanced further. Hence, I recommend this work required a substantial revision before considering for publications.
1. Provide the obtained results in the abstract in more concise.
2. Novelty of the work should be highlighted in the introduction in more clearly.
3. The authors designed the work nicely, merely presented the results but failed to discuss the observed results elaborately.
4. I suggest the authors to compare the previous literature similar to that work to find a merits of this work.
5. Refer and include the following references to strengthen the current version of the draft; Light-Science & Applications 11 (2022) 250; Applied Catalysis B: Environmental 316 (2022) 121603.
The authors Teles et al, reported their work on titled, Transformation of furfural-acetone condensation adduct over Mo/SBA-15 catalysts under atmospheric pressure. Although, this work contains some results, the organization and interpretation of the result should be enhanced further. Hence, I recommend this work required a substantial revision before considering for publications.
1. Provide the obtained results in the abstract in more concise.
2. Novelty of the work should be highlighted in the introduction in more clearly.
3. The authors designed the work nicely, merely presented the results but failed to discuss the observed results elaborately.
4. I suggest the authors to compare the previous literature similar to that work to find a merits of this work.
5. Refer and include the following references to strengthen the current version of the draft; Light-Science & Applications 11 (2022) 250; Applied Catalysis B: Environmental 316 (2022) 121603.
Author Response
Answers to the remarks of Reviewer 2 (Manuscript ID: catalysts-2552729)
Comment:
The authors Teles et al, reported their work on titled, Transformation of furfural-acetone condensation adduct over Mo/SBA-15 catalysts under atmospheric pressure. Although, this work contains some results, the organization and interpretation of the result should be enhanced further. Hence, I recommend this work required a substantial revision before considering for publications.
Comment:
- Provide the obtained results in the abstract in more concise.
Answer:
As requested by the reviewer, a new concise abstract was proposed (79 vs 132 words in the first version).
The transformation of the furfural-acetone condensation adduct (FAc) was investigated under atmospheric pressure at 300°C over a series of molybdenum supported on SBA-15 doped with different acid/oxophilic species (Zr, Fe and Al). FAc underwent several reactions including mainly hydrogenation, deoxygenation and cyclization. The order of activity was Mo/Zr-SBA > Mo/Al-SBA > Mo/Fe-SBA ≅ Mo/SBA demonstrating the positive effect of dopants. Likewise, the synergy between molybdenum with the oxophilic Zr4+ species significantly increased the selectivity toward the partially deoxygenated products.
Comment:
2 Novelty of the work should be highlighted in the introduction in more clearly.
Answer:
As novelty in our work we propose performing the transformation of the furfural-acetone condensation adduct in different reaction conditions that usually reported in most works, i.e. using a fixed bed reactor operating under atmospheric pressure. Besides that, to the best of our knowledge, (i) the use of molybdenum as active phase and (ii) the effect of catalyst properties such as oxophilicity and acidity, through the incorporation of oxophilic and/or acid dopants in the support were still not investigated in this reaction. New sentences were included in the introduction to highlighted it (p. 2):
“The development of such process under gas phase is highly desired due to the several advantages such as the easy scalability at industrial level, easy separation and regeneration of the catalyst, and carbon coverage can be mitigated in flow fixed-bed reaction by controlling the operating parameters” [18]. Besides that, operating at atmospheric pressure the consumption of hydrogen is limited, ideal for the production of FAS.
“To explore the effect of adding oxophilic or acidic sites, SBA-15 was also doped with low content of different species (Zr, Fe and Al). To the best of our knowledge, it was the first time that the catalytic properties of such solids were investigated for the transformation of the aldol condensation adduct over molybdenum based catalysts.”
Comment:
- The authors designed the work nicely, merely presented the results but failed to discuss the observed results elaborately.
Answer:
Aiming to improve the quality of our work, the manuscript was fully revised, with new characterization results (Figure 2 showing pore size distribution and Figure 3 showing SAXS patterns of Mo/SBA and Mo/Zr-SBA) and a more detailed discussion being included.
Comment:
- I suggest the authors to compare the previous literature similar to that work to find a merits of this work.
Answer:
As kindly suggested by the reviewer, we have included a more detailed discussion and comparison with the literature to explain our results. In addition, new references (21-23, 29, 33-36) were added in the revised manuscript.
21 Yoon, B.S.; Kim, K-J.; Cho, E.H.; Park, H-R.; Roh, H-S.; Ko, C.H. Enhanced Fe-Cr dispersion on mesoporous silica support using surfactant-assisted melt-infiltration for the water-gas shift reaction in waste-to-hydrogen processes. Int. J. Hydrog. Energy, 2023, 48, 24894-24903.
22 Wu, S.; Han, Y.; Zou, Y-C.; Song, J-W.; Zhao, L.; Di, Y.; Liu, S-Z.; Xiao, F-S. Synthesis of heteroatom substituted SBA-15 by the “pH-adjusting” method. Chem. Mater. 2004, 16, 486-492.
23 Ungureanu, A.; Dragoi, B.; Hulea, V.; Cacciaguerra, T.; Meloni, D.; Solinas, V.; Dumitriu, E. Microporous Mesoporous Mater. 2012, 163, 51-64.
33 Prasomsri, T.; Shetty, M.; Murugappan, K.; Roman-Leshkov, Y. Insights into the catalytic activity and surface modification of MoO3 during the hydrodeoxygenation of lignin-derived model compounds into aromatic hydrocarbon under low hydrogen pressures. Energy Environ. Sci. 2014, 7, 2660-2669.
34 Prasomsri, T.; Nimmanwudipong, T.; Roman-Leshkov, Y. Effective hydrodeoxygenation of biomass-derived oxygenates into unsaturated hydrocarbons by MoO3 using low H2 pressures. Energy Environ. Sci. 2013, 6, 1732-1738.
35 Valencia, D.; Garcia-Cruz, I.; Ramirez-verduzco, L.F.; Aburto, J. Adsorption of biomass-derived products on MoO3: hydrogen bonding interactions under the spotlight. ACS Omega, 2018, 3, 14165-14172.
36 Farah, B.; Lancelot, C.; Blanchard, P.; Richard, F.; Lamonier, C. Beneficial effect of W incorporation in supported Mo-based catalysts for the HDO of m-cresol. ChemCatChem, 2023, 15, e2022014.
Comment:
- Refer and include the following references to strengthen the current version of the draft; Light-Science & Applications 11 (2022) 250; Applied Catalysis B: Environmental 316 (2022) 121603.
Answer:
The article published in Appl. Catal B (ref 316 (2022) 121603) and entitled “Architecting the AuPt alloys for hydrazine oxidation as an anolyte in fuel cell: comparative analysis of hydrazine splitting and water splitting for energy-saving H2 generation” demonstrated that optimizing the various Au and Pt composition ratios could efficiently modulate the electronic structure of the AuPt alloys, increasing the feasibility of AuPt alloys for hydrazine fuel cells. Both catalytic systems (AuPt alloys) and reaction studied (oxidation) are very different from those studied in our article, therefore we believe that this article cannot be cited in our article.
The second article mentioned by the Reviewer entitled ‘Fundamentals and comprehensive insights on pulsed laser synthesis of advanced materials for diverse photo-and electronic applications” which was published in Science & Applications (11, 2022, 1-250) is an overview of the fundamental understanding and importance of the pulsed laser process. We don’t think it’s relevant to mention it in our article.
Author Response File: 
Author Response.doc
Reviewer 3 Report
The manuscript entitled “Transformation of furfural-acetone condensation adduct over Mo/SBA-15 catalysts under atmospheric pressure” was well written by the authors. Due to declining of non-renewable sources such as crude oil, the production of alternative fuels from biomass-derived platform molecules is emerging. The present manuscript comes under this category. Therefore, I recommend this article can be published after addressing the following comments.
1. The SAXS patterns after loading the MoO3 are missing in the manuscript. After the incorporation of 35% of MoO3 whether the mesoporous structure of SBA-15 remained intact or not. It is better to incorporate the SAXS patterns after MoO3 loading.
2. Oxophilic nature of dopants is helpful in deoxygenation explained by the authors but what about the acid sites? Do acid sites have any role in the deoxygenation process?
3. What is the role of Ethanol in the reaction? In my opinion, acid sites play a role in catalytic transfer hydrogenation. The authors need to clarify this.
4. Additionally, the authors need to perform the reaction with a Zr-SBA-15 catalyst also. Hence, the authors can come to a conclusion.
5. Furthermore, the authors need to conduct the reaction of the formation of adduct and deoxygenation in one step.
Typo graphical errors are there.
Author Response
Answers to the remarks of Reviewer 3 (Manuscript ID: catalysts-2552729)
Comment:
The manuscript entitled “Transformation of furfural-acetone condensation adduct over Mo/SBA-15 catalysts under atmospheric pressure” was well written by the authors. Due to declining of non-renewable sources such as crude oil, the production of alternative fuels from biomass-derived platform molecules is emerging. The present manuscript comes under this category. Therefore, I recommend this article can be published after addressing the following comments.
Comment:
- The SAXS patterns after loading the MoO3 are missing in the manuscript. After the incorporation of 35% of MoO3 whether the mesoporous structure of SBA-15 remained intact or not. It is better to incorporate the SAXS patterns after MoO3 loading.
Answer:
As requested by the reviewer, analysis of low angle XRD were performed over two supported molybdenum catalysts (Mo/SBA and Mo/Zr-SBA) and included in the figure 3(a). A discussion was also included (p. 4): “After introduction of molybdenum, those three peaks were always observed indicating that the mesopore structure was preserved. In addition, it was observed a broadening of the main reflection and slightly shift to higher 2θ values compared to the respective supports. This might be caused by a possibly slightly distortion of the mesoporous channels due to the deposition of MoO3 clusters on the pore walls”.
Comment:
- Oxophilic nature of dopants is helpful in deoxygenation explained by the authors but what about the acid sites? Do acid sites have any role in the deoxygenation process?
Answer:
The transformation of FAc may involve several reactions including hydrogenation, dehydration, deoxygenation, ring-opening and cyclisation. In this case, metal sites are usually employed for promoting the hydrogenation steps while acid and oxophilic sites are responsible for the dehydration and/or deoxygenation steps. However, side reactions such as isomerization or condensation can also happens depending on the catalyst properties, usually in the presence of acid sites. Also, reaction pressure has an important role and may determine the product distribution. As discussed in our manuscript, several authors perform this reaction under high H2 pressures which facilitate hydrogenation steps and ring-opening thus resulting in linear alcohols which in turn, are converted to linear alkanes via dehydration reaction, promoted by acid sites. This is not the case when the reaction is conducted at atmospheric pressure, as we have demonstrated. In our work, the catalysts were not able to promote the hydrogenation of the furan aromatic ring but cyclization after elimination of the carbonyl oxygen. Herein, the carbonyl group is first hydrogenated to produce an alcohol (product C), which in turn may be dehydrated to produce D over the acid sites, or hydrogenolysis of the C-OH bond over oxophilic sites followed by cyclization resulting in the product F. Indeed, hydrogenolysis followed by cyclization was promoted in more extent compared to dehydration in accordance with the best performance of the Mo/Zr-SBA catalyst.
Several sentences were added in the revised manuscript to improve discussion in part 2.2.
Comment:
- What is the role of Ethanol in the reaction? In my opinion, acid sites play a role in catalytic transfer hydrogenation. The authors need to clarify this
Answer:
In the transformation of FAc, ethanol was used as a solvent, due to the low miscibility of the reactant (4-(2-furyl)-3-buten-2-one) in nonpolar solvents. As mentioned by the Reviewer, it is known that alcohols such as ethanol may acts a hydrogen donor and thus may promote catalytic transfer hydrogenation (CTH), when performing the reaction in the absence of molecular hydrogen. In our work, we carried out the reaction under flow of molecular hydrogen thus probably minimizing the contribution of CTH. A new sentence was included in the revised manuscript (p. 7): “It is known that light alcohols may act as a hydrogen donor and thus, in the presence of specific catalysts it could promote catalytic transfer hydrogenation (CTH) reaction [29]. However, in our case, the reaction was carried out under flow of molecular hydrogen thus minimizing the contribution of CTH. Besides that, it is well stablished that secondary alcohols are more effective for CTH than primary alcohols such as ethanol [29]”.
A new reference (29) was added in the revised version:
- Panagiotopoulou, P.; Martin, N.; Vlachos, D.G. Effect of hydrogen donor on liquid phase catalytic transfer hydrogenation of furfural over a Ru/RuO2/C catalyst. J. Mol. Catal. A : Chem. 2014, 392, 223-228.
Comment:
- Additionally, the authors need to perform the reaction with a Zr-SBA-15 catalyst also. Hence, the authors can come to a conclusion
Answer:
The bare supports, including Zr-SBA, were tested and did show measurable conversion in the W/F value (73 mmol g-1 h-1) used. A sentence has been included in the revised manuscript (p. 7): “The supports without molybdenum did not show measurable conversion in such reaction conditions indicating that bare supports were inactive”.
Comment:
- Furthermore, the authors need to conduct the reaction of the formation of adduct and deoxygenation in one step.
Answer:
The Reviewer is right: the synthesis of alkanes by one step from a mixture composed by furfural and acetone is a very interesting challenge. Nevertheless, this study needs bifunctional catalyst allowing first the aldol condensation reaction by basic sites followed by hydrogenation/deoxygenation reactions that are favored over sites presents on molybdenum based catalysts as demonstrated in the present study. Such work will be done in the near future.
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
All the concerns raised were addressed except the comment related to energy content. It is very clear that the real content of SAF and the products obtained in this article are different. But, what about the energy content of the product mixture obtained in this work. Does the energy content of partially deoxygenated products meet the requirement of SAF to some extent? Any related information will be useful for the readers.
The article can be published after the minor revision.
Author Response
Answers to the remarks of Reviewer 1 round 2 (Manuscript ID: catalysts-2552729)
Comment:
All the concerns raised were addressed except the comment related to energy content. It is very clear that the real content of SAF and the products obtained in this article are different. But, what about the energy content of the product mixture obtained in this work. Does the energy content of partially deoxygenated products meet the requirement of SAF to some extent? Any related information will be useful for the readers.
Answer:
Based on our knowledge, it is very difficult to correctly answer to the remark of the reviewer. Nevertheless, it is well known that the energy content of oxygenated molecules is a little lower that the one of full deoxygenated compounds. For example, the calorific value of dimethylfuran, as an example of furan-based compound, is 33.7 MJ/kg compared to 43 MJ/kg of SAF. Note that our main product contains a furan ring and higher number of carbon and thus, we could expect a calorific value even higher. Therefore, it is an interesting intermediate to conduct to a final completely deoxygenated compound. In our work we propose to investigate new catalysts and less energy consuming procedure to convert the furfural-acetone condensation adduct compound. The complete deoxygenation of the product obtained here can be further investigated in future work. A new sentence was added in the revised version of our manuscript (p. 7-8): “It is well known that the heat of combustion (energy content) of oxygenated molecules is lower compared to the corresponding deoxygenated molecules and thus, energy content of the main product obtained here is still lower compared to SAF. For example, the calorific value of furan-based compounds such as dimethylfuran is 33.7 MJ/kg compared to 43 MJ/kg of SAF. As a consequence, the energy content of the mixture obtained under our experimental conditions is probably lower than the one of SAF”.
Reviewer 2 Report
May be considered for publication.
Author Response
No specific response
Reviewer 3 Report
I am completely satisfied with the responses by the authors. Now, I am pleased to accept the paper in its present form.
Author Response
No specific answer
