Effect of Support on Oxidative Esterification of 2,5-Furandiformaldehyde to Dimethyl Furan-2,5-dicarboxylate
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsAuthors must pay attention to the journal's submission requirements. They need to include results and discussions and reorganize the text.
1. Authors need to highlight the bibliographic review on the topic of the work and present more bibliographic references relevant to the proposed topic.
2. What is specifically new about this research and how does it advance the current state of knowledge in the field of catalysis and chemical reactions?
3. How does the choice of support materials, specifically oxide and hydrotalcite supports, impact the catalytic performance of gold (Au) catalysts in oxidative esterification?
4. What is the general significance of the FDMC yield reaching 97.8% when using Au/Mg3Al-HT as a catalyst, and how does it compare to previous research in the area?
5. Are there potential limitations or sources of error in the experimental setup that could affect the validity of the results and conclusions?
6. How well does the article address the issue of support material stability (e.g., the loss of alkaline sites due to magnesium detachment)? Are potential solutions or future research directions proposed?
7. Does the article provide a clear explanation of the mechanisms involved in the oxidative esterification of DFF, particularly in relation to the role of the support material and gold nanoparticles?
8. Were the characterizations, including CO2-TPD and XPS, conducted with appropriate rigor and detail to support the findings regarding the concentration of alkaline sites and the electronic structure of Au?
9. How well does the article discuss the practical implications and potential applications of the research, especially in the context of sustainable and biomass-derived chemical processes?
Comments on the Quality of English LanguageGood quality of english language
Author Response
Comments and Suggestions for Authors
Authors must pay attention to the journal's submission requirements. They need to include results and discussions and reorganize the text.
1. Authors need to highlight the bibliographic review on the topic of the work and present more bibliographic references relevant to the proposed topic.
Response: Thanks for your advice. We added the bibliographic references which are related to our research in our manuscript.
2. What is specifically new about this research and how does it advance the current state of knowledge in the field of catalysis and chemical reactions?
Response: Thank you for your constructive comments. As previous reports, most of substrate is HMF. However, the HMF as substrate has some shortcomings: (1) the HMF usually contains impurities and humins, resulting in poor quality of PEF. (2) PEF showing yellow is usually caused by the decomposition of FDCA at high temperature during the polymerization of FDCA with ethylene glycol. We also revised our manuscript.
3. How does the choice of support materials, specifically oxide and hydrotalcite supports, impact the catalytic performance of gold (Au) catalysts in oxidative esterification?
Response: We are very grateful to your question for the manuscript. The catalysts with surface hydroxyl groups (Au/Mg3Al-HT, Au/Mg2Al-HT, Au/ZnO, Au/MgO and Au/La2O3) can well catalyze the oxidative esterification of DFF to FDMC, while catalysts with more acidic sites could only obtain aldol condensation products after the reaction. On the other hand, the difference of the supports will also affect the metal- support interaction of the catalyst. The electron cloud density on the Au nanoparticles is directly related to the adsorption behavior of the substrate on the interface (Chem. Eng. J., 2023, 454: 140322). We also addressed this issue in the manuscript.
4. What is the general significance of the FDMC yield reaching 97.8% when using Au/Mg3Al-HT as a catalyst, and how does it compare to previous research in the area?
Response: We sincerely appreciate your comments. In this study, Au/Mg3Al-HT catalyst was used to catalyze the oxidative esterification of DFF, with a 97.8% yield of FDMC. This result was higher than the highest yield (97%) of FDMC prepared from DFF reported at present (Green Chem., 2019, 21: 3464–3468). This higher FDMC yield contributes to the synthesis of high-quality polyester from fructose.
5. Are there potential limitations or sources of error in the experimental setup that could affect the validity of the results and conclusions?
Response: Thank you for your questions. In our research, the experimental protocol has been verified several times to ensure the reliability of the experimental results.
6. How well does the article address the issue of support material stability (e.g., the loss of alkaline sites due to magnesium detachment)? Are potential solutions or future research directions proposed?
Response: We gratefully appreciate for your valuable suggestion. The low stability of Mg3Al-HT support results in the leaching of magnesium during the reaction. In future, we will continue to conquer this problem and strive to optimize the structure of the support to improve its stability.
7. Does the article provide a clear explanation of the mechanisms involved in the oxidative esterification of DFF, particularly in relation to the role of the support material and gold nanoparticles?
Response: Thanks for your valuable comments. In the presence of Au/Mg3Al-HT catalyst, DFF was easily adsorbed and activated on the electron-rich interface. In the reaction, DFF was first oxidized to 5-formylfuran-2-carboxylic acid, following by the esterification to form FFME. The further oxidative esterification of FFME is much easier than that of DFF, so FFME can be rapidly converted into FDMC. We also described this mechanism in the manuscript.
8. Were the characterizations, including CO2-TPD and XPS, conducted with appropriate rigor and detail to support the findings regarding the concentration of alkaline sites and the electronic structure of Au?
Response: Thank you so much for your carefully check. In this study, all of the CO2-TPD tests maintain the same dosage of catalysts and analytical procedures. The determination of the concentration of alkaline sites on the catalyst surface is based on the results of CO2-TPD mass spectrometry. Before the XPS analysis, all the catalysts were pretreated in the same method to ensure the reliability of the analysis results. In the "Results and Discussion" section of our manuscript, we compared the effects of support on the electronic structure of Au in detail.
9. How well does the article discuss the practical implications and potential applications of the research, especially in the context of sustainable and biomass-derived chemical processes?
Response: Thanks for your suggestion. In our study, DFF can be produced by the direct oxidative dehydration of fructose from biomass sources. Preparation FDMC from DFF can avoid the humins and impurities caused by HMF. We also illustrate the practical implications and potential applications of our research in the manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors reported oxidative esterification of 2,5-furandiformaldehyde to dimethyl Furan-2,5-dicarboxylate by using Au-based catalysts. The paper is generally well-written, but there are a few issues that could be improved for the benefit of the reader. I recommend that this paper be accepted after minor revisions. Detailed comments are shown below.
1. Page 5, line 133 (first sentence), incomplete sentence.
2. In Section 2.2, it is helpful to state the reasons for the reduced selectivity at RT and 500°C.
3. The increase at 2h and decrease at 3h in Fig. 7 may be an experimental fault, unless there is a clear reason for it, and should be tried again.
4. Is it possible that the leached Mg is acting as a base rather than as a solid base?
5. On page 4, the fourth line from the bottom, please specify which catalyst was used to observe the Mg leaching.
Comments on the Quality of English LanguageI have no comments.
Author Response
Comments and Suggestions for Authors
The authors reported oxidative esterification of 2,5-furandiformaldehyde to dimethyl Furan-2,5-dicarboxylate by using Au-based catalysts. The paper is generally well-written, but there are a few issues that could be improved for the benefit of the reader. I recommend that this paper be accepted after minor revisions. Detailed comments are shown below.
1. Page 5, line 133 (first sentence), incomplete sentence.
Response: Thank for pointing out this question. We corrected this mistake in manuscript.
2. In Section 2.2, it is helpful to state the reasons for the reduced selectivity at RT and 500°C.
Response: Thank you for your advice. The decrease of active sites on the catalyst surface, is the primary reason for the low selectivity at RT and 500 °C. There are two points: (1) In Au/Mg3Al-HT-RT, a portion of the gold nanoparticles were covered by surfactant (PVP); (2) In Au/Mg3Al-HT-500, the increase of calcination temperature made the gold nanoparticles grow significantly and the active sites decreased. In the manuscript, we supplied the TEM data for Au/Mg3Al-HT-RT and Au/Mg3Al-HT-500, and provided explanatory illustration.
3. The increase at 2h and decrease at 3h in Fig. 7 may be an experimental fault, unless there is a clear reason for it, and should be tried again.
Response: We appreciate your question. Due to the irregular of catalytic performance, we triple checked the results, which verified that the yield of FDMC after 2 hours were higher than that of 3 hours. In our opinion, with the increase of water content in the reaction system, the hydrolysis rate of FDMC may be higher than the oxidative esterification rate of FFME, leading to the decrease of FDMC yield after 3 hours reaction.
4. Is it possible that the leached Mg is acting as a base rather than as a solid base?
Response: We appreciate your question. We thought that Mg as a solid base in the catalyst can promote the activation of C-H bond (Chem. Eng. J., 2023, 454: 140322). But after leaching, Mg2+ bind with the furan- acid compounds in the solution, leading a decrease in the carbon balance.
5. On page 4, the fourth line from the bottom, please specify which catalyst was used to observe the Mg leaching
Response: Thanks for your question. The Au/Mg3Al-HT, Au/Mg2Al-HT and Au/MgO were observed the Mg leaching. We also added the detail information in the manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors tested Au/Mg3Al-HT catalyst on the oxidative esterification of 2, 5-furandin-formaldehyde to Dimethyl Furan-2, 5-dicarboxylate. The Au/Mg3Al-HT catalyst exhibited the best catalytic activity with a good selectivity and fractional conversion.
I have some comment that it could improve the study.
1. XRD and TEM analysis, why authors didn't put the gold card into the diffractograms? Because of the TEM analysis shows a small nanoparticles.
2. Figure 3 clearly shows that the effect of support increase the selectivity and fractional conversion. However, the XPS analysis is not deeply discussing what is the interaction between the Au and support and the XPS profile was not deconvolved.
3. The effect of calcination temperature of catalyst, the authors didn't explore what happened with the crystallite particle-size and this variation of calcination temperature also affected the support…
4. In testability of Au/Mg3Al-H catalyst, they first observed a decrease in intensity of hydrotalcite (001) plane, how can authors be sure on this phenomenon? And it was not related to the XRD equipment. However, authors said that ICP-OES, XRD, XPS and TEM results showed a loss of the support basic site. How did they prove this idea? They didn't deeply discuss this phenomenon and didn't apply another analysis.
Comments for author File: 
Comments.pdf
Author Response
Comments and Suggestions for Authors
The authors tested Au/Mg3Al-HT catalyst on the oxidative esterification of 2, 5-furandin-formaldehyde to Dimethyl Furan-2, 5-dicarboxylate. The Au/Mg3Al-HT catalyst exhibited the best catalytic activity with a good selectivity and fractional conversion.
I have some comment that it could improve the study.
1. XRD and TEM analysis, why authors didn't put the gold card into the diffractograms? Because of the TEM analysis shows a small nanoparticles.
Response: Thanks for bring up this question. We added the gold card in figure 1a and 1b. A weak gold diffraction peak was observed in Figure 1a.
2. Figure 3 clearly shows that the effect of support increase the selectivity and fractional conversion. However, the XPS analysis is not deeply discussing what is the interaction between the Au and support and the XPS profile was not deconvolved.
Response: Thank you very much for the valuable advice. The XPS profile was deconvolved, and the figure 5 was revised. We discussed the interaction of Au and supports in manuscript.
3. The effect of calcination temperature of catalyst, the authors didn't explore what happened with the crystallite particle-size and this variation of calcination temperature also affected the support
Response: Thank you for bringing the issue. We analyzed the particle size of the Au/Mg3Al-HT catalysts after calcination at different temperatures. The size of gold in Au/Mg3Al-HT-RT, Au/Mg3Al-HT-300 and Au/Mg3Al-HT-500 are 5.1 nm, 5.5 nm and 9.1 nm respectively. In addition, combined with XRD data, Mg3Al-HT was transformed into composite metal oxide after calcination at 500 ℃. We also supplied the relevant TEM and XRD data in the manuscript with corresponding illustration.
4. In testability of Au/Mg3Al-H catalyst, they first observed a decrease in intensity of hydrotalcite (001) plane, how can authors be sure on this phenomenon? And it was not related to the XRD equipment. However, authors said that ICP-OES, XRD, XPS and TEM results showed a loss of the support basic site. How did they prove this idea? They didn't deeply discuss this phenomenon and didn't apply another analysis.
Response: Thank you very much for your comments and professional advice. In our study, all of the XRD tests adopted the same analysis method, to guarantee the reliability of analysis results. After reaction, we used ICP-OES to confirm the magnesium ion content in the solution, and 0.4766% magnesium was lost from the catalyst. We also refined the experimental data for this section in the manuscript.
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors
Please check the word theat, it must be theta… in Figure 1, inset Figure 6 and Figure 9a.
