Metal Embedded Porous Carbon for Efficient CO2 Cycloaddition under Mild Conditions
, Meng Liu 1,2, Jichao Wang 1,2, Serge Zhuiykov 3 and Francis Verpoort 1,4,*Round 1
Reviewer 1 Report
Chennai,
15th March, 2022.
Referee report to Catalysts:
Manuscript ID: Catalysts-1654865
Title: Confined zeolitic imidazole frameworks template derived metal embedded porous carbon for efficient CO2 cycloaddition under mild conditions
Authors: Chen Qi, Somboon Chaemchuen, Meng Liu, Jichao Wang, Serge Zhuiykov, Francis Verpoort*
Summary: The original paper of Verpoort et al., deals with the synthesis of metal (Zn or both Zn and CO) encapsulated N doped porous carbon materials from zeolite imidazole framework (ZIF-8, ZIF-67, and ZnCo-ZIF) as templates. The materials thus obtained were used as catalysts for the fixation of CO2 via the cycloaddition of CO2 to epoxide by the synergistic activation of the epoxide (epichlorohydrin) and CO2 via the catalytic active sites, namely, the Lewis acid site (either Zn or both Zn and Co) and the Lewis base sites (pyrrolic N) yielding cyclic carbonates. Such cyclic carbonates have strategic significance as they are used as electrolytes in Li ion batteries apart from many other uses. Zn encapsulated N doped porous carbon obtained from the pyrolysis of ZIF-8 was found to be the best catalyst with consistent catalytic activity and high product yield for seven reaction runs under modest reaction conditions (90 °C and 1 bar CO2 and for 24 h). Though a web of Science search with the keywords, namely, CO2 cycloaddition and epoxide and cyclic carbonate and ZIF-8 showed 15 results none of them dealt with the findings disclosed by Verpoort et al., Owing to the originality and usefulness of the results, the work of Verpoort et al., is recommended for publication in the journal Catalysts after minor revision.
Major issues: None
Minor issues: Supplementary materials is missing. English language needs significant improvement throughout the paper. The names of Chinese authors need to be cited properly. Figures numbers to be properly referred. In addition, the following specific changes need to be made for improving the readability of the paper.
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The title can be rewritten as “Metal embedded porous carbon for efficient CO2 cycloaddition under mild conditions” The use of zeolite imidazole framework as template is not the novelty of the paper. Rather the use of Zn embedded porous carbon for CO2 cycloaddition to epoxides to form cyclic carbonates” is.
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The referee could not access the supplementary materials and so could not see Figs. S2 – S5; the supplementary material can be provided with the revised manuscript
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Rewrite “The evaporation temperature of zinc (> 908 °C) …. at 1000 °C” with “As the pyrolysis temperature of Zn-ZIF is 1000 °C and zinc is known to evaporate at a temperature above 908 °C, there is a chance that the diffraction peaks of Zn may not be seen in the pyrolyzed sample.”
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In Fig. 1, the colour notation followed is confusing. XRD pattern of ZIF-67 is shown in red where as its pyrolyzed products Co/CN is shown in blue. Follow the same colour notation for the XRD pattern of the template and the result carbon. Likewise, the order of representing the XRD plots of templates and the resulting carbon materials as well
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How Zn was retained in the pyrolyzed product ZnCo/CN while Zn was evaporated in the case of Zn/CN when the pyrolysis temperature of both ZnCo-ZIF and ZIF-8 are the same (1000 °C)?
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The nitrogen content in the pyrolyzed samples do not follow the order of thermal stability of ZIF templates (see Table 1). Why does the authors attribute the amount of N content in the pyrolysed samples to the strength of M-N bond (on metal nitrogen interaction or the thermal stability of ZIF). Clarify.
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How metal nanoparticles are formed in the presence of inert atmosphere? What is the reducing agent to reduce metal ions, namely, Zn2+ and Co2+ to Zn and Co respectively?
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Reference 29 does not deal with CO2 cycloaddition with epoxides
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Owing to constraint with time, these lines could not be read line by line but was only glanced through. The authors are advised to correct of any errors related to scientific/English language/typographical/misrepresentation of figure numbers, to avoid another revision.
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Detailed procedure adopted for the calculation of conversion of epoxide and yield of cyclic carbonates need to be provided. The supplementary material referred by the authors in lines 330 and 333 could not be accessed by the referee.
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The following papers can be cited: 1. Vitillo, J. G., Crocella, V., Bonino, F., ZIF-8 catalyst in ethylene oxide and propylene oxide reaction with CO2 to cyclic organic carbonates, Chem Engineering, 3 (3), 60, 2019. 2. Kuruppathparambil, R. R., Babu, R., Jeong, H. M., Hwang, G. Y., Jeong, G. S., Kim, M. I., Kim, D. W., Park, D. W., A solid solution zeolitic imidazolate framework as a room temperature efficient catalyst for the chemical fixation of CO2, Green Chemistry, 18 (23), 2016, 6349-6356. 3. Xiang, W. L., Shen, C. Y., Lu, Z., Chen, S., Li, X., Zou, R., Zhang, Y. P., Liu, C. J., CO2 cycloaddition over ionic liquid imidazolate frameworks: effect of Lewis acid/base sites. Chemical Engineering Science, 233, 2021, 116429.
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Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
In this manuscript, Verpoort et al. report the synthesis of nitrogen-doped porous carbon materials, properly characterized them and applied as catalysts for CO2 fixation into cyclic carbonates. While the characterization part is well presented, some other parts giving to me as a referee, big questions and the further clarifications are required to improve the manuscript. The present version of the manuscript is not publishable at the moment and should be revised. Below provided my comments and suggestions:
- The authors should make more clear, what the really new aspect of this study are in comparison to their previous report (reference 19). This should be emphasized in the conclusion part.
- It is difficult to understand how (and why?) suddenly the organic linker (2-MIM) has been appeared in the text on page 4, line 170? And what is it 2-MIM in fact? It should be properly described in the text when it is appearing.
- The authors mentioned about application of epoxides in the text (page 7, line 288), but in fact they provided only results with epichlorohydrin in the main text. I recommend to move the results with other epoxides from the SI to the main text and properly discuss about the obtained results.
- It is not clear under which conditions the 2-methylimidazole catalyzed the reaction (page 8, line 309). Also, the authors should include this result into Figure 6. If the reaction conditions are different, then should also be mentioned about it.
- The authors mentioned in the text “However, it is impossible to recycle 2-MIM as a catalyst from the reaction mixture, which is the main drawback to applying 2-MIM as a catalyst.” How about the removal of the obtained cyclic carbonate by distillation and reuse the remaining 2-MIM as a catalyst? It is a common practice in this case.
- Figure 6: In case of ZIF catalyst, is it possible to find out the metal % content in it, and then accurately calculate the catalyst loading based on metal weight. Otherwise, it is difficult to judge about activity without information about catalyst loading.
- In the footnote under Figures 6 and 7 it is provided the next phrase: “Conversion and yields (isolated) were determined by 1H NMR and using 1,3,5-trimethylbenzene as the internal standard.” In fact, isolated yield mostly is calculated on base of mass balance of isolated pure product. So, the authors should remove “isolated” or should provide the real isolated yield.
- The mechanism proposed on Figure 8 looks speculative. It is difficult to believe that a metal center acts a nucleophile and not as a Lewis acid as mentioned in the main text. Probably a nucleophilic part should be a nitrogen center which facilitates the ring opening process under activation of epoxide by a metal ion as a Lewis acid coordinated to an oxygen atom of epoxide. Moreover, it is nonsense that the electrophilic metal center stabilizes the formed carbcation as drawn on Figure 8. I recommend carefully revise the mechanism description.
- Does it possible the formation of polycarbonate products in the experiments? For example, the broad signals presented on Figure S21 in the SI looks like polypropylene carbonate. If it is true, then the authors also should discuss about it in the text. It is highly possible the formation of the polymers under the reported here conditions because the authors don’t use the nucleophilic co-catalyst.
- It is also desirable to compare the results with other zinc based heterogeneous catalysts (for example, see the papers: Chem. Eur. J. 2020, 26, 13686-13697; Appl. Catal. B 2019, 254, 380-390; ChemCatChem 2019, 11, 511-519; J. CO2 Utilization 2021, 53, 101718). Especially pay attention to the works: reference 40 and J. Catal. 2022, 407, 65-76.
- What does mean “[002]” on page 3, line 101?
- In Figure 3 the inset (b) is missing and moreover there is no Figure 3c!
- Delete double “The” on page 6 (line 215).
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
1. Please provide the ESI file.
2. Please clarify what's new in this work in comparison to results published earlier, especially [https://doi.org/10.1016/j.jcat.2018.11.027]
3. Are there any real evidences for Zn participation in catalytic process on Zn/CN? This sample is characterized not only by low Zn content but also by very high surface area compared to other samples. This feature might have made incorrect to compare Zn/CN sample with the usual activated carbon reference sample.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have carefully revised the manuscript taking into consideration the comments of the reviewers. The article can be published in Catalysts after changes made:
- It sounds strange for me the next sentence “Most importantly, no side reaction or polymeric product could be detected, demonstrating the high selectivity of Zn/CN as a catalyst.” In fact, the authors in their response have mentioned the formation of some amount of oligomeric or polymeric carbonates in case of several epoxides that was also evidenced in 1H NMR spectra (in some case it is in considerable amounts). So, I strongly recommend, at least, to mention a fact of the formation of oligomeric or polymeric carbonates, although the authors didn’t investigate it in detail. Otherwise, in my opinion, some part of story will contain the lying part.
- Instead of “catalyzes” should be “catalysis” (page 2, line 58).
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Authors did their best in the revision of the manuscript and now it seems suitable for publication. Finally, I'd recommend to thoroughly revise english grammar during the final proofreading.
Author Response
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