Effect of Pyrolysis Conditions on the MOFs-Derived Zinc-Based Catalysts in Acetylene Acetoxylation

Round 1

Reviewer 1 Report

 

The paper from Shen et al. analyzed how the synthesis of MOF would influence the catalyst performance of the pyrolyzed MOF toward acetylene acetylation reaction. The authors thoroughly investigated the effects of (1) ratio of starting materials of the MOF, (2) morphology of MOF (cracks etc.), (3) temperature of hydrothermal synthesis, (4) substituting MOF linkers, and (5) pyrolysis temperature. After that, the authors went on to characterize the materials pyrolyzed at different temperatures using XPS, ICP, Raman spectroscopy aiming to understand the chemistry behind the catalytic activity. The authors’ attempt toward a thorough and detailed study from both chemistry and catalytic performance is appreciated, however, I have a couple of questions toward some reasonings, evidences and writing:

1. The section discussing ICP, PXRD and XPS results (line 269-293) is poorly written. Not only there are a couple of incomplete sentences (see point 5), but also the claims are contradicting between paragraphs. In line 277, it was written “The Zn content of MOF5-800 as measured by ICP is only 0.6, which is consistent with the XRD results.” What is the unit of “0.6”, mass ratio, molar ratio, or some other units? It seems that author want to indicate that there is Zn exist in MOF5-800 although the level is low. Then, in 288, authors wrote “Comparison of the results measured by the two methods shows that the data differ significantly.”, seems to indicate that the XPS shows a high level of Zn content. What is the actual point that the authors want to make?

Following this question – the authors stated “…the surface-active component is most easily lost during high temperature calcination”, however, zinc’s evaporation point is at 907C, which is higher than any calcination temperature that was reported in this manuscript. How could Zn lost during this process? Also, previous report has shown that the reduction of ZnO by carbon happens above 750C (Fletcher, E. A. Ind. Eng. Chem. Res. 1999, 38, 2275; Yang, S. J.; Kim, T.; Im, J. H.; Kim, Y. S.; Lee, K.; Jung, H.; Park, C. R. Chem. Mater. 2012, 24, 464), I would suggest considering metallic Zn in MOF5-800 instead of ZnO.

2. From line 294-304 the authors drew conclusion from XPS of MOF5-700,750 and 800, stating that “a higher amount of -OH, -C=O and higher oxygen content is beneficial to the catalytic performance.” I would like the authors to further consider this statement in combination with the previous report that ZnO starts to be reduced to Zn at 750C. Furthermore, what is a plausible mechanism that -OH and -C=O would benefit acetylene acetylation reaction? According to previous reports, the mechanism requires a non-full coordination metal acting as either sigma-bonded acceptor (B.A. Morrow, Journal of Catalysis, 1984, 86, 328-332) or a pi-bonded acceptor followed by beta-hydride elimination (Stacchiola, D.; Calaza, F.; Burkholder, L.; Schwabacher Alan, W.; Neurock, M.; Tysoe Wilfred, T. Angew. Chem. Int. Ed. 2005, 44, 4572–4574). It seems that -OH and -C=O coordination contradicts with such mechanisms.

3. The MOF-5 precursor used by authors has a BET surface area of 301.40 m^2/g. This indicates either there’s significant defect or unwashed starting materials clogging the pore. A properly synthesized and evacuated MOF-5 should be able to reach to a BET surface area of 3000 m^2/g (S. S. Kaye, A. Dailly, O. M. Yaghi, J. R. Long, J. Am. Chem. Soc. 2007, 129, 14176-14177). I wonder if there is a specific reason that the authors decide so, for example leaving unwashed starting materials inside pores, if any, helps to increase catalytic performance.

A question related to this – in Figure 9, why MOF5-750 would have nitrogen in it?

4. There are a handful of statements that needs references:

·      Line 150-156, line 158: references needed to support authors’ interpretation on the TGA curves of MOF-5, especially for the statement at line 158 “…and above 600°C, the organic ligands were completely decomposed”. The authors didn’t provide any evidence that the organic ligands were fully decomposed.

·       Line 168: “The solvent DMF at 153°C decomposed to formic acid at high temperatures because of its boiling point.”

·       Line 172: “The cracking is due to the breakdown of gas from the solvent in the structure, resulting in the breakage of the morphology.” This was hypothesized by authors at line 169, however was directly written as a statement here. Reference is needed if it is a statement.

·       Line 319-322.

5. Grammatical error/typo/poorly written sentences/other issues

·       Line 164-166: suggest modifying “unformed nuclei” into smaller crystallites. In crystallization theory the nuclei should be a structure at very small length scale.

·       Line 275-277: “…indicating that the higher calcination temperature resulted in the loss of a large amount of Zn and O binds to C and evaporates in the form of CO or CO2, leaving only the carbon carrier.”

·       Line 284: “MOF5-750 contain Zn, O and C, but the presence of Zn and O is hardly observed in MOF5-800, indicating that the high temperature calcination.”

·       Line 291-292: “The comparison of the two methods. The comparison of the two methods also shows that…”

·       Line 294: (b) and (c) in which figure?

·       Line 303: “MOF5-800 compared to MOF5-700 and MOF5-750.” Where is the later part of the sentence?

·       Line 316: “With the increase of calcination temperature makes the graphitization of the catalyst gradually increase.”

 

Based on the above points, I suggest a minor revision to the manuscript before being accepted by the journal Catalysis.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Reviewing Report for the manuscript ID: catalysts-2222630

Here is my reviewing report for the manuscript under title “Effect of pyrolysis conditions on the MOFs-derived Zinc-based 2 catalysts in Acetylene Acetoxylation” with ID number: catalysts-2222630, 

In this manuscript, the authors reported the optimize the preparation conditions of MOFS under different conditions. They prepared MOF5-700, MOF5-750, MOF5-800 by pyrolysis of MOFS precursors under nitrogen, to be utilized as catalysts for acetylene acetylation reaction system. The results are interesting and varying from the catalytic activity of catalysts was significantly different (MOF5-700 (48%), MOF5-750 (62%), MOF5-800 (22%) with considerable stability.

Although the presented work is promising, the manuscript still needs to be carefully revised before acceptance for publication in this journal. The authors need to revise their manuscript according to the following suggestions.

 1-    The language of the manuscript needs to be extensive revised.

2-    The information mentioned in the abstruse is enough, however, the authors need to rewrite in a better way to be more accurate.

3-    In the manuscript, there are many Figures (17), I recommend to collecting them to be in smaller number.

4-    In line 133-142, can the authors cite some related articles to support theirs disc discussions?. Also, it seems that as decreasing the amount of H2BDC, the size became smaller, can the authors give a specific reason why the ratio 1:0.3 is better than the others?

5-     In line 150-151, the authors mentioned that “In the second stage, there was a period of rapid weight loss around 200°C–350°C” however, the figure show slow loss (almost stable), please revise.

6-    In line 153-154, the authors mentioned that “At around 153 350°C–480°C, the mass remained stable” however, the figure show rapid loss, please revise.

7-    In table 2, the authors need to add % to Mean (M) factor. Also, they can add the n=10 on the table caption, and no need to add next to each value.

8-    In XRD discussions (line 269-278), XRD peaks at high temp. show two broad bands at about 25, and 40 for carbon, the authors needs to discuss this in the revised form.

9-    In line 284, the authors mention “indicating that the high temperature calcination” I think they should delete it.

10-         The authors need to rewrite, and discuss the XPS section in lines (282-304)

11-         In Figure 16d, can the authors show why the ICP value of Zn is high?

12-         All figures needs to be in high resolution

Author Response

Please see the attachment

Author Response File: Author Response.pdf