Comparative Study on Ethanol-Based Oxygenate Synthesis via Syngas over Monometallic Rh Catalysts Supported on Different Zr-MOFs

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript “Comparative study on ethanol-based oxygenate synthesis via syngas over monometallic Rh catalysts supported on different Zr-MOFs” by R. Yu et al. is in line with previous ones (for example: https://doi.org/10.1016/j.fuproc.2012.08.020). The role of Rh-containing centers of different size, arrangement and valence state is widely discussed in the frame of oxygenate synthesis from CO and H₂. The author of this very elegant study clearly demonstrated at first effect of support morphology on Rh on-the-surface distribution, reducibility of Rh species and Ru chemical state on the surface. The further information about the surface intermediates taking part in hydrocarbons or oxygenates formation was obtained by FTIR investigations, where the authors demonstrated how the surface CO- and Rh-containing complexes of different structure behave under the reaction conditions. Combination of catalytic tests with the aforementioned results gave rather good evidence of importance of Rh⁺/Rh⁰ ratio        for oxygenation selectivity. The Rh/Zr-MOFs supported systems were found to be exhalent model for this purpose.

There are a couple of comments:

1. Line 76. The scanning range 2ϴ …
2. Lines 81-84. In line 82: to put point after 1 h. From “Temperature..to at 300 ^oC for 30 min.” mistake in a phrase composition.

Author Response

Comments1

Line 76. The scanning range 2ϴ …

Response1

Thanks for your suggestion. I made corrections in the manuscript.

Comments2

Lines 81-84. In line 82: to put point after 1 h. From “Temperature..to at 300 ^oC for 30 min.” mistake in a phrase composition.

Response2

Thanks for your suggestion. I made corrections in the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors investigated the performance of three different Rh catalysts supported on MOFs for converting syngas into ethanol and other C2+ oxygenates.

1. The catalytic activities of these catalysts are compared after 13 h of operation when steady state is reached. But XPS and DRIFTS are not taken under the same reaction condition, please justify the correlation between current charaterization results and catalytic activity after 13h reaction.

2. Please provide some post-reaction characterizations.

3. There are decent amounts of study on bimetallic RhM supported on MOF for conversion of syngas to C2+ oxygenates, which are not mentioned in the introduction.

4. How is the rate of reaction influenced by the different supports? It might be worthwhile to include the dispersion of nanoparticles and compare the TOF.

Author Response

Comments 1:

  The catalytic activities of these catalysts are compared after 13 h of operation when steady state is reached. But XPS and DRIFTS are not taken under the same reaction condition, please justify the correlation between current charaterization results and catalytic activity after 13h reaction.

Response 1:

  Thanks for the good suggestion. The catalyst exhibited good stability during the reaction, so the information obtained from XPS and DRIFTS characterization of the pre-reduced catalyst can represent the characteristics of the catalyst during the reaction process.

Comments 2:

  Please provide some post-reaction characterizations.

Response 2:

  Thanks for your constructive and professional comment.  XRD and TEM characterizations of post-reaction catalysts have been added in the last part of manuscript. and showed that the crystal of UiO-67 was basically maintained and no sintering of Rh particles can be seen, which was similar to that of the as-prepared catalyst.

Comments 3:

  There are decent amounts of study on bimetallic RhM supported on MOF for conversion of syngas to C₂⁺ oxygenates, which are not mentioned in the introduction.

Response 3:

 Thanks for the good suggestion. Three references about bimetallic Rh-M catalysts for conversion of syngas to C₂⁺ oxygenates have been added in the Introduction.

Comments 4:

  How is the rate of reaction influenced by the different supports? It might be worthwhile to include the dispersion of nanoparticles and compare the TOF.

Response 4:

  Thanks for your constructive and professional comment.  From the DRIFTS characterization results, there are different proportions of Rh clusters and Rh single atoms on different catalysts, and the calculation of TOF requires the establishment of a unified Rh particle size model. Therefore, the value obtained by TOF calculation is also a theoretical average, and cannot reflect the actual situation of the three catalysts. However, according to the reviewer's suggestion, we added a comparison of the amount of C₂⁺ oxygenates generated by each catalyst in unit time unit Rh molar quantity when discussing the reaction performance.