A Review of CeO2 Supported Catalysts for CO2 Reduction to CO through the Reverse Water Gas Shift Reaction
Round 1
Reviewer 1 Report
They have presented extensive work on the effect of ceria on RWGS reactions. They have focused more on catalytic effects than on characterization. I have suggested some changes in the order so that the reader's path is from fundamental to macroscopic/complex. Please review some units as wt.% changes during the text to wt%. Also, check the grammar, and possibly it is convenient to put some of the characterization results of some selected papers. This is mainly on the part of crystals and metal-support interactions.
Introduction
RWGS reaction is an interesting reaction, it depends on the conditions to be thermodynamically preferred or kinetically favorable. In which conditions are more spontaneous and in which one is fast? How does this affect the methanation? Please go deeper into this (line 26- line 57).
Line 102.- Su et al investigated the RWGS reaction with different materials, what else did this group find? Did these authors say something about ceria? What is concluded about this work that is important to mention?
The standard operating conditions of the RWGS and methanation reactions are not mentioned in the introduction, please include them.
2.- Mechanism
Did the reviewed works of the different catalytic systems change the reaction conditions? What conditions were used in each work? I know this would be tedious, so you may select the most important ones to make a better comparison.
Line 190.- Since Dai et al changed the ratios of ceria and gallium oxide, and you only mentioned what happened without ceria, what happened when the ceria content was augmented? How did the generated HCOOH* change?
Since there is no universal mechanism in RWGS and the reaction pathway is sensitive to the active metals, is it possible to condensate that information in a table that briefly explains the effect on the selectivity or functionality of Ga, Pt, Ce, Cu, and Ni oxides? To what the literature attributes the different mechanisms?
4.2. Active metal loading
Line 402.- Why low Cu content is better?
Line 411.- 1 wt.% and in other further lines should be corrected
Is it possible to conclude that a more dispersed active phase is better for activity and selectivity? could it be related to a property of the catalysts, e.g., acidity? This information could be important to link with the 4.3 section.
4.3. Shape and Crystal face effect
Line 478.- “The Co catalysts supported on NC ceria demonstrated slightly ______ catalytic activity than Co supported on rod-like…” there is a missing word; higher or lower?
4.5.- Bimetallic effect
Figure 11.- Fig 11 (a) should be improved.
4.6.- Metal size effect
As a suggestion, perhaps it would be better for this section to go after section 4.2. Perhaps the order of the subsections could be preparation methods, effect of crystal shape and face, metal-support interactions, active metal loading, then effect of metal size, the effect of CeO2 addition as promoters of reducible transition metal oxides, and bimetallic effect. In this order, you move from the fundamental to more complex macroscopic systems. If you first explain that shape and crystals are the basis of all catalytic activity because of the properties it provides, then the reader would better understand the rest of the subtopics. The crystal is fundamental because it provides active sites and properties. Next, metal-support interactions are essential (cause) to explain dispersion, metal charge effect, and metal size (consequence). Finally, complex systems of added ceria and their combination with other metals would be analyzed under the knowledge of fundamental characteristics.
If the figures exposed here are taken and not modified from other works please make sure the reference is correct or you have the corresponding permissions
Author Response
Please find the attached response to comments with details of modifications made in the manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review attached
Comments for author File: Comments.pdf
Author Response
Our response to the reviewer's comments and corresponding changes in the manuscript are presented in the attached file.
Author Response File: Author Response.pdf
Reviewer 3 Report
Generally it's an acceptable review. There are few grammatical faults which are negligible. The main criticism regarding this paper as review paper is that the authors have just reported other researchers findings. For example we can not conclude which synthesis method was the best or which reaction pathway was the main pathway and etc...., In the other words the discussion part should be revised. In the section related to Kinetics, other catalysts than ceo2 has been reported, if this paper focuses on CeO2 presenting other oxides kinetics doesn't seem to be right.
Author Response
Thank you for your review and suggestions. More detailed discussions are included in the revised version. We agree with the comments on the kinetics part. Unfortunately, only few kinetic studies are available on ceria based catalysts, and requires attention of researchers in their future studies. Nonetheless, the kinetic information is crucial to gain insights of the reaction system; so non-ceria based catalysts were also included in the review of kinetic models to provide a detailed framework for comparative analysis.
Round 2
Reviewer 1 Report
The new version is much better than the first one. The work is complete and makes a deep analysis of the system.
Reviewer 2 Report
I thank the authors for revising the manuscript which is now much improved.
