A Study on Activity of Coexistent CO Gas during the CO2 Methanation Reaction in Ni-Based Catalyst
Round 1
Reviewer 1 Report
The topic studied is very interesting and topical. Experimental studies can be considered sufficient for this stage.
1. What studies are the data in figure 2 based on? (1900??). It is not observed from the bibliography that there are studies under the year 2000 (there are 4 bibliographic references between 1980 - 2000).
2. It must be specified if it is a molar ratio H2/CO2 or H2/CO (or mass ratio??) It is not clear how to write the molar ratio H2/CO2 4 or H2/CO 3 (I suggest using the notations: H2 : CO2 = 4 : 1 or H2 : CO = 3 : 1)
3. Figure 3 does not show the composition analysis for the gaseous mixture initially introduced into the catalytic reactor.
4. Use the international system for units of measure (L, m3, not cc). Correlate the gas flow with normal conditions; or specify the working conditions each time in the legend of the figures.
5. The notations A, B, C and D in tables 2 and 3 must be correlated with the notations a, b, c and d in the figures and in the text with the related explanations. In the text it is written both in capital letters and in small letters (I suggest to standardize the notations).
6. Specify how long the conversion was followed for the influence of temperature (figures 4, 5, 6, 7 and 8).
7. If the journal allows, use different colors in the figures for the working conditions (0%, 5%, 10%, 15% CO); it will be easier to follow.
8. For the studies from point 3.2 (figures 5 and 6), I suggest to draw up a table for the gas composition at the inlet and outlet from the catalytic reactor.
9. It must be specified what "long term test" means. The qualitative and quantitative assessment of the catalyst deactivation process of is not sufficient by testing only at 1400 min.
10. The authors are asked to specify and scientifically explain the decrease in catalytic conversion in the presence of CO.
11. The final conclusion must include the specification regarding the recommendation of a working temperature, as well as some conditions in the studied range. It may possibly be a future study for process optimization.
Success!
Author Response
Dear Editors and Reviewers,
First of all, we thank the editor and the anonymous reviewers for the valuable comments and suggestions they offered to improve the quality of this manuscript. We have incorporated the reviewers' comments and suggestions into our revision of the manuscript. Our responses to the reviewers' comments are as follows.
>> Please check the attached file
Author Response File: 
Author Response.docx
Reviewer 2 Report
The topic selection is very meaningful, and the research background is clear. Unfortunately, the completed research work by the authors is a bit simple. Not only the characterization and analysis of catalyst structures are far from enough. More importantly, the analysis and discussion of the results are only a simple description of the phenomenon, without sufficient analysis and demonstration, which leads to the existing results can’t present valuable conclusions or rules. Therefore, this paper needs to be major revision before whether it can be published..
1. In page6 line179, the expression of "CO conversion It was high regardless of co concentration in inlet gas" has grammatical problems.
2. According to Page 6 Line 186-188, when CO and CO2 coexist, the reaction between CO and H2 takes precedence over CO2 only from the high conversion rate of CO. firstly, This conclusion is not enough to be drawn. Secondly, in the presence of CO, the reason for the decrease of CO2 conversion is not the insufficient amount of H2, because the H2/CO2 feed ratio in the experiment is 4. In addition, when CO is not present, the conversion rate of CO2 is very high, indicating that the amount of H2 is sufficient. However, the decrease of the CO2 conversion after the introduction of CO only indicates that CO2 cannot compete with CO.
3. The result analysis and discussion in 3.2 is too simple. There is no in-depth discussion and analysis of the results, nor can the influence of different CO concentrations on the composition of the out-gas be shown.
4. Similarly, the analysis and discussion of results in 3.3 is too simple, failing to discover what the author is trying to illustrate, and failing to reflect any meaningful results or rules.
5. The characterization of catalyst structure in section 3.4 is too simple, only elemental analysis is carried out. First, EDS quantitative analysis itself has a relatively large error. Second, it is difficult to prove whether the structure of the catalyst has changed by the change of element content alone. At least, it is necessary to characterize the structural information such as crystal phase (XRD) and surface (SEM and TEM). In addition, the 24h stability test is far from enough to prove the good stability of the catalyst compared with the life of the industrial catalyst.
Author Response
Dear Editors and Reviewers,
First of all, we thank the editor and the anonymous reviewers for the valuable comments and suggestions they offered to improve the quality of this manuscript. We have incorporated the reviewers' comments and suggestions into our revision of the manuscript. Our responses to the reviewers' comments are as follows.
>> Please check the attached file
Author Response File: Author Response.docx
Reviewer 3 Report
In this manuscript, the authors reported Ni-Ce-Zr catalysts for CO2 methanation reactions with coexistence of 0-15% CO feeding gas. The results demonstrated the key role of the sufficient H2 supply for the enhanced conversions of both CO2 and CO reactants. The catalytically long-term stability of the catalyst was also evaluated in the presence of CO gas. The manuscript is recommended for publication after a revision.
The specific issues list below.
(1) The structural information of the catalysts before and after the reactions should be provided, such as the dispersion of Ni, coke amount (thermogravimetric analysis rather than EDS).
(2) Based on the results in Figures 4 and 5, the CO2 conversion under 5-15% CO co-feeding exhibits flat curves with the increasing reaction temperature from 200 to 350 oC. On the other hand, from Figure 5, there still is unreacted H2 in the whole temperature range. At such relatively low temperatures, the CO2 conversion cannot reach the thermodynamic equilibrium. The reason should be discussed.
(3) For the thermodynamic equilibrium plot in Figure S1, the effect of the co-fed CO should be considered.
(4) It would be better if the stability test was performed under the optimal reaction conditions with sufficient partial pressure of H2 for achieving a high CO2 conversion.
Author Response
Dear Editors and Reviewers,
First of all, we thank the editor and the anonymous reviewers for the valuable comments and suggestions they offered to improve the quality of this manuscript. We have incorporated the reviewers' comments and suggestions into our revision of the manuscript. Our responses to the reviewers' comments are as follows.
>> Please check the attached file
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors responded and made additions to the manuscript text.
Author Response
Dear Editors and Reviewers,
Thank you for your review.
Reviewer 2 Report
Although the authors have revised and improved quite a few problems. However, there are many areas that need to be improved in the results discussion section before the paper is published.
1. As for questions 3 and 4 in the first revision, the author did not add more analysis in the revision. Therefore, the author is requested to supplement and analyze the changes of each component in the outlet gas with the introduction of CO in the corresponding position of the article, so as to reflect the influence of the introduction of CO on the outlet composition.
2.There are quite a few grammatical errors in the whole text, so it is recommended to check and revise it carefully. For example，”The presence of CO in the feed gas causes competitive adsorption of CO and CO2 at the metal active sites. and COconversion is decrease[32-33].”
Author Response
Dear Editors and Reviewers,
First of all, we thank the editor and the anonymous reviewers for the valuable comments and suggestions they offered to improve the quality of this manuscript. We have incorporated the reviewers' comments and suggestions into our revision of the manuscript. Our responses to the reviewers' comments are as follows.
>> Please check the attached file
Author Response File: Author Response.docx
