Effect of Zirconia on Pd–Pt Supported SBA-15 Catalysts for the Oxidation of Methane
Round 1
Reviewer 1 Report
1. In line 8, the authors mention “SBA-15”, please mention the stand of its abbreviations first.
2. The abstract should be broadened to give additional quantitative results.
3. Please end your abstract with a "take-home" message.
4. Reorder keywords based on alphabetical order.
5. Please do not use abbreviations in keywords.
6. It is unclear whether the author's something new in this work. According to evaluation, several published studies by other researchers in the past adequately explain the issues you made in the present paper. Please be careful to highlight in the introduction section anything really innovative in this work.
7. Previous study related needs to explain in the introduction section consisting of their work, their novelty, and their limitations to show the research gaps that intend to be filled in the present study.
8. Why present study using zirconia? Any specific reasons? Authors also needs to explain several commons materials used such as silicon nitride, alumina, and zirconia. Suggested to mention and explain it first before specifically mention zirconia. Please refer the relevant reference as follows: Minimizing Risk of Failure from Ceramic-on-Ceramic Total Hip Prosthesis by Selecting Ceramic Materials Based on Tresca Stress. Sustainability 2022, 14, 13413. https://doi.org/10.3390/su142013413
9. In the materials and methods, the authors need to add additional illustrations as a form of figure that explains the workflow of the present study to make the reader easier to understand rather than only the dominant text as a present form.
10. Additional information about tools used, such as the maker, country, and specification, should be included.
Author Response
Dear Reviewer 1, please find attached the document with all of the responses to your questions and comments
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This study developed a novel methane oxidation catalyst with hydrothermal stability and sulfur-resistant properties by adding Zr to Pd/Pt/SAB-15 catalyst. And the catalysts prepared with different content of Zr were systematically characterized to establish the physicochemical properties. Results show that the catalyst with the highest Zr concentration was the most active, stable, and sulfur resistant. The manuscript is very well organized with very interesting findings. I would suggest the manuscript be accepted. Several issues are as follows:
(1) Table 1 shows the nominal, SEM-EDX (a) and ICP MS (b) wt% values of the 2Pd/4Pt/xZr/SBA-15 catalysts, but “b” was not marked in it. In addition, it would be necessary to provide the SEM-EDS images for observing the dispersion of Pd/Pt/Zr active components.
(2) In XRD analysis, the Sherrer equation was used to calculate the particle size. Please provide a justification for which reflection is used for the calculation of PdO/Pt, such as (111), (200), (220), or (311) for PdO, and provide the corresponding selection basis.
(3) In XPS analysis, it can be seen that the intensity change of Pt0, Pt2+, and Pt4+ is obvious when adding the Zr content from 10 to 15 wt%. A brief discussion should be provided for the corresponding mechanism.
(4) During the test of aging in Fig.9, each curve seems to have a sudden drop process at the initial stage, especially for the catalysts with 10 or 15 wt% Zr. It should be explained in this part.
(5) The catalysts after the aging test should be characterized further to understand the effect of catalyst poisoning that may be caused by sulfate on pore structure and surface valence change on Pt/Pd.
Author Response
Dear Reviewer 2, please find attached the document with all of the responses to your questions and comments
Author Response File: Author Response.pdf
Reviewer 3 Report
In this work, authors studied effect of zirconia on performance of Pd-Pt supported catalysts for oxidation of methane. BET, XRD, XPS, and H2-TPR was used to characterize Pd-Pt active component and how that might affect the catalytic oxidation of methane. These data could potentially be useful to understand the catalytic property of Pd-Pt catalysts, which would be interesting to the catalysis researchers.
I think it can be accepted for publication after major revisions. I pointed below some important issues that might be helpful for the authors to improve their work.
- P 2, L. 50-52. When discussing "Pd-modified Mn-hexaaluminate catalysts", the authors gave a reference to the work [15], but this work does not discuss the catalysts of "Pd-modified Mn-hexaaluminate". Check the reference, please.
- P 2, L. 54-55. «Venezia et al. [15] found that a mesoporous SBA-15 supported Pd catalyst». Given in the list of references, the reference [15] has different authors. There is [15] Escandón, L.S.; Ordóñez, S.; Vega, A.; Díez, F. V. Sulphur Poisoning of Palladium Catalysts Used for Methane Combustion: 464 Effect of the Support. J. Hazard. Mater. 2008, 153, 742–750, doi:10.1016/j.jhazmat.2007.09.017. Check the references, please.
- It should be explained in the introduction why the authors chose the mesoporous support SBA-15? For its synthesis, it is required to use the Pluronic P123 template, which will increase the cost of the catalyst. Is it possible or impossible to take silica with a high surface area for the synthesis of the Pd-Pt supprted catalyst? What advantages does the mesoporous support SBA-15 provide? Is the mesoporous support SBA-15 stable enough in the presence of water vapor at temperatures of 600 C.
- The discussed catalysts had 2 wt% Pd and 4 wt% Pt. That is, the authors suggest using very high concentrations of noble metals, although all researchers are trying to reduce the content of noble metals. I recommend that the authors discuss this issue in the Introduction.
- H2 TPR profiles of Pd-Pt catalysts should be given starting from a temperature of 0 oC (Fig. 6 and 7). In this case, the reduction of highly dispersed PdO particles and the formation of palladium hydride will be visible. Then the authors can discuss whether there are PdO samples and possible reasons for platinum inhibition of PdHx formation.
- Table 4 is organized incorrectly. It is not clear what is given in the last two columns. I also recommend adding data for the catalyst on unmodified SBA-15.
- It should be rephrased "As such, there was no apparent change in the reducibility of Pt and Pd when they were added together on the same support" (L. 222), using the terms bimetallic and monometallic catalyst. Since only by referring to the experimental part, it can be understood that Pt and Pd were introduced sequentially, and not from a joint solution.
- A different designation has been used for the temperature of reaching 50% methane conversion: T50 (L 286, 287) and T50s (L291, 292). Are these really different values?
- It will be useful for the authors to analyze what proportion of the active component they observe using the XPS.
Author Response
Dear Reviewer 3, please find attached the document with all of the responses to your questions and comments
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Reviewers greatly appreciate the efforts that have been made by the author to improve the quality of their articles after peer review. I reread the author's manuscript and further reviewed the changes made along with the responses from previous reviewers' comments. Unfortunately, the authors failed to make some of the substantial improvements they should have made making this article not of decent quality with biased, not cutting-edge updates on the research topic outlined. In addition, the author also failed to address the previous reviewer's comments, especially on comments number 6 (lack of novel), 7 (not captured state of the art), and 8 (not incorporated the literature). Thank you very much for the opportunity to read the author's current work.
Reviewer 3 Report
I have no comments on the corrected version of the manuscript.
