The Effect of H2O2 Pretreatment on TiO2-Supported Ruthenium Catalysts for the Gas Phase Catalytic Combustion of Dichloromethane (CH2Cl2)
Round 1
Reviewer 1 Report (Previous Reviewer 2)
Comments and Suggestions for AuthorsI would like to commend the authors on their thorough revision of the manuscript. The major concerns raised in the previous review have been adequately addressed, and the manuscript has significantly improved in both clarity and scientific rigor. The authors have provided detailed responses to the questions, and the data now presents a coherent and convincing narrative regarding the influence of H2O2 pretreatment on the catalytic performance of TiO2-supported Ru catalysts.
Author Response
Thank you for your previous guidance and suggestions on this manuscript, which makes the manuscript more clear and scientific.
Reviewer 2 Report (New Reviewer)
Comments and Suggestions for AuthorsThe manuscript entitled ‘The effect of H2O2 pretreatment on TiO2-supported ruthenium catalysts for the gas phase catalytic combustion of dichloromethane (CH2Cl2)’ was submitted to the Journal Catalysis (MDPI). In this study, the authors used TiO2-supported Ru catalysts through treatment involving various H2O2 concentration doses and examined the catalytic combustion activity of DCM. Furthermore, the Ru-TiO2 catalyst was characterized by using different analytical techniques such as XRD, TEM, XPS, H2-TPR, NH3-TPD, and pyridine-IR methods to determine the effects of the morphology. I have the following queries for this manuscript:
Abstract:
The authors wrote 1 H2O2-Ru@TiO2 and 0 H2O2-Ru@TiO2 catalyst in the abstract, which seems confusing, as these numbers are 0, 1, and 3. Please write about these presentations in brackets.
The sentence ‘The sample characterization results illustrate that the 1 H2O2-Ru@TiO2 catalyst has a high number of acid sites (especially Brønsted acid sites), an appropriate amount of uniformly dispersed RuO2 particles and strong interaction between RuO2 and the TiO2 support, which are conducive to improving the catalytic combustion activity and stability of DCM.’ It isn't apparent. Please revise it.
Introduction:
Line 23, ‘Transition metal oxide catalysts are relatively inexpensive and antipoisoning’ what is the meaning of antipoisoning here?
Line 35, ‘TiO2 is often employed as a catalyst support due to its high surface area…’ Authors should include other metal oxides such as ZnO, CeO2, WO3, and LaMnO3. Improve the introduction using the current studies to degrade Chlorinated volatile organic compounds (CVOCs).
Result and discussion:
XRD:
(1) The authors should zoom the XRD graph to identify the RuO2 Peaks. Please use a line-matching graph of every JCPDS No in the XRD graph.
(2) The author did not mention P24 powder XRD graph in Figure 1. What is its necessity?
HRTEM and EDX: The particle size distribution for each system needs to be mentioned in Figure 2. The author should shift the EDX particle atomic mapping to the supplementary file.
XPS: Table 1 shows that XPS was done for the Fresh and Spent catalysts. Why did the fresh catalyst have Ruo % more than the spent catalyst? Is there a catalyst losing itself during CVOC degradation? The authors should explain it. After application of each catalyst, it should also be studied with XRD; nevertheless, at high temperatures, anatase TiO2 may transfer to the rutile phase (Stable phase). Write the TPR abbreviation and its application background in the manuscript, which broad readers cover.
Catalytic activity and discussion:
1- Line 154,’ These results prove the superiority of the catalyst preparation method.’ Please revise it.
2- Abbreviate the TPD test mentioned in Fig. 4 and line 171
3- During the DCM degradation using 1 H2O2-Ru@TiO2 system, the author should perform the Total Organic Carbon (TOC) test. Either carbon is going to oxidize or remove it as CO2 gas.
4- Figure 5, DCM conversion percent plot, shows degradation starting from 10 %, especially in 0 H2O2-Ru@TiO2, 1 H2O2-Ru@TiO2, and 3 H2O2-Ru@TiO2 systems. When using a mixture of RuO2 and TiO2, it starts from above 15 %. However, during the catalytic activities of these systems, the conversion % should start from zero. Please explore it.
5- —Figure 6: The authors used different systems until 150 hrs at various temperatures to check the DCM conversion %. These data points are confusing, such as at zero hr time when DCM conversion reached 98-99 % at a specific temperature. It is necessary to explore them to understand the apparent point of the findings.
Conclusion:
1- Revise the conclusion and include the core finding data point here, such as various temperature effects to degrade the DCM
Comments on the Quality of English LanguageOkay
Author Response
Thanks for your valuable comments. The response is on the attachment.
Author Response File: 
Author Response.pdf
Reviewer 3 Report (New Reviewer)
Comments and Suggestions for AuthorsRecommendation
Major Revision
Comments to Author:
No.: catalysts- 3276812
Title: The effect of H2O2 pretreatment on TiO2-supported ruthenium 2 catalysts for the gas phase catalytic combustion of 3 dichloromethane (CH2Cl2)
Major comments:
1. The title of the article and the title in the Electronic Supplementary Information differ. It is necessary to bring it to a single name.
2. The literary review in the «Introduction» does not reflect the problems and relevance of the research. The literary review is presented by only 17 sources, which date from 2002 to 2020. It is necessary to update the literature review and describe the research problem more specifically with references to the last 3 years.
3. In «3.1. Catalyst preparation»:
Authors need to be very careful in their formulations: « Approximately 0.0762 g…» How can such a value be approximate? «atheoretical 0.30 wt%»
In «3.3. Activity and stability tests»: How can different amounts of catalysts be compared with each other? «quantity of 254 0.2 g (0.0008 g for the sample of RuO2 only) catalyst….». Add the reaction temperature.
4. What is the «Pure RuO2» sample? Is it a commercial catalyst or synthesized by the authors? It is not mentioned anywhere. It is necessary to clarify this point. And add this sample to the XRD results.
5. What is this «Mixed RuO2 and TiO2»? How did you get it at work?
6. What is the specific surface area of the initial support TiO2 and catalysts? it is necessary to add this data to the text of the manuscript.
7. In the investigation of samples by the TPR method, there is no data on the amount of absorbed hydrogen for each sample and for each peak separately. These data are very important for understanding the degree of reduction of oxide phases.
Author Response
Thanks for your valuable comments. The response is on the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report (New Reviewer)
Comments and Suggestions for AuthorsI believe authors did the significant changes and corrections, after English proof reading manuscript is acceptable. Thank you
Comments on the Quality of English LanguageNeed one-time English proof reading.
Reviewer 3 Report (New Reviewer)
Comments and Suggestions for AuthorsThank you very much, now the article has become much better and can be published in its current state.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn general, I can recommend the article as presented, but there are some suggestions and comments:
1. I recommend expanding the introduction a little and, taking this into account, clearly articulating the purpose of the work.
2. On page 2 (line 48) it is written RuCl3·H2O (37.5%-41.0% Ru, Aladdin, China), what does (37.5%-41.0% Ru) mean?
3. Specify the concentration of ruthenium that was supposed to be introduced into TiO2 at the preparation stage. And for what reasons is this concentration taken?
Comments on the Quality of English LanguageMinor editing of English language required.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript by Zhiyong Fang and Xiangyu Song investigates the impact of H2O2 treatment on Ru-doped TiO2 catalysts for the catalytic combustion of dichloromethane (DCM). While the study presents interesting findings, several critical scientific and technical questions need to be addressed to enhance the robustness of the conclusions. The manuscript requires significant revisions before it can be considered for publication. The queries are noted below-
1. The catalytic material is a composite TiO2-RuO2 material and not Ru-doped TiO2 as the authors have claimed. The HR-TEM images show just the Bragg’s planes for TiO2 and the HAADF images along with electron mapping (combined with XRD) prove the presence of TiO2 and RuO2 in a discrete way. If the authors disperse TiO2 and RuO2 in the same ratios as in their catalyst (1H2O2-Ru@TiO2) using the same solvent and then take HRTEM and HAADF images, would they be different than the claimed catalyst?
2. In the XRD spectra (Figure 1), the reviewer do not see any differences in the spectrum for 0, 1 or 3-H2O2-Ru@TiO2. The peaks for RuO2 looks same in all three XRD spectra. What kind of conclusions the authors are drawing from here? Why the XRD peaks for RuO2 extremely poor? Can the authors provide a quantitative analysis of the crystallite size using Scherrer’s equation?
3. The authors have not provided any data for TiO2-RuO2 molar ratios. An ICP data will help here.
4. For catalytic DCM conversions, there are three important control experiments are missing- (a) catalysis using TiO2 only, (b) catalysis using RuO2 only using the same molar % of RuO2 (lab made RuO2 following the similar method) as is present in the catalyst, and (c) mixing TiO2 and RuO2 in the same amount just before catalysis and then running the catalytic experiments.
5. The catalytic activity is primarily discussed in terms of DCM conversion at a specific temperature. What about the selectivity towards different oxidation products? How does the formation of CO2 compare with other by-products?
6. The study claims that excessive H2O2 decreases catalytic activity due to weakened RuO2-TiO2 interaction. Is there any direct evidence (e.g., TEM or XPS) showing the physical separation or phase segregation of RuO2 at higher H2O2 concentrations?
7. The H2-TPR profiles are discussed in terms of reduction peaks, but the exact H2 consumption values are not provided. Can the authors include quantitative reduction data to strengthen their arguments?
8. The manuscript mentions Brønsted and Lewis acid sites as critical factors. However, the role of these sites in the reaction mechanism is not elaborated. Can the authors propose a detailed reaction pathway and the involvement of these acid sites?
9. The Deacon pathway is referenced for Ru catalysts. How does the H2O2 treatment specifically influence this pathway? Is there any experimental evidence (e.g., intermediate species detection) supporting this
10. The article lacks an entire section of post-catalytic catalyst characterisation.
11. The manuscript lacks any statistical analysis of the experimental data. Are the differences in catalytic performance statistically significant? Including error bars, standard deviations, or confidence intervals would add rigor to the data interpretation.
Comments on the Quality of English LanguageThe entire article is written in past tense which makes it so confusing to follow. A major grammar correction is needed.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have partially addressed questions raised by reviewer #2. Following are the point-to-point concerns of reviewer-
Comments 3: The authors have not provided any data for TiO2-RuO2 molar ratios. An ICP data will help here.
Response 3: Thanks for your valuable suggestion. I’m so sorry for not providing the loading amounts of Ru species, correlating to TiO2-RuO2 molar ratios. Actually, the amount of raw materials RuCl3 and TiO2 are the same, and there is no loss of Ru species and TiO2 during the preparation process, so the Ru species loading amount in all catalysts is the same. In my opinion, it might be acceptable to use theoretical values to represent the loading amount of Ru. To clarify, loading amounts of Ru were added in Section 3.1 Line 166: “…, and each catalyst contained an identical 0.3 wt% loading amount of Ru”
Reviewer question: “Actually, the amount of raw materials RuCl3 and TiO2 are the same, and there is no loss of Ru species and TiO2 during the preparation process, so the Ru species loading amount in all catalysts is the same”.
Where is the evidence for this claim?
“In my opinion, it might be acceptable to use theoretical values to represent the loading amount of Ru”.
In scientific contexts, opinions alone carry little weight without supporting evidence.
Comments 4: For catalytic DCM conversions, there are three important control experiments are missing- (a) catalysis using TiO2 only, (b) catalysis using RuO2 only using the same molar % of RuO2 (lab made RuO2 following the similar method) as is present in the catalyst, and (c) mixing TiO2 and RuO2 in the same amount just before catalysis and then running the catalytic experiments.
Response 4: Thanks for your logical and valuable suggestions. It is generally agreed that the TiO2 support provides abundant acid sites and has a high specific surface area, promoting the adsorption and dissociation of CVOCs. The chlorine species dissociatively adsorbed on the active sites can be removed in form of Cl2 via the Deacon pathway catalyzed by RuO2. Moreover, there might exist interaction between TiO2 and RuO2 and they both play important roles on the catalytic activity of DCM oxidation. Therefore, we did not test the catalytic activities of TiO2 or RuO2 separately.
Regarding (c) mixing TiO2 and RuO2 in the same amount, we think the physically mixing might not generate interaction between TiO2 and RuO2. Nevertheless, this is not the focus of this manuscript. As you know, this paper aims to studying the effect of various H2O2 concentrations on the TiO2-supported Ru catalysts and their catalytic performance. In my option, it might be acceptable that the catalytic testing lacks of the control experiments.
However, we really want to thank you again for your constructive comments. These control experiments provide a new idea to understand the role of separated composite, physically mixed composite, and supported composite. It is of vital importance to recognize the intrinsic reaction in our future work.
Reviewer question: The reviewer would like to see these crucial catalytic control experiment because it is central to this manuscript’s claim.
Comments 7: The H2-TPR profiles are discussed in terms of reduction peaks, but the exact H2 consumption values are not provided. Can the authors include quantitative reduction data to strengthen their arguments? Response 7: Thanks for your important comments on the H2-TPR characterization. We would like to apologize for not testing of H2 consumption values. The reduction peaks could represent the interactions between Ru species and TiO2. In my option, it might be acceptable to only analyze the reduction peaks. To make it more reasonable and coherent, we revise the analysis in Section 2.1 Line 127 and Line 130: “…, implying that the interaction between RuO2 species and the TiO2 support increased, which corresponds to the XPS analysis results for Ti 2p” “…, indicating that interaction between RuO2 species and the TiO2 support decreased. It can be inferred that the phase segregation of RuO2 nanorods, as shown in the TEM images, results in weakened interaction.”
Reviewer question: The authors didn’t understand the question and hence it is requested to answer the address it correctly.
Comments 10: The article lacks an entire section of post-catalytic catalyst characterization. Response 10: Thanks for your valuable comments. Actually, the post-catalytic catalysts were analyzed by XRD and TEM, but they are almost like to fresh catalysts due to the short time of testing. In addition, the post-catalytic catalyst characterization probably has little impact on the focus of this manuscript, so we hope that it could be allowed to ignore the post-catalytic catalyst characterization. As we all know, the characterization of post-catalytic catalyst or deactivated catalyst are important to understand the intrinsic reaction and promote the stability of catalyst. We plan to test the catalytic activities for a long time until it becomes inactive a little, and then conduct a comprehensive analysis of spent catalyst. The differences of fresh and spent catalyst will guide us to improve catalyst performance in the future.
Reviewer question: “In addition, the post-catalytic catalyst characterization probably has little impact on the focus of this manuscript, so we hope that it could be allowed to ignore the post-catalytic catalyst characterization”.
Absolutely no. The characterization of any colloidal catalyst post-catalysis is critical.
The authors are strongly recommended to address this issue.
Author Response
Please see attachment
Author Response File: Author Response.pdf
