Ru-Ti Oxide Based Catalysts for HCl Oxidation: The Favorable Oxygen Species and Influence of Ce Additive

Round 1

Reviewer 1 Report

The authors have reported catalytic HCl oxidation using Ru-Ti oxide based catalysts. Whereas there have been some reports on this reaction catalyzed by other catalysts, no reports are found for the Ru-Ti oxides. The catalysts have been well characterized. The finding in this manuscript will contribute to a new aspect on the HCl oxidation which results in a low energy-consuming and sustainable industrial route. However, some discussion is not enough. Major modifications are necessary before this manuscript is accepted for publication.

 

1) The authors have confirmed that the addition of ceria to Ru-Ti oxide decreases the activity for HCl oxidation. However, ceria itself is effective for promotion of HCl oxidation, as reported in ref. 10. The authors should discuss more in detail the cause of the difference in the effect of ceria addition on RuO2-free and RuO2-including catalysts.

 

2) In the description on Raman analysis, the authors should discuss relation between Raman peak shifts and catalyst structure more in detail: why the increase in the Ru loading changes the RuO2 crystal size (smaller or larger?), how the increase shifts the band for RuO2 towards a lower wavenumber (from 515 to 507 cm-1), and how the increase in the Ru-O-Ti interaction shifts the band for rutile TiO2 towards a higher wave number (from 234 to 258 cm-1).

 

3) The captions for Figs. 4 and 8 should be described more in detail. At least, what each figure (a, b, c, …) means should be explained.

 

4) Table 2, No. 6-8 – The meanings of Ru-“2”Ce-“R”/TiO2-r (No. 6), Ru-“2”Ce/TiO2-r (No.7), and Ru-“2”Ce-“C”/TiO2-r (No. 8) should be described not only in Experimental but also in the caption for Table 2, for readers’ better understanding.

 

5) The authors has described that “all the reagents were analytical grade, supplied by Aladdin (Shanghai) and used as received without further purification”. However, it seems that TiO(OH)2 is not available in this reagent company. The authors should report the correct company name for TiO(OH)2. If the authors synthesized TiO(OH)2 by themselves, the experimental process should be reported.

 

6) P. 6, L. 163 – The authors have mentioned that the spectra of Ce 3d exhibit an overall shift towards lower binding energy. Compared to what?

 

7) There are some English grammatical errors and unfavorable expressions. Some examples are shown below.

7-1) P. 1, L. 32 – “as follow” should be changed to “as follows”.

7-2) P. 6, L. 166 – “rang” should be corrected to “range”.

7-3) P. 13, L. 358 – “deacon” should be corrected to “Deacon”.

The English of this manuscript should be revised by a language-editing and copyediting service or a native English speaker.

Author Response

Dear reviewer:

First of all, thank you so much for concerning our manuscript entitled “Ru-Ti oxide based catalysts for HCl oxidation: the favorable oxygen species and influence of Ce additive”. We have carefully studied your comments and tried our best to revise our manuscript which we hope meet with your approval. In addition, revised portions have been highlighted in yellow in the revised manuscript. Attached please kindly find the responses for you. We would like to express our great appreciation to you for comments on our paper. Looking forward to hearing from you.

Kind regards,

Mr. Jian Lu

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors reported Ru-Ti oxides catalysts for HCl oxidation to produce chlorine gas. They characterized them with a variety of techniques and investigated the preferred oxygen species, active sites, Ce additive, and the interaction between Ru and Ti. Among them, the XPS spectra are very important for the Ru-specific activity, but better curve fitting is required for better analysis as well as addition spectra (e.g. Ce 3d). Comments and questions are the following. 

1. Figure 2

The size distributions of TiO2 particles need to be measured from the image data rather than simply mentioning "smaller" or "not much changed", which are uncertain.

2. Figure 3(b)

(page 3, line 82) It would be better if the aggregated areas are marked in the figures.

3. Figure 4(e)

The atomic concentration calculated from the EDX spectrum is required to be included.

4. Figure 5

A reference literature is required for the assignments to the reduction of oxygen species they believe. Otherwise, the coordination number is just one of possibilities. In addition, the loading amount (wt. %) of Ru has to be mentioned. 

5. Figure 7

The curve fitting of Ru-2Ce-C/TiO2-r and Ru-2Ce/TiO2-r need additional component at ~280.5 eV. Ce 3d spectra are also important and have to be included to this manuscript. The key point seems to be the Ru 3d5/2 peak, which shifts to a higher BE with catalysts, but the deconvolution results are poor for the above two samples. Additional components those are required for much better fitting seems to be ignored for their preferred conclusions. It doesn't look ok. 

6. Figure 9(a)

Authors interpreted the charge transfer from RuO2 to TiO2 declined the Ru-specific activity. It may be acceptable with any reference that reported a similar effect unless the deconvolution of Ru 3d spectra are updated. 

7. Figures 9 and 10, Table 2

Error bars obtained from the reproducibility tests are required for the yields of HCl conversions.

8. Table 2

TOF (turnover frequency) is popular in catalysis than STY (space time yield), even though the unit is the same.

Author Response

Dear reviewer:

First of all, thank you so much for concerning our manuscript entitled “Ru-Ti oxide based catalysts for HCl oxidation: the favorable oxygen species and influence of Ce additive”. We have carefully studied your comments and tried our best to revise our manuscript which we hope meet with your approval. In addition, revised portions have been highlighted in yellow in the revised manuscript. Attached please kindly find the responses for you. We would like to express our great appreciation to you for comments on our paper. Looking forward to hearing from you.

Kind regards,

Mr. Jian Lu

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Authors replied to the reviewer's comments and questions well, and revised the manuscript according to them. The additional comments and questions are the following. 

1. On page 3, line 83

In Figure 3b, it isn't clear yet whether the aggregated area is the active phase for the HCl oxidation or not from the TEM image only. "the active phase" seems not to be proper in the sentence. 

2. Additional explanation in the authors' reply about the reduction of oxygen species would be very helpful for readers, so it is strongly recommended to be included in the main text.

3. Error bars in Figures 9 and 10

What does"error bars based on the original data" mean? They seem to be "how much accurate the measurements are". The question was "how much they are reproducible in the repeated experiments".

Author Response

Dear reviewer:

Thank you very much for your kindly patience with our manuscript entitled “Ru-Ti oxide based catalysts for HCl oxidation: the favorable oxygen species and influence of Ce additive”. We are really grateful to your comments for the manuscript. Based on your advice, we have amended the relevant parts for your approval. Revised portions have been also highlighted in yellow in the revised version. Attached please kindly find the response for you. We would like to express sincere appreciation to you for the constructive comments. Looking forward to hearing from you.

Kind regards,

Mr. Jian Lu

Author Response File: Author Response.pdf