Catalytic Decontamination of Carbon Monoxide Using Strong Metal–Support Interactions on TiO₂ Microparticles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is in line with the scope of the Catalysts.

The following are detailed comments for this manuscript:
1. Lines 11 and 17: State quantitatively the efficiency of the TiO₂-Pt catalyst in oxidizing CO to CO₂.
2. Line 70: Therefore, we chose to show the structural characteristics of this preparation here 
Please revise this sentence.

3. Line 82: Show the abscissa and ordinate labels for EDS spectrum (E).

4. Line 104: Please explain each component and function from the design schematic illustration contained in Figure 2.

5. Please clarify the gram units you are using. There are inconsistencies, for example: Line 105: A and B - 15 g of eah, Table 1: C > 5 gr, 10 gr, and so on. Line 111: ... at about 20 gr of catalyst, ...

6. Lines 104-105: Check that all capital letters are written correctly in this manuscript.

7. The authors have not written down the interactions that occur between TiO₂ and TiO₂ together with transition metals (Ag, Au, Pd, Pt) in oxidizing CO to CO₂.

8. Line 120 (Figure 3): Why don't the authors use CO₂ concentrations in ppm to equate CO concentrations?

9. Line 151: What are the units used for CO_in and CO_out in Table 3?

10. Lines 199-205: You should write down the quantity of materials you use in concentration form.

11. Line 200: .... and prepared as described by [20].
State the name of the representative authors.

12.  Lines 200-201: (10 gr in 1 liter of ionized water).
grain or gram?

13. Line 237: You should still write down the ICP specifications and conditions used to make it easier for readers to know the analytical conditions you are using. 

14. Lines 247-256: Sharpen your conclusions.

15. It is recommended that you increase the quantity of the latest references.

Comments on the Quality of English Language

Moderate editing of English language required.

Author Response

1. Lines 11 and 17: State quantitatively the efficiency of the TiO2-Pt catalyst in oxidizing CO to CO2.

The catalytic efficiency of CO oxidation depends on the catalyst mass, the reactor’s dimensions, and the air flow rate.

 

The catalytic activity in µmoles /min was calculated as:

α˖CO₀(ppm)˖Flow rate (liter/min)/24.4.

The catalytic specific activity was calculated as the catalytic activity divided by catalyst mass (in gr)

These equations were added to the text (see lines  248-252 and 417-421).

A new Table was added to the text (Table 3) showing the activity and specific activity as a function of the catalyst load in the reactor, the flow rate, and the CO₀ concentration.

For example, the catalytic activity for a reactor containing 20 gr catalyst, flowing at 3  liter/min with an input of 1000 ppm CO, was calculated as 123 µmole/min or a specific activity of 6.1 µmole/min/gr catalyst, (172.2 µgr CO/min/gr catalyst).

See line 250 in the revised article.

2. Line 70: Therefore, we chose to show the structural characteristics of this preparation here

Please revise this sentence.

 Done. See line 89 in the revised article.

 

3. Line 82: Show the abscissa and ordinate labels for EDS spectrum (E).

Done. See Figure 1, lines 127 and 390-401 in the revised article.

 

4. Line 104: Please explain each component and function from the design schematic

illustration contained in Figure 2.

 

Fixed, See Figure 2 lines 155-172 in the revised article.

 

 5. Please clarify the gram units you are using. There are inconsistencies, for example: Line

105: A and B - 15 g of eah, Table 1: C > 5 gr, 10 gr, and so on. Line 111: ... at about 20 gr of

catalyst,

 Fixed

 

6. Lines 104-105: Check that all capital letters are written correctly in this manuscript.

Fixed

 

7. The authors have not written down the interactions that occur between TiO2 and

TiO2 together with transition metals (Ag, Au, Pd, Pt) in oxidizing CO to CO2.

The first step in SMSI methodology is the interaction of supported metal (Pt) with the substrate (CO) which does not require light activation. In turn, the metal undergoes significant modification upon interaction with the support (TiO­₂) that enhances its activity [1,2]

The explanation was added to the text. See lines 338-341 in the revised article.

 

8. Line 120 (Figure 3): Why don't the authors use CO2 concentrations in ppm to equate CO

concentrations?

 Fixed

 

9. Line 151: What are the units used for COin and COout in Table 3?

 

ppm, Fixed

 

9. Lines 199-205: You should write down the quantity of materials you use in concentration form.

Fixed

 

11. Line 200: .... and prepared as described by [20].

State the name of the representative authors.

Fixed 

 

12. Lines 200-201: (10 gr in 1 liter of ionized water).

grain or gram?

 

gram

 

 13. Line 237: You should still write down the ICP specifications and conditions used to make it easier for readers to know the analytical conditions you are using.

 

Done. See lines 403-407 in the revised article.

 

 

14. Lines 247-256: Sharpen your conclusions.

 

Fixed. See lines 426-433 in the revised article.

 

15. It is recommended that you increase the quantity of the latest references.

 

Done

 

Additional changes

• Table 1B was removed
• The data of Table 1C was moved to Figure 1(new) to demonstrate the first-order kinetics of the catalysis.
• A schematic structure of the reactor cell was added to Figure 3 (old Figure 2).
• Old Table 3 was removed due to calculation errors. Table 5 (new) was included instead.

 

 

1. Song, J.; Yang, Y.; Liu, S.; Li, L.; Yu, N.; Fan, Y.; Chen, Z.; Kuai, L.; Geng, B. Dispersion and support dictated properties and activities of Pt/metal oxide catalysts in heterogeneous CO oxidation. Nano Research 2021, 14, 4841-4847.
2. Green, R.; Morrall, P.; Bowker, M. CO Spillover and Oxidation on Pt/TiO 2. Catalysis letters 2004, 98, 129-133.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

The present manuscript entitled “Catalytic decomposition of carbon monoxide using strong metal support interactions on TiO₂ microparticles” described synthesis and characterization of various catalysts such as TiO₂-Pt, TiO₂-Au, TiO₂-Ag, TiO₂-Pd, Fe₂O₃-Pt, ZnO₂-Pt catalysts and catalytic activity screened in CO oxidation. Among various catalysts, TiO₂-Pt catalysts exhibit high activity at room temperature. However, there is no characterization results which supports the formation of strong metal support interaction (SMSI) in the prepared catalysts. Poor structure-catalytic activity relation and poor scientific discussion. Moreover, the presentation is not organized properly. The manuscript is not suitable for the publication in the “Catalysts” journal at the present format. The major concerns are as follows. 

1.      Though the Pt/TiO₂ catalyst reported to be exhibit SMSI in the literature, the catalyst preparation method followed by reduction parameters (especially, reducing agent, calcination and reduction temperature, reduction atmosphere) have significant effect on formation of SMSI. In this manuscript, NaBH₄ was used as reducing agent. To claim the strong metal support interaction (SMSI) phenomenon in TiO₂-Pt, TiO₂-Ag, etc., the catalysts need to characterize thoroughly to confirm the existence of SMSI in catalysts. In this manuscript, there are no characterization results which can confirm the existence of SMSI in catalysts presented.

2.      Authors prepared different catalysts such as TiO₂-Pt, TiO₂-Ag, TiO₂-Au, TiO₂-Pd, Fe₂O₃-Pt, ZnO₂-Pt catalyst, However, the actual wight of the catalyst was reported for TiO₂-Pt catalyst only, what about the metal’s nominal and actual weight exist in other catalysts? Please include the corresponding results

3.      There is no proper explanation of Figure 1 given in the manuscript. What do authors want to convey with Fuger 1.?  Explanation is needed.

4.      Authors mentioned that TiO₂-Pt, TiO₂-Au, TiO₂-Ag.. catalysts etc., it means TiO₂ supported Pt (Pt/TiO₂) catalyst? or Pt substituted into TiO₂ catalyst? Please clarify it. It would better to provide XRD patterns of synthesized catalysts with proper structural evaluation.

5.      In Figure 1F, UV-VIS-DRS spectra was reported, please calculate the bandgap of TiO₂-(blue) and TiO₂-Pt catalysts and correlate with its activity.

6.      Please explain why TiO₂-Pt catalyst higher exhibits activity in dark condition than other catalysts

7.      Authors have mentioned in line 163 that Ag-1, Au-4, Pd-4, Pt-4 and what does it mean? Is it oxidation states of the metal? If it is so, how authors confirmed these oxidation states? Please give clarification.

8.      Authors have prepared various catalysts such as TiO₂-Pt, TiO₂-Ag, TiO₂-Au, TiO₂-Pd, Fe₂O₃-Pt and ZnO₂-Pt and its activity is also reported. However there no explanation or reason is given for variation in the activity of different catalysts and why TiO₂-Pt catalyst shows better activity than others?

9.      Compare the activity of prepared catalysts with the catalysts reported in the literature to know the efficiency of the catalysts.

10.   What would be the activity difference when other TiO₂ forms (rutile, Degussa P25) used as support?

 

Author Response

1. Though the Pt/TiO₂catalyst reported to be exhibit SMSI in the literature, the catalyst preparation method followed by reduction parameters (especially, reducing agent, calcination and reduction temperature, reduction atmosphere) have significant effect on formation of SMSI. In this manuscript, NaBH₄ was used as reducing agent. To claim the strong metal support interaction (SMSI) phenomenon in TiO₂-Pt, TiO₂-Ag, etc., the catalysts need to characterize thoroughly to confirm the existence of SMSI in catalysts. In this manuscript, there are no characterization results which can confirm the existence of SMSI in catalysts presented.

In our work, the preparation of the various metal-oxides carefully followed the procedure described by Li et al. [1] In that paper the procedure was shown to lead the formation of SMSI catalysts. In addition, both TEM (Figure 1B) and HRSEM (Figure 1D) analyses of  the TiO₂-Pt microparticles were shown to consist of agglomerated nanoparticles (~70 nm) with ~10 nm clusters, shown to contain Pt (Figure 1E). This structure is also shown in the of the preparation. This structure is typical of SMSI preparations [2].

2. Authors prepared different catalysts such as TiO₂-Pt, TiO₂-Ag, TiO₂-Au, TiO₂-Pd, Fe₂O₃-Pt, ZnO₂-Pt catalyst, However, the actual wight of the catalyst was reported for TiO₂-Pt catalyst only, what about the metal’s nominal and actual weight exist in other catalysts? Please include the corresponding results

10 gr of each catalyst were initially prepared. The total metal percentage, determined by ICP, and the metal surface percentage, determined by EDS were added to the text. Surprisingly, the Ag- and Au- preparations, which had the highest metal percentage possessed the lowest catalytic efficiencies. See lines 101-106 in the revised article.

3. There is no proper explanation of Figure 1 given in the manuscript. What do authors want to convey with Fuger 1.?  Explanation is needed.

We accept the comment. The Figure and the text were modified and improved. See lines 85-98 and 128-134 in the revised article.

 

4. Authors mentioned that TiO₂-Pt, TiO₂-Au, TiO₂-Ag.. catalysts etc., it means TiO₂supported Pt (Pt/TiO₂) catalyst? or Pt substituted into TiO₂ catalyst? Please clarify it. It would better to provide XRD patterns of synthesized catalysts with proper structural evaluation.

According to Figure 1B and 1D, and because of the metal clusters which are shown, we believe that preparations consist of TiO₂-supported Pt.

Currently, we don’t have an XRD machine available to us for spectrum analysis. We will not be able to perform this analysis within the time-limit allowed for the re-submission to “catalysts”. Figure 1E, However, displays an EDS spectrum of TiO₂-Pt where Pt peaks are observed.

5. Please explain why TiO₂-Pt catalyst higher exhibits activity in dark condition than other catalysts

The first step in SMSI methodology is the interaction of supported metal (Pt) with the substrate (CO) which does not require light activation. In turn the metal undergoes significant modification upon interaction with the support (TiO­₂) that enhances its activity [3].[4]

The explanation was added to the text. See lines 338-341.

6. Authors have mentioned in line 163 that Ag-1, Au-4, Pd-4, Pt-4 and what does it mean? Is it oxidation states of the metal? If it is so, how authors confirmed these oxidation states? Please give clarification.

Sorry, we made a mistake. The line should be “ Ag+1, Au+2, Pd+2 and Pt+4 “. The oxidation states are as their oxidative numbers in the salts that were used as the source for the metal ions during the synthesis of the catalyst, namely: AgNO3, AuCl₂, PdCl₂, and K₂PtCl₆. See lines 343 and 387 in the revised article.

 

7. Authors have prepared various catalysts such as TiO₂-Pt, TiO₂-Ag, TiO₂-Au, TiO₂-Pd, Fe₂O₃-Pt and ZnO₂-Pt and its activity is also reported. However there no explanation or reason is given for variation in the activity of different catalysts and why TiO₂-Pt catalyst shows better activity than others?

 

We are not sure why TiO2-Pt is more active than the other preparations. However, higher activity of Pt-based catalysts is often reported in the Literature.

8. 8.      Compare the activity of prepared catalysts with the catalysts reported in the literature to know the efficiency of the catalysts.

 

The catalytic activity in µmoles /min was calculated as:

α˖CO₀(ppm)˖Flow rate (liter/min)/24.4.

The catalytic specific activity was calculated as the catalytic activity divided by catalyst mass (in gr).

These equations were added to the experimental Section and Table 3.

A new Table (Table 3) was added to the text showing the activity and specific activity as a function of the catalyst load in the reactor, the flow rate, and the CO₀ concentration.

For example, the catalytic activity for a reactor containing 20 gr catalyst, flowing at 3  liter/min with an input of 1000 ppm CO, was calculated as 123 µmole/min or a specific activity of 6.1 µmole/min/gr catalyst, (172.2 µgr CO/min/gr catalyst). See lines 145-150 in the revised article. See lines 248-252 and 418-421 in the revised article

It was hard to find parallel quantitative results in the literature. However, we were able to find one paper [5] that reported similar catalytic activities. See lines 343 and 387 in the revised article.

9. 9.   What would be the activity difference when other TiO₂forms (rutile, Degussa P25) used as support?

In this research, we have used anatase TiO₂ microparticle. However, in the past, we have shown that in UV photocatalysis the anatase form is much more active than the rutile form [6]  it is hard to predict the situation with SMSI catalysts as much of the activity, in the absence of exciting light, derives from the supporting metal.

 

 

Additional changes

• Table 1B was removed
• The data of Table 1C was moved to Figure 1(new) to demonstrate the first-order kinetics of the catalysis.
• A schematic structure of the reactor cell was added to Figure 3 (old Figure 2).
• Old Table 3 was removed due to calculation errors. Table 5 (new) was included instead.

 

 

1. Li, M.; Noriega-Trevino, M.E.; Nino-Martinez, N.; Marambio-Jones, C.; Wang, J.; Damoiseaux, R.; Ruiz, F.; Hoek, E.M. Synergistic bactericidal activity of Ag-TiO2 nanoparticles in both light and dark conditions. Environmental science & technology 2011, 45, 8989-8995.
2. Zhang, L.; Cheng, X.; Zhang, G.; Qiu, W.; He, H.; Chen, G. High active platinum clusters on titanium dioxide supports toward carbon monoxide oxidation. Applied Catalysis B: Environmental 2020, 266, 118629.
3. Green, R.; Morrall, P.; Bowker, M. CO Spillover and Oxidation on Pt/TiO 2. Catalysis letters 2004, 98, 129-133.
4. Song, J.; Yang, Y.; Liu, S.; Li, L.; Yu, N.; Fan, Y.; Chen, Z.; Kuai, L.; Geng, B. Dispersion and support dictated properties and activities of Pt/metal oxide catalysts in heterogeneous CO oxidation. Nano Research 2021, 14, 4841-4847.
5. Bamwenda, G.R.; Tsubota, S.; Nakamura, T.; Haruta, M. The influence of the preparation methods on the catalytic activity of platinum and gold supported on TiO2 for CO oxidation. Catalysis Letters 1997, 44, 83-87.
6. Dayan, A.; Mor Yosef, R.; Risphon, J.; Tuval, E.; Fleminger, G. In Situ Detoxification of Venomous Agent X Surrogate Profenofos by Doped Titanium Dioxide Nanoparticles under Illumination at the UV and Visible Ranges. The Journal of Physical Chemistry A 2019, 123, 9456-9461.

 

Reviewer 3 Report

Comments and Suggestions for Authors

This contribution reports the synthesis and potential application of a highly effective CO oxidation catalyst. TiO₂-Pt can be easily synthesized via the Strong Metal Support Interaction (SMSI) methodology and exhibits high efficacy in CO oxidation at room temperature in dark conditions. This is exciting for its potential in practical applications related to CO decontamination. However, the results are poorly presented. Therefore, I recommend acceptance in Catalysts after major revisions.

Comments:

1. In the abstract, the author claims that the catalyst remains stable for years under operational conditions. However, no evidence is presented in the paper to support this claim. To substantiate the stability of the catalyst, characterization after CO oxidation should be performed and compared to the catalyst before CO oxidation. Alternatively, a much longer CO oxidation period should be conducted and repeated at least twice.

2. The format of the two paragraphs in the abstract is inconsistent and should be combined into a single paragraph.

3. Lines 78-79: Please explain why ICP and EDS analysis gave very different Pt loadings and indicate which one is more reliable.

4. The quality of Figures 1C and 1D is poor, as the scale bar is barely visible. Please improve the quality of these figures.

5. The note for Figure 1F stating 'the black TiO₂-Pt powder fails to reflect light' is misleading. The use of different terms for the sample (powder vs. microparticles) may cause readers to wonder where the black spectrum for the powder sample is. Additionally, it would be beneficial to include this discussion in the main text rather than in the notes. Please clarify and relocate this information accordingly.

6. Line 98: Please add references or experimental data to support your claim that 'the catalytic oxidation of CO is a first-order reaction.

7. For Table 1, the author should avoid redundant notes by simply adding a column for catalyst loading. CO concentration range was mentioned in the main text. However, the initial CO concentration for the data presented in the table is missing. Additionally, please clarify what 'Max' refers to.

8. In Figure 3, please use the same unit for CO and CO₂ concentrations.

9. I assume that the entire space of your reactor cell is occupied by the catalyst; otherwise, the catalytic efficacy would not correlate well with the area of the reactor cell. If this is the case, then all your figures of the experimental setup are misleading. Please fix them.

10. Units in Table 3 are missing.

11. Line 157: please add references to support your claim: “There are currently no means to remove CO from the environment by adsorption or neutralization, only by catalysis.”

12. Lines 166-167: Please specify whether the efficacy is measured per gram of catalyst or per gram of Pt. The explanation of the nanostructure of the microparticles is confusing for two reasons: first, there is no clear correlation established between nanostructure and activity; second, nano-based catalysts also possess nanostructures.

13. Lines 222 and 237: Please include the details of these analyses rather than only providing references.

Comments on the Quality of English Language

There are numerous grammatical errors and typographical mistakes. Please refine and proofread your writing thoroughly

Author Response

1. In the abstract, the author claims that the catalyst remains stable for years under operational conditions. However, no evidence is presented in the paper to support this claim. To substantiate the stability of the catalyst, characterization after CO oxidation should be performed and compared to the catalyst before CO oxidation. Alternatively, a much longer CO oxidation period should be conducted and repeated at least twice.

 

Each of the experiments described in this paper was repeated many times with identical results, During these experiments. the same batches of TiO₂-Pt were used all over again without any apparent reduction in the catalytic efficiencies. However, since no consistent experiments have been carried out in this respect, we omitted the claim for “stability” from the text.

2. The format of the two paragraphs in the abstract is inconsistent and should be combined into a single paragraph.

Fixed. See lines 10-22 in the revised article.

3. Lines 78-79: Please explain why ICP and EDS analysis gave very different Pt loadings and indicate which one is more reliable.

ICP is used to determine the metal composition of a preparation after its acid dissolution. The result shows the % of each atom within the total preparation. EDS, which is based on electron scattering from the particle surface. Its results are % of each atom on the particle surface. As the metal is absorbed to the surface, the EDS results are expected to be higher than those of ICP.

4. The quality of Figures 1C and 1D is poor, as the scale bar is barely visible. Please improve the quality of these figures.

Fixed. See lines 127 in the revised article.

5. The note for Figure 1F stating 'the black TiO₂-Pt powder fails to reflect light' is misleading. The use of different terms for the sample (powder vs. microparticles) may cause readers to wonder where the black spectrum for the powder sample is. Additionally, it would be beneficial to include this discussion in the main text rather than in the notes. Please clarify and relocate this information accordingly.

We agree. The text was modified, accordingly. See lines 129-135 in the revised article.

6. Line 98: Please add references or experimental data to support your claim that 'the catalytic oxidation of CO is a first-order reaction.

At each catalyst concentration, at certain reaction conditions. the catalyzed reaction should be of first order as the outcome depends only on the CO concentration in the environment. The results of Table 1C were moved to a new figure to show the first order kinetics (Figure 2 in the revised article). See line 205 in the revised article.

7. For Table 1, the author should avoid redundant notes by simply adding a column for catalyst loading. CO concentration range was mentioned in the main text. However, the initial CO concentration for the data presented in the table is missing. Additionally, please clarify what 'Max' refers to.

We accept the comment. Table 1 has been modified and Figure 3 added. See lines 193-203 in the revised article.

The term ”Max” relates to a situation when maximal catalytic efficiency is achieved, namely α=1. This situation occurs when the air at the reactor’s exit is devoid of CO. This situation can be simulated by connecting the tubing at the reactor to fresh air.

8. In Figure 3, please use the same unit for CO and CO₂

Fixed. See line 220 in the revised article.

9. I assume that the entire space of your reactor cell is occupied by the catalyst; otherwise, the catalytic efficacy would not correlate well with the area of the reactor cell. If this is the case, then all your figures of the experimental setup are misleading. Please fix them.

The rector cell operates as a type of “floating bed”. Because the air flows from below the cell at a high rate, the particles float and fill the entire space. That’s the reason that the reactor cell is equipped with an upper microcin filter, as well. An illustration describing the structure and the operational conditions of the reactor cell was added to Figure 2/n Table 5, we wrongly concluded that the catalytic efficiency was a function of the surface area and not just the catalyst mass. This Table was modified. (Table 3 in the new version replaces Table 5). See line 245 in the revised article.

10. Units in Table 3 are missing.

Fixed. Table 3 is now Table 4, See lines 330-334 in the revised article.

 

11. Line 157: please add references to support your claim: “There are currently no means to remove CO from the environment by adsorption or neutralization, only by catalysis.”

This sentence was omitted.

 

12. Lines 166-167: Please specify whether the efficacy is measured per gram of catalyst or per gram of Pt. The explanation of the nanostructure of the microparticles is confusing for two reasons: first, there is no clear correlation established between nanostructure and activity; second, nano-based catalysts also possess nanostructures.

The efficacy is measured per gram of the catalyst.

We believe that the nano-structural nature of the TiO₂ microparticles increases the efficiency of all the catalysts examined in this article. We have decided to use microparticles rather than nanoparticles because of operational reasons. It may be that using nanoparticles, instead, may result in higher activities.

13. Lines 222 and 237: Please include the details of these analyses rather than only providing references.

Fixed. See lines 392-396 and 403-407  in the revised article.

 

Comments on the Quality of English Language

There are numerous grammatical errors and typographical mistakes. Please refine and proofread your writing thoroughly

The paper underwent professional English Editing and was fixed accordingly.

 

 

Additional changes

• Table 1B was removed
• The data of Table 1C was moved to Figure 1(new) to demonstrate the first-order kinetics of the catalysis.
• A schematic structure of the reactor cell was added to Figure 3 (old Figure 2).
• Old Table 3 was removed due to calculation errors. Table 5 (new) was included instead.

 

Reviewer 4 Report

Comments and Suggestions for Authors

Comments to author

            Author prepared the Ti based nanoparticle for the conversion of CO to CO₂. Author discussed the obtained results in well manner. Though, the manuscript has some flaws. So, the manuscript requires major revision before publication. The comments to the authors are given below.

1.      In line number 12, there is a typo error in the sentence starts with “we a a number”. I suggest the author to check the typo and grammatical error in the entire manuscript.

2.      The sentence started in line 11 is not clear. I suggest the author to rewrite the sentence.

3.      I suggest the author to include the health effects of CO in introduction section.

4.      The introduction section is very general. I suggest the author to include some literature based on the work in the introduction section.

5.      In line No 78, author mentioned PT instead of Pt. I suggest the author to change it.

6.      Did the author check the CO to CO₂ conversion for TiO₂ nanoparticles and without catalyst?

7.      I suggest the author to provide SI units.

8.      I suggest the author to include the obtained results in conclusion part.

9.      There are too many catalysts were there to convert CO to CO₂. Why do you choose the Ti based nanoparticles?

10.  How will you convert CO to CO₂? What is the source of CO? I suggest the author to mention the conversion process in the materials section.

11.  I suggest the author to mention the conversion % in the result part.

12.  I suggest the author to include the conversion mechanism.

13.  I suggest the author to provide the comparison table for the conversion study.

14.  Did the author check the stability of the catalyst?

15.  Which catalyst is efficient for conversion study and why?

 

16.  Author only mentioned the structural and UV results Pt –TiO₂ and did not provide the structural and UV results. Why?

Author Response

Author prepared the Ti based nanoparticle for the conversion of CO to CO₂. Author discussed the obtained results in well manner. Though, the manuscript has some flaws. So, the manuscript requires major revision before publication. The comments to the authors are given below.

1. In line number 12, there is a typo error in the sentence starts with “we a a number”. I suggest the author to check the typo and grammatical error in the entire manuscript.

 

Corrected

 

2. The sentence started in line 11 is not clear. I suggest the author to rewrite the sentence.

 

Corrected

 

3. I suggest the author to include the health effects of CO in introduction section.

 

We included information about the health effects of CO in the Introduction (including new references). Sea lines 46-56.

 

4. The introduction section is very general. I suggest the author to include some literature based on the work in the introduction section.

 

The Introduction Section was modified. See lines 46-56.

 

5. In line No 78, author mentioned PT instead of Pt. I suggest the author to change it.

 

Corrected

 

6. Did the author check the CO to CO₂conversion for TiO₂ nanoparticles and without catalyst?

 

TiO₂ particles without supported metals do not possess any catalytic activity toward CO oxidation.(see Table 1).

 

 

7. I suggest the author to provide SI units.

 

Units have been converted to SI units: sec to s; mole to mol; ml to mL; liter to L.

 

 

8. I suggest the author to include the obtained results in conclusion part.

 

The Conclusion Section was modified accordingly. See lines 431-441.

 

 

 

9. There are too many catalysts were there to convert CO to CO₂. Why do you choose the Ti based nanoparticles?

 

 

We have prepared and analyzed several metal-oxide for their activities in catalytic CO oxidation. TiO₂ was found to be far more efficient than the others (Fe₂O₃ and ZnO). This information was included in the original version of this manuscript but omitted in the first revision upon the request of one of the referees. TiO₂-Pt is known to be a very efficient SMSI catalyst in Literature.

 

 

 

10. How will you convert CO to CO₂? What is the source of CO? I suggest the author to mention the conversion process in the materials section.

 

The mechanism of the catalytic conversion of CO to  CO₂ is described in detail in the Discussion Section (See lines 334-339). There is no reason to include this information in the Materials Section.

 

11. I suggest the author to mention the conversion % in the result part.

 

The catalytic efficiency is represented by α where full conversion is α = 1. Obviously, %=α*100.

 

12. I suggest the author to include the conversion mechanism.

 

See answer to comment 10.

 

13. I suggest the author to provide the comparison table for the conversion study.

 

We are sorry, but we don’t understand what this comment means. A comparison Table of the catalytic efficiencies of the different catalysts appears in Table 1

 

14. Did the author check the stability of the catalyst?

 

We found the catalyst to be stable in experiments conducted with the same batch for at least 2 years. The stability is both mechanical (no disintegration of the microparticles) and functional (full catalytic efficiency). This information was included in the original manuscript but removed in the revised version upon request of one of the referees.

 

15. Which catalyst is efficient for conversion study and why?

 

See answer to Comment 16.

 

16. Author only mentioned the structural and UV results Pt –TiO₂and did not provide the structural and UV results. Why?

 

As described in the text, TiO₂-Pt exhibited the highest catalytic efficiency toward CO oxidation among the investigated catalysts. Therefore, we concentrated on the study of this catalyst both structurally and functionally.

SMSI, in contrast to photocatalysis, does not require UV activation. Therefore, no UV experiments were conducted in this manuscript

 

 

 

Reviewer 5 Report

Comments and Suggestions for Authors

The manuscript focuses on the investigation of catalytic decontamination of carbon monoxide using strong metal-support interactions on TiO2 microparticles. However, it cannot be recommended for publication at this time for the following reasons:

Comments:

1. There are significant discrepancies in the performance of different metal catalysts, and the underlying mechanisms need to be explained in greater detail. Are the effective loading amounts of the metals, as well as the size and distribution of the loaded metal nanoparticles, comparable?
2. What is the effective loading amount of platinum (Pt), and how does it correlate with the amount added?
3. The turnover frequency (TOF) of the active sites requires further calculation.
4. The structure of the loaded metal Pt necessitates additional characterization, including its phase state, particle size, and relationship with the support material.
5. What is the stability of the catalyst?
6. A comparative analysis of performance with relevant peer-reviewed research should be included.

Author Response

The manuscript was modified according to the c

Author prepared the Ti based nanoparticle for the conversion of CO to CO₂. Author discussed the obtained results in well manner. Though, the manuscript has some flaws. So, the manuscript requires major revision before publication. The comments to the authors are given below.

1. In line number 12, there is a typo error in the sentence starts with “we a a number”. I suggest the author to check the typo and grammatical error in the entire manuscript.

 

Corrected

 

2. The sentence started in line 11 is not clear. I suggest the author to rewrite the sentence.

 

Corrected

 

3. I suggest the author to include the health effects of CO in introduction section.

 

We included information about the health effects of CO in the Introduction (including new references). Sea lines 46-56.

 

4. The introduction section is very general. I suggest the author to include some literature based on the work in the introduction section.

 

The Introduction Section was modified. See lines 46-56.

 

5. In line No 78, author mentioned PT instead of Pt. I suggest the author to change it.

 

Corrected

 

6. Did the author check the CO to CO₂conversion for TiO₂ nanoparticles and without catalyst?

 

TiO₂ particles without supported metals do not possess any catalytic activity toward CO oxidation.(see Table 1).

 

 

7. I suggest the author to provide SI units.

 

Units have been converted to SI units: sec to s; mole to mol; ml to mL; liter to L.

 

 

8. I suggest the author to include the obtained results in conclusion part.

 

The Conclusion Section was modified accordingly. See lines 431-441.

 

 

 

9. There are too many catalysts were there to convert CO to CO₂. Why do you choose the Ti based nanoparticles?

 

 

We have prepared and analyzed several metal-oxide for their activities in catalytic CO oxidation. TiO₂ was found to be far more efficient than the others (Fe₂O₃ and ZnO). This information was included in the original version of this manuscript but omitted in the first revision upon the request of one of the referees. TiO₂-Pt is known to be a very efficient SMSI catalyst in Literature.

 

 

 

10. How will you convert CO to CO₂? What is the source of CO? I suggest the author to mention the conversion process in the materials section.

 

The mechanism of the catalytic conversion of CO to  CO₂ is described in detail in the Discussion Section (See lines 334-339). There is no reason to include this information in the Materials Section.

 

11. I suggest the author to mention the conversion % in the result part.

 

The catalytic efficiency is represented by α where full conversion is α = 1. Obviously, %=α*100.

 

12. I suggest the author to include the conversion mechanism.

 

See answer to comment 10.

 

13. I suggest the author to provide the comparison table for the conversion study.

 

We are sorry, but we don’t understand what this comment means. A comparison Table of the catalytic efficiencies of the different catalysts appears in Table 1

 

14. Did the author check the stability of the catalyst?

 

We found the catalyst to be stable in experiments conducted with the same batch for at least 2 years. The stability is both mechanical (no disintegration of the microparticles) and functional (full catalytic efficiency). This information was included in the original manuscript but removed in the revised version upon request of one of the referees.

 

15. Which catalyst is efficient for conversion study and why?

 

See answer to Comment 16.

 

16. Author only mentioned the structural and UV results Pt –TiO₂and did not provide the structural and UV results. Why?

 

As described in the text, TiO₂-Pt exhibited the highest catalytic efficiency toward CO oxidation among the investigated catalysts. Therefore, we concentrated on the study of this catalyst both structurally and functionally.

SMSI, in contrast to photocatalysis, does not require UV activation. Therefore, no UV experiments were conducted in this manuscript

 

 

 

There are significant discrepancies in the performance of different metal catalysts, and the underlying mechanisms need to be explained in greater detail. Are the effective loading amounts of the metals, as well as the size and distribution of the loaded metal nanoparticles, comparable?

 

The detailed mechanism of SMSI catalysis has been added to the discussion Section.

The different catalysts investigated were of the same size (10 µm)) and covered a similar amount of metal on the surface as shown by ICP and ADS analyses.

 

• What is the effective loading amount of platinum (Pt), and how does it correlate with the amount added?

 

As mentioned in the results, the metal contents (Pt) on the TiO2 surface was 1.83%, similar to the other TiO₂-Me preparations.

 

• The turnover frequency (TOF) of the active sites requires further calculation.

 

We have included in the text the calculation of the activity (equal to TOF) and the specific activity of the catalyst (Table 3).

 

• The structure of the loaded metal Pt necessitates additional characterization, including its phase state, particle size, and relationship with the support material.

 

The TiO₂ phase used was anatase. The particle size of the microparticle was 10 µm as informed by the manufacturer. In the structural characterization (Figure 1) we have shown clusters of Pt 2-5 µm, typical of SMSI.

 

• What is the stability of the catalyst?

We found the catalyst to be stable in experiments conducted with the same batch for at least 2 years. The stability is both mechanical (no disintegration of the microparticles) and functional (full catalytic efficiency). This information was included in the original manuscript but removed in the revised version upon request of one of the referees.

 

• A comparative analysis of performance with relevant peer-reviewed research should be included.

 

As mentioned in the answer to reviewer 1, it is difficult to perform such an analysis because, in many papers, no numerical data for the activity is given. In one paper, we were able to find the activities were of the same order of magnitude as found in our paper. [1]

1. Bamwenda, G.R.; Tsubota, S.; Nakamura, T.; Haruta, M. The influence of the preparation methods on the catalytic activity of platinum and gold supported on TiO2 for CO oxidation. Catalysis Letters 1997, 44, 83-87.

 

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for the manuscript revision.

Some points that still need to be considered are as follows:

1. There is no mechanical stress data for TiO₂.
Line 99: The TiO₂ microparticles, composed of clusters of nanoparticles (Figure 1C), are stable and do not disintegrate under mechanical stress.

2. Is the concentration of CO not measured accurately?
Line 143 The environmental model (Figure 2) consists of a 20 L container filled with air containing CO at a certain concentration (usually 400-1000 ppm).

3. The formula is not completely written. Is it the concentration of CO, the volume of CO, or the mass of CO? Explain.
Line 227: a=1-COout/COin (eq. 5)
What is meant by CO in and CO out in Eq. 5?

4. Provide the mechanism of what happens between the catalyst and the facts you obtain regarding the effect of flow rate (L/min) 1.8; 2, and 3 on the concentration of CO out in Table 2.

5. The interactions between these metal cations, TiO₂, and CO need to be discussed in depth. Provide the mechanism involved in this reaction.
Lines 342-343: We used the SMSI methodology to prepare four catalysts that were based on the interaction of Ag⁺¹, Au⁺², Pd⁺², and Pt⁺⁴ with TIO₂ microparticles. We chose to use TiO₂ microparticles.

6. Lines 377-378: Clearly state the sonication conditions (frequency and temperature).

7. The justification for the choice of microparticle size is unclear.
Lines 99-100: The author writes: The TiO2 microparticles, composed of clusters of nanoparticles (Figure 1C), are stable and do not disintegrate under mechanical stress. Please clarify your interpretation with the statements in lines 343-344.

8. Will the use of the mask be included with the catalytic reactor?
Lines 429: Secondly, integrating this catalytic capability into breathing systems, such as masks, equipped with a catalytic reactor, offers users personal protection against CO exposure.

9. Sharpen your abstract and conclusion.

10. Please add your references.
_______________________________
Minor comments:
Please check and revise:

11. Line 380: Ph 10.

12. Unit gr mean grain or gram?

13. Line 183: Tabel 1, 3,  > Authors should write numbers in a more uniform number of decimal points.

14. Line 343: ... with TIO2 microparticles ...
Please pay attention to the correct spelling of TiO₂.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

1. Open Review
2. ( ) I would not like to sign my review report
   (x) I would like to sign my review report
3. Quality of English Language
4. ( ) I am not qualified to assess the quality of English in this paper.
   ( ) The English is very difficult to understand/incomprehensible.
   ( ) Extensive editing of English language required.
   ( ) Moderate editing of English language required.
   (x) Minor editing of English language required.
   ( ) English language fine. No issues detected.

5.  

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	(x)	( )	( )
Is the research design appropriate?	( )	( )	(x)	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	( )	( )	(x)	( )

                 

 

 

1. There is no mechanical stress data for TiO₂.

Line 99: The TiO₂ microparticles, composed of clusters of nanoparticles (Figure 1C), are stable and do not disintegrate under mechanical stress.

 

We have not collected mechanical stress data. Yet, we have not noticed any disintegration of the microparticles which would cause leakage of broken particles through the 1 µm filters. We have omitted “are stable and”.

2. Is the concentration of CO not measured accurately?
   Line 143 The environmental model (Figure 2) consists of a 20 L container filled with air containing CO at a certain concentration (usually 400-1000 ppm).
   
   

Of course, the CO concentration were measured accurately by CO detectors. We meant that in most experiments CO₀ at a range of 400-1000 ppm was used.

3. The formula is not completely written. Is it the concentration of CO, the volume of CO, or the mass of CO? Explain.
   Line 227: a=1-COout/COin (eq. 5)
   What is meant by CO in and CO out in Eq. 5?
   
   

COin and COout are the CO concentrations (in ppm) at the entrance to and the exit from the reactor cell. The text in line 227 has been changed. In Eq. 5 a is the catalytic efficiency (α).

4. Provide the mechanism of what happens between the catalyst and the facts you obtain regarding the effect of flow rate (L/min) 1.8; 2, and 3 on the concentration of CO out in Table 2.

The  catalytic activity of the reactor depends on two factors – the catalyst’s mass and the flow rate. For each mass, there is a maximal flow rate that enables maximal catalytic efficiency (Table 3). This is exemplified in Table 2 for 12.8 gr where the maximal flow rate is 1.8 liter/min. At higher flow rates the catalytic efficiency diminishes. It is pertinent to note that the higher the flow rate the shorter is the residence time of CO in the reactor. Namely, the higher the catalyst mass the shorter the residence times in the reactor cell that enables high catalytic efficiencies.

This is explained in lines 175-176.

5. The interactions between these metal cations, TiO₂, and CO need to be discussed in depth. Provide the mechanism involved in this reaction.
   Lines 342-343: We used the SMSI methodology to prepare four catalysts that were based on the interaction of Ag⁺¹, Au⁺², Pd⁺², and Pt⁺⁴with TIO₂microparticles. We chose to use TiO₂ microparticles.

Unlike Photocatalysis by TiO₂, which requires activation of the oxide at the UV range to produce Reactive Oxygen Species (ROS), The SMSI methodology is based on the adsorption of CO on the metal cluster (Pt in our case) which leads to changes in electronic properties, surface structure, and catalytic activity of the metal. In parallel, O₂ is absorbed on the TiO₂ support resulting in ROS formation due to electron transfer between Pt and TiO₂. Finally, CO reacts with the activated oxygen to form CO₂ which is desorbed. See lines 337-342.

6. Lines 377-378: Clearly state the sonication conditions (frequency and temperature).

100 kHz at 50^oC or at room temperature. Lines 380, 396-397, and 402-403 were modified.

7. The justification for the choice of microparticle size is unclear.
Lines 99-100: The author writes: The TiO2 microparticles, composed of clusters of nanoparticles (Figure 1C), are stable and do not disintegrate under mechanical stress. Please clarify your interpretation with the statements in lines 343-344.

The reactor’s cell contains 1 µm filters on both sides of the cell (Figure 2B). These filters restrict the passage of 10 µm Microparticles, in contrast to  nanoparticles whose passage is not restricted.and may leak from the reactor.

 

8. Will the use of the mask be included with the catalytic reactor? Lines 429: Secondly, integrating this catalytic capability into breathing systems, such as masks, equipped with a catalytic reactor, offers users personal protection against CO exposure.
   
   

In this article we have investigated the catalytic activity of the reactor in a single-passage manner. We propose that the reactor can be incorporated into a personal protection device (e.g. a mask).

 

 9. Sharpen your abstract and conclusion.

The Abstract and Conclusions were rewritten

10. Please add your references.

____I don’t understand what you mean___________________________

Minor comments:
Please check and revise:

11. Line 380: Ph 10.

            Fixed

12. Unit gr mean grain or gram?

gram

13. Line 183: Tabel 1, 3,  > Authors should write numbers in a more uniform number of decimal points.

Fixed

14. Line 343: ... with TIO2 microparticles ...
    Please pay attention to the correct spelling of TiO₂.

Fixed

 

Comments on the Quality of English Language

 

Minor editing of English language required.

Fixed

 

Reviewer 2 Report

Comments and Suggestions for Authors

1.      The author’s response to the most of my comments are not satisfied. Moreover, the manuscript is lack of thorough catalyst characterization and missing structure-activity correlation study. This manuscript is like a report rather than scientific article, thus, this manuscript is not suitable for "Catalysts" Journal.

In addition, The references mentioned (Science 1981, 474 211, 1121-1125 and Journal of Catalysis 1978, 55, 29-35) in the manuscript is used H₂ to reduce the catalyst at 500 °C which facilitates the SMSI formation, whereas NaBH4 was used as reducing agent in the present manuscript. SMSI state formation is significantly influenced by various factors, calcination temperature, reduction atmosphere, reduction temperature, etc., therefore, authors can not claim the formation of SMSI on the synthesized catalysts under the conditions reported in the manuscript.

 

 

 

Author Response

See a rebuttal letter

Reviewer 3 Report

Comments and Suggestions for Authors

All the comments are well addressed

Author Response

Thank you

Reviewer 4 Report

Comments and Suggestions for Authors

Author revised the manuscript as per the comments given by the reviewer. So the manuscript maybe accepted for publication 

Author Response

Thanks

Reviewer 5 Report

Comments and Suggestions for Authors

 Comments are not well addressed in the  revised version.

Author Response

Thanks. We did our best. 

TOF cannot be calculated because we don't know the number of active sites on the catalyst's surface. Even though we know the percentage of Pt on the surface of the microparticles we do not know the surface itself.

We believe that the other comments have been answered as good as we can.