Plasmonic-Assisted Water–Gas Shift Reaction of Gold Particles on TiO2
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript "Plasmonic-assisted water gas shift reaction of gold particles on TiO2" is devoted to the localized surface plasmon (LSP) effect of Au particles in water vapor reactions. The manuscript is well written and of interest to readers. I have no significant comments on this study. However, there are some minor comments regarding the design.
1) The reaction equations are poorly formed, for example, in equation 5, the electron is designated as “e”, in the future it will be designated as “e -”.
Overall, the work is worthy of publication in Catalysts after minor edits.
Author Response
...The manuscript is well written and of interest to readers. I have no significant comments on this study. However, there are some minor comments regarding the design.
Thank you very much for your positive assessment of our manuscript.
1) The reaction equations are poorly formed, for example, in equation 5, the electron is designated as “e”, in the future it will be designated as “e -”.
Unified
2) The notation “OH radical” is used in equations 8 and 9, although radicals are normally designated “OH*”.
Overall, the work is worthy of publication in Catalysts after minor edits.
OH radical is changed to OH* in the text and equations.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors presented a very valuable and systematic research work on plasmonic-assisted water gas shift reaction with Au/TiO2 catalysts. The characterizations and discussion are very carefully. Therefore, I recommend publishing this article directly on Catalysts.
Two minor suggestions,
1) If possible, some relative papers on plasmonic-assisted reactions are recommended, such as Micropor. Mesopor. Mater. 2022, 337, 111949; J. Am. Chem. Soc. 2018, 140, 27, 8497-8508.
2) There is a small question about chromatographic analysis of CO2 with molecular sieve 5A column (Line 145). To my knowledge, CO2 and H2O can be captured by molecular sieve, so that we are hardly to analyze both CO2 and H2O with molecular sieve 5A column. Please check!
Good work!
Author Response
The authors presented a very valuable and systematic research work on plasmonic-assisted water gas shift reaction with Au/TiO2 catalysts. The characterizations and discussion are very carefully. Therefore, I recommend publishing this article directly on Catalysts.
Thank you very much for finding our work to be suitable for publication and for your positive comments.
Two minor suggestions,
- If possible, some relative papers on plasmonic-assisted reactions are recommended, such as Micropor. Mesopor. Mater. 2022, 337, 111949; J. Am. Chem. Soc. 2018, 140, 27, 8497-8508.
The references are added, together with others.
- There is a small question about chromatographic analysis of CO2with molecular sieve 5A column (Line 145). To my knowledge, CO2 and H2O can be captured by molecular sieve, so that we are hardly to analyze both CO2 and H2O with molecular sieve 5A column. Please check!
Yes, thank you these are accurate. Probably you meant at room temperature CO2 is trapped. At 80 oC CO, CO2 and O2 are well separated using molecular sieve 5A. We did not quantify water vapor (much harder to quantify accurately).
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this study, the effects of Localized Surface Plasmon (LSP) of 5 nm mean size Au particles deposited on TiO2 P25 during the photo-thermal water gas shift reaction (WGSR) were primarily discussed. The research examined the influence of CO concentration, excitation light flux and energy, as well as the addition of molecular oxygen during the reaction. The results revealed that under light excitation with wavelengths ranging from 320 to 1100 nm, the photocatalytic WGSR rate was higher than the thermal reaction alone at the same temperature (85°C). At higher concentrations of CO, the ratio of H2/CO2 approached unity. The addition of molecular oxygen during the reaction led to a slight decrease in the production rate of molecular hydrogen, while the rates of CO2 formation and CO consumption changed significantly. Importantly, it was observed that the WGSR rates remained high under visible light excitation (600-700 nm) alone. These findings demonstrate that Au LSP alone can trigger this chemical reaction without the need to excite the semiconductor on which they are deposited. Therefore, I recommend acceptance of the manuscript after the authors address additional content, clarify ambiguous points, and rectify formatting issues.
1. Is there a side reaction for the water gas shift reaction (WGSR)?
2. Please provide a detailed explanation of the effect of Localized Surface Plasmon.
3. Why use TiO2 P25 as a catalyst support? What distinguishes it from conventional TiO2.
4. Add XRD (X-ray diffraction) data for Au/TiO2 P25 with different loading amounts.
5. The author mentioned that the nanoparticle size of Au is 5 nm, but there isn't sufficient data in the article to support this conclusion. The data is incomplete, and I would appreciate additional information to supplement it.
6. Have you attempted to examine the difference in UV-Vis-IR absorbance spectra in Figure 1A between 10 wt% Au and 12 wt% Au, or 15wt% Au?
7. Why is there a decreasing trend in H2 production after the addition of O2 in Figure 4A? I would appreciate an explanation.
Comments on the Quality of English LanguageModerate editing of English language required.
Author Response
... Therefore, I recommend acceptance of the manuscript after the authors address additional content, clarify ambiguous points, and rectify formatting issues.
- Is there a side reaction for the water gas shift reaction (WGSR)?
The possible side reactions would be related to the further reaction of CO (reactant) and H2 (product) to make hydrocarbons. This is in general negligible. We have detected some traces of methane; mentioned in the manuscript.
- Please provide a detailed explanation of the effect of Localized Surface Plasmon.
Added in the introduction section now.
- Why use TiO2P25 as a catalyst support? What distinguishes it from conventional TiO2.
Considerable effort over the years was put to see why this is the case. See for example, some of our previous work on this J. Catalysis 352, 657–671 (2017), Catalysis Today, 240, 242–247 (2015) and others Catalysis Today 300 (2018) 12–17. Many explanations were provided and yet we are still uncertain if it is an interfacial effect or individual crystallite properties effect.
- Add XRD (X-ray diffraction) data for Au/TiO2P25 with different loading amounts.
XRD was conducted and published (ref. 39) - we have added a short description in the revised manuscript.
- The author mentioned that the nanoparticle size of Au is 5 nm, but there isn't sufficient data in the article to support this conclusion. The data is incomplete, and I would appreciate additional information to supplement it.
The mean particle size of Au is 5.1 nm. We have added more HRTEM and TEM images in the supporting information.
- Have you attempted to examine the difference in UV-Vis-IR absorbance spectra in Figure 1A between 10 wt% Au and 12 wt% Au, or 15wt% Au?
10% was the highest we have prepared. We have only conducted the study on the 8 wt.%
- Why is there a decreasing trend in H2production after the addition of O2 in Figure 4A? I would appreciate an explanation.
The initial decrease is due to oxidation to water. There is however a second decrease after all oxygen has been consumed (compare photothermal lines before and after oxygen injection). We do not know the origin of the second decrease. A plausible explanation is that O2 increases the concentration of formate species and these have weak decomposition kinetics at the experimental conditions (equation 9) blocking some sites for the regenerative mechanism to occur. We have added this sentence to the manuscript. We thank the referee for raising this point.
Reviewer 4 Report
Comments and Suggestions for AuthorsIn this manuscript authors have reported the synthesis of Au/P25 TiO2 catalysts with different gold contents through the deposition–precipitation and studied their catalytic activities in photocatalytic water gas shift reaction at room temperature and thermal water gas shift reactions at elevated temperatures. Results have merit. But several areas need revisions. See the comments below:
1) Although it is written in the experimental that powder XRD analysis is done to characterize the catalysts, but I don’t find XRD data in the manuscript. This is necessary for the identification of Au NPs and TiO2 phases.
2) In Figure 1A, along with the UV-vis DRS data TEM images of some of the samples are provided. But more high resolution TEM images are necessary for understanding particle size and shape. More indepth analysis is necessary.
3) What are the band gaps of different Au loaded Au/TiO2 P25 samples?
4) H2 evolution rate of Au/P25 TiO2 samples should be compared with related Au-catalysts reported in the literature.
Comments on the Quality of English LanguageModerate language editing is necessary.
Author Response
In this manuscript authors have reported the synthesis of Au/P25 TiO2 catalysts with different gold contents through the deposition–precipitation and studied their catalytic activities in photocatalytic water gas shift reaction at room temperature and thermal water gas shift reactions at elevated temperatures. Results have merit. But several areas need revisions. See the comments below:
We thank the reviewer for her/his positive evaluation of our work.
1) Although it is written in the experimental that powder XRD analysis is done to characterize the catalysts, but I don’t find XRD data in the manuscript. This is necessary for the identification of Au NPs and TiO2 phases.
XRD was done for the complete series, Ref. 39. We have added more description of the results.
2) In Figure 1A, along with the UV-vis DRS data TEM images of some of the samples are provided. But more high resolution TEM images are necessary for understanding particle size and shape. More indepth analysis is necessary.
We have added more images in the revised version (supporting information) with further comments.
3) What are the band gaps of different Au loaded Au/TiO2 P25 samples?
The band gap of TiO2 does not change with the addition of a metal on top. It may change for substitutional metal cations but this is for different type of studies.
4) H2 evolution rate of Au/P25 TiO2 samples should be compared with related Au-catalysts reported in the literature.
The photo-catalytic reaction rate is a function of light flux and exposed area while catalytic reactions are directly a function of the amount of matter. So direct comparison may not be made easily without a devoted study focusing on quantifying the needed parameters for comparison. A typical rate for low-temperature WGSR Au catalyst is about 0.5 mol/g(catal)/h (see this review article Phys. Chem. Chem. Phys., 2013, 15, 15260-15270). We have added a short paragraph on this at the end of the manuscript.
Round 2
Reviewer 4 Report
Comments and Suggestions for AuthorsAuthors have made necessary revisions as suggested by the reviewers. Now this manuscript may be accepted for publication.
