New and Facile Preparation Method for Highly Active Iron Oxide Catalysts for CO Oxidation
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsOverview and general recommendation:
Development of methods for the synthesis of effective nanoparticles and their application in various catalytic processes, such as the neutralization of waste and greenhouse gases is an important topic of modern science. Materials based on iron oxides are of particular interest because these metals are very cheap, widespread in nature, non-toxic metals with unique magnetic and electronic properties.
I recommend the article for publication after making major changes.
Major comments:
1. The «Introduction» is written in confusion and is not informative. The authors provide "abstract" references in the range [10–18] and [19–34], but authors need to provide more detailed information about the synthesis of supported iron oxides and their application in CO oxidation reaction so that we can correlate with the results obtained in the work.
2. The authors should make a TEM analysis of the obtained systems and provide histograms of particle size distribution, and this would also be useful from the point of view of studying the morphology of nanoparticles.
3. It is necessary to make a comparison with the data of iron-containing catalysts known from the literature on the CO conversion under similar reaction conditions.
4. The title of the picture caption must begin with a capital letter «Figure 8. Turnover frequencies of FE01….».
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
Overview and general recommendation:
Development of methods for the synthesis of effective nanoparticles and their application in various catalytic processes, such as the neutralization of waste and greenhouse gases is an important topic of modern science. Materials based on iron oxides are of particular interest because these metals are very cheap, widespread in nature, non-toxic metals with unique magnetic and electronic properties.
I recommend the article for publication after making major changes.
Major comments:
First of all, we want to thank the reviewer for reading our manuscript and giving valuable advice to improve in quality and to get it on a publishable level.
- The «Introduction» is written in confusion and is not informative. The authors provide "abstract" references in the range [10–18] and [19–34], but authors need to provide more detailed information about the synthesis of supported iron oxides and their application in CO oxidation reaction so that we can correlate with the results obtained in the work.
We thank the reviewer for pointing this out. The given references were intended to provide an overview over the most important applications of heterogeneous catalysts. We revised the paragraph according to your suggestion, reduced the number of references and assigned them in a clearer way. The introduction has been edited and expanded regarding synthesis and catalytic activities to allow the reader a classification of the obtained results in CO oxidation.
- The authors should make a TEM analysis of the obtained systems and provide histograms of particle size distribution, and this would also be useful from the point of view of studying the morphology of nanoparticles.
Unfortunately, it was not possible to arrange TEM measurements in the shortness of time and the paper is not aiming at a TEM analysis. In order to address the valuable comment, SEM pictures were recorded instead. Pictures of all investigated catalysts were added in the SI. The most interesting finding is the comparison of the 10 wt% loaded catalyst prepared by multi-step impregnation (FE10) with the single step impregnated reference (SI10). It is clearly visible, that the reference catalyst SI10 exhibits nanoparticles of about 50nm on the surface, which is absolutely not visible in the catalysts FE01-FE10. Pictures of FE10 and SI10 were added in the manuscript. We thank the reviewer to give us the recommendation to apply electron microscopy, since these pictures support and complement our findings by spectroscopic methods.
- It is necessary to make a comparison with the data of iron-containing catalysts known from the literature on the CO conversion under similar reaction conditions.
The need of the reviewer for a comparison is absolutely understandable. We added this information in the introduction and compared our results with them in the discussion.
- The title of the picture caption must begin with a capital letter «Figure 8. Turnover frequencies of FE01….».
We changed this error, thank you very much for noticing.
Reviewer 2 Report
Comments and Suggestions for Authors(1) The introduction section fails to give a clear background of the research topic. It is lengthy and lacks focus. The literature cited is overly reliant on historical study and does not incorporate recent advances on this topic. Meanwhile, the meaning and novelty of the work should be emphasized.
(2) The author only demonstrated that the multistep method allows for the facilitated generation of tetrahedrally coordinated iron species, but did not well explain the relationship between the tetrahedral coordination and CO oxidation activity. Therefore more characterization related to CO oxidation is needed, e.g. XPS, CO-TPD, H2-TPR, in situ FTIR .
(3) The author should consult more literature or conduct relevant tests to explain the experimental phenomena, rather than simply stating in general terms like “could not be identified by the applied characterization methods” or “cannot be explained on available data”, e.g. lines 153, 183, 282, 375.
(4) The conclusion in line 313 is based on the assumption that iron oxides are far less mobile on the support surface than their precursor, but no evidence is provided to support this assumption.
(5) In line 319, the author claim that “the formation of larger (crystalline) agglomerates is avoided as no indications for X-ray crystalline species could be found by PXRD”. However, the reference sample (SI10) also did not exhibit peaks of crystalline iron species. Therefore, the conclusion from the PXRD analysis that the multistep method avoids agglomeration is untenable.
(6) In line 236, the author identified iron oxides as amorphous or nanoparticulate by the absence of Bragg reflexes. However, the broad hump corresponding to the amorphous species can not be observed in PXRD patterns. Thus, the amorphous iron species need to be evidenced by additional characterizations.
Comments on the Quality of English LanguageMinor editing.
Author Response
We would like to thank the reviewer for the time he has invested and for his valuable and detailed comments.
(1) The introduction section fails to give a clear background of the research topic. It is lengthy and lacks focus. The literature cited is overly reliant on historical study and does not incorporate recent advances on this topic. Meanwhile, the meaning and novelty of the work should be emphasized.
The introduction has been revised and expanded with regard to synthesis and activities in CO oxidation to provide a better overview and allow a classification of the results. The “historic” background was shortened. Indeed, the meaning and novelty was emphasized.
(2) The author only demonstrated that the multistep method allows for the facilitated generation of tetrahedrally coordinated iron species, but did not well explain the relationship between the tetrahedral coordination and CO oxidation activity. Therefore more characterization related to CO oxidation is needed, e.g. XPS, CO-TPD, H2-TPR, in situ FTIR .
The reviewer is absolutely right in this point. However, we want to emphasize here that this relationship was already demonstrated in previous publications (Schlicher et al., Catalysis 2022, DOI: 10.3390/catal12060675; Schoch et al., ChemSusChem 2016, DOI: 10.1002/cssc.201600508). Here we focus on the preparation approach to realize a large fraction of such species. To further elucidate the reaction mechanism, indeed additional (in-situ) techniques will be needed, which will be subject of upcoming publications.
(3) The author should consult more literature or conduct relevant tests to explain the experimental phenomena, rather than simply stating in general terms like “could not be identified by the applied characterization methods” or “cannot be explained on available data”, e.g. lines 153, 183, 282, 375.
The mentioned passages (results from DRUVS and catalytic tests), where the mentioned weak formulation were made, seem to describe the result of the same effect. After several attempts to solve this riddle, we decided to publish our results like this, since the main findings of the work is not affected. We want to investigate this effect in future by temperature-dependent DRUVS and in-situ XAS measurements, where we hope to see structural changes at the temperature the catalytic conversion stagnates.
(4) The conclusion in line 313 is based on the assumption that iron oxides are far less mobile on the support surface than their precursor, but no evidence is provided to support this assumption.
We made our assumption by determining the Tamann and Hüttig temperatures for the formed Fe2O3 and the precursor and decided based on the comparably big temperature difference, that we can use this property to reduce sintering. The corresponding paragraphs in the introduction and the discussion were rewritten and supplemented with literature references.
(5) In line 319, the author claim that “the formation of larger (crystalline) agglomerates is avoided as no indications for X-ray crystalline species could be found by PXRD”. However, the reference sample (SI10) also did not exhibit peaks of crystalline iron species. Therefore, the conclusion from the PXRD analysis that the multistep method avoids agglomeration is untenable.
Thank you very much for this comment. In fact, small reflexes can be seen in the diffractogram of SI10, which can be assigned to a mixture of α- and γ-Fe2O3. This was not easy to see in the figure and we missed to discuss this in the manuscript. We added now a corresponding explanation in the manuscript and a magnified diffractogram comparing SI10 with Fe10 and the references in the SI. Furthermore, we carried out SEM measurements and added pictures of SI10 and FE10 in the manuscript, where a particle formation of SI10 is clearly visible, while FE10 does not show any indication for these pictures of FE01, FE03, FE05, FE07, FE08, FE09 can also be found in the SI).
(6) In line 236, the author identified iron oxides as amorphous or nanoparticulate by the absence of Bragg reflexes. However, the broad hump corresponding to the amorphous species can not be observed in PXRD patterns. Thus, the amorphous iron species need to be evidenced by additional characterizations.
The corresponding sentence was deleted in the EXAFS analysis section, since it does not give relevant information to follow the EXAFS analysis at this point. Nevertheless, the argument, that no reflexes in FE01-Fe10 are visible, which indicate non-crystalline species present is (still) given in the discussion. Due to the low reflex intensity, which comes with loading and non-crystalline characteristics of the sample, a broadening of possible Fe-oxidic reflexes can not be seen in the diffractograms. We therefore applied PDF, DRUVS and XAFS to analyze the present Fe-oxidic species as outlined in the manuscript to obtain satisfying structural results.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDevelopment of methods for the synthesis of effective nanoparticles and their application in various catalytic processes, such as the neutralization of waste and greenhouse gases is an important topic of modern science. Materials based on iron oxides are of particular interest because these metals are very cheap, widespread in nature, non-toxic metals with unique magnetic and electronic properties.
I recommend the article for publication
Reviewer 2 Report
Comments and Suggestions for AuthorsMy questions have been answered carefully and I think it can be acceptable.
