Microstructural Changes in La0.5Ca0.5Mn0.5Fe0.5O3 Solid Solutions under the Influence of Catalytic Reaction of Methane Combustion
, Vladimir A. Rogov 1,2, Igor P. Prosvirin 1, Lyubov A. Isupova 1 and Sergey V. Tsybulya 1,2Round 1
Reviewer 1 Report
attached in a file
Comments for author File: 
Comments.pdf
Author Response
Author's Reply to the Review Report (Reviewer 1) attached in the file
Author Response File: Author Response.pdf
Reviewer 2 Report
According to the abstract and the title, the paper deals with changes in the La0.5Ca0.5Mn0.5Fe0.5O3 perovskite structure after its treatment in CH4 combustion mixture. However, the discussion on that issue is very poor and the whole manuscript seems to be chaotic. The topic itself is quite interesting, but the authors must rearrange and improve the manuscript's content. The paper is not suitable for publication in the present form. It should be either rejected or subjected to a major revision, addressing the below-given comments:
The carbon layer should be indicated on the HRTEM Image (Fig.2). Where is this carbon coming from?
The discussion of the XPS spectra, especially in terms of iron ( Fe 2+ and Fe3+) and manganese (Mn 3+ and Mn4+) presence should be enriched with the Fe2p and Mn2p spectra, including their deconvolution.
What are the contributions of particular oxidation states in the initial sample?
Experimental:
Catalytic tests: The residence time at each temperature was 20 min. It is way too short for catalyst stabilisation and to speak of catalyst activity, especially when the authors write "After reducing the temperature to 500o C, the conversion is slightly reduced, but remains almost at the same level with the previous value". The tests at each T should be performed for a longer time with constant monitoring of the outlet gas composition.
After describing the H2-TPR profile, the authors discuss the "recovery profile" that has been shown in a publication from 2008 [ref 23]. What is the link between presented H2-TPR and the recovery profile? What is the importance of the recovery profile study, how was it conducted and finally - was the same sample discussed now and 11 years ago?
What is the role of Ca1-xMnxO on the catalyst surface in the methane combustion?
TGA: low T mass decrease is ascribed to the removal of loosely coupled functional groups - where are they coming from?
Desorption of weakly bound lattice oxygen, which is said to occur at 300-600 C may be questionable since no MS data are provided to prove this. On which grounds the authors claim that said mass loss is due to oxygen desorption?
Catalyst preparation and characterisation: The La0.5Ca0.5Mn0.5Fe0.5O3 was calcined at 900C/4h - in what atmosphere?
If the catalyst was calcined at such a high T, why the authors observe changes in XRD at 750 C in flowing He?
Author Response
Author's Reply to the Review Report (Reviewer 2) attached in the file.
Author Response File: Author Response.pdf
Reviewer 3 Report
To improve manuscript further, I suggest to complete at least below shown points:1. Introduction should be extended with recent literature. I think at least effect of water vapor (and sulfur poisoning) could be good to add.
2. At least Lines 26-27 and 35-37: Authors stated that something have been studied extensively or numerous studies have been carried out, only with two references.
3. Authors are comparing dry and wet condition results to each others (lines 36-43). It is quite obvious that difference is clear. Recent references should be added where the dry/wet conditions were compared well, even in very complex mixtures.
4. Lines 44-54: Introduction includes own opinions and discussion without any references.
5. Authors should clarify the aims.
6. Lines 82-85: The statement is unclear.
7. The analysis is impossible to do from Figure 3 as shown on lines 89-102. How atomic ratios changes during/after reaction?
8. Water vapor is always present in the burning process. Thus, its effect on catalyst performance should be added. Also conversion curves would be informative to compare with noble metal catalyst (PdO-alumina). Based on my industrial experience, noble metal catalyst (same amount in mass) may perform better performance if st least 1% Pd metal loading is applied. The higher loading increases durability of the catalyst.
9. What was a detector in TPR measurements? If qudrupole mass spectrometer was used its sensitivity is really critical in quantification.
10. Scale and axis of Figure 6 might be missleading. Is it 3D figure or are peak positions changing?
11. How Authors comment on Table 2 results, since after reaction Atomic ratio is changing which indicates that the catalyst is not stable.
12. Methods must be modified extensively. Catalyst form in experiment (powder, monolith...)? Detector to quantify the methane concentration in the measurement (critical to justify the results!).
13. XRD, TG, TPR parameters are incomplete to be repeated.
14. Was TPR measured during cooling, since heating rate is -10C/min?
15. Connection should be built between the data in a rational way.
Author Response
Author's Reply attached in the file.
Author Response File: Author Response.pdf
Reviewer 4 Report
The research article entitled »Microstructural Changes in La0.5Ca0.5Mn0.5Fe0.5O3 Solid Solutions under the Influence of Catalytic Reaction of Methane Combustion« relates to characterization of La0.5Ca0.5Mn0.5Fe0.5O3 catalyst and investigation of its activity in methane combustion reaction. Indeed, as presented in review ref. [12], perovskites ABO3-type materials are widely investigated as a potential alternative for noble metals supported catalysts in catalytic methane combustion. Moreover, the presented reactivity of investigated catalyst is quite good compering with the other materials of this perovskites ABO3-type class. The authors focused in the paper on the formation of Ca1-xMnxO solid solution during deCH4 reaction. However, in my opinion the presented results do not reveal unequivocally the changes of the catalyst properties during the reaction.
In my opinion, the presented research article can be considered for publication in Catalysts, however the following points should be addressed:
1. The linguistics of the manuscript should be improved. There is a lot of formulations that could be misleading. This is inter alia the case of the fragment of the manuscript: lines 46-50 page 2. Moreover, words impurities and contaminants are synonyms (line 91, page 3). There is also a lot of places where the superscript/subscript should be used. In my opinion, also the sentence order raises doubts in few places (line 199-200, page 8).
2. There is a disproportion in the experiment descriptions. Some methods are described with all details (for example XPS) while for others the basic information are missing (catalytic activity tests – no information about detection; TPR-H2 – no information about sample mass).
3. I would like to suggest to the authors to improve the Introduction part of the manuscript. Mainly, I am thinking about the paragraph devoted to the modification of perovskite oxide. From what I know, the perovskite-type oxides could have the formula A3+B3+O2-3 as well as A2+B4+O2-3. Therefore, the sentence starting in line 50 (page 2) is misleading. Moreover, it would be good to give some quantitative information about the optimal level of doping. I suppose that for each dopant there is such? It would be good for justify the particular selection of the La0.5Ca0.5Mn0.5Fe0.5O3 oxide.
4. In the part of paper devoted to the catalytic activity results there is no information about the products of the CH4 combustion. There is information in the conclusions, however in my opinion it should be mentioned here as well.
5. The authors mentioned that the phase composition of the samples after reaction was determined. Nevertheless, the XRD patterns were not included in the paper. In my opinion this results should be presented. Especially because the authors claimed no significant changes in the structure basing on xrd pattern while this changes are observed in the results of other characterization methods (HRTEM, H2-TPR, XPS). Moreover, in Fig. 6 the Co1-xMnxO phase is observed for the sample heated at 600°C. So, why it is not observed (as the authors have claimed) for the sample after reaction?
6. Moreover, looking on the presented results it is not clear for me whether the Co1-xMnxO phase is arising during the deCH4 reaction or is already existing in the fresh sample? From the authors interpretation of Fig. 7 it seems that the Co1-xMnxO phase is already existing before methane combustion. On the other hand from xrd data (no presented in the manuscript) the authors have claimed no other phases, just perovskite structure. Please, discuss this issue more carefully.
7. The authors have mentioned that the measurement of the interplanar spacing observed in HRTEM images were done and have confirmed the presence of Co1-xMnxO phase. This should be presented in the paper (Fig.4 should be extended).
8. In my opinion it would be good to quantify the amount of arising Co1-xMnxO phase. It could be done basing on the H2-TPR data (from the difference in the H2-uptake for sample before and after the reaction).
9. The y-axis legend in Figs 1 and 8 is missing.
Comments for author File: Comments.pdf
Author Response
Author's Reply attached in the file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have accepted most of my suggestions given in my review round 1. The manuscript has been updated accordingly. The revised manuscript is much better. The research by the authors on changes in perovskite surface structure during methane combustion is a good contribution in the area of heterogeneous catalysis.
Author Response
Dear Reviewer,
Thank you very much for reviewing the manuscript. Adjustments were added to the article.
Reviewer 2 Report
The authors have improved the manuscript substantially.
However, I still think that the experiments were not designed properly, mainly owing to too short residence time at each T during CH4 oxidation. To improve the quality of the paper the authors should carry out the tests for a longer time. They should stop the experiment at a given T when the concentrations of reagents are stable for some time. Either 20 or 30 minutes is to short. The authors should also show (e.g. in the supporting materials) the concentrations of the reagents vs. time, to prove, that the steady state was achieved.
The authors can not discuss the present catalyst using the results obtained many years ago for another sample. The new test must be done, for the actual sample.
Author Response
Thank you for your review. Please see the reply in the attached file.
Author Response File: Author Response.pdf
Reviewer 4 Report
In my opinion the manuscript has been significantly improved and now warrants publication in Catalysts.
Author Response
Dear Reviewer,
Thank you very much for reviewing the manuscript. Adjustments were added to the article.
