Effect of Pressure on Na_0.5La_0.5Ni_0.3Al_0.7O_2.5 Perovskite Catalyst for Dry Reforming of CH₄

Round 1

Reviewer 1 Report

Some good modifications to the manuscript have been made, but it is still unpublishable in its current form for the same general reasons as in the original review. The authors’ claim that the whole manuscript was restructured is not true and many of the concerns haven’t been seriously addressed. In this reviewer’s opinion, the manuscript doesn’t really need restructuring anyway – the results and order of presentation seem fine - it needs fleshing out with discussion of the results in the context of the literature, and it needs to highlight the contribution of this work to the field and the significance of the results. I suggest that the authors read catalysis papers by other groups to get a feeling for what is expected at the standard of publication in a scientific journal.

A couple of new and informative papers are cited and discussed in the introduction, and this is a step in the right direction, but it is still far too lacking. Some sections have small modifications and there is new, good experimental data. However, most of the data is simply presented and the significance is not discussed, especially in the context of other literature.

The addition of Table 1 is welcome, and it’s good that the activity is compared with the literature, but the conversion is a meaningless number without the associated GHSV from each study, so that should also be included in the table. The authors could also calculate activity per gram of catalyst or per m2 for slightly better metrics.

The new Raman data are interesting and evaluated correctly and in such a way as to give information about the carbon formed. The authors could note in the text that there is no effect of pressure on the type of carbon observed by Raman. However, the plot looks as if there is a significant shift in the data obtained at 1 bar, is this correct?

There are no numbers on the BJH y axis, x axis says “nm” but I guess it should be Angstroms according to the text. The CO2 TPD data are not evaluated beyond describing them.

Figure 12 – the new TPO results disagree with the TGA results, the 8 hr sample has more coke according to TPO and a higher temperature peak than the 30 hr sample. This is the opposite of the TGA results.

Finally, the authors do not appear to have taken the previous reviews seriously. Two examples below:

1. In the previous review, this reviewer’s concern about inappropriate referencing was supported by two examples from the first page, and the authors responded by changing only those two references. It is not the job of a reviewer to go through and correct each reference, and from this response I am not at all confident that the authors have cited anything correctly.

2. In my previous review I wrote, “the SEM images are so zoomed out that they could have been taken by an optical microscope and give no useful information.” In response, the authors wrote, “necessary modification has been done to the SEM images.” No discernible modification has been made to the SEM images – they are just the same images as in the original manuscript. There are still no grounds for the claim that the SEM images show sintering.

Author Response

Comments and Suggestions of Reviewers

The authors greatly thank the reviewers for their valuable comments. All the points were thoroughly considered, certainly improving the manuscript quality. We hope that the provided responses are satisfactory, wishing that now the manuscript is worthy to be published.

 

Reviewer #1:

 

Comment #1:

A couple of new and informative papers are cited and discussed in the introduction, and this is a step in the right direction, but it is still far too lacking. Some sections have small modifications and there is new, good experimental data. However, most of the data is simply presented and the significance is not discussed, especially in the context of other literature.

Response #1:

The authors are grateful for this comment of the reviewer. Further discussion is performed in the result sections of the revised manuscript.  

Comment #2:

The addition of Table 1 is welcome, and it’s good that the activity is compared with the literature, but the conversion is a meaningless number without the associated GHSV from each study, so that should also be included in the table. The authors could also calculate activity per gram of catalyst or per m2 for slightly better metrics.

Response #2:

Table 1 in the revised manuscript, values of GHSV, weight of catalysts and CH₄ conversion per gram catalyst are inserted.

Comment #3:

The new Raman data are interesting and evaluated correctly and in such a way as to give information about the carbon formed. The authors could note in the text that there is no effect of pressure on the type of carbon observed by Raman. However, the plot looks as if there is a significant shift in the data obtained at 1 bar, is this correct?

Response #3:

The Raman figure displays the coordinate of the peaks. There is no appreciable shift due the pressure. In addition, slight shift would not create change of explanation given on its degree of graphitization.

Comment #4:

There are no numbers on the BJH y axis, x axis says “nm” but I guess it should be Angstroms according to the text. The CO2 TPD data are not evaluated beyond describing them.

Response #4:

In the revised manuscript, numbers are included in BHJ y axis, in the x axis nanometer is used often and interchangeable with Angstroms. Since (1 nm -= 10 Å). From the CO₂-TPD analysis, it can be concluded that the catalyst manifested strong basic sites which enhances the adsorption of CO₂ on the catalyst surface.

Comment #5:

Figure 12 – the new TPO results disagree with the TGA results, the 8 hr sample has more coke according to TPO and a higher temperature peak than the 30 hr sample. This is the opposite of the TGA results.

Response #5:

Authors are grateful to acute observation of the reviewer on the discrepancy in the TPO and TGA results. To solve this, the TPO analysis is repeated and the output is used in the revised manuscript, where the results of TPO are found consistent to those of TGA and hence removed the inconsistency in the previous manuscript. The activity results are validated by TGA results, since we have got less inferior catalyst performance with time and TGA results show high carbon deposit at longer time.  

 

Comment #6:

Finally, the authors do not appear to have taken the previous reviews seriously. Two examples below:

1. In the previous review, this reviewer’s concern about inappropriate referencing was supported by two examples from the first page, and the authors responded by changing only those two references. It is not the job of a reviewer to go through and correct each reference, and from this response I am not at all confident that the authors have cited anything correctly.
2. In my previous review I wrote, “the SEM images are so zoomed out that they could have been taken by an optical microscope and give no useful information.” In response, the authors wrote, “necessary modification has been done to the SEM images.” No discernible modification has been made to the SEM images – they are just the same images as in the original manuscript. There are still no grounds for the claim that the SEM images show sintering.

 

Response #6:

The authors are thankful to reviewer’s comment. The references both in the text and in the list are revised and arranged accordingly. In the case of the SEM, the description is circumscribed to the present illustrations:  In the fresh catalyst individual leaf-blade shapes are in majority but in used catalyst this identity vanishes.

I am citing some investigators who used SEM to show the change of particle morphology due to agglomeration and sintering [1-4].

[1] Aditi B. Khadilkar, Peter L. Rozelle, Sarma V. Pisupati ‘ Investigation of fluidized bed agglomerate growth process using simulations and SEM-EDX characterization of laboratory-generated agglomerates’, Chemical Engineering Science, Volume 184, 20 July 2018, Pages 172-185.

[2] Jeachun Park ByoungseungYoo’ Particle agglomeration of gum mixture thickeners used for dysphagia diets’, Journal of Food Engineering, Volume 279, August 2020, 109958.

[3] Michael J. Coutts, Michael B. Cortie, Michael J. Ford, and Andrew M. McDonagh, ‘Rapid and Controllable Sintering of Gold Nanoparticle Inks at Room Temperature Using a Chemical Agent’, J. Phys. Chem. C 2009, 113, 1325–1328.

[4] Jing-Feng Li, Zhen-Liang Xu, Hu Yang, Li-Yun Yu, Min Liu ‘Effect of TiO₂ nanoparticles on the surface morphology and performance of microporous PES membrane ‘Applied Surface Science 255 (2009) 4725–4732

 

Reviewer 2 Report

The proposed manuscript reports the catalytic activity of Na0.5La0.5Ni0.3Al0.7O2.5 under various temperature and pressure range. Presented results are very interesting and worth to publish, however there some issues that need to be reconsidered:

The novelty of the research should be clearly underlined. Investigation of dry reforming process parameters seems not sufficient. How did authors confirm the real composition of the catalysts? ICP data should be added. Did authors measure the activity of the perovskite catalyst that doesn’t contain nickel particles? The discussion regarding the comparison of catalytic activity and literature date must be improved. The manuscript should be improved in terms of editorial requirements: line 156: no caption under the picture, line 74: paragraph 3.2 should be somewhere else The manuscript contains a lot of interesting results but in my opinion, the discussion and comparison between results for particular pressures and temperatures should be extended. It would be valuable to add discussion on how examined parameters affect the mechanism of dry reforming. What is the role of particular perovskite elements?

Author Response

Comments and Suggestions of Reviewers

The authors greatly thank the reviewers for their valuable comments. All the points were thoroughly considered, certainly improving the manuscript quality. We hope that the provided responses are satisfactory, wishing that now the manuscript is worthy to be published.

 

Reviewer #2:

The proposed manuscript reports the catalytic activity of Na0.5La0.5Ni0.3Al0.7O2.5 under various temperature and pressure range. Presented results are very interesting and worth to publish, however there some issues that need to be reconsidered:

Comment #1:

The novelty of the research should be clearly underlined.

Response #1:

In this work, perovskite catalyst is used. The interest of perovskite-type oxides has grown up particularly for catalytic dry reforming of methane [1]. These catalysts have high thermal and hydrothermal stability as well as high mechanical strength among other properties. perovskite catalysts are comparable even with a catalyst commercially used in steam reforming [2]. The influence of pressure, temperature which are essential operating conditions upon the production synthesis gas is thoroughly studied.

[1] H.S. Kim,Y. Jeon, J.H. Kim, G.Y.Jang, S.P. Yoon, J.W. Yun,’ Characteristics of Sr1−xYxTi1−yRuyO3+/−δ and Ru-impregnated Sr1−xYxTiO3+/−δ perovskite catalysts as SOFC anode for methane dry reforming, Applied Surface Science Volume 51030 April 2020 Article 145450.

[2] M.R. Goldwasser, M.E. Rivas, E. Pietri, M.J. Pe´ rez-Zurita, M.L. Cubeiro, L. Gingembre, L. Leclercq, G. Leclercq, Appl. Catal. A: Gen. 255 (2003) 45–57.

Comment#2:

Investigation of dry reforming process parameters seems not sufficient. How did authors confirm the real composition of the catalysts? ICP data should be added.

Response #2:

The analytical composition of the catalyst is measured using ICP:

Element	Weight %
Na	4.5
La	29.3
Ni	9.85
Al	11.25

 

Comment #3:

Did authors measure the activity of the perovskite catalyst that doesn’t contain nickel particles?

Response # 3:

It is well known that Ni is an ideal for dry reforming reaction due to its property of high activity. However, it has strong drawback due to its rapid deactivation. perovskite catalyst has been tested without Ni, the activity dropped significantly [1]. In this work the catalyst without Ni is not tested.

[1] S. K. Chawla, M. George, F. Patel, S. Patel. Production of synthesis gas by carbon dioxide reforming of methane over nickel based and perovskite catalysts, Procedia Engineering 51 (2013) 461 – 466.

 

Comment #4:

The discussion regarding the comparison of catalytic activity and literature date must be improved.

Response #4:

Table 1 in the revised manuscript is augmented by not only quoting the space velocity and the methane conversion of different investigation. However new columns are added showing the weight of the catalyst used and the methane activity per weight of catalyst. 

Comment #5:

The manuscript should be improved in terms of editorial requirements: line 156: no caption under the picture, line 74: paragraph 3.2 should be somewhere else.

Response #5:

The authors are grateful to reviewer ‘s keen observation. In line 56, the caption and the pictures are harmonized. The paragraph 3.2 is placed in the right position.

Comment #6:

The manuscript contains a lot of interesting results but in my opinion, the discussion and comparison between results for particular pressures and temperatures should be extended. It would be valuable to add discussion on how examined parameters affect the mechanism of dry reforming.

 

 

Response #6:

The discussion of the results is further expanded in the revised manuscript, by stating the output of the studied parameters. For instance, the Raman analysis denotes the formation of the carbon and that the operating pressure do not pose any difference. Both the TGA and TPO analysis display the formation of carbon deposit which affected by the operating pressure and the duration of the reaction. The CO2-TPD analysis exhibits that the catalyst is characterized by strong basic sites which enhances the absorption of CO₂ on the catalyst surface.

Comment #7:

What is the role of particular perovskite elements?

Response #7:

In this catalyst the main elements are (Ni, La, Na, Al). Their role may be summarized as:  Ni is the source for high activity of the reforming reaction; La decreases Ni aggregation and increases the resistance to coking; Na modifies the Ni active phase by suppressing deactivation by carbon. Al improves the stability of the Ni.

Round 2

Reviewer 2 Report

I propose to accept the manuscript in current form. After the revision the manuscript has been improved and meets standard for Catalysts journal. 

Author Response

Comments and Suggestions of Reviewer

The authors grateful to the reviewer for their valuable comments. All the points were carefully addressed, to upgrade the manuscript’s quality. We hope that the delivered responses are all right, paving the manuscript for publishing.

 

Comment #1:

Incorrect use of English (e.g. “The rise of reaction temperature from 500°C to 800°C promoted methane and carbon dioxide activities” – the activity of a molecule is a concept, but it is not what they mean. They mean activity of the catalyst for the reaction. This is a crucial distinction.

Response# 1

The authors are thankful to the reviewer. The sentence is reworded to observe the fundamental concept.

The increase of reaction temperatures from 500°C to 800°C increased the reaction rate and hence the methane and carbon dioxide conversions are increased.

Comment #2:

 The H₂/CO ratio obtained at 1 bar pressure depicted a unity ratio” – depicted is used incorrectly.

Response# 2

The word depicted is removed. The sentence is paraphrased as:

A unity ratio of H₂/CO was obtained at 1 bar

Comment #3:

The TGA analysis showed the drop of mass due to the carbon deposition – authors mean “due to oxidation of carbon deposits”;

Response# 3

The authors are thankful to the reviewer for this keen observation and the sentence is corrected as per suggestion.

 “The TGA analysis showed the drop of mass due to oxidation of carbon deposits”

Comment #4:

The concept of “conversion per gram of catalyst” is physically meaningless, because the conversion depends on the flow rate as much as the mass of catalyst;

Response# 4

The authors agree with the reviewer that the conversion per gram of catalyst” is not required although in the previous comments one reviewer asked for calculation of activity per gram.

To comply to this comment, in the revised manuscript the column CH₄ conversion /gram catalyst of table 1 is deleted.

 

Comment #5:

SEM images are not of sufficient resolution and are skewed/thin.

Response #5:

The resolutions of SEM images are improved.

Author Response File: Author Response.docx