Thermal and Plasma-Assisted CO2 Methanation over Ru/Zeolite: A Mechanistic Study Using In-Situ Operando FTIR
, Arnaud Travert 2, Carlos Henriques 1,* and Federico Azzolina-Jury 2,*
Round 1
Reviewer 1 Report
Reviewer’s Comments:
The manuscript “Study and comparison on the mechanism of thermal and plasma-assisted CO2 methanation over Ru-zeolite catalyst using in-situ operando FTIR” is very interesting work. This paper investigates the CO2 methanation is an attractive reaction to convert CO2 into a widespread fuel such as methane. As a thermocatalytic reaction, its performances might be hindered by its need to be carried out at high temperatures. Thus, utilizing a dielectric barrier discharge (DBD) plasma to activate the re-action, synergistic effects stemming from the combination of plasma and catalyst could produce beneficial effects on the catalyst’s performances. In this work, we compared the thermal and plasma-assisted reaction mechanisms through in-situ operando FTIR. Under plasma-catalytic conditions (barely studied in similar setups in literature) CO was found to be the main product of the reaction coming from CO2 dissociation by plasma. CO2 is also excited by the plasma, facilitating its adsorption on the surface of the Ru catalysts in the form of oxidized carbon species (formates, al-dehydes, carbonates, carbonyls etc.) that are then progressively hydrogenated to methane. However, the following issues should be carefully treated before publication.
1. The title of the manuscript is not impressive so rewrite the title.
2. In the abstract, the author should add more scientific findings.
3. Keywords: There are so many keywords in this manuscript and reduce it. So, modify the keywords.
4. In the introduction part, the introduction part is not well organized and cited references should cite recently published articles such as 10.3390/toxics10110657, 10.1016/j.rinp.2022.105817
5. Introduction part is not impressive and systematic. In the introduction part, the authors should elaborate on the scientific issues in CO2 methanation research.
6. Results and Discussion …, The author should provide reason about this statement “It is possible that the incorporation of Ru on the catalysts’ surface removes some sites that are favorable for the adsorption of water, for example AlO4 tetrahedra”.
7. The authors should explain regarding the recent literature why “As the temperature increases, the methanation reaction starts to occur at 225°C, as highlighted by the appearance of the band at 1305 cm-1 (C-H bending, gas-phase methane)”.
8. Plasma-catalysis. The author should explain the latest literature “First, it’s important to point out that is not possible to extract information from the region below 1250 cm-1 because of the noise introduced in the spectra by the zeolite framework”.
9. The author should provide reason about this statement, “The formation of more stable dicarbonyl species on Ru is indicated by the band appearing at 2193 cm-1, linked to their CO stretching mode”.
10. Comparison of the present results with other similar findings in the literature should be discussed in more detail. This is necessary in order to place this work together with other work in the field and to give more credibility to the present results.
11. The author should provide SEM images after catalysts performance for stability test.
12. The conclusion part is very week. Improve by adding the results of your studies.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this work, Ru was impregnated in CsUSY(38) zeolite to prepare 3Ru/CsUSY(38) catalyst, and then to study the performance and mechanism of CO2 methanation. It is interesting that the performance was studied in plasma-catalytic conditions; however, I still have some concerns. The main one is that it lacks the comparison of catalytic performance without plasma conditions. I recommend a major revision before acceptance.
(1). Generally, the CO2 methanation reaction exhibits a high methane selectivity, while in this study, the methane was relatively low when the temperature was lower than 425oC, more explanation should be given.
(2). What does the role of Cs in CsUSY(38) zeolite? How about the catalyst without Cs?
(3). The conclusions are too long, it should be concise and refined, moreover, the inference should be not appeared in the conclusions.
(4). The CsUSY(38) can be shorted as CsUSY.
(5). The writing can be further improved. The format of the references should be uniformed, such as the Journal abbreviation.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have replied the comments, and the language has been improved, I believe it can be accepted now.
