Effect of the Ni-to-CaO Ratio on Integrated CO2 Capture and Direct Methanation
, Ju-Eon Kim 1, Tae-Young Kim 3, Han-Dong Son 1, Ho-Jung Ryu 4, Byungwook Hwang 4, Jae-Chang Kim 1,*, Soo-Chool Lee 3,* and Kandis Leslie Gilliard-AbdulAziz 2,5,*Round 1
Reviewer 1 Report
In this work, Ni/CaO catal-sorbents with different Ni-to-CaO ratios were synthesized using the sol-gel method. The basic physicochemical characteristics of the synthesized samples were analyzed. The purpose was to determine the effects of these ratios on the microporosity of CaO and the dispersion of Ni. The CO2 capture performance (capacity and kinetics) and direct methanation performance (productivity and kinetics) of the catal-sorbents were investigated. It was found that the 10Ni/CaO sample exhibited the best CO2 capture capacity, kinetics, and CH4 production rate, with thermal stability observed for both Ni and CaO species. Additionally, the cycle stability of the catal-sorbents in CO2 capture and direct methanation processes was revealed. Therefore, I suggest that this manuscript can be accepted after the authors address the questions, clarify ambiguous information, and revise the formatting issues.
1. In Table 1 on page 3, the provided values are for the CaO content, but the first row of the table specifies the metal content. In the case of 20Ni/CaO, the given Ni% is 18.0, but the CaO content is unexpectedly listed as 92.0. It is requested that the authors provide a reasonable explanation for this discrepancy.
2. In Figure 2 on page 4, in the annotation explanation for (b), “Ni 2p2/3” should be corrected to “Ni 2p3/2”.
3. There are errors in the labeling of the table on page 6, as they do not correspond accurately.
4. Why does the capture amount of CO2 increase for 10Ni/CaO after three cycles in the table on page 6? I would like the authors to provide an explanation.
5. Are there any side reactions in the CO2 capture reaction and direct methane conversion reaction?
6. In the given reaction provided on page 2, ‘CO2 capture: NiO/CaO(s) + CO2(g) ↔ NiO/CaCO3(s)’, it can be inferred that the capture amount of CO2 is associated with CaO. However, why does a higher content of CaO result in a decrease in the capture amount of CO2
7. In Figure 2(a) on page 4, there is a shoulder peak around 30-40 for 2Ni/CaO. Why does this peak disappear in 10Ni/CaO and 20Ni/CaO? Can the authors explain what substance this is and why it disappears with an increase in Ni content?
8. How can the XPS spectra provided by the authors explain the catalyst’s performance? Why do 2Ni/CaO and 10Ni/CaO exhibit such weak peak intensities in their XPS spectra?
9. Between NiO form and NiO-CaO form, which one contributes more to the direct methane conversion of CO2? Please explain the reasons.
10. Why does the methane production decrease in the case of 20Ni/CaO according to the table on page 6?
No Comments on the Quality of English Language.
Author Response
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Author Response.pdf
Reviewer 2 Report
The paper addresses Effect of the Ni-to-CaO Ratio on Integrated CO2 Capture and Direct Methanation.
The manuscript is well structured and easy to follow. However there are some aspects to be improved:
-Introduction does not provide sufficient up-to-date references particularly for capture so the following references could be added:
https://0-doi-org.brum.beds.ac.uk/10.1016/j.cep.2016.07.004
https://0-doi-org.brum.beds.ac.uk/10.1016/j.micromeso.2014.06.032
-The research gap is covered but the contribution is unclear. At the end of the introduction the authors explained previous work but they do not clearly specified the impact of this manuscript.
-Why were only five cycles considered? Could more cycles be considered as this is quite low for CCSU?
-Conclusions are too general and they do not specify the main findings from the results.
English is good but some sentences are too long to be understood.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
