RuNi/MMO Catalysts Derived from a NiAl-NO3-LDH Precursor for CO Selective Methanation in H2-Rich Gases
Round 1
Reviewer 1 Report
After carefully reviewing the paper “RuNi/MMO catalysts derived from NiAl-NO3-LDHs precursor for CO selective methanation in H2-rich gases” I recommend that it should be accepted after minor revision. The paper is well written and documented. Here are some recommendations:
- page 5, rows 136-138: “This indicates that RuNi/MMO-N has an enhanced hydrogen overflow effect caused by the addition of Ru due to its abundant acid sites [42], which promote the reduction of NiO in MMO-N” – would the authors please explain what they mean by hydrogen overflow effect and how is it linked to the number of acid sites;
- page 6, row 152: “enhanced CO adsorption capacity of the RuNi/MMO-N catalyst” – there are no values for th CO adsorption capacity, and the curves in Figure 6 do not show this enhancement; please explain;
- page 6, rows 171-172: “The peak areas after CO2-TPD of the RuNi/MMO-C and RuNi/MMO-N catalysts were listed in Table S3.” Table S3 does not show peak areas for the CO2-TPD experiments, please verify and add the values;
- page 7, row 194: the Ni/MMO-N catalyst was never mentioned before in the paper, was not characterized in any way, so a discussion about its activity does not seem appropriate;
- page 8, row 228: “weight loss above 350 °C is ascribed to the oxidation of the deposited carbon” – please explain briefly the reaction that leads to the deposition of carbon on the catalyst;
- page 11, row 320: please give the diameter of the quartz tubular fixed-bed reactor;
- page 11, row 329: why was a FID detector needed for the chromatographic analysis?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The main question for the authors of the article is the choice of comparison systems: if nickel and ruthenium do not form alloyed particles, then it is necessary to compare the activity with Ni/support and Ru/support systems. The conclusion that the addition of a noble metal increases the activity seems obvious. As a rule, the authors strive to obtain active catalysts without the use of platinum group metals (ruthenium in this case). From this point of view, the article does not contain new and valuable information.
The authors do not explicitly indicate the ratio of ruthenium/nickel in the article. From the XPS spectra, it can be assumed that there is a significant amount of nickel. I would like an explicit indication of the weight composition of the active components in the text of the article.
The observed binding energy of the main state of nickel (E_b = 856.1 eV), is too high for Ni2+ in NiO. Rather, it is Ni3+ in the composition of Ni2O3. The interpretation of the state as Ni2+ requires additional evidence or explanations for the increased binding energy.
Why did the authors not investigate the most intense line of ruthenium Ru3d? Its proximity to the carbon C1s line is not a problem for analysis with curve fitting procedure.
Data on the chemical composition of impurities on the surface (carbon and nitrogen in the first place) were not disclosed, although the XPS method was available to the authors. The authors do not explain what is the reason for the constantly increasing background of the CO signal in the TPD-CO spectra in Figure 6. An attempt to evaluate the contributions of various centers to the TPD-CO2 experiment looks like a valuable idea. The number of states and temperature maxima can be estimated without fitting. The quantification based on the presented fitted pectra raises questions, since the shape of TPD peaks, unlike XPS peaks, has not been determined.
From a general point of view, the TPR-H2, TPR-CO, and TPD-CO2 data for the systems under study look almost the same with minimal statistical differences. The difference in catalytic activity of Ru-containing samples is obvious and not new.
Thus, despite the rather accurate methodical execution of the work, the lack of new scientific knowledge in it makes its publication unclaimed.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The following comments should be considered during the revision process.
1) The metal contents for each catalyst should be analyzed with ICP and reported.
2) The surface area of each catalyst should be measured and reported.
3) The particle size of Ru and Ni should be determined based on the TEM images and reported.
4) It would be better to report the dispersion of Ni and/or Ru based on the chemisorption data.
5) It is highly recommended to detect the effluent gas with mass spectrometer during CO, CO2, and NH3-TPD.
6) It is not clear why RuNi/MMO-N(0.09M) is much better than the other RuNi/MMO-N catalysts.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Authors made cosmetic changes to the article, removed minor flaws. The main problem, due to which it was recommended to reject the article, has not been resolved in any way - The article does not contain important new scientific data, the choice of comparison objects does not allow us to correlate the difference in activity with any properties of the catalysts.
Reviewer 3 Report
The authors have tried to revise the manuscript bases on the reviewers' comments.
