Thermo-Catalytic Decomposition of Natural Gas: Connections Between Deposited Carbon Nanostructure, Active Sites and Kinetic Rates

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Q1:

The abstract contains several overly long sentences. It is recommended that the authors break them into shorter, more concise statements, avoiding sentences that extend beyond three lines. In addition, the abstract should include specific quantitative data (e.g., methane conversion percentages, changes in activation energy) rather than only describing general trends. 

Q2:
keywords: Fuel Composition, Transmission Electron Microscopy (TEM), The selection of keywords does not appear to be fully suitable. I suggest the authors carefully revise the keywords and consider removing those that are less relevant.

Q3: 

Lines 48–52:
The English expression in this section is confusing and requires revision for clarity and grammatical accuracy.

Q4:

Lines ~68 (Discussion on active sites in carbon materials):
The current description of active sites in carbon materials is not clearly articulated and may cause confusion. Specifically, the mention of “vacancies” is uncommon in the context of carbon-based catalysts, as such terminology is more frequently associated with metal oxides or alloys. For carbon materials, the discussion of structural irregularities is typically framed in terms of edge sites, lattice defects, heteroatom doping, or dislocations.

Q5:

Reaction conditions and flow specification (critical):
The reporting of catalytic activity using “s⁻¹ g⁻¹cat” without an explicit definition and without the corresponding gas‐phase flow information is ambiguous and prevents reproducibility and fair benchmarking. For methane decomposition studies, it is standard to report space velocity and/or explicit flow rates alongside the catalyst loading.

Q6:

Lines 157 and 231: The figure numbers/citations appear to be incorrect. Please correct the numbering and ensure consistency between the in-text citations and the corresponding figure captions.

Q7:

Line 157 (Figure 2):
Figure 2 lacks a scale bar and a complete schematic of the experimental setup, which makes reproduction of the work difficult. It is recommended to include an experimental setup schematic to improve clarity and reproducibility.

Q8:

Figure 3.1a raises several concerns regarding axis labeling, data interpretation, and conversion calculation.

1. Y-axis labeling issue The left y-axis is labeled as “CH₄ Conversion (%)”, but the plotted curves clearly represent CH₄ mole fraction (or concentration) measured at the outlet, rather than actual conversion. This labeling is misleading. I recommend correcting the y-axis label to “CH₄ mole fraction (vol%)” or “CH₄ concentration (vol%)”.

2. Typographical error The word “Coversion” on the y-axis is misspelled; it should be corrected to “Conversion”.

Summary: The manuscript presents interesting results on methane thermo-catalytic decomposition, but significant revisions are needed to improve the quality and reproducibility of the Results and Discussion section. In particular, figures must be reformatted, quantitative data reported with uncertainties, and surface chemistry analysis (XPS) expanded. Addressing these issues will substantially strengthen the manuscript and align it with Catalysts standards.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have attempted to test the carbon black as a catalyst for TCD, comparing virgin with the that of oxidized form. The presentation of the work is unconventional as compared to the vast literature in this field. The authors should present in conventional style to compare the results with literature. The following should be addressed and resubmitted for fresh consideration for publication.

1. The experimental part should be detailed with more details. It is not clear whether the reactions were conducted at fixed temperature or temperature ramping was used. Fig.3 shows temperature ramping.
2. How the conversion was calculated. Looking at Fig. 3.1, it looks like the plot of concentration with time. It should be presented in the form of conversion with time. 
3. The conversions are generally too low for carbon based material and stability is an important issue which was not addressed.
4. How long the reactions were conducted at steady state and should present the product balance in terms of hydrogen yield and carbon yield.
5. Should present the results with the literature in terms of conversion and stability at comparable conditions.
6. The reactivity of the formed carbon to catalyze the TCD reaction should be confirmed with tests performed for a longer duration.
7. 3.5 A, what causes NK at 1000 C, is better than the non oxidized state. Contradicting, need further explanation.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. The abstract should be revised and made more concise. There is no need to include excessive background information in the abstract.
2. The introduction discusses the use of carbon materials in the decomposition of CH₄, but it fails to establish a clear connection between this work and previous studies. The authors should provide this linkage in the final paragraph of the introduction.
3. The carbon materials presented are mainly microporous. Why did the authors not employ full pore analysis to quantify the respective surface area contributions of micropores and mesopores, and to describe the pore size distribution (from micropores to mesopores) more accurately using the DFT method?
4. In Section 3.3, the O 1s and C 1s XPS peak deconvolutions should be provided.
5. The authors need to explain why the TEM images of 75% POX M1300 and 75% POX Ketjenblack in Fig. 3.3 are extremely similar.
6. Please provide the detailed calculation process and raw data for the Arrhenius plots.
7. Raman characterization, which is a key technique for carbon materials, is missing in this study. The authors should include Raman spectra and integrate the results into the current analysis to draw more reliable conclusions.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitled “Thermo-Catalytic Decomposition of Natural Gas: Connections between Deposited Carbon Nanostructure, Active Sites and Kinetic Rates” presents a systematic study on methane decomposition using carbon black catalysts. The authors investigate the role of carbon nanostructure, partial oxidation, and feed composition (pure CH₄ vs. SNG) on catalytic performance, activation energy, and deposit reactivity. The work provides valuable mechanistic insights into the autocatalytic behavior of deposited carbon, highlighting how self-generated carbon eventually governs long-term TCD activity. The manuscript is well structured, clearly written, and fits well within the scope of Catalysts. The data quality is high and the results are supported by multiple complementary techniques (FT-IR, TGA, HRTEM, XPS). Overall, the study represents a meaningful contribution to the field of catalytic methane decomposition and hydrogen production.

Q1:
References – Double-check consistency in reference formatting. Some journal titles appear in full while others are abbreviated. Align all references with the Catalysts style and ensure that DOIs are included.

I recommend acceptance after minor revisions. The manuscript is scientifically sound and provides valuable insights into the mechanistic understanding of methane decomposition over carbon catalysts. Addressing the minor points above will further improve readability and compliance with journal standards.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In Fig. 3.3, the TEM images of 75% POX M1300 and 75% POx Ketjenblack are in fact the same image. We request that the authors provide a direct response to this issue.

Author Response

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Author Response File: Author Response.pdf