Review Reports

Round 1

Reviewer 1 Report

In this manuscript, Zhang and Lu et al. report the syntheses and characterization of a series of electrospun Ni-Co metallic catalysts of varying Ni/Co ratios on a carbonaceous support and studied their reactivity in the thermal hydrogenation of CO₂. They discovered that a mixed-metal catalyst containing a Ni/Co ratio of approximate 1:2 calcined at a temperature of 1050°C outperformed all other catalysts tested and attributed this exceptional reactivity to a combination of morphological qualities in the metal catalyst, as well as interactions between the catalyst and support. While the characterization of the catalysts is extensive and the paper appears, on the whole, to be well-written, I have several concerns about the content of the manuscript which should be addressed prior to the paper being accepted for publication. Once these have been addressed, I feel that this paper will be of general interest to the readership of Catalysts.

1)    The authors report that a carbonaceous material forms from the PAN upon calcination. This leads to the possibility that the CO₂ reduction products observed by the authors could, in part, result from hydrogenation of the carbonaceous catalyst support. A simple control experiment where a reagent stream containing no CO₂ (i.e., only H₂) is subject to the same reaction conditions must be performed to rule out this possibility, as it potentially may undermine the authors’ interpretation of the majority of their results. I feel that this experiment is absolutely necessary if the paper is to be published.

 2)    The comparison of the different catalysts with regards to their CO₂ reduction conversion is not an apples-to-apples comparison as catalysts of different Ni/Co compositions contain different amounts of total metal. The authors should present data that have been normalized for the total amount of metal in each catalyst.

 3)    In the abstract, the authors claim to have performed XRF to characterize their catalysts. However, no XRF data are present in the manuscript.

 4)    ‘AcO’ is the commonly accepted abbreviation for ‘acetate,’ rather than ‘Ac’ as used by the authors, which typically implies ‘acetyl.’

 5)    The authors’ explanation for the perceived superiority of the 1:2 Ni/Co catalyst is not entirely supported by their data. For instance, the authors invoke metal-support interactions as one possible reason, yet no data were presented in the manuscript which probed this. Furthermore, their attribution of the superior reactivity of this catalyst to the crystallinity of the carbon support is also unsatisfying, as crystalline carbon peaks could be seen in the diffractograms of all of their catalysts that have been calcined at 850°C and above. I suggest that the authors remove these speculative mechanistic claims and instead emphasize their empirical finding that 1:2 Ni/Co outperforms the other compositions, and leave the mechanism for another more detailed study.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This study systematically explored the thermal transformation of Ni/Co-PAN nanofibers, establishing a clear understanding of the role of heating temperature in the formation and conversion of PAN, Ni(Ac)₂, and Co(Ac)₂ to carbon structures and metallic nanoparticles. However, many revisions are required before final acceptance, as detailed in the following comments.

1. What is the performance of Ni: Co= 1:3, with no optimal performance in proportional control.

2. Please complete the data in Figure 3, the data that does not appear at 1300℃, and whether there is a new peak of Co after 1200 ℃.

3. It is suggested to complete the error bar in Figure 7D, and record the test temperature in Figure 7C and D clearly.

4. It is necessary to supplement the EDS characterization, explore the element distribution, and determine what elements are the nanoparticles on the nanofibers.

5. In this paper, it is necessary to clarify the total metal loading capacity of each proportion of bimetallic materials.

       6. The authors need to supplement experiments to show that the C element in the product does not come from the carbon fiber in the catalyst.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

In this research, the nanofiber catalysts, incorporating nickel and cobalt and their bimetallic blend, NiCo were prepared by electrospinning technique. The catalytic performance of these mono- and bi-metallic Ni/Co nanofiber catalysts was evaluated for CO2 hydrogenation reactions.

Some characterizations have been done, but as a work on catalysis, more relevant characterizations should be done to reveal the relationship between catalyst structure and performance.It is recommended that the author make major revisions.

 

1.More characterizations with catalytic properties should be performed. For example, some carbon nanofibers were calcined at 1050 °C.It will significantly reduce the specific surface area and increase the particle size. This would change the catalytic performance.Thus,the physisorption method should be performed to obtain the change of specific surface area.

2.HRTEM should be performed to observe the nanocrystal size, Ni-Co-C interactions, Co-Ni state.

3. Chemisorption should be performed,E.g. CO₂-sorption and H2-TPR.

4.XPS can be carried out to analysis valence of Co-Ni status.

5.Lines4-8,Page12, the author mentions that “Interestingly, among the five nanofiber catalysts preheated at 850 °C, the monometallic Ni and Co catalysts exceeded the bimetallic NiCo catalysts in CO₂ conversion, achieving 12.01% and 5.97%”. Why the monometallic Ni (Ni only) has the best performance?

English is OK.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I would like to thank the authors for providing a revised manuscript addressing some of the concerns. However, my main reservation with this paper as stated in my previous review, namely the lack of a control whereby only hydrogen was flowed over the catalyst to see if hydrogenation of the carbon support was partially responsible for the products attributed to CO2 reduction, was not resolved to my satisfaction in the authors' reply. The authors put forth the data in figure 7B in their reply, but these do not fully rule out the possibility that the supposed CO2 reduction using catalysts calcined at higher temperatures may be conflated with hydrogenation of the support as the activity/morphology of the catalysts calcined at different temperatures are different, as shown in the paper. Thus, saying that the catalyst calcined at 450 degrees did not yield appreciable CO2 reduction products is not in itself an argument against the possibility that the catalysts calcined at 850 and 1050 degrees are capable of hydrogenating the carbon support. They also claim that carbon nanofibers are innately inert, but this claim is insufficient as no one has previously attempted to hydrogenate carbon nanofibers using the same catalysts and under the conditions reported in this manuscript. Given how simple the control experiment that I proposed was (namely, repeating the CO2 hydrogenation experiment with only an H2 stream in the absence of CO2, and comparing the products from that reaction to that done in the presence of CO2), and how crucial it would be in ruling out a potential competing reaction (which if it occurs to any significant extend, would call into question all of the authors’ major claims), I cannot, in good conscience, recommend this manuscript for publication in its current form in the absence of this critical experiment. Therefore, my recommendation is for the authors to perform this simple control experiment and include the results in a subsequent revision.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

N/A

Author Response

Dear Reviewer,

We are truly grateful for your time, effort, and constructive input throughout the review process of our work for Catalysts! We genuinely appreciate your contributions in helping us improve and refine our research.

Sincerely,

Ping Lu

Reviewer 3 Report

Rowan university is a good univesity. Some necessary analytical instruments can be found possibly. I still strongly recommend using relevant characterizations to better analyze the performance of catalytic materials. These characterizations can be conducted, so that the paper would be of higher quality of data completion.

Only minor editing of English language is required.

Author Response

Dear Reviewer,

We truly appreciate your constructive feedback and the high regard you hold for our university. We agree that further analytical characterizations would contribute to a more comprehensive understanding of the performance of the catalytic materials.

Unfortunately, not all of the recommended characterizations are readily available at our university. While our institution possesses a vast array of equipment, some of the highly specialized instruments necessary for certain analyses are not within our current resources. We understand the value these could add and are exploring potential collaborations with other institutions to access such facilities for future studies.

Nevertheless, we've strived to utilize the available resources to their fullest extent to provide a thorough investigation and characterization of the catalysts. We firmly believe that the data presented, albeit not as complete as it could be with all possible analyses, are robust and support the conclusions drawn.

We appreciate your understanding, and we are committed to continuing our endeavors in improving the quality of our research. Thank you once again for your invaluable input.

Sincerely,

Ping Lu