Catalytic Hydrogenation of Nitrocyclohexane with CuCo/SiO2 Catalysts in Gas and Liquid Flow Reactors
Round 1
Reviewer 1 Report
The present manuscript reports the preparation of monometallic and bimetallic catalysts consisting of Cu and Co, and the catalyts evaluation in the hydrogenation of nitrocyclohexane in gas and liquid flow reactors. The authors observed that Cu/SiO2 catalyst gives high cyclohexanone selectivity and Co/SiO2 steers into the production of cyclohexylamine. Bimetallic catalysts are more active than Cu/SiO2 and less active than Co/SiO2, shows high cyclohexylamine selectivity, which similar to Cu based catalysts.
However, the synergistic interaction between Cu and Co is not clear, and the reaction mechanism has not been well discussed. The purpose of the experiment design is not clear. Therefore, I cannot recommend the manuscript to be published in Catalysts. The specific questions and comments are listed as follows:
1. The current characterizations of the CuCo/SiO2 do not give sufficient information to understand the structure and composition of the bimetallic NPs. The authors are request to conduct p-XRD and/or XPS to determine the chemical state of Cu and Co and their synergistic interaction.
2. TEM images corresponding to the mapping image should be include in the revised manuscript. And the lattice spacing of CuCo NPs using HR-TEM is suggested to be added.
3. Have the authors characterized the monometallic Cu or Co/SiO2 by TEM?
4. Have the authors calculated the carbon balance of the hydrogenation reaction? And were any other by-products detected? It is very likely that dicyclohexylamine, cyclohexyl-cyclohexylidene amine and cyclohexanol could be produced when the amine and ketone compounds were coexisted.
5. The authors claimed that cyclohexanone oxime was the raw material to produce cyclohexylamine and cyclohexanol (scheme 1). However, cyclohexylamine could also be produced through consecutive hydrogenation, with cyclohexylhydroxylamine as the intermediate. Have the authors considered this reaction pathway?
6. Compared to the monometallic catalysts, the alloying functions of bimetallic catalysts on catalytic performance should be discussed in the main text. To this end, the detailed characterization of CuCo/SiO2 and more control experiments are recommended.
7. It seems like the authors just test three different catalysts in the hydrogenation of nitrocyclohexane. What is the purpose to design the bimetallic CuCo catalyst? To modulate the electronic or geometric properties of the first metal? Or to get higher cyclohexylamine selectivity? I would like to suggest authors to clarify the main topic of the manuscript.
Author Response
Please see the attachement.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Main question addressed by the research: The work addresses catalytic hydrogenation of nitrocyclohexane with CuCo/SiO2 catalysts in G-L flow reactors.
Originality and relevance of the topic: The topic is relevant to the field and it considers a suitable research gap.
Added value of the paper: The manuscript takes into account the study of this gas-liquid catalytic flow reactor, however the main purpose of it is not clearly stated. The paper should include what aspects are critical for these assessments and clearly explain why they are analysing those and why they are needed at the end of the Introduction.
Quality of figures: Formatting is very good, but how to read the results is unclear. It should be specified, particularly from Figures 5 to 11.
Abstract is too short and it should summarize the main findings from the paper.
The conclusions are poor and they would need more elaboration so they clearly match the results.
Author Response
Please see the attachement.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thanks, this revision is good.
