Catalytic Acetone Oxidation over MnO_x Catalysts: Regulating Their Crystal Structures and Surface Properties

Round 1

Reviewer 1 Report

The authors present the characterization of and catalytic properties of MnO2 samples with different crystal structures, obtained by two different methodologies and the effect of calcination environment on the final structures.

The manuscript is well presented and ordered, with vast use of characterization techniques.

I recommend the publication if the authors address the following comments.

1) Perhaps the "roasting" is not the appropriate term to describe the calcination process.

2) Figures 3f and 3g are very low quality. The Figure must be highly improved in resolution. In figure 3f, additional to PDF numbers, it must be indicated the corresponding phase and labeling of the main peaks (indexing) is desirable. I recommend to redistribute the reference patterns to match with the order of the samples (i.e. alpha to gamma phase from the upper to the bottom part).

The XRD pattern of MnO2-WN sample shows differs from the MnO2-WK sample, and small extra peaks are observed. The authors should discuss about these differences. Does the improved intensity could be related to a mixture of crystal phases for this sample? It looks that calcination environment had an impact on their structures.

Also, can the difference in peak intensities provide some information on the crystallographic texture or particles shape?

Crystallite size from XRD should be added to table 2 to complement the information, since the diffraction peaks are quite different from each other.

3) SEM figures should be improved. From these images, cauliflower-like and skeletal morphology are quite vague descriptions. Did the authors considered the sheet-like morphology of the particles produced by the microwave method? It could also explain the surface area increase and XRD data.

4) Figures 4 and 5, resolution must be highly improved. Labels fonts should be increased.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In this manuscript, the authors reported how regulating the crystal structures and surface properties of MnOx catalysts could lead to enhanced catalytic performance toward the acetone oxidation. Various types of MnOx catalysts were synthesized using hydrothermal methods and their properties were tuned by altering the synthesis parameters. Notably, α-MnO2, calcined in an N2 atmosphere via the microwave hydrothermal method (MnO2-WN), exhibited the best catalytic performance. The reaction mechanisms were also studied by in situ characterizations. Overall, this work has good novelty and the results are likely to appeal to the readership of the journal Processes. However, the below detailed comments need to be addressed before possible publication.

1. The Introduction was generally well structured and presented. However, the last paragraph of the Introduction could use some revision to further highlight the key novelty and main findings of the present work.

2. Recent works on alcohol oxidation can be included in the Introduction (e.g., Appl. Catal. B 2023, 325, 122388).

3. Figure 3a-e, for the nitrogen adsorption/desorption isotherms, it is suggested that the authors use different labelling to distinguish the adsorption branch and the desorption branch.

4. In the discussion of EPR data (Fig. 6a), related works can be referenced (e.g., ACS Sustainable Chem. Eng. 2022, 10, 1899).

5. The authors identified oxygen vacancies in the EPR data, then why such vacancy oxygen species were not identified in the XPS data? Currently the XPS data only identified adsorbed oxygen species (Oads) and lattice oxygen species (Olatt).

6. Figure 3f and 3g, the visibility needs to be enhanced. The same applies for Figure 4.

7. Figure 4 caption, the “MnO2-WN-S” sample should also be included in the caption.

8. Table 4, what is the unit for the peak area listed in the table?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed the suggested comments. I recommend publication of the manuscript.