Au-Pd Bimetallic Nanocatalysts Incorporated into Carbon Nanotubes (CNTs) for Selective Oxidation of Alkenes and Alcohol

Round 1

Reviewer 1 Report

In this article authors Hamed et al presented their research work on loading Au-Pd bimetallic catalyst onto two types of NTs. The paper is not hard to follow and the results are well presented. I have a few questions: 1. Could the authors provide BET for both samples 2. The authors are using same amount of sample 200mg for functional testing. Could the authors provide a couple of lines to show how this 200 mg can translate to amount of actual metal loading. 3. Could the authors provide a particle size distribution chart for both samples. 4. The P-NT sample has shown a very different selectivity under the two testing conditions. Under condition 2, the P-NT and O-NT selectivity are almost the same but very different under condition 1. Could the authors add a couple of lines to discuss this phenomena.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript discusses two different approaches to modifying carbon nanotubes and then applying bimetallic particles to them. This approach is quite common and interesting to use as catalysts in the decomposition of hydrocarbons.

The manuscript contains research methods such as FTIR, Raman spectroscopy, electron microscopy, and catalytic experiments. Quite interesting results were obtained. However, the reviewer believes that the manuscript should be revised and expanded.

First, the authors claim to have obtained bimetallic particles, but they did not provide evidence that the particles are bimetallic. In this case, the reviewer recommends conducting experiments on chemical mapping of elements using electron microscopy.

Secondly, the catalytic experiments are given in insufficient volume, and there is no comparison of the results with other works. Reviewer would also like to see the temperature dependence, since the conversion in the first case is observed at the level of 2 %.

The reviewer also has several questions and remarks:

1. How were the samples prepared for electron microscopy experiments?
2. It is necessary to sign the shift length for the D and G lines in Raman spectra, since it is quite difficult to consider the spectra without additional processing.
3. It is necessary to provide histograms of the particle size distribution from the TEM results.
4. Since there is no dependence of conversion and selectivity on temperature, it is necessary to estimate the measurement error and provide data on the catalytic activity for modified carbon nanotubes without an active component. In table 1 and 2, change the names of the catalysts from Au/XXX to Au-Pd/xxx.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The article with the following title "Au-Pd bimetallic nanocatalysts incorporated into carbon nanotubes (CNTs) for selective oxidation of alkene and alcohols” is not recommended for publication due to the following:

1. The work miss the novelty, beside the introduction doesn’t contain any comparison or results from literature
2. What is the importance of the products
3. One catalyst was discussed for the preparation of the catalysts. No nominations of the different prepared catalysts
4. In the catalytic tests line 120-121 was mentioned that the tests were measured under solvent free conditions, however in Tble 1 it is written TBHP was used. Also in the experimental part the conditions of the reaction is missed as temperature, concentration ,…
5. The prepared catalysts were not characterized with XRD or to measure its surface area which must be present
6. Also in the preparation two catalysts were prepared but then in the results 3 types of catalysts were characterized (Raw CNT should be mentioned as a reference catalyst in the preparation)
7. In Fig.1 what changes on immobilizing the Au on the Polymer CNTs, oxidized and raw CNT
8. The resolution of TEM and SEM pictures are not clear. The author discusses the particle size distribution but where this can be seen? In line 194 it should be Fig.4a and not 3a not Au particles in Fig.3
9. In line 216-217 Did the author tried to support Au on the raw CNT and compare it with his prepared CNT
10. No comparison of the results with literature

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thank you for providing the corrected version of the manuscript.

The reviewer has some questions.

1. The statistics provided for particle sizes are not presentable. It is necessary to significantly increase it. You also need to remove the green labels in figure 5, since the particle size is not visible or present the image in a good resolution.
2. Table 3 : It is unclear why the authors believe their catalysts are effective. If we compare the reaction with benzyl alcohol at 120 C, we can see that the catalysts based on MUNT are almost half as effective as catalyst based on CeO2. Please provide an explanation.
3. Comparison with cyclooctene reaction also does not reveal the advantages of catalysts, since in [47] the catalyst selectivity is slightly higher and other catalysts show higher activity in given table. Also in work [47], it was shown that 1% Au on graphite is more effective in this reaction. It is necessary to explain the meaning of the use of bimetallic catalysts described in this manuscript in this process.

Author Response

Response to Reviewer #2

Remark (1): The statistics provided for particle sizes are not presentable. It is necessary to significantly increase it. You also need to remove the green labels in figure 5, since the particle size is not visible or present the image in a good resolution.

Response: We thank the reviewer for providing assistance. The histograms of the particle size distribution from the TEM results was provided based on Guassian statistical of the nanoparticles presented in the TEM image. The green labels in Figure 5 are omitted in the revised version.

Remark (2): Table 3 : It is unclear why the authors believe their catalysts are effective. If we compare the reaction with benzyl alcohol at 120 C, we can see that the catalysts based on MUNT are almost half as effective as catalyst based on CeO₂. Please provide an explanation.

Response: Thank you for your careful reviewing. We agree with the reviewer at this point. The noble metals, as compared to transition metal oxides,are active at lower temperatures. However, if not properly supported they may easily sinter and deactivated. By playing with several parameters, such as method of synthesis, particle sizes, and support morphology, it is possible to improve their catalytic performance.So that, the aims of our work to study the effect of functionalize CNTs on the dispersion of metallic and bimetallic nanoparticles and their effect on the catalytic performance and compared our catalyst with cerium (IV) oxide with high oxygen mobility which is particularly appropriate as a support for catalysts used in oxidation reactions. Besides, our catalyst is still give high selectivity for benazaldye and we still contionous work to improve the yield.

Remark (3): Comparison with cyclooctene reaction also does not reveal the advantages of catalysts, since in [47] the catalyst selectivity is slightly higher and other catalysts show higher activity in given table. Also in work [47], it was shown that 1% Au on graphite is more effective in this reaction. It is necessary to explain the meaning of the use of bimetallic catalysts described in this manuscript in this process.

Response: We thank the reviewer for this very important comment.Bimetallic are a class of important heterogeneous catalysts as they frequently exhibit much enhanced catalytic stabilities, activities and selectivities, as compared with their single-metal constituents. The Ponec and Bond definition of bimetallic alloy is the following: alloy is most conveniently defined as a metallic system containing two or more components, irrespective of their intimacy of mixing or, precise manner of mixing. Bimetallic induces multiple changes in the physical and chemical properties of the metallic components. Where catalytic properties are concerned, two alloy effects are significant: (1) ensemble effects, i.e., a finite number of atoms in a particular geometric orientation that are required for facilitating a particular catalytic process; and (2) ligand effects, i.e., electronic modifications resulting from hetero-nuclear metal– metal bond formation. The latter could involve charge transfer between the metals or orbital rehybridization of one or both metallic components.

Regarding 1% Au on graphite, as mentioned in Table 3, the reaction time was 24 hours, which is high compared to 6 hours of our catalyst.

Response to the academic editor's comments:

Remark (1): line 208, the word "images" is repeated in the sentence.

Response: The repeated word “images” in the sentence is deleted in the revised version.

Remark (2): in the comments concerning Table 3, I would slightly modify the sentence on
line 268. Indeed, the catalysts prepared in the manuscript do not seem to be
the more active (Au-Pd/CeO₂ seems more active for the cyclooctene oxidation
and Cu3(BTC)₂ seems more active for the benzyl alcohol oxidation). So I would
change "showed the highest activity" to "showed the highest
activity/selectivity combination".

Response: The sentence “showed the highest activity" is changed to "showed the highest
activity/selectivity combination based on the editor’s suggestion.