Advanced High-Loaded Ni–Cu Catalysts in Transfer Hydrogenation of Anisole: Unexpected Effect of Cu Addition
Round 1
Reviewer 1 Report
Review Catalysts-1983606
The manuscript reports the preparation of binary heterogeneous metal catalyst Cu-Ni. The efficacy of Cu-Ni complex in the transfer hydrogenation reaction was discussed. The kinetics of transfer hydrogenation reaction of anisole was analysed. The manuscript can be of interest for researchers working in the heterogeneous catalysis field, particularly those who works in binary metal catalyst. The following queries need to be addressed by the author before the manuscript can be published in Catalysts:
1. Editorial: To move materials & method to Section 2 for easy reading
2. Editorial: To spell out EtOH, 2-PrOH, Cu(OAc)2, etc first before using the acronym repeatedly in the manuscript.
3. Suggest including graphics to illustrate the preparation method – for easy reference.
4. Why there is a different in temperature for the reduction of Cu- and Cu-free catalyst?
5. Editorial: Please check all the chemical names. Names such as H2, SiO2 without the subscript still can be seen throughout the document.
6. Need to explain why the anisole conversion reaction was modelled after first order kinetics.
7. Why the presence of Cu for Cu-containing catalyst cannot be detected by XRD? What is the broad peak at 22-23°? Suggest combining the 3 graphs into 1 figure for easy reference.
8. Kindly provide the TEM images for sample B and C.
9. In my opinion, same amount of catalysts should be used for the conversion of anisole at different temperatures.
10. For data presented in Table 1, 2, 3, 4, and 5 kindly provide the standard deviations.
11. How does the results obtained in this work are in comparison with other recently published data of similar study?
Author Response
Reviewer #1.
We would like to thank the Reviewer for the work and time in reviewing this manuscript. We are very grateful for the Reviewer’s excellent suggestions, and we firmly believe that they make our work better. The significant changes and correction according to the reviewers’ suggestions has been made.
- Editorial: To move materials & method to Section 2 for easy reading
We agree that the materials and methods section is more typical in the second place. At the same time, the template of Catalysts as well as Editorial office recommends placing this section in the third place.
- Editorial: To spell out EtOH, 2-PrOH, Cu(OAc)2, etc first before using the acronym repeatedly in the manuscript.
The spelling out was added in the text (marked in yellow).
- Suggest including graphics to illustrate the preparation method – for easy reference.
The picture demonstrating the catalyst preparation procedure has been added to the text (see Figure 9 in the revised manuscript).
- Why there is a different in temperature for the reduction of Cu- and Cu-free catalyst?
According to the literature data (for example, references 12 and 13 in the text) copper has the lower reduction temperature compared to nickel that decreases the reduction temperature of the Ni-Cu system. Moreover, in our study, completeness of reduction was controlled by XRD and it was demonstrated that 400 °C is enough for the Cu-containing samples.
- Editorial: Please check all the chemical names. Names such as H2, SiO2 without the subscript still can be seen throughout the document.
The names have been checked.
- Need to explain why the anisole conversion reaction was modelled after first order kinetics.
To be more accurate the anisole transformations were considered as the quasi-first order kinetics because the concentration of 2-PrOH is much higher. Our suggestion is based on three facts: 1) literature data [J.S.M. Samec et al. Chem. Soc. Rev. 2006, 35, 237–248, doi:10.1039/b515269k, M.J. Gilkey et al. ACS Catal. 2015, 5, 3988–3994, doi:10.1021/acscatal.5b00586] show that the mechanism of transfer hydrogenation includes adsorption of the substrate on the catalyst surface and its further reduction. Taking this into account, the process should be considered as the quasi-first order kinetics. 2) The quasi-first order kinetics describes the anisole conversion over Ni(36)-SiO2 very well, and we suggest that the Cu addition does not change the mechanism so much as to change the kinetic model. 3) The conversion of anisole over the Cu-containing catalysts cannot be described well enough using any kinetic model if the influence of acetone is not taken into account.
- Why the presence of Cu for Cu-containing catalyst cannot be detected by XRD? What is the broad peak at 22-23°? Suggest combining the 3 graphs into 1 figure for easy reference.
The presence of Cu cannot be detected by XRD because it does not form the separated phases. Instead the formation of the solid solution, which has the structure of Ni, is observed. That is why the lattice parameter increases for the Cu-containing samples.
The broadened peak at 22-23° relates to silica. Amorphous silica is typically manifested in XRD profiles measured with use of the copper radiation as diffuse peak over wide angular range from 10° to 30° [R.K. Biswas et al. Journal of Non-Crystalline Solids. 488, (2018), 1-9, doi:10.1016/j.jnoncrysol.2018.02.037; L. Khouchaf Materials. 13, (2020), 4393, doi:10.3390/ma13194393; J.R.Martínez. Materials Letters. 60, (2006), 3526-3529, doi: 10.1016/j.matlet.2006.03.044].
The graphs in Figure 2 were combined according the reviewer’s suggestion.
- Kindly provide the TEM images for sample B and C.
The TEM images of B and C samples (Figure 3) have been provided.
- In my opinion, same amount of catalysts should be used for the conversion of anisole at different temperatures.
We started from the same idea and used 0.36-0.37 g of the reduced catalysts at 250 °C. The conversion of anisole over Ni(36)-SiO2 exceeded 50% when the goal temperature was reached and 100% after 1 h, so, no kinetic data can be obtained. Similar results are presented in our recent work [A.A. Philippov et al. Appl. Catal. A Gen. 2022, 643, 118792, doi:10.1016/j.apcata.2022.118792]. The similar observations were demonstrated when 0.11 g of the catalysts were used at 150 °C because the anisole conversion over Ni(41)Cu(4)-SiO2 is slightly higher than 5% after 5 h. It is also important to notice that the specific catalytic activity calculated in this study takes into account the mass of the catalysts, so, these values can be compared at both temperatures.
- For data presented in Table 1, 2, 3, 4, and 5 kindly provide the standard deviations.
The standard deviations have been provided. Also, some values in the tables have been checked and changed.
- How does the results obtained in this work are in comparison with other recently published data of similar study?
Unfortunately, we failed to find any information about using Ni-Cu catalysts in anisole transfer hydrogenation, although one study considers H2 hydrogenation of anisole over the very similar catalysts [N.S. Nesterov et al. Catal. Today 2021, 379, 262–271, doi:10.1016/j.cattod.2020.09.006] at 320 °C. The key feature of this study is the acetone influence which is obviously not relevant for conventional hydrogenation. Also, there are several studies describing transformations of furfural and its derivatives in TH over Ni-Cu, we discuss them in the Introduction section. In contrast to anisole, furfural demonstrates significantly higher reactivity due to the presence of carbonyl group, so, in our opinion, it cannot be accurately compared with anisole transformations. Thus, it is difficult to understand the parameters by which our work can be compared with others.
Reviewer 2 Report
1) Should mention “Cu” diffraction peaks in XRD data and figure.
2) Page 4, line 108, “with a diameter not exceeding several nanometers” should be provided several nanometer scale values.
3) How did the authors measure the particle size of about 6.5 nm?
4) Should provide GC-MS data for successful transfer hydrogenation of anisole.
Author Response
Reviewer #2.
We would like to thank the Reviewer for the work and time in reviewing this manuscript. We are very grateful for the Reviewer’s excellent suggestions, and we firmly believe that they make our work better. The significant changes and correction according to the reviewers’ suggestions has been made.
- Should mention “Cu” diffraction peaks in XRD data and figure.
Cu does not form the separated phases, therefore, we cannot mention them in XRD data. Ni and Cu form one phase, which has the structure of Ni0 visible by XRD. The lattice parameter of the formed Ni0 is increased (see Table 1) that shows the presence of Cu in the joint lattice. The discussion of the mentioned facts is provided in details in the first paragraph on page 3.
- Page 4, line 108, “with a diameter not exceeding several nanometers” should be provided several nanometer scale values.
Figure 3 has been changed and the TEM microphotographs demonstrating the nanosized metal crystallites have been added.
- How did the authors measure the particle size of about 6.5 nm?
To be more accurate 6.5 nm is the mean crystallite size which was measured by XRD.
- Should provide GC-MS data for successful transfer hydrogenation of anisole.
The examples of the GC-MS data have been added in Supplementary materials.
Reviewer 3 Report
"unexpected effect of Cu addition" in the abstract means that there is no report for copper catalysts in the literature.
Selectivity is very important I didn't see any discussion about selectivity within the text.
Authors should compare their catalyst with the literature.
Please characterize the catalysts after their utilization in the reactions.
The recyclability of the catalyst should be checked several times.
Please provide a table for a comparison of this method with previously reported articles.
Author Response
Reviewer #3.
We would like to thank the Reviewer for the work and time in reviewing this manuscript. We are very grateful for the Reviewer’s excellent suggestions, and we firmly believe that they make our work better. The significant changes and correction according to the reviewers’ suggestions has been made.
- "unexpected effect of Cu addition" in the abstract means that there is no report for copper catalysts in the literature.
We did not mean there are no reports for copper catalysts in the literature. In the most literature reports Cu was demonstrated to facilitate catalytic properties, in particular, it can increase the rate of hydrodeoxygenation (references 8, 22 in the text). For example, in H2 hydrogenation of anisole the Ni-Cu catalysts prepared via supercritical antisolvent precipitation show the higher activity compared to Cu-free samples in hydrodeoxygenation [N.S. Nesterov et al. Catal. Today 2021, 379, 262–271, doi:10.1016/j.cattod.2020.09.006]. In our study the Cu addition demonstrates the opposite effect decreasing the yield of cyclohexane and cyclohexanol that was quite unexpected. At the same time, we demonstrated that this effect relates to the acetone influence.
- Selectivity is very important I didn't see any discussion about selectivity within the text.
The more specific information about the yield of each product have been added to the text.
- Authors should compare their catalyst with the literature.
It is important to notice that the number of the reports describing the Ni-Cu catalysts prepared via supercrititical antisolvent precipitation is very limited. However, the new paragraph has been added in the end of subchapter 2.1.
- Please characterize the catalysts after their utilization in the reactions.
The spent catalysts were characterized and the information is given in Supplementary materials (see Table S1 and Figure S1).
- The recyclability of the catalyst should be checked several times.
We agree that stability of the catalysts is one of the most important parameter. At the same time, in this study, the deactivation of the catalysts is obvious, so, we do not think that this process should be demonstrated one more time. Also, we would like to emphasize that in our study the anisole-to-nickel mole ratio was about 1/40 which is low enough for heterogeneous catalysts.
- Please provide a table for a comparison of this method with previously reported articles.
In our opinion, it is not completely clear what parameters should be compared. There are many studies describing conventional hydrogenation of the phenolic compounds over Ni-Cu catalysts. At the same time, the key feature of our work is the acetone influence, which is relevant only for transfer hydrogenation. Also, we failed to find any literature information about TH of anisole over Ni-Cu catalysts. Comparison with other substances such as furfural and its derivatives does not seem to be a revealing information due to the high reactivity of carbonyl compounds.
Round 2
Reviewer 1 Report
Thanks for the editing the manuscript. I trust the current version of manuscript warrant a publication in Catalysts.
Reviewer 3 Report
The article can be accepted in this form.
