Deactivation and Regeneration of Palladium Catalysts for Hydrogenation Debenzylation of 2,4,6,8,10,12-Hexabenzyl-2,4,6,8,10,12-Hexaazaisowurtzitane (HBIW)
Round 1
Reviewer 1 Report
The search of the way of the regeneration of Pd/C catalysts in mentioned reactions is a very interesting and important challenge for the researchers. It is really interesting to read the manuscript devoted to this problem.
There are some comments:
1. The chemical state of the Pd has to be discussed in more detail. XRD is not enough.
The evolution of the chemical state of Pd during reaction is important for the understanding of the deactivation processes. The deactivation mechanism proposed in the present manuscript looks not enough to drop the activity to zero.
Please, find the paper Troitskii S.Y., Nartova A.V., Moroz E.M., Low-Temperature Carbonization of the active centers is the reason of Pd/C catalysts deactivation // J. of Structural chemistry, 2021. V. 62. # 1. P. 163-170. DOI 10.1134/S0022476621010194
Perhaps, it can help.
2. Section 1.3 Recovering methods 4 methods described, but only 3 are mentioned in Table 1.
Minor comment:
Please, add the labels of the compounds on scheme 1.
Manuscript can be published after minor revision.
Author Response
Q1
Response:We are grateful for the suggestion. We agree that they are critical to the explanation of the deactivation mechanism. Therefore, we added the XPS diagram of Pd3d. According to our characterization results, the main reason for catalyst deactivation is that the active site of the catalyst is covered, rather than carbon deposition. Our regenerative method can effectively remove the blockage and recover the activity of the catalyst.
Q2
Response:Thank you for your advise.We have completed the catalyst regeneration method in Table 1 and the tag to Scheme 1.
Reviewer 2 Report
Reviewer Comments：
The deactivation of Pd(OH)2/C catalyst for the hydrodebenzylation reaction of HBIW is a tough problem. This manuscript discussed several methods to treat the used Pd(OH)2/C or Pd/C catalyst and found that the treatment using the mixture of chloroform and glacial acetic acid was an effective method. The regenerated catalyst can be reused four times with comparable yields. The results are interesting, and the topic also falls well into the scope of Catalysts. However, the following issues still need to be revised.
(1) The manuscript described that the regenerated Pd/C or Pd(OH)2/C catalysts maintained high activity and the yields in second recycle were similar to the data of fresh catalysts. The evaluation of catalyst activity and stability should also be revealed by kinetic (time-resolved) studies, and not only by isolated yields obtained by repeated runs (Fig . 3).
(2) In table 2, entry 8 and 9, the TADBIW yields were 76.29% and 67.84%, respectively, under the same regeneration treatment method, chloroform and glacial acetic acid mixture treatment. It is puzzled.
(3) For the 5wt.% Pd/C catalyst, the average particle size of spent one, 3.55 nm, was large than the fresh catalyst (2.74 nm). It was also one reason leading to the deactivation. The author should discuss it in the manuscript.
(4) In the experimental part, for 5g substrate (HBIW), 0.5g 5wt.% Pd(OH)2/C or 5wt.% Pd/C catalyst was used. However, in page 4 under Figure 3, for 5 g HBIW, 0.25 g regenerated catalyst was used. Why?
(5) The effects of Pd consumption in the HBIW hydrodebenzylation reaction on the product yield should be investigated.
(6) Reference 3 and 5 was the same one.
Author Response
Q3
Q1
Response:We think this is an excellent suggestion, we have added the suggested content to the manuscript, it includes the hydrogen consumption curve of both new and regenerated catalysts .
Q2
Response :We are really sorry for our incorrect writing. Thank you for your reminder, we have changed it to “77.84%” in the revision and marked it with red revision.
Q3
Response:Thanks for your comment.we have added the suggested content to the manuscript.For 5wt% Pd/C catalyst, particle size is also one of the reasons for catalyst deactivation.
Q4
Response:We are really sorry for our incorrect writing. Thank you for your reminder, we have changed it to “0.5g” in the revision and marked it with red revision.
Q5
Response :We think this is an excellent suggestion, we have added the suggested content to the manuscript, it includes the effect of Pd consumption on product yield .
Q6
Response:Thanks for your suggestion. Duplicate references have been corrected to the manuscript.
