Heterogeneous Gold Catalysis: From Discovery to Applications
Round 1
Reviewer 1 Report
The tittle of this short review article is general but its content focuses on the methods of preparation of Au nanoparticles and on a few specific aerobic oxidation applications such as the transformation of alcohols to aldehydes or cyclohexane to adipic acid. At least some general other applications must be mentioned very briefly in the introductory text, such as the recent developments in addition reactions to pi systems, a rather unexpected outcome given that such reactions are catalyzed by the non-isoelectronic to Au(0), Pd(0) or Pt(0), in the alkynophilicity of Au(0) nanoparticles, also unexpected given that ionic gold compounds of Au(I) or Au(III) are strongly alkynophilic, and its consequences in organic transformations, in the reductive applications (hydrogenation or transfer hydrogenation), etc. Some recent important articles or review articles would suffice to give to the reader the wide applications of Au nanoparticles in catalysis, beyond aerobic oxidative processes.
Author Response
Reply to the comments of Reviewer 1:
- The tittle of this short review article is general but its content focuses on the methods of preparation of Au nanoparticles and on a few specific aerobic oxidation applications such as the transformation of alcohols to aldehydes or cyclohexane to adipic acid. At least some general other applications must be mentioned very briefly in the introductory text, such as the recent developments in addition reactions to pi systems, a rather unexpected outcome given that such reactions are catalyzed by the non-isoelectronic to Au(0), Pd(0) or Pt(0), in the alkynophilicity of Au(0) nanoparticles, also unexpected given that ionic gold compounds of Au(I) or Au(III) are strongly alkynophilic, and its consequences in organic transformations, in the reductive applications (hydrogenation or transfer hydrogenation), etc. Some recent important articles or review articles would suffice to give to the reader the wide applications of Au nanoparticles in catalysis, beyond aerobic oxidative processes.
Response: We thank the reviewer for his valuable comments to improve the quality of the reviewer. Regarding the reviewer first comment, some new application of Au catalyst is now included in the introduction part (L43-L48).
Regarding the second point, the effect of the ionic gold compounds of Au(I) or Au(III) has been extensively extended in the effect of gold oxidation state. The new discussion was explored the important of different oxidation state of AU and linked them to its catalytic activity. New lines L316-L343 have been included in the revised version. In addition, some new reference were also included in appropriate place.
Reviewer 2 Report
The paper of Alshammari is a comprehensive review with an emphasis on 2 oxidation reactions, i.e. benzyl acohol oxidation and that of cyclohexane. I would recommend publication of this manuscript in Catalysts after the following points have been taken into account:
- There are some typos throughout the ms, for example: L24: “mportant years” should read “important year”; L220: “demonstrated” should read “demonstrated”; L366: “re-cycling” should read “recycling”; L394: “ues” should read “use”. Please check carefully.
- L377: “AA” needs to be defined
- It is said on L295 that “The applications of gold catalysts in the oxidation of alcohols, amines and cyclohexane are discussed in the present section” however no amine oxidation is discussed in this section.
- In the « Effect of Gold-support interaction » paragraph (L211) some examples on the use of carbon nanotubes as support are missing. The latter are however key supports in gold-mediated catalysis.
Author Response
Reply to the comments of Reviewer 2:
- The paper of Alshammari is a comprehensive review with an emphasis on 2 oxidation reactions, i.e. benzyl acohol oxidation and that of cyclohexane. I would recommend publication of this manuscript in Catalysts after the following points have been taken into account:
Response: We thank the reviewer for highlighting the importance of our work and I am thankful to the reviewer for recommending this work to be accepted in Catalysts J. after
answering all of his concerns.
- There are some typos throughout the ms, for example: L24: “mportant years” should read “important year”; L220: “demonstrated” should read “demonstrated”; L366: “re-cycling” should read “recycling”; L394: “ues” should read “use”. Please check carefully.
Response: The revised manuscript has undergone to heavy English editing and corrected all typos raised by the reviewer.
- L377: “AA” needs to be defined
Response: It has been defined as adipic acid (AA) in the revised manuscript.
- It is said on L295 that “The applications of gold catalysts in the oxidation of alcohols, amines and cyclohexane are discussed in the present section” however no amine oxidation is discussed in this section.
Response: Thanks to the reviewer for his accurate observation and word, "amine oxidation" is deleted in the revised manuscript.
- In the « Effect of Gold-support interaction » paragraph (L211) some examples on the use of carbon nanotubes as support are missing. The latter are however key supports in gold-mediated catalysis.
Response: I thank the reviewer for his valuable comments. The use of carbon nanotubes as support is now included in the revised manuscript and highlighted in yellow background (L305-L314).
Reviewer 3 Report
In my opinion, in this review the author would like to find trends and frequent properties of gold nanoparticles, but in many cases this aim takes to an oversimplification and generalization of the problems and of the properties, so that the conclusions are not completely correct. For example, the discussion on the “factors affecting the activity of Au catalyst” is too general and specific examples should be cited. This is fundamental when discussing the nature of the support, which can be a co-catalyst or have an active role in the catalytic reaction. As stated above, a discussion of this type on the role of the support in ca. 20 lines is an oversimplification of the possible variables. This is only an example, but many other can be discussed; for example in the description of the methods for the synthesis of Au NPs, the role of possible stabilizers has not been discussed. In the “effect of gold particle size and shape”, no comments are present for the shape of the Au NPs.
In the section 5.2, ca. 40 lines have been dedicated to the discussion of the industrial or laboratory process for the production of adipic acid, but only 20 to the discussion of the gold catalysis. The author does not justify why he chose this specific reaction, in the frame of the several organic transformations catalyzed by Au NPs. The same considerations can be extended to the oxidation of alcohols (benzylic alcohol?) to benzaldehyde.
Another problem with this manuscript arises from the literature citations: in the first paragraph of the instruction (as well as in the fourth one), the results of several groups are cited without the proper citation (no references present). Bond, Sermon, Haruta, Hutchings, Prati (not Pratti) and Rossi are cited, withour reference to their original manuscripts.
Finally, the title is misleading: the review deals only with heterogeneous gold catalysis, but there is an increasing interest also in homogeneous gold catalysts. For this reason I suggest to change the title in "Heterogenous Gold Catalysis:...".
I did a bibliographic research on the topic of this review and in my opinion some references are missing, like for example:
ACS Cent. Sci. 2018, 4, 1095
Acc. Chem. Res. 2014, 47, 729
Chem Soc Rev 2008, 37, 2096
J Phys Chem C 2018, 122, 7749
Chem Rev 2012, 112, 4469
These are only some examples. For this reason, I would suggest a careful check
of the literature; please cite them in your manuscript if you think they would be useful.
As a whole, I do not believe that this manuscript is suitable for publication in the present form and needs to be extended and revised.
Author Response
Reply to the comments of Reviewer 3:
- In my opinion, in this review the author would like to find trends and frequent properties of gold nanoparticles, but in many cases this aim takes to an oversimplification and generalization of the problems and of the properties, so that the conclusions are not completely correct. For example, the discussion on the “factors affecting the activity of Au catalyst” is too general and specific examples should be cited. This is fundamental when discussing the nature of the support, which can be a co-catalyst or have an active role in the catalytic reaction. As stated above, a discussion of this type on the role of the support in ca. 20 lines is an oversimplification of the possible variables. This is only an example, but many other can be discussed; for example in the description of the methods for the synthesis of Au NPs, the role of possible stabilizers has not been discussed. In the “effect of gold particle size and shape”, no comments are present for the shape of the Au NPs.
Response: Thanks to the reviewer for his valuable comments and hope to convince him and cover all of his points one-by-one as follows:
For example, the discussion on the “factors affecting the activity of Au catalyst” is too general and specific examples should be cited. This is fundamental when discussing the nature of the support, which can be a co-catalyst or have an active role in the catalytic reaction. As stated above, a discussion of this type on the role of the support in ca. 20 lines is an oversimplification of the possible variables".
Answer: Now, this section has revised and new specific examples were included to strengthen the manuscript. These changes are between L235-L39 and L257-270.
for example in the description of the methods for the synthesis of Au NPs, the role of possible stabilizers has not been discussed.
Answer: The role of stabilizers has been discussed and included in new section i.e. L148-L164.
In the “effect of gold particle size and shape”, no comments are present for the shape of the Au NPs.
Answer: Agreed and apologized about missing the influence of the shape of gold particles on the catalytic activity. Now, the effect of this was extensively included in L157-L192 and L201-209.
- In the section 5.2, ca. 40 lines have been dedicated to the discussion of the industrial or laboratory process for the production of adipic acid, but only 20 to the discussion of the gold catalysis. The author does not justify why he chose this specific reaction, in the frame of the several organic transformations catalyzed by Au NPs. The same considerations can be extended to the oxidation of alcohols (benzylic alcohol?) to benzaldehyde.
Response: Yes, this is right observation. However, I would like to bring the reviewer attention that KA-oil were the main products of most published work in this process and the adipic acid was relatively in minor proportions. Therefore, there are limited number of references about the direct oxidation of CH to AA using heterogeneous gold catalyst. However, the discussion about the use of gold catalyst to produce AA has been extended in the revised manuscript.
Regarding the second point, the oxidation of cyclohexane and alcohols has been selected in the present review for two reasons. The first reason is that both processes (i.e. oxidation of alcohols and cyclohexane) are very important as they are starting materials for a variety of ketones, aldehydes, acids, etc. which requires to produce plastics, detergents, paints, cosmetics, food additives, drug tec. In addition, the application of gold catalyst in both processes is tremendously high as evident by the high member of the published papers. Therefore, the aim of the present review is to summarize the development in both processes. Besides addressing the basic issues and recent development of both applications, the second reason for selecting those reaction is to highlighted our previously published work, where different parameters were extensively studied for both reactions. Such work was also citied at appropriate place.
-Another problem with this manuscript arises from the literature citations: in the first paragraph of the instruction (as well as in the fourth one), the results of several groups are cited without the proper citation (no references present). Bond, Sermon, Haruta, Hutchings, Prati (not Pratti) and Rossi are cited, withour reference to their original manuscripts.
Response: Completly agreed about this point. The revasied manuscript has included the missing citations.
-Finally, the title is misleading: the review deals only with heterogeneous gold catalysis, but there is an increasing interest also in homogeneous gold catalysts. For this reason I suggest to change the title in "Heterogenous Gold Catalysis:...".
Response: Agreed with the reviewer about this point. The title of the revised manuscript has changed to "Heterogeneous Gold Catalysis: From Discovery to Applications".
-I did a bibliographic research on the topic of this review and in my opinion some references are missing, like for example:
ACS Cent. Sci. 2018, 4, 1095
Acc. Chem. Res. 2014, 47, 729
Chem Soc Rev 2008, 37, 2096
J Phys Chem C 2018, 122, 7749
Chem Rev 2012, 112, 4469
-These are only some examples. For this reason, I would suggest a careful check of the literature; please cite them in your manuscript if you think they would be useful.
Response: Thanks to the reviewer for his suggestion to include some important papers, which help to strength the present review. All references were included in the appropriate place.
-As a whole, I do not believe that this manuscript is suitable for publication in the present form and needs to be extended and revised.
Response: Based on the reviewer`s above comments, the revised manuscript has been significantly extended and improved so that it meets all reviewers` comments. Therefore, it would be great to accept it after modification.
Round 2
Reviewer 3 Report
The authors have addressed the suggestions and comments made by the referees. In my opinion the manuscript can be accepted in the present form.
