Peer review of: Entropy-stabilized single-atom Pd catalysts via high-entropy fluorite oxide supports (2020)


RR2
REVIEWERS' COMMENTS:
Reviewer #1 (Remarks to the Author):
I have read through the revised manuscript and “response to reviewers”. The authors have done many experiments according to the comments of the reviewers and some new data have been put into the revised manuscript and the support information. Most concerns have been addressed.Although many papers have been published for the SACs, fabricating SACs with thermodynamic stability on high-entropy supports by using a solvent-free synthetic strategy is very interesting. Therefore, I am happy to recommend this paper for publication in Nature Communications. Only several minor points should be considered before the publication:
Please check the procedure of CO adsorption ( Page 19, line 365-372).
Please double check the related data in the revised manuscript and the data in the “response to reviewer”:
CO (11.10 μmol/pluse);
Adsorption amount 0.0644 μmol CO/ μmol Pd for Pd1@HEFO;
14.77 μL g-1 of CO adsorbed on Pd1@HEFO sample
Page 5, line 101-102:
“EDS-mapping results shows the highly homogeneous dispersion of......”
Should be “EDS-mapping results show the highly homogeneous dispersion of......”?
Page 7, Line 122-123:
In the revised manuscript, authors have confirmed that only a small amount of Pd atoms are exposed (6%), but they still claimed that “...suggests that a small portion of Pd may be incorporated into HEFO sublattice for the formation of PdyCeZrHfTiLaOx solid solution”. It should be changed to “a large portion” instead of “a small portion”.
Page 8, line 175-176:
“Fig. 3 (a) HAADF-STEM image of Pd1@HEFO and corresponding EDS mapping of (b) Pd.”
Should be “Fig. 3 (a) HAADF-STEM image of Pd1@HEFO and (b) corresponding EDS mapping of Pd.”?
Page 15, line 277-278:
“A catalyst loading of 20 mg, 1 vol.% and CO balance in air”
Should be“A catalyst loading of 20 mg, and 1 vol.% CO balance in air”?
Two new references about solvent-free synthesis of SACs should be included in the revised manuscript. (Nature Communications 11, 1263 (2020); Cell Report Phys. Sci. 1, 10004 (2020).)

Reviewer #2 (Remarks to the Author):
The experimental work that the authors have conducted is certainly impressive. All the technical points have been addressed. The work merits publication, but it would require a minor revision in order to communicate better the key points.
This is because the previous comments regarding:
i) “placing the work in perspective with respect to the current state-of-the-art”, and
ii) “the manuscript should be re-evaluated/re-written. In the current form, it is not apparent whether there is significant novelty or not for further consideration in the journal.” have not been adequately addressed.
Since this work aims to a broad-interest journal, the key findings should/could be presented within a broader perspective and in a more consistent way.
In particular, the authors, replying to the previous comment from reviewer #2:
“Therefore, it is not quite clear what are the new insights/findings which the present work conveys. The attempts of the authors to put the work in perspective with the current state of the art, is probably limited on too general comparison/statements to properly highlight the novelty.”,
they mentioned three novelties: 1. Solvent-free synthesis, 2. Sintering-stable SACs from high configurational entropy; 3. Outstanding thermal and hydrothermal stability for CO oxidation. Regarding claim “2”, authors explained in the reply that this refers particularly to Pd. If the authors found a way for sintering-stable Pd single-atom catalysts which was not achieved before, it is of very broad interest. Nevertheless, this is not presented in the key points of the work (i.e. abstract, introduction-rational or conclusions).
The same stands for the claim of outstanding thermal and hydrothermal stability – this information is missing in the abstract and Introduction part. Although, in the conclusions the authors mentioned:
“The as-synthesized single-atom Pd catalyst displays not only superior CO oxidation activity but also outstanding resistance to hydrothermal degradation compared to Pd@CeO2 counterpart prepared using the same method.” , this statement leaves the impression that the outstanding stability is attained in comparison only to some control materials presented in this work; in this way the broader importance/novelty is lost.
In another example, the current abstract mentions: “More importantly, the significantly improved reducibility of lattice oxygen existing in Pd-O-M form for Pd1@HEFO are observed compared to Pd-O-Pd bonds of Pd@CeO2 in CO atmosphere, thus exhibiting extremely higher low-temperature CO oxidation activity.”, nevertheless, the authors mentioned in their reply to the revisions form reviewer #2, that the activity is not the best, but the stability at high temperatures and in presence of other gases (water vapours, NO and C3H6) is outstanding. Therefore, this is contradicting, pointing to the need for clarifying the key findings consistently and more clearly.
The rational which is developed in the introduction highlights only the technical novelty of preparing sintering-stable single atom catalysts without using a solvent. This is also interesting, but if this is the only new insight of the work (which seems it is not), then probably it is not of a broad interest.
As a result, the previous comments from reviewer #2 regarding:

i) “placing the work in perspective with respect to the current state-of-the-art”,.
ii) “the manuscript should be re-evaluated/re-written. In the current form, it is not apparent whether there is significant novelty or not for further consideration in the journal.”
could be addressed better.
In summary, from the authors reply and from the additional experiments that were presented it appears that the work merits publication, but the most important findings must be presented in a broad perspective and in a more consistent way providing a clear comparison with state-of-the-art systems.