Carbon Dioxide Activation and Hydrogenation into Value-Added C1 Chemicals over Metal Hydride Catalysts

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript is well documented, well discussed and easy to read. Therefore, I can only congratulate the authors and accept it for publication.

As an answer I can remark that the revised contribution is a review of the literature, so questions about methodology or conclusions (there are not in this manuscript but “Future outlook and perspective”) are not applicable. Also, many of the specific questions are less relevant, and for those related to originality, relevance or references; I have a very positive view. Finally I agree with a decision of publishing this manuscript as it is.

Author Response

Please see the file attached.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Carbon dioxide hydrogenation to C1 products is extremely ecologically important direction of C1 chemistry. The idea of this review: to show how effective are various metal hydrides, oxyhydrides, homogeneous hydride complexes and other active hydrogen containing compounds in CO₂ hydrogenation to CH₄ and even to methanol and formic acid was realized successfully. The authors point their attention on metal hydrides properties; explain role of hydride hydrogen in CO₂ transformation including special features of different processes. Effectiveness of supported and oxide-containing catalysts with very complicate hydrogen activation mechanism is also explained. Additionally, “in situ” CO₂ and CaCO₃ hydrogenation to CH₄ under the mechanical treatment (ball milling conditions) is also included in the review. List of References includes a wide range of publications.

Here are several comments to this review:

1. Lines 42-43. Water solubility of CO₂ is not very poor.
2. Line 98. Cu(110) surface instead of phase.
3. Line 104. Dissociated O₂ or O atom on the surface.
4. Lines 114-115. Metal hydrides are compounds that consist of metal cations and hydride anions. When pressurized, metals bind with hydrogen to form stable metal hydrides, which can be used for convenient hydrogen storage. From HYPERLINK "https://www.sciencedirect.com/book/9780857095220/alternative-fuels-and-advanced-vehicle-technologies-for-improved-environmental-performance"
5. Line 125. What means “They chemically bind hydrogen and form an interface”? What kind of interface?
6. Line 130. To explain a strange term: “interfacial reaction rate”.
7. Table 3. Is it really that PdH₀₆ and TiH₂ have ionic Me-H bond?; “high energy cost to desorbs hydrogen”.
8. Line 179. Group 13 metal from Table 2.
9. Line 205. The dissociated… start from the new line.
10. Line 207. C2-C4- subscripts.
11. Line 196. As mentioned above, both selective and non selective reactions were observed.
12. Line 213. Alkenes and alkynes are always unsaturated.
13. Line 218-129. Unfortunately, no optimistic information about perspective of CO₂ transformation to C1 chemicals is given above. The authors only demonstrated potential of different hydrides as catalysts for various hydrogenation processes.    
14. Line 257. Rate determining step instead of determining rate.
15. Line 259. If the authors give no details concerning crystallization features, it does not need to write about them.
16. Lines 265-268. The phrase is too complicate. It better to divide it to several parts.
17. Line 266. ….in MgO(110).
18.  Lines 275-276. What means "shortened distance of H‾ hydride mobility on the LaNi5H5 hydride”?
19. Line 279. Strange term: neutrophilic H^-. What it means?
20. Lines 276-283. This phrase has to be revised.
21. Line 282. …at 230.
22. From Lines 292 to 320. If complex Mg-containing hydride transforms to MgO, it can't be transformed to hydride again. It means that the process described is non-catalytic process.
23. Line 339. …of aluminum-based.
24. Line 341. ….of hydrogenation on Al-MOF?
25. Line 346. MH-DUT-5 - abbreviation.
26. Lines 263-280. In this part is described a non-catalytic process of pure H₂ production from CH₃OH coupled with CO₂ utilization.
27. Line 362. …me?
28. Part 2.3: Throughout the text, the authors need to distinguish between  hydridic hydrogen (H^-), which they called "hydride," and hydride as a compound or compound-like state. Lines 408, 416, 420, 429, 443, 448 etc.
29. Line 458. …on instead of of.
30. Lines 509-510. This phrase needs explanation: what means "reduced H₂ poisoning by spillover"?
31. References. DOI is needed.

 

Comments on the Quality of English Language

The manuscript is very difficult to read and the text requires revision.

Author Response

Please see the file attached.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article entitled "Carbon dioxide activation and hydrogenation into value-added C1 chemicals over metal hydride catalysts" is a review article on the latest scientific advances on the capture and conversion of CO2 into C1 chemicals, especially in the development of catalysts and the mechanisms associated with them. The topic is quite interesting and important in our society today, however it needs to improve several aspects to be published in this magazine, namely:

1) The authors should highlight the advantages of producing C1 products instead of products with higher carbon chains.
2) The figures should be of better quality;
3) There should be a conclusions chapter summarizing everything that was said in the article.
4) There should not be a period before references. It should be like "(...) [X]."
5) Pressure, flow and temperature effects were little (or practically not at all) discussed in this article. The quality of the article could be improved.

Author Response

Please see the file attached.

Author Response File: Author Response.pdf