Continuous-Flow Sunlight-Powered CO2 Methanation Catalyzed by γ-Al2O3-Supported Plasmonic Ru Nanorods
, Fidel Valega Mackenzie 1, Man Xu 1,2, Marcel A. Verheijen 3,4, Pascal Buskens 1,5,* and Francesc Sastre 1,*Round 1
Reviewer 1 Report
The presented work here investigates the plasmonic methanation via γ-Al2O3-supported Ru nanorods which were done under continuous flow conditions without conventional heating. They obtained a CO2 conversion >98% with complete selectivity towards CH4 and a stable production rate for at least 12 h. The idea of this work is interesting, however, this paper lacks scientific characterization to support their findings.
My comments are as below:
- Section 2.1: The authors should provide the individual XRD for the Ru-NRs/ɣ-Al2O3 materials before and after combining. By doing this, a more detailed explanation of the change in crystallinity can be included in their discussion section.
- Figure 1: Please include the JCPDS card no. in this figure.
- HRTEM: Please label the Ru NR and ɣ-Al2O3 structures. It is hard to see which one belongs to which one.
- HRTEM: The authors should provide TEM, high-resolution TEM, lattice fringe pattern, and EDS analysis.
- Section 2.2: On what basis that the presence of RuO2 promote the spike in the sudden increase in catalyst bed temperature?
- Please provide proof for this statement "photomethanation is strongly dependent on temperature"
- Please include the TGA analysis.
- Section 3.1: How did the authors ensure that the formulation of Ru and ɣ-Al2O3 used in this work is the optimum or best formulation? Is there are prelim work been performed before?
- What is the key factor affecting the CO2 conversion efficiency? Please discuss further in the discussion section and relate to the properties of the material.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In the present work, the authors studied “Continuous flow sunlight-powered CO2 methanation catalyzed by γ-Al2O3-supported plasmonic Ru nanorods”. The manuscript needs to be improved in the characterization section. The authors are more focused on active metal Ru in the catalysts but they are completely forgetting the effect of the support in the reaction. As a reviewer, I would suggest that this manuscript is not acceptable at the present standard, but with major changes, it can be.
First of all, the introduction of the manuscript should be changed in a way that the use of Al2O3 support this reaction. Authors mainly focus on the introduction about different active metals Ni and Cu but it is advised to change and more focused on Ru based catalysts. This is important because the authors can show the main difference of their work from others
Authors should also provide a state of the art because they already published the same kind of catalysts in recent years with other publishers, please also elaborate on details of the difference between the other publication and this article.
In my opinion, the usage of 10% Ru is such a high-cost material for industrial purposes. SO, what is the use of this catalyst or upscaling of this catalyst with 10% Ru?
The abstract should be changed in a way that the main objectives of the article. In the abstract, they are talking about 14.4 suns but during the experiment, I can see only 1 or 2 experiments done using 14.4. however, more experiments are related to 12.5suns.
As I mentioned above the characterizations need to be improved here the UV-Vis spectrum should be improved or re-measure, because the broad peak mentioned by the authors can not be seen. They are doing a photoreaction so I also suggest providing band gap values of the catalyst.
TEM image should be changed and provided with a good image where everyone can see the nanospheres and rods. Here this TEM image is not appreciated.
Fig 2. With the spike of high temperature, I am confused to see authors refereeing the spike at high temperature related to RuO2 to metal. Is this a reduced catalyst? XRD they are showing Ru but here RuO2? How is this possible to explain?
Fig 3 I think this figure should also contain the CO2 conversion graph with different suns up to 14.4 suns. the current figure also changed up to 14.4suns.
Authors should also perform a standard mass transfer limitation experiment with different flows and different suns.
Fig 4 here the legend is a bit confusing where a is studied with 12.5 and b is studied with 14.4, what is the reason? Why they are showing temperature with 14.4 suns and why they are showing a conversion and production with 12.5 suns?
Finally, the blank experiment should be repeated without catalyst with the same flow with light and dark. Here the authors carried out blank experiments at 150C? where during the reaction in the dark mode they were using external heating at 220C.
After doing the necessary changes please modify the conclusions and the abstract of the manuscript in a way with the new data.
About supplymentary data they did not mention what is the use of this data in the manuscript?
I believe the authors need one more chance to provide more characterization study and good interpretation of data.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The submitted work can be accepted as it is.
Reviewer 2 Report
The revised version of the manuscript is highly improved and this manuscript can be accepted as it is.
