The Activity and Stability of Promoted Cu/ZnO/Al2O3 Catalyst for CO2 Hydrogenation to Methanol
, Raihan Mahirah Ramli 3 and Nur Amirah Suhaimi 2Round 1
Reviewer 1 Report
The authors have studied the Cu/ZnO-based catalyst for its stability and activity in methanol synthesis via CO2 hydrogenation. The results are interesting and straight forward. The authors should update the manuscript keeping in view the following comments.
1. The authors should show all the reactions taking place in the methnaol production and also highlight if any side reactions occour.
2. The authors may highlight the future reserach direction in light of limitations in the current work.
3. The authors may write few lines on the economic aspect of the catalyst sysntheis by this new formulation.
Author Response
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Reviewer 2 Report
The authors have used Cu/ZnO to hydrogenate CO2 toward methanol. Therefore, the application presented in this manuscript is interesting for carbon capture and renewable energy potentials. However, several serious shortcomings must be addressed before this manuscript meets publication standards:
1. This manuscript has only focused on the durability of the catalyst, and there is no proper characterization of the synthesized materials system. The authors have only presented the microscopic images showing random size distribution, with enormous sizes being dominant. Some additional crystallographic characterization must be added, attesting to suitability as a catalyst.
2. The authors should compare this catalyst with similar ZnO-based materials for the reported reactions.
3. No crystallographic characterization shows how the catalyst changes during the reactions.
4. Also, the current methods for synthesizing ZnO and CuO should be noted in the introduction, such as in the following paper: Doustkhah et al. Chemosphere 303, 134932 (2022); Singh et al. Applied Surface Science, 521, p.146420 (2020).
5. The fact that alumina support was used in synthesizing the catalyst should be reflected in the title.
Author Response
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Reviewer 3 Report
In this paper, the authors investigated the stability and activity of CZMNZA catalysts at reaction durations of 5 h (reference), 2 days, 7 days and14 days. In addition, the physicochemical properties of the spent catalysts were analyzed, including textural properties, morphological and elemental composition, and grain size distribution. Nevertheless, there are a series of major problems in this paper, including format, tables, figures, etc., which result in poor rigorous as well as readability of this paper, which require further revision, as follows:
1. In Section 1, the authors mention that “the Cu-Zn-Al2O3 catalyst has been widely utilized in industrial methanol synthesis”, in this sentence the format for writing catalysts is “Cu-Zn-Al2O3” nevertheless in the title and abstract is “Cu/ZnO/Al2O3”. I suggest that the authors unify the hyphenation between catalysts.
2. In Section 1, the authors mention that “catalysts always exhibit deactivation behavior during industrial application”，For this phenomenon, the authors do not give detailed examples or indicate references, etc.
3. In Section 2, the authors narrative in the section on catalyst performance evaluation is too brief, I think authors should state that certain properties of catalysts are assessed and what are the indicators for performance assessment, etc.
4. In Section 3, in their analysis of the data in Table 1, the authors mention that “when the reaction duration was prolonged to 14 days, the CO2 conversion and methanol yield decreased by about 9% and 7%, ...”, however, the data in Table 1 shows that the CO2 conversion and methanol yield are not decreased by about 9% and 7%. It is advised that the authors use the information in the table to create a precise and thorough analysis.
5. In Section 3，as can be seen in Table 3, the sum of the elemental percentages in both fresh catalysts and spent catalyst 7 days was greater than 1, and in Figure 4, the sum of elemental percentages in fresh catalysts, spent catalyst 2 days, 7 days and 14 days also have such problems. It is recommended that the authors check these data.
6. In Section 3, there was a problem with the inter-page layout of Table 5, and it is hoped that the authors will make appropriate adjustments to the layout of the article so that Table lies within a single page.
7. In Section 3, in their analysis of Fig.5, the authors mention that “the Zn 2p3/2 peaks moved toward slightly higher BEs at 1021.1 and 1021.2 eV,...” and “The appearance of the doublet peaks at 3d3/2 and 3d5/2 for fresh catalyst at 205.5 eV and 204.4 eV,...”, in these two sentences, there is a problem of inconsistency in the writing form for BEs data. The authors are recommended to be consistent in the writing form throughout the writing process of their articles.
8. In Section 3, the formulae is not labeled with serial numbers, and the authors are advised to label the formulae with serial numbers in line with the previous section.
9. In Section 3, the wireframe of Table 8 is not omitted and is inconsistent with the form of the table in the previous article. It is suggested that the authors should unify all the forms of the table in the article.
10. Some of the images in the article can be found to be less aesthetically pleasing. For example, in Fig.1, there are more gaps at the top, the scale is not labeled in the figure, and the dashed line has too large a dot compared to the small scale in the figure, which can cause a bias in the reader's reading. The tracer elements on the right-hand side of Fig.2 are unlabelled. In addition, in Fig.5, the text of the labels within the figure is blurred, etc.
11. The spacing of the fonts in the articles does not match the requirements of the writing standards in many locations.
12. Regarding the conclusion of this paper, the authors describe it too superficially and suggested that the authors make a deep and detailed summary in the conclusion part of the paper based on the research they have conducted.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
This paper does not belong to scientific literature and must be rejected. My initial concern was about the claims made about the materials synthesized. The authors have used a variety of precursors containing a few metals and synthesized the presented samples, claiming the successful formation of Cu/ZnO. In the absence of crystallographic characterizations, the sample might well be something totally different like Zn/CuO2. In response to my comments, the authors fail to provide any scientific grounds to address the shortcomings in the paper. Based on pure semantics and without substance, they either argue that answering my questions would be out of scope or that they do not have the data. For a scientific paper, the scope must include basic minimum standards to ensure validity and reproducibility, and the data must support the claims. Lose either one, and your paper falls outside of science.
Author Response
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