Understanding the Catalytic Deactivation upon Hydrothermal Aging at 850 °C of WO3/Fe-Cu-ZSM-5 Catalyst for Selective Catalytic Reduction of NO by NH3
, Alessandra de Marcos-Galán 3, Imène Mejri 1,2, Rahma Bensouilah 1, Mourad Mhamdi 1,2, Teresa Blasco 3 and Gérard Delahay 4
Round 1
Reviewer 1 Report
The article focus in on NO selective reduction of modified ZSM-5. The topic fits the journal and the work is conducted with some care. There are however many parts that are not clear and in need of considerable revisions.
The first issue is that the reaction is not well stated nor clear. What are the reaction products, we are only given at the end (figure 8) NO conversion without being told to what products (presumably to N2 using NH3 as the reducing agent)? What about the selectivity? The reaction is monitored with a mass spectrometer therefore quantitative analysis of reaction products would be problematic because N2 (amu 28 would be difficult to quantify) and NH3 (amu 17) would be difficult to separate from that of water (amu 18 with m/e 17 and 16). A TCD would have been far more convenient.
The other issue is the methodology, mechanical mixing of the compounds will inevitably make separate phases. How much cations are incorporated into the zeolites and how much is present as a separate phase. Probably doing TEM would some understanding of structure of the prepared catalysts prepared.
Figure 2 needs to include peak attribution either on the figure or in the form of a table as a supporting information, as such it is not very helpful.
Figure 4. The UV vis deconvolution is not convincing without standard. How these deconvoluted peaks are made, what is their parameters? Overall the figure does not add much and can be deleted.
Figure 6 (TPR). While some changes are obvious, these are by no means clear without doing the standard (Fe2O3, CuO, WO3) separately.
Figure 7. The IR data are convincing, yet they need to be explained in more details. For example, it is stated the following: two bands at 1450 and 1610 cm-1 assigned to pyridine coordinated to Lewis acid sites. Explain their nature, stretch, etc... either in the text or in table 4. (please repalce the commas by dots).
Figure 8. It is not clear if the study is catalytic. For that steady state conditions needs to be shown. In other words, separate runs at a given temperature as a function of time are needed (at selected temperatures for each catalyst).
The article suffers from a weak language in many parts (here is an example from the bottom of page 8).
Table 4 shows that the ratio between Lewis acid sites (L350/L150) was [maintined] for W-Fe-Cu-Zag compared to [bimettalic] sample, probably owing to the presence [of] tungsten oxide species in tetrahedral coordination, detected previously from UV-vis and H2-TPR techniques, presenting the characteristics of Lewis acid centers [38]. Meanwhile B350/B150 ratio has considerably decreased upon aging showing [that indicating that] the [lost] of Brönsted sites is greater than that of Lewis sites upon hydrothermal treatment for trimetallic catalyst.
Author Response
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Reviewer 2 Report
The authors reported a novel trimetallic ion-exchanged zeolite-type catalyst for NH3-SCR. The structural changes after hydrothermal treatment have been well analyzed by the characterization, especially the influence of tungsten was investigated. While the catalytic analysis of aged zeolites is slightly insufficient. In general, the manuscript is well written, and the presented results validate the conclusions. I suggest this work can be accepted after a minor revision to address the following questions.
1. The end of the title should be NH3-SCR, as NO is the target for conversion, NH3 is the reductant which is the key factor in the reaction.
2. On page 7 line 210, the numbers in the chemical formula should be subscripted
3. NH3-TPD might be a better option for the detection of Lewis and Brösted acid sites in catalysts, the authors may consider using the technique either for this work or for future studies.
4. Compared with the well analyzed structural property, the SCR catalytic evaluation is weak. As the authors also recognize the importance of side reactions, the current manuscript lacks some data to support the analysis. Therefore, I suggest the N2O formation and the NH3 oxidation should be added to complete the NH3-SCR evaluation.
Author Response
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Reviewer 3 Report
I think the instruction of the paper should be improved, and the reviewing suggestions are modified as followings: This paper has sufficient test data, complete structure. The paper is recommended to be accepted if the following problems are modified: 1. The title of the thesis should be modified appropriately; 2. The research status at home and abroad needs to be further refined, such as the application objects of this kind of catalyst, etc. The following articles can be cited such as： Catalysts. 2019; 9(4):349. https://doi.org/10.3390/catal9040349； Chemical Engineering Journal，2020，384, 123253.https://doi.org/10.1016/j.cej.2019.123253; Atmosphere 2022, 13, 731. https://doi.org/10.3390/atmos13050731. 3、 The conclusions need to be further concise and scientific.Author Response
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Round 2
Reviewer 1 Report
The authors' answer is largely convincing. Please redo figure 6, its quality is not acceptable. Remove the significant digits of the values in table 4.
Author Response
Dear Reviewer
We are grateful for your pertinent remarks; according to your suggestions, corrections have been made: please check Table 4 and Figures 6 and 7.
Regards
