Characterization of the Evolution of Noble Metal Particles in a Commercial Three-Way Catalyst: Correlation between Real and Simulated Ageing
, Sara Morandi 1, Samir Bensaid 3, Gabriele Ricchiardi 1 and Mauro Sgroi 2Round 1
Reviewer 1 Report
In their manuscript, Giuliano et al. characterize different commercial TWCs and relate physical and chemical phenomena with the catalytic performance observed. This is a solid piece of work that covers an important topic, although I must admit that I expected a bit more when I read the title. In the end the correlation between real and simulated ageing is just the presentation of the results of TWCs that have been aged differently. The material characterization is relatively simplified (there is no use of X-ray techniques or elemental analysis, and so I would not call that “in depth”), and I am not sure all the assignments of the peaks of the FT-IR spectra are correct. This first section 2.1 is relatively long, but there is no discussion of the relevance of the different bonding and IR spectra observed (especially related to Pd) other than that they are different for the different catalysts. There are a few more detailed comments below that should be addressed in the revision.
Line 65: This is somewhat confusing. You first say that “for these reasons, laboratory accelerated ageing methods are becoming more and more attractive”, only to then say these should be substituted? Further, the logic of the sentence is not clear: Why would the catalyst’s behavior affect the new laboratory ageing protocol; should it not be the other way around?
Line 78, section 2: You may want to be consistent in the use of tense (past vs. present) when writing about the experimental results. Currently there is a strange mix.
Line 114/115: Is this sentence correct? There seems to be a verb missing after “the fact that”.
Line 116: Can you please discuss the peak near 2200 cm-1? Is it significant in (b) because the intensity of the other tow peaks is lower than in (a)?
Line 132, Figure 1: General comment, the quality (resolution) of the figures is rather poor and can certainly be improved.
Line 132, Figure 1: What is the meaning of the black curve if the other curves correspond to different partial pressures of CO? Maybe this information can be added to the caption. Same comment for Figures 2 and 3.
Line 174: Did you run any elemental analysis to verify that, e.g. ICP?
Line 208: Why is there a reference given? Is that because that paper describes a method that was used to calculate the particle size of 2 nm?
Line 258: This is difficult to understand and requires clarification: You say that the small white particles in the SEM image correspond to Pd. Their size is very small, certainly smaller than 50 nm (based on the poorly visible scale bar). Yet, Table 1 reports a d min of 210 nm for the sample FUL. Why is that?
Line 339: Is it correct that you actually mean “km” rather than “miles”?
Author Response
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Author Response.pdf
Reviewer 2 Report
The changes of noble metal particles in an automotive catalyst were studied with different methods. The results clearly demonstrate that the Pd particle size increases significantly with use and the deactivation was attributed to the agglomeration of the nanoparticles.
The role of Rh, the changes of the oxidation state of the Pd and the component of the washcoat (Ce, Zr), the amount and the reactivity of carbon deposit, the changes of the basicity were not discussed. Could you comment and discuss these questions?
The assignment of CO peaks is just the opposite, as it was written in rows 153-154.
Author Response
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Reviewer 3 Report
In this study, the authors studied the effect of three different kinds of conditions, namely, on-vehicle aging, engine-bench aging, and laboratory aging, on one commercial Pd/Rh three-way catalyst. The authors compared the Pd size and CO/HCs oxidation activity after different aging treatments using FT-IR, CO-chemisorption, and SEM. Finally, the authors concluded that the widely used lab aging protocol shows a similar effect to that of intermediate mileage aging. The conclusion to some extent is interesting and publishable. The reviewer has several concerns and comments. A major revision is therefore suggested.
1. The ref 13 of this paper is from the same authors and focuses on a very similar topic with this paper, that is, "CHARACTERIZATION OF VEHICLE AND LABORATORY AGED COMMERCIAL THREE-WAY CATALYST: A MORPHOLOGICAL AND FUNCTIONAL CORRELATION BETWEEN REAL AND SIMULATED AGEING". The reviewer, however, has no access to the full article of ref 13 and make the above statement based on the abstract. The authors should clarify the difference between the two papers and the necessity of this paper.
2. The authors employed a Pd/Rh TWC. However, all characterization is about Pd. How does the Rh in the TWC evolve during those aging treatment?
3. For CO/HCs oxidation measurements, the authors should provide the details like CO/HCs concentration, H2O concentration, GHSV, the HCs included, etc.
4. For three-way catalysis, in addition to CO/HCs oxidation, NO reduction by CO/HCs is also very important. There are no performance measurements regarding NO reduction. Do different aging treatments make a difference in this reaction? The authors need to clarify the two types of reactions.
5. The literature has widely reported the huge and negative impact of chemical aging (formation of Pd/Ce(III)-SO3/SO4 species) on the performance of catalysts in CO or HCs oxidation (ACS Catal. 2020, 10, 23, 14304–14314, Catal. Today 2003, 83, 45– 57, etc.) Based on the results here, the 60K aged sample shows a similar particle size to that of the lab aged. In addition, the 60K aged sample shows chemical aging while the lab aged does not. However, the two samples show similar performance in the oxidation reaction, and the 60K aged sample even shows a slightly lower T50 for CO oxidation. Can the authors explain the possible reasons for this?
6. For the conclusion that the lab aging shows a similar effect with that of intermediate mileage aging, is this universal for different TWCs, different engines, or gasoline? It would be much better if the authors could provide more thoughts on this point.
Author Response
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Reviewer 4 Report
The current work deals with PGMs nanoparticles in automotive catalysts. Unfortunately, it is not a well written paper and several amendments and additions must be done in order to be reconsidered for publication:
- There are severe mistakes in the use of English. An extensive editing of English is necessary (e.g. lines: 36, 96 and many others). In many cases, it is hard to understand the meaning.
- Abstract: Several syntax errors. A better editing of English is needed in the whole abstract.
- Introduction: The literature review is poor. Additional references are needed.
- Discussion: The discussion of the results is inadequate. Further scientific argumentation is obligated.
- There is no conclusions section on the article.
- References: More references must be added.
Author Response
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Round 2
Reviewer 3 Report
The comments from the reviewer have been reasonably responded to and addressed. Therefore, I suggest accepting the current manuscript for publication.
Author Response
Dear Reviewer 3.
Thank you for your precise and interesting comments. They were useful to improve the quality of our manuscript.
Best regards.
Reviewer 4 Report
The authors made some amendments in the manuscript. However, a closing paragraph is needed after the Figure 8 either as Conclusions section or not. Moreover, a richer literature review of the manuscript and the addition of extra references will not only offer a more accurate roadmap to your readers, but also will give credits to scientists of the field before you.
Author Response
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