Nano-Hollow Zeolite-Encapsulated Highly Dispersed Ultra-Fine Fe Nanoparticles as Fischer–Tropsch Catalyst for Syngas-to-Olefins
Round 1
Reviewer 1 Report
This paper reports on the synthesis of hollow zeolites with Fe2O3 nanoparticles inside the holes and their use as catalysts in the Fisher-Tropsch reaction of syngas to hydrocarbons. Fe is first impregnated on a standard silicalite, then this is subject to a dissolution-recrystallization process that provides the hollow structure and finally a steam hydrothermal treatment converts Fe (supposedly in framework positions) into Fe2O3 inside the holes. Among the three materials the last one is the one with a best performance in the reaction. The paper looks interesting but I would like some revisions to be done before publication.
Apparently, if I understand correctly, the disolution-recrystallizaton process results in the insertion of Fe atoms (initially in the outer surface, since it was just deposited by impregnation and then calcined) into framework positions (substituting for Si). If this is true there must be a clear change in the unit cell dimension of the zeolite. Please, index the XRD patterns of S1, Fe/n-hS, Fe@n-hS and Fe@n-hS-HT and provide the resulting unit cells. Is there a significant increase in unit cell volumen when going from Fe/n-hS to Fe@n-hS due to Fe insertion?
Other revision needed:
Frequently there is a period "." in the middle of a phrase after a [reference]. For instance, p-. 1, "Wang et al[6]. reported ". This is incorrect, please correct all the instances of similar mistakes.
If I understand correctly, the first catalyst described in 2.2.2, denoted as Fe/n-hS catalyst is not prepared by a disolution-recrystallization method but just by an impregnation method on "standard" silicalite 1. Hence, in my guess this catalyst should not show a "hollow sphere" morphology (this agrees with Fig. 2A,B). Then its notation as Fe/n-hS is misleading and, I think, wrong. It should rather be Fe/S.
Please define the meaning of the FTY acronym the first time mentioned (yield of CO converted to hydrocarbons per gram Fe per second?).
In the caption to Fig 2, please indicate that the inset in 2F2 is the particle size distribution. And also indicate what are the yellow circles marking in the main Fig. 2F2.
In p. 9 the authors refer to "framework FeO". I don't think there is any evidence of FeO in framework positions, I suggest to leave it as FeO.
In the same page what do you actually mean by "skeleton Fe"? I think after steaming it is quite unlikely that Fe may remain in framework positions.
The authors only compare their three materials as catalysts in the F-T reaction. I think they should compare them with other catalysts from the literature.
There are some instances that need revision:
"maximum aviation selectivity": it must be an error to place "aviation" there, please, correct.
Some words are wrong and should be correct (e.g., "donated" in p. 3 should be "denoted")
p. 10: I guess "high-exhibition catalysts" should rather be "high-performance catalysts"
Please, correct "Ultra" in the title.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The design of catalytic systems with improved performance is a key area of ​​pure and applied research in the field of heterogeneous catalysis. This article just corresponds to this direction on the example of designing new catalysts for an important Fischer-Tropsch process. The manuscript includes a very beautiful structural part on the synthesis of catalysts and a somewhat cursory comparison of three types of catalytic systems in the F-T reaction. The authors do not consider the mechanism of the process and the possible evolution of the catalytic system during the catalytic process in a reducing atmosphere. But nevertheless, in view of the significance of the synthetic part of the study, the manuscript can be published, taking into account the comments made. The main comments are summarized below, in addition, there are some typos in the text.
Introduction:
1. Wang et al [6 Is this “Niu X, Li X, Yuan G, et al.”?] reported a maximum aviation selectivity of 45% (what reaction?) over the hollow hierarchical S-1 (give a full name here and then abbreviate)
2. Fe-based catalysts have been researched and used the most for Fischer-Tropsch (F-T) synthesis owing to their high availability favorable light olefins selectivity… [11].
There should probably be many more references to catalysis of FT synthesis by Fe-containing systems. Could authors compare their results with known data?
3. The ideal Fe loading was 4%.Why the authors think it's the ideal content? Experimental:
4. The micro- and meso- (what?) were calculated….
5. The FTY (give an explanation of this value here and then abbreviate) of the catalyst were calculated…. Results and Discussion:
6. The accuracy of the values ​​in Tables 1-3 is clearly overestimated.
7. Why XPS data were not used to estimate the Fe electronic state? It was interesting to compare the results obtained for different catalysts before and after catalysis. It is known that α-Fe2O3 can be a precursor of the active form of the catalyst, including magnetite and iron carbide. Based only on XRD data it is difficult to exclude the formation of other highly dispersed states of iron, which may be poorly distinguishable, in particular, γ-Fe2O3. Of course, Mössbauer spectroscopy studies would be useful here. It’s very interesting catalytic system.
8. Then ”All the samples were reduced in a 50% H2/N2 flowing…” What is the Fe state after this treatment? Why does the CO conversion increase slightly after long-term operation?
9. As noted above, it would be better to compare the results obtained not only with each other but also with that for known catalysts.
There are some typos and too long sentences.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
