The Effect of Atomic Layer Deposited Overcoat on Co-Pt-Si/γ-Al₂O₃ Fischer–Tropsch Catalyst

Round 1

Reviewer 1 Report

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Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is an interesting study of optimizing the thickness of an ALD overcoat and monitoring the impact of the treatment on the catalyst properties. The paper is well written with only some minor issues with numbers which should be subscripts or superscripts, but there are some more serious, general concerns which need to be addressed.

1. Your write that the deposition of the layers does not change the availability of the active sites, whereas your O₂ titration results indicate otherwise. Please provide an explanation of this in the manuscript.
2. The TOF values for CO are misleading because the worst catalyst with the lowest CO conversion and the worst properties has the highest value. This would only be possible if your treatment increased the activity of the sites, which id does not. Since no active sites are lost or changed by your treatment, please recalculate the TOF values in respect to the original number of active sites on the surface of the untreated catalyst.
3. An analysis of the diffraction patterns does not support your statement from lines 265-267 that a higher temperature is needed for the reduction of Co₃O₄ to CoO for the ALD samples than for the starting materials. Both diffraction patterns for line 3 (Figure 2) show no signs of CoO, whereas both diffraction patterns from line 4 show a signal from CoO at a scattering angle of approx. 43deg. This means the same temperatures are required for reduction to occur. The fact that the signal is smaller for the sample which has a deposited layer might be due to the fact the crystallite size of the forming phase is smaller in these samples because of the special restrictions. Nevertheless, only your TPR indicate a hindrance of reduction. The diffraction patterns which you presented do not. Please support your statement with additional XRD information which led you to that conclusion, or modify the statement to fit the presented data.
4. You wrote that “Typically, the favourable effects of ALD overcoating on catalysts is explained by the nanoporous structure achieved by thermal annealing [25, 42][3, 25]”. Your results do not support such a statement because the nitrogen physisorption study shows a porosity which is the same (within experimental error) as that of the untreated catalyst and nitrogen physisorption is usually not a method used for determining nanoporosity. Please relate your own results to the statement which you wrote.
5. There are two “Results” sections and the numbering in the first one is incorrect (e.g. 2.1.1 instead of 2.2.1). In this journal, the Materials and Methods section comes after the Results section and therefore is section number 3. Therefore, your numbers of subsections for Materials and Methods should be: 3.1, 3.2, 3.2.1, 3.2.2, etc.
6. Please specify the atmosphere in which the samples were cooled after the 12h reduction. Presumably it was hydrogen, but please write it explicitly.
7. Minor linguistic issues:

Please make sure that all subscripts (lines 121, 125, 151) and superscripts (lines 177 and 239) are correctly formatted.

Please don’t start a line with a comma.

Author Response

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Author Response File: Author Response.pdf