Abundant Oxygen Vacancies Induced by the Mechanochemical Process Boost the Low-Temperature Catalytic Performance of MnO₂ in NH₃-SCR

Round 1

Reviewer 1 Report

This paper investigated a highly efficient MnO₂ (MnO₂-M) catalyst preparing by a facile ball-milling-assisted redox strategy for the selective catalytic reduction (SCR) of NO with NH₃. The methods of ball-milling process to prepare the catalysts is interesting, but there is not much improvement. Thereby, some revisions are necessary and provided as follows to further improve the quality of this paper.

1. In the section of preparing MnO₂, how were the subsequent preparation steps?  Please describe more details. And what is the difference between MnO₂-M and M- MnO₂? There was no characterization of M-MnO₂ in this research.

2. In XRD section, the peak attributed to (110) did not point the value of 2θ. And some diffraction peaks on MnO₂ were not marked in Figure 1. Please add.

3. In Figure 5, the peaks of Mn 2p and O 1s were not fitted well, the curves of original data and fitting did not match. Generally, the spectra of Mn 2p_3/2 were fitted into three peaks assigned to Mn⁴⁺, Mn³⁺ and Mn²⁺, but there was wrong in the Figure 5.

4. In the section of 2.2, which effect of zirconia balls was in the preparation of catalysts? How did the zirconia balls influence for the formation mechanism of MnO₂-M?

5. In section 2.3, the NO conversion of MnO₂ in Figure 7a was around 90% at 150 ^oC, but the NO conversion of MnO₂ in Figure 9 was 100% at 150 ^oC, is the condition of the tests different? And when SO₂ and H₂O were added, the NO conversion of the two catalysts decreased gradually, both of them were not stable, why not prolong the testing time to obtain the final experimental data?

6. In my opinion, the paper was emphasized that MnO₂ prepared by ball milling treatment increased the specific surface area and pore size of the catalyst, but there was little analysis and discussion on the experimental results of the increase of oxygen vacancy. It could be better to add Raman test to characterize the oxygen vacancy of the catalyst.

7. Some new published related papers are suggested to refer and cite, for example "J. Environ. Chem. Eng., 2022, 10: 108239; Fuel, 2022, 321:124113".

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

1.       For the calculation of crystal size of MnO2, the peak at 37.5° seems to be an overlapping peak and not suitable for the calculation.

2.       The unit in Figure 1b is μm and the unit in the discussion is nm. Please check.

3.       “The relative surface content of Mn4+(Mn4+/Mn) over MnO2-M (0.63) is much higher than that of MnO2 (0.37).” But the ratio in table 3 is Mn⁴⁺/Mn³⁺+Mn²⁺. Please check.

4.       Based on XPS, the majority of the Mn seem to be Mn³⁺. Is it possible that in TPR there is one small overlapped peak at ~300 C is the MnO₂ to Mn₂O₃, while two other peaks are Mn₂O₃ to Mn₃O₄ at ~ 367 C and Mn₃O₄ to MnO at ~486 C.

5.       In NH3-TPD, the acid sites are generally at low temperature and should be Bronsted acid sites. Similar results should be seen in REF34.

6.       There is a big problem with this work that the M-MnO2 has a better result than the MnO2-M. This is an interesting result and possibly further work can be done to investigate the M-MnO2 and figure out what really happened. Looking forward to the further work.

 

7.       There is no O2 in catalytic test (Figure 7, 8, and 9). The Scheme 2 should not involve O2.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised manuscript can be accepted.