ZIF-67 Derived Cu-Co Mixed Oxides for Efficient Catalytic Oxidation of Formaldehyde at Low-Temperature
Round 1
Reviewer 1 Report
The results show considerable improvement of the performance of the Cu-doped catalysts towards formaldehyde oxidation, and so they deserve publication. However, the article needs a major revision, in the following topics.
a) The authors do not explain how they calculated the activation energies (Fig 1b, Table 1). But, in any case,"ignition" curves, which are useful to compare the performance of the catalysts (Fig. 1a), cannot be used to extract activation energies in the absence of a properly determined rate law, or kinetic equation, which is best obtained by carrying out isothermal experiments. This was not done by the authors. So, Figure 1b) must be removed, as well as the activation energies collected in Table 1, and any mention to activation energies in the text must be deleted. Authors are also requested to indicate the heating rate used to obtain the results in Fig. 1a, and they should refer the particle size of the catalysts in SI units (mm) rather than "mesh" sizes (supporting info.)
b) Table 2 presents data for S(BET) and pore size with 4 significant figures, which is an accuracy that the experimental method does not allow. In general the BET surface areas are determined with an error of +/- 5%. So, please round up these values (eg, 43 m2/g and 20 nm, for the cobalt oxide sample). Also, the crystallite sizes must be presented with only 2 figures (eg, 18 nm for cobalt oxide), unless the authors present a detailed statistical analysis for these.
c) However, there is a bigger problem with the BET surface areas, which CANNOT correspond to the isotherms presented in Figure 7a). If the BET values in Table 2 are correct, then the corresponding isotherms cannot be separated by such large values of adsorbed nitrogen (about 40 cm3/g) as shown in the YY-axis. I suspect that the authors might have displaced vertically the isotherms to avoid superimposed curves.... But this must be corrected.
d) The text in lines 240-241, "partial electrons of Co species transferred to Cu species via the lattice oxygen" must be revised; What is the meaning of "partial electrons"? and how is the "lattice oxygen electron density" increased?
In summary, major revision is required.
Author Response
We appreciate the reviewer for the constructive and insightful comments on our manuscript. According to the reviewer’s suggestions, we have carefully revised the manuscript and supplementary material. The details of response were displayed in the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript deals with the complete oxidation of formaldehyde over Cu-doped Co3O4 catalysts prepared from a ZIF-67 MOF. The characterisation of the catalysts is thorough and detailed, and the manuscript includes the proposition of a reaction mechanism based on some in situ DRIFTS experiments. The manuscript can be recommended for publication, although the following points should be addressed beforehand:
1. In general, Figures should be made slightly larger so they are easier to read and interpret. It is difficult to follow the manuscript with the current Figure size.
2. The important differences in the apparent activation energies between the Co3O4 catalyst and the Cu-doped catalysts suggest a difference in the mechanism followed by the reaction over each catalyst. What is the explanation for this?
3. The Scherrer equation depends on two parameters (the shape factor and the instrumental contribution to the peak width) that are chosen arbitrarily, and therefore the crystallite size results calculated from it cannot be reported with decimal positions since they are too imprecise. Also, given the small differences between the calculated crystallite sizes, it cannot be said that the crystallite size decreased significantly with the addition of Cu to the cobalt catalysts.
Author Response
We appreciate the reviewer for the constructive and insightful comments on our manuscript. According to the reviewer’s suggestions, we have carefully revised the manuscript and supplementary material. The details of response were displayed in the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have revised the manuscript according to the recommendations. The paper has been improved and can be published.
