Comparison of Different Metal Doping Effects on Co3O4 Catalysts for the Total Oxidation of Toluene and Propane
, Jose Luis Valverde 2 and Anne Giroir-Fendler 1,*Round 1
Reviewer 1 Report
The manuscript describes an effect of doping of the Co3O4 phase with a small admixture (5 at.%) of another transition metal (Cu, Mn, Ni or Fe) on its properties, and in particular a catalytic activity in the combustion of volatile organic compounds (VOCs), studied in this work on an example of propane and toluene. The choice of unsupported catalysts is somewhat surprising, as they show significantly worse dispersion of the active phase and high production costs. Nevertheless, the selected approach has highlighted several interesting aspects, which after revising with regard to the comments raised in this report, should give a more systematic insight into the topic of development of oxide catalysts for the removal of VOCs.
- Typically, in the case of hydroxycarbonate precursors containing Cu2+ cations (e.g. materials with a hydrotalcite-like structure), strong stabilization of carbonate ions is observed. Was this effect not found for the copper-doped material studied in this study? Hence, was the selected calcination temperature of 500 °C sufficient to eliminate the structural carbonates?
- Was any method used to remove water from the gas stream exiting the TPR reactor? The presence of water may distort significantly a TCD signal.
- It is necessary to determine a content of benzene among the products of toluene combustion, because oxide catalysts tend to form this by-product at low temperatures. My research for similar systems revealed that at temperatures up to approx. 300 °C the selectivity to benzene exceeded even 10%.
- Lines 108-109 say that "two characteristic peaks corresponding to Co3O4 spinel were observed for all samples". It is not clear which bands are meant.
- How do Authors explain the lack of a clear correlation between reducibility and catalytic activity in the VOCs combustion? It is usually assumed that the process of total oxidation of VOCs occurs according to the Mars-van Krevelen mechanism, where there should be a close relationship between these two parameters.
Author Response
see attached file
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Authors present a well-written report about the activity of some Co3O4 metal-doped catalysts for the total oxidation of toluene and propane.
The authors thoroughly characterised all the materials and investigated the catalytic activity both in the presence and in the absence of water.
Mn-doped catalyst resulted the most active in the oxidation of the two organic compounds and a reasonable explanation for that was provided.
I recommend the publication of this paper after few issues will be fixed:
- (mandatory) errors for the results reported in Tables 3--6 have to be added.
- (mandatory) more details about the analytical methods for CO2 detection should be provided. From the manuscript it seems that the selectivity of the process is 100% towards CO2. What about other byproducts (H2O, CO, etc.)? What does it happen to the selectivity of the process when the doping metal lower the catalytic efficiency? Please comment.
- (desirable) SEM-type measurements would improve the morphological analysis of the materials.
Author Response
see attached file
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
My remarks have been taken into account and the manuscript has been corrected accordingly.
Reviewer 2 Report
The authors properly addressed my concerns. I recommend the publication of the paper in its present form.
