Surface Modification of GdMn2O5 for Catalytic Oxidation of Benzene via a Mild A-Site Sacrificial Strategy
Round 1
Reviewer 1 Report
Gao et al. studied catalytic oxidation of Benzene over surface modification of GdMn2 O5 via a mild A-site sacrificial strategy. It is rather a comprehensive study with systematic physicochemical characterizations and performance evaluations. The research topic is related to environmental protection, thus is meaningful for publication in this journal. On the other hand, there are a few concerns about the current manuscript and they are listed below for further consideration:
1. (line 20, 370, 378, 383)
The article mentions thermal stability in several places. In my opinion, thermal stability refers to stability at a relatively higher temperature, in other words, temperature exceeding 100% conversion, so I think the experiment in the article should be activity stability.
2. (line 182-184)
“The morphology of GMO (Figures 2a-c and g-i) includes nanoparticles with a diameter of about 60 nm, nanorods with a length of about 200-250 nm, and nanosheets with a width of about 200-500 nm.” Does it mean there are three morphologies in GMO and why?
3. (line 214-215)
“which may be because the mullite structure of the sample is damaged by the acid etching for too long.” For too long, then what? Why the pore size tends to increase as the time of acid etching increases for too long? Please explain in depth.
4. In order to enrich the content of the article, the following experiments are suggested to be supplemented, Ea, effect of WHSV and cyclic activity over the catalyst. In addition, in view of the water presence in the practical VOCs combustion, it is necessary to investigate the effect of water vapor on Benzene conversion, so please supplement the water resistance experiment.
5. There are some mistakes in word form, word choice or spelling, for instance, Mn4+ should be Mn4+ in line 347.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The present work deals with GdMn2O5 and modified GdMn2O5 for total oxidation of benzene. While the catalysts are not new (please see next point), their application for benzene oxidation has not been reported. However, most of the work regards discussion of the characterization studies. This, together with the fact that the journal is Catalysts, makes the reader somewhat unsatisfied.
There are two studies of GdMn2O5 for catalytic oxidation; one of them was cited in the present manuscript, but the other seems to be missing and is important because it also deals with deep oxidation of VOC: “Enhanced catalytic activity of oxygenated VOC deep oxidation on highly active in-situ generated GdMn2O5/GdMnO3 catalysts”, Journal of Colloid and Interface Science Volume: 578 (2020) 229-241, DOI 10.1016/j.jcis.2020.05.095 . In that published article, the catalysts were also prepared by acid etching using different HNO3 concentrations (including the same concentration used in the present manuscript), and comparable characterization studies were carried out. This leaves poor novelty to the prepared catalysts and thus it is fundamental to compare the characterization results to that publication and clarify the improvements made.
Additional points require attention.
CHARACTERIZATION:
Regarding the characterization results, the authors refer to composition in % given by EDS and XPS, but these are surface techniques and give a normalized % which may be erroneous. They are more suited to give surface atomic ratios (e.g., Gd/Mn). Please revise “hydroxyl oxygen (OO-H),” (this seems more like a hydroperoxyl group).
The differences % amount of Gd (EDS) discussed by the authors (paragraph lines 222-232) are sometimes very small. The deviations (errors) should be included for these measurements.
It is wrong to say that “ICP is a monolithic characterization” (line 243).
Please revise “N2 (equilibrium)” (line 319) because it is not understandable what this has to do with equilibrium.
A reference should be cited in the sentence, “When the concentration of Mn3+ in the compound is equal to that of Mn4+, ΔE is 5.0 eV.”.
Please comment on the oxidation state of Gd.
The authors discuss, “The area of the hydrogen consumption peak (12.47) for GMO-H at lower 292 temperatures is larger than that (11.06) of GMO (Table 2),”, but the areas are very similar. What is the range of error? Also, please specify the temperature range used for calculating these areas.
CATALYSIS:
Regarding the catalytic studies, Table 2 required a footnote to explain where are the results of benzene conversion.
Some aspects of the catalytic studies which are crucial were not addressed, such as characterization of the used catalysts (this should be done).
A black test without catalyst should be made and discussed.
The authors discuss “Table 2 lists the activities of the four catalysts in the order of Benzene oxidation activity as 327 follows: GMO-H(T50 = 220 °C，T90 = 310 °C) > GMO-H-9(T50 = 235 °C，T90 = 345 °C) > GMO-328 H-19(T50 = 225 °C，T90 = 405 °C) > GMO(T50 = 310 °C，T90 = 405 °C).” which is very confusing. The activity should be compared for the same reaction temperature, in separate sentences. Please include the formula of activity in the experimental section.
In Supplementary Material, please include the Benzene conversion versus time on-stream curves for each point given in Figure 6 (left side plot). Also, this figure needs to be identified with A and B in each plot, and presented accordingly in the figure caption.
Please specify if each point in Figure 6 corresponds to steady-state conditions.
EXPERIMENTAL:
There are missing experimental details.
Regarding GC quantification, the authors should give details amount the calibrations for at least benzene and CO2.
Please also specify the flow rate of pure benzene which makes part of the feed.
It is necessary to indicate: the flow rate of pure benzene which makes part of the feed, the material (stainless-steel?) and dimensions of the reactor (internal diameter, length) and the dimensions of the catalytic bed (occupied by 0.1 g catalyst).
For the TPD and TPR analyses, the authors should indicate the details regarding mass of sample, evacuation time of physisorbed H2 or O2 (prior to exposure of the sample to H2 or O2), heating rates (for pretreatment and analysis) and composition (and purity and suppliers) of the H2 or O2 gas mixtures used.
For the sake of clarity please include the formula for GHSV.
WRITING AND CLARITY:
The English and scientific languages make some sentences unclear and confusing and should be revised throughout.
Scientifically wrong/unclear terms in the Abstract: “rich oxygen vacancies”, “the catalyst remains constant” (possibly the authors meant “catalytic activity”), “ at 90% of the Benzene removal rate at 300 °C,” (% is not a “rate”), “the reaction for removing 90% Benzene temperature GMO-H catalyst was dropped”.
Please rewrite the following which appears in the main text: “fundamental precursors of haze”, “inhibits the number”, “distorted (green boxed part),”, “Benzene gas molecules reactant”.
Author Response
Please see the attachment.Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors have answered the issues, and the revised manuscript can be accepted in Catalysts.
Author Response
On behalf of my co-authors, we thank you again for your helpful suggestions during the manuscript revision process.
Reviewer 2 Report
The authors have improved their work, which is now clearer. I believe it is not necessary to reevaluate (may be done in the proofs stage) , but I kindly ask the authors to please specify LIQUID (if they agree) in "The LIQUID flow rate of pure Benzene is 38 ml min -1 .” and please indicate the molar ratio of O2:N2 in "600 ppm benzene 415 and 20% O2 and N2 (balance) at a total flow rate of 50 mL min-1"
Author Response
Thank you very much for your comment. During the experiment we used air bottles in which the 600 ppm Benzene was configured. To avoid ambiguity, we have changed "pure benzene" to "600 ppm benzene" in line 417 of the revised manuscript. The molar ratio of O2/N2 was 0.25, which was added in line 417 of the revised manuscript.
