Magnesium-Modified Co3O4 Catalyst with Remarkable Performance for Toluene Low Temperature Deep Oxidation
Round 1
Reviewer 1 Report
Dear authors,
I have reviewed your paper and, unfortunatly, I do not consider it suitable to be published in MDPI Catalysts journal.
Here are the main reasons:
- The Introduction section does not provide the current state-of-the-art and yor contribution beyond it. The novelty of your research is not highlighted at all.
- You haven't determined the catalytic stability of Co3O4 and MgO even though you prepared them. You not even get this characteristic from literature.
Basically, the paper is more similar to a technical report than to a research paper since it only presents the preparation and full characterization of just one catalyst MgCo2O4. Even so, its performances are average. According to table ESI 1, your catalyst is showing the third best T90 after 219 (Cu-Co3O4) and 230 (Pd/Co3AlO) and the second best T100 after 340 (Co3O4 from literature). So, you have prepared an catalyst that has slightly above avreage catalytic activity and you have presented it within this paper.
Other small issues are:
- You haven't provide the provenance of the chemicals you used within your work
- You haven't ptovide justification for one of your actions. (e.g.: why you treated 60 mg of sample in Ar from room temperature to 400 )
Author Response
Reviewer #1:
Reviewer recommendation: I have reviewed your paper and, unfortunatly, I do not consider it suitable to be published in MDPI Catalysts journal.
Reply: First of all, we thank the reviewer for his/her unfavorable opinion on the manuscript. Our responses to his/here reasons of rejection are therefore addressed one by one as following.
Reviewer General comment: Basically, the paper is more similar to a technical report than to a research paper since it only presents the preparation and full characterization of just one catalyst MgCo2O4. Even so, its performances are average. According to table ESI 1, your catalyst is showing the third best T90 after 219 (Cu-Co3O4) and 230 (Pd/Co3AlO) and the second best T100 after 340 (Co3O4 from literature). So, you have prepared an catalyst that has slightly above avreage catalytic activity and you have presented it within this paper.
Reply: We thank the reviewer for his/her comment. The Reviewer declare that “Basically, the paper is more similar to a technical report than to a research paper since it only presents the preparation and full characterization of just one catalyst MgCo2O4.” We are really surprised by this reviewer comment and we are afraid that he /her may have not really examined in details our manuscript. In fact, three set of catalyst including single oxides (MgO and Co3O4) and mixed oxide (MgCo2O4) were prepared and systematically characterized please check carefully on figures 1(XRD), 2(SEM) 3 and 4(XPS), 6 (H2-TPR). More importantly the entire prepared metals oxides have been tested as catalysts and the mixed oxide (MgCo2O4) exhibited the best performance (see Fig.7a). Because MgCo2O4 our target catalyst was the most performant, we have exclusively performed catalytic stability test only on it. As far as the comparison of the catalyst performance is concerned, we agree with the reviewer that according to table ESI 1( Now Table ESI 2), Co3O4 catalyst is showing the third best T90 after 219 (Cu-Co3O4) and that MgCo2O4 is showing T90 after 230 (Pd/Co3AlO) and the second best T100 after 340 (Co3O4 from literature). However, the reviewer has limited and just focus his comparison on T90 for both Co3O4 and MgCo2O4. He did not taken into consideration another important (if not one of the most ) parameters of comparison that is the weight of catalyst which were the small (0.06 g) as now corrected presented in the experimental section although a mistake was made on the Table ES12 were the weight of catalyst was 0.06 g instead of 0.2 gas mentioned in the submitted version of the ESI2. In addition, the as-prepared catalyst (MgCo2O4) are a composed of available and environmentally friendly earth metal (Mg) and Transition metal (Co) compared for example to expensive, less available supported noble metal catalyst (Pd/Co3AlO). More importantly, MgCo2O4 was synthesized by a facile, inexpensive and easily replicatable coprecipitation method.
Main reasons:
C1) The introduction section does not provide the current state-of-the-art and your contribution beyond it. The novelty of your research is not highlighted at all.
A1: We thank the reviewer for this interesting and important point of our manuscript. In this study, as far as the current state-of-art of our manuscript is concerned, we have cited in the second paragraph of the manuscript more than 20 references existing in literature on the catalytic performance of many Co-based transition mixed oxides (TMOs) over volatile organic compounds. In the second paragraph we have clearly provided technic such as partial substitution of Co by other metals to improve catalytic activity of pure Co3O4 catalyst. TMOs and rare earth were clearly identified with appropriate references including our previous work published in Catal. Sci. Technol and Appl. Catal. A Gen. As for the novelty the present investigation is on the best of our knowledge the first report on the enhancement of Co3O4 by partial substitution of Co2+ with small amount of an alkali earth metal (Mg) toward the low temperature deep oxidation of toluene. More importantly, the mixed catalyst MgCo2O4 was fabricated by a simple and inexpensive coprecipitation method that can be replicated easily.
C2) You haven't determined the catalytic stability of Co3O4 and MgO even though you prepared them. You not even get this characteristic from literature.
A2: We thank for the reviewer for his/her comment. The determination of the catalytic stability of Co3O4 as well as MgO is out of the scope of this investigation. In fact, Co3O4 is well known as one of the most active and stable TMOs. The main objective was to improve the catalytic performance of pure Co3O4 by modifying his matrix with an environmentally friendly metal Mg. Thus, our catalyst target in this study was MgCo2O4. As for MgO because of poor catalytic activity they were no reasons the perform his catalytic stability.
small issues:
C1): You haven't provided the provenance of the chemicals you used within your work
A1) Thanks for the reviewer’s comment, we have provided the provenance of the chemicals as following:
…. All chemicals were provided by Sigma-Aldrich Pty Ltd, Germany. For MgO and Co3O4………
C2): You haven't ptovide justification for one of your actions. (e.g.: why you treated 60 mg of sample in Ar from room temperature to 400 )
A2) According to the reviewer’s comment, we have justified the catalyst annealing at 400 oC as follows.
……..TCD detector. As annealing facilitates the formation of catalysts possessing the largest surface area and reducibility, prior to the test, 60 mg………….
We hope that our manuscript is now suitable for publication in Catalysts
Sincerely yours
Reviewer 2 Report
This is an interesting investigation on the application of a MgCo2O4 binary oxide catalyst for deep oxidation of toluene at lower temperatures. The designed combination catalyst was found to exhibit better catalytic performance than its component oxides namely, MgO and Co3O4. As revealed by various characterization techniques, the insertion of MgO into the Co3O4 matrix plays a key role in controlling the physicochemical and catalytic properties. Most importantly, the combination catalyst was prepared by a simple and inexpensive coprecipitation method that can be replicated easily. The quality of data presented is worthy of publication. The interpretation of the results is lucid. In view of the significance of subject addressed and simplicity of the catalyst designed, I recommend this article for publication in the journal. However, needs substantial improvement in the English language usage before acceptance.
Author Response
Reviewer #2:
Reviewer General comment:
This is an interesting investigation on the application of a MgCo2O4 binary oxide catalyst for deep oxidation of toluene at lower temperatures. The designed combination catalyst was found to exhibit better catalytic performance than its component oxides namely, MgO and Co3O4. As revealed by various characterization techniques, the insertion of MgO into the Co3O4 matrix plays a key role in controlling the physicochemical and catalytic properties. Most importantly, the combination catalyst was prepared by a simple and inexpensive coprecipitation method that can be replicated easily. The quality of data presented is worthy of publication. The interpretation of the results is lucid. In view of the significance of subject addressed and simplicity of the catalyst designed, I recommend this article for publication in the journal. However, needs substantial improvement in the English language usage before acceptance.
Reply: First of all, we thank the reviewer for his/her favorable comments on the manuscript. In the revised manuscript, as recommended by the reviewer, we have carefully checked and corrected errors in order to improve the English language usage (see related changes highlighted in the revised manuscript).
We hope that our manuscript is now suitable for publication in Catalysts
Sincerely yours
Reviewer 3 Report
Comments are attached as a file.
Comments for author File: 
Comments.pdf
Author Response
Please see the document attached
Author Response File: Author Response.pdf
Reviewer 4 Report
The scientific concept of the paper is good. This study is interesting to be published; the manuscript adds important information to the existing literature. However, the manuscript needs some minor revision before considered for publishing:
* Page 3: L 102-103: What do you mean by "to remove any impurities"?; degassing is used to evacuate water and CO2 molecules.
* The authors need to explain how the accuracy and precision of experiments and measurements were assessed. How many samples were done for the determination of the concentration of toluene.
Author Response
Reviewer #4:
Reviewer General comment:
The scientific concept of the paper is good. This study is interesting to be published; the manuscript adds important information to the existing literature. However, the manuscript needs some minor revision before considered for publishing:
Reply: We thank the reviewer for his/her favorable comments on the manuscript. In the revised manuscript, as recommended by the reviewer, we have carefully checked and corrected errors in order to improve the quality of our manuscript.
Minor revision concern
C1: Page 3: L 102-103: What do you mean by "to remove any impurities"?; degassing is used to evacuate water and CO2 molecules.
A1: We thank the reviewer for this important remarque. We have replaced "to remove any impurities" by “to evacuate water and CO2 molecules” in the revised version
C2: The authors need to explain how the accuracy and precision of experiments and measurements were assessed. How many samples were done for the determination of the concentration of toluene.
A2: Measurement errors can be divided into two components: random error and systematic error. A random error is related to the precision of the instrument. These are inherent errors that are dependent on the instrument and can not be eliminated without changing the instrument. A systematic error is human error. These are errors related to imperfect experimental technique. Some examples include errors in experimental readings and imperfect instrument calibration. Systematic errors may be decreased as the laboratory techniques of the analyst improve. The accuracy of an experimental value is best determined by the average value of multiple measurements where xi represents a measurement and n is the number of measurements.
In this investigation, we have used several instruments for the analysis which can be responsible of random error, therefore since such error are not dependant on us, we have performed such analysis three times to make sure the spectra obtained are inconsistence.
As an example, XRD, XPS, SEM/EDS, H2-TPR, as well as the light-off curves of toluene total oxidation were recorded three times and compared.
As for the systematic error which are inherent to human during synthesis step, we have prepared for each sample three liquid feedstock in order to prepare three sample. After we have performed the XRD analysis the obtained the same spectrum.
We hope that our manuscript is now suitable for publication in Catalysts
Sincerely yours
Round 2
Reviewer 1 Report
Dear authors,
I have revised again your manuscript, and, unfortunatly, I stick to my first opinion that the paper is not suitable to be published in Catalysts.
Even though you have adressed most of my comments and suggestions, you haven't adressed the most important one: the comparison of catalytic activity of the prepred catalysts: Co3O4, MgCo2O4 and MgO.
You said: "In fact, Co3O4 is well known as one of the most active and stable TMOs. The main objective was to improve the catalytic performance of pure Co3O4 by modifying his matrix with an environmentally friendly metal Mg. Thus, our catalyst target in this study was MgCo2O4. As for MgO because of poor catalytic activity they were no reasons the perform his catalytic stability.", then why you even prepared and structurally characterized them in the firs place? I reffer to Co3O4 and MgO.
The fact that you have mistaken and written within the initial table ESI 1 wrong and different amounts for catalysts, doesn't mean I have misread the values. If you want a fair comparison between different catalysts, then you must use the same quantities, and the same experimental parameters.
Moreover, the paper does not clearly show the novelty of the work.
Author Response
Reviewer #1:
Reviewer recommendation: I have revised again your manuscript, and, unfortunatly, I stick to my first opinion that the paper is not suitable to be published in Catalysts.
Reply: First of all, we thank the reviewer for his/her unfavorable opinion on the manuscript. Our responses to his/her reasons of rejection are therefore addressed one by one as following.
C1: Even though you have adressed most of my comments and suggestions, you haven't adressed the most important one: the comparison of catalytic activity of the prepred catalysts: Co3O4, MgCo2O4 and MgO.
You said: "In fact, Co3O4 is well known as one of the most active and stable TMOs. The main objective was to improve the catalytic performance of pure Co3O4 by modifying his matrix with an environmentally friendly metal Mg. Thus, our catalyst target in this study was MgCo2O4. As for MgO because of poor catalytic activity they were no reasons the perform his catalytic stability.", then why you even prepared and structurally characterized them in the firs place? I reffer to Co3O4 and MgO.
A1: We thank the reviewer for his/her comment. If we have well understood the reviewer, since our target catalyst is MgCo2O4, it was not useful to synthesised and comprehensibly characterize single Co3O4 and MgO. We are sorry but we insist that it was important to synthesised and characterized those single oxides and also test their performance for many reasons:
- MgCo2O4 is a mixed or binary oxide made of Mg and Co, therefore it was important for us to start from single Co3O4 and MgO before achieving MgCo2O4.
- To attest of the better performance of MgCo2O4 toward toluene total oxidation, it was important to compared the results with that of Co3O4 prepared at the same condition and by the same synthesis approach.
- MgO has not been reported as catalyst towards VOCs total oxidation, although the catalytic test was not satisfactory, it is useful for the scientific community to be aware of the ineffectiveness of MgO as catalyst.
C2: The fact that you have mistaken and written within the initial table ESI 1 wrong and different amounts for catalysts, doesn't mean I have misread the values. If you want a fair comparison between different catalysts, then you must use the same quantities, and the same experimental parameters.
Moreover, the paper does not clearly show the novelty of the work.
A2: We thank the reviewer for his/her comment. We agree with the reviewer that for a fair comparison between different catalysts, the same quantities, and the same experimental parameters should have been used. But in this investigation, we have based our comparison on three parameters: catalyst weight, toluene concentration and the WHSV. Compared with other catalysts from the literature we have used less amount of catalyst (some things to our disadvantage) and the same WHSV. However, our catalyst exhibits good performance.
We can understand that our work is not interesting to the reviewer. But his/her requirements are out of the scope of this work.
We hope that our manuscript is now suitable for publication in Catalysts
Sincerely yours
Reviewer 3 Report
The suggestions/comments are appropriately addressed.
Author Response
Reviewer #3:
Reviewer Comments and Suggestion
The suggestions/comments are appropriately addressed.
Reply: We are very grateful to the reviewer for his/her favorable opinion on our manuscript.
We have double checked minor orthographic and grammatical errors and hope that our manuscript is now suitable for publication in Catalysts
Sincerely yours
