Acid-Modified Sepiolite-Supported Pt (Noble Metal) Catalysts for HCHO Oxidation at Ambient Temperature
, Minghao Fang 1 and Zhaohui Huang 1Round 1
Reviewer 1 Report
The article presents a straightforward language that facilitates the review, however some details and specific issues need to be better presented or discussed by the authors, as described below:
2. Materials and methods
a) in line 94: authors should describe the type of sensor used for HCHO quantification in the catalytic test, including detection range, accuracy, etc.
3. Results and discussion
In item 3.1: Textural properties
b) In Table 1, what does the term C(B/M) mean? This needs to be reported in the text.
c) in Table 1 the values of Average pore diameter, as well as the area found relative to the micro and mesopores in the structure must be presented. The effect of these properties, when possible, should be discussed in the article text.
In item 3.4: HCHO catalytic oxidation
3.4.1: The influence of PT loading
d) Authors must present the actual levels of Pt incorporated into the Sep catalyst after treatment with chloroplatinic acid solution. The results obtained must be explained and related to the catalytic activity of the materials for the oxidation of HCHO. This is very important for understanding the catalytic results.
e) In Figure 8, the authors should explain the meaning of the values of 10, 20, 30, 40, 50 and 60. Do they correspond to concentrations of 0.01 M to 0.06 M of chloroplatinic acid solution? This relationship needs to be clarified!
f) General considerations: As in the Catalyst oxidation mechanism item, the authors must present other references to works in the literature related to the studies of: Effect of Pt loading and Effect of calcination temperature on HCHO conversion.
Author Response
Response to Editor and Reviewer
Dear Reviewer:
Thank you very much for giving us an opportunity to revise our manuscript, we appreciate reviewer very much for your positive and constructive comments and suggestions on our manuscript entitled “Acid-modified sepiolite-supported Pt (noble metal) catalysts for HCHO oxidation at ambient temperature” (catalysts-1945315). Those comments are valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
Point 1: In line 94: authors should describe the type of sensor used for HCHO quantification in the catalytic test, including detection range, accuracy, etc.
Responses 1: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. After re-reading, we found that the description of sensor used for HCHO quantification was not clear enough, so we have added content as following:
The constant signals on the attached detector (PN-2000-CH2O; Range: 0-500 ppm; Accuracy: 0.1 ppm) shows the complete and even dispersion of HCHO in the airtight chamber and the connecting rods of the lid helps to evenly expose the Pt/Sep in HCHO gas.
Point 2: In Table 1, what does the term C(B/M) mean? This needs to be reported in the text.
Responses 2: Thank you very much for your suggestion. The term C(B)/M means the concentration of HCl. C represents the concentration, B represents the substance HCl, and M represents the unit of concentration. I think it might be clear to use the term C(HCl)/mol L-1.
|
C(HCl)/mol L-1 |
0 |
0.04 |
0.06 |
0.08 |
|
Specific Surface Area (m2/g) |
13.065 |
24.853 |
25.581 |
23.374 |
|
Pore Volume (cm3/g) |
0.016 |
0.040 |
0.040 |
0.039 |
Point 3: In Table 1 the values of Average pore diameter, as well as the area found relative to the micro and mesopores in the structure must be presented. The effect of these properties, when possible, should be discussed in the article text.
Responses 3: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. The maximum pore size can better reflect the pore size and distribution of the sample, and the average pore size is calculated from the adsorption capacity and specific surface area, which can not reflect the real pore distribution of the reaction material. So the average pore size is not listed in the table. Instead, the maximum pore size is more illustrative, so I analyzed the maximum pore size in the main text. The specific surface area of micropores and mesopores is 3.9 and 16.8 m2/g, respectively.
Point 4: Authors must present the actual levels of Pt incorporated into the Sep catalyst after treatment with chloroplatinic acid solution. The results obtained must be explained and related to the catalytic activity of the materials for the oxidation of HCHO. This is very important for understanding the catalytic results.
Responses 4: Thank you for pointing out this problem. I have stated the actual levels of Pt loading of the optimal catalyst in the conclusion.
Point 5: In Figure 8, the authors should explain the meaning of the values of 10, 20, 30, 40, 50 and 60. Do they correspond to concentrations of 0.01 M to 0.06 M of chloroplatinic acid solution? This relationship needs to be clarified!
Responses 5: Thanks very much for your kind suggestion. The accurate explaination will make the content clearer and make it easier for readers to read. Therefore, we have explained the meaning of the values of 10, 20, 30, 40, 50 and 60. The corresponding changes have been marked in red in the article, and the changes are as follows:
The catalytic oxidation of HCHO by the Pt/Sep catalysts with different Pt loadings at ambient temperature is shown in Fig. 8(The values of 10, 20, 30, 40, 50 and 60 correspond to concentrations of 0.01 M to 0.06 M of chloroplatinic acid solution.).
Point 6: General considerations: As in the Catalyst oxidation mechanism item, the authors must present other references to works in the literature related to the studies of: Effect of Pt loading and Effect of calcination temperature on HCHO conversion.
Responses 6: Thank you very much for your great efforts on our manuscript. We have added relevant references to the revised manuscript, which are ref 39, 40. Thank you for all of your help.
Reviewer 2 Report
Review (reject):
The article “Acid-modified sepiolite-supported Pt (noble metal) catalysts 2 for HCHO oxidation at ambient temperature” by Zhou et al., discusses the oxidation of HCHO over a sepiolite supported platinum catalyst. As a general observation, the English in the present manuscript needs improvement.
Introduction
The introduction part describes the topics of the manuscript well. Some improvements in English are necessary.
Materials and methods
The Materials and methods part should be extended. The experiments/characterizations should be described more in depth. For instance:
· “Later, the samples were separated, washed and dried in an oven at 75°C for 12h.” Separated from what? Washed with what (water, ethanol, acetone)?
· “…stirred at room temperature for 1h in chlo-proplatinic acid solution for the purpose of vacuum impregnation.” What solvent? What concentration? Beaker or flask? How was the vacuum made?
Results and discussion
1. The BET specific surface area is determined between relative pressures of about 0.1 to 0.3. The isotherm for sepiolite in this range exhibits a negative slope. This would indicate an experimental error. How was the surface area calculated?
2. There is an obvious diffraction peak located at approximately 56° 2 Theta in the sample 0.04Pt/Sep in Figure 3b. What is the authors discussion about that?
3. In Figure 4 what is Sep and what is sepiolite? If Sep is the acid modified sepiolite, why did acid treatment introduce hydroxyls on the surface?
4. Why did the Pt nanoparticles not reduce at 500 °C and in H2? The peak broadening can also be the result of sample charging. If the particles have an average diameter of 3 nm they should surely reduce at 500 °C.
5. From the fit of the spectra in Figure 6b it looks like the peak at 531.86 does not fit the experimental data. What was the reduced chi squared in both fits? This part should be repeated.
6. Where is the size distribution of the nanoparticles shown? How many particles were included in the calculation of the average particle size?
7. Why does the lattice of Pt contract and then expand with growing particle size?
8. If agglomeration is the mayor issue for the activity of the higher loaded samples, why does the 60 sample outperform the 30 – 50 samples? Were the experiment repeated several times? What is the relative error between the repeated experiments?
9. Why is 400 °C not enough for Pt reduction? Was H2-TPR performed? Most of the literature states Pt reduces below 400 °C.
10. In DRIFTS the authors indicate that surface hydroxyls are essential for good reactivity, however, they are not included in the reaction mechanism. How would these facilitate the adsorption of HCHO?
Conclusion
The conclusion part is written well, only the English has to be revised somewhat.
Author Response
Response to Editor and Reviewer
Dear Reviewer:
Thank you very much for giving us an opportunity to revise our manuscript, we appreciate reviewer very much for your positive and constructive comments and suggestions on our manuscript entitled “Acid-modified sepiolite-supported Pt (noble metal) catalysts for HCHO oxidation at ambient temperature” (catalysts-1945315). Those comments are valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
Point 1: The BET specific surface area is determined between relative pressures of about 0.1 to 0.3. The isotherm for sepiolite in this range exhibits a negative slope. This would indicate an experimental error. How was the surface area calculated?
Responses 1: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. I think the reason for the negative slope is that the actual pressure is higher than pressure calculated by the computer due to the change of pressure in the tube during the test, resulting in the negative slope. The specific surface area was measured by Multi-Point BET.
Point 2: There is an obvious diffraction peak located at approximately 56° 2 Theta in the sample 0.04Pt/Sep in Figure 3b. What is the authors discussion about that?
Responses 2: Thank you very much for your suggestion. The peaks at 56° is ascribed to CaCO3. To prevent the structure of the sepiolite from being destroyed, I used a small concentration of acid, so the impurities may not have been completely removed
Point 3: In Figure 4 what is Sep and what is sepiolite? If Sep is the acid modified sepiolite, why did acid treatment introduce hydroxyls on the surface?
Responses 3: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. Sep stands for acid-modified sepiolite and sepiolite stands for untreated sepiolite. I didn't express it quite correctly, what I wanted to express was that the peak at 3442 cm-1 was attributed to OH, not hydroxyls. and the changes are as follows:
The peaks after acid treatment are found at 1661 and 3442 cm-1 that are ascribed to δ (H2O) and stretching vibration absorption peak of OH, respectively.
Point 4: Why did the Pt nanoparticles not reduce at 500 °C and in H2? The peak broadening can also be the result of sample charging. If the particles have an average diameter of 3 nm they should surely reduce at 500 °C
Responses 4: Thank you for pointing out this problem. I agree with what you said, and I think that the characteristic diffraction peak of Pt was not observed in the XRD pattern due to its high degree of dispersion.
Point 5: From the fit of the spectra in Figure 6b it looks like the peak at 531.86 does not fit the experimental data. What was the reduced chi squared in both fits? This part should be repeated.
Responses 5: Thanks very much for your kind suggestion. We have added experimental data, and the changes are as follows:
The binding energy of O-1s in 0.02Pt/Sep sample is shifted lower relative (531.86 eV) to Sep (Fig. 6(b)). The reduced peak area was 28%.
Point 6: Where is the size distribution of the nanoparticles shown? How many particles were included in the calculation of the average particle size?
Responses 6: Thank you very much for your great efforts on our manuscript. We have added the size distribution of the nanoparticles to the revised manuscript. I counted the particle size of 50 particles.
Point 7: Why does the lattice of Pt contract and then expand with growing particle size?
Responses 7: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. The lattice space of Pt is 0.232nm. The lattice space measured manually is probably normal within a certain error range, which does not indicate that there is some relationship between lattice space and particle size.
Point 8: If agglomeration is the mayor issue for the activity of the higher loaded samples, why does the 60 sample outperform the 30 – 50 samples? Were the experiment repeated several times? What is the relative error between the repeated experiments?
Responses 8: Thank you for pointing out this problem. It is speculated that the HCHO oxidation efficiency of the catalyst is related to the load, particle size and dispersion. When the load exceeds a certain amount, the catalytic effect of the catalyst is mainly affected by the loading of Pt.
Point 9: Why is 400 °C not enough for Pt reduction? Was H2-TPR performed? Most of the literature states Pt reduces below 400 °C.
Responses 9: Thank you very much for your great efforts on our manuscript. The temperature of 400 °C is enough for Pt reduction, but the calcination temperature of 400 °C is not optimal for this type of catalyst. We made same revision in manuscript, and the changes are as follows:
The Suitable temperature is beneficial to the reduction of platinum precursor and the improvement of the catalytic performance of the catalyst.
Point 10: In DRIFTS the authors indicate that surface hydroxyls are essential for good reactivity, however, they are not included in the reaction mechanism. How would these facilitate the adsorption of HCHO?
Responses 10: Thanks very much for your kind suggestion. In the reaction mechanism, the formaldehyde shown in the first figure has been adsorbed to the catalyst surface by the hydroxyl group.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
Recommendation: Minor revision
Comments:
In the manuscript entitled "Acid-modified sepiolite-supported Pt (noble metal) catalysts for HCHO oxidation at ambient temperature", X. Min et. al., reported sepiolite supported Pt-catalysts for the removal of formaldehyde through catalysis. The results are convinced enough to support their point of view. There are some minor issues that the authors need to be considered while submitting the revised version. Thus, I recommend this manuscript for publication in this esteemed journal after following modifications:
1. The title “Pt (noble metal)” needs to be modified. I would suggest to avoid any bracket in the title. Also, the author can use another word directly instead of ‘noble metal’ in the title.
2. Abstract: a. The author can rewrite this sentence without bracket ‘(by impurities)’. b. No full stop (.) in line no. 22 ‘transmission electron microscopy The results showed’. c. In line no. 23, the author needs to explain somewhere about the abbreviation used for the phrase ‘the 0.02Pt/Sep catalyst’. Also, one space is missing in between ‘the number 0.02 and Pt’.
3. Introduction: a. The English language can be polished wherever needed e.g. line no 59 ‘in dye removal wastewater’. b. Space needed in the line no. 50 ‘by supporting materials25such as silica (SiO2)’.
4. Results and Discussion:
a. The space between the unit and number is not consistence. Like: ‘0.06M HCl’ should be ‘0.06 M HCl’.
b. The author should insert a reference corresponding to the observation ‘2θ = 18.1°, 28.7° and 34.1° corresponding to Ca(OH)2’ at line no. 130.
c. Need a reference for line no. 154 i.e., ‘new peak at 153 2967 cm-1 is ascribed to the formate (CHO2-) species’.
d. The author should explain the major peak around 1400 cm-1 in Figure 4.
e. The author needs to put some specific references for high-resolution XPS spectra of Pt 4f.
f. Line no. 204: the sentence should be rewritten ‘The oxidation rate by the 0.02Pt/Sep sample calcined at 500°C could reach 52%, which is evidently higher than the catalysts calcined at 400, 600 205 and 700 degrees Celsius temperatures.’
g. Oxidation mechanism illustration can be simplified.
5. General suggestion: it can be observed throughout the manuscript that there are some missing spaces between numbers and units. A similar thing can also be observed in the figures.
Author Response
Response to Editor and Reviewer
Dear Reviewer:
Thank you very much for giving us an opportunity to revise our manuscript, we appreciate reviewer very much for your positive and constructive comments and suggestions on our manuscript entitled “Acid-modified sepiolite-supported Pt (noble metal) catalysts for HCHO oxidation at ambient temperature” (catalysts-1945315). Those comments are valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
Point 1: The space between the unit and number is not consistence. Like: ‘0.06M HCl’ should be ‘0.06 M HCl’.
Responses 1: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. I have made the modification as you said. And the changes are as follows:
Sepiolite modified by 0.06 M HCl (noted as Sep) gives off the largest specific surface area and been chosen fr subsequent studies.
Point 2: The author should insert a reference corresponding to the observation ‘2θ = 18.1°, 28.7° and 34.1° corresponding to Ca(OH)2’ at line no. 130.
Responses 2: Thank you very much for your suggestion. We have added relevant references to the revised manuscript, which are ref 35. Thank you for all of your help.
Point 3: Need a reference for line no. 154 i.e., ‘new peak at 153 2967 cm-1 is ascribed to the formate (CHO2-) species’.
Responses 3: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. We have added relevant references to the revised manuscript, which are ref 36. Thank you for all of your help.
Point 4: The author should explain the major peak around 1400 cm-1 in Figure 41.
Responses 4: Thank you for pointing out this problem. The peaks are found at 1425 is ascribed to (O-H).
Point 5: The author needs to put some specific references for high-resolution XPS spectra of Pt 4f.
Responses 5: Thanks very much for your kind suggestion. We have added relevant references to the revised manuscript, which are ref 37. Thank you for all of your help.
Point 6: Line no. 204: the sentence should be rewritten ‘The oxidation rate by the 0.02Pt/Sep sample calcined at 500°C could reach 52%, which is evidently higher than the catalysts calcined at 400, 600 205 and 700 degrees Celsius temperatures’.
Responses 6: Thank you very much for your great efforts on our manuscript. I will revise it according to your suggestion. And the changes are as follows:
Among the catalysts calcined at 400, 500, 600 and 700 degrees, the catalyst calcined at 500 degrees has the best performance and the formaldehyde degradation rate is 52%
Point 7: Oxidation mechanism illustration can be simplified.
Responses 7: Thanks very much for your kind suggestion. We have simplified the oxidation mechanism illustration. And the changes are as follows:
Firstly, HCHO, H2O and O2 are adsorbed onto the 0.02Pt/Sep. And O2 is excited by Pt nanoparticles to oxygen radicals. Later, the oxygen radicals oxidize HCHO and H2O to dioxymethylene (DOM) and OH- ions, respectively. DOM reacts with -OH to create formate species, Which further reacts with OH- to form CO2 and H2O. The OH- ions on the sepiolite surface are conductive to adsorption of HCHO throughout the mechanism. The catalyst wettability plays a critical role for the desorption and transfer of water2, by the current water forming reaction:
Therefore, the physical and chemical properties of sepiolite support and enhance the catalytic oxidation of HCHO.
- Y. Sarıkaya, N. D. Kahya, A. D. Pekdemir and M. Önal, CLAY MINERALS, 2021, 55, 375-382.
Round 2
Reviewer 2 Report
Unfortunately, the authors did not answer most of my questions in any relevant way. Some answers, such as the ones referring to BET, XPS, and catalytic results are paramount to this work. A negative slope in BET would result in a negative area, regardless of the multi-point method used. The fit data for the XPS should also be reported. Therefore, I cannot agree with the publication of this manuscript.
Author Response
Dear Reviewer:
Thank you very much for giving us an opportunity to revise our manuscript, we appreciate reviewer very much for your positive and constructive comments and suggestions on our manuscript entitled “Acid-modified sepiolite-supported Pt (noble metal) catalysts for HCHO oxidation at ambient temperature” (catalysts-1945315). Those comments are valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
Point 1: The BET specific surface area is determined between relative pressures of about 0.1 to 0.3. The isotherm for sepiolite in this range exhibits a negative slope. This would indicate an experimental error. How was the surface area calculated?
Responses 1: Thank you for pointing out this problem. In order to eliminate the influence of experimental error, the test was done again, and the result showed that there was no negative slope. The specific surface area was calculated by BET model based on nitrogen molecule as the adsorption medium. The remeasured specific surface area has been corrected in the table 1.
Point 2: There is an obvious diffraction peak located at approximately 56° 2 Theta in the sample 0.04Pt/Sep in Figure 3b. What is the authors discussion about that?
Responses 2: Thank you for pointing out this problem. The obvious diffraction peak located at approximately 56° 2 Theta may be the sample was not ground fully befor testing, which results large particles during samples preparation, resulting in an obvious diffraction peak. After fully grinding the sample, I re-conducted XRD test, and the test results are shown in Figure 3.
Point 3: In Figure 4 what is Sep and what is sepiolite? If Sep is the acid modified sepiolite, why did acid treatment introduce hydroxyls on the surface?
Responses 3: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. Sep stands for acid-modified sepiolite and sepiolite stands for untreated sepiolite. The acid modified might caused the sepiolite fibers to peel away from each other, thus exposing some hydroxyl group, but because the acid concentration was small, the hydroxyl group was retained.
Point 4: Why did the Pt nanoparticles not reduce at 500 °C and in H2? The peak broadening can also be the result of sample charging. If the particles have an average diameter of 3 nm they should surely reduce at 500 °C
Responses 4: Thank you for pointing out this problem. Fig. 5 shows that the sample has Pt0 under heat treatment at 500 °C. As shown in Figure 7e, also proved the existence of Pt particles, indicating that Pt could be reduced at 500℃.
Point 5: From the fit of the spectra in Figure 6b it looks like the peak at 531.86 does not fit the experimental data. What was the reduced chi squared in both fits? This part should be repeated.
Responses 5: Thanks very much for your kind suggestion. We have added experimental data, and the changes are as follows:
The binding energy of O-1s in 0.02Pt/Sep sample is shifted lower relative (531.86 eV) to Sep (Fig. 6(b)). The reduced peak area was 28%.
Point 6: Where is the size distribution of the nanoparticles shown? How many particles were included in the calculation of the average particle size?
Responses 6: Thank you very much for your great efforts on our manuscript. We have added the size distribution of the nanoparticles to the revised manuscript. We counted the particle size of 50 particles.
Point 7: Why does the lattice of Pt contract and then expand with growing particle size?
Responses 7: We are grateful for your valuable comments and suggestions which help improve the quality of the paper. The lattice space of Pt is 0.232nm. The lattice space measured manually is probably normal within a certain error range, which does not indicate that there is some relationship between lattice space and particle size.
Point 8: If agglomeration is the mayor issue for the activity of the higher loaded samples, why does the 60 sample outperform the 30 – 50 samples? Were the experiment repeated several times? What is the relative error between the repeated experiments?
Responses 8: Thank you for pointing out this problem. It is speculated that the HCHO oxidation efficiency of the catalyst is related to the load, particle size and dispersion. When the load exceeds a certain amount, the catalytic effect of the catalyst is mainly affected by the loading of Pt.
Point 9: Why is 400 °C not enough for Pt reduction? Was H2-TPR performed? Most of the literature states Pt reduces below 400 °C.
Responses 9: Thank you very much for your great efforts on our manuscript. The temperature of 400 °C is enough for Pt reduction, but the calcination temperature of 400 °C is not optimal for this type of catalyst. We made same revision in manuscript, and the changes are as follows:
The Suitable temperature is beneficial to the reduction of platinum precursor and the improvement of the catalytic performance of the catalyst.
Point 10: In DRIFTS the authors indicate that surface hydroxyls are essential for good reactivity, however, they are not included in the reaction mechanism. How would these facilitate the adsorption of HCHO?
Responses 10: Thanks very much for your kind suggestion. I added adsorption process of formaldehyde by hydroxyl group to the reaction mechanism. There is hydrogen-bond between HCHO and hydroxyl group, which can facilitate the adsorption of HCHO. I have made some additions to the manuscript and the corresponding changes are as follows:
Because there is hydrogen-bond between HCHO and hydroxyl group, which can facilitate the adsorption of HCHO. Thus, the oxidation procession is accelerated.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
The authors sufficiently answered all my questions.
