Recent Advances in Formaldehyde Catalytic Oxidation Catalysts

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

“Recent advances in formaldehyde catalytic oxidation catalysts” is an important review describing many aspects of catalytic oxidation of formaldehyde: several types of catalysts for the formaldehyde total oxidation, effect of reaction conditions on the oxidation process, and, finally, the mechanisms that can be realized on different types of catalysts. Information given in this review is very useful and complete. However, the text of the review contains many errors and omissions. Here are only the main comments.

1. Lines 96-98. The sentence needs to be continued.
2. Lines 110-111. Why does “excellent thermal stability” of support lead to low-temperature HCHO conversion?
3. Line 115. To remove word “carrier”.
4. Lines 119-124. The sentence needs to be revised.
5. Table 1. Several abbreviations (rGO, USY, DZ200, etc need to be clarified. Is RH – relative humidity?
6. Line 136. Researchers’ findings.
7. Lines 137-143. Apparently, further clarification of the results from [83] is needed, i.e., a brief comparison of the catalytic properties with the results shown in these Figures 2.
8. Line 150. To remove: it increased from. There instead of there.
9. Line 174. What means P123-assisted?
10. Line 175. If in [85] Pt-Vo-ZrO2 is used to label the catalyst and Vo to label the oxygen vacancies, then in the present manuscript it is probably better to use the same label.
11. Line 191. from Figure 7d.
12. Line 215. Intervals.
13. Line 230 and other lines. Every were to put point after al. Additionally: What means USY?
14. Line 235. What does “improved Pd particle size” mean. Clarification is needed.
15. Line 253. How much metal was present at the “ultra-low” content?
16. Lines 278-284. Description of Figure 14 needs to be improved and clarified.
17. Table 2. Abbreviations in this Table need to be clarified. Especially in Catalysts column.
18. Figure 15. An explanation is needed of what dynamic and static tests mean.
19. Figure 16. The significant difference in the catalytic properties of MnOx catalysts depending on their processing conditions (Figure 16b) requires some details about the preparation of the catalysts: what is the difference between MnO₂-KL and MnOx-S-A?
20. Line 359. Shown.
21. Figure 18. Here is necessary to clarify abbreviations CeO₂-C and CeO₂-R.
22. Line 426. Abbreviations Ti-NS and Ti-NP need to be clarified.
23. Line 429. This sentence has to be revised.
24. Line 433. What means DOM?
25. Effect of preparation method. Reference [120] has to be included in this part too. Line 482. What it means: lattice oxygen reduction on the catalyst surface? Line 494. As the lowest 2.31?
26. Three articles (references [110], [111] and [122] ) are included in full in this part of  the review. The information is interesting and important, but its presentation could be shortened.
27. Lines 621-622. As follows from the above description, activity "increases with the increase in humidity" only within a certain range.
28. Lines 654-661. The sentence needs revision.
29. Line 777. There is an error here. According to the title of the article [133], the catalyst is a mixed oxide catalyst MnOx-decorated anatase TiO₂ {001}.
30. References. Need to add “doi” in the list.

 

  

Author Response

Reviewer #1:

Q1. Lines 96-98. The sentence needs to be continued.

Answer: Thank you for your suggestion. The author has improved his expression. “Due to the sintering and oxidation of precious metals, they are usually loaded on certain oxide carriers with excellent thermal stability, which makes HCHO easy to convert at low temperatures.”

Q2. Lines 110-111. Why does “excellent thermal stability” of support lead to low-temperature HCHO conversion?

Answer: The meaning of this sentence is that the noble metal loaded onto the carrier with excellent thermal stability can make formaldehyde easier to convert, rather than having a low conversion rate.

Q3. Line 115. To remove word “carrier”.

Answer: Thank you for your suggestion. The author has removed the term "carrier".

Q4. Lines 119-124. The sentence needs to be revised.

Answer: Thank you for your suggestion. The author has revised this sentence.

Q5. Table 1. Several abbreviations (rGO, USY, DZ200, etc need to be clarified. Is RH – relative humidity?

Answer: Thank you for your suggestion. The author has added the abbreviation. rGO stands for reduced Graphene Oxide, USY stands for Ultra-Stable Y zeolite, Meso-ZSM-5 stands for mesopore-modified zeolite, AC stands for activated carbon, DZ200 stands for desilicated zeolite.

Q6. Line 136. Researchers’ findings.

Answer: The author has stated the findings of the researchers in the text.

Q7. Lines 137-143. Apparently, further clarification of the results from [83] is needed, i.e., a brief comparison of the catalytic properties with the results shown in these Figures 2.

Answer: Thank you for your suggestion. The author has revised this part. As show in figure 3, after pretreatment of the SiO₂ support with H₂ reduction, HNO₃, or NH₃×H₂O solution, the catalytic performance of all Pd/SiO₂ catalysts in formaldehyde oxidation was significantly enhanced. Specifically, the removal efficiencies were 4% for Pd/SiO₂-R, 59% for Pd/SiO₂(HNO₃)-R, 94% for Pd/SiO₂(NH3·H₂O)-R, and 100% for Pd/SiO₂(H₂)-R. Among them, Pd/SiO₂(H₂)-R demonstrated the highest activity for HCHO oxidation.

 

Q8. Line 150. To remove: it increased from. There instead of there.

Answer: Thank you for your suggestion. Following your suggestion, the author has removed this part.

Q9. Line 174. What means P123-assisted?

Answer: Thank you for your inspiring question. The author has provided additional explanations. P123 is the abbreviation of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (PEO20-PPO70-PEO20), which is a nonionic surfactant commonly used as a template for the synthesis of mesoporous molecular sieves (such as SBA-15).

Q10. Line 175. If in [85] Pt-Vo-ZrO2 is used to label the catalyst and Vo to label the oxygen vacancies, then in the present manuscript it is probably better to use the same label.

Answer: Thank you for your suggestion. The author has unified the use of Vo for oxygen vacancies throughout the entire text.

Q11. Line 191. from Figure 7d.

Answer: Thank you for your suggestion. The author has changed, “from figure 7d”

Q12. Line 215. Intervals.

Answer: Thank you for your suggestion. The author has revised the interval, “Figure 9b, 9c, 9d, 9e”

Q13. Line 230 and other lines. Every were to put point after al. Additionally: What means USY?

Answer: Thank you for your suggestion. The author has revised and the meaning of USY has been explained. Li et al.

Q14. Line 235. What does “improved Pd particle size” mean. Clarification is needed.

Answer: Thank you for your suggestion. The author has revised the wording. shows smaller Pd particle size than others.

Q15. Line 253. How much metal was present at the “ultra-low” content?

Answer: Thank you for your suggestion. The author has made changes and additions. with low content (0.7%).

Q16. Lines 278-284. Description of Figure 14 needs to be improved and clarified.

Answer: Thank you for your suggestion. The author has improved the description of Figure 14, bifunctionality of ZSM-5−Ag/SBA-15, ZSM-5, and Ag/SBA-15 catalyst in HCHO conversion to CO₂.

Q17. Table 2. Abbreviations in this Table need to be clarified. Especially in Catalysts column.

Answer: Thank you for your suggestion. The author has completed the abbreviation. NiTi-LDH stands for Nickel titanium layered double hydroxide, R-Bir stands for Reduced Birnessite, Am-MnO2-AC stands for Amorphous Manganese Dioxide Loaded on Activated Carbon, δ-MnO2@GO-RT stands for δ-MnO₂ Nanosheets Anchored on Graphene Oxide.

Q18. Figure 15. An explanation is needed of what dynamic and static tests mean.

Answer: Thank you for your suggestion. The author has supplemented the meaning of static testing and dynamic testing in the article. Static testing and dynamic testing are conducted in a sealed, airflow-free reaction chamber and under continuous airflow conditions in a fixed bed, respectively.

Q19. Figure 16. The significant difference in the catalytic properties of MnOx catalysts depending on their processing conditions (Figure 16b) requires some details about the preparation of the catalysts: what is the difference between MnO2-KL and MnOx-S-A?

Answer: Thank you for your suggestion. The author has provided a brief explanation of their preparation details. These three catalysts are all based on MnO₂-KL and synthesized using different ratios and hydrothermal temperatures)

Q20. Figure 18. Here is necessary to clarify abbreviations CeO2-C and CeO2-R.

Answer: Thank you for your suggestion. The author has provided additional explanations. “CeO₂-S, CeO₂-C, CeO₂-R represent spherical, cubic, and rod morphologies of cerium oxide, respectively.”

Q21. Line 426. Abbreviations Ti-NS and Ti-NP need to be clarified.

Answer: Thank you for your suggestion. The author has already explained in the article. Ti-NS and Ti-NP stands for TiO2{001} and TiO2{101}, respectively.

Q22. Line 429. This sentence has to be revised.

Answer: Thank you for your suggestion. The author has revised this sentence.

Q23. Line 433. What means DOM?

Answer: Thank you for your suggestion. DOM stands for Dioxymethylene.

Q24. Effect of preparation method. Reference [120] has to be included in this part too. Line 482. What it means: lattice oxygen reduction on the catalyst surface? Line 494. As the lowest 2.31?

Answer: Thank you for your suggestion. The author's meaning is the difficulty level of reducing the lattice oxygen on the surface of the catalyst. The author has revised. “as the highest 2.31”

Q25. Three articles (references [110], [111] and [122] ) are included in full in this part of  the review. The information is interesting and important, but its presentation could be shortened.

Answer: Thank you for your suggestion. The author has shortened the content.

Q26. Lines 621-622. As follows from the above description, activity "increases with the increase in humidity" only within a certain range.

Answer: Thank you for your suggestion. The author has revised this section. increases with the increase in humidity within a certain humidity range.

Q27. Lines 654-661. The sentence needs revision.

Answer: Thank you for your suggestion. Thank you for your reminder. But this paragraph is not repeated, carefully read the different catalysts used in the text.

Q28. Line 777. There is an error here. According to the title of the article [133], the catalyst is a mixed oxide catalyst MnOx-decorated anatase TiO2 {001}.

Answer: Thank you for your suggestion. After verification, this is not an error, and the wording in the original text [133] is also the same.

Q29. References. Need to add “doi” in the list.

Answer: Thank you for your suggestion. Thank you for reminding me. The author has added DOI to all the references.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The review, Recent Advances in Formaldehyde Catalytic Oxidation Catalysts, provides an overview of the latest developments in catalysts utilized for the oxidation of formaldehyde, given that this process has practical applications in eliminating hazardous formaldehyde from the atmosphere by transforming it into CO₂ and H₂O. This review article offers a concept for presenting research findings that have been published in the last five years. The main factors affecting HCHO oxidation efficiency are explained. A minor revision is needed by taking into account the following aspects:

The abstract is too long, and it is recommended to shorten the text. It is highly recommended to use the term oxygen species instead of oxygen, as it was used in section 5.1.

Page 3, line 96-98: unfinished sentence

Page 3, lines 102-103: This last sentence is overemphasized, and it is necessary to make a correction.

Figure 17: error bars are invisible for Co3O4-60, 120, 250 catalysts

Page 17, line 358: through hydrothermal… what? The word is missing.

It is recommended to discuss the strategies for improving the stability of catalysts.

Author Response

Reviewer #2:

Q1. The abstract is too long, and it is recommended to shorten the text. It is highly recommended to use the term oxygen species instead of oxygen, as it was used in section 5.1.

Answer: Thank you for your valuable suggestions. The author has successfully shortened the abstract and clarified that the term "oxygen" in the text refers to oxygen gas.

Q2. Page 3, line 96-98: unfinished sentence.

Answer: Thank you for your suggestion. The author has refined the sentence, and here is the improved version, “In order to better understand the commonly used catalyst systems in the field of formaldehyde catalytic oxidation, as well as the influencing factors during the reaction process and the reaction mechanism, in order to improve and perfect the formaldehyde catalytic oxidation reaction.”

Q3. Page 3, lines 102-103: This last sentence is overemphasized, and it is necessary to make a correction.

Answer: Thank you for your suggestion. Thank you for your feedback. The following is the sentence after the change “The first type of carrier materials has a large specific surface area, which favorable for the adsorption of formaldehyde molecules”

Q4. Figure 17: error bars are invisible for Co3O4-60, 120, 250 catalysts

Answer: Thank you for your feedback. Upon verification, the initial source of the image is indeed as provided.

Q5. Page 17, line 358: through hydrothermal… what? The word is missing.

Answer: Thank you for your valuable feedback. The author has revised the phrasing.” prepared three different morphologies of cerium oxide (CeO₂) by hydrothermal method and systematically studied their performance differences in the catalytic oxidation of formaldehyde (HCHO)”

Q6. It is recommended to discuss the strategies for improving the stability of catalysts.

Answer: Thank you for your valuable feedback. The author has incorporated strategies to enhance catalyst stability into the conclusion and outlook section. As follows: Strategies for improving catalyst stability:

1. Surface modification and functionalization, the introduction of specific functional groups or protective layers on the surface of catalysts can improve their resistance to corrosion and poisoning.
2. Optimization of carrier structure, by regulating the pore structure, surface defects, or morphology of the carrier, the interaction between the active component and the carrier can be enhanced, inhibiting its migration and agglomeration.
3. Doping modification, introducing heteroatoms (such as transition metals or non-metallic elements) into the catalyst can optimize the electronic structure of the active sites, inhibit sintering and agglomeration.
4. Core-shell structure design, constructing a structure with an active component as the core and an inert material as the shell (such as a carbon shell or an oxide shell) can effectively isolate the reactants from the active sites, preventing their loss or poisoning.