Porous Nanostructured Catalysts Based on Silicates and Their Surface Functionality: Effects of Silica Source and Metal Added in Glycerol Valorization
, Joabson Nogueira 1, Gabriela M. Bertoldo 1, Francisco E. Clemente 1, Alcineia C. Oliveira 1,*, Adriana F. Campos 2, Gian C. S. Duarte 2, Samuel Tehuacanero-Cuapa 3, José Jiménez-Jiménez 4 and Enrique RodrÃguez-Castellón 4,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsGeneral Comment: The authors conducted an interesting study where they synthesized a series of nanospherical silicates containing heteroatoms (Al, Zr, or Ti) using TEOS or silica colloids as the silicon source and utilized them to create silicalite zeolites with improved micro-mesoporosity and physical properties. These materials are used for the esterification of glycerol. Before considering the manuscript for publication, the authors should address the issues that are listed as follows:
Major Comments:
- The authors synthesized two types of silicate materials. They did a comprehensive analysis of their structure, surface, and porous properties, but the way the manuscript is written doesn't give a clear and coherent story. Thus, I encourage the authors to rewrite and represent the whole characterization section that makes a coherent story, having direct and clear messages and findings and making it more relevant to the catalysis application (which is not profoundly discussed) at the end of the manuscript.
- The authors should add a paragraph describing what materials they synthesized, indicating the method of preparation. This can be added either at the beginning of the results and discussions or at the last paragraph of the introduction.
- The authors should provide high-magnification SEMs in Fig.1 to accurately comment on the size and shape of the nanoparticles.
- The term "textural properties" is a broad terminology that might be misleading. All the properties shown in this section reveal the porous structure of the silicate zeolites' materials.
- The authors should provide a reference for the "IUPAC classification. "
- As shown in Figure 3b, the pore size distribution of SAT is not 14 nm, as shown in Table 1. The author should revise this number.
- The authors should separate the microporous surface area from the external surface area (including meso and macroporous surface area). This might be a helpful reference: Atwa, M., Li, X., O’Connell, D., Sui, R., Marriott, R. and Birss, V., 2023. Chemistry of Materials, 35(2), pp.395-404.
- How do the catalytic activity and stability of the author's listed solid materials for the EG reaction compare to the state-of-the-art or previously reported materials for the same reaction?
Minor Comments:
- In Fig. 1, all inset images should have a scale bar.
- What is the title of the section "3.1"
- What does "de" mean here, "mol de ethanol "?
- "were added dropwise to the previous solution with a peristaltic pump. " What is the exact flow rate and the pump's specifications?
- "A solution of copper(II) nitrate and iron(III) nitrate was dispersed on 1 g of the solids with the mixture placed in a rotatory evaporator at 70 °C. " How is this solution made (e.g., using what solvent, etc.)?
Comments on the Quality of English Language
- Language issues: the authors need to proofread the manuscript, which is tough to understand. In addition, the abbreviations and acronyms are very confusing
Author Response
The answer to comments of reviewer 1 is included in the enclosed file
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript describes the porous silicate nanocatalysts for glycerol valorization. After improving the following aspects, it could be considered for further process.
1. The abstract should be revised regarding more details and results.
2. Please add several sentences to describe the significance of this work and more explanations are needed to improve the paper's novelty.
3. Authors should write a paragraph at the end of the introduction about what they did, without discussing achievements.
4. My challenge Seriously with this paper is the arrangement of sections! What is the aim of the authors in bringing the materials and methods section after the discussion section?????
5. Abbreviations should be identified in the first use.
6. The effect of each component should be discussed on the performance.
7. Where are the active sites for catalysis?
8. The mechanism must be discussed as a separate heading in the revision.
9. The performance of the proposed catalyst should be compared with other new works in a separate Table.
10. The conclusion should be revised regarding more results.
Author Response
The answers to the comments of reviewer 2 is included in the enclosed file
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. Please add a scheme for the esterification reaction of glycerol with acetic acid showing the chemical structure of the starting materials and the obtained products.
2. In order to support the data obtained from EDS, please add the elemental composition % obtained by XPS for the analyzed samples.
3. Please add a schematic illustration of the possible active sites responsible for the esterification reaction.
4. The authors need to highlight their successful one-pot synthesis. In this regard, the authors need to highlight the advantages of one-pot synthesis of metal-doped porous materials instead of the conventional two-step process (synthesis and post-synthesis functionalization). Please highlight and cite some key works on this topic, such as RSC Adv. 2015, 5, 92743-92756, DOI: 10.1039/C5RA12057H and Catalysts 2023, 13(8), 1159, DOI: 10.3390/catal13081159.
Author Response
The answers to the comments of reviewer 3 is included in the enclosed file
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors made most of the required revision except for two remaining issues:
1. The authors claimed that "The manuscript was rewritten to make clear to readers the whole characterization with a coherent story to show the catalysis application. The focus of our work is the use of soft-templating method, i.e., surfactant-directed sol–gel to feature different reactivities of porous (nano)spheres and mesostructured zeolite silicates. These porous siliceous materials with metal centers incorporated such as Ti, Al or Zr zeolite framework generated active sites in zeolites, and therefore, different local environments in the solids. Silica source imparts an important feature in porous (nano)spheres and mesostructured zeolite silicates with TEOS precursor working efficiently to obtain (nano)spheres. Remarkable surface functionality was achieved, when Ti, Al, or Zr were included in the mesostructured spheres and zeolite silicates. Cu or Fe improved the catalytic performances of zeolite supports. " based on the first major comment, but I can't spot any major changes that have been made in the story of the characterization part.
2. My previous comment: As shown in Figure 3b, the pore size distribution of SAT is not 14 nm, as shown in Table 1. The author should revise this number.
Authors's Reply: With the due respect to the reviewer’s opinion, the Figure 3b represents the pore diameters values. The average pore size of SAT is 14 nm, as written in Table 1. Such a value was taken from the average pore sizes calculated from the BJH method. The International Union of Pure and Applied Chemistry (IUPAC) classifies pore sizes in the range of 2-50 nm as mesoporous materials [M. Thommes et al. Pure Appl. Chem.87 , 2015, 1051-1069/ Kumar et al.(2022). Characterization of Mesoporous Materials. In: Uthaman, A., Thomas, S., Li, T., Maria, H. (eds) Advanced Functional Porous Materials. Engineering Materials. Springer, Cham. https://doi.org/10.1007/978-3-030-85397-6_6].
Comment 2: The peak of Figure 3b of AST (middle top Figure) is very broad (0-120 nm). First, it is outside the mesoporous range, and second, it is not centered at 14 nm. Thus, the pore size can't be 14 nm. There is a significant difference between this Figure and the Figures of SAS and STS, for instance. I do believe the pore size is not 14 nm, and the authors should recheck that and comment on why this peak of BJH pore size distribution is so broad, unlike other materials such as SAS and STS.
Comments on the Quality of English LanguageThe flow of the characterization part of the article needs some work.
Author Response
The answers to the questions of reviever 1 is enclosed
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsAccept.
Author Response
The answers to reviewer 3 is enclosed as attachment
Author Response File: Author Response.pdf
