Bioethanol Upgrading to Renewable Monomers Using Hierarchical Zeolites: Catalyst Preparation, Characterization, and Catalytic Studies

Round 1

Reviewer 1 Report

Title: Bioethanol upgrading to renewable monomers using hierarchical zeolites: Catalyst preparation, characterization, and catalytic studies

Author(s): Ploychanok Iadrat and Chularat Wattanakit

 

Comments:

This contribution describes the review of bioethanol conversion technologies for the production of monomers including catalyst preparation, characterization, and catalytic studies. Although the authors systematically summarized synthesis of hierarchical zeolites for bioethanol conversion, and their characterization, as well as their performance in bioethanol dehydration, bioethanol to hydrocarbon and butadiene conversions, the manuscript is too descriptive to directly compare the performances of the reported catalysts. And there are numerous grammatical and typographical errors which should be revised. So, I recommend to publish this paper on Catalysts after major revision.

My comments on this manuscript are as follows:

1. The comparisons of catalytic performances on bioethanol dehydration, bioethanol to hydrocarbons, and bioethanol to butadiene are too descriptive. I recommend to insert three Tables to compare the catalytic performances of reported catalysts.
2. 2. Mechanistic studies section also too descriptive. I recommend to insert reaction schemes to illustrate reaction pathways of each reaction.
3. In Introduction section, line 45, the sentence “… the ethylene production from bioethanol dehydration is an environmentally friendly process without greenhouse gas emission…” should be revised because ethanol dehydration to ethylene is an endothermic process requiring heat input and inevitably generates greenhouse gas. The conversions of bioethanol to chemicals are more meaningful in a view of carbon neutrality.
4. In 2.2. Top-down approach section, line 167, the oxalic acid treatment of ZSM-5 does not lead the generation of mesopores, because three moles oxalic acid form a chelate with a mole of aluminum on external surface. This aluminum leaching occurs only on the external surface and internal Al sites are intact because this chelates are too bulky to generate on the internal pores. Please check this again.

There are numerous grammatical and typographical errors which should be revised.
- Line 55 and 852, “porous structures” should be changed to “pore structures”.
- Line 63, “For this review” should be changed to “In this review”.
- Line 78 and 102, “an alkaline agent” should be changed to “a mineralizing agent”.
- Line 98, “mesoporous agents” should be changed to “mesopore generating agents”.
- Line 133, “hierarchically mesoporous nanosized ZSM-5” should be changed to “hierarchical nanosized ZSM-5”. 
- Line 135, “a mesoporous template” should be changed to “a mesopore generating template”.
- Line 166, “a propylene bottle” should be changed to “a polypropylene bottle”.
- Line 233, “zeolite framework cations” should be changed to “zeolite framework atoms”.
- Line 333, “thress times” should be changed to “three times”.
- Line 370, “to compare between” should be changed to “to compare the difference between”.
- Line 376, “significant different” should be changed to “significantly different”.
- Line 705, “porous properties” should be changed to “textural properties”.
- Line 746, “in the term of” should be changed to “in terms of”.
- Line 851, “mesoporous connectivity” should be changed to “mesopore connectivity”.
- Line 865, “gas hydrocarbon” should be changed to “gaseous hydrocarbons”.
- Line 865, “For the comparison” should be changed to “For comparison”.
- In the whole text, the use of Si/Al and SiO2/Al2O3 should be uniform. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript Number: catalysts-1376394

 

Article type: Review Paper

 

Full Title: Bioethanol upgrading to renewable monomers using hierarchical zeolites: Catalyst preparation, characterization, and catalytic studies

 

Remarks to the Authors:

The authors presented a review of different types of zeolite catalysts (mostly MFI, BEA, and less MOR, FAU, CHA) including their preparation (top-down and bottom-up approaches), characterization (textural properties, pore architecture, acidic properties, and active species), and catalytic evaluation in the bioethanol upgrading to renewable monomers (bioethanol dehydration, bioethanol to hydrocarbons, and bioethanol to butadiene). This review is in the scope of Catalysts and can be interesting for the journal readership. I can recommend this paper for publication in MDPI Catalysts but only after major revision. Please, find my comments below.

 

1. The authors should include to the 2. Design and preparation of hierarchical zeolite catalysts (2.1. Bottom-up approach) discussion about ZSM-5 zeolite (its application, structure, etc.). It should be clear for the journal readership why the authors select this zeolite and start their discussion with ZSM-5.

 

2. The authors should explain to the journal readers the difference among structure-directing agents (SDA) such as TPOAC, CTAB, TPABr, TPAOH, TEAOH. This explanation/discussion should be included in 2.1. Bottom-up approach section.

 

3. The authors should include before Line 140 information and some discussion about Beta zeolite (e.g. its application, structure, etc.).

 

4. The same as above should be done but for the CHA and FAU zeolites (start with Line 153-154).

 

5. The section 2.2. Top-down approach should be expanded. For instance, the authors missed the possible impregnation of zeolites by CsNO3 and other alkali salts. The same with alkali (Cs, K, etc.) hydroxides. The references below can be applied.

 

One-step synthesis of glycidol from glycerol in a gas-phase packed-bed continuous flow reactor over HZSM-5 zeolite catalysts modified by CsNO3

10.1016/j.cej.2020.124945

 

Effect of alkali metal cations modification on the acid/basic properties and catalytic activity of ZSM-5 in cracking of supercritical n-dodecane

10.1016/j.fuel.2019.01.105

 

Synthesis and characterization of aluminium-free ZSM-5 type chromosilicates in different alkaline systems and investigation of their pore structures

10.1016/j.micromeso.2013.07.011

 

6. Please, also include discussion/information about mordenite (MOR) zeolite which should start in Line 241.

 

7. The authors should expand section 2.3. Incorporation of metal species into zeolite supports. I suggest describing more bi- and trimetallic ZSM-5 and other zeolite supports.

You can use recently published articles presented below:

 

Allyl alcohol production by gas phase conversion reactions of glycerol over bifunctional hierarchical zeolite-supported bi- and tri-metallic catalysts

10.1016/j.cej.2020.125430

 

Trimetallic Cu−Ni−Zn/H-ZSM‑5 Catalyst for the One-Pot Conversion of Levulinic Acid to High-Yield 1,4-Pentanediol under Mild Conditions in an Aqueous Medium

10.1021/acscatal.0c04216

 

ZSM-5-supported V-Cu bimetallic oxide catalyst for remarkable catalytic oxidation of toluene in coal-fired flue gas

10.1016/j.cej.2021.129675

 

8. The authors should decrypt/explain all abbreviations in the manuscript body, e.g. HZSM-5_(S50), HZSM_(S50), HZSM-5_PT(S500), etc. (Line 372-373).

 

9. Fig. 6 must be substituted. Unfortunately, I was not able to recognize in Fig. 6 “extremely weak, weak, moderate, and strong acid sites”. Moreover, what is going on with the baseline of the NH3-TPD profiles? Why the axis Y is signed as “Intensity” with useless numbers? It should be at least a TCD signal or better to present the MS signal of NH₃ with m/z = 17 or 15.

 

10. I suggest to the authors provide more Figures related to the discussion of acid-base properties and active species (section 3.2). For instance, the authors discussed the Pyridine-FTIR technique without a corresponding Figure. It will be inconvenient for the journal readership to read the discussion with all details and many numbers without presented spectra. The same for CDCl3-FTIR, CO-FTIR, dTBPy-FTIR, Pn-FTIR, UV-vis diffuse reflectance spectroscopy, and Raman spectroscopy. I recommend to the authors combine some spectra and present them as one Figure.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript tried to review the recent progress in the hierarchical zeolite materials for the production of renewable monomers from bioethanol in terms of catalyst preparation, characterization, and catalytic studies. Overall, this manuscript is well composed, the language is qualified, and the reference is updated. However, introduction part should be improved and the literature information should be summarized in a better way. Therefore, I suggest a minor revision before publishing this review manuscript in catalysts. My comments are as follows:

1. An additional paragraph should be added to the end of the Introduction Section to describe the organization of this review paper, and in which order you will review this topic, so that it can be easier for the readers to grasp the information they need.
2. The authors review the progress of the hierarchical zeolite catalysts in terms of preparation (Section 2), characterization (Section 3), and catalytic performance (Section 4). The review is comprehensive, however, the literature information should be summarized in a better way, not just copy and paste. The authors should summarize the key information in a table for each section. For example, for the synthesis section, the choice of different chemicals, organic templates, the metal precursors and the post-synthetic treatments; for the catalytic performance section, the choice of the catalysts, the testing conditions, the reported performance. If a these information can be summarized in a table for each section and supported by the corresponding reference, this review paper can be more readable.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

This manuscript is acceptable gor publocation in Catalysts.

Reviewer 2 Report

The authors significantly improved their manuscript. I can recommend this paper to be accepted by Catalysts.