CHA-Type Zeolite Prepared by Interzeolite Conversion Method Using FAU and LTL-Type Zeolite: Effect of the Raw Materials on the Crystallization Mechanism, and Physicochemical and Catalytic Properties

Round 1

Reviewer 1 Report

The manuscript entitled "CHA-type zeolite prepared by interzeolite conversion method using LTL-type zeolite: effect of the raw materials on the crystallization mechanism, and physicochemical and catalytic properties", reports a study on the preparation of CHA type zeolite using as raw materials other zeolites such as LTL and FAU, and as organic structure directing agent (OSDA) trymethyladamantyl ammonium hydroxide and tetraethyl ammonium hydroxide. The work reported both the synthesis and the characterization of the species obtained.

The manuscript deals with a topic consistent with the purpose of the journal, although it does not present elements of particular relevance and originality. However, it can be a valid contribution for researchers working in this sector because it reports a detailed characterization of the phases obtained. I found in the manuscript some parts that must be improved especially the part dedicated to the description of the synthesis.

Therefore I believe that the work can be considered for its publication after a particular revision.

Here are some suggestions for authors:

Title: The title does not seem to be inconsistent with the manuscript which shows that the CHA zeolite is prepared from both LTL and FAU zeolite. The title, on the other hand, only reports the use of LTL zeolite.

2.Results

In figure S2 it could be useful to insert also the XRD spectrum of the CHA phase used as seed.

Figure 4- It is not very clear. It is not clear what the dotted lines represent. Perhaps it should be proposed differently.

Materials and methods

In the manuscript it is reported that

“ in the presence of TMAdaOH the following system was used: 1 SiO2 /0.033 Al2O3 /0.2 NaOH /0.2 TMAdaOH / 40 H2O. The10 wt% seed crystal (CHA-type zeolite synthesized by Ref. 24) was added to the mother gel”

“in the presence of TEAOH the following system was used: 1 SiO2 / 0.033 Al2O3 /0.3 NaOH / 0.1KOH /0.55 TEAOH / 40 H2O. The 10 wt% seed crystal was added to the mother gel.”

How were these systems calculated? How was the composition of the raw materials considered? Were the two systems used for both LTL and FAU?

It would be better to give the weights of each reagent used to synthesize the specific species. Furthermore, for each reagent it is necessary to introduce the degree of purity.

Were NaOH / KOH solutions used?

More information should be given on the CHA zeolite used as a seed. What was its degree of crystallinity?

This whole part needs to be revised because it needs more details to be clear.

3.2 Characterization

(line 316) in the manuscript it is reported: “The sum of peak intensity of CHA at 5days”, are the crystals of CHA used as seeds in the synthesis? In the paragraph “Materials and methods”, it is not written that the CHA used as seeds was at 5 days.

Author Response

Replies to comments from Reviewer 1

Comments and Suggestions for Authors

The manuscript entitled "CHA-type zeolite prepared by interzeolite conversion method using LTL-type zeolite: effect of the raw materials on the crystallization mechanism, and physicochemical and catalytic properties", reports a study on the preparation of CHA type zeolite using as raw materials other zeolites such as LTL and FAU, and as organic structure directing agent (OSDA) trymethyladamantyl ammonium hydroxide and tetraethyl ammonium hydroxide. The work reported both the synthesis and the characterization of the species obtained.

The manuscript deals with a topic consistent with the purpose of the journal, although it does not present elements of particular relevance and originality. However, it can be a valid contribution for researchers working in this sector because it reports a detailed characterization of the phases obtained. I found in the manuscript some parts that must be improved especially the part dedicated to the description of the synthesis.

Therefore I believe that the work can be considered for its publication after a particular revision.

Here are some suggestions for authors:

Title:

1. The title does not seem to be inconsistent with the manuscript which shows that the CHA zeolite is prepared from both LTL and FAU zeolite. The title, on the other hand, only reports the use of LTL zeolite.

Reply: The title has been changed to

“CHA-type zeolite prepared by interzeolite conversion method using FAU and LTL-type zeolite: effect of the raw materials on the crystallization mechanism, and physicochemical and catalytic properties”

Results

2. In figure S2 it could be useful to insert also the XRD spectrum of the CHA phase used as seed.

Reply: The data of the seed crystals have been added to the SI as Figure S1c.

3. Figure 4- It is not very clear. It is not clear what the dotted lines represent. Perhaps it should be proposed differently.

Reply: Figure 4 has been modified to clearly understand.

3.2 Materials and methods

4. In the manuscript it is reported that

“ in the presence of TMAdaOH the following system was used: 1 SiO2 /0.033 Al2O3 /0.2 NaOH /0.2 TMAdaOH / 40 H2O. The10 wt% seed crystal (CHA-type zeolite synthesized by Ref. 24) was added to the mother gel”

“in the presence of TEAOH the following system was used: 1 SiO2 / 0.033 Al2O3 /0.3 NaOH / 0.1KOH /0.55 TEAOH / 40 H2O. The 10 wt% seed crystal was added to the mother gel.”

Reply: Based on this comments, “3.1. Synthesis of CHA-type zeolite from FAU- and LTL-type zeolite” has been modified.

5. How were these systems calculated? How was the composition of the raw materials considered? Were the two systems used for both LTL and FAU?

Reply:　The systems were based on the Si/Al ratio in FAU and LTL. Fumed silica (Cab-O-Sil M5) was added as additional silica source to achieve the targeted composition of mother gel.

We have modified “3.1. Synthesis of CHA-type zeolite from FAU- and LTL-type zeolite”

6. It would be better to give the weights of each reagent used to synthesize the specific species. Furthermore, for each reagent it is necessary to introduce the degree of purity.

Reply: Based on this comments, “3.1. Synthesis of CHA-type zeolite from FAU- and LTL-type zeolite” has been modified. Note, in the presence of TMAdaOH, the molar ratio of the mother gel was 1 SiO₂ /0.033 Al₂O₃ /0.2 NaOH /0.2 TMAdaOH /40 H₂O. In this work, 15 mmol SiO₂ was applied to synthesize the CHA-type zeolite.

7. Were NaOH / KOH solutions used?

Reply: In this work, sodium hydroxide pellet (Wako,99.8%) and potassium hydroxide pellet (Wako,99.8%) were used.

8. More information should be given on the CHA zeolite used as a seed. What was its degree of crystallinity?

Reply: The data of the seed crystal used in this work have been added to SI.

9. This whole part needs to be revised because it needs more details to be clear.

Reply: “3.2 Materials and methods” has carefully been rechecked and revised.

3.2 Characterization

10. (line 316) in the manuscript it is reported: “The sum of peak intensity of CHA at 5days”, are the crystals of CHA used as seeds in the synthesis? In the paragraph “Materials and methods”, it is not written that the CHA used as seeds was at 5 days.

Reply:　No, the seed was synthesized according to ref. 24. There are several methods for calculating the crystallinity. In this work, as described in “3.2 Characterization”, the relative crystallinity of the CHA-type zeolite was based on the sum of the peak intensity ascribed to CHA-phase at 5 days. Several groups have used a similar method to evaluate the crystallinity.

Author Response File: Author Response.pdf

Reviewer 2 Report

Please refer to the attached file.

Comments for author File: Comments.pdf

Author Response

Replies to comments from Reviewer 2

In this manuscript, Nishitoba and coworkers investigated the preparation of CHA zeolite starting from LTL or FAU zeolites as Al and Si sources, and TEAOH or TMAda as organic structural directing agents (OSDA). They analyzed the variation of Si/Al ratio within the product and studied the crystallization mechanism over 120 h. The authors studied the thermal stability of the CHA samples and tested their behavior towards MTO reaction. TMAda-based catalysts appeared to have longer catalytic life and higher selectivity towards ethene production. 

Despite the numerous and diverse experiments performed, the manuscript suffers from several issues that prevents its publication in the current form. I suggest a major revision of the manuscript taking into consideration the following remarks:  

1. The title is not clear and does not reflect the totality of the work. (1) Authors specified only LTL zeolite as a starting zeolite, whereas 50% of the manuscript was dedicated to FAU-type zeolite as a parent zeolite. (2) The term “raw materials” is confusing and unclear. In case it stands to OSDA, the term must be replaced by “structural directing agents”. If it stands for Si, Al sources and OSDA, FAU type zeolite must be included in the title.

Reply:　In this work, “raw materials” means two kinds of parent zeolites, LTL and FAU and two kinds of structural directing agents, TMAdaOH and TEAOH. The title has been changed to

“CHA-type zeolite prepared by interzeolite conversion method using FAU and LTL-type zeolite: effect of the raw materials on the crystallization mechanism, and physicochemical and catalytic properties”

2. The introduction is very small and should be developed. The authors are asked to shed more light on previously published similar work. For instance, the authors claim in this manuscript a new method for the synthesis of CHA starting from LTL. They also investigated the influence on OSDA. However, they mentioned in page 2 lines 44-46: “CHA has also been synthesized using LTL type aluminosilicate zeolite (hereinafter called LTL) in the presence of TMAda+ [28, 29, 37]. In addition to the type of zeolite as raw material, the influence of OSDA on the composition of the final product has been studied [31, 32]. ” The authors are asked to justify what is the novelty of their work compared to the references they cited.

Reply: Based on your valuable comments, “Introduction” part has been revised. Our originalities in this work are as follows.

1. To develop a new synthesis route to the CHA-aluminosilicate in the presence of OSDA via IZC method. A new synthesis route of CHA-type aluminosilicate zeolite by interzeolite conversion method using the LTL-type zeolite was investigated. In utilization of the LTL-type zeolite, the effect of the raw materials including parent zeolite as aluminosilicate sources and organic structure-directing agent (OSDA) on the crystallization mechanism, and physicochemical and catalytic properties was investigated. Then we firstly found that the CHA-type aluminosilicate zeolite was crystallized from the combination of the LTL-type zeolite and tetraethyl ammonium hydroxide as raw materials.
2. To clarify the relationship between parent zeolite and OSDA. We successfully found that OSDA greatly affects the composition of the final products, and that the raw materials strongly affected the Al distribution in the final products, affecting the catalytic performance in the methanol to olefins reaction. Although the synthesis of zeolites using the IZC method has been reported by several groups, there are few reports on the relationship between the type of parent zeolite and the organic structure-regulating agent”

The results obtained from this study clearly showed that the raw materials for the CHA-type zeolite should be optimized depending on its application. Furthermore, our findings will contribute to the diversification of the IZC method, and also to the control of the distribution of the heteroatoms in the zeolite framework.

3. The definition of the samples’ abbreviation (CHA-FAU-TMAda, CHA-LTL-TMAd, CHA-FAU-TEA, and CHA-LTL-TEA) should be introduced before their first use. In the manuscript, they are defined in the materials and methods section page 12.

Reply: We've added the definition of the samples’ abbreviation to lines 73-74 and 82-83.

4. Table 1: column 2: convert Al/Si into Si/Al to stay homogeneous and allow an easier comparison with column 6.

Reply: We've corrected this mistake.

5. Figure 2: the XRD patterns are very small and the differences are not easily visualized. The authors are asked to reproduce the figures with two samples per raw instead of four.

Reply: Figure 2 has been modified to clearly understand.

6. Page 6: line 182-183: ”Although the yield was increased for 12 h, it was not significantly changed after 12 h, implying that the crystallization of CHA was almost completed within 12 h.” The authors need to comment on the continuous evolution of Si/Al ratio from 4.5 to 6.3 (40%variation) after the CHA was almost fully crystalized.

Reply: For CHA-FAU-TEA, as the reviewer pointed out, the Si/Al ratio was continuously and slightly increased from 4.5 to 6.3 after 12 h. In the original MS, we claimed that the yield was not significantly changed after 12 h. However, we carefully re-considered the result again, and we have found that the yield was slightly increased. Therefore, the following sentences have been revised as follows: 　

From: For CHA-FAU-TEA, when the crystallization time varied from 1 to 120 h, the Si/Al ratio was significantly increased from 2.8 to 4.5, and it finally reached 6.3 at 120 h. Although the yield was increased for 12 h, it was not significantly changed after 12 h, implying that the crystallization of CHA was almost completed within 12 h.

To: For CHA-FAU-TEA, the yield was drastically increased to 31 % for 12 h, and it finally reached 40 %. Correspondingly, the Si/Al ratio was increased to 4.5 for 12 h, and it was on the slight increase. It finally reached 6.3 at 120 h. These result imply that the crystallization of CHA was mostly completed within 12 h.

7. Page 6 Lines 190-194. “Like CHA-LTL-TMAda, the TEAOH/Al ratio in CHA-LTL-TEA was gradually increased to 0.78 for 72 h.” This statement is contradictory to lines 186-187: “For CHA-LTL-TMAda, the TMAdaOH in product was stable (ca. 0.4 mmol187 g-1) until 24 h, and it was dramatically increased up to 0.8 at 48 h.” Consequently, the claim that the crystallization does not depend on OSDA is not true. Additionally, the trend line in Figure 5a for the evolution of OSDA is misleading and should be corrected to avoid wrong conclusions such as the one in lines 190-194. The points evolve in an “s”-shape like model and not in a gradual increment as in current form.

Reply: As the reviewer pointed out, CHA-LTL-TMAda, the TMAdaOH in product was stable (ca. 0.4 mmol g^-1) until 24 h, and it was dramatically increased up to 0.8 at 48 h.”We've revised this part and modified Figure 5a. The following sentences have been revised as follows: 　

From: Like CHA-LTL-TMAda, the TEAOH/Al ratio in CHA-LTL-TEA was gradually increased to 0.78 for 72 h. On the other hand, that in CHA-FAU-TEA reached 0.2 within 6 h, and it was almost unchanged after 6 h. Thus, the behavior of the OSDA/Al ratio against the crystallization time was dependent on the type of the parent zeolites, not OSDA.

To: The TEAOH/Al ratio in CHA-LTL-TEA was gradually increased to 0.78 for 72 h. On the other hand, that in CHA-FAU-TEA reached 0.2 within 6 h, and it was almost unchanged after 6 h. Thus, the behavior of the OSDA/Al ratio against the crystallization time was dependent on the type of the parent zeolites, not OSDA.

8. Figure 8: the symbol to conversion (most probably white circle) is missing in the legend.

Reply: We've corrected this mistake.

9. The conclusion (lines 356-358) states that the new method is based on the use of LTL as a parent zeolite and TEAH as OSDA. This statement neglects the FAU as parent zeolite and TMDAda as OSDA. Thus only 1 system is credited out of 4 equally studied samples throughout the manuscript. Addionally, CHA-LTL-TEAOH is of lower catalytic life and selectivity compared to CHA-LTL-TMAda and CHA-FAU-TMAda. Considering this catalyst as the major finding reduces the impact of the work.

Reply: As described in Reply 2, our work has focused on two things, new synthesis route and clarification of relationship between zeolite and OSDA in IZC method. We have considered that we were able to conduct the study on the clarification of relationship between parent zeolite and OSDA in IZC method. Although CHA-LTL-TEA exhibited a low catalytic performance in the MTO reaction, we believe that CHA-LTL-TEA is expected to be a potential catalyst for selective reduction of NO_x due to its high hydrothermal stability.

The following sentence has been added to the revised MS, line 255-256.

“Such properties would be advantageous for the application to the selective reduction of NOx.”

10. The manuscript should be spelling-checked and grammar-checked.

Reply: English has carefully been checked by a specialist.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript “CHA-type zeolite prepared by interzeolite conversion method using LTL-type zeolite: effect of the raw materials on the crystallization mechanism, and physicochemical and catalytic properties” was submitted to Crystals for publication as an article by the authors Toshiki Nishitoba, Takuya Nozaki, Sungsik Park, Yong Wang, Junko N. Kondo, Hermann Gies and Toshiyuki Yokoi. The authors report the synthesis of CHA-type materials using various starting materials and organic structure directing agents. The experimental data support the claims in the manuscript and the results merit publishing. However, there are some mistakes in English and some points need to be clarified in more details. Hence, the manuscript requires minor revision prior to publication. Below are listed some specific comments.

• Abstract: “dissolubility” It should be “solubility”.
• Abstract, line 24: The meaning of “one” is not clear.
• line 30: “CHA-type zeolites such as an eight ring (8-R) zeolite” This expression is not clear.
• line 63: “FAU and LTL were used as raw material”. It should be “materials”.
• line 297: “1h” Space is missing.
• line 297-298: “the mother gel was hydrothermally treated at 443 K in a stirring 298 for 1–120 h for evaluated.” It is not clear what should be evaluated.
• line 314-316: “Relative intensity” I guess it should be “Relative crystalinity”.
• line 340-341: “hydrothermal treatment at 1073 K for 5 h using a (N2 balance).” Something is strange here.
• XRD results: In the LTL-derived CHA samples there is a small peak at 5.5° 2q that might arise from unreacted LTL. Hence the claim in lines 144-145: “the LTL-phase completely disappeared after 120 h irrespective of type of OSDA” should be rephrased and commented in a different manner.
• line 72: “being almost accordance”. “in” is missing
• line 73: “In this case, the yields of the products, which was calculated”. It should be either “yield” either “were”.
• lines 78-80: “Although the synthesis conditions will be optimized, the CHA-type aluminosilicate zeolite was firstly crystallized via the IZC method from the combination of the LTL type zeolite and TEA⁺ as starting materials.” I don’t see the point of this sentence in the context with the previous text.
• line 105: “which were corresponded” It should be “which correspond”.
• line 121: “LTL in alkaline solution might much produce” This is not clear.
• Table 2: It would be easier to follow the data if the Q4 species were grouped together, not to have Q3 in between.
• lines 210-212: “The formation of the cubic particles began at 6 h (Figure 3 (a)), and cubic particles were clearly observed at 12 h for CHA-FAU-TMAda, while amorphous particles were still observed for CHA-LTL-TMAda at this time.” How the authors know that these are amorphous particles?
• line 241: “water vapor is easily reacted” It should be “water vapor reacts easily”.
• line 249: “zeolite with contained of more Q4(1Al)” Maybe “zeolite with more Q4(1Al)”?
• lines 249-250: “defective sites” It should be “defect sites”.
• lines 257: “after (red line) hydrothermal treatment samples” It should be “after (red line) hydrothermal treatment of the samples”.
• lines 356: “A new route to synthesis of CHA-type” It should be “A new route to synthesize CHA-type” or “A new synthesis route of CHA-type”
• Table S1: It is not clear how the product selectivity was defined.
• It would be good to add the XRD pattern and the SEM images of the seed crystals in the SI.

Author Response

Replies to comments from Reviewer 3

The manuscript “CHA-type zeolite prepared by interzeolite conversion method using LTL-type zeolite: effect of the raw materials on the crystallization mechanism, and physicochemical and catalytic properties” was submitted to Crystals for publication as an article by the authors Toshiki Nishitoba, Takuya Nozaki, Sungsik Park, Yong Wang, Junko N. Kondo, Hermann Gies and Toshiyuki Yokoi. The authors report the synthesis of CHA-type materials using various starting materials and organic structure directing agents. The experimental data support the claims in the manuscript and the results merit publishing. However, there are some mistakes in English and some points need to be clarified in more details. Hence, the manuscript requires minor revision prior to publication. Below are listed some specific comments.

1. Abstract: “dissolubility” It should be “solubility”.

Reply:　We've corrected this mistake.

2. Abstract, line 24: The meaning of “one” is not clear.

Reply:　We've modified this part.

3. line 30: “CHA-type zeolites such as an eight ring (8-R) zeolite” This expression is not clear.

Reply:　We've modified this part.

4. line 63: “FAU and LTL were used as raw material”. It should be “materials”.

Reply:　We've corrected this mistake.

5. line 297: “1h” Space is missing.

Reply:　We've corrected this mistake.

6. line 297-298: “the mother gel was hydrothermally treated at 443 K in a stirring 298 for 1–120 h for evaluated.” It is not clear what should be evaluated.

Reply:　“3.1. Synthesis of CHA-type zeolite from FAU- and LTL-type zeolites” has been revised to clearly understand.

7. line 314-316: “Relative intensity” I guess it should be “Relative crystallinity”.

Reply:　We've corrected this mistake.

8. line 340-341: “hydrothermal treatment at 1073 K for 5 h using a (N2 balance).” Something is strange here.

Reply: “3.3. Hydrothermal stability” has been revised to clearly understand.

9. XRD results: In the LTL-derived CHA samples there is a small peak at 5.5° 2q that might arise from unreacted LTL. Hence the claim in lines 144-145: “the LTL-phase completely disappeared after 120 h irrespective of type of OSDA” should be rephrased and commented in a different manner.

Reply: Based on this comment, the following sentences have been revised as follows: 　

From:  In the synthesis from LTL, the crystallinity of LTL was gradually decreased along with the crystallization time, and the LTL-phase completely disappeared after 120 h irrespective of type of OSDA.

To: In the synthesis from LTL, the crystallinity of LTL was gradually decreased along with the crystallization time, and the LTL-phase mostly disappeared after 120 h irrespective of type of OSDA.

10. line 72: “being almost accordance”. “in” is missing

Reply:　We've corrected this mistake.

11. line 73: “In this case, the yields of the products, which was calculated”. It should be either “yield” either “were”.

Reply:　We've corrected this mistake.

12. lines 78-80: “Although the synthesis conditions will be optimized, the CHA-type aluminosilicate zeolite was firstly crystallized via the IZC method from the combination of the LTL type zeolite and TEA+ as starting materials.” I don’t see the point of this sentence in the context with the previous text.

Reply: Based on this comment, the following sentences have been revised as follows: 　

From: Although the synthesis conditions will be optimized, the CHA-type aluminosilicate zeolite was firstly crystallized via the IZC method from the combination of the LTL-type zeolite and TEA⁺ as starting materials.

To: In addition, in the case of CHA-LTL-TEA, the crystallization of the CHA structure proceeds after the dissolution of LTL, as described later, and the crystallization is progressed by the IZC method.

13. line 105: “which were corresponded” It should be “which correspond”.

Reply:　We've corrected this mistake.

14. line 121: “LTL in alkaline solution might much produce” This is not clear.

Reply:　The following sentence (line 121 in the original MS), which was just based on our consideration, has been removed.

“The low dissolubility of LTL in alkaline solution might much produce the amorphous aluminosilicate species with Q⁴(1Al) species (described below).”

15. Table 2: It would be easier to follow the data if the Q4 species were grouped together, not to have Q3 in between.

Reply:　We've revised Table 2 based on this comment.

16. lines 210-212: “The formation of the cubic particles began at 6 h (Figure 3 (a)), and cubic particles were clearly observed at 12 h for CHA-FAU-TMAda, while amorphous particles were still observed for CHA-LTL-TMAda at this time.” How the authors know that these are amorphous particles?

Reply:　We've added the following sentences to the revised MS.

“At the initial stages of the crystallization until 3 h, particles attributed to the amorphous were observed. The presence of amorphous product was consistent with the observation of the so-called “halo peak” at 20° in the XRD measurement (Figure 1).”

17. line 241: “water vapor is easily reacted” It should be “water vapor reacts easily”.

Reply: Based in this comments, we've changed “water vapor is easily reacted” to “water vapor reacts easily”

18. line 249: “zeolite with contained of more Q4(1Al)” Maybe “zeolite with more Q4(1Al)”?

Reply:　We've corrected this mistake.

19. lines 249-250: “defective sites” It should be “defect sites”.

Reply:　We've corrected this mistake.

20. lines 257: “after (red line) hydrothermal treatment samples” It should be “after (red line) hydrothermal treatment of the samples”.

Reply: We've corrected this mistake.

21. lines 356: “A new route to synthesis of CHA-type” It should be “A new route to synthesize CHA-type” or “A new synthesis route of CHA-type”

Reply: We've corrected to “A new synthesis route of CHA-type”

22. Table S1: It is not clear how the product selectivity was defined.

Reply: We've added to lines 360-362 about the definition of conversion and product distribution.

23. It would be good to add the XRD pattern and the SEM images of the seed crystals in the SI.

Reply: The data of the seed crystal have been added to SI.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been sufficiently improved so I believe that it can be considered for its publication