Theoretical Analysis of the Catalytic Hydrolysis Mechanism of HCN over Cu-ZSM-5

Round 1

Reviewer 1 Report

Comments for authors:

In this paper " Theoretical analysis of the catalytic hydrolysis mechanism of 1 HCN over Cu-ZSM-5" the authors presented HCN catalytic hydrolysis mechanism over Cu-ZSM-5 was investigated based on the density functional theory (DFT) with 6-31++g (d, p) basis set. Five paths (A, B, C, D, and E) were designed. For path A and path B, the first step is the nucleophilic attack of water molecule. Next, the 1 hydrogen atom of H₂O is transferred to the nitrogen atom first for path A, while in path B, the hydrogen atom of the HCN is first transferred to the nitrogen atom. In path C, HCN isomerizes to  HNC initially, and the remaining steps are similar to that of path A. The H atom of HCN shifts to  Cu-ZSM-5 initially in path D, and the H atom is transferred to N atom subsequently. The last step  is the attack on water molecule. The first step for path E is similar to that of path D. The next step is the attack on water molecule, in which the H atom of water molecule shifts to N atom, and the H on  Cu-ZSM-5 shifts to the N atom. Meanwhile, the H atom of oxygen atom is transferred to the N atom. The results show that path C is the most favorable path, with the lowest free energy barrier (35.45 kcal/mol). The results indicate that the Cu-ZSM-5 strongly reduces the energy barrier of HCN isomerizes to HNC, making it an effective catalyst for HCN hydrolysis.

Comments:

1) line 6 - change the formatting of the e-mail address E-mail address: xiafuting@163.com 6

2) lines 11 - space H2Ois

3) line 84 Fig. 1 (A) ZSM-5 zeolite (B) optimized geometries for 5T ZSM-5 cluster, there should be a space (A) ..... ZSM-5

4) it is absolutely necessary to unify the captions under the figures

5) it is absolutely necessary to format the entire reviewed article in accordance with the requirements of the journal, this applies to quoting literature, tables and figures

6) in table 1, 2, 3, 4 and 5, patterns are inserted that cover the bottom line of the table, the patterns should be entered directly into the tables.

The same error is repeated in each of the tables.

7) it is advisable to improve the legibility of signatures on all presented drawings, too small captions / descriptions of the presented structures hinder the interpretation of the presented drawings,

8) the presented method is only a theoretical model, were there similar trials in reality?

Comments for author File: Comments.pdf

Author Response

Reviewer #1 recommendation:
Question 1: line 6 - change the formatting of the e-mail address E-mail address:
xiafuting@163.com 6.
Response comments 1: Thank you very much for helping us to correct these details.
We are very sorry for the mistake. The formatting of the e-mail address ischanged.We
have modified the revision manuscript.
Question 2: lines 11 - space H2Ois
Response comments 2: Thank you very much for helping us to correct these details.
We are very sorry for the mistake. The space isadded.We have modified the revision
manuscript.
Question 3: line 84 Fig. 1 (A) ZSM-5 zeolite (B) optimized geometries for 5T ZSM-5
cluster, there should be a space (A) .....ZSM-5.
Response comments 3: Thank you very much for helping us to correct these details.
We are very sorry for the mistake. The space of “(A) ZSM-5” is added. We have
modified the revision manuscript.
Question 4: it is absolutely necessary to unify the captions under the figures.
Response comments 4: Thank you very much for helping us to correct these details.
We have modified the revision manuscript.
Question 5: it is absolutely necessary to format the entire reviewed article in
accordance with the requirements of the journal, this applies to quoting literature,
tables and figures.
Response comments 5: Thank you very much for helping us to correct these details.
We have modified the revision manuscript.
Question 6: In table 1, 2, 3, 4 and 5, patterns are inserted that cover the bottom line of
the table, the patterns should be entered directly into the tables. The same error is
repeated in each of the tables.
Response comments 6: Thank you for your careful work. We are very sorry for our
negligence in the manuscript. Those errors have been corrected in the revision
manuscript.
Question 7: It is advisable to improve the legibility of signatures on all presented
drawings, too small captions/descriptions of the presented structures hinder the
interpretation of the presented drawings.
Response comments 7: Thank you very much for helping us to correct these details.
According to your good views, the presented structures have been decorated in the
revision manuscript.
Question 8: The presented method is only a theoretical model, were there similar
trials in reality?
Response comments 8: Thanks for your reminding. In 2009, Kröcher et al. reported
that Fe-ZSM-5 and Cu-ZSM-5 had excellentcatalyticactivity for hydrolysis of HCN,
and the converted HCN efficacy of Cu-ZSM-5 was higher than that of Fe-ZSM-5.
Please see lines 63-64 of Page 3. Related literature has been cited in reference 16 in
the revision manuscript.

Reviewer 2 Report

In this report authors presented some interesting theory calculations to identify the possible mechanistic pathways for the catalytic hydrolysis of HCN using Cu-ZSM-5. Though authors gave some interesting background in the introduction to their study, the manuscript in its current form is far from publishable. At times it is hard to fallow what authors were trying to explain through the text.

This manuscript need to be revised before being considered for publishing.

Some key points to address and changes suggested:

1. H atoms needs to be labelled consistently in the figures, which makes it easier to track the movement of these atoms in the transition states and intermediates.
2. Line 117-118:  The sentence 'The proton(H1)...... produts Co and NH3' was added well before it actually happens. Need to be placed/discussed at appropriate state of mechanism in order to avoid confusion. Please check for similar misplacements.
3. In figure 2, are there any other transition states between Cu-INT3 and Cu-TSA4? Seems like bonds were broken and made abruptly? what is the driving force?
4. In some Figures, there seems to be no interactions between Cu and O atoms of ZSM. Is there a rationale for this?Curious. For example in Cu-Int-5, Cu-RC-2.
5. Sentence 236. 'Immigration'? need to be changed to appropriate word.

 

Author Response

Reviewer #2 recommendation:

Question 1: H atoms needs to be labelled consistently in the figures, which makes it

easier to track the movement of these atoms in the transition states and intermediates.

Response comments 1: Thank you very much for helping us to correct these details.

According to your good views, the H atoms of Fig. 4,5,6,7,8 have been labelled

consistently in the revision manuscript.

Question 2: Line 117-118: The sentence 'The proton (H1)...... produts Co and NH3'

was added well before it actually happens. Need to be placed/discussed at appropriate

state of mechanism in order to avoid confusion. Please check for similar

misplacements.

Response comments 2: Thank you very much for helping us to correct these details.

We are very sorry for the mistake. This sentence should not be added before it

actually happens.We have removed this sentence in order to avoid confusion.We have

modified the revision manuscript. The similar misplacements of whole manuscript

have been checked again.

Question 3: In figure 2, are there any other transition states between Cu-INT3 and

Cu-TSA4? Seems like bonds were broken and made abruptly? what is the driving

force?

Response comments 3: We are sorry that we made some improper expressions about

figure 2. We are very sorry that we misplaced the structure of Cu-INT3, and we have

replaced the structure and the Gibbs free energy of Cu-INT3 in the figure 2. (The

figure 2 has become the figure 4. In the revison manuscript) The corresponding

change has been made in the revision manuscript.

Question 4: In some Figures, there seems to be no interactions between Cu and O

atoms of ZSM. Is there a rationale for this? Curious. For example in Cu-Int-5,

Cu-RC-2.

Response comments 4: Thank you for your comment. Unrestricted calculationsfor

the full geometries optimization were employed for all of the reactant complexes (RC),

transition states (TS), intermediates (INT) and product complexes (PC).All

calculations were performed using Gaussian 03 package. All structures were shown in

Gaussian-View software. The bond is displayed when the bond length is below a

certain value, and the bond is not displayed when the bond length exceeds a certain

range. Consequently, no bond does not mean no interaction.

Question 5: Sentence 236. 'Immigration'? need to be changed to appropriate word.

Response comments 5: Thank you very much for helping us to correct these details.

We have change “immigration” to “transfer”. Please see line 281 (page 16).

Author Response File: Author Response.pdf

Reviewer 3 Report

In the manuscript by Futing Xia et al., a detailed DFT mechanism of HCN hydrolysis over Cu-ZSM5 is proposed. Five routes were analyzed, and the most favorable one was identified. The authors used B3LYP/6-31++g (d, p) and LANL2DZ for the Cu level of theory, with a standard approach for calculating the corresponding Gibbs free energies. The manuscript is interesting, and the results might be important for understanding this catalytic reaction. In my opinion, the manuscript should be published in Catalysts after the Authors address the bellow issues.

Methodology – In this type of reaction, dispersion corrected DFT should be used. There are hydrogen transfers, hydrogen bonding, etc., in structures (intermediates, transition states…), so correcting for dispersion might influence both energies and geometries of the investigated species. Something like B3LYP-D3(BJ) or -D4 is typical nowadays and does not increase computational time significantly. Minnesota functionals (e.g., M06-2X) are an alternative, as they have mid-range dispersion included in the functional form (trough parameterization). It is crucial to have this correction included, as it might change not only detailed numbers but also conclusions.

Details of the Cu-ZSM model are missing. What is the oxidation state of Cu? Cu(II)? What is the total charge of the system? If Cu(II) is considered, are unrestricted calculations done?

The Authors talk about Cu-RC and Cu-PC as reactant and product complexes. These are proper complexes of Cu(II) (presumably). Authors should describe those in more detail. What are the coordination number and coordination geometry of Cu(II) in these model systems? Coordination bonds with Cu are not shown in the figures. It seems that Cu-RCs are 3-coordinate – Cu bonded with two O from ZSM and HCN (trough N or C); Cu-PCs seem 4-coordinate with two O (ZSM), NH3, and CO (except in path A, if I am correct). What would be the most stable complex PC, and what RC? Their figure would be helpful. Is the Cu(II) 3-coordinated? I would assume Cu(II) to be 4-coordinate (distorted square planar? Or?) or even 5-coordinate. What would be the missing ligand in RCs? Would water molecule bind as the 4^th ligand in RCs? What is the more favorable binding of HCN to Cu(II)? Trough C or trough N atom? The structures of Cu(II) model complexes are critical for the entire analysis. These are starting and ending points for all considered pathways.

Presentation – I would suggest authors draw a scheme at the beginning of the Results and discussion, showing all five considered pathways. These are more clearly explained in the abstract than in the main text, but a 2D scheme would be more helpful.

Authors state that “list relative energies with respect to the separate reactants.” It seems that the energies are relative to RCs. 

How did the Authors consider adding H2O in, e.g., path C? Did they add H2O optimized energies to the part of the path without explicit H2O?

What step is the rate determined? That with the highest activation barrier, or the one with the highest energy of the transition state relative to the RC?

What temperature did the Authors consider for the calculation of the free energies? In the Introduction, the Authors mention 300 or 400 C. Does it make sense to talk about rate-determining steps at such temperatures? Wouldn’t the reaction be thermodynamically controlled? Would that imply that energies of Cu(II) complexes are the most important ones?

Some minor issues:

• Line 42 “lolite” -zeolite?
• 2 – Cu-TS5 has higher energy than any other specie in this pathway, which is not qualitatively drawn.
• DA in figures is not explained
• Table 1 – Cu-TS2, delta H, error in the entry point
• Captions in Tables do not include which path the results are for.
• Formatting should be improved (often spaces missing, fonts, etc.)

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors' corrections are in line with the review suggestions. I have no further comments on the manuscript.

Reviewer 3 Report

The authors improved the manuscript. 

I still believe that dispersion corrections should be taken into account for this study. However, I understand the problems the authors are facing.  One suggestion to the authors is to consider some of the free program packages (like orca, nwchem...). I also understand that redoing calculations with a new program demands lots of time and effort and is not something that should be done in the reviewing stage. Therefore, I will not insist on this point, and I believe the manuscript is now in the acceptable stage. 

 

and therefore I will not insist on this point.