Roles of Nanostructured Bimetallic Supported on Alumina-Zeolite (AZ) in Light Cycle Oil (LCO) Upgrading

Round 1

Reviewer 1 Report

The article describes the performance of the nanostructured bimetallic catalysts for light cycle oil upgrading. The results of the studies are of interest for the wide catalysis community as they concern production of fuels. Authors examine three catalytic systems: CoMo-alumina-zeolite, NiMo-alumina-zeolite, and NiW-alumina-zeolite. The catalysts are characterised by low temperature nitrogen sorption, XRD, TEM, and FTIR and applied in hydro-upgrading of the model light cycle oil and the real feeds.

Despite interesting results the study should be ameliorated before being considered for publication. My main concerns are listed below.

Authors report concentration of Brønsted and Lewis acid sites determined based on the FTIR results. The methodology section lacks information about the peak positions and extinction coefficients used.

XRD profiles reveal existence of MoS₂ and WS₂. Was XRD done for fresh catalysts or after the catalytic tests? If fresh catalysts were tested, what is the origin of sulfides? Why are oxides not visible?

Morphology of the catalysts is judged based on TEM images. They are of poor quality and the discussed structures (MoS₂, WS₂, Ni, Co) are hardly visible. The figure should be ameliorated.

What data support the statement: "Ni atoms enter into the zeolite channels more readily and tend to be evenly distributed across the support" (lines 194-195)?

Article contains data on HDS and HDA performance for CoMo/AZ catalyst (Figures 6, 7, 9 and 10), but the acidity measurements are reported for NiMo/AZ and NiW/AZ catalysts (Figure 12). Why? One cannot make the connection between the acid properties of the catalysts and their activity. 

It's difficult to understand what data is listed in Table 2. Are these kinetic rate constants? It should be specified.

What do "Model 1" and "Model 2" mean?

It is very difficult to follow data presented in Table 4. Maybe it would be easier if two tables are made, one reporting S content and the second reporting N content.  

Authors state that their results are in agreement with the DFT calculation results (line 292 - 293). Please specify. Which data? Add the reference.

Discussion of the acidity is difficult to follow. Data in Figure 12 should be better presented in order: "oxidised catalyst" first, "sulfidem catalyst" next. Then, the discussion (lines 394-409) would be easier.

Language should be ameliorated. In particular, an expression "Bi-metal" can be misleading, indicting bismuth containing systems. There are some typographical errors (eg. Frenquence in Figure 4). 

Author Response

Reviewer #1

The article describes the performance of the nanostructured bimetallic catalysts for light cycle oil upgrading. The results of the studies are of interest for the wide catalysis community as they concern production of fuels. Authors examine three catalytic systems: CoMo-alumina-zeolite, NiMo-alumina-zeolite, and NiW-alumina-zeolite. The catalysts are characterised by low temperature nitrogen sorption, XRD, TEM, and FTIR and applied in hydro-upgrading of the model light cycle oil and the real feeds.

Despite interesting results the study should be ameliorated before being considered for publication. My main concerns are listed below.

Response:

Thanks you for reviewing the manuscript, giving positive words to our work, and putting forward many detailed and reasonable comments, which have provided great help to the improvement of its scientific quality. We give our responses to the comments one by one as follow.

• Authors report concentration of Brønsted and Lewis acid sites determined based on the FTIR results. The methodology section lacks information about the peak positions and extinction coefficients used.

Response:

Thanks for the comment. We have added the relevant information for pyridine FTIR testing, including the determination of peak positions, in the experimental section “ 2.2 Catalyst characterization” section. 

• XRD profiles reveal existence of MoS2and WS2. Was XRD done for fresh catalysts or after the catalytic tests? If fresh catalysts were tested, what is the origin of sulfides? Why are oxides not visible?

Response:

Thanks for your comment. The XRD tests were done for the catalysts after being sulfided; therefore, the oxides on catalysts were sulfide into sulfided states, and the sulfides are visible, but the oxides not. Sorry for the confusing expression. We have modified the sentence in section “2.2 catalyst characterization” from “X-ray powder patterns were measured using a Bruker D8 Advance spectrometer” to “X-ray powder patterns of the three sulfided catalysts were measured using a Bruker D8 Advance spectrometer”.

• Morphology of the catalysts is judged based on TEM images. They are of poor quality and the discussed structures (MoS2, WS2, Ni, Co) are hardly visible. The figure should be ameliorated.

Response:

Thanks for the comment. We have added three “10 nm” pictures for the three catalysts and highlighted the slabs as well. Please find them in Fig. 4.

• What data support the statement: "Ni atoms enter into the zeolite channels more readily and tend to be evenly distributed across the support" (lines 194-195)?

Response:

Thanks for your comment. The atomic radiuses of Ni and Co are respectively 115 pm and 116 pm, and therefore Ni atoms easier enter the zeolite channels than Co atoms do. We have modified the words from “Comparing the NiMo/AZ and CoMo/AZ, Ni atoms entering the zeolite channels more readily and tend to be evenly distributed across the support, forming more narrowly distributed NiMo/AZ slabs. ” to “Comparing to NiMo/AZ and CoMo/AZ, Ni atoms enter the zeolite channels more readily as having smaller atom radius, tend to be more evenly distribution across the support, and form more narrowly distributed NiMo/AZ slabs.”

Besides, the TEM testing results shown in Table 1, Figure 5, and Figure 6 also support this statement.

• Article contains data on HDS and HDA performance for CoMo/AZ catalyst (Figures 6, 7, 9 and 10), but the acidity measurements are reported for NiMo/AZ and NiW/AZ catalysts (Figure 12). Why? One cannot make the connection between the acid properties of the catalysts and their activity. 

Response:

Thanks for your comment. We have added the FTIR test of CoMo/AZ and listed the testing results of these three catalysts in Table 2. also the following words "As can be seen in Table 2, The total B acids on the three catalyst barely have difference, but it not the case for L acids, which on NiMo/AZ is nearly double fold and four fold respectively to that on NiW/AZ and CoMo/AZ. As to acid types, the acids on both NiMo/AZ and NiW/AZ are mainly L acids, especially for the former; whereas the and L acids on CoMo/AZ are basically the same. In the terms of acid strength, the acids on NiW/AZ are mainly weak acids, and those on CoMo/AZ weak and middle acids, while there is a average distribution of weak, middle, and strong acids on NiMo/AZ.".

• It's difficult to understand what data is listed in Table 2. Are these kinetic rate constants? It should be specified.

Response:

According to your comment, we have revised all related information into: the kinetic rate constant(s) of HDS reaction or HDS kinetic rate constant(s).

• What do "Model 1" and "Model 2" mean?

Response:

Thanks for your comment. We have modified the words in section 2.3 Catalyst evaluation, “The 4,6-DMDBT was first tested and hexadecane was used as solvent. Then carbazole and ……” into “The 4,6-DMDBT was first tested and hexadecane was used as solvent (named as Model 1). Then carbazole (named as Model 2) and……”.

• It is very difficult to follow data presented in Table 4. Maybe it would be easier if two tables are made, one reporting S content and the second reporting N content. 

Response:

Thanks for your comment. As you suggested, we have split Table 4 into 2 tables, Table 5(a) and Table 5(b).

• Authors state that their results are in agreement with the DFT calculation results (line 292 - 293). Please specify. Which data? Add the reference.

Response:

Thanks for your comment. We have added the reference, [18].

• Discussion of the acidity is difficult to follow. Data in Figure 12 should be better presented in order: "oxidised catalyst" first, "sulfidem catalyst" next. Then, the discussion (lines 394-409) would be easier.

Response:

Thanks for your suggestion and we have rearranged the report format in Fig. 3 according to your comment.

• Language should be ameliorated. In particular, an expression "Bi-metal" can be misleading, indicting bismuth containing systems. There are some typographical errors (eg. Frenquence in Figure 4). 

Response:

Thank you for pointing out the errors. We have fixed those mistakes in the manuscript, including “Frenquence” in Figure 5, and the expression of “Bi-metal”; we either changed it to “bimetallic” or deleted the expression in the paper. In addition, we have polished the language of the whole paper. Please find the details in the revised manuscript.

Reviewer 2 Report

Dear authors,

The topic you have chosen is quite relevant, and a large number of works are published on it every year. It is difficult to overestimate the importance of studying the processes of refining petroleum fractions, and your work can contribute to the development of this topic. However, in its current form, I cannot recommend it for publication in the journal - I believe that it can and should be improved. Below are my comments for work:

1) It is necessary to carefully proofread the article and correct the shortcomings in the English language;
2) Based on the introduction, it is not clear why it was necessary to take two zeolites to create catalysts;
3) Similar studies on the composition of catalysts have been carried out before. What is the uniqueness and scientific novelty of your work?
4) Usually, the application of metals to zeolites or extrudates is carried out by impregnation with an aqueous solution of salts. 
5) In your case, you are using a mechanical mixture of zeolites, metal sources and binder. How justified is this approach? Does it allow you to achieve a uniform distribution of metal throughout the catalyst volume?
6) Typically, the catalysts for the process you are investigating are metal sulfides. Based on Figure 2, you also have metal sulfides - however, the experimental part does not say about the sulfiding of catalysts (except for the description of the experiment with LCO)
7) In the work, first of all, graphs of nitrogen adsorption should be given - these are "primary" data, and the pore size distribution is the result of their mathematical processing. Analyzing nitrogen adsorption graphs alone can provide a lot of useful information.
8) Information should be given on the textural properties of the original zeolites.
9) The formation of sulfide phases must be proved primarily by the XPS method.
10) Please provide photomicrographs of catalysts showing one layer of metal sulphides. In the micrographs presented in this work, most of the particles are composed of 2-4 layers

General note - if you draw any conclusion, try to support it with visual evidence. Or at least by references to works in which similar results were obtained under similar conditions.

Author Response

Reviewer #2

Dear authors,

The topic you have chosen is quite relevant, and a large number of works are published on it every year. It is difficult to overestimate the importance of studying the processes of refining petroleum fractions, and your work can contribute to the development of this topic. However, in its current form, I cannot recommend it for publication in the journal - I believe that it can and should be improved. Below are my comments for work:

Response:

Thank the reviewer for taking the time to review our paper, giving positive words to our work, and putting forward many detailed and reasonable comments, which have provided great help to the improvement its quality. We will response the comments one by one.

• It is necessary to carefully proofread the article and correct the shortcomings in the English language;

Response:

As reviewer’s comments, we have polished the language of the whole manuscript. Please find the details in the revised manuscript.

• Based on the introduction, it is not clear why it was necessary to take two zeolites to create catalysts;

Response:

Thanks for the comment. We have added the following words in the introduction section. “The addition of zeolite components in the support matrix of the hydrotreating catalysts led to the enhancement in its HDN, HDS, and HDA performances, such as zeolite beta, zeolite Y, and ZSM-5, and so on; and 3) the addition of the combination of zeolite beta and Y in the support matrix of hydrotreating catalysts had achieved better performances than single zeolite beta or Y.”

• Similar studies on the composition of catalysts have been carried out before. What is the uniqueness and scientific novelty of your work?

Response:

The synergistic effects between active components and supports are quite different [1-6]. Our previous studied have investigated the effects of modified zeolite supports on the reactivity of HDS, HDN, and HAD, and found that AZ is a good support for the hydrotreating catalyst. This manuscript is just a following work to investigated the role the NiW/NiMo/CoMo supported by AZ plays, and the synergistic effects between the different types of active components and AZ. This is the first study to investigate the performances and properties/structures of the NiW/AZ, NiMo/AZ, and CoMo/AZ catalysts.

[1] H. Wang, G. Li, K. Rogers, H. Lin, Y. Zheng, S. Ng, Hydrotreating of waste cooking oil over supported CoMoS catalyst Catalyst - deactivation mechanism study, Molecular Catalysis, 443 (2017) 228-240.

[2] J.C. Cortes, C. Rodriguez, R. Molina, S. Moreno, Hydrocracking of 1-methylnaphtalene (1MN) over modified clays-supported NiMoS and NiWS catalyst, Fuel, 295 (2021).

[3] P.P. Dik, I.S. Golubev, M.O. Kazakov, V.Y. Pereyma, M.Y. Smirnova, I.P. Prosvirin, E.Y. Gerasimov, D.O. Kondrashev, V.A. Golovachev, A.V. Kleimenov, O.S. Vedernikov, O.V. Klimov, A.S. Noskov, Influence of zeolite content in NiW/Y-ASA-Al2O3 catalyst for second stage hydrocracking, Catalysis Today, 377 (2021) 50-58.

[4] M.A. Salam, Y.W. Cheah, P.H. Ho, L. Olsson, D. Creaser, Hydrotreatment of lignin dimers over NiMoS-USY: effect of silica/alumina ratio, Sustainable Energy & Fuels, 5 (2021) 3445-3457.

[5] B.M. Santos, W. Zhao, J.L. Zotin, M.A.P. da Silva, L. Oliviero, F. Mauge, Impact of proximity between NiMoS and zeolitic HY sites on cyclohexene hydroconversion: An infrared operando study of sulfide catalysts, Journal of Catalysis, 396 (2021) 92-103.

• Usually, the application of metals to zeolites or extrudates is carried out by impregnation with an aqueous solution of salts. In your case, you are using a mechanical mixture of zeolites, metal sources and binder. How justified is this approach? Does it allow you to achieve a uniform distribution of metal throughout the catalyst volume?

Response:

Loading the active component on the support is usually via salt solution impregnation, drying, and calcinations. In this work, the active component of MoO₃ was loaded onto the surface of the support directly by mechanical mixing, drying, and calcination, instead of impregnation.

The reviewer is right. Usually, the dispersion of active components obtained by mechanical mixing, which is widely used in the industrial scale-up production of catalysts, is not as good as that by impregnation method. From the catalyst activity evaluation and characterization results, the HDS, HDN, HAD activities are all good. Besides, the microstructures and properties of the investigated catalysts are distributed uniformly. One of the goals of the current work is to provide reference to catalyst industrial amplification.

• Typically, the catalysts for the process you are investigating are metal sulfides. Based on Figure 2, you also have metal sulfides - however, the experimental part does not say about the sulfiding of catalysts (except for the description of the experiment with LCO)

Response:

Thanks for your comment. We actually describe the presulfuriding procedures in the last two sentences of the first paragraph of “2.3 catalyst evaluation”, The catalyst was sulfided with DMDS at 593 K for 2 hrs and 633 K for another 2 hrs.

• In the work, first of all, graphs of nitrogen adsorption should be given - these are "primary" data, and the pore size distribution is the result of their mathematical processing. Analyzing nitrogen adsorption graphs alone can provide a lot of useful information. Information should be given on the textural properties of the original zeolites.

Response:

Thanks for your comment. As reviewer’s comment, we have added the isotherm linear plot of the AZ and the three catalysts; please find the information in Figure 1 (a). Besides, we have added the following discussion in Section 3.1.1 Texture structures: “It can be seen from Figure 1(a) that the surface structures of AZ changed significantly after the active metals loaded. The isotherm of AZ is type I, rich of the microporous structure. An obvious hysteresis loop appeared on the isotherms curves after the active components was loaded on AZ; therefore, the adsorption and desorption curves of the supported catalysts are of type IV, mainly mesoporous structures.”

• The formation of sulfide phases must be proved primarily by the XPS method.

Response:

As reviewer’s comment, we have added the XPS tests for the three catalysts in Fig. 5 and the following words were added in section 3.1.2 Morphology, too: “Figure 5 shows the states of S 2p and Mo 3d or W 4f on the sulfided catalysts. According to the literature[23-27], combining with the information in Figure 5, all these three catalysts exhibit the signals of both sulfur S 2p_3/2 and MoS₂ or WS₂, and confirms the formation of sulfide phases on the catalysts, which is accordance with the XRD results.”

• Please provide photomicrographs of catalysts showing one layer of metal sulphides. In the micrographs presented in this work, most of the particles are composed of 2-4 layers

Response:

Thanks for your comment. We have added three “10 nm TEM images” in Figure 4.

• General note - if you draw any conclusion, try to support it with visual evidence. Or at least by references to works in which similar results were obtained under similar conditions.

Response:

Thanks for your suggestions. We improve our works in the future. 

Round 2

Reviewer 1 Report

The article ameliorated a lot after all changes were introduced. I suggest English polishing, in particular of the fragments added during the revision.

Author Response

Dear editor and reviewer,
 
Thanks for your time and positive responses for our revised manuscript. According to reviewer’s comment, we have had our manuscript carefully revised by  Dr. Kyle Rogers again, who is one of the co-authors, an English native speaker with PhD in Chemical Engineering, and now a research scientist at University of New Brunswick, Canada. We have used the “Track Changes” function during our revising. Please find the details in the revised manuscript. Thanks!
 
Best,
 
Hui Wang

Author Response File: Author Response.pdf

Reviewer 2 Report

Good work