Preparation and Performance of the Lipid Hydrodeoxygenation of a Nickel-Induced Graphene/HZSM-5 Catalyst

Round 1

Reviewer 1 Report

This article presents a detailed investigation of the nickel-induced graphene /HZSM-5 catalysts were prepared with various binders, and the shaped catalysts were tested via oleic acid hydrodeoxygenation and compared with traditional catalysts. A wide range of experimental research methods has been used. This experimental research will be useful for expanding knowledge in the field of noble metal encapsulated nanostructured catalysts synthesis for industrial applications.  In general, the article meets the requirements of the journal. However, in the «Introduction» part it would be possible to be reduced. The title and abstract correspond to the content of the article in full. The conclusions of the article are confirmed by the results of experimental studies conducted by the authors.

Author Response

Response to Reviewer 1 Comments

 

Point 1: This article presents a detailed investigation of the nickel-induced graphene /HZSM-5 catalysts were prepared with various binders, and the shaped catalysts were tested via oleic acid hydrodeoxygenation and compared with traditional catalysts. A wide range of experimental research methods has been used. This experimental research will be useful for expanding knowledge in the field of noble metal encapsulated nanostructured catalysts synthesis for industrial applications.  In general, the article meets the requirements of the journal. However, in the «Introduction» part it would be possible to be reduced. The title and abstract correspond to the content of the article in full. The conclusions of the article are confirmed by the results of experimental studies conducted by the authors.

 

Response 1: Thank you for your comments. The «Introduction» part was altered. Please see below:

The global carbon reduction plan is related to the sustainable development of the environment and ecology. Biomass energy is considered an alternative to fossil fuels, with the advantages of low carbon emissions, environmental protection, and sustainable development of new energy sources [1]. The development of biomass energy will help accelerate the process of global carbon reduction. The conversion of oil into bio-jet fuel through hydrodeoxidation, cracking, aromatization and isomerization is an important biomass conversion route [2]. Compared to conventional petroleum-based jet fuels, bio-jet fuel can reduce CO₂ emissions by more than 55% and up to 90% during the whole life cycle[3-5]. Therefore, it is more and more attractive to produce bio-jet from renewable oil, such as saturated or unsaturated fatty acids (SFAs) found in vegetable oils, triglycerides, animal fats and waste cooking oils (WCO) [6].

The conversion process of bio-jet fuel mainly consists of two steps. The first step is to convert triglyceride and unsaturated fatty acids into saturated fatty acids by hydrogenation. Then saturated fatty acids are converted to C17-C18 linear alkanes through hydrodeoxygenation and decarboxylation reactions. The second step is the selective hydrocracking and deep isomerization of the deoxygenated linear alkanes to generate mixed liquid fuel of highly branched alkanes [7]. The common catalysts for these steps require Lewis and Brønsted acid site and metal centers [8,9]. Conventional sulfide state catalysts NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ exhibited high activity, but they deactivated rapidly due to potential toxicity in aqueous solution and carbon deposition [10]. Noble metals (such as Pt, Pd, and Ru) pose high activity and selectivity for fatty acid conversion, but the high prices hinder their large-scale applications [11]. Therefore, the researchers turned their attention to non-noble metal catalysts. Nickel-based catalyst is currently the most widely used non-noble metal catalyst in the industry. The cost of nickel is only one-thousandth of the noble metal, and it is more suitable for industrial applications as metal centers [12,13]. Nickel has high hydrogenation activity due to the electron holes in the d orbital. In addition, nickel can effectively activate the C-C bond during the deoxygenation of fatty acids (Cn) to generate Cn-1 alkanes [8,9,11]. However, traditional nickel-based catalysts are prone to deactivation during a continuous reaction. On the one hand, metal particles are easily leached or agglomerated. On the other hand, polycyclic aromatic hydrocarbons are formed during lipid hydrodeoxygenation, resulting in carbon deposits that cover the active sites of the catalyst [14,15]. HZSM-5 zeolite molecular sieve poses Lewis and Brønsted acid sites required for hydrodeoxygenation, high specific surface area, thermostability, and hydrothermal stability. It has become the most promising catalyst for the preparation of bio-jet fuel. In our previous research, the catalyst Ni@C/HZSM-5 was obtained by loading the graphene-encapsulated nickel nanoparticle structure (Ni@C) on the zeolite HZSM-5. It found that the Ni@C effectively protected the metal nanoparticles from the acid solution, enhanced the activity of the catalyst, and slowed down the deactivation rate of the metal center due to the synergistic effect of carbon materials and metal nanoparticles [2].

In a packed bed reactor (PBR), the powder of the catalysts may block the reaction pipe and cause an increase in the reactor pressure[16]. Therefore, catalyst molding is crucial for the industrial application of catalysts. During the molding process of a catalyst, binders are as indispensable additives so that the catalyst can meet the mechanical strength requirements for industrial applications [17]. Among them, the enhancement of mechanical strength is realized by the adhesion force of the binder and the cross-linking of terminal hydroxyl groups between adjacent binder particles [18]. Commonly used binders are Al₂O₃ [19,20], SiO₂ [21,22], pseudo-boehmite [23,24], and ZrO₂ [25]. The ion exchange capacity and acid catalytic activity of shaped HZSM-5 was significantly enhanced when the catalyst was extruded with an Al₂O₃ binder [26]. Al₂O₃ provided more acid sites, and the shaped catalyst also had a good pore structure [21]. After adding a pseudo-boehmite binder to the catalyst, the shaped catalyst PtS/Z-A30-650 showed higher n-C5/C6 isomerization activity and mechanical strength [24]. Furthermore, the added ZrO₂ provided an additional diffusion path for mass transfer between SAPO-34 crystals, making the shaped catalyst SAPO-34/ZrO₂ show a higher catalytic lifespan than SAPO-34 [25]. However, adding a binder also generates negative effects on the catalyst, such as the silica as a binder decreasing the catalytic activity by blocking the porosity of zeolites and reducing mass transfer efficiency[14,17]. Since the formation of Ni@C catalyst is a crucial step towards its industrial application, which has never been reported, the influence of the binder on the nucleation process of graphene-encapsulated Ni clusters remains unclear.

In this work, we used three common binders, pseudo-boehmite, alumina and zirconia, as raw materials to study the molding preparation of Ni@C coupled with traditional zeolite HZSM-5. Furthermore, the stability of various-shaped catalysts for continuous hydrogenation to prepare bio-aviation kerosene was investigated in a fixed bed high temperature and high-pressure reactor, and the performance was compared with that of traditional Ni/HZSM-5. In this paper, we use zeolite HZSM-5 as support and study the ability of different binders to form carbon-encapsulated nickel structures by adding nickel, carbon source, and binder at one time. Moreover, the study investigates the utilization of oleic acid as a model compound and analyzed the hydrodeoxygenation performance and catalytic lifespan of the shaped catalysts and assessed their capability to produce bio-jet fuel.

References:

1. Silveira Junior, E.G.; Perez, V.H.; Reyero, I.; Serrano-Lotina, A.; Justo, O.R. Biodiesel production from heterogeneous catalysts based K2CO3 supported on extruded γ-Al2O3. Fuel 2019, 241, 311-318, doi:10.1016/j.fuel.2018.12.074.
2. Li, M.; Fu, J.; Lv, P.; Zhang, X.; Liu, X.; Zeng, Q.; Yang, L.; Wang, Z.; Yuan, Z. ZSM-5-Supported Graphene-Encapsulated Nickel Nanoparticles: Formation, Properties, and Exceptional Performance in Lipid Hydrogenation. ACS Sustainable Chemistry & Engineering 2020, 8, 15484-15495, doi:10.1021/acssuschemeng.0c03559.
3. Bond, J.Q.; Upadhye, A.A.; Olcay, H.; Tompsett, G.A.; Jae, J.; Xing, R.; Alonso, D.M.; Wang, D.; Zhang, T.; Kumar, R.; et al. Production of renewable jet fuel range alkanes and commodity chemicals from integrated catalytic processing of biomass. Energy Environ. Sci. 2014, 7, 1500-1523, doi:10.1039/c3ee43846e.
4. Melero, J.A.; Iglesias, J.; Garcia, A. Biomass as renewable feedstock in standard refinery units. Feasibility, opportunities and challenges. Energy & Environmental Science 2012, 5, doi:10.1039/c2ee21231e.
5. Olcay, H.; Subrahmanyam, A.V.; Xing, R.; Lajoie, J.; Dumesic, J.A.; Huber, G.W. Production of renewable petroleum refinery diesel and jet fuel feedstocks from hemicellulose sugar streams. Energy Environ. Sci. 2013, 6, 205-216, doi:10.1039/c2ee23316a.
6. Wei, H.; Liu, W.; Chen, X.; Yang, Q.; Li, J.; Chen, H. Renewable bio-jet fuel production for aviation: A review. Fuel 2019, 254, doi:10.1016/j.fuel.2019.06.007.
7. Morgan, T.; Santillan-Jimenez, E.; Harman-Ware, A.E.; Ji, Y.; Grubb, D.; Crocker, M. Catalytic deoxygenation of triglycerides to hydrocarbons over supported nickel catalysts. Chemical Engineering Journal 2012, 189-190, 346-355, doi:10.1016/j.cej.2012.02.027.
8. Wang, Y.; Tao, Z.; Wu, B.; Xu, J.; Huo, C.; Li, K.; Chen, H.; Yang, Y.; Li, Y. Effect of metal precursors on the performance of Pt/ZSM-22 catalysts for n -hexadecane hydroisomerization. Journal of Catalysis 2015, 322, 1-13, doi:10.1016/j.jcat.2014.11.004.
9. Zarchin, R.; Rabaev, M.; Vidruk-Nehemya, R.; Landau, M.V.; Herskowitz, M. Hydroprocessing of soybean oil on nickel-phosphide supported catalysts. Fuel 2015, 139, 684-691, doi:10.1016/j.fuel.2014.09.053.
10. Sotelo-Boyás, R.; Liu, Y.; Minowa, T. Renewable Diesel Production from the Hydrotreating of Rapeseed Oil with Pt/Zeolite and NiMo/Al2O3 Catalysts. Industrial & Engineering Chemistry Research 2010, 50, 2791-2799, doi:10.1021/ie100824d.
11. Wang, D.; Ma, B.; Wang, B.; Zhao, C.; Wu, P. One-pot synthesized hierarchical zeolite supported metal nanoparticles for highly efficient biomass conversion. Chem Commun (Camb) 2015, 51, 15102-15105, doi:10.1039/c5cc06212h.
12. Shi, Y.; Xing, E.; Cao, Y.; Liu, M.; Wu, K.; Yang, M.; Wu, Y. Tailoring product distribution during upgrading of palmitic acid over bi-functional metal/zeolite catalysts. Chemical Engineering Science 2017, 166, 262-273, doi:10.1016/j.ces.2017.03.052.
13. Srifa, A.; Faungnawakij, K.; Itthibenchapong, V.; Assabumrungrat, S. Roles of monometallic catalysts in hydrodeoxygenation of palm oil to green diesel. Chemical Engineering Journal 2015, 278, 249-258, doi:10.1016/j.cej.2014.09.106.
14. Ginosar, D.M.; Thompson, D.N.; Burch, K.C. Recovery of alkylation activity in deactivated USY catalyst using supercritical fluids: a comparison of light hydrocarbons. Applied Catalysis A: General 2004, 262, 223-231, doi:10.1016/j.apcata.2003.11.030.
15. Wang, N.; Zhi, Y.; Wei, Y.; Zhang, W.; Liu, Z.; Huang, J.; Sun, T.; Xu, S.; Lin, S.; He, Y.; et al. Molecular elucidating of an unusual growth mechanism for polycyclic aromatic hydrocarbons in confined space. Nat Commun 2020, 11, 1079, doi:10.1038/s41467-020-14493-9.
16. Wang, J.; Gao, X.; Chen, G.; Ding, C. Forming pure shaped ZSM-5 zeolite bodies by a steam-assisted method and their application in methanol to aromatic reactions. RSC Advances 2019, 9, 28451-28459, doi:10.1039/c9ra05513d.
17. Zhou, J.; Teng, J.; Ren, L.; Wang, Y.; Liu, Z.; Liu, W.; Yang, W.; Xie, Z. Full-crystalline hierarchical monolithic ZSM-5 zeolites as superiorly active and long-lived practical catalysts in methanol-to-hydrocarbons reaction. Journal of Catalysis 2016, 340, 166-176, doi:10.1016/j.jcat.2016.05.009.
18. Freiding, J.; Patcas, F.-C.; Kraushaar-Czarnetzki, B. Extrusion of zeolites: Properties of catalysts with a novel aluminium phosphate sintermatrix. Applied Catalysis A: General 2007, 328, 210-218, doi:10.1016/j.apcata.2007.06.017.
19. Duan, Y.; Zhou, Y.; Sheng, X.; Zhang, Y.; Zhou, S.; Zhang, Z. Influence of alumina binder content on catalytic properties of PtSnNa/AlSBA-15 catalysts. Microporous and Mesoporous Materials 2012, 161, 33-39, doi:10.1016/j.micromeso.2012.05.016.
20. Kong, X.; Liu, J. Influence of alumina binder content on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone. PLoS One 2014, 9, e101744, doi:10.1371/journal.pone.0101744.
21. Du, X.; Kong, X.; Chen, L. Influence of binder on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone. Catalysis Communications 2014, 45, 109-113, doi:10.1016/j.catcom.2013.10.042.
22. Zhou, S.; Zhang, C.; Li, Y.; Shao, B.; Luo, Y.; Shu, X. A facile way to improve zeolite Y-based catalysts' properties and performance in the isobutane–butene alkylation reaction. RSC Advances 2020, 10, 29068-29076, doi:10.1039/d0ra03762a.
23. Zheng, Y.; Song, J.; Xu, X.; He, M.; Wang, Q.; Yan, L. Peptization Mechanism of Boehmite and Its Effect on the Preparation of a Fluid Catalytic Cracking Catalyst. Industrial & Engineering Chemistry Research 2014, 53, 10029-10034, doi:10.1021/ie501060g.
24. Hongyan, Z.; Yueqin, S.; Haiwei, N.; Jun, X.; Xiaolong, Z. Moldeling and lifetime test of solid superacid catalyst for n-C5/C6 isomerization. Petroleum processing and petrochemicals 2018, 49, 79-.
25. Lee, S.-G.; Kim, H.-S.; Kim, Y.-H.; Kang, E.-J.; Lee, D.-H.; Park, C.-S. Dimethyl ether conversion to light olefins over the SAPO-34/ZrO2 composite catalysts with high lifetime. Journal of Industrial and Engineering Chemistry 2014, 20, 61-67, doi:10.1016/j.jiec.2013.04.026.
26. Aghamohammadi, S.; Haghighi, M. Spray-dried zeotype/clay nanocatalyst for methanol to light olefins in fluidized bed reactor: Comparison of active and non-active filler. Applied Clay Science 2019, 170, 70-85, doi:10.1016/j.clay.2019.01.006.

 

Reviewer 2 Report

In the present work, the authors report the synthesis, characterization and catalytic performance of graphene-encapsulated Ni@C /HZSM-5 catalysts. Among the different catalysts, the Ni@C/Z5+Zr and Ni@C/Z5+Al catalysts showed enhanced stability in the hydrodeoxidation of oleic acid. This has been attributed to a good dispersion of Ni particles thanks to a protective carbon layer, and a high number of acid sites, less prone to deactivation. However, these arguments are not fully articulated, and need to be supported by experimental evidences. In particular, the graphene layer, which is key in the stabilization of the Ni particles, has not been characterised in detail. Raman and carbon analysis of fresh and spent catalysts need to be included and discussed. On the other hand, the acid properties of the fresh and spent Nickel based catalysts need to be included. Thus, a detailed IR-analysis and discussion of the Brönsted acidity with the catalytic performance need to be included. The authors should also discuss coke formation and catalyst regeneration. In addition, the chemical composition of the samples is missed and need to be included. Finally, what is the role of nickel in the catalytic performance, specifically if a “complete graphene-encapsulated Nickel particle structure “has been reported? What about the accessibility of nickel sites to the reactants? (line 118).

Beside these comments, some other points need to be clarified: 1) please explain “acid pickling test”. 2) What the authors want to say with “cracking of the catalyst and the loss of the metal center (line 214,215)”. 3) Please indicate how the quantitative data of Brönsted and Lewis acid sites (line 176) have been done.

In summary, the referee recommendation is rejection. The authors should do more experimental work to support the hypothesis before a new re-submission.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Main question addressed by the research: The work addresses the issues related to Preparation and performance in lipid hydrodeoxygenation of nickel-induced graphene /HZSM-5 catalyst.
Originality and relevance of the topic: The topic is relevant to the field and it considers a suitable research gap.
Added value of the paper:  The manuscript takes into account the study of the the ability of different binders to form carbon-encapsulated nickel structures by adding nickel, carbon source and binder, however the main purpose of it is not clearly stated. The paper should include clearly why they are analysing those and why they are needed. 

Quality of figures: Formatting should be consistent and quality should be improved for readability.
Specific improvements for the paper to be considered:

1. Abstract is too short and general. It should summarize the main findings and applications of the paper. 
2. There is a big issue with structure in this paper. Materials and methods should go before Results or then it is difficult to follow what was done.
3. Why is the stabilization of the metal interface of Ni@C/Z5+Zr delayed the accumulation rate of carbon deposits?
4. The selection of the optimal catalytic conditions is unclear, please add more results and discussion.
5. The conclusions are poor and they would need more elaboration so they clearly match the results.

Author Response

Response to Reviewer 3 Comments

 

Point 1: Main question addressed by the research: The work addresses the issues related to Preparation and performance in lipid hydrodeoxygenation of nickel-induced graphene /HZSM-5 catalyst. Originality and relevance of the topic: The topic is relevant to the field and it considers a suitable research gap. Added value of the paper:  The manuscript takes into account the study of the ability of different binders to form carbon-encapsulated nickel structures by adding nickel, carbon source and binder, however the main purpose of it is not clearly stated. The paper should include clearly why they are analyzing those and why they are needed.

 

Response 1: Thank you for your comments. We have added the part 3.1 about analysis of nuclear of Ni@C. Please see part 3.1.

According to our previous work [1], carbohydrates such as citric acid, glucose, and sorbitol can be used as carbon sources to generate graphene layers. In comparison, sucrose is more conducive to reducing the size of nickel cores under the same addition amount and is more conducive to industrial application for its low cost. The nucleation process of Ni@C was carefully studied by TG-FTIR in previous reports [1]. The impregnation process ensured that the nickel nitrate and sucrose were uniformly mixed and well dispersed on the surface of the molecular sieve. During the roasting and heating process, the sucrose and the nickel nitrate were decomposed into amorphous carbon and nickel oxide, respectively. Due to the high surface energy of nickel species, nickel species were very easy to agglomerate. In this system, the nickel nitrate originally mixed in sucrose was gradually decomposed into nickel oxide and rapidly enriched into small clusters with the calcination temperature increase. Then a solid dispersion was formed in amorphous carbon. In the subsequent process, the nickel nucleus increased to a certain extent, and an amorphous-carbon inert layer was formed, which blocked the continuous increase of nickel species. The nickel oxide was subsequently reduced to Ni0 by the surrounding amorphous carbon, and Ni⁰ as a "catalyst" induced the rearrangement of the amorphous carbon to form multilayer graphene.

Reference:

1. Li, M.; Fu, J.; Lv, P.; Zhang, X.; Liu, X.; Zeng, Q.; Yang, L.; Wang, Z.; Yuan, Z. ZSM-5-Supported Graphene-Encapsulated Nickel Nanoparticles: Formation, Properties, and Exceptional Performance in Lipid Hydrogenation. ACS Sustainable Chemistry & Engineering 2020, 8, 15484-15495, doi:10.1021/acssuschemeng.0c03559.

 

Point 2: Quality of figures: Formatting should be consistent and quality should be improved for readability.

 

Response 2: Figures have been re-edited. Please the

 

Point 3: Abstract is too short and general. It should summarize the main findings and applications of the paper.

 

Response 3: We have rewritten the abstract. Please see below:

Graphene encapsulating nickel nanoclusters is a feasible strategy to inhibit nickel deactivation of nickel-based catalysts. In this work, the graphene-encapsulated catalysts (Ni@C/HZSM-5) were prepared by a compression forming process, using pseudo-boehmite, Al₂O₃, and ZrO₂ as binders. The pseudo-boehmite was gradually transformed from amorphous to crystalline alumina during high temperature, which destroyed the nucleation of Ni@C. In contrast, the crystal-stabilized zirconia was more favorable for the nucleation of Ni@C. The extensive dispersion of alumina on the surface of HZSM-5 makes the acid sites of HZSM-5 covered. In contrast, when zirconia was used as the binder, the binder exists in the form of direct aggregation of ~100 nm zirconia spheres, and this distribution form better reduced the damage of the binder to the acid site of the catalyst. Furthermore, the particle size of Ni crystals in the graphene-encapsulated catalysts decreased significantly (mostly < 11 nm), and no evident agglomeration of nickel particles appeared. It was found that the stabilization of the metal interface delayed to an extent the accumulation rate of carbon deposits and thus postponed the deactivation of acid sites. After 8 h of continuous reaction, the conversion of traditional catalyst Ni/Z5+Zr dropped significantly to 60%. In contrast, the conversion of Ni@C catalysts prepared with ZrO₂ remained above 90%. The regeneration test showed that air roasting could effectively remove carbon deposits and restore catalyst activity.

 

Point 4: There is a big issue with structure in this paper. Materials and methods should go before Results or then it is difficult to follow what was done.

 

Response 4: We have adjusted the "Materials and methods".

 

Point 5: Why is the stabilization of the metal interface of Ni@C/Z5+Zr delayed the accumulation rate of carbon deposits?

 

Response 5: The reason for the stabilization of the metal interface of Ni@C/Z5+Zr delayed the accumulation rate of carbon deposits was added in Part 3.5. “There is a competitive relationship between the metal center and the acid site corresponding to the adsorption of the substrate, and the two active sites have different conversion routes for the substrate components. The stability of the metal center effectively inhibits the activity of the acid site. This is because Ni@C catalyst has a slower rate of aromatics selectivity decline compared with traditional catalysts, indicating that its acid site deactivation is slower. This is precise because Ni@C effectively inhibits the acid site-dominated aromatization process, delaying carbon deposition. accumulation.”

 

Point 6: The selection of the optimal catalytic conditions is unclear, please add more results and discussion.

 

Response 6: The setting of the test conditions in this part was based on the previous research basis[1]. This work aims to discuss the influence of adding different binders on the product components, and the component generation process is based on the above analysis.

Reference:

1. Li, M.; Fu, J.; Lv, P.; Zhang, X.; Liu, X.; Zeng, Q.; Yang, L.; Wang, Z.; Yuan, Z. ZSM-5-Supported Graphene-Encapsulated Nickel Nanoparticles: Formation, Properties, and Exceptional Performance in Lipid Hydrogenation. ACS Sustainable Chemistry & Engineering 2020, 8, 15484-15495, doi:10.1021/acssuschemeng.0c03559.

 

Point 7: The conclusions are poor and they would need more elaboration so they clearly match the results.

 

Response 7: We have rewritten the conclusions. Please see beolw:

It was found that ZrO₂ and Al₂O₃ were suitable binders for forming a complete graphene carbon layer, while pseudo-boehmite was not conducive to the formation of Ni@C, due to the calcination of pseudo-boehmite affecting the nucleation of Ni@C. The easy leaching and accumulation of the metal center led to shortening the lifespan of the shaped traditional catalyst Ni/Z5+Zr. The method of graphene encapsulating nickel particles mitigated this phenomenon effectively. After graphene encapsulation, the particle size of Ni crystals in the catalyst was (mostly < 11 nm), and no obvious accumulation of nickel particles appeared. The graphene-encapsulated catalysts exhibit better stability and longer lifespan compared to the traditional catalysts. When the conversion rate was reduced to 60%, the continuous reaction time of the traditional catalyst Ni/Z5+Zr was 8 h, while that of Ni@C/Z5+Zr was prolonged to 12 h. Ni@C/Z5+Zr and Ni@C/Z5+Al offer more stable activity and more increased catalytic lifespan compared with the binder-free Ni@C/Z5+N. After 8 h of continuous reaction time, the aromatics selectivity of Ni@C/Z5+Zr was 93.7%, while 51.6% aromatics selectivity was observed with the Ni@C/Z5+Al. After 7 hours of continuous hydrogenation, regeneration was carried out and the conversion increased by 8.8%. The conversion of the refresh catalyst could still be maintained above ~90% after four hours of continuous reaction, indicating that the catalyst activity could be effectively recovered after regeneration, although the activity of the refresh catalyst was not fully restored after regeneration. It is reasonable to believe that Ni@C/Z5+Zr has good application potential in industrial hydrodeoxygenation processes, based on the advantages of Ni@C/Z5+Zr in activity, selectivity, stability, and cost, as well as realizing efficient regeneration to prolong catalyst lifespan.

 

Round 2

Reviewer 2 Report

The manuscript has been carefully revised by the authors, however some points are still unclear and some data are still missing, therefore I recommend the authors to work a little more before final publication of the manuscript. Some of these comments are the following:

 Acidity. One point already commented during the first round was to include IR-Pyridine spectra of the different set of catalysts before and after reaction. According to the reviewer suggestion, the authors included a new Figure, i.e. 7b regarded to the IR –Pyridine of the Ni@C/Z5+Zr sample. However, they didn’t  included the IR spectra of the Ni@C/Z5+Al sample (before and after reaction) which is important due to their different aromatic selectivity. These results are necessary to complete the discussion in line 416-421.

Catalyst regeneration. It is confusing. Several points need to be clarified: 1) from the experimental point of view, (line 139-142) Why the sample after air calcination was transferred to a solution of Ni(NO3)2 and sucrose?. 2) from the catalytic performance, (line 454-455) Why after regeneration the catalyst activity increased by 8.8%?. 3) from the discussion in the text (line 459, and 482) why the authors conclude that the activity of the refresh catalyst was not fully restored after regeneration. Probably “refresh” and “regenerated” samples are not the same, in that case it need to be define clearly in order to avoid confusion. 4) from fundamental point of view, (line 459) “air rosting could not completely remove all carbon deposits. These carbon deposits acted as a template for subsequent carbon deposits…” please give some experimental evidence.

Additional comments, which are difficult to understand and need to be explained better:

1)      In line 429 a competitive relationship between the metal center and the acid site are argued. This type of competitiveness is not clearly shown.

2)      Line 273, what is the meaning of diffusion distance of heterogeneous intermediates,? Please comment on it and how it influence the catalytic performance of the samples.

3)      Line 256 “The binder ZrO2 was distributed at the junction of the molecular sieve and did not cover the surface of the molecular sieve, which was beneficial for exposing more active sites on the surface of the carrier” . How can the authors conclude that the ZrO2 is distributed at the junction of the molecular sieve

4)      Line 98 the performance was compared with that of traditional Ni/HZSM5? That is incorrect, please modify

5)      Line 236 “… resulting in the loss of nickel particles in the process of pickling”. Quantitative data supporting this assumption need to be included

6)      In figure 2 the TEM of the Ni@C/Z5+PB is not found, while discussed in the text.

7)      Line 203 , instead of Figure 2 it should be figure 1.

 

In addition, some typos need to be corrected: line 435 delaying carbon deposition.accumulation. Also typos in Caption of figure 2 need to be revised

Author Response

Response to Reviewer 2 Comments

Point 1: One point already commented during the first round was to include IR-Pyridine spectra of the different sets of catalysts before and after the reaction. According to the reviewer’s suggestion, the authors included a new Figure, i.e. 7b regarded to the IR –Pyridine of the Ni@C/Z5+Zr sample. However, they didn’t include the IR spectra of the Ni@C/Z5+Al sample (before and after reaction) which is important due to their different aromatic selectivity. These results are necessary to complete the discussion in lines 416-421.

 

Response 1: Thank you very much for your comments. We supplemented the IR-Pyridine of Ni@C/Z5+Al. The difference in the amount of strong Brønsted acid of the Ni@C/Z5+Al and Ni@C/Z5+Zr before the reaction was determined at a desorption temperature of 350 °C, which is enough to explain the difference in the selectivity of aromatics between the two catalysts. The sentence “As shown in Figure 7, the amount of strong Brønsted acid of Ni@C/Z5 +Zr is 0.053 mmol/g, while Ni@C/Z5+Al is 0.041 mmol/g. Furthermore, it can be seen from Figure 6 that Ni@C/Z5 + Zr also maintains better catalytic activity in aromatic hydrocarbon formation and exhibits more active acid centers than Ni@C/Z5+Al.” and Figure 7 were added in lines 417-420.

 

 

 

Point 2: From the experimental point of view, (line 139-142) Why the sample after air calcination was transferred to a solution of Ni(NO₃)₂ and sucrose?.

 

Response 2: In the air calcination process, the carbon deposit and graphene carbon layer are considered to be removed. Then the corresponding stoichiometric Ni(NO₃)₂ and sucrose solution are added to the solution to form a new graphene-encapsulated nickel particle structure to achieve regeneration. So the samples were calcined in air and transferred to nickel nitrate and sucrose solutions for impregnation. The sentence “After calcination at 500 °C, the carbon content was largely eliminated, and the carbon content was decreased from 12.75wt% to 0.99wt% (Table 2). The previous experimental study showed that after calcination in air at 500℃, the nickel would agglomerate, thereby reducing the activity of the metal center. Therefore, it is considered that the calcined catalyst is reimpregnated with a corresponding stoichiometric amount of nickel nitrate and sucrose solution. After calcination, the graphene-encapsulated nickel particle structure is reformed.” was added in lines 139-145.

 

Point 3: Why after regeneration the catalyst activity increased by 8.8%?.

 

Response 3: After refresh, the catalyst conversion increased from 91.0% to 99.8% at the 8th h in Figure 8a, increasing by 8.8%.

 

Point 4: From the discussion in the text (line 459, and 482) why the authors conclude that the activity of the refresh catalyst was not fully restored after regeneration. Probably “refresh” and “regenerated” samples are not the same, in that case it need to be define clearly in order to avoid confusion.

 

Response 4: Figure 8 shows that the conversion of the regenerated catalyst dropped to 90.3% after four hours of continuous reaction, which was more than the first four hours of the fresh catalyst. Moreover, after air calcination, it can be seen from the data in Table 2 that the carbon content still contains 0.99wt%, which cannot be completely removed. This regeneration process can restore most activity, but it cannot be completely restored. The meanings of refresh and regeneration are the same. In order to avoid confusion, we have unified the word “refresh” in the article (line 475, and 497).

 

Point 5: In line 429 a competitive relationship between the metal center and the acid site are argued. This type of competitiveness is not clearly shown.

 

Response 5: The conversion paths of substrates are different at different active sites, and the site with stronger activity plays a leading role. This part has been explained in detail in Part 3.4 (lines 336~356). When the acid center dominates the reaction, the products are mainly aromatics. When metal centers compete with acid centers, the products are mainly alkanes [1]. The sentences “When the acid center dominates the reaction, the products are mainly aromatics. When a competitive relationship between the metal center and the acid site center, the products are mainly alkanes[35].” was added in lines 443~445.

 

 

Point 6: Line 273, what is the meaning of diffusion distance of heterogeneous intermediates,? Please comment on it and how it influence the catalytic performance of the samples.

 

Response 6: The diffusion distance of heterogeneous intermediates represents the contact between the substrate and the active site. Reducing the particle size of metal nanoparticles can significantly increase the contact between the substrate and the active site and improve the catalytic efficiency. We chose a more straightforward expression “The dispersity of loaded metal affects the contact between the substrate and the active site [28,29]. Improving the dispersity of metal particles can increase the contact between the substrate and the active site which is one of the most favorable means to improve the catalytic efficiency greatly.” in lines 278~282.

 

Point 7: Line 256 “The binder ZrO2 was distributed at the junction of the molecular sieve and did not cover the surface of the molecular sieve, which was beneficial for exposing more active sites on the surface of the carrier”. How can the authors conclude that the ZrO2 is distributed at the junction of the molecular sieve.

 

Response 7: What we want to express is to observe from Figure 2c that when zirconia was used as the binder, the binder existed in the form of direct aggregation of ~100 nm zirconia spheres, and this distribution form better reduced the damage of the binder to the acid site of the catalyst. After consideration, the original sentence was replaced with a more clear sentence “The binder ZrO2 exists in the form of direct aggregation of ~ 100nm zirconia spheres, and this distribution better reduces the coverage of the catalyst by the binder, thereby reducing the damage of the acid site of the catalyst.” in lines 261~264.

 

Point 8:  Line 98 the performance was compared with that of traditional Ni/HZSM5? That is incorrect, please modify

 

Response 8: In response to this problem, we have revised the manuscript by replacing Ni/HZSM5 with Ni/Z5 + Zr in line 99.

 

Point 9: Line 236 “… resulting in the loss of nickel particles in the process of pickling”. Quantitative data supporting this assumption need to be included

 

Response 9: The quantitative data was added in Table 2. The sentence “It means that the formed graphene carbon layer did not completely encapsulate the nickel particles, resulting in the loss of nickel loading ratio from 4.23 wt% to 1.02 wt% in the process of pickling(Table 2).” was added in line 243.

 

Point 10: in figure 2 the TEM of the Ni@C/Z5+PB is not found, while discussed in the text.

 

Response 10: We have added the TEM of the Ni@C/Z5 + PB in Figure 2c.

 

 

Point 11: Line 203 , instead of Figure 2 it should be Figure 1.

 

Response 11: We have replaced Figure 2 with Figure 1 in line 209.

 

Point 12: Some typos need to be corrected: line 435 delaying carbon deposition.accumulation. Also typos in Caption of figure 2 need to be revised

 

Response 12: We changed the typo from “delaying carbon deposition.accumulation” to “which delaying the accumulation of carbon deposition.” in line 450.