Core-sandwich-shell structured catalysts with stepped interconnected channels and their preparation methods

Abstract

This invention discloses a core-sandwich-shell structured catalyst with hierarchical interconnected channels, its preparation method, and its applications. The catalyst uses a microporous zeolite core, and a mesoporous zeolite sandwich layer is constructed in situ on the outer layer of the zeolite through controlled desilication, directly connecting it to the core micropores. Based on this, mesoporous silica is induced to grow epitaxially along the sandwich pore direction using a surfactant micelle template, constructing a continuously interconnected hierarchical pore structure. An active metal is supported within the mesoporous silica shell. This structure is beneficial for improving the mass transfer behavior of macromolecular intermediates and achieving spatial partitioning of hydrogenation and acidification functions, making it suitable for the hydrodeoxygenation reaction of biomass-derived oxygen-containing compounds.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and preparation technology of hierarchical porous nanomaterials. Specifically, it relates to a core-sandwich-shell structure catalyst with a ladder-connected pore structure, its preparation method, and the application of the catalyst in the hydrodeoxygenation reaction of biomass-derived oxygen-containing compounds and other cascade catalytic reactions involving metal-acid synergistic effects. Background Technology

[0002] Biomass hydrodeoxygenation (HDO) is a crucial pathway for converting lignocellulosic biomass into high-value chemicals, particularly significant in the fields of renewable energy and green chemistry. HDO reactions involve complex multi-step cascade reactions such as aromatic ring hydrogenation and C–O bond breaking. These reactions require not only effective catalysts but also excellent mass transfer performance during the diffusion and conversion of hydrogenation intermediates. Since reaction intermediates are typically large, the catalyst's mass transfer efficiency becomes a key factor affecting its reactivity. If the mass transfer pathway within the catalyst is obstructed, hydrogenation intermediates can easily become trapped inside, leading to secondary polymerization reactions, resulting in coking and the blockage and deactivation of active sites. Improving the mass transfer capacity of catalysts and avoiding catalyst deactivation due to coking remains one of the core challenges in catalyst design.

[0003] Existing technologies typically employ spatial partitioning designs. For example, CN108033456A discloses a catalyst with a mesoporous silica shell coated on the outer layer of a zeolite molecular sieve. However, traditional encapsulation processes face severe interfacial bottlenecks: the micelle size of the template agent used to construct the mesopores is much larger than the pore size of the zeolite micropores. The micelles cannot penetrate deep into the micropores and accumulate on the outer surface of the zeolite, resulting in the physical blockage of the micropore openings by the generated mesopore walls, forming a "mass transfer discontinuity" at the interface. This discontinuous pore structure hinders the migration of hydrogenation products across the interface and causes extensive coking at the pore openings, failing to fundamentally solve the problem of rapid catalyst deactivation. In addition, Chinese patent CN119909734A discloses a metal-encapsulated micro-mesoporous hierarchical molecular sieve catalyst, which adopts a core-sandwich-shell structure, where the sandwich layer contains active metal components (such as WOx and Pt), and the outer shell is a zeolite molecular sieve. This design aims to improve the stability of the metal components and enhance reaction efficiency by spatially partitioning the catalyst at different levels. However, this structure may have the following limitations: (1) Its active metal is located in the interlayer, which may be spatially adjacent to the acidic sites of the zeolite. In cascade reactions involving hydrogenation and deoxygenation, such as guaiacol hydrodeoxygenation (HDO), the intermediate products are prone to excessive condensation at the metal-acid interface, leading to coking and decreased selectivity; (2) The microporous nature of its zeolite shell may restrict the diffusion of larger hydrogenation intermediates (such as cyclohexanol), failing to completely solve the mass transfer bottleneck between the core and shell, i.e., the mass transfer fault problem. These problems limit the application effect of this catalyst in biomass HDO reactions. Summary of the Invention

[0004] The purpose of this invention is to provide a novel core-shell structure catalyst, which aims to solve the problems in the prior art through the following aspects: (1) By optimizing the core-shell structure of the catalyst, the spatial partitioning of the metal active site and the acidic site is realized, avoiding the excessive condensation of intermediate products during the hydrogenation and deoxygenation reaction, reducing coking problems, and improving the stability of the catalyst; (2) Constructing an intrinsically continuous and interconnected mass transfer channel from the core micropores to the shell mesopores, completely solving the mass transfer bottleneck problem between the reactants and products between the "core" and the "shell", significantly improving the mass transfer efficiency of the catalyst, thereby improving the selectivity, activity and long-term stability of the biomass HDO reaction.

[0005] To achieve the above objectives, this invention selectively desilicates zeolite containing a template agent, thereby constructing an in-situ zeolite interlayer with interconnected mesopores. This interlayer acts as a crucial bridge, with its mesopores intrinsically connected to the core micropores, and its abundant silanol groups on its surface providing anchoring points for subsequent shell growth.

[0006] By utilizing the directional adsorption and filling of surfactant micelles within the mesoporous zeolite interlayer as a template, a mesoporous silica shell is epitaxially grown from a silicon source along the interlayer pore direction. This method ensures high alignment and continuous connectivity (average deviation angle <20°) between the shell mesopores and the interlayer mesopores at the interface, fundamentally eliminating mass transfer discontinuities in traditional core-shell structures.

[0007] By selectively loading active metals into a mesoporous silica shell while retaining Brønsted acid centers within the zeolite core and interlayers, a precise spatial partitioning of hydrogenation and acid catalysis functions is achieved. This design effectively suppresses secondary polymerization of unsaturated hydrogenation intermediates at acid centers within the HDO reaction network, thereby significantly improving the selectivity of target products (such as cyclohexane).

[0008] The present invention provides a core-sandwich-shell structured catalyst with a stepped interconnected channel, comprising: The core is composed of microporous zeolite; The mesoporous zeolite interlayer covering the core is formed in situ by selectively desilicationizing zeolite crystals containing a structure-directing agent and is connected to the micropores of the core. The mesoporous silica shell covering the mesoporous zeolite interlayer contains an active metal loaded therein; wherein the active metal is mainly distributed in the mesoporous silica shell, and the Brønsted acidic sites are mainly distributed in the microporous zeolite core and the mesoporous zeolite interlayer, thereby achieving spatial isolation between the hydrogenation active sites and the acidic sites.

[0009] In the catalyst of the present invention, the average deviation angle between the axial direction of the mesoporous silica shell and the axial direction of the mesoporous zeolite interlayer at the interface is less than 20°.

[0010] In the catalyst of the present invention, the microporous zeolite is at least one of MFI, BEA, FAU or MOR type zeolite; the active metal is at least one of Ni, Pt, Pd, Ru, Co, Cu or Mo.

[0011] This invention provides a method for preparing a core-sandwich-shell structured catalyst with stepped interconnected channels, comprising the following steps: (1) Provide zeolite crystals containing structure guiding agents.

[0012] (2) The crystal obtained in step (1) is subjected to controlled etching in an alkaline solution to obtain an intermediate with mesoporous zeolite interlayers.

[0013] (3) The intermediate, surfactant, auxiliary directing agent and silicon source obtained in step (2) are mixed and subjected to hydrothermal reaction to allow silicon dioxide to grow epitaxially on the surface of the mesoporous zeolite interlayer to form a mesoporous silicon dioxide shell, thereby obtaining the coating material.

[0014] (4) The active metal precursor is loaded into the mesoporous silica shell of the coating material obtained in step (3) by impregnation, and the catalyst is obtained by post-treatment.

[0015] In the preparation method described above, the alkaline solution in step (2) is a NaOH, Na3PO4, or Na2CO3 solution with a concentration of 0.05–0.5 M, an etching temperature of 60–100 °C, and an etching time of 0.5–5 h. The surfactant in step (3) is hexadecyltrimethylammonium bromide, and the auxiliary directing agent is sodium salicylate, with a molar ratio of sodium salicylate to hexadecyltrimethylammonium bromide of 0.1–2.

[0016] This invention provides an application of a core-shell structured catalyst with a stepped interconnected pore structure in the hydrodeoxygenation of guaiacol to cyclohexane. The application method includes: firstly, activating the catalyst to bring the active metal component into a catalytically hydrogenating state; then, adding the guaiacol raw material, catalyst, and optional solvent to a reactor, and carrying out the hydrodeoxygenation reaction under a hydrogen atmosphere; during the reaction, the guaiacol molecule sequentially passes through the outer metal hydrogenation sites, the interconnected mesoporous channels, and the inner nucleic acid sites, achieving continuous transformations such as hydrogenation, demethoxylation, dehydroxylation, and deep deoxygenation, ultimately producing cyclohexane.

[0017] The catalyst design provided by this invention achieves a leap in reaction selectivity and catalytic stability through the synergistic effect of two major mechanisms: "continuous interconnected channels" and "spatial partitioning." Specifically, the continuous interconnected channel design effectively promotes the diffusion of reactants and products, reducing the retention time of hydrogenation intermediates within the catalyst. Sample E exhibits the largest mesopore volume (0.781 cm³ / g) and a relatively large pore size (6.96 nm), indicating that its catalyst possesses a highly ordered and interconnected pore structure. This structural design improves the mass transfer efficiency of reactants and products, reduces the residence time of hydrogenation intermediates in the catalyst, thereby inhibiting secondary condensation reactions and coke formation. Experimental results show that the coke deposition of Sample E in long-cycle reactions is only 7.2%, significantly lower than other samples, demonstrating its excellent anti-coke deposition ability and stability. On the other hand, the spatial partitioning design effectively suppresses side reactions at the metal-acid interface by rationally isolating metal active sites from acidic sites. In the hydrodeoxygenation of guaiacol, side reactions at the metal-acid interface often lead to excessive condensation of intermediates, generating byproducts and reducing selectivity. By placing the active metal in the interlayer, avoiding direct contact with acidic sites, this invention successfully reduces the occurrence of side reactions, thereby ensuring high selectivity. Data shows that sample E almost completely formed cyclohexane (99.4%) in the reaction, with extremely low byproduct formation (0.1%), further demonstrating the significant improvement in selectivity due to spatial partitioning design. This synergistic effect of continuous through-channels and spatial partitioning overcomes the limitations of traditional catalyst design, not only solving the mass transfer bottleneck but also effectively suppressing the formation of side reactions, demonstrating superior technical performance.

[0018] The core-sandwich-shell structured catalyst with stepped interconnected channels provided by this invention has the following outstanding substantive features: (1) By introducing an in-situ formed mesoporous zeolite interlayer between microporous zeolite and mesoporous silica, the physical blockage of the micropore opening by the mesoporous pore wall during the traditional external coating process is avoided, and a continuous and interconnected stepped mass transfer channel is established between the micropores and the mesopores. (2) The mesoporous silica shell grows outward along the direction of the mesoporous zeolite interlayer pores, so that the multi-level pores maintain good structural continuity at the interface, which is conducive to the rapid diffusion of macromolecular reaction intermediates. (3) By loading the active metal onto the mesoporous silica shell and retaining the acidic sites in the zeolite core and interlayer, the spatial partitioning of hydrogenation function and acidic function is achieved, which helps to reduce the probability of side reactions. (4) In the hydrodeoxygenation reaction of guaiacol, the above structural design is beneficial to suppress the formation of carbon deposits at the pore openings, and improve the stability of the catalyst and the selectivity of the target product.

[0019] (5) Compared with the catalyst disclosed in CN119909734A, the catalyst provided by this invention exhibits significantly higher cyclohexane selectivity (>99% vs. approximately 85%) and significantly stronger resistance to carbon deposition and deactivation (activity retention rate >90% vs. <70% after 10 hours of reaction). These unexpected technical effects stem from the synergistic effect of continuous stepwise pores and metal-acid spatial partitioning. Attached Figure Description

[0020] Figure 1 The image shows a transmission electron microscope (TEM) image of the silica-encapsulated sample prepared in Example 1 of this invention. As can be seen from the image, the silica-encapsulated layer has a dense structure and no obvious mesoporous structure was observed.

[0021] Figure 2 The image shows a transmission electron microscope (TEM) image of the material prepared in Example 2 of the present invention. As can be seen from the image, the outer layer of silicon dioxide of the material exhibits obvious mesoporous structure characteristics.

[0022] Figure 3 The image shows a transmission electron microscope (TEM) image of the material prepared in Example 3 of the present invention. As can be seen from the image, the outer silicon dioxide layer of the material has a larger mesoporous encapsulation layer than that in Example 2.

[0023] Figure 4 This is an ultrathin section TEM image of Example 3 of the present invention. The image shows that the catalyst has a continuous three-dimensional network of pores from the core to the shell, without obvious breaks.

[0024] Figure 5 The image shows a transmission electron microscope (TEM) image of the material prepared in Example 4 of the present invention. As can be seen from the image, the outer silicon dioxide layer of the material has a larger mesoporous encapsulation layer than that in Example 3.

[0025] Figure 6 The image shows a transmission electron microscope (TEM) image of the material prepared in Example 5 of the present invention. As can be seen from the image, the outer layer of silica of the material exhibits a mesoporous structure, and the active metal Ni is loaded in a dispersed state in the outer layer of silica.

[0026] Figure 7 The STEM-EDS elemental distribution map of the material prepared in Example 5 of this invention shows that the Ni signal is enriched only in the outer shell region, while the Al signal is concentrated in the core and interlayer regions, providing direct visual evidence of spatial partitioning.

[0027] Figure 8The figures show nitrogen adsorption-desorption curves of the materials prepared in Examples 5-7 and Comparative Example 1 of this invention. The figures show that Example E has the most obvious hysteresis loop, indicating that it has a highly ordered and interconnected mesoporous system. Detailed Implementation

[0028] The present invention will be described in detail below with reference to embodiments, but the scope of protection of the present invention is not limited thereto. Example

[0029] In this embodiment, a silica-encapsulated catalyst was prepared with a NaSal / CTAB ratio of 0. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water, and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide, stir evenly, then add 4.25 g of fumed silica, stir for 2 h, transfer to a hydrothermal reactor, and hydrothermally heat at 160 °C for 2 days. After centrifugation, washing, and drying, obtain Beta zeolite containing a template agent. Disperse 1 g of the above zeolite in 30 mL of 0.2 M sodium hydroxide solution, stir in an 80 °C water bath for 2 h, centrifuge, wash, and calcine at 550 °C for 6 h to obtain Beta zeolite containing an outer mesoporous layer. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB and 24 mg of triethanolamine, stir evenly at 80 °C, add 1 mL of tetraethyl orthosilicate, continue stirring for 2 h, and calcine at 550 °C for 4 h to obtain the final product, designated A. Example

[0030] This embodiment prepares a core-layer-shell structured catalyst with a stepped interconnected pore structure, with a NaSal / CTAB ratio of 0.5. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water, and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide, stir evenly, then add 4.25 g of fumed silica, stir for 2 h, transfer to a hydrothermal reactor, and hydrothermally heat at 160 °C for 2 days. After centrifugation, washing, and drying, obtain Beta zeolite containing a template agent. Disperse 1 g of the above zeolite in 30 mL of 0.2 M sodium hydroxide solution, stir in an 80 °C water bath for 2 h, centrifuge, wash, and calcine at 550 °C for 6 h to obtain Beta zeolite containing an outer mesoporous layer. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB, 24 mg of triethanolamine, and 29 mg of sodium salicylate, stir evenly at 80 °C, add 1 mL of tetraethyl orthosilicate, continue stirring for 2 h, and calcine at 550 °C for 4 h to obtain the final product, designated as B. Example

[0031] This embodiment prepares a core-layer-shell structured catalyst with a stepped interconnected pore structure, with a NaSal / CTAB ratio of 1. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water, and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide, stir evenly, then add 4.25 g of fumed silica, stir for 2 h, transfer to a hydrothermal reactor, and hydrothermally heat at 160 °C for 2 days. After centrifugation, washing, and drying, obtain Beta zeolite containing a template agent. Disperse 1 g of the above zeolite in 30 mL of 0.2 M sodium hydroxide solution, stir in an 80 °C water bath for 2 h, centrifuge, wash, and calcine at 550 °C for 6 h to obtain Beta zeolite containing an outer mesoporous layer. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB, 24 mg of triethanolamine, and 58 mg of sodium salicylate, stir evenly at 80 °C, add 1 mL of tetraethyl orthosilicate, continue stirring for 2 h, and calcine at 550 °C for 4 h to obtain the final product, designated C. Example

[0032] This embodiment prepares a core-layer-shell structured catalyst with a stepped interconnected pore structure, with a NaSal / CTAB ratio of 2. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide and stir until homogeneous. Then add 4.25 g of fumed silica and stir for 2 h. Transfer to a hydrothermal reactor and hydrothermally heat at 160 °C for 2 days. After centrifugation, washing, and drying, obtain Beta zeolite containing a template agent. Disperse 1 g of the above zeolite in 30 mL of 0.2 M sodium hydroxide solution and stir in an 80 °C water bath for 2 h. After centrifugation and washing, calcine at 550 °C for 6 h to obtain Beta zeolite containing an outer mesoporous layer. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB, 24 mg of triethanolamine, and 116 mg of sodium salicylate. Stir until homogeneous at 80 °C, add 1 mL of tetraethyl orthosilicate and continue stirring for 2 h. After calcination at 550 °C for 4 h, obtain the final product, designated D. The structural parameters of Examples 1-4 are shown in Table 1. Example

[0033] This embodiment prepares a core-layer-shell structured catalyst with a stepped interconnected pore structure, with a NaSal / CTAB ratio of 1 and Ni as the supported metal at a loading of 10 wt%. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water, and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide, stir evenly, then add 4.25 g of fumed silica, stir for 2 h, transfer to a hydrothermal reactor, and hydrothermally heat at 160 °C for 2 days. After centrifugation, washing, and drying, obtain Beta zeolite containing a template agent. Disperse 1 g of the above zeolite in 30 mL of 0.2 M sodium hydroxide solution, stir in an 80 °C water bath for 2 h, centrifuge, wash, and calcine at 550 °C for 6 h to obtain Beta zeolite containing an outer mesoporous layer. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB, 24 mg of triethanolamine, and 58 mg of sodium salicylate, stir evenly at 80 °C, add 1 mL of tetraethyl orthosilicate, continue stirring for 2 h, and calcine at 550 °C for 4 h to obtain the coated product. The above 0.16 g product was dispersed in 10 mL of ethanol, 100 mL of ethylenediamine and nickel nitrate ethanol solution were added, stirred for 4 h, and then dried in a vacuum oven. Finally, it was reduced under a mixed atmosphere of H2 / Ar to obtain the final product, numbered E. Example

[0034] This embodiment prepares a microporous Beta-encapsulated mesoporous silica catalyst with a NaSal / CTAB ratio of 1 and Ni as the supported metal at a loading of 10 wt%. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide and stir until homogeneous. Then add 4.25 g of fumed silica and stir for 2 h. Transfer the solution to a hydrothermal reactor and hydrothermally heat at 160 °C for 2 days. Centrifuge, wash, dry, and calcine to obtain Beta zeolite. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB, 24 mg of triethanolamine, and 58 mg of sodium salicylate, and stir until homogeneous at 80 °C. Add 1 mL of tetraethyl orthosilicate and continue stirring for 2 h. Calcinate at 550 °C for 4 h to obtain the coated product. Disperse 0.16 g of the above product in 10 mL of ethanol, add 100 mL of ethylenediamine and nickel nitrate ethanol solution, stir for 4 h, and dry in a vacuum oven. Finally, reduce under a H2 / Ar mixed atmosphere to obtain the final product, designated F. In this structure, no in-situ formed mesoporous zeolite interlayer is introduced between the microporous zeolite and the mesoporous silica, resulting in poor channel continuity between the micropores and mesopores. Example

[0035] In this embodiment, a core-shell Beta-encapsulated mesoporous silica catalyst was prepared with a NaSal / CTAB ratio of 1 and Ni as the supported metal at a loading of 10 wt%. The preparation method is as follows: Weigh 0.05 g of sodium hydroxide and 0.33 g of sodium aluminate, dissolve them in 8 g of water, and stir until a clear solution is obtained. Add 23.5 g of tetraethylammonium hydroxide, stir evenly, then add 4.25 g of fumed silica, stir for 2 h, transfer to a hydrothermal reactor, and hydrothermally heat at 160 °C for 2 days. Centrifuge, wash, dry, and calcine to obtain Beta zeolite. Disperse 1 g of the above zeolite in 0.1 M sodium phosphate solution, treat at 80 °C for 12 h, centrifuge, wash, dry, and calcine to obtain core-shell Beta zeolite. Disperse 100 mg of the above zeolite in 7 mL of water, add 0.132 g of CTAB, 24 mg of triethanolamine, and 58 mg of sodium salicylate, stir evenly at 80 °C, add 1 mL of tetraethyl orthosilicate, continue stirring for 2 h, and calcine at 550 °C for 4 h to obtain the coated product. The above 0.16 g product was dispersed in 10 mL of ethanol, and 100 mL of ethylenediamine and nickel nitrate ethanol solution were added. After stirring for 4 h, the mixture was dried in a vacuum oven and finally reduced under a H2 / Ar mixed atmosphere to obtain the final product, designated G. In this structure, a large cavity is formed between the microporous zeolite and the mesoporous zeolite, and the continuity of the channels between the micropores and mesopores is poor. Detailed parameters are shown in Table 2. Example

[0036] Catalyst performance test for the hydrogenation and deoxygenation of guaiacol to cyclohexane 25 mg of the above-mentioned catalysts E, F, and G were respectively placed in a 25 mL high-pressure reactor, 0.10 g of guaiacol and 10 mL of dodecane were added as solvent, and the reactor was purged with 3 MPa H2 and heated to 200 °C for 3 h. After the reaction was completed, the system was rapidly cooled to room temperature, the liquid product was collected, and hexadecane was added as an internal standard. Subsequently, the composition and conversion rate of the product were analyzed by gas chromatography (GC). GC was performed using an appropriate column and temperature program. Quantitative analysis was performed by comparing the peak area ratio of the product and the internal standard, combined with a standard curve, to accurately calculate the yield and conversion efficiency of cyclohexane. Table 3 shows the experimental results. Example

[0037] Comparison of long-term performance and anti-carbon deposition performance of catalysts Reaction conditions: 0.1 g guaiacol, 10 mL dodecane, 25 mg catalyst, H2 3 MPa, 200 °C. Evaluation indicators included initial activity (3 h), conversion retention rate after 10 h of long-term operation, carbon deposition on the catalyst after reaction (measured by TGA), and product distribution. Results are shown in Table 4.

[0038] Comparative Example 1 Comparative Example 1 (prepared according to Example 1 of CN119909734A): A Pt-WOx@zeolite catalyst with a core-sandwich-shell structure was prepared according to the method of this patent example. The specific steps were as follows: First, ammonium metatungstate solution was mixed with Beta zeolite molecular sieve, dried by rotary evaporation, and calcined at 550℃ for 5 hours to obtain a core loaded with W oxide. Next, a Pt nanoparticle solution was prepared by reflux reaction. Then, the core loaded with W oxide was mixed with the Pt nanoparticle solution, ultrasonically stirred, and dried to obtain the first preproduct, Beta@Pt-W. Next, Beta@Pt-W was mixed with SiO2, sodium hydroxide, TEOS, etc., and subjected to a hydrothermal reaction to obtain the second preproduct. Finally, after centrifugation, drying, and calcination at 450℃ for 3 hours, the final Beta@Pt-W@Beta metal-encapsulated micro-mesoporous molecular sieve catalyst was obtained. This catalyst is denoted as H.

[0039]

[0040] Catalytic data were obtained by loading metals onto the samples in Examples 1-4. According to the data in Table 1, sample C has the optimal mesoporous system, which supports the improvement of mass transfer, proving that the ratio between sodium salicylate and CTAB is the key to regulating the pore quality.

[0041]

[0042] Table 2 provides the structural parameters of catalyst E of the present invention and Examples 5, 6, and 7. The data shows that the catalyst of the present invention has the largest mesoporous pore volume, indicating that its highly ordered and interconnected mesoporous system significantly improves mass transfer performance.

[0043]

[0044] As can be seen from Table 3, sample E exhibits the best catalytic performance, with high conversion rate and good selectivity, mainly producing cyclohexane. In contrast, samples F and G have poor catalytic performance and produce more byproducts, indicating that good pore connectivity is the key to achieving high cyclohexane selectivity.

[0045]

[0046] As shown in Table 4, Sample E exhibits better long-cycle performance and resistance to carbon deposition, demonstrating higher conversion retention and lower carbon deposition, with a more homogeneous product distribution, primarily producing cyclohexane. In contrast, Sample H in Comparative Example 1 shows significant performance degradation during long-cycle operation, with higher carbon deposition, more byproducts, and poorer catalytic performance.

Claims

1. A core-sandwich-shell structured catalyst with a stepped interconnected pore structure, characterized in that, include: The core is composed of microporous zeolite; The mesoporous zeolite interlayer covering the core is formed in situ by selectively desilicationizing zeolite crystals containing a structure-directing agent and is connected to the micropores of the core. A mesoporous silica shell covering the mesoporous zeolite interlayer, wherein the mesoporous silica shell is loaded with an active metal; The active metal is mainly distributed in the mesoporous silica shell, and the Brønsted acidic sites are mainly distributed in the microporous zeolite core and the mesoporous zeolite interlayer, thereby achieving spatial isolation between the hydrogenation active sites and the acidic sites.

2. The catalyst according to claim 1, characterized in that, The average deviation angle between the axial direction of the mesoporous silica shell and the axial direction of the mesoporous zeolite interlayer at the interface is less than 20°.

3. The catalyst according to claim 1 or 2, characterized in that, The microporous zeolite is at least one of MFI, BEA, FAU or MOR type zeolite.

4. The catalyst according to claim 1 or 2, characterized in that, The active metal is at least one of Ni, Pt, Pd, Ru, Co, Cu, or Mo.

5. A method for preparing the catalyst according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Provide zeolite crystals containing structure-directing agents; (2) The crystal obtained in step (1) is subjected to controlled etching in an alkaline solution to obtain an intermediate with mesoporous zeolite interlayers; (3) The intermediate, surfactant, auxiliary directing agent and silicon source obtained in step (2) are mixed and subjected to hydrothermal reaction to allow silicon dioxide to grow epitaxially on the surface of the mesoporous zeolite interlayer to form a mesoporous silicon dioxide shell, thereby obtaining a coating material; (4) The active metal precursor is loaded into the mesoporous silica shell of the coating material obtained in step (3) by impregnation, and the catalyst is obtained by post-treatment.

6. The method according to claim 5, characterized in that, The alkaline solution mentioned in step (2) is a NaOH, Na3PO4 or Na2CO3 solution with a concentration of 0.05 to 0.5 M, an etching temperature of 60 to 100 °C, and an etching time of 0.5 to 5 h.

7. The method according to claim 5, characterized in that, The surfactant mentioned in step (3) is hexadecyltrimethylammonium bromide, and the auxiliary directing agent is sodium salicylate. The molar ratio of sodium salicylate to hexadecyltrimethylammonium bromide is 0.1 to 2.

8. The use of the catalyst according to any one of claims 1-4 in the hydrodeoxygenation reaction of guaiacol to prepare cyclohexane.

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