Composite molecular sieve catalyst, preparation method and application thereof

Abstract

The invention provides a composite molecular sieve catalyst as well as a preparation method and application thereof, the preparation method of the composite molecular sieve catalyst comprises the following steps: carrying out alkaline dissociation on the surface of an HZSM-5 molecular sieve to generate aluminosilicate fragments, carrying out self-assembly under the guiding action of a template agent to form an HZSM-5-MCM-41 core-shell structure, and carrying out equivalent-volume impregnation loading of a metal oxide to obtain the composite molecular sieve catalyst. Integration of inner core micropores and shell mesopores and uniform distribution of active sites are realized; mesoporous channels of the MCM-41 molecular sieve in the obtained catalyst can break through mass transfer limitation of tar macromolecules (polycyclic aromatic hydrocarbon and the like), tar is pre-cracked through the metal oxide, small molecules are deeply converted through strong acid sites of the inner core HZSM-5 molecular sieve, tar reforming, CH4 / CO2 reforming reaction and the like can be efficiently catalyzed through the synergistic effect generated by the metal oxide pre-cracked tar and the inner core HZSM-5 molecular sieve, and hydrogen-rich synthesis gas is prepared; meanwhile, the metal site can promote gasification of deposited carbon, and the technical problems that tar is blocked and inactivated, the quality of synthesis gas is low and carbon emission is high in the biomass gasification process are solved.

Description

Technical Field

[0001] This application relates to the field of catalyst preparation technology, and more specifically, to a composite molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Biomass energy, as a renewable resource, is crucial for reducing dependence on fossil fuels and lowering carbon emissions through efficient conversion. Gasification technology can convert biomass into syngas (H2, CO, etc.), but the tar produced in the process (polycyclic aromatic hydrocarbons, phenols, etc.) can clog equipment, corrode pipelines, and degrade the quality of syngas. Tar has a complex composition, including oxygenated aromatic hydrocarbons (such as guaiacol), polycyclic aromatic hydrocarbons (such as naphthalene), and long-chain hydrocarbons, exhibiting high chemical stability and making it difficult to completely crack.

[0003] Current methods for treating tar mainly include physical purification and chemical conversion. Chemical conversion methods primarily include high-temperature pyrolysis gasification and catalytic cracking. However, catalytic cracking is limited by carbon deposition and heat transfer constraints, preventing large tar molecules (such as lignin derivatives) from entering the micropores. These molecules easily polymerize and coke on the catalyst surface, leading to catalyst deactivation and low tar conversion rates. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a composite molecular sieve catalyst, its preparation method, and its application. The catalyst is prepared by alkaline dissociation of HZSM-5 molecular sieves to generate aluminosilicate fragments, which self-assemble into a core-shell structure under the action of a template agent and are then loaded with metal oxides. This catalyst utilizes the mesopores of MCM-41 molecular sieves to promote mass transfer and pre-cracking of tar macromolecules, the micropores of HZSM-5 molecular sieves to achieve deep conversion of small molecules, and the metal components to catalyze the gasification of carbon deposits. The synergistic effect of these three elements enables highly efficient catalysis of tar and CH4 / CO2 reforming to produce hydrogen-rich syngas, while simultaneously solving the problems of catalyst deactivation due to carbon deposits and carbon emissions.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a composite molecular sieve catalyst, the method comprising: S1. Place the dispersion containing HZSM-5 molecular sieve and alkaline catalyst in a water bath at 65℃-80℃ to promote the dissociation of the surface of HZSM-5 molecular sieve and obtain a dispersion system containing aluminosilicate fragments. Add a template agent to the dispersion system and treat it with sol-gel at 100℃-120℃ for 22h-26h to obtain a gel system containing MCM-41 molecular sieve precursor. S2. After the gel system is cooled, its pH is adjusted to 8.5-9.0, and then crystallized at 100℃-120℃ for 22h-26h. The resulting system is filtered, washed, dried and calcined to form a composite molecular sieve with an HZSM-5-MCM-41 core-shell structure. S3. The composite molecular sieve is impregnated in a metal salt solution in equal volume. After drying and calcining, the resulting impregnation system is used to obtain the composite molecular sieve catalyst. The metal salt in the metal salt solution is selected from at least one of nickel nitrate, cobalt nitrate, and iron nitrate.

[0006] Optionally, the silica-alumina ratio of the HZSM-5 molecular sieve is (25-30):1.

[0007] Optionally, in step S1, the alkaline catalyst is any one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; The mass-to-volume ratio of the HZSM-5 molecular sieve to the dispersion is (8-12) g: 100 mL.

[0008] Optionally, the template agent is hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride; The template agent has a volume percentage of 1.5wt%-2.5wt% in the dispersion system.

[0009] Optionally, in step S2, the calcination temperature is 500℃-600℃, the heating rate is 1.5℃ / min-2.5℃ / min, and the calcination time is 5h-7h.

[0010] Optionally, in step S3, the metal salt is nickel nitrate and cobalt nitrate; The mass ratio of nickel nitrate to cobalt nitrate is 1:(0.95-1).

[0011] Optionally, in step S3, the calcination temperature is 600℃-700℃, the heating rate is 1.5℃ / min-2.5℃ / min, and the calcination time is 5h-7h.

[0012] In a second aspect, the present invention provides a composite molecular sieve catalyst, wherein the composite molecular sieve catalyst is prepared by the preparation method described in the first aspect above; The composite molecular sieve catalyst is composed of a core-shell structure formed by combining HZSM-5 molecular sieve and MCM-41 molecular sieve as a support, and loaded with metal oxides. The metal oxide is at least one of nickel oxide, cobalt oxide, and iron oxide; The metal oxide accounts for 20%-25% of the total mass of the composite molecular sieve catalyst.

[0013] Optionally, in the composite molecular sieve catalyst, the mesoporous shell formed by the MCM-41 molecular sieve has a pore size of 3nm-5nm; and the micropore size of the HZSM-5 molecular sieve has a pore size of 0.5nm-0.6nm.

[0014] Thirdly, the present invention provides an application of a composite molecular sieve catalyst, wherein the composite molecular sieve catalyst is prepared by the preparation method described in the first aspect above, and the composite molecular sieve catalyst is used to catalyze tar reforming, CH4 reforming or CO2 reforming to obtain H2-rich gas.

[0015] In summary, the present invention has at least the following beneficial technical effects: 1. This invention provides a method for preparing a composite molecular sieve catalyst. Under alkaline catalyst and mild water bath conditions, the surface of HZSM-5 molecular sieve undergoes controlled dissociation. This avoids excessive damage to the core framework structure of the HZSM-5 molecular sieve, maintaining the strong acidity and microporous properties of the core. Simultaneously, it releases highly reactive aluminosilicate fragments, serving as "nano-building units" for the growth of MCM-41 molecular sieves. A template agent is added as a structure directing agent to guide the fragments to self-assemble on the surface of the HZSM-5 molecular sieve, forming the MCM-41 molecular sieve shell. This ensures a tight connection and interfacial stability of the core-shell structure, overcoming the defects of easy peeling at the interface of traditional core-shell materials. It also maintains structural integrity under high-temperature carbon deposition conditions, providing diffusion channels for tar molecules. This invention utilizes fragments generated from the dissociation of HZSM-5 molecular sieves to self-assemble into an MCM-41 molecular sieve shell under the guidance of a template agent. This shell possesses short-range ordered vertical mesoporous channels, significantly improving the diffusion efficiency of tar macromolecules (such as lignin-derived polycyclic aromatic hydrocarbons). It achieves functional division of labor between "mesoporous pre-cleavage of macromolecules in the shell and deep deoxygenation and aromatization in the microporous core," avoiding the irreversible loss of strong acid sites caused by traditional pore-expansion methods. An equal-volume impregnation method is then used to load active metals onto a pre-constructed core-shell molecular sieve support, ensuring that the metal salt solution fully fills the mesoporous channels and that the metal precursor is preferentially and uniformly dispersed on the MCM-41 molecular sieve shell. The metal active sites formed after calcination and the internal nucleic acid sites form a spatially synergistic catalytic network, overcoming the bottleneck of mass transfer limitations and the difficulty in balancing activity and stability in the catalytic cracking of tar and other substances.

[0016] 2. This invention provides a composite molecular sieve catalyst. In this core-shell structured support, the regular mesopores of the MCM-41 molecular sieve shell provide diffusion channels for tar macromolecules (such as polycyclic aromatic hydrocarbons and long-chain hydrocarbons), breaking through the mass transfer limitations of traditional microporous molecular sieves. The acidic sites of the HZSM-5 molecular sieve core catalyze the deoxygenation / aromatization reaction of small molecule intermediates within the micropores. The active sites of the metal oxides can directly contact and crack the macromolecules of tar that diffuse into the pores of the MCM-41 molecular sieve, realizing the combined catalysis of "macromolecule pre-cracking - small molecule deep conversion". This solves the problems of the complexity of components such as biomass tar, mass transfer resistance, and carbon deposition deactivation, achieving efficient and stable tar conversion.

[0017] 3. This invention provides an application of a composite molecular sieve catalyst. Through the core-shell mass transfer and metal / inner nucleic acid dual-function synergy of the composite molecular sieve catalyst, it can efficiently catalyze tar cracking and CH4 / CO2 directional reforming, achieve deep tar removal, generate hydrogen-rich gas, realize the resource conversion of greenhouse gases (CO2, CH4), and provide strong technical guidance for the integration of efficient biomass energy conversion and carbon emission reduction.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of the preparation method of the composite molecular sieve catalyst proposed in the embodiments of this application. Detailed Implementation

[0020] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0022] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0023] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] Among related technologies, biomass energy, as a renewable resource, is crucial for reducing dependence on fossil fuels and lowering carbon emissions through efficient conversion. Gasification technology can convert biomass into syngas (H2, CO, etc.), but the tar produced in the process has a complex composition, including oxygenated aromatics (such as guaiacol), polycyclic aromatics (such as naphthalene), and long-chain hydrocarbons. These hydrocarbons are chemically stable and difficult to completely crack, making it impossible for traditional technologies to convert them into high-value-added products. Furthermore, untreated tar emissions will lead to the formation of toxic substances such as dioxins.

[0025] Current methods for treating tar mainly include physical purification and chemical conversion. Physical purification methods are primarily implemented through technologies such as cyclone separation and electrostatic precipitators, but the tar still needs to be treated as hazardous waste after condensation, which increases disposal costs. Chemical conversion methods mainly include high-temperature pyrolysis gasification and catalytic cracking. Among these, catalytic cracking is limited by carbon deposition and heat transfer constraints; large tar molecules (such as lignin derivatives) cannot enter the micropores and easily polymerize and coke on the catalyst surface.

[0026] Based on the problems existing in related technologies, some solutions have been proposed in the current technology. For example, patent CN119565662A proposes a Ni-Fe bimetallic catalyst supported by aluminum ash (ASA) in conjunction with HZSM-5 molecular sieve, using aluminum ash to replace part of the HZSM-5 molecular sieve as a co-support. However, the free radical chain reaction in this technology will generate toxic byproducts such as naphthalene and benzo[a]pyrene. In addition, the aluminum ash co-supported catalyst proposed in this technology lacks a hierarchical pore design, and tar macromolecules easily block the active sites. After four cycles, the catalyst suffers from severe carbon buildup, leading to catalyst deactivation.

[0027] The catalyst proposed in patent CN202510106462.X still lacks a hierarchical pore design, allowing tar macromolecules to polymerize directly on the catalyst surface, clogging active sites and reducing reaction efficiency. Furthermore, this catalyst is difficult to regenerate; it is prone to carbon buildup in plasma environments, and conventional coking regeneration easily damages the catalyst. High-temperature environments accelerate metal migration and aggregation, reducing active sites.

[0028] Based on this, refer to Figure 1 This invention provides a method for preparing a composite molecular sieve catalyst, the method comprising: Step S1: Place the dispersion containing HZSM-5 molecular sieve and alkaline catalyst in a water bath at 65℃-80℃ to promote the dissociation of the surface of HZSM-5 molecular sieve and obtain a dispersion system containing aluminosilicate fragments. Add a template agent to the dispersion system and treat it with sol-gel at 100℃-120℃ for 22h-26h to obtain a gel system containing MCM-41 molecular sieve precursor. In this embodiment of the invention, the HZSM-5 molecular sieve is a crystalline material composed of aluminosilicates; In this embodiment of the invention, the silicon-aluminum ratio of the HZSM-5 molecular sieve is (25-30):1.

[0029] In practice, the silica-alumina ratio of HZSM-5 molecular sieve is 25:1, 26:1, 27:1, 28:1, 29:1 or 30:1.

[0030] This invention employs an HZSM-5 molecular sieve with a silicon-to-aluminum ratio of (25-30):1. This helps maintain high acid strength, ensuring effective deep catalytic cracking of small molecule cracking intermediates entering the core, converting them into target small molecule gases. It also avoids excessive acid density leading to over-cracking and intensified hydrogen transfer reactions, thereby effectively inhibiting the formation of polycyclic aromatic hydrocarbons (PAHs). The aluminum atoms in the HZSM-5 molecular sieve framework serve as the primary anchoring sites for subsequently impregnated and loaded metal ions. A silicon-to-aluminum ratio limited to (25-30):1 provides sufficient aluminum sites, ensuring effective and uniform dispersion of the active metal components on the molecular sieve surface and within the pores, forming a sufficient number of active sites. Furthermore, it avoids excessively dense aluminum sites that could cause metal ions to migrate and aggregate due to close proximity during high-temperature reactions or regeneration, thus maintaining high catalytic activity at the loaded metal active sites.

[0031] In this embodiment of the invention, in step S1, the alkaline catalyst is any one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; The mass-to-volume ratio of the HZSM-5 molecular sieve to the dispersion is (8-12) g: 100 mL.

[0032] In specific implementation, the mass-to-volume ratio of HZSM-5 molecular sieve to dispersion is 8g:100mL, 9g:100mL, 10g:100mL, 11g:100mL, or 12g:100mL.

[0033] In this embodiment of the invention, the etching effect of the above-mentioned alkaline catalyst on the surface of HZSM-5 molecular sieve is milder and more controllable, which can effectively promote the preferential dissociation of the surface of HZSM-5 molecular sieve to generate aluminosilicate fragments required to construct the shell of MCM-41 molecular sieve, while protecting the integrity of the core microporous structure and acidic sites to the greatest extent, and avoiding crystal structure damage or severe acid loss caused by excessive etching.

[0034] In this embodiment of the invention, the mass-to-volume ratio of HZSM-5 molecular sieve to dispersion affects the degree of dissociation. Within the mass-to-volume ratio range of g:100mL in embodiments (8-12), the etching requirements and core protection can be balanced, ensuring that a sufficient number and quality of fragments are generated to construct a complete and appropriately thick mesoporous shell layer, while minimizing etching damage to the core and ensuring its microporous structure and acidic function. This avoids the problems of too little HZSM-5 molecular sieve, resulting in a relatively high alkali concentration per unit volume, leading to excessive etching, excessive fragmentation, and excessive damage to the core; and too much HZSM-5 molecular sieve, resulting in a relatively insufficient alkali concentration, leading to insufficient etching and an insufficient number of effective aluminosilicate fragments, resulting in a subsequently formed MCM-41 molecular sieve shell layer that is too thin, discontinuous, or incomplete, and unable to effectively play the role of macromolecular pre-lysis and diffusion channels.

[0035] In practice, the water bath temperature is 65℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, or 80℃. This temperature range can induce moderate dissociation on the surface of the HZSM-5 molecular sieve, ensuring controlled and uniform dissociation. This primarily generates aluminosilicate fragments needed to construct the shell layer of the MCM-41 molecular sieve, maximizing the protection of the core's integrity and inherent acidity, which helps in the subsequent formation of a clear, firmly bonded core-shell structure. Furthermore, within this temperature range, the dissociated aluminosilicate fragments possess suitable solubility and reactivity. Too low a temperature results in insufficient solubility and activity, while too high a temperature may lead to excessive agglomeration or deactivation. The 65℃-80℃ range ensures effective release of the fragments while maintaining their reactivity as precursors, facilitating sufficient and uniform interaction with the template agent in the subsequent sol-gel step, forming a continuous, dense, and uniformly pore-sized mesoporous shell layer of the MCM-41 molecular sieve.

[0036] In this embodiment of the invention, the template agent is hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride; The template agent has a volume percentage of 1.5wt%-2.5wt% in the dispersion system.

[0037] In this embodiment of the invention, the hydrophobic hexadecyl long chains in hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride form micelles during self-assembly, which can directionally form a uniform, ordered hexagonal mesoporous structure MCM-41 molecular sieve with a pore size of 3nm-5nm. The sufficiently large mesoporous pore size provides an unobstructed diffusion channel for macromolecules in tar (such as lignin derivatives), allowing them to smoothly enter the interior of the catalyst. This effectively avoids the problem of macromolecules polymerizing and clogging the pore openings due to micropore limitations in the prior art, achieving highly efficient macromolecule pre-cracking.

[0038] Furthermore, combined with the aluminosilicate fragments generated by the surface dissociation of HZSM-5 molecular sieve, hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride guides these fragments to self-assemble around their micelles. Aluminum species are embedded in the amorphous silica pore walls of MCM-41 molecular sieve, forming acidic mesoporous pore walls. These acidic mesoporous pore walls have a pre-cracking capability for the entering tar macromolecules, partially dissociating them into smaller fragments. This reduces the number of macromolecules that directly enter the microporous core for deep cracking, lowering the risk of core coking. It allows macromolecules to initially depolymerize in relatively open mesopores, reducing the probability of them directly polymerizing on the catalyst surface to form stubborn carbon deposits, significantly improving the overall anti-carbon deposition capability of the catalyst and extending its service life.

[0039] In specific implementation, the template agent's volume percentage in the dispersion system is 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, or 2.5wt%. In practice, the temperature for sol-gel treatment is 100℃, 105℃, 110℃, 115℃, or 120℃.

[0040] In this embodiment of the invention, a homogeneous dispersion system formed under a mild water bath environment is combined with a sol-gel treatment at 100℃-120℃ to form a gel system with a uniform structure and fewer defects, which helps to obtain a core-shell composite molecular sieve with a stable structure and good mechanical strength after subsequent crystallization and calcination.

[0041] It should also be noted that the alkaline catalyst in step S1 not only promotes the dissociation of the HZSM-5 molecular sieve surface, but its molecules also exist in the dispersion system. In the subsequent sol-gel process, these pre-existing quaternary ammonium ions can also cooperate with the template agent to guide the self-assembly of aluminosilicate fragments, forming a highly ordered mesoporous structure of MCM-41 molecular sieve. This can improve the epitaxial growth of the mesoporous shell layer on the surface of the HZSM-5 molecular sieve core, so as to form a continuous, uniform, pore-sized MCM-41 molecular sieve shell layer that is tightly bound to the core.

[0042] Step S2: After the gel system is cooled, its pH is adjusted to 8.5-9.0, and then crystallized at 100℃-120℃ for 22h-26h. After filtration, washing, drying and calcination, the resulting system forms a composite molecular sieve with an HZSM-5-MCM-41 core-shell structure. In this embodiment of the invention, the pH of the gel system after condensation is adjusted to 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0. Since the dispersion system is alkaline, acidic solutions such as hydrochloric acid can be used to adjust the pH of the gel system to make the pH range between 8.5 and 9.0.

[0043] Under weakly alkaline conditions, the hydrolysis and condensation rates of silicate species reach equilibrium, enabling them to slowly and orderly deposit around the template micelles, ultimately forming a long-range ordered, uniform-sized, dense-walled, and mechanically strong MCM-41 molecular sieve mesoporous shell.

[0044] In practice, the crystallization temperature is 100℃, 120℃, 140℃, 160℃, 180℃ or 200℃; The crystallization temperatures are 22h, 22.5h, 23h, 23.5h, 24h, 24.5h, 25h, 25.5h, or 26h.

[0045] In this embodiment of the invention, within this crystallization temperature range, the template agent is encouraged to form stable micelles and guide the orderly self-assembly of aluminosilicate fragments into MCM-41 molecular sieves. This ensures that aluminum species are effectively embedded in the mesoporous silica framework, forming acidic pore walls with pre-cleavage activity. If the temperature is too low, the assembly motive force is insufficient, leading to disordered pores; if the temperature is too high, the stability of the template micelles is easily destroyed. This crystallization time allows the mesoporous structure to fully crystallize and grow completely, overcoming the problems of insufficient time resulting in a thin and discontinuous shell that affects the pre-cleavage and diffusion functions of macromolecules, and excessive time resulting in a thick shell or template agent degradation that increases mass transfer resistance.

[0046] In the embodiments of the invention, the crystallized system can be cooled and centrifuged, the product obtained after separation can be washed with ethanol, and after washing, it can be placed in an oven for drying to obtain dried crystals.

[0047] In this embodiment of the invention, in step S2, the calcination temperature is 500℃-600℃, the heating rate is 1.5℃ / min-2.5℃ / min, and the calcination time is 5h-7h.

[0048] In practice, the calcination temperature is 500℃, 520℃, 550℃, 570℃ or 600℃; this temperature range can ensure that the template agent is completely decomposed and burned, fully exposing the ordered mesoporous channels and avoiding residual organic matter from clogging the active sites. The heating rates are 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min, 2.0℃ / min, 2.1℃ / min, 2.2℃ / min, 2.3℃ / min, 2.4℃ / min, or 2.5℃ / min; at these heating rates, thermal stress shock can be reduced, preventing the mesoporous shell from collapsing or cracking. The calcination time is 5h, 5.5h, 6h, 6.5h or 7h; this calcination time can ensure the gradual removal of the template agent and maintain the orderliness of the pores and mechanical strength.

[0049] S3. The composite molecular sieve is impregnated in a metal salt solution in equal volume. After drying and calcining, the resulting impregnation system is used to obtain the composite molecular sieve catalyst. The metal salt in the metal salt solution is selected from at least one of nickel nitrate, cobalt nitrate, and ferric nitrate; In embodiments of the present invention, a single metal load can be used, such as Fe@H / M or Ni@H / M, etc. This invention employs an equal-volume impregnation method to precisely load metal salts onto a hierarchical porous support, forming highly dispersed metal active centers within the mesoporous shell and core micropores. These centers, in conjunction with the acidic sites of the molecular sieve, enhance the deep cracking and deoxygenation activity of tar. Ni / Co / Fe can catalyze hydrogenation / dehydrogenation reactions, promoting the hydrogenation saturation of tar intermediates, blocking the formation pathway of polycyclic aromatic hydrocarbons, and simultaneously reducing the polymerization of carbon deposit precursors.

[0050] In this embodiment of the invention, in step S3, the metal salt is nickel nitrate and cobalt nitrate; The mass ratio of nickel nitrate to cobalt nitrate is 1:(0.95-1).

[0051] Ni can efficiently break C-C bonds to achieve deep tar cracking, while Co can selectively catalyze deoxygenation reactions. The bimetallic synergy can completely convert oxygen-containing macromolecules into small-molecule hydrocarbons and CO / H2, reducing oxygen-containing tar byproducts. Furthermore, the hydrogenation activity of Co can saturate the olefin fragments generated by Ni cracking, blocking the formation pathway of polycyclic aromatic hydrocarbons (such as benzo[a]pyrene), while reducing carbon deposition tendency and delaying catalyst deactivation.

[0052] In this embodiment of the invention, Ni-Co is loaded with nearly equal amounts to form highly dispersed dual active sites on a hierarchical porous carrier (HZSM-5@MCM-41), which mutually inhibit high-temperature migration and aggregation, and maintain long-term activity.

[0053] In this embodiment of the invention, Fe can be introduced on the basis of Ni and Co, with Fe acting as an additive to form a Ni-Co-Fe ternary alloy on the support. The three metals can produce a synergistic effect, further enhancing the anti-carbon deposition ability of the composite molecular sieve catalyst.

[0054] In this embodiment of the invention, a MOF (metal-organic framework) porous material structure can be introduced, with MOFs, HZSM-5 molecular sieve, and MCM-41 molecular sieve forming a support. Specifically, by mixing the MOF precursor solution with the HZSM-5-MCM-41 core-shell structure, followed by a solvothermal reaction and calcination, the MOFs are loaded onto the outer surface of the core-shell structure, forming a three-tiered structure of micropores, mesopores, and macropores. This further enhances the specific surface area and pore connectivity of the support, promotes the diffusion of tar and water vapor, and the desorption of products H2 and CO, thereby strengthening catalytic efficiency and contributing to high hydrogen selectivity.

[0055] In this embodiment of the invention, in step S3, the calcination temperature is 600℃-700℃, the heating rate is 1.5℃ / min-2.5℃ / min, and the calcination time is 5h-7h.

[0056] In specific implementation, the calcination temperature is 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃ or 700℃; this temperature range can ensure that nickel nitrate / cobalt nitrate is completely decomposed into highly active NiO / CoO, avoid residual nitrate poisoning of the catalyst, and promote the formation of strong bonds between the metal oxide and the surface of the composite molecular sieve support (HZSM-5@MCM-41), inhibiting metal migration and agglomeration during the reaction; The heating rate is 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min, 2.0℃ / min, 2.1℃ / min, 2.2℃ / min, 2.3℃ / min, 2.4℃ / min or 2.5℃ / min; The calcination time is 5h, 5.5h, 6h, 6.5h or 7h; by slowly raising the temperature and combining it with sufficient calcination time, thermal stress impact can be reduced, core-shell structure collapse or mesopore blockage can be avoided, and the diffusion channels of tar macromolecules can be kept open.

[0057] In summary, the method for preparing the composite molecular sieve catalyst provided in this invention constructs an HZSM-5-MCM-41 core-shell structure, combining micropores (HZSM-5 molecular sieve core) and mesopores (MCM-41 molecular sieve shell). This allows the large-pore mesoporous shell (MCM-41 molecular sieve) to allow tar macromolecules (such as lignin derivatives) to enter and undergo preliminary cracking, preventing them from directly polymerizing and clogging at the micropore inlet. The microporous core (HZSM-5 molecular sieve) provides strongly acidic sites, enabling deep cracking of smaller molecules generated from preliminary cracking into target small-molecule gases. This structure effectively overcomes the problem of large molecules being unable to access active sites due to micropore limitations in traditional catalysts (such as pure HZSM-5 molecular sieves or catalysts lacking hierarchical channels), reducing pore clogging and surface coking. Furthermore, the introduction of the mesoporous shell provides a larger space to accommodate tar molecules and their cracking intermediates, delaying the polymerization of coking precursors at active sites and the formation of coke deposits. The hierarchical pore structure improves the diffusion efficiency of reactants and products, reduces the residence time of pyrolysis products (such as carbon deposit precursors) in the pores, thereby reducing the probability of deep dehydrogenation polymerization forming stubborn carbon deposits.

[0058] This invention also provides a composite molecular sieve catalyst, wherein the composite molecular sieve catalyst is composed of, for example, Figure 1 The sample was prepared by the method shown. The composite molecular sieve catalyst is composed of a core-shell structure formed by combining HZSM-5 molecular sieve and MCM-41 molecular sieve as a support, and loaded with metal oxides. The metal oxide is at least one of nickel oxide, cobalt oxide, and iron oxide; The metal oxide accounts for 20%-25% of the total mass of the composite molecular sieve catalyst.

[0059] In this embodiment of the invention, the HZSM-5-MCM-41 core-shell support integrates microporous deep pyrolysis and mesoporous macromolecular pre-pyrolysis / diffusion functions, solving the problems of inlet blockage and surface polymerization coking caused by pore limitation of tar macromolecules (such as lignin derivatives). Furthermore, the acidic sites of the support and the supported metal oxides form dual active centers for acid-catalyzed pyrolysis and metal hydrogenation / deoxygenation, achieving efficient and deep conversion of tar while simultaneously inhibiting the formation of polycyclic aromatic hydrocarbons (such as benzo[a]pyrene) and reducing carbon deposition. The core-shell structure protects the micropores of the core, while the mesoporous shell delays carbon deposition covering the active sites, significantly improving the catalyst's cycle stability and regeneration tolerance.

[0060] In this embodiment of the invention, in the composite molecular sieve catalyst, the mesoporous shell formed by the MCM-41 molecular sieve has a pore size of 3nm-5nm; the micropore size of the HZSM-5 molecular sieve is 0.5nm-0.6nm.

[0061] Utilize Figure 1 The illustrated preparation method can produce mesoporous shells of MCM-41 molecular sieves with pore sizes of 3nm-5nm to match the size of tar macromolecules (such as lignin derivatives, with kinetic diameters of 1nm-3nm), eliminating diffusion resistance and preventing pore blockage. Simultaneously, it restricts the condensation growth of polycyclic aromatic hydrocarbons (such as benzo[a]pyrene precursors) within the pores. The acidic sites on the pore walls interact deeply with the macromolecules in full contact, achieving efficient pre-pyrolysis and reducing surface polymerization and coking at the source.

[0062] In practice, the 5nm upper limit can prevent the acid site density from being insufficient due to excessively large pores, thus ensuring pre-fracture efficiency; the 3nm lower limit can ensure unimpeded passage of macromolecules and maintain a high diffusion rate.

[0063] This invention also provides an application of a composite molecular sieve catalyst, wherein the composite molecular sieve catalyst is composed of, for example... Figure 1 The composite molecular sieve catalyst, prepared by the method shown, is used to catalyze tar reforming, CH4 reforming, or CO2 reforming reactions to obtain H2-rich gas.

[0064] In this embodiment of the invention, tar reforming is used to completely crack macromolecules into H2 / CO, thus solving the problems of clogging and toxic byproducts. CH4 / CO2 is reformed into highly efficient activated small molecules, which are then converted into syngas (H2+CO).

[0065] When applying, such as Figure 1 The composite catalyst prepared by the illustrated method, with its hierarchical pore structure and internal nucleic acid cleavage and metal deoxygenation / reforming, can efficiently catalyze tar reforming and CH4 / CO2 reforming. In practice, the pre-cleavage of the mesoporous shell reduces coke formation, allowing the catalyst to maintain high activity and stability in the reforming environment, providing an efficient, low-toxicity, and deactivation-resistant industrial-grade solution for green hydrogen production.

[0066] To enable those skilled in the art to more clearly understand the present invention, the following embodiments are provided to illustrate in detail the composite molecular sieve catalyst, its preparation method, and its application.

[0067] Example 1 A composite molecular sieve catalyst was prepared, as detailed below: 10.0 g of HZSM-5 molecular sieve (silicon-aluminum ratio of 27:1) was added to 100 mL of 2.12 mol / L tetrapropylammonium hydroxide (hereinafter referred to as TPAOH) solution. Under the conditions of 65 °C provided by water bath, the surface of HZSM-5 molecular sieve was dissociated to obtain a dispersion system containing aluminosilicate fragments. 125 ml of 0.59 mol / L hexadecyltrimethylammonium bromide (hereinafter referred to as CTAB) solution was added to the dispersion system as a mesoporous template agent, and the system was treated with sol-gel at 110°C for 24 h in a high-pressure reactor to obtain a gel system. After cooling, the solution of the gel system is alkaline. The pH is then adjusted to 8.5-9.0 with hydrochloric acid, and the system is placed in a high-pressure reactor again. It is crystallized at 110°C for 24 hours. After cooling, the system is centrifuged, filtered, washed with ethanol, and dried in an oven to obtain the crystallized product. The crystallized product is placed in a tube furnace and calcined at 550°C for 6 hours at a heating rate of 2°C / min to form a composite molecular sieve with an HZSM-5-MCM-41 core-shell structure, referred to as H / M core-shell molecular sieve. 2.477 g Ni(NO3)2·6H2O and 2.469 g Co(NO3)2·6H2O were successively dissolved in deionized water, and 10.0 g H / M molecular sieve was impregnated by an equal volume impregnation method. The resulting impregnated system was then dried at 120°C to constant weight to remove moisture, and finally calcined in a tube furnace at 650°C for 6 h at a heating rate of 2°C / min to obtain a composite molecular sieve catalyst, wherein the mass percentage of Ni to Co was 1:1.

[0068] Example 2 The only difference between Example 2 and Example 1 is that Example 2 uses HZSM-5 molecular sieve with a silicon-to-aluminum ratio of 25:1.

[0069] Example 3 The only difference between Example 3 and Example 1 is that Example 2 uses HZSM-5 molecular sieve with a silicon-to-aluminum ratio of 30:1.

[0070] Example 4 The difference between Example 4 and Example 1 is that the mass-volume ratio of HZSM-5 molecular sieve (silicon-aluminum ratio of 27:1) to TPAOH solution is 8g:100mL.

[0071] Example 5 The difference between Example 5 and Example 1 is that the mass-volume ratio of HZSM-5 molecular sieve (silicon-aluminum ratio of 27:1) to TPAOH solution is 12g:100mL.

[0072] Example 6 The difference between Example 6 and Example 1 is that the volume percentage of CTAB solution in the dispersion system is 2.5 wt%.

[0073] In summary, this invention provides a composite molecular sieve catalyst, its preparation method, and its application. The catalyst is prepared by alkaline dissociation of HZSM-5 molecular sieves to generate aluminosilicate fragments, which self-assemble into a core-shell structure under the action of a template agent and are then loaded with metal oxides. This catalyst utilizes the mesopores of MCM-41 molecular sieves to promote mass transfer and pre-cracking of tar macromolecules, the micropores of HZSM-5 molecular sieves to achieve deep conversion of small molecules, and the metal components to catalyze the gasification of carbon deposits. The synergistic effect of these three elements can efficiently catalyze the reforming of tar and CH4 / CO2 to produce hydrogen-rich syngas, while simultaneously solving the problems of catalyst deactivation due to carbon deposits and carbon emissions.

[0074] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a composite molecular sieve catalyst, characterized in that, The method includes: S1. Place the dispersion containing HZSM-5 molecular sieve and alkaline catalyst in a water bath at 65℃-80℃ to promote the dissociation of the surface of HZSM-5 molecular sieve and obtain a dispersion system containing aluminosilicate fragments. Add a template agent to the dispersion system and treat it with sol-gel at 100℃-120℃ for 22h-26h to obtain a gel system containing MCM-41 molecular sieve precursor. S2. After the gel system is cooled, its pH is adjusted to 8.5-9.0, and then crystallized at 100℃-120℃ for 22h-26h. The resulting system is filtered, washed, dried and calcined to form a composite molecular sieve with an HZSM-5-MCM-41 core-shell structure. S3. The composite molecular sieve is impregnated in a metal salt solution in equal volume. After drying and calcining, the resulting impregnation system is used to obtain the composite molecular sieve catalyst. The metal salt in the metal salt solution is selected from at least one of nickel nitrate, cobalt nitrate, and iron nitrate.

2. The method for preparing the composite molecular sieve catalyst according to claim 1, characterized in that, The silica-alumina ratio of the HZSM-5 molecular sieve is (25-30):

1.

3. The method for preparing the composite molecular sieve catalyst according to claim 1, characterized in that, In step S1, the alkaline catalyst is any one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; The mass-to-volume ratio of the HZSM-5 molecular sieve to the dispersion is (8-12) g: 100 mL.

4. The method for preparing the composite molecular sieve catalyst according to claim 1, characterized in that, The template agent is hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium chloride; The template agent has a volume percentage of 1.5wt%-2.5wt% in the dispersion system.

5. The method for preparing the composite molecular sieve catalyst according to claim 1, characterized in that, In step S2, the calcination temperature is 500℃-600℃, the heating rate is 1.5℃ / min-2.5℃ / min, and the calcination time is 5h-7h.

6. The method for preparing the composite molecular sieve catalyst according to claim 1, characterized in that, In step S3, the metal salt is nickel nitrate and cobalt nitrate; The mass ratio of nickel nitrate to cobalt nitrate is 1:(0.95-1).

7. The method for preparing the composite molecular sieve catalyst according to claim 1, characterized in that, In step S3, the calcination temperature is 600℃-700℃, the heating rate is 1.5℃ / min-2.5℃ / min, and the calcination time is 5h-7h.

8. A composite molecular sieve catalyst, characterized in that, The composite molecular sieve catalyst is prepared by the preparation method described in any one of claims 1-7; The composite molecular sieve catalyst is composed of a core-shell structure formed by combining HZSM-5 molecular sieve and MCM-41 molecular sieve as a support, and loaded with metal oxides. The metal oxide is at least one of nickel oxide, cobalt oxide, and iron oxide; The metal oxide accounts for 20%-25% of the total mass of the composite molecular sieve catalyst.

9. The composite molecular sieve catalyst according to claim 8, characterized in that, In the composite molecular sieve catalyst, the mesoporous shell formed by the MCM-41 molecular sieve has a pore size of 3nm-5nm; the micropore size of the HZSM-5 molecular sieve is 0.5nm-0.6nm.

10. An application of a composite molecular sieve catalyst, characterized in that, The composite molecular sieve catalyst is prepared by the preparation method described in any one of claims 1-7. The composite molecular sieve catalyst is used to catalyze tar reforming, CH4 reforming or CO2 reforming to obtain H2-rich gas.

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