A structure-directing agent and a rare earth molecular sieve catalyst and their preparation method

Abstract

This invention provides a structure-directing agent, a rare earth molecular sieve catalyst, and a preparation method thereof. The structure-directing agent comprises a compound with the structural formula shown in Formula (I). This structure-directing agent, by regulating the encapsulation of rare earth metals and the growth direction of molecular sieve crystals, enables the obtained rare earth molecular sieve catalyst to possess a multi-level pore structure with micropores and mesopores interconnected in three dimensions, and the rare earth metals in the rare earth molecular sieve catalyst are encapsulated within the multi-level pore structure with micropores and mesopores interconnected in three dimensions.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve materials technology, and in particular to a structure-directing agent and a rare earth molecular sieve catalyst and their preparation methods. Background Technology

[0002] Against the backdrop of advancing the "dual carbon" goals and accelerating energy transformation, my country's oil refining industry is undergoing a profound transformation. The core development direction of the industry is to efficiently convert heavy oil into high-value-added low-carbon olefins such as ethylene and propylene by relying on catalytic cracking technology. This process places stringent requirements on catalysts, and it is necessary to solve multiple challenges such as the limited diffusion of heavy oil macromolecules, the selective control of catalytic reactions, and the structural stability of catalysts under high-temperature hydrothermal environments.

[0003] Molecular sieves have become the core catalytic materials in this field due to their excellent shape-selective catalytic performance. However, their intrinsic microporous structure can easily lead to impeded mass transfer of macromolecules, carbon deposition and deactivation, and difficulty in stably loading active metals. Furthermore, it is difficult to achieve stable loading and dispersion of active metals.

[0004] To address the aforementioned issues, existing technologies primarily focus on two dimensions: molecular sieve pore structure regulation and active metal encapsulation. Regarding pore structure regulation, patent document CN103922362A discloses a method for preparing novel MTW zeolites using a specially formulated organic template agent. This method involves a hydrothermal reaction of tetravalent oxides, trivalent oxides, an alkali source, and an organic template agent at 140℃–200℃ to form regular hexagonal disk-shaped crystals, thus guiding the construction of a specific zeolite framework. However, this method only focuses on the construction of the zeolite framework structure and fails to simultaneously integrate metal elements with the molecular sieve framework and encapsulate them within the molecular sieve. Regarding metal encapsulation, the patent document… CN114655966A discloses a method for preparing ZSM-5 molecular sieves loaded with rare earth metals. First, a hierarchical porous molecular sieve is synthesized, and then rare earth elements are loaded by solution impregnation. However, due to the spatial limitation of the single microporous structure of the ZSM-5 molecular sieve, rare earth species cannot easily enter the interior of the molecular sieve channels and only adhere to the surface of the molecular sieve. Stable dispersion of rare earth metals within the molecular sieve system cannot be achieved. Furthermore, the prepared molecular sieve has poor pore connectivity and insufficient structural stability of the molecular sieve framework, making it difficult to achieve effective loading of rare earth elements within the molecular sieve framework. The existing technical solution still has significant limitations and cannot meet the actual industrial needs of heavy oil catalytic cracking.

[0005] Therefore, developing rare earth modified molecular sieves that combine multi-level pore structure and encapsulation is a current research focus and technological bottleneck in the field of catalytic materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a structure-directing agent. By regulating the growth direction of rare earth molecular sieve precursor crystals, the prepared rare earth molecular sieve catalyst possesses a multi-level pore structure with micropores and mesopores interconnected in three dimensions, while simultaneously achieving the encapsulation of rare earth metals within the molecular sieve system.

[0007] The present invention also provides a method for preparing a structure-directing agent. The above-mentioned structure-directing agent can be prepared by multi-step substitution and process parameter control. The process is simple and low cost.

[0008] This invention also provides a method for preparing a rare earth molecular sieve catalyst, which uses the above-mentioned structure directing agent to encapsulate rare earth metals in situ within the micropores and mesopores of the rare earth molecular sieve catalyst, thereby obtaining a hierarchical porous rare earth molecular sieve catalyst with both excellent mass transfer performance and structural stability.

[0009] The present invention also provides a rare earth molecular sieve catalyst, which is prepared by the above-mentioned structure directing agent, has a multi-level pore structure, and the rare earth metal is in situ encapsulated in the multi-level pore structure.

[0010] In a first aspect, the present invention provides a structure-directing agent comprising a compound having the structure shown in formula (I).

[0011] Equation (Ⅰ).

[0012] In a second aspect, the present invention provides a method for preparing a structure-directing agent as described in the first aspect, comprising the following steps:

[0013] 1) 5,5'-dimethyl-2,2'-bipyridine, N-bromosuccinimide and the first solvent are mixed and a single substitution reaction is carried out to give the first intermediate product;

[0014] 2) The first intermediate product, tetramethylhexanediamine, and the second solvent are mixed to undergo a secondary substitution reaction to obtain the second intermediate product;

[0015] 3) The second intermediate product, 1-bromohexane and the third solvent are mixed to undergo a three-stage substitution reaction to obtain the structure-directing agent.

[0016] Furthermore, the molar ratio of the 5,5'-dimethyl-2,2'-bipyridine to the N-bromosuccinimide is 1:(1~2);

[0017] And / or, the molar ratio of the first intermediate product to the tetramethylhexanediamine is 1:(10~20);

[0018] And / or, the molar ratio of the second intermediate to the 1-bromohexane is 1:(2~6).

[0019] Furthermore, the temperature of the primary substitution reaction is 60℃~80℃, and the time is 10h~20h;

[0020] And / or, the secondary substitution reaction is carried out at a temperature of 70°C to 85°C for a time of 20 h to 48 h;

[0021] And / or, the temperature of the three substitution reactions is 70℃~85℃, and the time is 20h~48h.

[0022] Thirdly, the present invention provides a method for preparing a rare earth molecular sieve catalyst, comprising the following steps:

[0023] Rare earth metal source, complexing agent, solvent, alkali source, structure directing agent as described in claim 1, silicon source and aluminum source are mixed, and pH is adjusted to obtain precursor liquid gel;

[0024] The precursor liquid gel was subjected to hydrothermal crystallization treatment to obtain the crystallized product;

[0025] The crystallized product is calcined under an oxygen-containing atmosphere to obtain the rare earth molecular sieve catalyst.

[0026] Furthermore, the mass ratio of the rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source and aluminum source is (0.0078~0.0235):(0.047~0.14):(20~24):0.33:1:3.5:0.014.

[0027] Furthermore, the complexing agent includes sodium citrate;

[0028] And / or, the silicon source includes at least one of tetraethyl orthosilicate, sodium silicate, fumed silica, and silica gel;

[0029] And / or, the aluminum source includes at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum isopropoxide.

[0030] Furthermore, the crystallization temperature of the hydrothermal crystallization treatment is 140℃~160℃, and the crystallization time is 3 days~7 days;

[0031] And / or, stirring is performed during the hydrothermal crystallization treatment, and the stirring speed is 30 rpm to 70 rpm;

[0032] And / or, the calcination treatment is carried out at a temperature of 500℃~600℃ for a time of 4h~8h.

[0033] Fourthly, the present invention provides a rare earth molecular sieve catalyst obtained using the preparation method of the rare earth molecular sieve catalyst as described in the third aspect.

[0034] Furthermore, the rare earth molecular sieve catalyst comprises a molecular sieve framework and a rare earth metal, the molecular sieve framework comprises channels, the rare earth metal is disposed in at least a portion of the channels of the molecular sieve framework, and the mass ratio of the rare earth metal to the molecular sieve framework is 1:(67~200).

[0035] And / or, the total pore volume of the rare earth molecular sieve catalyst is 0.2 cm³. 3 / g~0.4cm 3 / g;

[0036] And / or, the specific surface area of ​​the rare earth molecular sieve catalyst is 350 m². 2 / g~450m 2 / g.

[0037] The structure-directing agent provided by this invention includes the compound shown in formula (Ⅰ) (a multi-quaternary ammonium salt organic molecule). The compound with the structure of formula (Ⅰ) can play a structure-directing role in the hydrothermal crystallization system of molecular sieves, regulate the growth mode and pore configuration of molecular sieve crystals, construct a molecular sieve framework with a three-dimensional interconnected multi-level pore structure of micropores and mesopores, and prepare structurally stable rare earth molecular sieve catalysts.

[0038] The rare earth molecular sieve catalyst prepared using this structure-directing agent provided by the present invention can reduce the mass transfer resistance of macromolecules; at the same time, the oxygen atoms on the molecular sieve framework can interact with rare earth metals, guiding the rare earth metals to enter the pores of the three-dimensional interconnected multi-level pore structure of micropores and mesopores during the molecular sieve crystallization process, realizing the in-situ dispersion and fixation of rare earth metals, and improving the binding stability of rare earth metal components in the molecular sieve framework. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The X-ray diffraction analysis diagram of the rare earth molecular sieve catalyst in Example 2 is shown below.

[0041] Figure 2 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 2. Figure 2 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0042] Figure 3 The nitrogen-adsorption-desorption curve of the rare earth molecular sieve catalyst in Example 2 is shown.

[0043] Figure 4 The image shows the pore size distribution curve of the rare earth molecular sieve catalyst in Example 2.

[0044] Figure 5 This is a SEM-Mapping elemental distribution map of the rare earth molecular sieve catalyst in Example 2. Figure 5 In the figure, (a), (b), (c), and (d) are the SEM-Mapping element surface distributions of La, O, Al, and Si elements, respectively.

[0045] Figure 6 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 3. Figure 6 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0046] Figure 7 The image shows the X-ray diffraction pattern of the rare earth molecular sieve catalyst in Example 3.

[0047] Figure 8 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 4. Figure 8 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0048] Figure 9 The image shows the X-ray diffraction pattern of the rare earth molecular sieve catalyst in Example 4.

[0049] Figure 10 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 5. Figure 10 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0050] Figure 11 The image shows the X-ray diffraction pattern of the rare earth molecular sieve catalyst in Example 5.

[0051] Figure 12 This is a SEM-Mapping elemental distribution map of the rare earth molecular sieve catalyst in Example 5. Figure 12 In the figure, (a), (b), (c), and (d) are the SEM-Mapping element surface distributions of Ce, O, Al, and Si elements, respectively.

[0052] Figure 13 The image shows a scanning electron microscope (SEM) image of the ZSM-5 molecular sieve catalyst in Comparative Example 1.

[0053] Figure 14 The image shows the X-ray diffraction pattern of the ZSM-5 molecular sieve catalyst in Comparative Example 2. Detailed Implementation

[0054] To enable those skilled in the art to better understand the solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0055] In a first aspect, the present invention provides a structure-directing agent comprising a compound having the structure shown in formula (I).

[0056] Equation (Ⅰ).

[0057] The structure-directing agent of this invention includes a compound (a multi-quaternary ammonium salt organic molecule) as shown in formula (Ⅰ). The compound with the structure of formula (Ⅰ) guides the orderly assembly of the molecular sieve framework through the electrostatic interaction between the quaternary ammonium cation and the silicon-aluminum species. It forms nanocrystals and intergranular mesopores by relying on molecular rigidity and steric hindrance, and finally constructs a three-dimensional interconnected multi-level pore structure of micropores and mesopores. This multi-level pore structure can be used for in-situ encapsulation of catalytically active substances (such as rare earth metals) to achieve in-situ dispersion and fixation of catalytically active substances.

[0058] On the one hand, this structure-directing agent constructs a molecular sieve framework with a three-dimensional interconnected multi-level pore structure of micropores and mesopores by regulating the crystal growth direction of rare earth molecular sieve catalysts.

[0059] On the other hand, this structure-directing agent regulates the in-situ encapsulation and chemical bonding of rare earth metals, enabling the rare earth metals to be encapsulated in at least part of the micropores and mesopores of the molecular sieve framework, thereby achieving in-situ dispersion and fixation of rare earth metals.

[0060] Secondly, the present invention provides a method for preparing a structure-directing agent, comprising the following steps:

[0061] 1) 5,5'-dimethyl-2,2'-bipyridine, N-bromosuccinimide and the first solvent are mixed and a single substitution reaction is carried out to give the first intermediate product;

[0062] 2) The first intermediate, tetramethylhexanediamine, and the second solvent are mixed to undergo a secondary substitution reaction, yielding the second intermediate;

[0063] 3) The second intermediate, 1-bromohexane and the third solvent are mixed to undergo a three-stage substitution reaction to obtain the structure-directing agent of the first aspect.

[0064] This preparation method achieves precise synthesis of structure-directing agents through the synergistic effect of the three substitution reactions (primary substitution, secondary substitution, and tertiary substitution), ensuring the uniformity of the product structure. The structural formula of the prepared structure-directing agent is shown in formula (Ⅰ). This preparation method is simple in steps, has mild reaction conditions, and can stably prepare high-purity structure-directing agents.

[0065] In step 1), azobisisobutyronitrile decomposes upon heating to generate free radicals, which trigger the release of halogen radicals from N-bromosuccinimide, thereby achieving the bromination modification of the methyl group in 5,5'-dimethyl-2,2'-bipyridine, and yielding the first intermediate product with the structural formula (II). The reaction route for the primary substitution reaction is shown in reaction formula (1).

[0066] Reaction formula (1).

[0067] In step 2), the tertiary amine group in the tetramethylhexanediamine molecule undergoes nucleophilic substitution with the bromoalkyl group of the first intermediate (II) to obtain the second intermediate, which has the structural formula (III). The second intermediate (III) is a quaternary ammonium salt structure and has bifunctional activity. The reaction route of the secondary substitution reaction is shown in reaction formula (2).

[0068] Reaction formula (2).

[0069] In step 3), the structure of the structure-directing agent is formula (Ⅰ): the remaining tertiary amine group undergoes nucleophilic substitution with 1-bromohexane to complete the full quaternization modification, resulting in structure-directing agent formula (Ⅰ). Structure-directing agent formula (Ⅰ) has structure-directing function. The reaction route of the three substitution reaction is shown in reaction formula (3):

[0070] Reaction formula (3).

[0071] In some embodiments, the first solvent includes, but is not limited to, azobisisobutyronitrile and / or carbon tetrachloride.

[0072] In some embodiments, the second solvent includes, but is not limited to, acetonitrile and / or toluene.

[0073] In some embodiments, the third solvent includes, but is not limited to, acetonitrile.

[0074] In some embodiments, the molar ratio of 5,5'-dimethyl-2,2'-bipyridine to N-bromosuccinimide is 1:(1~2);

[0075] And / or, the molar ratio of the first intermediate to tetramethylhexanediamine is 1:(10~20);

[0076] And / or, the molar ratio of the second intermediate to 1-bromohexane is 1:(2~6).

[0077] For example, the molar ratio of 5,5'-dimethyl-2,2'-bipyridine to N-bromosuccinimide is any value of 1:1, 1:1.5, 1:2, or any range of both.

[0078] For example, the molar ratio of the first intermediate to tetramethylhexanediamine is any value of 1:10, 1:15, 1:20, or any range of both.

[0079] For example, the molar ratio of the second intermediate to 1-bromohexane is any value of 1:2, 1:3, 1:4, 1:5, 1:6, or any combination of both.

[0080] Within this ratio range, the reactants can react fully, improving the selectivity of primary and secondary substitution reactions, reducing the formation of mono- and poly-substituted byproducts, increasing the conversion rate and purity of the first intermediate, and ensuring its structure-directing effect in the subsequent preparation of rare earth molecular sieve catalysts.

[0081] In some embodiments, the temperature of a single substitution reaction is 60°C to 80°C, and the time is 10h to 20h.

[0082] And / or, the temperature for the secondary substitution reaction is 70℃~85℃, and the time is 20h~48h;

[0083] And / or, the temperature for the three substitution reactions is 70℃~85℃, and the time is 20h~48h.

[0084] For example, the temperature of a single substitution reaction is any value or a range of any two of 60°C, 70°C, 80°C, etc.; the time is any value or a range of any two of 10h, 15h, 20h, etc.

[0085] For example, the temperature of the secondary substitution reaction is any value or a range of any two of 70°C, 75°C, 80°C, 85°C, etc.; the time is any value or a range of any two of 20h, 30h, 40h, 48h, etc.

[0086] For example, the temperature of the three substitution reaction is any value or a range of any two of 70°C, 75°C, 80°C, 85°C, etc.; the time is any value or a range of any two of 20h, 30h, 40h, 48h, etc.

[0087] Within the above-mentioned reaction temperature and time range, the substitution reaction can be carried out smoothly in each step, and the occurrence of side reactions can be suppressed. The primary substitution reaction, secondary substitution reaction, and tertiary substitution reaction can all achieve a high degree of reaction, shorten the reaction cycle, improve the purity of the product, ensure the synthesis quality and efficiency of structure-directing agents, and meet the needs of large-scale preparation of structure-directing agents.

[0088] In some embodiments, after a substitution reaction is completed, a first reaction solution is obtained; the first reaction solution is further subjected to filtration to remove the first solvent to obtain a first retentate, and the first retentate is recrystallized to obtain a first intermediate product.

[0089] In some embodiments, after the secondary substitution reaction is completed, a second reaction solution is obtained; the second reaction solution is further filtered to remove the second solvent to obtain a second retentate, and the second retentate is washed and dried to obtain a second intermediate product; the liquid used for washing includes, but is not limited to, ethyl acetate.

[0090] In some embodiments, after the three substitution reactions are completed, a filtration process is included to remove the third solvent to obtain a third retentate. The third retentate is then washed and dried to obtain a structure-directing agent. The liquid used for washing includes, but is not limited to, ethyl acetate.

[0091] Thirdly, the present invention provides a method for preparing rare earth molecular sieve catalysts using the structure-directing agent of the first aspect, comprising the following steps:

[0092] Rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source and aluminum source are mixed and the pH is adjusted to obtain precursor liquid gel;

[0093] The precursor liquid gel was subjected to hydrothermal crystallization treatment to obtain the crystallized product;

[0094] The crystallized product was calcined in an oxygen-containing atmosphere to obtain a rare earth molecular sieve catalyst.

[0095] The rare earth molecular sieve catalyst prepared using the above-mentioned structure-directing agent in this invention comprises rare earth metals and a molecular sieve framework.

[0096] During the precursor gel mixing process, the rare earth metal source is uniformly dispersed in a mixed system consisting of a silicon source, an aluminum source, a structure-directing agent, a complexing agent, an alkaline source, and a solvent. The rare earth metal source contains rare earth metal ions, and the complexing agent forms a coordination structure with the rare earth metal ions, maintaining the stable dispersion of the rare earth metal in the alkaline system. The structure-directing agent is uniformly dispersed in the silicon-aluminum precursor system, providing directional growth sites for the condensation assembly of the silicon and aluminum sources. During the hydrothermal crystallization process, the silicon and aluminum sources undergo directional condensation and growth along the framework of the structure-directing agent molecules, forming a molecular sieve framework containing the structure-directing agent. The hydrothermal crystallization process is synchronized with the construction of the molecular sieve framework, encapsulating the stably dispersed rare earth metal ions inside the pores of the multi-level porous structure of the molecular sieve framework, thus completing the in-situ encapsulation of the rare earth metal ions.

[0097] The calcination process removes the structure-directing agent from the system, forming a molecular sieve framework with complete crystal structure and interconnected multi-level pores. Simultaneously, the calcination process is carried out in an oxygen-containing atmosphere, causing the rare earth metal ion complexes to undergo an oxidation reaction to generate rare earth metal oxides, which encapsulates the rare earth metals in situ within the multi-level pores. This method achieves the simultaneous construction of the multi-level pore structure molecular sieve framework and the in-situ encapsulation of rare earth metals, simplifying the preparation process.

[0098] In some preferred embodiments, after mixing the rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source and aluminum source, the pH is adjusted to 11-13, preferably 12, using an acid solution.

[0099] For example, the pH is adjusted to any value among 11, 12, 13, etc., or a range of any combination of both.

[0100] Acids include, but are not limited to, at least one of sulfuric acid, hydrochloric acid, and acetic acid.

[0101] In some preferred embodiments, the rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source, and aluminum source are mixed, specifically including the following process:

[0102] 1) The rare earth metal source, complexing agent, and solvent are mixed to obtain the first mixture;

[0103] 2) The alkali source, structure directing agent, and solvent are mixed and then heated to obtain a second mixture;

[0104] 3) The silicon source, aluminum source, second mixture, and first mixture are mixed to undergo a hydrolysis reaction;

[0105] After the hydrolysis reaction is complete, a precursor solution is obtained. The pH value of the precursor solution is adjusted with acid to obtain a precursor solution gel.

[0106] The solvents mentioned above include, but are not limited to, deionized water.

[0107] In the above process, the rare earth metal source and the complexing agent are mixed in a solvent, so that the complexing agent and the rare earth metal ions form a stable rare earth-complex. Through the complexation effect, the rare earth elements are bound in the single ionic state of the rare earth metal ions, which fundamentally solves the problem of the large radius and easy aggregation of rare earth metal hydrated ions.

[0108] A first mixed solution containing rare earth metal ions, a silicon source, an aluminum source (molecular sieve precursor), and a second mixed solution are mixed to undergo a hydrolysis reaction. During the mixing process, the rare earth metal ions are uniformly dispersed in the silicon-aluminum precursor gel system, which inhibits the agglomeration of rare earth metals and enables the rare earth metals to achieve a uniform overall distribution in the precursor gel before molecular sieve crystallization.

[0109] The compounds of this invention possessing the structure of formula (I) are bipyridine organic molecules functionalized with quaternary ammonium salts, comprising a rigid bipyridine aromatic ring skeleton, a quaternary ammonium salt center bridged by tetramethylhexanediamine in the middle, and long-chain alkyl groups at both ends; the quaternary ammonium cation (N) in the structure-directing agent molecule + It carries a high density of positive charges and can react with the negatively charged SiO in the aluminosilicate gel system. - AlO - Strong electrostatic interactions are generated, guiding the orderly arrangement, condensation, and cross-linking of silicon-aluminum tetrahedral species along the long axis of the structure-directing agent molecules, gradually forming primary crystal nuclei of molecular sieves with MFI topology. The structure-directing agent molecules have rigid aromatic rings and extended alkyl chains, occupying a certain space volume, generating steric hindrance during the crystal nucleus growth process, limiting the excessive growth of molecular sieve grains, and keeping the crystals at the nanoscale. As the crystallization reaction proceeds, the nanoscale crystal nuclei stack up with each other, and the stacking of the formed primary nanoparticles yields aggregates.

[0110] Meanwhile, the orderly growth of the molecular sieve framework (MFI type) spatially confines and structurally fixes the single-ion rare earth metal ions: In the silica-alumina gel system, the quaternary ammonium cations in the structure-directing agent molecules carry positive charges and can generate charge repulsion with the rare earth metal cations coordinated by the complexing agent, causing the rare earth metal cations to accumulate in the negatively charged silica-alumina hydroxyl species region of the system; During the process of silicon and aluminum sources growing along the structure-directing agent molecules and constructing the molecular sieve pore framework, the rare earth metal cations enriched in the silica-alumina species region are confined and encapsulated inside the pores of the molecular sieve framework as the framework condenses and assembles; After crystallization, the rare earth metal cations form coordination interactions with the framework oxygen atoms in the molecular sieve framework, and are stably fixed inside the pores, achieving high dispersion and stable fixation of rare earth metal ions.

[0111] After the crystallization reaction is completed, calcination is performed. On the one hand, the template agent is removed, leaving intracrystalline mesopores in the molecular sieve framework that match the molecular size of the structure-directing agent. At the same time, the accumulation of nano-primary particles containing micropores forms intercrystalline mesopores, which are interconnected with the inherent micropores of the nano-primary particles. Finally, a multi-level pore structure with three-dimensional interconnection of micropores and mesopores is constructed, so that the molecular sieve framework has both high specific surface area and total pore volume, thereby improving its mass transfer efficiency. On the other hand, in an oxygen-containing atmosphere, the complexes of rare earth metal ions undergo an oxidation reaction to generate rare earth metal oxides, which significantly increases the thermal stability, chemical stability and structural stability of the rare earth metal components, preventing the loss, migration and agglomeration of rare earths during subsequent use or high-temperature reactions.

[0112] In some embodiments, the mass ratio of rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source and aluminum source is (0.0078~0.0235):(0.047~0.14):(20~24):0.33:1:3.5:0.014.

[0113] For example, the mass ratio of rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source and aluminum source is any value or a range of any two of the following: 0.0078:0.047:20:0.33:1:3.5:0.014, 0.0178:0.1:22:0.33:1:3.5:0.014, 0.0235:0.14:24:0.33:1:3.5:0.014.

[0114] The solvent includes, but is not limited to, deionized water.

[0115] Within this mass ratio range, a uniform and stable precursor liquid gel system can be formed, ensuring the smooth crystallization of the molecular sieve framework and the effective loading of rare earth metals.

[0116] In some implementations, the complexing agent includes sodium citrate.

[0117] The aforementioned complexing agents can form stable coordination structures with rare earth metal ions contained in the rare earth metal source, thereby improving the dispersibility of rare earth metals. In particular, sodium citrate, as a complexing agent, can maintain the gel morphology of the precursor solution gel system at pH=12.

[0118] During the calcination process of the crystallized product, the complexing agent is completely oxidized and decomposed into gas and escapes, while the rare earth metals, which are confined and fixed by the molecular sieve framework and pores, remain inside the molecular sieve without agglomeration, thus achieving uniform encapsulation of rare earth metals in the molecular sieve.

[0119] In some embodiments, the silicon source includes at least one of tetraethyl orthosilicate, sodium silicate, fumed silica, and silica gel.

[0120] In some embodiments, the aluminum source includes at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum isopropoxide.

[0121] The aforementioned silicon and aluminum sources can be fully hydrolyzed in the hydrothermal crystallization system, providing stable precursors for the formation of the molecular sieve framework and ensuring the crystallinity and structural integrity of the molecular sieve framework.

[0122] In some preferred embodiments, the alkali source includes, but is not limited to, sodium hydroxide.

[0123] In some preferred embodiments, the rare earth metal source includes, but is not limited to, lanthanum nitrate and / or cerium nitrate.

[0124] In some embodiments, the crystallization temperature of the hydrothermal crystallization treatment is 140°C to 160°C, and the crystallization time is 3 to 7 days;

[0125] And / or, during hydrothermal crystallization treatment, stirring is performed at a speed of 30 rpm to 70 rpm;

[0126] And / or, the calcination temperature is 500℃~600℃, and the time is 4h~8h.

[0127] For example, the crystallization temperature of the hydrothermal crystallization treatment is any value of 140℃, 150℃, 160℃, or any combination thereof, and the crystallization time is any value of 3 days, 4 days, 5 days, 6 days, 7 days, or any combination thereof.

[0128] For example, the stirring speed mentioned above is any value or a range of any two of the following: 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, etc.

[0129] For example, the calcination temperature is any value or a combination of two of 500℃, 550℃, 600℃, etc., and the time is any value or a combination of two of 4h, 6h, 8h, etc. Within this crystallization temperature and time range, it is beneficial to form a molecular sieve framework with high crystallinity and stable structure.

[0130] Stirring and the above-mentioned speed range can improve the uniformity of the system and promote the uniform distribution of rare earth metals in the framework.

[0131] These calcination conditions can completely remove organic template agents while maintaining the stability of the molecular sieve framework structure and rare earth metals, thereby improving the specific surface area and pore connectivity of the catalyst.

[0132] Fourthly, the present invention provides a rare earth molecular sieve catalyst obtained using the preparation method of the rare earth molecular sieve catalyst as described in the third aspect.

[0133] Through the above preparation method, the rare earth molecular sieve catalyst forms a three-dimensional interconnected structure of micropores and mesopores under the regulation of the first aspect of the structure-directing agent. At the same time, the rare earth metal is combined in situ in the molecular sieve framework, which has both excellent mass transfer performance and structural stability, thereby improving the catalytic reaction efficiency and service life.

[0134] In some embodiments, the rare earth molecular sieve catalyst includes a molecular sieve framework and a rare earth metal. The molecular sieve framework includes channels, and the rare earth metal is disposed in at least a portion of the channels of the molecular sieve framework. The mass ratio of the rare earth metal to the molecular sieve framework is 1:(67~200).

[0135] And / or, the total pore volume of the rare earth molecular sieve catalyst is 0.2 cm³. 3 / g~0.4cm 3 / g;

[0136] And / or, the specific surface area of ​​the rare earth molecular sieve catalyst is 350 m². 2 / g~450m 2 / g.

[0137] For example, the mass ratio of rare earth metals to molecular sieve framework is any value or a range of any two of the following: 1:67, 1:100, 1:150, 1:200.

[0138] For example, the total pore volume of the rare earth molecular sieve catalyst is 0.2 cm³. 3 / g, 0.3cm 3 / g, 0.4cm 3 Any value in / g, or a range consisting of any two of them.

[0139] For example, the specific surface area of ​​the rare earth molecular sieve catalyst is 350 m². 2 / g、400m 2 / g、450m 2 Any value in / g, or a range consisting of any two of them.

[0140] The aforementioned specific surface area and pore volume range can further solve the problem of limited diffusion in pores, thereby increasing the exposure of active sites and mass transfer efficiency of rare earth molecular sieve catalysts, and adapting to the diffusion requirements of macromolecular reactants.

[0141] The distribution of rare earth metals in a multi-level channel structure with micropores and mesopores can enhance the activity and stability of rare earth molecular sieve catalysts.

[0142] The aforementioned molecular sieve framework has a multi-level pore structure with micropores and mesopores interconnected in three dimensions.

[0143] In some embodiments, the three-dimensional interconnected hierarchical pore structure of micropores and mesopores includes micropores and mesopores, wherein, taking the total specific surface area of ​​the rare earth molecular sieve catalyst as 100%, the specific surface area ratio of micropores is x, the specific surface area ratio of mesopores is 100-x, 40%≤x≤60%, and the unit of x is .

[0144] In some implementations, the silicon-to-aluminum ratio of the rare earth molecular sieve catalyst is 50 to 200.

[0145] For example, x is any value of 40%, 50%, 60%, etc., or a range of any two of them.

[0146] For example, the silicon-to-aluminum ratio of the rare earth molecular sieve catalyst is any value or a range of any two of 50, 75, 100, 200, etc.

[0147] Within this mass ratio and / or silicon-aluminum ratio range, the molecular sieve framework stability, rare earth metal dispersion, and catalytic activity achieve optimal synergy, thereby improving the overall performance of the catalyst.

[0148] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0149] The present invention will be further described below with reference to specific embodiments.

[0150] Information on the pharmaceuticals used in the embodiments and comparative examples of this invention: Lanthanum nitrate hexahydrate (La(NO3)3·6H2O), cerium nitrate hexahydrate (Ce(NO3)3·6H2O), and trisodium citrate (Na3C6H5O7·2H2O) were all purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and were all of analytical grade (AR); Sodium hydroxide (NaOH), sulfuric acid (H2SO4), tetraethyl orthosilicate (Si(OC2H5)4), and sodium aluminate (NaAlO2) were all purchased from Sinopharm Chemical Reagent Co., Ltd., and were all of analytical grade (AR). 5,5'-Dimethyl-2,2'-Bipyridine (CH3C 10 H6N2CH3 was purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd., and was of analytical grade (AR). N-bromosuccinimide (CH3C) was also purchased. 10 H6N2CH3 was purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd., and was of analytical grade (AR).

[0151] Example 1

[0152] 3.7 g (20 mmol) of 5,5'-dimethyl-2,2'-bipyridine, 7.1 g (40 mmol) of N-bromosuccinimide and a first solvent (the first solvent includes 1 g (6 mmol) of azobisisobutyronitrile and 80 mL of carbon tetrachloride) were mixed and subjected to reflux treatment (a single substitution reaction occurred at 80 °C for 20 h). After the single substitution reaction was completed, a first reaction solution was obtained. The first reaction solution was filtered to remove the first solvent and obtain a first retentate. Then, 100 mL of methanol was added to recrystallize the first retentate, filtered, and dried to obtain the first intermediate product with the structure shown in Formula II.

[0153] 4.7 g (15 mmol) of the first intermediate, 63 mL (300 mmol) of tetramethylhexanediamine, and a second solvent (the second solvent consisted of 100 mL of acetonitrile and 100 mL of toluene) were mixed to undergo a secondary substitution reaction (the temperature of the secondary substitution reaction was 85 °C, and the time of the secondary substitution reaction was 48 h). After the secondary substitution reaction was completed, a second reaction solution was obtained. After cooling to room temperature, the second reaction solution was filtered to remove the second solvent and obtain a second retentate. The second retentate was washed with ethyl acetate and dried to obtain the second intermediate with the structure shown in Formula III.

[0154] 4.12 g (6 mmol) of the second intermediate, 4.95 g (30 mmol) of 1-bromohexane and the third solvent (100 mL of acetonitrile) were mixed to undergo a three-stage substitution reaction (the temperature of the three-stage substitution reaction was 85 °C and the time of the three-stage substitution reaction was 48 h). After cooling, the mixture was filtered to remove the third solvent and obtain the third retentate. The third retentate was washed with ethyl acetate and dried to obtain the structure-directing agent DX-1 with the structure shown in formula (I).

[0155] Example 2

[0156] Rare earth metal source (0.0047g lanthanum nitrate hexahydrate), complexing agent (0.028g sodium citrate) and solvent (0.3g deionized water) were added to a beaker and stirred magnetically until homogeneous to obtain the first mixture.

[0157] Add the alkali source (0.2g NaOH) and the structure directing agent (0.6g of the structure directing agent DX-1 prepared in Example 1) to a beaker, add the solvent (14.1g deionized water), stir magnetically until homogeneous, and heat at 65°C for 12h to obtain the second mixture;

[0158] The silicon source (2.08g Si(OC2H5)4), aluminum source (0.0082g NaAlO2), and the second mixture were mixed and magnetically stirred at room temperature for 12h. During the stirring process, the first mixture was added to the second mixture to allow it to undergo a hydrolysis reaction to obtain the precursor solution.

[0159] After hydrolysis is complete, acid solution (2 mol / L sulfuric acid) is added dropwise to adjust the pH of the precursor solution to 12, and the precursor solution gel is obtained.

[0160] The precursor liquid gel was subjected to hydrothermal crystallization treatment to obtain the crystallized product. The specific process included the following steps: the precursor liquid gel was transferred into a 25ml reaction vessel and stirred. The mixture was kept at 150℃ and 50rpm for 5 days to obtain the crystallized product.

[0161] The crystallized product was filtered, washed with distilled water, and dried thoroughly in an oven at 80°C. Then, it was calcined in air to remove the template agent (temperature 550°C, duration 6 hours) to obtain a rare earth molecular sieve catalyst, denoted as La. 0.5 @ZSM-5.

[0162] La 0.5 The mass ratio of rare earth metals to molecular sieve framework in @ZSM-5 is 1:200.

[0163] Example 3

[0164] This example is essentially the same as Example 2, except that the rare earth metal source is 0.0094 g of lanthanum nitrate hexahydrate and the complexing agent is 0.056 g of sodium citrate; denoted as La. 1.0 @ZSM-5.

[0165] La 0.5 The mass ratio of rare earth metals to molecular sieve framework in @ZSM-5 is 1:100.

[0166] Example 4

[0167] This example is essentially the same as Example 2, except that the rare earth metal source is 0.0141g of lanthanum nitrate hexahydrate and the complexing agent is 0.084g of sodium citrate; denoted as La. 1.5 @ZSM-5.

[0168] La 1.5 The mass ratio of rare earth metals to molecular sieve framework in @ZSM-5 is 1:67.

[0169] Example 5

[0170] This example is essentially the same as Example 2, except that the rare earth metal source is 0.0093g of cerium nitrate hexahydrate and the complexing agent is 0.056g of sodium citrate; denoted as Ce. 1.0 @ZSM-5.

[0171] Ce 1.0 The mass ratio of rare earth metals to molecular sieve framework in @ZSM-5 is 1:100.

[0172] Comparative Example 1

[0173] ZSM-5 molecular sieve catalyst was synthesized using tetrapropylammonium hydroxide as a structure directing agent. The specific preparation method was as follows: 1.22g of tetrapropylammonium hydroxide, 14g of deionized water, 0.0082g of sodium aluminate and 2.08g of tetraethyl orthosilicate were added sequentially to the reaction system. After stirring evenly, hydrothermal crystallization was carried out. The product was washed, dried and calcined to obtain the ZSM-5 molecular sieve catalyst.

[0174] Comparative Example 2

[0175] Add the alkali source (0.2g NaOH) and the structure directing agent (0.41g of the second intermediate product with the structure shown in formula (Ⅲ)) to a beaker, add the solvent (14.4g deionized water), stir magnetically until homogeneous, heat at 65℃ for 12h, and then slowly add the silicon source (2.08g Si(OC2H5)4) and the aluminum source (0.0082g NaAlO2) to the above solution, and stir magnetically at room temperature for 12h for hydrolysis;

[0176] After hydrolysis is complete, acid solution (2 mol / L sulfuric acid) is added dropwise to adjust the pH of the precursor solution to 12, and the precursor solution gel is obtained.

[0177] The precursor liquid gel was subjected to hydrothermal crystallization treatment to obtain the crystallized product. The specific process included the following steps: the precursor liquid gel was transferred into a 25ml reaction vessel and stirred. The mixture was kept at 150℃ and 50rpm for 5 days to obtain the crystallized product.

[0178] The crystallized product was filtered, washed with distilled water, and dried thoroughly in an oven at 80°C. Then, the crystallized product was calcined in air to remove the template agent (temperature 550°C, duration 6h) to obtain the crystallized product. XRD characterization showed that the crystallized product was amorphous and no ZSM-5 molecular sieve crystalline phase was formed.

[0179] Comparative Example 3

[0180] Add the alkali source (0.2g NaOH) and the structure directing agent (0.2g first intermediate product formula (II)) to a beaker, add the solvent (14.4g deionized water), stir magnetically until homogeneous, heat at 65℃ for 12h, then slowly add the silicon source (2.08g Si(OC2H5)4) and the aluminum source (0.0082g NaAlO2) to the above solution, and stir magnetically at room temperature for 12h for hydrolysis;

[0181] After hydrolysis is complete, acid solution (2 mol / L sulfuric acid) is added dropwise to adjust the pH of the precursor solution to 12, and the precursor solution gel is obtained.

[0182] The precursor gel was transferred into a 25ml reactor and stirred. The mixture was kept at 150℃ and 50rpm for 5 days. No solid was formed in the liquid phase, and no crystallized product was obtained.

[0183] Test Example 1

[0184] The structure and morphology of the rare earth molecular sieve catalysts in Examples 2-5 and the ZSM-5 molecular sieve catalysts in Comparative Examples 1-2 were characterized by X-ray diffraction and scanning electron microscopy.

[0185] The morphology and elemental distribution of the catalyst samples were tested using a JSM-7900F thermal field emission scanning electron microscope from Japan Electronics. After uniformly dispersing the samples and sputtering them with gold, scanning electron microscope images were acquired under an accelerating voltage of 5 kV to observe the grain morphology and particle dispersion state. At the same time, elemental surface scanning analysis was performed using the matching X-ray energy dispersive spectroscopy (EDS) attachment to obtain SEM-Mapping elemental distribution maps, which characterize the uniformity of the distribution of elements such as silicon, aluminum, and rare earth elements in the catalyst.

[0186] The nitrogen adsorption-desorption curves and pore size distribution of the samples were tested using a low-temperature nitrogen adsorption-desorption method. Before testing, the samples were degassed under vacuum at 300℃ for 6 hours to remove adsorbed impurities. Nitrogen adsorption-desorption isotherms were measured at 77K liquid nitrogen. Based on the adsorption branch, the mesopore distribution was calculated using the BJH model. The pore size distribution was plotted with pore size (nm) as the x-axis and the differential value of pore volume with respect to the logarithm of pore size (dv / dlog(w) Pore Volume, cm⁻¹) as the pore volume. 3 Plot the aperture distribution curve with / g) as the vertical axis.

[0187] The testing methods were based on "A New Compilation of Modern Catalysis Research Methods" (edited by Xin Qin et al., Science Press, 2018). The results are as follows: Figures 1-12 As shown.

[0188] Figure 1 The X-ray diffraction analysis diagram of the rare earth molecular sieve catalyst in Example 2 is shown below.

[0189] Figure 2 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 2. Figure 2 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0190] Figure 3 The nitrogen-adsorption-desorption curve of the rare earth molecular sieve catalyst in Example 2 is shown.

[0191] Figure 4 The image shows the pore size distribution curve of the rare earth molecular sieve catalyst in Example 2.

[0192] Figure 5 This is a SEM-Mapping elemental distribution map of the rare earth molecular sieve catalyst in Example 2. Figure 5 In the figure, (a), (b), (c), and (d) are the SEM-Mapping element surface distributions of La, O, Al, and Si elements, respectively.

[0193] Figure 6 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 3. Figure 6 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0194] Figure 7 The image shows the X-ray diffraction pattern of the rare earth molecular sieve catalyst in Example 3.

[0195] Figure 8 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 4. Figure 8 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0196] Figure 9 The image shows the X-ray diffraction pattern of the rare earth molecular sieve catalyst in Example 4.

[0197] Figure 10 This is a scanning electron microscope image of the rare earth molecular sieve catalyst from Example 5. Figure 10 In the middle (a) and (b), scanning electron microscopes are shown at different scales, respectively;

[0198] Figure 11 The image shows the X-ray diffraction pattern of the rare earth molecular sieve catalyst in Example 5.

[0199] Figure 12 This is a SEM-Mapping elemental distribution map of the rare earth molecular sieve catalyst in Example 5. Figure 12 In the figure, (a), (b), (c), and (d) are the SEM-Mapping element surface distributions of Ce, O, Al, and Si elements, respectively.

[0200] Figure 13 The image shows a scanning electron microscope (SEM) image of the ZSM-5 molecular sieve catalyst in Comparative Example 1.

[0201] Figure 14 The image shows the X-ray diffraction pattern of the ZSM-5 molecular sieve catalyst in Comparative Example 2.

[0202] Depend on Figure 1 , Figure 7 , Figure 9 , Figure 11It can be seen that the rare earth molecular sieve catalysts provided in Examples 2-5 exhibit typical MFI structural diffraction peaks at 7.9°, 8.8°, 23.1°, 23.2° and 23.8°, and no impurity phase peaks were observed, proving that pure phase ZSM-5 molecular sieves were successfully synthesized using the structure directing agent provided in Example 1 and the preparation methods of Examples 2-5.

[0203] Depend on Figure 2 , Figure 6 , Figure 8 , Figure 10 As can be seen, the rare earth molecular sieve catalysts provided in Examples 2-5 are composed of uniformly sized (100-200 nm) primary nanoparticles. These primary nanoparticles exhibit significant aggregation, forming larger aggregates through symbiotic stacking. During this symbiotic stacking process, abundant mesoporous structures are formed, which, together with the micropores of the primary nanoparticles, constitute a three-dimensional interconnected hierarchical pore structure. This three-dimensional interconnected hierarchical pore structure, composed of mesoporous channels between primary particles and micropores within the particles, provides an efficient and unobstructed pathway for molecular transport.

[0204] Depend on Figure 3 The nitrogen adsorption-desorption test results show that the nitrogen adsorption-desorption curve exhibits an H3-type hysteresis loop, indicating that the rare earth molecular sieve catalyst provided in Example 2 has a slit or wedge-shaped pore structure formed by the accumulation of plate-like particles, that is, the rare earth molecular sieve catalyst has a mesoporous structure.

[0205] Depend on Figure 4 It can be seen that the pore size distribution of the rare earth molecular sieve catalyst provided in Example 2 is mainly concentrated in 3 nm, and exhibits a relatively wide distribution in the range of 4~10 nm, indicating that the rare earth molecular sieve catalyst provided in Example 2 has significant hierarchical pore characteristics.

[0206] Depend on Figure 5 , Figure 12 It can be seen that La and Ce elements exhibit uniform and clear distributions within the rare earth molecular sieve catalysts provided in Examples 2 and 5, respectively, proving that La and Ce have been doped into the corresponding rare earth molecular sieve catalysts. Furthermore, the physical adsorption of the rare earth molecular sieve catalyst sample from Example 3 was tested using a TriStar II 3020 surface area and porosity analyzer; the test results show that the rare earth molecular sieve catalyst sample from Example 3 has a high specific surface area (410 m²). 2 / g), of which the mesoporous specific surface area is 242m³. 2 / g, total pore volume is 0.32cm³ 3 / g.

[0207] In summary, as Figures 1-14As shown, compared to the comparative example, the structure-directing agent provided in Example 1 can regulate the encapsulation of rare earth metals and the growth direction of molecular sieve crystals, thus preparing the rare earth molecular sieve catalysts of Examples 2-5. The rare earth molecular sieve catalysts include a molecular sieve framework and rare earth metals. Compared to the comparative example, the molecular sieve framework of the rare earth molecular sieve catalysts provided by the present invention includes a multi-level channel structure with three-dimensional interconnection of micropores and mesopores, which can reduce the mass transfer resistance of the channels. The rare earth metals are dispersed in at least a portion of the channels of the molecular sieve framework. The rare earth molecular sieve catalysts provided by the present invention can improve the stability of the rare earth metal components.

[0208] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A structure-directing agent, characterized in that, The structure-directing agent comprises a compound with the structural formula shown in formula (I). Equation (Ⅰ).

2. A method for preparing the structure-directing agent as described in claim 1, characterized in that, Includes the following steps: 1) 5,5'-dimethyl-2,2'-bipyridine, N-bromosuccinimide and the first solvent are mixed and a single substitution reaction is carried out to give the first intermediate product; 2) The first intermediate product, tetramethylhexanediamine, and the second solvent are mixed to undergo a secondary substitution reaction to obtain the second intermediate product; 3) The second intermediate product, 1-bromohexane and the third solvent are mixed to undergo a three-stage substitution reaction to obtain the structure-directing agent.

3. The method for preparing the structure-directing agent according to claim 2, characterized in that, The molar ratio of the 5,5'-dimethyl-2,2'-bipyridine to the N-bromosuccinimide is 1:(1~2); And / or, the molar ratio of the first intermediate product to the tetramethylhexanediamine is 1:(10~20); And / or, the molar ratio of the second intermediate to the 1-bromohexane is 1:(2~6).

4. The method for preparing the structure-directing agent according to claim 2 or 3, characterized in that, The temperature of the primary substitution reaction is 60℃~80℃, and the time is 10h~20h; And / or, the secondary substitution reaction is carried out at a temperature of 70°C to 85°C for a time of 20 h to 48 h; And / or, the temperature of the three substitution reactions is 70℃~85℃, and the time is 20h~48h.

5. A method for preparing a rare earth molecular sieve catalyst, characterized in that, Includes the following steps: Rare earth metal source, complexing agent, solvent, alkali source, structure directing agent as described in claim 1, silicon source and aluminum source are mixed, and pH is adjusted to obtain precursor liquid gel; The precursor liquid gel was subjected to hydrothermal crystallization treatment to obtain the crystallized product. The crystallized product is calcined under an oxygen-containing atmosphere to obtain the rare earth molecular sieve catalyst.

6. The method for preparing the rare earth molecular sieve catalyst according to claim 5, characterized in that, The mass ratio of the rare earth metal source, complexing agent, solvent, alkali source, structure directing agent, silicon source and aluminum source is (0.0078~0.0235): (0.047~0.14): (20~24): 0.33: 1: 3.5: 0.

014.

7. The method for preparing the rare earth molecular sieve catalyst according to claim 5 or 6, characterized in that, The complexing agent includes sodium citrate; And / or, the silicon source includes at least one of tetraethyl orthosilicate, sodium silicate, fumed silica, and silica gel; And / or, the aluminum source includes at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum isopropoxide.

8. The method for preparing the rare earth molecular sieve catalyst according to any one of claims 5-7, characterized in that, The hydrothermal crystallization treatment has a crystallization temperature of 140℃~160℃ and a crystallization time of 3 days~7 days; And / or, stirring is performed during the hydrothermal crystallization treatment, and the stirring speed is 30 rpm to 70 rpm; And / or, the calcination treatment is carried out at a temperature of 500℃~600℃ for a time of 4h~8h.

9. A rare earth molecular sieve catalyst obtained using the preparation method of the rare earth molecular sieve catalyst as described in any one of claims 5-8.

10. The rare earth molecular sieve catalyst according to claim 9, characterized in that, The rare earth molecular sieve catalyst includes a molecular sieve framework and a rare earth metal. The molecular sieve framework includes channels, and the rare earth metal is disposed in at least a portion of the channels of the molecular sieve framework. The mass ratio of the rare earth metal to the molecular sieve framework is 1:(67~200). And / or, the total pore volume of the rare earth molecular sieve catalyst is 0.2 cm³. 3 / g~0.4cm 3 / g; And / or, the specific surface area of ​​the rare earth molecular sieve catalyst is 350 m². 2 / g~450m 2 / g.

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