A method for preparing a molecular sieve containing a defect molecular sieve-anchored metal

Abstract

A method for preparing a defective molecular sieve anchoring metal molecular sieve, comprising the following steps: 1) preparing an aluminum-free high-silicon framework defect-rich molecular sieve seed; 2) preparing a low-silicon aluminum ratio gel; adding the high-silicon framework defect-rich molecular sieve seed to the low-silicon aluminum ratio gel, stirring and adding fluoride, and obtaining a molecular sieve precursor after crystallization; 3) after calcination of the molecular sieve precursor, treating the molecular sieve precursor with an alkali solution and an ammonium salt solution, then loading a transition metal, and drying to obtain a metal-loaded molecular sieve; 4) preparing a recrystallization precursor powder or gel; 5) crystallizing the metal-loaded molecular sieve with the recrystallization precursor powder or gel, drying or not drying after taking out the sample, calcining, and washing and drying to obtain a defective molecular sieve anchoring metal molecular sieve. The method introduces metal into a molecular sieve with a defective structure, and then disperses the metal in the interior of the molecular sieve by secondary crystallization, to obtain a defective multi-level pore molecular sieve.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis technology, and relates to a molecular sieve containing a defective molecular sieve anchoring a metal and its preparation method. Background Technology

[0002] Molecular sieves are inorganic crystalline materials with regular pore structures, possessing shape selectivity, thermal stability, acid strength, and chemical stability due to their unique pore structure. They have long played a crucial role in petroleum-related processes such as hydrocracking, isomerization, alkylation, and dewaxing. In heterogeneous catalytic systems, metal-supported molecular sieve catalysts occupy an important position. Heterogeneous catalysts have advantages such as easy separation from products and the ability to be recycled and reused, leading to their wide application in industry. The first step in preparing metal-supported catalysts is usually to add the metal to the molecular sieve through impregnation or ion exchange methods. However, due to the small pore size of molecular sieves, typically only 0.5-0.7 nm, metal diffusion within the pores is slow, making it difficult for metal to enter the pores. Therefore, most metal nanoparticles are loaded on the outer surface of the molecular sieve crystal, which may lead to metal migration and sintering during catalysis, resulting in loss of activity. To overcome this problem, a novel catalyst—the core-shell catalyst—has been developed. This catalyst introduces metal species into the molecular sieve crystal, and the metal nanoparticles are stabilized within the molecular sieve framework through recrystallization. Core-shell catalysts exhibit better resistance to metal sintering than supported catalysts.

[0003] In bifunctional catalysts, metal@zeolite materials possess both the shape selectivity of the zeolite channel structure and the active sites of the metal. The acidic function is typically provided by the zeolite. In heterogeneous catalysis, secondary seeding to create core-shell structures is a more widely used technique, where the core and shell have different compositions or crystal structures, and is one of the most effective methods to improve the desired product selectivity in tandem catalysis processes. Catalysts with core-shell structures achieve reactant selectivity more easily than supported catalysts. Previous studies have shown that the proximity between the active sites of the metal and the zeolite provides synergistic effects between the two types of sites in the catalyst. The size of the metal and its spatial distribution within the zeolite play a significant role in catalysis. Indeed, small-sized and highly dispersed metal core-shell catalysts exhibit high catalytic activity and product selectivity, demonstrating unique advantages in reactions.

[0004] Therefore, a seed-assisted method for synthesizing molecular sieves is employed. Taking advantage of the preferential action of alkalis on unstable structural units of the molecular sieve framework, molecular sieves with surface hydroxyl groups are obtained. Alkali treatment of the molecular sieves is then used to anchor metals, thereby controlling the spatial distribution of the metals. Steam-assisted recrystallization is used to achieve metal coating and to control the size and spatial distribution of the metals.

[0005] CN101885493A discloses a method for synthesizing ZSM-5 / β core-shell molecular sieves. By using ZSM-5 core-phase molecular sieves as seed crystals, and after surface pretreatment and adsorption of β nanocrystals, a low-cost silicon source is added to prepare ZSM-5 / β core-shell zeolite molecular sieves with high shell coverage, which effectively reduces the preparation cost and improves the shell coverage of the product.

[0006] CN114713281A discloses a catalyst for the hydroisomerization of n-alkanes. The preparation method involves preparing a hydrogen-form composite molecular sieve by alkali washing and ion exchange of a low silica-to-alumina ratio TON / MRE composite molecular sieve. The hydrogen-form composite molecular sieve is then mixed with a binder to form a support. This support is impregnated in a soluble salt containing the active component for a period of time, followed by drying and calcination to obtain the catalyst. This catalyst exhibits better catalytic activity and product selectivity in the hydroisomerization reaction of Fischer-Tropsch wax straight-chain alkanes. Summary of the Invention

[0007] Given that the size of the metal and its spatial distribution in the molecular sieve significantly affect the performance of the metal / molecular sieve composite material, this invention improves the preparation process of the metal / molecular sieve composite material. It proposes to use a molecular sieve with surface hydroxyl groups after alkali treatment to encapsulate the metal, prepare metal-supported molecular sieve seed crystals, so that the metal exists in the molecular sieve in the form of crystalline salt, control the size and distribution of the metal in the molecular sieve crystal, and combine the recrystallization method to prepare a molecular sieve with defective molecular sieves anchoring the metal.

[0008] This invention first utilizes alkali treatment to preferentially act on Si species in the molecular sieve framework, introducing surface hydroxyl groups into the molecular sieve. Through impregnation, metal species exist within the molecular sieve in the form of exchange ions, crystalline salts, etc. Then, secondary crystallization encapsulates the metal within the recrystallized material, improving the metal's dispersibility within the molecular sieve. The main innovation of this invention lies in using a molecular sieve with a defective structure to stably introduce metal, and then using secondary crystallization to disperse the metal within the molecular sieve, simultaneously obtaining a mesoporous molecular sieve.

[0009] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0010] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0011] 1) Add silicon source to structure directing agent solution to prepare uniform sol or gel; transfer sol or gel obtained in step 1) to self-pressurized crystallization kettle for crystallization to obtain high silicon molecular sieve seed crystals rich in framework defects; no aluminum source is added to the sol or gel;

[0012] 2) Add silicon source, structure directing agent and aluminum source to deionized water, stir evenly to obtain low silicon-to-aluminum ratio gel; add the high silicon molecular sieve seed crystals rich in framework defects obtained in step 1) to the low silicon-to-aluminum ratio gel, add fluoride while stirring, transfer the resulting mixture to a crystallization kettle for high-temperature crystallization, filter and separate after crystallization, wash with deionized water until neutral and dry to obtain molecular sieve precursor;

[0013] 3) After calcining the molecular sieve precursor obtained in step 2), the molecular sieve precursor is treated with alkaline solution and ammonium salt solution, then loaded with transition metal, and dried to obtain metal-loaded molecular sieve.

[0014] 4) Add the structure-directing agent, aluminum source, silicon source, and fluoride to deionized water and stir evenly. Dry for 24-36 hours or do not dry to obtain recrystallization precursor powder or gel.

[0015] 5) Grind the metal-loaded molecular sieve and recrystallization precursor powder or gel evenly in a mortar and place them in a crystallization kettle for crystallization. After taking out the sample, dry or not dry it, transfer it to a muffle furnace for calcination, wash and dry it to obtain a molecular sieve with defective molecular sieve anchored metal.

[0016] In step 1), the molar ratio of the silicon source and the structure directing agent is 5-15:1; the crystallization conditions are crystallization at 50-200℃ for 24-100 hours, preferably at 100-120℃ for 50-80 hours; and the particle size of the high-silicon molecular sieve seed crystals rich in framework defects is 70-80 nm.

[0017] The stirring time in step 2) is 3-12 h; the silica-alumina ratio of the low silica-alumina ratio gel is 10-30; the mass ratio of the high silica molecular sieve seed crystal rich in framework defects to the low silica-alumina ratio gel is 10-30:70-90, wherein the mass ratio of fluoride to aluminum source is 10-15:1; the crystallization conditions are crystallization at 50-200℃ for 24-100 hours, preferably at 100-120℃ for 50-80 hours.

[0018] In step 3), the ammonium salt solution is an aqueous solution of one or more of ammonium fluoride, ammonium chloride, ammonium sulfate, and urea; the alkaline solution is an aqueous solution of one or more of sodium hydroxide and potassium hydroxide; the treatment conditions for the alkaline solution and ammonium salt solution in step 3) are 50-100℃ for 0.5-2h; the transition metal loading is 0.5-10wt% based on the mass of the molecular sieve loaded with metal; and the calcination temperature is 400-650℃.

[0019] In step 4), the mass ratio of aluminum source, silicon source, structure guiding agent, fluoride, and deionized water is 0.02-0.05:1-3:0.1-0.2:0.3-0.8:10-50.

[0020] In step 5), the mass ratio of the metal-loaded molecular sieve to the recrystallization precursor powder or gel is 1-2; the crystallization conditions are crystallization at 150-200℃ for 48-100 hours, preferably at 150-170℃ for 48-72 hours; the calcination conditions are calcination at 500-600℃ for 12-24 hours with a heating rate of 2℃ / min.

[0021] The molecular sieve prepared by the method is a molecular sieve or a molecular sieve-like structure with arbitrary topology, wherein the molecular sieve with arbitrary topology is one of MFI, BETA, CHA, MTW, TON, FER, MOR, and LTA.

[0022] The silicon source is one or more of tetraethyl orthosilicate, silica sol, sodium silicate, and silica fume, wherein the structure directing agent is one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and ethylenediamine; the aluminum source is one or more of aluminum hydroxide, aluminum powder, aluminum sulfate, aluminum nitrate, aluminum chloride, sodium aluminate, and aluminum isopropoxide; and the fluoride is one or more of sodium fluoride, ammonium fluoride, and hydrogen fluoride.

[0023] The structure directing agent is one of tetrapropylammonium bromide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, or ethylenediamine.

[0024] In a preferred embodiment, the sample obtained in step 3) is dried or left untreated. The drying method can be room temperature drying, low temperature drying in an oven, or freeze-drying. Preferably, freeze-drying is used for 24-36 hours to obtain a molecular sieve containing metal crystal salts.

[0025] In a preferred embodiment, in step 3), the transition metal is one or more of Cu, Fe, Co, Ni, V, Mo, W, Pt, P, and Ti, preferably a soluble metal salt solution thereof, with a metal salt solution concentration of 0.1-30 wt%.

[0026] In a preferred embodiment, the gel obtained in step 4) may be dried or left untreated. The drying method may be room temperature drying, low temperature drying in an oven, or freeze-drying. Preferably, freeze-drying is used for 24-36 hours to obtain synthetic molecular sieve precursor powder or gel.

[0027] In a preferred embodiment, the alkali treatment is preferably performed using a sodium hydroxide solution at a concentration of 0.1-1 mol·L⁻¹. -1 The mass ratio of the molecular sieve to sodium hydroxide solution is 1:1-1:30, the temperature is 20-100℃, and the treatment time is 0.5-3h.

[0028] In a preferred embodiment, the crystallization method described in step 5) can be hydrothermal crystallization or steam-assisted crystallization, preferably using steam-assisted crystallization recrystallization, with a powder-to-water ratio of 1:1, and preferably crystallization at 150-170°C for 48-72 hours.

[0029] The present invention also discloses a molecular sieve prepared by the method described herein.

[0030] Unless otherwise specified, the silicon-aluminum ratio mentioned in this invention refers to the molar ratio of silicon to aluminum calculated based on the number of moles of silicon atoms and aluminum atoms.

[0031] Because molecular sieve seed crystals have an inducing crystallization effect, under certain conditions, previously added molecular sieve seed crystals can be embedded into the next generation of molecular sieve crystal framework while retaining part or even all of the crystal structure. Based on the molecular sieve formation and erosion mechanism, this invention first designs and synthesizes high-silica molecular sieve seed crystals rich in framework defects, and then uses these seed crystals to induce the synthesis of ZSM-5 molecular sieves. The molecular sieves are then subjected to alkali treatment, which preferentially removes the silicon-rich portion of the framework and selectively dissolves the defect-rich framework seed crystals in the molecular sieve, introducing surface hydroxyl groups into the treated molecular sieve. Because the aluminosilicate framework is electronegative, "free cations," such as Na+, exist in the micropores. + This makes it electrically neutral. Because these cations have good mobility and are easily exchanged, metal cations can pass through with Na... + The molecular sieve is introduced through exchange. Hydroxyl groups anchor metals, stabilizing metal species and enhancing the interaction between metal precursors and molecular sieve structural units, which is crucial for improving catalyst stability. Drying allows the anchored metal to exist in the molecular sieve as a crystalline salt; steam-assisted recrystallization fixes the metal within the sieve; and finally, calcination allows the metal to exist as a small-sized oxide. Furthermore, alkali treatment improves the mesopores of the molecular sieve, enhancing metal dispersibility.

[0032] The beneficial technical effects of this invention are as follows: This invention utilizes a seed-assisted method to synthesize molecular sieves and improves the mass transfer capacity of traditional molecular sieves through chemical post-treatment. By selectively removing the core portion of the molecular sieve with high framework silicon content and high defect density, a defect-rich hierarchical porous molecular sieve is prepared, thereby effectively reducing the mass transfer and diffusion resistance within the molecular sieve crystal. The defect sites formed by the hierarchical porous molecular sieve achieve an anchoring effect on the metal, and steam-assisted recrystallization enables the regulation of the metal size and spatial distribution within the metal@molecular sieve. Attached Figure Description

[0033] Figure 1 This is a scanning electron microscope image of the initial silicalite-1 seed crystal in Example 1;

[0034] Figure 2 The left side of the middle image shows molecular sieve sample Z from Example 1. P The right image is a scanning electron microscope image of molecular sieve sample Z from Example 1; the left image is a scanning electron microscope image of molecular sieve sample Z from Example 1. P Transmission electron microscope image;

[0035] Figure 3 The left image is molecular sieve sample Z from Example 1. OH The right image is a scanning electron microscope image of molecular sieve sample Z from Example 1; the left image is a scanning electron microscope image of molecular sieve sample Z from Example 1. OH Transmission electron microscope image;

[0036] Figure 4 The left image shows the molecular sieve sample Co@Z from Example 1. OH The image is a scanning electron microscope image at -1.8; the right image is the molecular sieve sample Co@Z from Example 1. OH Transmission electron microscope image at -1.8;

[0037] Figure 5 The molecular sieve sample Co@Z in Example 1 OH EDS plot of -1.8;

[0038] Figure 6 It is the molecular sieve sample Z in Example 1. P Z OH Co@Z OH -1.8, Comparative Example 1 Co@Z P XRD pattern at -1.8;

[0039] Figure 7 It is the molecular sieve sample Z in Example 1. P Z OH Co@Z OH -1.8, Comparative Example 1 Co@Z P -1.8 BET chart;

[0040] Figure 8 The left side shows the molecular sieve sample Co@Z in Comparative Example 1. P The right image is a scanning electron microscope image at -1.8; the left image is the molecular sieve sample Co@Z from Comparative Example 1. P Transmission electron microscope image at -1.8;

[0041] Figure 9 The molecular sieve sample Co@Z in Example 1 P EDS plot of -1.8;

[0042] Figure 10 The left side is molecular sieve sample Z in Comparative Example 2. P -Scanning electron microscope image of Co; right is molecular sieve sample Z in Comparative Example 2. P Transmission electron microscopy image of -Co;

[0043] Figure 11The left side is molecular sieve sample Z in Comparative Example 2. OH -Scanning electron microscope image of Co; right is molecular sieve sample Z in Comparative Example 2. OH Transmission electron microscopy image of -Co. Detailed Implementation

[0044] To better understand the present invention, specific embodiments are used to further illustrate the content of the present invention. The structural parameters of the obtained samples are summarized in Table 1. The present invention is not limited to the following embodiments.

[0045] Example 1

[0046] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0047] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a homogeneous sol; the molar ratio of silicon source to organic structure directing agent was 15:1; the silicon-to-aluminum ratio of the system was ∞; the obtained sol was transferred to a self-pressurized crystallization reactor and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, the morphology of which is as follows: Figure 1 As shown, its size is concentrated in the range of 70-80nm;

[0048] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The obtained molecular sieve seed crystal, silicalite-1, was added to the low silica-to-alumina ratio gel at a concentration of 15%. After stirring until homogeneous, ammonium fluoride was added and mechanically stirred for 2 hours to obtain a homogeneous mixture with the following ratio: 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. The resulting mixture was placed in a crystallization vessel and crystallized at 100℃ for 72 hours. It was then thoroughly washed with deionized water until neutral and dried. Finally, it was calcined at 550℃ for 12 hours and named Z. P .

[0049] 3) Prepare 0.2 mol·L -1 The sodium hydroxide solution was used to prepare the sample Z. P A molecular sieve was added to a sodium hydroxide solution at a mass ratio of 30:1, and the solution was treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ solution was prepared. -1 The obtained cyclic molecular sieve sample was added to an ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90℃ for 3 hours, repeated three times. The sample was then thoroughly washed with deionized water until neutral and dried. Finally, it was calcined at 550℃ for 12 hours and named Z. OH Molecular sieve sample ZOH The metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0050] 4) Add silicon source, aluminum source, structure directing agent to deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain a freeze-dried gel.

[0051] 5) Grind the metal-loaded molecular sieve sample obtained in step 3) and the lyophilized gel obtained in step 10) at a mass ratio of 1.5:1 in a mortar until homogeneous. Transfer the mixture to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 h. Remove the sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 h. Then, calcine it in a muffle furnace at 550℃ for 12 h. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the final sample, named Co@Z. OH -1.8.

[0052] Example 2

[0053] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0054] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform gel; the molar ratio of silicon source to organic structure directing agent was 10:1; the silicon-to-aluminum ratio of the system was ∞; the obtained gel was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0055] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%. After stirring until homogeneous, ammonium fluoride was added and mechanically stirred for 2 hours to obtain a homogeneous mixture with a mixture ratio of 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. The resulting mixture was placed in a crystallization kettle and crystallized at 100℃ for 72 hours. The resulting sample was removed from the crystallization kettle, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550℃ for 12 hours and named Z. P .

[0056] 3) Prepare 0.2 mol·L -1 The sample obtained in step 6) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ sodium hydroxide solution was prepared. -1 An ammonium chloride solution was used to treat the cyclic molecular sieve sample. The sample was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90℃ for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The sample was then calcined at 550℃ for 12 hours and named Z. OH The obtained molecular sieve sample Z OH The metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0057] 4) Add silicon source, aluminum source, structure directing agent to deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain a freeze-dried gel.

[0058] 5) Grind the metal-loaded molecular sieve obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 1:1 until homogeneous. Transfer the gel to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 hours. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 hours. Then, calcine it in a muffle furnace at 550℃ for 12 hours. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the sample, named Co@Z. OH -1.5.

[0059] Example 3

[0060] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0061] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform sol; the molar ratio of silicon source to organic structure directing agent was 5:1; the silicon-to-aluminum ratio of the system was ∞; the obtained sol was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0062] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%. After stirring until homogeneous, ammonium fluoride was added and mechanically stirred for 2 hours to obtain a homogeneous mixture with a mixture ratio of 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. The resulting mixture was placed in a crystallization kettle and crystallized at 100℃ for 72 hours. The resulting sample was removed from the crystallization kettle, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550℃ for 12 hours and named Z. P .

[0063] 3) Prepare 0.2 mol·L -1 The sample obtained in step 6) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ sodium hydroxide solution was prepared. -1 An ammonium chloride solution was used to treat the cyclic molecular sieve sample. The sample was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90℃ for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The sample was then calcined at 550℃ for 12 hours and named Z. OH The obtained molecular sieve sample Z OH The metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0064] 4) Add silicon source, aluminum source, structure directing agent to deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain a freeze-dried gel.

[0065] 5) The metal-loaded molecular sieve sample and the lyophilized gel were ground evenly in a mortar at a mass ratio of 2:1, transferred to a crystallization vessel, and deionized water was added at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 h. The resulting sample was removed from the crystallization vessel, freeze-dried in a freeze dryer for 24 h, and then calcined in a muffle furnace at 550℃ for 12 h. The resulting sample was thoroughly washed with deionized water until neutral and dried to obtain the sample, named Co@Z. OH -2.

[0066] Example 4

[0067] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0068] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform gel; the molar ratio of silicon source to organic structure directing agent was 13:1; the silicon-to-aluminum ratio of the system was ∞; the obtained gel was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0069] 2) The structure-directing agent and silicon source were added sequentially to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%. After stirring until homogeneous, ammonium fluoride was added and mechanically stirred for 2 hours to obtain a homogeneous mixture with a mixture ratio of 1.0 TEOS:0.13 TPABr (98%):0.56 NH4F:23.13 H2O. The resulting mixture was placed in a crystallization vessel and crystallized at 100°C for 72 hours. The resulting sample was removed from the crystallization vessel, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550°C for 12 hours and named S. P .

[0070] 3) Prepare 0.2 mol·L -1 Sodium hydroxide solution, according to molecular sieve S P Add the cyclic molecular sieve sample to the sodium hydroxide solution at a mass ratio of 30:1 and treat at 65℃ for 30 min to obtain the cyclic molecular sieve sample; prepare a 1 mol·L⁻¹ solution. -1 An ammonium chloride solution was used to treat the cyclic molecular sieve sample. The sample was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90℃ for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The resulting product was then calcined at 550℃ for 12 hours and named S. OH Molecular sieve sample S OH The metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0071] 4) Add aluminum source, structure directing agent and deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 1.0TEOS:0.13TPABr (98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain freeze-dried gel.

[0072] 5) Grind the metal-loaded molecular sieve obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 1:1 until homogeneous. Transfer the gel to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 hours. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 hours. Then, calcine it in a muffle furnace at 550℃ for 12 hours. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the sample, named S. OH @Co-1.5.

[0073] Example 5

[0074] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0075] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform sol; the molar ratio of silicon source to organic structure directing agent was 15:1; the silicon-to-aluminum ratio of the system was ∞; the sol was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0076] 2) The structure-directing agent and silicon source were added sequentially to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%, stirred until homogeneous, and then ammonium fluoride was added. The mixture was mechanically stirred for 2 hours to obtain a homogeneous mixture with a ratio of 1.0 TEOS:0.13 TPABr (98%):0.56 NH4F:23.13 H2O. The resulting mixture was placed in a crystallization vessel and crystallized at 100°C for 72 hours. The resulting sample was removed from the crystallization vessel, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550°C for 12 hours and named S. P .

[0077] 3) Prepare 0.2 mol·L -1 The sample obtained in step 6) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ sodium hydroxide solution was prepared. -1 An ammonium chloride solution was used to treat the cyclic molecular sieve sample. The sample was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90℃ for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The resulting product was then calcined at 550℃ for 12 hours and named S. OH The obtained molecular sieve sample S OHThe metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0078] 4) Add aluminum source, structure directing agent and deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 1.0TEOS:0.13TPABr (98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain freeze-dried gel.

[0079] 5) Grind the metal-loaded molecular sieve obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 1.5:1 until homogeneous. Transfer the gel to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 h. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 h. Then, calcine it in a muffle furnace at 550℃ for 12 h. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the sample, named Co@S. OH -1.8.

[0080] Example 6

[0081] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0082] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform gel; the molar ratio of silicon source to organic structure directing agent was 10:1; the silicon-to-aluminum ratio of the system was ∞; the obtained gel was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0083] 2) The structure-directing agent and silicon source were added sequentially to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%, stirred until homogeneous, and then ammonium fluoride was added. The mixture was mechanically stirred for 2 hours to obtain a homogeneous mixture with a ratio of 1.0 TEOS:0.13 TPABr (98%):0.56 NH4F:23.13 H2O. The resulting mixture was placed in a crystallization vessel and crystallized at 100°C for 72 hours. The resulting sample was removed from the crystallization vessel, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550°C for 12 hours and named S. P .

[0084] 3) Prepare 0.2 mol·L -1The sample obtained in step 2) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample. A 1 mol·L⁻¹ solution of the sample was prepared. -1 The resulting cyclic molecular sieve sample was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90℃ for 3 hours, repeated three times. The sample was then thoroughly washed with deionized water until neutral and dried. Finally, it was calcined at 550℃ for 12 hours and named S. OH The obtained molecular sieve sample S OH The metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0085] 4) Add aluminum source, structure directing agent and deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 1.0TEOS:0.13TPABr (98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain freeze-dried gel.

[0086] 5) Grind the metal-loaded molecular sieve obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 2:1 until homogeneous. Transfer the gel to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 hours. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 hours. Then, calcine it in a muffle furnace at 550℃ for 12 hours. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the final sample, named Co@S. OH -2.

[0087] Example 7

[0088] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0089] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure-directing agent to prepare a uniform gel; the molar ratio of silicon source to organic structure-directing agent was 15:1; the silicon-to-aluminum ratio of the system was ∞; the obtained gel was transferred to a self-pressurized crystallization autoclave and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, the morphology of which is as follows: Figure 1 As shown, its size is concentrated in the range of 70-80nm;

[0090] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%. After stirring until homogeneous, ammonium fluoride was added and mechanically stirred for 2 hours to obtain a homogeneous mixture with a mixture ratio of 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. The resulting mixture was placed in a crystallization kettle and crystallized at 100℃ for 72 hours. The resulting sample was removed from the crystallization kettle, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550℃ for 12 hours and named Z. P .

[0091] 3) Prepare 0.2 mol·L -1 The sample obtained in step 6) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ sodium hydroxide solution was prepared. -1 The sample obtained in step 7) was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90°C for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The sample was then calcined at 550°C for 12 hours and named Z. OH The obtained molecular sieve sample Z OH The metal salt solution was impregnated with the molecular sieve at a volume ratio of 1:1 using the equal volume method, wherein the content of metal Fe was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0092] 4) Add silicon source, aluminum source, structure directing agent to deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain a freeze-dried gel.

[0093] 5) Grind the metal-loaded molecular sieve obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 1.5:1 until homogeneous. Transfer the gel to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 h. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 h. Then, calcine it in a muffle furnace at 550℃ for 12 h. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the sample, named Fe@Z. OH -1.8.

[0094] Example 8

[0095] A method for preparing a metal-anchored molecular sieve containing defective molecular sieves includes the following steps:

[0096] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform sol or gel; the molar ratio of silicon source to organic structure directing agent was 10:1; the silicon-to-aluminum ratio of the system was ∞; the obtained sol or gel was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0097] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the low silica-to-alumina ratio gel at an addition amount of 15%, stirred until homogeneous, and then ammonium fluoride was added. The mixture was mechanically stirred for 2 hours to obtain a homogeneous mixture with a ratio of 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. The resulting mixture was placed in a crystallization vessel and crystallized at 100°C for 72 hours. The resulting sample was removed from the crystallization vessel, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550°C for 12 hours and named Z. P .

[0098] 3) Prepare 0.2 mol·L -1 The sample obtained in step 6) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ sodium hydroxide solution was prepared. -1 The sample obtained in step 7) was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90°C for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The sample was then calcined at 550°C for 12 hours and named Z. OH The obtained molecular sieve sample Z OH Using the equal volume method, the metal salt solution and molecular sieve were impregnated with a metal salt solution at a volume ratio of 1:1, wherein the content of metal Ni was 10% of the mass of the molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours to obtain the metal-loaded molecular sieve.

[0099] 4) Add silicon source, aluminum source, structure directing agent to deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain a freeze-dried gel.

[0100] 5) Grind the metal-loaded molecular sieve obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 1.5:1 until homogeneous. Transfer the gel to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 h. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 h. Then, calcine it in a muffle furnace at 550℃ for 12 h. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the sample, named Ni@Z. OH -1.8.

[0101] Comparative Example 1

[0102] A method for preparing synthetic metal oxide@molecular sieves includes the following steps:

[0103] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform sol; the molar ratio of silicon source to organic structure directing agent was 10:1; the silicon-to-aluminum ratio of the system was ∞; the obtained sol was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with a defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0104] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the obtained low silica-to-alumina ratio gel at an addition amount of 15%. After stirring until homogeneous, ammonium fluoride was added and mechanically stirred for 2 hours to obtain a homogeneous mixture with a mixture ratio of 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. The resulting mixture was placed in a crystallization kettle and crystallized at 100℃ for 24 hours. The resulting sample was removed from the crystallization kettle, thoroughly washed with deionized water until neutral, and dried. It was calcined at 550℃ for 12 hours and named Z. P .

[0105] 3) The obtained molecular sieve sample Z PThe metal salt solution was impregnated with a 1:1 volume ratio of metal Co salt solution to molecular sieve using the equal volume method. The content of metal Co was 10% of the mass of molecular sieve. The solution was dried at room temperature for 12 hours and then freeze-dried in a freeze dryer for 24 hours.

[0106] 4) Add silicon source, aluminum source, structure directing agent to deionized water and stir evenly. Then add ammonium fluoride. The solution ratio is 0.033Al2(SO4)3·18H2O:1.0TEOS:0.13TPABr(98%):0.56NH4F:23.13H2O. Stir mechanically for 2 hours. Place the resulting gel in a freeze dryer and freeze dry for 24 hours to obtain a freeze-dried gel.

[0107] 5) Grind the sample obtained in step 3) and the lyophilized gel obtained in step 4) in a mortar at a mass ratio of 1.5:1 until homogeneous. Transfer the mixture to a crystallization vessel and add deionized water at a solid-liquid mass ratio of 1:1 for steam-assisted recrystallization at 170℃ for 72 hours. Remove the resulting sample from the crystallization vessel and freeze-dry it in a freeze dryer for 24 hours. Then, calcine it in a muffle furnace at 550℃ for 12 hours. Wash the resulting sample thoroughly with deionized water until neutral and dry it to obtain the final sample, named Co@Z. P -1.8.

[0108] Comparative Example 2

[0109] A method for preparing a supported metal-molecular sieve includes the following steps:

[0110] 1) Tetraethyl orthosilicate was added to a solution of tetrapropylammonium hydroxide organic structure directing agent to prepare a uniform gel; the molar ratio of silicon source to organic structure directing agent was 10:1; the silicon-to-aluminum ratio of the system was ∞; the obtained gel was transferred to a self-pressurized crystallization kettle and crystallized at 100°C for 24 hours to obtain nano-high silicon molecular sieve seed crystals with defect-rich framework, whose size was concentrated in the range of 70-80 nm.

[0111] 2) The aluminum source, structure-directing agent, and silicon source were sequentially added to deionized water and stirred until homogeneous to obtain a low silica-to-alumina ratio gel with a silica-to-alumina ratio of 15. The molecular sieve seed crystals obtained in step 1) were added to the resulting low silica-to-alumina ratio gel at an addition amount of 15%, and stirred until homogeneous. Ammonium fluoride was then added, and the mixture was mechanically stirred for 2 hours to obtain a homogeneous mixture. The resulting mixture was placed in a crystallization vessel and crystallized at 100°C for 72 hours. The resulting sample was removed from the crystallization vessel, thoroughly washed with deionized water until neutral, and dried. It was then calcined at 550°C for 12 hours and named Z. P .

[0112] 3) Prepare 0.2 mol·L -1The sample obtained in step 6) was added to a sodium hydroxide solution at a mass ratio of molecular sieve to sodium hydroxide solution of 30:1, and treated at 65℃ for 30 min to obtain a cyclic molecular sieve sample; a 1 mol·L⁻¹ sodium hydroxide solution was prepared. -1 The sample obtained in step 7) was added to the ammonium chloride solution at a solid-liquid mass ratio of 1:30. Ion exchange was performed at 90°C for 3 hours, repeated three times. After three exchanges, the sample was thoroughly washed with deionized water until neutral and dried. The sample was then calcined at 550°C for 12 hours and named Z. OH The obtained molecular sieve sample Z P Using the equal-volume method, a metal Co salt solution and a molecular sieve were impregnated at a volume ratio of 1:1, with the metal Co content being 10% of the molecular sieve mass. The mixture was dried at room temperature for 12 hours, then transferred to an 80℃ oven for another 12 hours. The resulting molecular sieve was calcined at 550℃ for 6 hours to obtain an encapsulated molecular sieve, named Co-Z. P ;

[0113] With Z P ( Figure 2 For example, after alkali treatment, a molecular sieve Z with a cyclic structure is obtained. OH The surface has defects and small mesopores. Figure 3 ).

[0114] From Co-Z of Comparative Example 1 P The transmission electron microscope image shows that ( Figure 10 ), untreated Z P When metals are loaded onto molecular sieves, the metals agglomerate on the surface of the molecular sieves, resulting in large metal aggregates with poor dispersibility.

[0115] From Co-Z of Comparative Example 1 OH The transmission electron microscope image shows that ( Figure 11 Z after alkali treatment OH Molecular sieves loaded with metals exhibit higher metal dispersion compared to Co-Z. P There is a significant improvement, and the size is significantly reduced;

[0116] With Co@Z OH -1.8( Figure 4 For example, compared to Co@Z in Comparative Example 1 P Transmission electron microscopy image at -1.8 ( Figure 8 In comparison, the size of the metal in the molecular sieve recrystallized after alkali treatment was significantly smaller than that in the untreated recrystallized molecular sieve.

[0117] Through XRD ( Figure 6 The spectra show that the structure of ZSM-5 was still preserved after alkali treatment and recrystallization, and it also has a high degree of crystallinity.

[0118] By nitrogen adsorption-desorption curve ( Figure 7 As can be seen, the adsorption capacity of the molecular sieve increased significantly after alkali treatment. Hysteresis loop indicates the presence of intracrystalline and intercrystalline mesoporous structures, and the mesoporous specific surface area and pore volume of the treated sample increased significantly, further demonstrating that the treated molecular sieve possesses abundant secondary pore structures while retaining the microporous structure. The decrease in adsorption capacity of the molecular sieve after recrystallization of the loaded metal indicates that some metal is loaded within the mesoporous channels.

[0119] EDS plot of Co@ZOH-1.8 ( Figure 5 EDS plots of Co@ZP-1.8 Figure 9 The comparison shows that the molecular sieve metal oxides recrystallized after alkali treatment have significantly smaller sizes and higher dispersion.

[0120] The Fischer-Tropsch synthesis performance of molecular sieve samples before and after recrystallization was tested. The FTS experiment was conducted in a fixed-bed reactor with a catalyst loading of 0.5 g (particle size 0.25-0.42 mm). Before the reaction, the catalyst was reduced in H₂ at 400 °C for 10 h. After reduction, the catalyst was reacted in syngas at 220 °C and 2 MPa (CO / H₂ = 1 / 2, W / F = 5.1 g Cathmol). -1 Catalytic experiments were conducted. The recrystallized metal oxide@mesoporous molecular sieve composite material exhibited higher catalytic stability compared to the unrecrystallized supported metal molecular sieve material. Smaller metal particles possess more active sites, which generates more reaction intermediates within the confined space, prolonging their contact time and promoting chain growth and high selectivity for heavy hydrocarbons. The coating structure confines the metal particles within the molecular sieve framework, making migration and aggregation during the reaction difficult and providing excellent anti-sintering properties. The selectivity of the FTS product can be adjusted by modifying the size and distribution of the metal.

[0121] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by the present invention, and all such modifications and additions should fall within the protection scope of the present invention.

Claims

1. A method for preparing a molecular sieve containing a defective molecular sieve anchored to a metal, comprising the following steps: 1) Add silicon source to structure directing agent solution to prepare uniform sol or gel; transfer sol or gel obtained in step 1) to self-pressurized crystallization kettle for crystallization to obtain high silicon molecular sieve seed crystals rich in framework defects; no aluminum source is added to the sol or gel; 2) Add silicon source, structure directing agent and aluminum source to deionized water, stir evenly to obtain low silicon-to-aluminum ratio gel; add the high silicon molecular sieve seed crystals rich in framework defects obtained in step 1) to the low silicon-to-aluminum ratio gel, add fluoride while stirring, transfer the resulting mixture to a crystallization kettle for high-temperature crystallization, filter and separate after crystallization, wash with deionized water until neutral and dry to obtain molecular sieve precursor; 3) After calcining the molecular sieve precursor obtained in step 2), the molecular sieve precursor is treated with alkaline solution and ammonium salt solution, then loaded with transition metal, and dried to obtain metal-loaded molecular sieve. 4) Add the structure-directing agent, aluminum source, silicon source, and fluoride to deionized water and stir evenly. Dry for 24-36 hours or do not dry to obtain recrystallization precursor powder or gel. 5) Grind the metal-loaded molecular sieve and recrystallization precursor powder or gel evenly in a mortar and place them in a crystallization kettle for crystallization. After taking out the sample, dry or not dry it, transfer it to a muffle furnace for calcination, wash and dry it to obtain a molecular sieve with defective molecular sieve anchored metal. The molar ratio of silicon source and structure directing agent in step 1) is 5-15:1; the crystallization conditions are crystallization at 50-200℃ for 24-100 hours; the particle size of the high-silicon molecular sieve seed crystals rich in framework defects is 70-80nm. The stirring time in step 2) is 3-12 h; the silica-alumina ratio of the low silica-alumina ratio gel is 10-30; the mass ratio of the high silica molecular sieve seed crystal rich in framework defects to the low silica-alumina ratio gel is 10-30:70-90, wherein the mass ratio of fluoride to aluminum source is 10-15:1; the crystallization conditions are 50-200℃ for 24-100 hours. In step 5), the mass ratio of the metal-loaded molecular sieve to the recrystallization precursor powder or gel is 1-2; the crystallization conditions are crystallization at 150-200℃ for 48-100 hours; and the calcination conditions are calcination at 500-600℃ for 12-24 hours with a heating rate of 2℃ / min.

2. The method according to claim 1, characterized in that: In step 1), the crystallization conditions are crystallization at 100-120℃ for 50-80 hours.

3. The method according to claim 1, characterized in that: In step 2), the crystallization conditions are crystallization at 100-120℃ for 50-80 hours.

4. The method according to claim 1, characterized in that: The ammonium salt solution mentioned in step 3) is an aqueous solution of one or more of ammonium fluoride, ammonium chloride, and ammonium sulfate, and the alkali solution is an aqueous solution of one or more of sodium hydroxide and potassium hydroxide; the treatment conditions for the alkali solution and ammonium salt solution in step 3) are 50-100℃ for 0.5-2h; the transition metal loading is 0.5-10wt% based on the mass of the molecular sieve loaded with metal; and the calcination temperature is 400-650℃.

5. The method according to claim 1, characterized in that: The mass ratio of aluminum source, silicon source, structure guiding agent, fluoride and deionized water in step 4) is 0.02-0.05:1-3:0.1-0.2:0.3-0.8:10-50.

6. The method according to claim 1, characterized in that: The crystallization conditions described in step 5) are crystallization at 150-170℃ for 48-72 hours.

7. The method according to claim 1, characterized in that: The molecular sieve prepared by the method is a molecular sieve or molecular sieve-like structure with arbitrary topology, and the molecular sieve with arbitrary topology is one of MFI, BETA, CHA, MTW, TON, FER, MOR, and LTA.

8. The method according to claim 1, characterized in that: The silicon source is one or more of tetraethyl orthosilicate, silica sol, sodium silicate, and silica fume; the structure directing agent is one or more of tetrapropylammonium bromide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetramethylammonium hydroxide, and ethylenediamine; the aluminum source is one or more of aluminum hydroxide, aluminum powder, aluminum sulfate, aluminum nitrate, aluminum chloride, sodium aluminate, and aluminum isopropoxide; and the fluoride is one or more of sodium fluoride, ammonium fluoride, and hydrogen fluoride.

9. The method according to claim 1, characterized in that: The sample obtained in step 3) may be dried or left untreated. The drying methods are room temperature drying, low temperature drying in an oven, and freeze-drying. In step 3), the transition metal is one or more of Cu, Fe, Co, Ni, V, Mo, W, Pt, and Ti; The gel obtained in step 4) may be dried or left untreated. Drying methods include room temperature drying, low temperature drying in an oven, and freeze-drying. The crystallization method described in step 5) is hydrothermal crystallization or steam-assisted crystallization.

10. The method according to claim 9, characterized in that: The sample obtained in step 3) was dried by freeze-drying for 24-36 hours to obtain a molecular sieve containing metal crystal salts. In step 3), when loading the transition metal, a soluble metal salt solution is used, and the concentration of the metal salt solution is 0.1-30 wt%. The gel obtained in step 4) was lyophilized for 24-36 hours to obtain synthetic molecular sieve precursor powder. The alkaline solution is an aqueous solution of sodium hydroxide, and the concentration of the aqueous solution of sodium hydroxide is 0.1-1 mol·L⁻¹. -1 The mass ratio of molecular sieve precursor to sodium hydroxide solution is 1:1-1:30, the temperature is 20-100℃, and the treatment time is 0.5-3h. The crystallization method described in step 5) is steam-assisted crystallization and recrystallization, with a powder to water ratio of 1:

1.

11. The method according to claim 10, characterized in that... The crystallization described in step 5) is carried out at 150-170℃ for 48-72 hours.

12. A molecular sieve prepared by the method according to any one of claims 1-11.

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