A highly crystalline two-dimensional MWW zeolite molecular sieve and its preparation method
The synthesis of high-crystallinity two-dimensional MWW zeolite nanosheets using hexagonal boron nitride templates addresses diffusion and accessibility issues in traditional zeolites, resulting in enhanced catalytic performance and selectivity for xylene isomers.
Patent Information
- Application Number
- CN202311173825.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-12
- Publication Date
- 2025-07-15
- Estimated Expiration
- 2043-09-12
AI Technical Summary
The existing two-dimensional MWW zeolite synthesis method is complex, costly and difficult to achieve two-dimensional zeolite preparation with high crystallinity and consistent plane orientation, resulting in insufficient catalytic efficiency and diffusion performance.
A thin layer of two-dimensional material dispersion was prepared by liquid phase peeling method, combined with organic structure guide agent and hydrothermal crystallization technology, and high crystallization two-dimensional MWW zeolite molecular sieve was epitaxially grown through hexagonal boron nitride or molybdenum sulfide as templates, and the crystallization conditions were controlled to obtain a regular hexagonal structure and high horizontal and aspect ratio.
A high crystalline two-dimensional MWW zeolite molecular sieve was prepared, which has excellent diffusion performance and catalytic activity, improved diffusion rate and enhanced selectivity, and is suitable for the fields of catalytic and gas separation.
Smart Images
Figure CN117208926B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of the synthesis of two-dimensional zeolite molecular sieves, and particularly relates to a highly crystalline two-dimensional MWW zeolite molecular sieve and a preparation method thereof. Background Art
[0002] Zeolites are crystalline aluminosilicates with excellent adsorption and catalytic properties. Especially in the petrochemical industry, zeolites, as a commonly used heterogeneous catalyst, have very important applications in the fields of catalytic cracking, hydrocracking, and reforming of petroleum refining. With the increasing depletion of petroleum resources worldwide and the continuous aggravation of the trend of heavy and inferior petroleum resources globally, the demand for zeolite-catalyzed macromolecular reactions is increasing day by day. However, traditional zeolites are three-dimensional rigid materials. On the one hand, it is difficult for macromolecules to enter the internal acidic sites through pores and voids, resulting in poor molecular accessibility; on the other hand, there are serious diffusion limitations in the pores, and the diffusion rates of reactant molecules and products are relatively slow, which both lead to a decrease in the catalytic efficiency and catalytic activity of zeolites and cannot fully exert the catalytic effect of zeolites.
[0003] In view of this, the synthesis of two-dimensional zeolite molecular sieve nanosheets that expose more active sites and have shorter diffusion lengths has become a hot topic of concern. MWW zeolites have a layered structure, with a monolayer thickness of only 2.5 nm, a large specific surface area, and a special twelve-membered ring supercage structure. By constructing thin-layer two-dimensional MWW zeolites, not only the openness of the sheets is improved, more active sites are increased, but also it is beneficial to the diffusion of macromolecular reactants in the pores and their contact with the active sites, thus showing excellent shape selectivity and catalytic activity in macromolecular reactions.
[0004] At present, the commonly used methods for the synthesis of two-dimensional MWW zeolites mainly include the post-treatment method and the direct synthesis method. The post-treatment method mainly exfoliates zeolites through swelling and ultrasonic treatment, with complex processes, cumbersome steps, low yields, and serious damage to the zeolite structure and morphology. The direct synthesis method mainly directly synthesizes two-dimensional zeolites by designing special template agents with complex molecular structures. However, the design of special template agents is complex and expensive, which is not conducive to industrialization, and the synthesized zeolite sheets grow cross-stacked with each other, unable to exert the shape selectivity effect of the zeolite pores. Therefore, it is very necessary to develop an efficient and low-cost method for synthesizing highly crystalline two-dimensional zeolites with a consistent planar orientation. Summary of the Invention
[0005] The present invention is made to solve the above problems, and the purpose is to provide a highly crystalline two-dimensional MWW zeolite molecular sieve and a preparation method thereof.
[0006] The present invention provides a method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve, which has the following characteristics and includes the following steps: Step S1, adding the powder of the two-dimensional material into a reaction vessel, then dropping an organic structure-directing agent and mixing evenly to obtain a mixed solution. After subjecting the mixed solution to ultrasonic treatment and centrifugation treatment in sequence, the supernatant is taken to obtain a dispersed solution of exfoliated thin-layer two-dimensional material;
[0007] Step S2, formulating the dispersed solution of the thin-layer two-dimensional material, deionized water, an alkali metal source, and an aluminum source into a solution, then slowly adding a silicon source to the solution, stirring and dissolving it, and after aging treatment, a sol-gel is obtained;
[0008] After the sol-gel is subjected to hydrothermal crystallization, a reaction product is obtained. After the reaction product is washed, centrifuged, and dried in sequence, a highly crystalline two-dimensional MWW zeolite molecular sieve is obtained. Among them, the concentration of the two-dimensional material contained in the dispersed solution of the thin-layer two-dimensional material is 0.005 mg / mL to 0.06 mg / mL, the lateral dimension of the two-dimensional material is 0.5 μm - 3 μm, and the thickness is 10 nm - 30 nm. In step S2, the aging treatment duration is 1 h - 6 h. In the sol-gel, the molar ratio of the silicon source:aluminum source:alkali metal source:structure-directing agent:deionized water is 22:0.2 - 1.5:1 - 6.5:2 - 10:400 - 1000. In step S3, when hydrothermal crystallization is carried out, the crystallization temperature is 120 °C - 180 °C, and the crystallization time is 7 days - 14 days.
[0009] In the method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve provided by the present invention, it may also have the following characteristics: Among them, in step S1, the two-dimensional material is hexagonal boron nitride or molybdenum disulfide, and the organic structure-directing agent is hexamethyleneimine or piperidine.
[0010] In the method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve provided by the present invention, it may also have the following characteristics: Among them, in step S1, the duration of ultrasonic treatment is 6 h - 12 h, and the rotation speed during centrifugation treatment is 8000 rpm - 10000 rpm, and the duration is 10 min - 30 min.
[0011] In the method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve provided by the present invention, it may also have the following characteristics: Among them, in step S2, the alkali metal source is sodium hydroxide or potassium hydroxide, the aluminum source is sodium aluminate, aluminum isopropoxide, aluminum chloride, or aluminum sulfate octadecahydrate, and the silicon source is an aqueous solution of silica sol, water glass, or white carbon black.
[0012] In the method for preparing the highly crystalline two-dimensional MWW zeolite molecular sieve provided by the present invention, it may further have the following characteristics: wherein, in step S2, the dropping rate of the silicon source is 0.5 mL / min - 1.5 mL / min. When stirring and dissolving, it is stirred at room temperature for 1 h - 3 h under the rotation speed condition of 400 r / min to 800 r / min.
[0013] In the method for preparing the highly crystalline two-dimensional MWW zeolite molecular sieve provided by the present invention, it may further have the following characteristics: wherein, in step S3, the hydrothermal crystallization method is dynamic crystallization or static crystallization. Dynamic crystallization is carried out under the rotation speed of 15 rpm to 30 rpm for hydrothermal crystallization.
[0014] In the method for preparing the highly crystalline two-dimensional MWW zeolite molecular sieve provided by the present invention, it may further have the following characteristics: wherein, in step S3, when washing and centrifuging, it is centrifuged at a rotation speed of 3000 rpm to 5000 rpm for 3 min to 5 min, and then washed with deionized water. The operation is repeated 3 to 4 times until the upper layer solution after centrifugation becomes clear. When performing the drying treatment, it is dried at a constant temperature in a vacuum drying oven at 50 °C to 100 °C for 12 h to 24 h.
[0015] The present invention also provides a highly crystalline two-dimensional MWW zeolite molecular sieve, which has the following characteristics: it is prepared by the method for preparing the highly crystalline two-dimensional MWW zeolite molecular sieve described above. Among them, the highly crystalline two-dimensional MWW zeolite molecular sieve is in a hexagonal flake structure, with a transverse size of 500 nm to 1000 nm and a thickness of 2.5 nm to 25 nm.
[0016] Functions and effects of the invention
[0017] According to a highly crystalline two-dimensional MWW zeolite molecular sieve and its preparation method involved in the present invention, first, a thin-layer two-dimensional material dispersion is obtained by a liquid-phase exfoliation method; subsequently, after mixing and aging the dispersion with the zeolite synthesis raw materials, and heating and growing for a certain time through hydrothermal crystallization, a highly crystalline two-dimensional MWW zeolite molecular sieve can be obtained.
[0018] According to the principle of lattice symmetry matching, two-dimensional MWW zeolite with a consistent c-axis orientation is epitaxially grown using hexagonal boron nitride or molybdenum disulfide as a template. Compared with the intergrown zeolite structure obtained by traditional direct synthesis methods, the two-dimensional MWW zeolite molecular sieve epitaxially grown in this invention has a tiled structure with a consistent orientation, a thin layer thickness of 2.5 - 15 nm, a large lateral size of 500 - 1000 nm, and a high aspect ratio. Moreover, the two-dimensional MWW zeolite molecular sieve prepared in this invention has high crystallinity. The two-dimensional MWW zeolite obtained by the epitaxial growth method has a regular planar hexagonal structure with good structural integrity. At the same time, due to its good crystallinity and the degree of framework openness, the highly crystalline two-dimensional MWW zeolite molecular sieve prepared by the epitaxial growth method in this invention has a very high diffusion rate and selectivity for xylene molecules, and has broad application prospects in the fields of catalysis and gas separation. Description of the Drawings
[0019] Figure 1 is a schematic process flow diagram of a preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve in an embodiment of the present invention;
[0020] Figure 2 is a transmission electron microscope image and an atomic force microscope image of two-dimensional hexagonal boron nitride obtained by liquid phase exfoliation in Example 1 of the present invention;
[0021] Figure 3 is a scanning electron microscope image of MWW zeolite epitaxially grown on a hexagonal boron nitride substrate in Example 1 of the present invention;
[0022] Figure 4 is a transmission electron microscope and a scanning electron microscope image of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention;
[0023] Figure 5 is a transmission electron microscope of the cross-section of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention, an atomic force microscope image of the two-dimensional MWW zeolite molecular sieve, and a thickness statistical chart;
[0024] Figure 6 is an XRD spectrum of the highly crystalline two-dimensional MWW zeolite molecular sieve and the traditional three-dimensional MCM-22P zeolite prepared in Example 1 of the present invention.
[0025] Figure 7 is an adsorption and diffusion rate diagram of the highly crystalline two-dimensional MWW zeolite molecular sieve and the traditional three-dimensional MCM-22P zeolite for o-xylene and p-xylene prepared in Example 1 of the present invention. Detailed Embodiments
[0026] A method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve of the present invention includes the following steps:
[0027] Step S1: Add the powder of the two-dimensional material into a reaction vessel, then dropwise add an organic structure-directing agent and mix evenly to obtain a mixed solution. After sequentially performing ultrasonic treatment and centrifugation on the mixed solution, take the supernatant to obtain a dispersed solution of the exfoliated thin-layer two-dimensional material.
[0028] The concentration of the two-dimensional material contained in the dispersed solution of the thin-layer two-dimensional material is 0.005 mg / mL to 0.06 mg / mL, the lateral size of the two-dimensional material is 0.5 μm - 3 μm, and the thickness is 10 nm - 30 nm. Preferably, the concentration of the two-dimensional material dispersed solution is 0.03 mg / mL, the lateral size of the two-dimensional material is 1 μm, and the thickness is 10 nm, which is beneficial to improving the template effect of the two-dimensional material and obtaining large-sized two-dimensional MWW zeolite single crystals.
[0029] In step S1, the two-dimensional material is hexagonal boron nitride or molybdenum disulfide, and the organic structure-directing agent is hexamethyleneimine or piperidine.
[0030] In step S1, the duration of ultrasonic treatment is 6 h - 12 h, the rotation speed during centrifugation is 8000 rpm to 10000 rpm, and the duration is 10 min to 30 min. Further, the power during ultrasonic treatment is 200 W - 400 W, and the frequency is 20 - 40 KHz. Preferably, the duration of ultrasonic treatment is 10 h, the duration of centrifugation is 20 min, the power during ultrasonic treatment is 400 W, and the frequency is 40 KHz.
[0031] In step S1, during ultrasonic treatment, place the reactor in an ultrasonic instrument, and use the shear force generated by ultrasonic waves and the polarity of the solvent to exfoliate the two-dimensional material powder. The thickness and yield of the exfoliated two-dimensional material can be regulated by adjusting the power and time of ultrasonic waves to obtain a dispersed solution of the two-dimensional material with a suitable concentration.
[0032] Step S2: Prepare a solution by mixing the dispersed solution of the thin-layer two-dimensional material, deionized water, an alkali metal source, and an aluminum source, then slowly add a silicon source to the solution, stir to dissolve it, and after aging treatment, obtain a sol-gel.
[0033] In step S2, when preparing a solution using the dispersed solution of the thin-layer two-dimensional material, deionized water, an alkali metal source, and an aluminum source, stir and mix evenly at a rotation speed of 100 - 800 r / min at room temperature (for example, room temperature 15 - 35 °C) for 10 - 30 min to prepare an alkaline solution.
[0034] The duration of aging treatment is 1 h - 6 h. Preferably, the duration of aging treatment is 1 h - 3 h.
[0035] In the sol-gel, the molar ratio of silicon source:aluminum source:alkali metal source:structure-directing agent:deionized water is 22:0.2 to 1.5:1 to 6.5:2 to 10:400 to 1000. Further, the silicon-aluminum ratio of the feedstock in the preparation system of the present invention is 15 to 110, the water-silicon ratio is 18 to 45, and the alkalinity is OH - :SiO2 = 0.05 to 0.3, and the ratio of silicon source to structure-directing agent is 2 to 11.
[0036] Among them, the aluminum source consumes the alkali in the system, thus causing a change in the alkalinity of the system. The alkalinity affects the formation of short-chain polymers of silicon and aluminum. In a low-alkali system, when the alkalinity increases, the number of crystal nuclei in the initial gel increases, promoting the crystallization process. While at a high water content, the solubility of silicon-aluminum species decreases, and the system saturation decreases, resulting in a reduction in the number of nucleation sites and the growth of zeolite size. The structure-directing agent induces the formation of primary and secondary structural units of silicon-aluminum species. Increasing the content of the structure-directing agent in the system increases the number of nucleation, accelerating the crystallization process. Preferably, the silicon-aluminum ratio of the feedstock in the preparation system of the present invention is 25, the water-silicon ratio is 25, and the alkalinity is OH - :SiO2 = 0.15, and the ratio of silicon source to structure-directing agent is 5.
[0037] In step S2, the alkali metal source is sodium hydroxide or potassium hydroxide, the aluminum source is sodium aluminate, aluminum isopropoxide, aluminum chloride or aluminum sulfate octadecahydrate, and the silicon source is an aqueous solution of colloidal silica, water glass or fumed silica. Further, the aqueous solution of colloidal silica is an aqueous solution of colloidal silica with a mass fraction of 25% to 40%. Preferably, when the aluminum source is sodium aluminate, the aqueous solution of colloidal silica with a mass fraction of 40% is used as the silicon source; when the aluminum source is aluminum sulfate octadecahydrate, water glass is used as the silicon source; and silicon, aluminum and aluminum are dissolved separately, and then the silicon source is slowly added dropwise to the aluminum source, and the silicon-aluminum ratio of the feedstock is 18 to 45, which is beneficial to improving the solubility of silicon-aluminum species, facilitating the formation of the initial sol-gel system and improving the yield of MWW zeolite.
[0038] In step S2, the dropping rate of the silicon source is 0.5 mL / min - 1.5 mL / min. When stirring and dissolving, it is stirred at room temperature for 1 h to 3 h under the rotation speed condition of 400 r / min to 800 r / min. Preferably, the dropping rate of the silicon source is 1 mL / min. When stirring and dissolving, it is stirred at room temperature for 2 h under the rotation speed condition of 600 r / min, which is beneficial to the slow release of the silicon source and the full combination with the aluminum source, forming a more uniform sol-gel system. In the present invention, the dropping rate of the liquid-phase silicon source is controlled and adjusted by a dropping funnel.
[0039] In step S3, after the sol-gel is hydrothermally crystallized to obtain a reaction product, the reaction product is successively washed, centrifuged and dried to obtain a highly crystalline two-dimensional MWW zeolite molecular sieve.
[0040] In step S3, during hydrothermal crystallization, the crystallization temperature is 120°C - 180°C, and the crystallization time is 7 days - 14 days.
[0041] In step S3, the hydrothermal crystallization method is dynamic crystallization or static crystallization. Dynamic crystallization is carried out at a rotation speed of 15 rpm to 30 rpm.
[0042] In step S3, during washing and centrifugation, centrifugation is carried out at a rotation speed of 3000 rpm to 5000 rpm for 3 min to 5 min, and then washed with deionized water. The operation is repeated 3 to 4 times until the upper layer solution after centrifugation becomes clear. During drying, it is dried at a constant temperature in a vacuum drying oven at 50°C to 100°C for 12 h to 24 h. Preferably, in step S3, dynamic crystallization is carried out at 25 rpm for 10 days, washed with deionized water, centrifuged at 5000 rpm for 3 min. Dynamic crystallization can promote the migration and mass transfer of silicon and aluminum species in the sol, which is beneficial to obtaining a thin-layer two-dimensional MWW zeolite with a uniform particle size distribution.
[0043] The high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by the preparation method of the high-crystallinity two-dimensional MWW zeolite molecular sieve in the present invention is in a hexagonal sheet structure, with a lateral size of 500 nm to 1000 nm. And through the two-dimensional template effect, the thickness of the synthesized two-dimensional zeolite is significantly reduced, and the thickness is 2.5 nm to 25 nm (1 - 10 layers). Preferably, the thickness is 2.5 nm to 15 nm, and the average thickness is 10 nm, which greatly improves the openness of the zeolite framework, exposes more internal active sites, and the aspect ratio reaches as high as 50 - 100, which is beneficial to the preparation and application of gas separation membranes.
[0044] At the same time, the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared in the present invention has strong MWW zeolite (300) and (500) characteristic peaks.
[0045] Furthermore, due to the good crystallinity and the degree of framework openness of the high-crystallinity two-dimensional MWW zeolite molecular sieve prepared by epitaxial growth in the present invention, it has a high diffusion rate and selectivity for xylene molecules, and can be applied to the diffusion separation of xylene molecules.
[0046] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the following examples will specifically describe a high-crystallinity two-dimensional MWW zeolite molecular sieve and its preparation method of the present invention in conjunction with the accompanying drawings.
[0047] <Example 1>
[0048] The preparation method of a high-crystallinity two-dimensional MWW zeolite molecular sieve in this example includes the following steps:
[0049] Step S1: Add the powder of the two-dimensional material into a reaction vessel, then dropwise add an organic structure-directing agent and mix evenly to obtain a mixed solution. After successively performing ultrasonic treatment and centrifugation on the mixed solution, take the supernatant to obtain a thin-layer two-dimensional material dispersion after liquid-phase exfoliation. The specific process is as follows:
[0050] Add 25 mg of commercial hexagonal boron nitride powder (PT110) and 5 mL of hexamethyleneimine (98%) into a reaction vessel, stir at 400 r / min for 30 min to mix evenly and obtain a mixed solution. Perform ultrasonic treatment on the mixed solution to exfoliate hexagonal boron nitride by liquid phase. The power of the ultrasonic wave is 400 W, the frequency is 40 KHz, and the duration is 10 h. During the ultrasonic process, keep the temperature of the ultrasonic instrument constant at 20 °C. After the ultrasonic treatment, transfer the mixed solution of hexagonal boron nitride and hexamethyleneimine after ultrasonic treatment to a 50 mL centrifuge tube, centrifuge at 10000 rpm for 10 minutes, take the supernatant, centrifuge at 10000 rpm again for 10 minutes and take the supernatant to obtain a two-dimensional hexagonal boron nitride dispersion. Put the dispersion into a 20 mL glass bottle and place it in a vacuum drying oven for standby. The concentration of hexagonal boron nitride in the dispersion is 0.006 mg / mL.
[0051] Step S2: Prepare a solution by mixing the thin-layer two-dimensional material dispersion, deionized water, an alkali metal source, and an aluminum source, then slowly add a silicon source to the solution, stir to dissolve it, and perform aging treatment to obtain a sol-gel. The specific process is as follows:
[0052] Add 28.2675 g of deionized water into a 100 mL reactor, then add 0.2532 g of flaky sodium hydroxide, stir to dissolve for 5 minutes with the rotation speed controlled at 500 rpm, then add 0.2360 g of sodium aluminate powder, stir to dissolve at 500 rpm for 5 minutes, and then add 1.25 g of the two-dimensional hexagonal boron nitride dispersion prepared in Step S1, stir and mix evenly to obtain a clear solution, and stir at 500 rpm for 30 min. Then, slowly dropwise add an aqueous solution of 40% mass fraction silicon sol to the solution at a speed of 1 mL / min through a dropping funnel, stir and age vigorously at 800 rpm for 2 hours until there is no solid deposit at the bottom to obtain a sol-gel. The molar ratio of each component in the sol-gel is: SiO2:Al2O3:NaOH:HMI:H2O = 22:0.44:3.3:4.4:660.
[0053] Step S3: After performing hydrothermal crystallization on the sol-gel, obtain a reaction product. After successively performing washing, centrifugation, and drying treatments on the reaction product, obtain a highly crystalline two-dimensional MWW zeolite molecular sieve. The specific process is as follows:
[0054] The aged sol-gel was dispensed into a 25 mL stainless-steel reactor lined with polytetrafluoroethylene, and the reactor was transferred to a dynamic rotary oven with a rotation speed of 25 rpm for hydrothermal crystallization at 150 °C for 10 days. Subsequently, it was taken out and naturally cooled to obtain a crystalline product. The crystalline product was washed with deionized water and centrifuged at 5000 rpm for 5 minutes. The washing and centrifugation operations were repeated 3 - 4 times until the product turned white and the supernatant had a neutral pH. Subsequently, the centrifuged bottom product was placed in a vacuum drying oven at 85 °C for drying for 12 h to obtain a fully crystalline two-dimensional MWW zeolite molecular sieve.
[0055] Figure 1 It is a schematic diagram of the preparation process of a method for preparing a highly crystalline two-dimensional MWW zeolite molecular sieve in an embodiment of the present invention.
[0056] As Figure 1 shown, in this embodiment, through the strategy of lattice-matched epitaxial growth, hexagonal boron nitride with an alternating surface charge distribution was used as the two-dimensional template, and hexamethyleneimine was used as the organic structure-directing agent. Under the induction of the organic structure-directing agent, the silicon-aluminum and aluminum sources underwent hydrothermal crystallization to form a silicon-aluminum precursor, and under the templating effect of hexagonal boron nitride, a thin-layer highly crystalline two-dimensional MWW zeolite molecular sieve was epitaxially grown through electrostatic interaction and lattice symmetry matching. The two-dimensional MWW zeolite molecular sieve has a regular planar hexagonal structure.
[0057] Figure 2 It is a transmission electron microscope image and an atomic force microscope image of two-dimensional hexagonal boron nitride obtained by liquid-phase exfoliation in Example 1 of the present invention. Figure 2 In (a) is the transmission electron microscope image of two-dimensional hexagonal boron nitride obtained by liquid-phase exfoliation in Example 1 of the present invention, and in (b) is the atomic force microscope image of two-dimensional hexagonal boron nitride obtained by liquid-phase exfoliation in Example 1 of the present invention.
[0058] As Figure 2 shown, the size of hexagonal boron nitride is 500 nm and the thickness is 10 nm. In this embodiment, the organic structure-directing agent hexamethyleneimine was used as the exfoliation solvent for hexagonal boron nitride (h-BN), and thin-layer hexagonal boron nitride was successfully exfoliated, which also facilitated the rapid epitaxial growth of silicon-aluminum tetrahedrons formed under the guidance of HMI at the initial stage of crystallization on the h-BN template.
[0059] Figure 3 It is a scanning electron microscope image of MWW zeolite epitaxially grown on a hexagonal boron nitride substrate in Example 1 of the present invention.
[0060] As Figure 3 shown, on the hexagonal boron nitride (h-BN) substrate, the MWW zeolites are parallel to each other and have a consistent crystal orientation, achieving the epitaxial growth of two-dimensional MWW zeolite.
[0061] Figure 4 These are the transmission electron microscope and scanning electron microscope images of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention. Among them, Figure 4 in (a), (b), and (c) are the transmission electron microscopes of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention at different magnifications, Figure 4 in (d), (e), and (f) are the scanning electron microscope images of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention at different magnifications.
[0062] As Figure 4 shown, the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in this example has a regular hexagonal structure and a consistent planar spreading orientation, and the lateral size is ~500 nm.
[0063] Figure 5 These are the transmission electron microscope of the cross-section of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention, the atomic force microscope image of the two-dimensional MWW zeolite molecular sieve, and the thickness statistical chart. Figure 5 In (a) is the transmission electron microscope of the cross-section of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention, (b) is the atomic force microscope image of the highly crystalline two-dimensional MWW zeolite molecular sieve prepared in Example 1 of the present invention, and (c) is the thickness statistical chart of the two-dimensional MWW zeolite molecular sieve.
[0064] As Figure 5 shown, the number of epitaxially grown two-dimensional MWW layers mainly concentrates on 3 - 6 layers, and the average thickness is 10 nm.
[0065] Figure 6 These are the XRD spectra of the highly crystalline two-dimensional MWW zeolite molecular sieve and the traditional three-dimensional MCM-22P zeolite prepared in Example 1 of the present invention.
[0066] As Figure 6 shown, the two-dimensional MWW zeolite molecular sieve prepared in this example has (300) and (500) MWW zeolite characteristic peaks at 2θ = 21.8° and 35.6°, and the full width at half maximum is 0.334° and 0.246° respectively, which is due to the high in-plane crystallinity of the two-dimensional MWW zeolite caused by epitaxial growth.
[0067] In this example, the prepared two-dimensional MWW zeolite molecular sieve was also used to compare the adsorption and diffusion of p-xylene and o-xylene with the traditional three-dimensional MCM-22P zeolite molecular sieve. Figure 7It is the adsorption and diffusion rate diagram of high-crystalline two-dimensional MWW zeolite molecular sieve and traditional three-dimensional MCM-22P zeolite prepared in Example 1 of the present invention for o-xylene and p-xylene.
[0068] As Figure 7 shown, whether it is p-xylene or o-xylene, the more open two-dimensional MWW zeolite molecular sieve prepared in this example has a higher diffusion rate. At room temperature, the diffusion rates of o-xylene and p-xylene in the two-dimensional MWW zeolite molecular sieve are 43 times and 203 times that of the MCM-22 zeolite molecular sieve, respectively. And according to the ideal solution adsorption theory, the selectivity of the two-dimensional MWW zeolite molecular sieve for o-xylene / p-xylene is 10 times that of the MCM-22 zeolite molecular sieve.
[0069] Furthermore, the two-dimensional MWW zeolite molecular sieve prepared in this example has good crystallinity and a high aspect ratio. The more exposed 10-membered ring channels (0.55 nm) inside the zeolite enable p-xylene with an absolute diameter of 0.41 nm to easily diffuse in, but there is a large diffusion resistance for o-xylene with a diameter of 0.53 nm. Based on this, the diffusion rate and selectivity of the two-dimensional MWW zeolite for p-xylene are greatly improved.
[0070] <Example 2>
[0071] A preparation method of a high-crystalline two-dimensional MWW zeolite molecular sieve in this example includes the following steps:
[0072] Step S1, add 20 mg of commercial hexagonal boron nitride powder (PT110) and 20 mL of deionized water into a reaction vessel, stir at 400 r / min for 30 min to mix evenly to obtain a mixed solution. Ultrasonically treat the mixed solution to exfoliate hexagonal boron nitride in the liquid phase. The power of ultrasonic treatment is 400 W, the frequency is 40 KHz, and the duration is 10 h. During the ultrasonic process, keep the temperature of the ultrasonic instrument constant at 20 °C. After the ultrasonic treatment, transfer the mixed solution of hexagonal boron nitride and deionized water to a 50 mL centrifuge tube, centrifuge at 10000 rpm for 10 minutes, take the supernatant, centrifuge again at 10000 rpm for 10 minutes and take the supernatant to obtain a two-dimensional hexagonal boron nitride dispersion. Put the dispersion into a 20 mL glass bottle and place it in a vacuum drying oven for standby. The concentration of hexagonal boron nitride in the dispersion is 0.030 mg / mL.
[0073] Step S2: Add 28.2675 g of two-dimensional hexagonal boron nitride dispersion into a 100 mL reactor, then add 0.2532 g of flaky sodium hydroxide, stir and dissolve for 5 minutes with the rotation speed controlled at 500 rpm. Then add 0.2360 g of sodium aluminate powder, stir and dissolve at 500 rpm for 5 minutes. Then add 1.25 g of hexamethyleneimine, stir and mix evenly to obtain a clear solution, and stir at 500 rpm for 30 min. Then, slowly dropwise add an aqueous solution of silicon sol with a mass fraction of 40% into the solution at a rate of 1 mL / min through a dropping funnel, and vigorously stir and age for 2 hours at 800 rpm until there is no solid deposit at the bottom to obtain a sol-gel. The molar ratio of each component in the sol-gel is: SiO2:Al2O3:NaOH:HMI:H2O = 22:0.44:3.3:4.4:660.
[0074] In this example, the subsequent preparation steps are the same as those in step S3 of Example 1, and finally a highly crystalline two-dimensional MWW zeolite molecular sieve is prepared.
[0075] <Example 3>
[0076] A preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve in this example is based on the same specific preparation steps as in Example 1, and replaces the hydrothermal crystallization method in step S3 with static crystallization, specifically as follows:
[0077] Dispense the sol-gel obtained by aging into a 25 mL stainless steel reaction kettle with a polytetrafluoroethylene lining, transfer the reaction kettle to an oven, perform hydrothermal crystallization at 150 °C for 10 days, then take it out and cool naturally to obtain a crystalline product. And based on the preparation steps of Example 1, use the same preparation conditions for subsequent preparation, and finally prepare a highly crystalline two-dimensional MWW zeolite molecular sieve with a lateral size of 500 nm - 1500 nm and an average thickness of 25 nm.
[0078] <Example 4>
[0079] A preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve in this example is based on the same specific preparation steps as in Example 1, and only adjusts the usage amount of flaky sodium hydroxide in step S2, specifically as follows:
[0080] Add 28.2675 g of deionized water to a 100 mL reactor, then add 0.1688 g of flaky sodium hydroxide, stir and dissolve for 5 minutes with the rotation speed controlled at 500 rpm. Then add 0.2360 g of sodium aluminate powder, stir and dissolve at 500 rpm for 5 minutes. Then add 1.25 g of the two-dimensional hexagonal boron nitride dispersion prepared in step S1, stir and mix evenly to obtain a clear solution, and stir at 500 rpm for 30 min. Then, slowly dropwise add an aqueous solution of silicon sol with a mass fraction of 40% into the solution at a rate of 1 mL / min through a dropping funnel, and vigorously stir and age at 800 rpm for 2 hours until there is no solid deposit at the bottom to obtain a sol-gel. The molar ratio of each component in the sol-gel is: SiO2:Al2O3:NaOH:HMI:H2O = 22:0.44:2.2:4.4:660. And based on the preparation steps of Example 1, use the same preparation conditions for subsequent preparations, and finally prepare a highly crystalline two-dimensional MWW zeolite molecular sieve.
[0081] <Example 5>
[0082] A method for preparing a two-dimensional MWW zeolite molecular sieve in this example, based on the same specific preparation steps as in Example 1, replaces the concentration of hexagonal boron nitride in the two-dimensional hexagonal boron nitride dispersion prepared in step S1 from 0.006 mg / mL to 0.0015 mg / mL, specifically as follows:
[0083] Add 25 mg of commercial hexagonal boron nitride powder (PT110) and 20 mL of hexamethyleneimine (98%) to a reaction vessel, stir at 400 r / min for 30 min, mix evenly to obtain a mixed solution, perform ultrasonic treatment on the mixed solution to exfoliate hexagonal boron nitride by liquid phase. The power of ultrasonic is 400 W, the frequency is 40 KHz, and the duration is 10 h. During the ultrasonic process, keep the temperature of the ultrasonic instrument constant at 20 °C. After the ultrasonic treatment, transfer the mixed solution of hexagonal boron nitride and hexamethyleneimine after ultrasonic treatment to a 50 mL centrifuge tube, centrifuge at 10000 rpm for 10 minutes, take the supernatant, centrifuge again at 10000 rpm for 10 minutes and take the supernatant to obtain a two-dimensional hexagonal boron nitride dispersion. Put the dispersion into a 20 mL glass bottle and place it in a vacuum drying oven for standby. The concentration of hexagonal boron nitride in the dispersion is 0.0015 mg / mL. And based on the preparation steps of Example 1, use the same preparation conditions for subsequent preparations, and finally prepare a two-dimensional MWW zeolite molecular sieve.
[0084] <Example 6>
[0085] A method for preparing a two-dimensional MWW zeolite molecular sieve in this example, based on the same specific preparation steps as in Example 1, replaces the hydrothermal crystallization duration in step S3 from 10 days to 4 days, specifically as follows:
[0086] The sol-gel obtained by aging was dispensed into a 25 mL stainless-steel autoclave lined with polytetrafluoroethylene and transferred to a dynamic rotary oven. The rotation speed was 25 rpm, and hydrothermal crystallization was carried out at 150 °C for 4 days. Subsequently, it was taken out and naturally cooled to obtain a crystalline product. And subsequent preparations were carried out using the same preparation conditions based on the preparation steps of Example 1, and finally, a two-dimensional MWW zeolite molecular sieve was prepared.
[0087] <Comparative Example 1>
[0088] A method for preparing a two-dimensional MWW zeolite molecular sieve in this comparative example includes the following steps:
[0089] Step S1, add 28.2675 g of deionized water into a 100 mL reactor, then add 0.2532 g of flaky sodium hydroxide, stir and dissolve for 5 minutes, control the rotation speed at 500 rpm, then add 0.2360 g of sodium aluminate powder, stir and dissolve at 500 rpm for 5 minutes, then add 1.25 g of hexamethyleneimine, stir and mix evenly to obtain a clear solution, and stir at 500 rpm for 30 min. Then, a 40% by mass aqueous solution of silica sol was slowly added dropwise to the solution at a rate of 1 mL / min through a dropping funnel, and vigorously stirred and aged at 800 rpm for 2 hours until there was no solid deposit at the bottom to obtain a sol-gel. The molar ratio of each component in the sol-gel was: SiO2:Al2O3:NaOH:HMI:H2O = 22:0.44:3.3:4.4:660.
[0090] In this Comparative Example 1, a two-dimensional hexagonal boron nitride dispersion was not added during the preparation, and the subsequent preparation steps were the same as those of Step S3 in Example 1, and finally, a two-dimensional MWW zeolite molecular sieve was prepared.
[0091] <Comparative Example 2>
[0092] A method for preparing a two-dimensional MWW zeolite molecular sieve in this comparative example includes the following steps:
[0093] Step S1: Add 25 mg of commercial mica powder and 5 mL of hexamethyleneimine (98%) into a reaction vessel, stir at 400 r / min for 30 min to mix evenly, obtaining a mixed solution. Perform ultrasonic treatment on the mixed solution to exfoliate mica in the liquid phase. The power of ultrasonic treatment is 400 W, the frequency is 40 KHz, and the duration is 10 h. During the ultrasonic process, keep the temperature of the ultrasonic instrument constant at 20 °C. After the ultrasonic treatment, transfer the mixed solution of mica and hexamethyleneimine after ultrasonic treatment to a 50 mL centrifuge tube, centrifuge at 10000 rpm for 10 minutes, take the supernatant, centrifuge again at 10000 rpm for 10 minutes and take the supernatant to obtain a two-dimensional mica dispersion. Put the dispersion into a 20 mL glass bottle and place it in a vacuum drying oven for standby. The concentration of mica in the dispersion is 0.006 mg / mL.
[0094] Step S2: Add 28.2675 g of deionized water into a 100 mL reactor, then add 0.2532 g of flaky sodium hydroxide, stir and dissolve for 5 minutes with the rotation speed controlled at 500 rpm. Then add 0.2360 g of sodium aluminate powder, stir and dissolve at 500 rpm for 5 minutes. Then add 1.25 g of the mica dispersion prepared in Step S1, stir and mix evenly to obtain a clear solution, and stir at 500 rpm for 30 min. Then, slowly dropwise add an aqueous solution of silicon sol with a mass fraction of 40% into the solution at a speed of 1 mL / min through a dropping funnel, and stir vigorously at 800 rpm for 2 hours until there is no solid deposit at the bottom to obtain a sol-gel. The molar ratio of each component in the sol-gel is: SiO2:Al2O3:NaOH:HMI:H2O = 22:0.44:3.3:4.4:660.
[0095] Step S3: The specific steps of Step S3 in this comparative example are the same as those in Example 1, and finally a two-dimensional MWW zeolite molecular sieve is prepared.
[0096] In this comparative example, based on the specific preparation steps of Example 1, replace hexagonal boron nitride with mica, and the subsequent preparation steps are the same as those of Step S3 in Example 1. Finally, a two-dimensional MWW zeolite molecular sieve is prepared.
[0097] <Comparative Example 3>
[0098] A preparation method of a two-dimensional MWW zeolite molecular sieve in this comparative example includes the following steps:
[0099] Step S1: Add 25 mg of commercial hexagonal boron nitride powder (PT110) and 5 mL of aniline (99%) into a reaction vessel, stir at 400 r / min for 30 min to mix evenly, obtaining a mixed solution. Perform ultrasonic treatment on the mixed solution to exfoliate hexagonal boron nitride in the liquid phase. The power of ultrasonic is 400 W, the frequency is 40 KHz, and the duration is 10 h. Keep the temperature of the ultrasonic instrument constant at 20 °C during the ultrasonic process. After the ultrasonic treatment, transfer the mixed solution of hexagonal boron nitride and aniline after ultrasonic treatment to a 50 mL centrifuge tube, centrifuge at 10000 rpm for 10 minutes, take the supernatant, centrifuge again at 10000 rpm for 10 minutes and take the supernatant to obtain a two-dimensional hexagonal boron nitride dispersion. Put the dispersion into a 20 mL glass bottle and place it in a vacuum drying oven for standby. The concentration of hexagonal boron nitride in the dispersion is 0.006 mg / mL.
[0100] In this comparative example, based on the specific preparation steps of Example 1, replace the structure-directing agent hexamethyleneimine with aniline, and the subsequent preparation steps are the same as those of steps S2 and S3 in Example 1, and finally obtain two-dimensional MWW zeolite molecular sieve.
[0101] <Comparative Example 4>
[0102] A preparation method of a two-dimensional MWW zeolite molecular sieve in this comparative example includes the following steps:
[0103] Step S1: Add 28.2675 g of deionized water into a 100 mL reactor, then add 0.2532 g of flaky sodium hydroxide, stir and dissolve for 5 minutes with the rotation speed controlled at 500 rpm. Then add 0.2360 g of sodium aluminate powder, stir and dissolve at 500 rpm for 5 minutes. Then add 1.25 g of hexamethyleneimine, and then add 0.025 g of hexagonal boron nitride powder (PT110), stir and mix evenly to obtain a clear solution, and stir at 500 rpm for 30 min. Then, slowly drip the aqueous solution of silicon sol with a mass fraction of 40% into the solution at a speed of 1 mL / min through a dropping funnel, and stir and age vigorously at 800 rpm for 2 hours until there is no solid sediment at the bottom to obtain a sol-gel. The molar ratio of each component in the sol-gel is: SiO2:Al2O3:NaOH:HMI:H2O = 22:0.44:3.3:4.4:660.
[0104] In this comparative example, a two-dimensional hexagonal boron nitride dispersion is not prepared and used during the preparation. During the preparation, hexagonal boron nitride powder and hexamethyleneimine are directly added, and the subsequent preparation steps are the same as those of step S3 in Example 1, and finally a two-dimensional MWW zeolite molecular sieve is prepared.
[0105] For the two-dimensional MWW zeolite molecular sieves prepared in Examples 1-6 and Comparative Examples 1-4, XRD patterns and morphological data were obtained respectively, and the specific data are shown in Table 1.
[0106] Table 1 XRD patterns and morphological data of two-dimensional MWW zeolite molecular sieves
[0107]
[0108] In Table 1, the symbol: “—” indicates that the zeolite has an intergrown structure and the performance indicators cannot be tested.
[0109] According to Table 1, the highly crystalline two-dimensional MWW zeolite molecular sieves prepared by the preparation method of the present invention in Examples 1-3 all have the characteristic peaks of (300) and (500). At the same time, the prepared highly crystalline two-dimensional MWW zeolite molecular sieves all have a regular hexagonal structure, a larger lateral size of 500-1000 nm, and all have a high aspect ratio.
[0110] In Examples 4-6, although hexagonal boron nitride was also used, and hexagonal boron nitride was used as a template for epitaxial growth of two-dimensional zeolites, the two-dimensional MWW zeolite molecular sieves prepared under the conditions of a concentration of 0.0015 mg / mL of the two-dimensional hexagonal boron nitride dispersion, a hydrothermal crystallization time of 4 days, and an alkalinity of OH-:SiO2 = 0.1 do not have the characteristic peaks of (300) and (500).
[0111] Furthermore, hexagonal boron nitride was not used in Comparative Examples 1 and 2, aniline was used as a structure-directing agent in Comparative Example 3, and hexagonal boron nitride powder and hexamethyleneimine were directly added for preparation in Comparative Example 4. The two-dimensional MWW zeolite molecular sieves prepared by the preparation methods of Comparative Examples 1-4 do not have the characteristic peaks of (300) and (500), and the prepared two-dimensional MWW zeolite molecular sieves all have an intergrown structure.
[0112] Functions and effects of the examples
[0113] Comparing Example 1 and Example 2, it can be seen that when preparing the thin-layer two-dimensional hexagonal boron nitride dispersion, different exfoliating solvents will affect the exfoliation effect. In Example 1, the organic structure-directing agent hexamethyleneimine was used as the exfoliating solvent for h-BN, and thin-layer h-BN was successfully exfoliated to obtain a two-dimensional hexagonal boron nitride dispersion with a concentration of 0.006 mg / mL; in Example 2, deionized water was used as the exfoliating solvent for h-BN to obtain a two-dimensional hexagonal boron nitride dispersion with a concentration of 0.030 mg / mL. Therefore, in this example, using hexamethyleneimine and water as the exfoliating solvents for two-dimensional hexagonal boron nitride can obtain better exfoliation effects and can successfully exfoliate to obtain a thin-layer two-dimensional hexagonal boron nitride dispersion. Further, when choosing HMI as the exfoliating reagent, since a large amount of HMI adsorbs on the surface of h-BN, it is beneficial to the rapid epitaxial growth of the silicon-aluminum tetrahedron formed under the guidance of HMI in the initial stage of crystallization on the h-BN template;
[0114] Comparing Example 1 and Example 3, it can be seen that in the two-dimensional MWW zeolite molecular sieve prepared by the dynamic crystallization method, the average lateral size is ∼500 nm and the aspect ratio is 50. The dynamic crystallization method can promote the migration and mass transfer of silicon-aluminum species in the sol, which is beneficial to obtaining thin-layer two-dimensional MWW zeolites with a uniform particle size distribution; in the two-dimensional MWW zeolite molecular sieve prepared by the static crystallization method, the lateral size is larger, but the particle size distribution is uneven and the zeolite layer thickness increases significantly. The average thickness is 25 nm, and the average lateral size of the prepared MWW zeolite is ∼1000 nm and the aspect ratio is 40. Therefore, different hydrothermal crystallization methods will affect the lateral size and aspect ratio of the prepared two-dimensional MWW zeolite molecular sieve. Under static crystallization conditions, the lateral size of the zeolite becomes larger but the longitudinal direction becomes thicker.
[0115] Comparing Example 1 and Example 4, it can be seen that in the preparation system of this example, the alkalinity will affect the formation of short-chain polymers of silicon and aluminum. When the alkalinity increases in a low-alkalinity system, the number of crystal nuclei in the initial gel will increase, promoting the crystallization process, but the particle size decreases. When the alkalinity is OH⁻:SiO₂ = 0.15, the average lateral size of the prepared two-dimensional MWW zeolite molecular sieve is ∼500 nm and the aspect ratio is 50, with a complete hexagonal structure and (300), (500) characteristic peaks; when the alkalinity is OH⁻:SiO₂ = 0.1, the average lateral size of the prepared two-dimensional MWW zeolite molecular sieve is ∼1000 nm and the aspect ratio is 100, but the structure is damaged and does not have (300), (500) characteristic peaks. Therefore, the alkalinity in the system will affect the structure and size of the prepared two-dimensional MWW zeolite molecular sieve. When prepared at an alkalinity of OH⁻:SiO₂ = 0.1, although the aspect ratio increases, the structure is no longer a complete regular hexagon and no longer has the (300) and (500) characteristic peaks of XRD.
[0116] Comparing Example 1 with Examples 5 and 6, it can be seen that by using hexagonal boron nitride as a template for epitaxial growth of two-dimensional zeolite, two-dimensional MWW zeolite molecular sieves with a regular hexagonal structure can be prepared. However, both the concentration of the two-dimensional material dispersion and the duration of hydrothermal crystallization will affect the synthesis results. Only under the preparation conditions where the concentration of the two-dimensional material dispersion in the present invention is 0.005 mg / mL to 0.06 mg / mL and the hydrothermal crystallization duration is 7 - 14 days, can a two-dimensional MWW zeolite molecular sieve with high crystallinity, large lateral size, and aspect ratio be obtained.
[0117] Comparing Example 1 with Comparative Examples 1 - 4, it can be seen that only under the preparation method of this example, by using the organic structure-directing agent hexamethyleneimine as a stripping solvent for hexagonal boron nitride, the exfoliated thin-layer hexagonal boron nitride is beneficial to the rapid epitaxial growth of silicon-aluminum tetrahedrons formed under the guidance of hexamethyleneimine at the initial stage of crystallization on the hexagonal boron nitride template. Finally, a highly crystalline two-dimensional MWW zeolite molecular sieve with a regular hexagonal structure, large lateral size, and aspect ratio can be successfully prepared.
[0118] In summary, according to a highly crystalline two-dimensional MWW zeolite molecular sieve and its preparation method involved in this example, first, a thin-layer two-dimensional material dispersion is obtained by liquid-phase exfoliation; then, after mixing and aging the dispersion with zeolite synthesis raw materials, and heating and growing for a certain time through hydrothermal crystallization, a highly crystalline two-dimensional MWW zeolite molecular sieve can be obtained.
[0119] In this example, based on the principle of lattice symmetry matching, two-dimensional MWW zeolite with a consistent c-axis orientation was epitaxially grown using hexagonal boron nitride as a template. Compared with the interpenetrating zeolite structure obtained by the traditional direct synthesis method, the two-dimensional MWW zeolite molecular sieve epitaxially grown in this example has a flat structure with a consistent orientation, and has a thin-layer thickness of 2.5 - 15 nm, a large lateral size of 500 - 1000 nm, and a high aspect ratio.
[0120] Moreover, the two-dimensional MWW zeolite molecular sieve prepared in this example has high crystallinity. The two-dimensional MWW zeolite obtained by the epitaxial growth method has a regular planar hexagonal structure with good structural integrity; in the XRD pattern, not only the characteristic peaks of traditional MWW zeolite appear, but also sharp and strong characteristic peaks of MWW zeolite (300) and (500) appear. This is a two-dimensional MWW zeolite with high in-plane crystallinity obtained by epitaxial growth using hexagonal boron nitride as a template through lattice symmetry matching. Its framework structure is complete, and there are few silicon-aluminum species defects, having good stability and crystallinity.
[0121] Meanwhile, the highly crystalline two-dimensional MWW zeolite molecular sieve prepared by the epitaxial growth method in this embodiment has a very high diffusion rate and selectivity for xylene molecules due to its good crystallinity and framework openness. At room temperature, the diffusion rates of o-xylene and p-xylene in the two-dimensional MWW zeolite molecular sieve are 43 times and 203 times that of the conventional molecular sieve MCM-22, respectively. The selectivity of the two-dimensional MWW zeolite for o-xylene / p-xylene calculated according to the ideal solution adsorption theory is 10 times that of MCM-22. Therefore, the highly crystalline two-dimensional MWW zeolite molecular sieve prepared by the present invention has broad application prospects in the fields of catalysis and gas separation.
[0122] The above embodiments are preferred cases of the present invention and are not used to limit the protection scope of the present invention.
Claims
1. A preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve, characterized in that, It includes the following steps: Step S1: Add the powder of two-dimensional material into a reaction vessel, then dropwise add an organic structure-directing agent and mix evenly to obtain a mixed solution. After subjecting the mixed solution to ultrasonic treatment and centrifugation in sequence, take the supernatant to obtain a thin-layer two-dimensional material dispersion liquid after liquid-phase exfoliation; Step S2: Prepare a solution from the thin-layer two-dimensional material dispersion liquid, deionized water, an alkali metal source, and an aluminum source. Then slowly add a silicon source to the solution, stir to dissolve it, and after aging treatment, obtain a sol-gel; Step S3: After hydrothermal crystallization of the sol-gel, obtain a reaction product. After washing, centrifuging, and drying the reaction product in sequence, obtain a highly crystalline two-dimensional MWW zeolite molecular sieve, wherein, in step S1, the two-dimensional material is hexagonal boron nitride or molybdenum disulfide, the organic structure-directing agent is hexamethyleneimine, the concentration of the two-dimensional material contained in the thin-layer two-dimensional material dispersion liquid is 0.005 mg / mL - 0.06 mg / mL, the lateral size of the two-dimensional material is 0.5 μm - 3 μm, and the thickness is 10 nm - 30 nm, in step S2, the aging treatment duration is 1 h - 6 h, and in the sol-gel, the molar ratio of silicon source:aluminum source:alkali metal source:structure-directing agent:deionized water is 22:0.2 - 1.5:3.3 - 6.5:2 - 10:400 - 1000, in step S3, when performing hydrothermal crystallization, the crystallization temperature is 120 °C - 180 °C, and the crystallization time is 7 days - 14 days.
2. The preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that: Among them, In step S1, the ultrasonic treatment duration is 6 h - 12 h, and the rotation speed during centrifugation is 8000 rpm - 10000 rpm, and the duration is 10 min - 30 min.
3. The preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that: Among them, In step S2, the alkali metal source is sodium hydroxide or potassium hydroxide, the aluminum source is sodium metaaluminate, aluminum isopropoxide, aluminum chloride, or aluminum sulfate octadecahydrate, the silicon source is an aqueous solution of silica sol, water glass, or silica white.
4. The preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that: Among them, In step S2, the dropping rate of the silicon source is 0.5 mL / min - 1.5 mL / min, when stirring and dissolving, stir at room temperature for 1 h - 3 h at a rotation speed of 400 r / min - 800 r / min.
5. The preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that: Among them, In step S3, the hydrothermal crystallization method is dynamic crystallization or static crystallization, and the dynamic crystallization is to perform the hydrothermal crystallization at a rotation speed of 15 rpm - 30 rpm.
6. The preparation method of a highly crystalline two-dimensional MWW zeolite molecular sieve according to claim 1, characterized in that: Among them, In step S3, when washing and centrifuging, centrifuge at a rotational speed of 3000 rpm to 5000 rpm for 3 minutes to 5 minutes, then wash with deionized water, and repeat the operation 3 to 4 times until the supernatant after centrifugation becomes clear. When performing the drying treatment, keep drying at a constant temperature in a vacuum drying oven at 50 °C to 100 °C for 12 hours to 24 hours.
7. A highly crystalline two-dimensional MWW zeolite molecular sieve, characterized in that, Prepared by the preparation method of the highly crystalline two-dimensional MWW zeolite molecular sieve according to any one of claims 1 to 6. Among them, the highly crystalline two-dimensional MWW zeolite molecular sieve has a hexagonal flake structure, a lateral dimension of 500 nm to 1000 nm, and a thickness of 2.5 nm to 25 nm.