Preparation method of nano-hollow beta molecular sieve

Abstract

This application provides a method for preparing nano-hollow Beta molecular sieves. The method involves mixing and stirring raw materials such as a silicon source, an aluminum source, an inorganic alkali, an inorganic salt, Beta seed crystals, and water to form a homogeneous gel. This gel is then subjected to hydrothermal crystallization, centrifugation, washing, and drying to obtain the molecular sieve. The method for synthesizing nano-hollow Beta molecular sieves provided in this application requires no addition of any organic template agent, has a short crystallization time, and produces a product with high crystallinity, showing promising application prospects.

Description

Technical Field

[0001] This application belongs to the field of porous materials technology, specifically relating to a method for preparing a nano-hollow Beta molecular sieve. Background Technology

[0002] Beta molecular sieves possess a unique cageless three-dimensional twelve-membered ring macroporous structure, with straight channels oriented along the

[100] and

[010] directions, and pore sizes of approximately 0.77 × 0.67 nm; and curved channels penetrating the straight channels along the

[001] direction, with pore sizes of approximately 0.56 × 0.56 nm. Due to its large pore size, tunable acidity, and excellent thermal and hydrothermal stability, it is widely used in the petrochemical industry, for example in processes such as benzene alkylation with olefins (production of ethylbenzene and cumene), alkyl transfer of heavy aromatics, hydrocarbon hydrocracking, and hydroisomerization.

[0003] Although Beta molecular sieves are widely used in many fields, their narrow pore size distribution makes it difficult for reactant molecules to access the acidic sites, affecting their utilization. Larger product molecules also have difficulty detaching from active sites, leading to side reactions and causing problems such as low catalytic efficiency and rapid catalyst deactivation due to carbon deposition. Nanoscale hollow molecular sieves, with their shorter molecular diffusion paths, can effectively improve the transport efficiency of reactant and product molecules within the micropores of the molecular sieve, thus potentially increasing reaction rates and delaying catalyst deactivation.

[0004] Zheng et al. (Zheng Z, Sun C, Dai R, et al. Catalysis Science & Technology, 2016, 6: 6472-6475) prepared Pt-coated hollow Beta molecular sieves using Pt-loaded carbon spheres as hard templates through layer-by-layer self-assembly technology.

[0005] CN110054200A discloses a method for preparing hollow Beta molecular sieves. The method involves directly preparing hollow Beta molecular sieves by one-step hydrothermal crystallization of a gel formed by thoroughly mixing Y-type molecular sieves, an inorganic base, a microporous template agent (TEAOH aqueous solution), and N-methyl-2-pyrrolidone. This technique not only utilizes the organic template agent tetraethylammonium hydroxide and the hollowness inducing agent N-methyl-2-pyrrolidone, but also employs crystalline Y-type molecular sieves as the silica-alumina source, resulting in higher preparation costs and larger, submicron-sized Beta molecular sieve crystals.

[0006] In summary, the preparation processes of currently reported hollow Beta molecular sieves are cumbersome, require stringent conditions, and are costly, which to some extent limits their industrial application. Therefore, there is an urgent need to develop a new method for preparing nano-hollow Beta molecular sieves that is environmentally friendly, easy to operate, and inexpensive. Summary of the Invention

[0007] The purpose of this application is to develop a novel method for preparing nano-hollow Beta molecular sieves, which is environmentally friendly, simple, and inexpensive.

[0008] According to one aspect of this application, a method for preparing nano-hollow Beta molecular sieves is provided, comprising the following steps:

[0009] Raw materials containing silicon source, aluminum source, inorganic alkali, inorganic salt, Beta seed crystals and water are mixed and reacted in a sealed container to obtain the nano-hollow Beta molecular sieve.

[0010] The silicon source is selected from at least one of silica gel, fumed silica, and silica sol.

[0011] The aluminum source is selected from at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum hydroxide, and aluminum powder;

[0012] The inorganic base is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water;

[0013] The inorganic salt is selected from at least one of lithium chloride, sodium chloride, potassium chloride, and ammonium chloride;

[0014] The Beta seed crystals are selected from pure silicon Beta molecular sieve powder and / or high silicon Beta molecular sieve powder.

[0015] Optionally, the silicon-to-aluminum ratio of the Beta seed crystal is greater than or equal to 100.

[0016] The molar ratio of the silicon source to the aluminum source is 1:0.0025 to 0.05;

[0017] Optionally, the molar ratio of the silicon source to the aluminum source is any value from 1:0.0025, 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, or any range between the two.

[0018] The molar ratio of the silicon source to the inorganic base is 1:0.05 to 0.25;

[0019] Optionally, the molar ratio of the silicon source to the inorganic base is any value from 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, or any value between two of them.

[0020] The molar ratio of the silicon source to the inorganic salt is 1:0.05 to 0.25;

[0021] Optionally, the molar ratio of the silicon source to the inorganic salt is any value from 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, or any value between two of them.

[0022] The molar ratio of the silicon source to the water is 1:5 to 25;

[0023] Optionally, the molar ratio of the silicon source to the water is any value among 1:5, 1:10, 1:15, 1:20, and 1:25, or any range between the two.

[0024] Wherein, the molar amount of the silicon source is expressed as the molar amount of silicon dioxide;

[0025] The molar amount of the aluminum source is expressed as the molar amount of aluminum oxide;

[0026] The amount of the Beta seed crystal is 5 to 30 wt% of the weight of the silicon source.

[0027] Optionally, the amount of the Beta seed crystal is any value among 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, and 30wt% of the weight of the silicon source, or a range between any two.

[0028] The reaction is a high-temperature hydrothermal crystallization reaction.

[0029] The reaction temperature is 100–140°C;

[0030] Optionally, the temperature of the reaction is any value among 100°C, 110°C, 120°C, 130°C, and 140°C, or a range between any two.

[0031] The reaction time is 12–48 hours.

[0032] Optionally, the reaction time is any value among 12h, 24h, 36h, and 48h, or a range between any two.

[0033] The reaction is followed by acid exchange;

[0034] The acid exchange uses dilute sulfuric acid and / or dilute nitric acid with a concentration of 0.25–0.5 M.

[0035] The acid exchange temperature is 60–80°C;

[0036] The acid exchange time is 4–8 hours;

[0037] Optionally, the acid exchange time is any value among 4h, 6h, and 8h, or a range between any two.

[0038] Stirring is performed during the acid exchange process.

[0039] Further, the acid treatment includes:

[0040] After centrifugation and washing, the crystallized product is directly exchanged with 0.25-0.5M dilute sulfuric acid and / or dilute nitric acid, heated to 60-80℃, stirred at a constant temperature for no less than 4 hours, filtered, and dried.

[0041] According to another aspect of this application, a nano-hollow Beta molecular sieve is provided, prepared by the above-described preparation method.

[0042] The silicon-to-aluminum ratio of the nano-hollow Beta molecular sieve is 15–100.

[0043] The nano-hollow Beta molecular sieve has a hollow structure.

[0044] The particle size of the nano-hollow Beta molecular sieve is 25–90 nm.

[0045] Optionally, the particle size of the nano-hollow Beta molecular sieve is any value among 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, and 90nm, or any value between two of them.

[0046] The advantages of this application are:

[0047] The nano-hollow Beta molecular sieve synthesized by the method described in this application has the advantages of both nano-size and hollow interior, and no organic template agent is used in the preparation process, resulting in short crystallization time and good product crystallinity. Attached Figure Description

[0048] Figure 1 This is the X-ray diffraction pattern of the nano-hollow Beta molecular sieve obtained in Example 1 of this application;

[0049] Figure 2 This is a TEM image of the nano-hollow Beta molecular sieve obtained in Example 1 of this application. Detailed Implementation

[0050] The present application will be further illustrated by the following embodiments, but the embodiments do not limit the content of the present application.

[0051] Example 1:

[0052] Using solid silica gel as the silicon source, sodium aluminate as the aluminum source, sodium hydroxide as the inorganic base, sodium chloride as the inorganic salt, and high-silica Beta molecular sieve powder with a SiO2 / Al2O3 ratio of 100 as seed crystals, the specific formulation (molar ratio) of the synthesis system is as follows: Al2O3 / SiO2 = 0.0025, NaOH / SiO2 = 0.05, NaCl / SiO2 = 0.10, H2O / SiO2 = 5, and the amount of high-silica Beta seed crystals is 30%. After the raw materials are mixed evenly, they are transferred to a crystallization kettle and dynamically crystallized in an oven at 140℃ for 12 hours. Nano-hollow Beta molecular sieves are obtained through filtration, separation, and drying. The obtained nano-hollow Beta molecular sieves have good crystallinity, and their X-ray diffraction pattern is shown below. Figure 1 As shown; the sample morphology is as follows Figure 2 As shown, it exhibits a hollow structure with a particle size of 50 nm, and elemental analysis shows that its SiO2 / Al2O3 molar ratio is 100.

[0053] Example 2:

[0054] Using silica sol as the silicon source, aluminum sulfate as the aluminum source, potassium hydroxide as the inorganic base, potassium chloride as the inorganic salt, and high-silica Beta molecular sieve powder with a SiO2 / Al2O3 ratio of 500 as seed crystals, the specific formulation (molar ratio) of the synthesis system is as follows: Al2O3 / SiO2 = 0.0075, KOH / SiO2 = 0.15, KCl / SiO2 = 0.05, H2O / SiO2 = 10, and the amount of high-silica Beta seed crystals is 25%. After the raw materials are mixed evenly, they are transferred to a crystallization kettle and dynamically crystallized in an oven at 120℃ for 24 hours. Nano-hollow Beta molecular sieves are obtained through filtration, separation, and drying. The obtained nano-Beta molecular sieves have good crystallinity and exhibit a hollow structure with a particle size of 78 nm. Elemental analysis shows that its SiO2 / Al2O3 molar ratio is 80.

[0055] Example 3:

[0056] Using silica as the silicon source, aluminum nitrate as the aluminum source, ammonia as the inorganic base, ammonium chloride as the inorganic salt, and high-silica Beta molecular sieve powder with a SiO2 / Al2O3 ratio of 1000 as seed crystals, the specific formulation (molar ratio) of the synthesis system was as follows: Al2O3 / SiO2 = 0.01, NH4OH / SiO2 = 0.25, NH4Cl / SiO2 = 0.25, H2O / SiO2 = 15, and the amount of high-silica Beta seed crystals was 20%. After the raw materials were mixed evenly, they were transferred to a crystallization kettle and dynamically crystallized in an oven at 110℃ for 42 hours. Nano-hollow Beta molecular sieves were obtained through filtration, separation, and drying. The obtained nano-Beta molecular sieves exhibited good crystallinity and a hollow structure with a particle size of 75 nm. Elemental analysis showed that its SiO2 / Al2O3 molar ratio was 50.

[0057] Example 4:

[0058] Using silica gel powder as the silicon source, aluminum powder as the aluminum source, ammonia water as the inorganic base, sodium chloride as the inorganic salt, and pure silicon Beta molecular sieve powder as the seed crystal, the specific formulation (molar ratio) of the synthesis system is: Al2O3 / SiO2 = 0.05, NH4OH / SiO2 = 0.25, NH4Cl / SiO2 = 0.20, H2O / SiO2 = 20, with 5% pure silicon Beta seed crystals. After the raw materials are mixed evenly, they are transferred to a crystallization kettle and dynamically crystallized in a 100℃ oven for 48 hours. The nano-hollow Beta molecular sieve is obtained through filtration, separation, and drying. The obtained nano-Beta molecular sieve has good crystallinity and exhibits a hollow structure with a particle size of 90 nm. Elemental analysis shows that its SiO2 / Al2O3 molar ratio is 15.

[0059] Example 5:

[0060] Using silica gel as the silicon source, aluminum hydroxide as the aluminum source, sodium hydroxide as the inorganic base, lithium chloride as the inorganic salt, and pure silicon Beta molecular sieve powder as the seed crystal, the specific formulation (molar ratio) of the synthesis system is as follows: Al₂O₃ / SiO₂ = 0.025, NaOH / SiO₂ = 0.20, LiCl / SiO₂ = 0.20, H₂O / SiO₂ = 25, with 10% pure silicon Beta seed crystal. After the raw materials are mixed evenly, they are transferred to a crystallization kettle and dynamically crystallized in a 100℃ oven for 48 hours. The nano-hollow Beta molecular sieve is obtained through filtration, separation, and drying. The obtained nano-Beta molecular sieve has good crystallinity and exhibits a hollow structure with a particle size of 25 nm. Elemental analysis shows that its SiO₂ / Al₂O₃ molar ratio is 33.

[0061] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a nano-hollow Beta molecular sieve, characterized in that, Includes the following steps: Raw materials containing silicon source, aluminum source, inorganic alkali, inorganic salt, Beta seed crystals and water are mixed and reacted in a sealed container to obtain the nano-hollow Beta molecular sieve. The Beta seed crystals are selected from pure silicon Beta molecular sieve powder and / or high silicon Beta molecular sieve powder. The silicon-to-aluminum ratio of the Beta seed crystals is greater than or equal to 100; The reaction is a hydrothermal crystallization reaction; The reaction temperature is 100~140℃; The reaction time is 12-48 hours; The inorganic salt is selected from at least one of lithium chloride, sodium chloride, potassium chloride, and ammonium chloride; The molar ratio of the silicon source to the aluminum source is 1:0.0025~0.05; The molar ratio of the silicon source to the inorganic base is 1:0.05~0.25; The molar ratio of the silicon source to the inorganic salt is 1:0.05~0.25; The molar ratio of the silicon source to the water is 1:5~25; Wherein, the molar amount of the silicon source is expressed as the molar amount of silicon dioxide; The molar amount of the aluminum source is expressed as the molar amount of aluminum oxide; The amount of the Beta seed crystal is 5 to 30 wt% of the weight of the silicon source.

2. The preparation method according to claim 1, characterized in that, The silicon source is selected from at least one of silica gel, fumed silica, and silica sol. The aluminum source is selected from at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum hydroxide, and aluminum powder; The inorganic base is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

3. The preparation method according to claim 1, characterized in that, The reaction is followed by acid exchange; The acid exchange uses dilute sulfuric acid and / or dilute nitric acid with a concentration of 0.25~0.5M; The acid exchange temperature is 60~80℃; The acid exchange time is 4-8 hours; Stirring is performed during the acid exchange process.

4. A nano-hollow Beta molecular sieve, characterized in that, Prepared by the preparation method according to any one of claims 1 to 3.

5. The nano-hollow Beta molecular sieve according to claim 4, characterized in that, The silicon-to-aluminum ratio of the nano-hollow Beta molecular sieve is 15-100.

6. The nano-hollow Beta molecular sieve according to claim 4, characterized in that, The nano-hollow Beta molecular sieve has a hollow structure.

7. The nano-hollow Beta molecular sieve according to claim 4, characterized in that, The particle size of the nano-hollow Beta molecular sieve is 25~90nm.

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