Preparation method and application of sn-beta molecular sieve

Abstract

The application discloses a preparation method and application of Sn-Beta molecular sieve, and belongs to the technical field of chemical synthesis and catalysts. The method comprises the following steps: adding pure silicon Beta molecular sieve seeds into raw materials containing a silicon source, an inorganic salt M, an organic template agent R1, an organic template agent R2 and water, and performing first crystallization; and adding a tin source into the obtained mixture, and performing second crystallization to obtain the Sn-Beta molecular sieve.

Description

Technical Field

[0001] This application belongs to the field of chemical synthesis and catalyst technology, specifically relating to a method for preparing Sn-Beta molecular sieves and their applications. Background Technology

[0002] As is well known, my country is a resource-rich country with abundant natural resources, but due to its large population, the per capita resource availability is not high. With increasing environmental awareness, alternative routes for petrochemical products using renewable resources as raw materials are receiving growing attention. Biomass is a widely available and sustainably utilized renewable resource, with glucose, as a typical example, already widely used. The preparation of lactate esters from glucose alcoholysis is an important chemical reaction. Lactate esters, as a commonly used, high-value-added platform chemical in industry, are widely applied in various sectors such as food, pharmaceuticals, and cosmetics.

[0003] Currently, Sn-Beta molecular sieves are frequently used as catalysts in the preparation of lactate esters from glucose alcoholysis. As a typical representative of metal-substituted molecular sieves, Sn-Beta molecular sieves introduce Lewis acid centers by implanting tin (Sn) atoms into the *BEA framework.

[0004] The synthesis methods of Sn-Beta molecular sieves are mainly divided into direct synthesis and post-treatment methods. The post-treatment method typically uses commercially available Al-Beta molecular sieves as the parent material, generating framework vacancies through nitric acid dealumination, and then grafting Sn sources onto these vacancies using various methods to obtain Sn-Beta molecular sieves. This method involves lengthy synthesis steps, requires strong acids, is hazardous, and easily causes environmental pollution. Furthermore, the resulting product has poor hydrophobicity due to numerous defect sites; and the introduction of Sn into the framework is difficult, easily forming exoskeletal tin. The direct synthesis method typically uses fluoride ions as a mineralizing agent. The product obtained through this method has good crystallinity and adjustable Sn content, with fewer internal defect sites, exhibiting high hydrophobicity, which is beneficial for improving catalytic performance in aqueous systems. However, the long crystallization time (approximately 20 days), low upper limit of Sn content, and large crystal size all restrict the industrialization of this method, and it often requires the use of hydrofluoric acid, leading to equipment corrosion and environmental pollution. The technology for the direct synthesis of Sn-Beta molecular sieves without fluorine is currently progressing slowly. Although the dry gel synthesis method can achieve fluorine-free synthesis, the synthesis process is cumbersome and the resulting product has many defect sites, poor hydrophobicity, and unsatisfactory catalytic activity. Summary of the Invention

[0005] This application provides a method for directly synthesizing Sn-Beta molecular sieves in a fluorine-free environment. This method promotes the synthesis of Sn-Beta molecular sieves in a green and safe manner by adding pure silicon molecular sieve seeds and introducing alkali metal / alkaline earth metal ions into the gel system used for synthesis, and adding a tin source after crystallization under specific conditions.

[0006] According to one aspect of this application, a method for preparing Sn-Beta molecular sieves is provided, comprising:

[0007] Pure silicon Beta molecular sieve seed crystals were added to a raw material containing a silicon source, inorganic salt M, organic template agent R1, organic template agent R2, and water to perform the first crystallization; and

[0008] A tin source was added to the resulting mixture to perform a second crystallization, thereby obtaining the Sn-Beta molecular sieve.

[0009] Optionally, the method includes the following steps:

[0010] a) Mix the raw materials containing silicon source, inorganic salt M, organic template agent R1, organic template agent R2 and water to obtain an initial gel;

[0011] b) Add pure silicon Beta molecular sieve seed crystals to the initial gel obtained in step a) to obtain a synthetic gel;

[0012] c) The synthetic gel obtained in step b) is subjected to a first crystallization, which includes crystallization at 120-160°C for 0.25-2.5 days;

[0013] d) Add a tin source to the mixture obtained in step c) and carry out a second crystallization, the second crystallization including crystallization at 110-170°C for 0.5-5.5 days;

[0014] e) Centrifuge, wash, and dry the product obtained in step d) to obtain the Sn-Beta molecular sieve.

[0015] Optionally, in step a), the molar ratio of each component in the initial gel is:

[0016] SiO2∶M∶R1∶R2∶H2O=1.0∶0.05-0.4∶0.15-0.45∶0.05-0.35∶6-20

[0017] Wherein, the number of moles of the silicon source is calculated based on the number of moles containing SiO2; the number of moles of the organic template agent R1 is calculated based on the number of moles of R1 itself; the number of moles of the organic template agent R2 is calculated based on the number of moles of R2 itself; and the number of moles of the inorganic salt M is calculated based on the number of moles of M itself.

[0018] Optionally, in step a), the silicon source is at least one selected from silicon powder, silica, organosilicone esters and silica sol.

[0019] Optionally, in step a), the organic template agent R1 is at least one selected from tetraethylammonium hydroxide, triethyl-hydroxyethylammonium hydroxide, tetrapropylammonium hydroxide, tripropyl-hydroxyethylammonium hydroxide, and tetrabutylammonium hydroxide;

[0020] Optionally, in step a), the organic template agent R2 is selected from at least one of tetrapropylammonium bromide, tripropyl-isobutylammonium bromide, tetrabutylammonium chloride, tetraethylammonium chloride, tetraethylammonium bromide, N,N,N-tripropyl-adamantylammonium chloride and N,N,N-triethyl-adamantylammonium chloride;

[0021] Optionally, in step a), the inorganic salt M is at least one selected from sodium chloride, potassium chloride, magnesium chloride, sodium bromide, potassium bromide, magnesium bromide, sodium sulfate, potassium sulfate, and magnesium sulfate.

[0022] Optionally, in step b), the amount of pure silicon Beta molecular sieve seed crystals added is 1-10% of the mass of SiO2 contained in the silicon source.

[0023] Optionally, in step b), the pure silicon Beta molecular sieve seed crystals are used after being calcined at 500-800°C.

[0024] Optionally, in step d), the tin source is at least one selected from tin tetrachloride pentahydrate, stannous chloride dihydrate, and dimethyl tin dichloride.

[0025] Optionally, in step d), the molar ratio of the tin source to the silicon source is:

[0026] SiO2∶SnO2=1.0∶0.001-0.020, wherein the molar number of the tin source is calculated in terms of the molar number of SnO2, and the molar number of the silicon source is calculated in terms of the molar number of SiO2.

[0027] Optionally, in step d), the upper limit of the amount of tin source added is independently selected from 1 / 50, 1 / 60, 1 / 70, 1 / 80, 1 / 90, 1 / 100, 1 / 110, 1 / 120, 1 / 130, 1 / 140, 1 / 150, 1 / 160, 1 / 170, 1 / 180, 1 / 190, 1 / 200, 1 / 300, 1 / 400, 1 / 500, 1 / 600, 1 / 700, 1 / 800, and 1 / 900. The lower limit is independently selected from 1 / 60, 1 / 70, 1 / 80, 1 / 90, 1 / 100, 1 / 110, 1 / 120, 1 / 130, 1 / 140, 1 / 150, 1 / 160, 1 / 170, 1 / 180, 1 / 190, 1 / 200, 1 / 300, 1 / 400, 1 / 500, 1 / 600, 1 / 700, 1 / 800, 1 / 900, and 1 / 1000, based on the number of moles of SiO2 contained in the silicon source.

[0028] Optionally, in step c), the upper limit of the temperature for the first crystallization is independently selected from 160°C, 157°C, 155°C, 152°C, 150°C, 148°C, 145°C, 143°C, 140°C, 138°C, 135°C, 132°C, 130°C, 127°C, 125°C, and 122°C, and its lower limit is independently selected from 157°C, 155°C, 152°C, 150°C, 148°C, 145°C, 143°C, 140°C, 138°C, 135°C, 132°C, 130°C, 127°C, 125°C, 122°C, and 120°C.

[0029] Optionally, in step c), the upper limit of the first crystallization time is independently selected from 2.5 days, 2.25 days, 2 days, 1.75 days, 1.5 days, 1.25 days, 1 day, 0.75 days, and 0.5 days, and the lower limit is independently selected from 2.25 days, 2 days, 1.75 days, 1.5 days, 1.25 days, 1 day, 0.75 days, 0.5 days, and 0.25 days.

[0030] Optionally, in step d), the upper limit of the second crystallization temperature is independently selected from 170°C, 165°C, 160°C, 155°C, 150°C, 145°C, 140°C, 135°C, 130°C, 125°C, 120°C, and 115°C, and the lower limit is independently selected from 165°C, 160°C, 155°C, 150°C, 145°C, 140°C, 135°C, 130°C, 125°C, 120°C, 115°C, and 110°C.

[0031] Optionally, in step d), the upper limit of the second crystallization time is independently selected from 5.5 days, 5 days, 4.5 days, 4 days, 3.5 days, 3 days, 2.5 days, 2 days, 1.5 days, and 1 day, and the lower limit is independently selected from 5 days, 4.5 days, 4 days, 3.5 days, 3 days, 2.5 days, 2 days, 1.5 days, 1 day, and 0.5 days.

[0032] Optionally, in step c), the first crystallization includes crystallization at 130-150°C for 0.5-2 days.

[0033] Preferably, in step c), the first crystallization includes crystallization at 135-145°C for 0.75-1.5 days.

[0034] Optionally, in step d), the second crystallization includes crystallization at 120-160°C for 1-5 days.

[0035] Preferably, in step d), the second crystallization includes crystallization at 140-150°C for 1.5-4 days.

[0036] Optionally, in steps c) and d), the first crystallization and the second crystallization are carried out independently under autogenous pressure.

[0037] Optionally, in steps c) and d), the first crystallization and the second crystallization are performed independently under static or dynamic conditions. That is, in the method of this application, the crystallization mode in steps c) and d) can be either dynamic crystallization or static crystallization, or a combination of the two crystallization modes.

[0038] In this application, dynamic crystallization refers to the slurry in the crystallization vessel being in a non-static state, while static crystallization refers to the slurry in the crystallization vessel being in a static state.

[0039] In the method of this application, there are no particular limitations on the centrifugation, washing, and drying in step e). In one embodiment, the drying is performed by placing the product at 80-110°C for 10 hours.

[0040] In one specific implementation, the synthesis process of the Sn-Beta molecular sieve is as follows:

[0041] a1) Preparation of initial gel: The silicon source, inorganic salt M, organic template agent R1, organic template agent R2 and deionized water were mixed and stirred evenly at room temperature according to the molar ratio of SiO2:M:R1:R2:H2O = 1.0:0.05-0.2:0.2-0.4:0.05-0.2:6-10 to obtain the initial gel;

[0042] b1) Preparation of synthetic gel: Add 1-10% pure silicon Beta molecular sieve seed crystals based on SiO2 by mass to the obtained initial gel, stir for 7-10 hours to obtain synthetic gel;

[0043] c1) First crystallization: The resulting synthetic gel is subjected to first crystallization at 130-150℃ and autogenous pressure for 0.5-2 days;

[0044] d1) Second crystallization: Add Sn source to the mixture obtained above, stir evenly, and carry out second crystallization for 1.5-5 days at 120-160℃ and autogenous pressure;

[0045] e1) Preparation of Sn-Beta molecular sieve: The product obtained above is centrifuged, the solid is washed with deionized water until neutral, and dried to obtain Sn-Beta molecular sieve.

[0046] According to another aspect of this application, a Sn-Beta molecular sieve is provided, which is prepared by the method described above.

[0047] Optionally, the Sn-Beta molecular sieve includes micropores, the specific surface area of ​​which is 450-650 m². 2 / g, the volume of the micropores is 0.15-0.3cm. 3 / g.

[0048] Optionally, the Sn-Beta molecular sieve is a truncated octahedron.

[0049] Optionally, the Sn-Beta molecular sieve has a particle size of 0.2-0.6 μm.

[0050] According to another aspect of this application, a catalyst is provided, said catalyst comprising the Sn-Beta molecular sieve as described above.

[0051] According to another aspect of this application, a method for preparing the above-mentioned catalyst is provided, the method comprising: subjecting the Sn-Beta molecular sieve powder to ammonium exchange, and then calcining it at 550-700℃ for 1-8 hours. This application does not impose any particular limitation on the ammonium exchange process. The purpose of ammonium exchange is to remove alkali metal or alkaline earth metal ions contained in the molecular sieve powder before calcination, which is beneficial to maintaining the microstructure of the molecular sieve after calcination.

[0052] According to another aspect of this application, the application of the Sn-Beta molecular sieve as described above or the catalyst as described above in Lewis acid catalytic reactions is provided.

[0053] The beneficial effects that this application can produce include:

[0054] 1) The method for preparing Sn-Beta molecular sieve provided in this application involves adding pure silicon molecular sieve seeds to the gel system used for synthesis and introducing alkali metal / alkaline earth metal ions for direct synthesis. The synthesis process is simple and the crystallization speed is fast.

[0055] 2) The Sn-Beta molecular sieve preparation method provided in this application involves adding a tin source after crystallization under specific conditions, without the need to use fluoride ions as a mineralizing agent, making it green, environmentally friendly, and highly safe. Attached Figure Description

[0056] Figure 1 Comparison of X-ray powder diffraction (XRD) spectra of Sample 1 and Comparison Sample 1.

[0057] Figure 2 This is a scanning electron microscope (SEM) image of sample 1.

[0058] Figure 3 The UV-Vis spectra of samples 6 and 31 are shown.

[0059] Figure 4 To compare the ultraviolet-visible (UV-vis) spectrum of sample 1.

[0060] Figure 5 To compare the X-ray powder diffraction (XRD) pattern of sample 2.

[0061] Figure 6 To compare the X-ray powder diffraction (XRD) pattern of sample 3.

[0062] Figure 7 To compare the X-ray powder diffraction (XRD) pattern of sample 4. Detailed Implementation

[0063] As mentioned above, the purpose of this application is to provide a method for preparing Sn-Beta molecular sieves. This method involves adding pure silicon molecular sieve seeds to a gel system used for synthesis and introducing alkali metal / alkaline earth metal ions, while controlling the timing of adding the tin source during the crystallization process, thereby synthesizing Sn-Beta molecular sieves.

[0064] The present application is further described below with reference to embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0065] Experimental methods not specified in the following examples are generally performed under standard conditions or as recommended by the manufacturer.

[0066] Unless otherwise specified, all raw materials used in this application were purchased commercially and used directly without special treatment.

[0067] The instruments and methods used for analysis in the embodiments of this application are as follows:

[0068] Elemental composition was determined using a Philips Magix 2424 X-ray fluorescence analyzer (XRF).

[0069] X-ray powder diffraction (XRD) phase analysis was performed using an X'Pert PRO X-ray diffractometer from PANalytical, Netherlands, with a Cu target, a Kα radiation source (λ = 0.15418 nm), a voltage of 40 kV, and a current of 40 mA.

[0070] Scanning electron microscopy (SEM) tests were performed using a Hitachi SU8020 field emission scanning electron microscope with an accelerating voltage of 2kV.

[0071] The specific surface area and pore size distribution of the samples were determined using an ASAP 2020 physical adsorption analyzer from Micromeritics, USA. Before analysis, the samples were pretreated by vacuum heating at 350℃ for 6 h, and the free volume of the sample tube was measured using He as the medium. During analysis, nitrogen was used as the adsorbate gas, and physical adsorption and desorption were measured at liquid nitrogen temperature (77 K). The specific surface area of ​​the material was determined using the BET formula. The total pore volume of the material was calculated using the amount of N2 adsorbed at a relative pressure (P / P0) of 0.99. The micropore specific surface area and micropore volume were calculated using the t-plot method. In the calculations, the cross-sectional area of ​​the N2 molecule was taken as 0.162 nm. 2 .

[0072] The ultraviolet-visible spectra were measured using a VARIAN Cary-5000 UV-Vis-NIR spectrometer, with a scanning range of 200-800 nm.

[0073] Example 1

[0074] The proportions of raw materials and crystallization conditions are shown in Table 1. The sample preparation process is as follows:

[0075] Dissolve 0.41g tetraethylammonium chloride (TEACl), 7.41g tetraethylammonium hydroxide (35wt%) and 0.51g sodium chloride in 1.52g deionized water and stir until clear. Then add 3.00g solid silica powder and stir for 0.5h. Add 0.3g pure silicon Beta zeolite as seed crystals and continue stirring for 7.5h.

[0076] The synthesized gel obtained above was transferred to a stainless steel reactor and crystallized by rotation at 140°C and autogenous pressure for 1 day. Then, 0.29 g of tin tetrachloride pentahydrate was added to the resulting mixture, and after stirring for 0.5 h, it was transferred back to the stainless steel reactor and crystallized by rotation at 140°C and autogenous pressure for 3 days. After crystallization, solid-liquid separation was performed, and the solid product was washed until neutral and dried at 100°C for 10 h, which was recorded as sample 1.

[0077] The X-ray powder diffraction (XRD) pattern of sample 1 is shown below. Figure 1 As shown, this indicates that the sample is a molecular sieve with a *BEA framework structure. Ammonium exchange was performed on sample 1, with the following steps: Sample 1 was mixed with a 1 mol / L ammonium chloride aqueous solution at a solid-liquid ratio of 1:50, stirred for 1 hour in an 80℃ water bath, and the solid was separated by centrifugation. This process was repeated once. The ammonium-exchanged sample 1 was calcined at 550℃ for 5 hours to remove the template agent, and then its microporous specific surface area and pore volume were measured. The microporous specific surface area and pore volume of this sample were calculated using the t-plot method to be 401 m². 2 ·g -1 and 0.32cm 3 ·g -1 The scanning electron microscope (SEM) image of sample 1 is shown below. Figure 2 As shown, the sample particles have a truncated octahedral structure with a size of approximately 200-600 nm.

[0078] Example 2-31

[0079] The proportions of raw materials and crystallization conditions are shown in Table 1. Samples were prepared according to the process described in Example 1, and the resulting samples were designated as Samples 2-31.

[0080] The samples were analyzed by XRD and XRF. The results showed that samples 2-31 prepared in Examples 2-31 were all high-purity, high-crystallinity Sn-Beta molecular sieves, and their morphology was similar to that of sample 1 prepared in Example 1.

[0081] Table 1. Raw material types, proportions, seed crystal addition amount, crystallization conditions, and yields of samples 1-31

[0082]

[0083]

[0084] R1 a : Tetraethylammonium hydroxide; R1 b Tripropyl-hydroxyethylammonium hydroxide; R1 c : Tetrapropylammonium hydroxide; R1 d Tetrabutylammonium hydroxide; R1 eTriethyl-hydroxyethylammonium hydroxide

[0085] R2 a Tetraethylammonium chloride; R2 b : Tetraethylammonium bromide; R2 c Tetrabutylammonium chloride; R2 d N,N,N-tripropyl-adamantyl ammonium chloride

[0086] M a Sodium chloride; M b Potassium chloride; M c Magnesium chloride; M d Magnesium bromide; M e Potassium bromide

[0087] SiO2 a Silicon powder; SiO2 b : Silica; SiO2 c Tetraethyl orthosilicate; SiO2 d Silica sol

[0088] SnO2 a : Tin tetrachloride pentahydrate; SnO2 b : Stannous chloride dihydrate; SnO2 c Dimethyltin dichloride

[0089] Example 32

[0090] Following the same procedure described in Example 1, the raw powder samples obtained in Examples 6, 30, and 31 were subjected to ammonium exchange and calcination treatment. The Sn content analysis results of samples 1, 6, 30, and 31 by XRF are shown in Table 2. The UV-Vis spectra of samples 6 and 31 are illustrated in... Figure 3 The results showed that samples 6 and 31 both exhibited strong absorption peaks at approximately 220 nm, which can be attributed to tetracoordinated skeletal Sn species.

[0091] Table 2 Sn content results for samples 1, 6, 30 and 31

[0092] Example Sn content (mass fraction) 1 3.03％ 6 3.40％ 30 0.52％ 31 1.45％

[0093] Comparative Example 1

[0094] The sample was prepared according to the procedure in Example 1, except that the Sn source (tin tetrachloride pentahydrate) was directly added to the initial gel. The resulting sample was designated as Control Sample 1.

[0095] XRD and XRF analyses were performed on control sample 1, and the results were compared with those of control sample 1. Figure 1As shown in the figure. The results indicate that control sample 1 is also a Sn-Beta molecular sieve, but its relative crystallinity is lower than that of sample 1. Control sample 1 was subjected to ammonium exchange and calcined to remove the template agent before UV-Vis testing, and the results are shown in the figure. Figure 4 As shown, it reveals the presence of numerous skeletal tin species.

[0096] Comparative Example 2

[0097] The sample was prepared according to the procedure in Example 1, except that the organic template agent R2 was not added. The resulting sample was designated as Control Sample 2.

[0098] XRD analysis was performed on control sample 2, and the results are as follows: Figure 5 As shown, this indicates that the sample is a mixture of Sn-Beta and ZSM-5.

[0099] Comparative Example 3

[0100] The sample was prepared according to the procedure in Example 1, except that the amount of water added was reduced, and the molar ratio of deionized water in the gel system was reduced to 4. The resulting sample was designated as Control Sample 3.

[0101] XRD analysis was performed on control sample 3, and the results are as follows: Figure 6 As shown, this indicates that the sample contains a layered phase in addition to Sn-Beta.

[0102] Comparative Example 4

[0103] The sample was prepared according to the procedure in Example 1, except that inorganic salt M was not added. The resulting sample was designated as control sample 4.

[0104] XRD analysis was performed on control sample 4, and the results are as follows: Figure 7 As shown, this indicates that the sample has low crystallinity and contains a large amount of amorphous material.

[0105] The above descriptions are merely several embodiments of this application and are not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, these embodiments are not intended to limit this application. Any modifications or alterations made by those skilled in the art using the disclosed technical content without departing from the scope of the technical solution of this application are equivalent to equivalent implementations and fall within the scope of the technical solution of this application.

Claims

1. A method for preparing Sn-Beta molecular sieves, characterized in that, The preparation steps are as follows: a) Mix the raw materials containing silicon source, inorganic salt M, organic template agent R1, organic template agent R2 and water to obtain an initial gel; b) Add pure silicon Beta molecular sieve seed crystals to the initial gel obtained in step a) to obtain a synthetic gel; c) The synthetic gel obtained in step b) is subjected to a first crystallization, which includes crystallization at 120-160°C for 0.25-2.5 days; d) Add a tin source to the mixture obtained in step c) and perform a second crystallization, the second crystallization comprising crystallization at 110-170°C for 0.5-5.5 days; e) Centrifuge, wash, and dry the product obtained in step d) to obtain the Sn-Beta molecular sieve; in, In step a), the molar ratio of each component in the initial gel is: SiO2∶M∶R1∶R2∶H2O=1.0∶0.05-0.4∶0.15-0.45∶0.05-0.35∶6-20 Wherein, the number of moles of the silicon source is calculated based on the number of moles containing SiO2; the number of moles of the organic template agent R1 is calculated based on the number of moles of R1 itself; the number of moles of the organic template agent R2 is calculated based on the number of moles of R2 itself; and the number of moles of the inorganic salt M is calculated based on the number of moles of M itself. The organic template agent R1 is selected from at least one of tetraethylammonium hydroxide, triethyl-hydroxyethylammonium hydroxide, tetrapropylammonium hydroxide, tripropyl-hydroxyethylammonium hydroxide, and tetrabutylammonium hydroxide; The organic template agent R2 is selected from at least one of tetrapropylammonium bromide, tripropyl-isobutylammonium bromide, tetrabutylammonium chloride, tetraethylammonium chloride, tetraethylammonium bromide, N,N,N-tripropyl-adamantylammonium chloride, and N,N,N-triethyl-adamantylammonium chloride; The inorganic salt M is selected from at least one of sodium chloride, potassium chloride, magnesium chloride, sodium bromide, potassium bromide, magnesium bromide, sodium sulfate, potassium sulfate, and magnesium sulfate; In step b), the amount of pure silicon Beta molecular sieve seed crystals added is 1-10% of the mass of SiO2 contained in the silicon source; In step d), the molar ratio of the tin source to the silicon source is: SiO2∶SnO2=1.0∶0.001-0.020, wherein the number of moles of the tin source is calculated as the number of moles of SnO2, and the number of moles of the silicon source is calculated as the number of moles of SiO2.

2. The method according to claim 1, characterized in that, In step a), the silicon source is at least one selected from silicon powder, silica, organosilicone ester and silica sol.

3. The method according to claim 1, characterized in that, In step b), the pure silicon Beta molecular sieve seed crystals are used after being calcined at 500-800℃.

4. The method according to claim 1, characterized in that, In step d), the tin source is at least one selected from tin tetrachloride pentahydrate, stannous chloride dihydrate, and dimethyl tin dichloride.

5. The method according to claim 1, characterized in that, In step c), the first crystallization includes 130-150 °C. o Crystallization at C for 0.5-2 days.

6. The method according to claim 1, characterized in that, In step d), the second crystallization includes 120-160 o Crystallize at C for 1-5 days.

7. The method according to claim 1, characterized in that, In steps c) and d), the first crystallization and the second crystallization are performed independently under static or dynamic conditions.

8. A Sn-Beta molecular sieve, characterized in that, Prepared by the method according to any one of claims 1 to 7.

9. The Sn-Beta molecular sieve according to claim 8, characterized in that, The Sn-Beta molecular sieve comprises micropores, the specific surface area of ​​which is 450-650 m². 2 / g, the volume of the micropores is 0.15-0.3 cm³. 3 / g; And / or the Sn-Beta molecular sieve is a truncated octahedron; And / or the Sn-Beta molecular sieve has a particle size of 0.2-0.6 μm.

10. A catalyst, characterized in that, Including the Sn-Beta molecular sieve according to claim 8.

11. The application of the Sn-Beta molecular sieve according to claim 8 or 9 or the catalyst according to claim 10 in Lewis acid catalytic reactions.

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