Synthesis method of nano titanium silicalite molecular sieve TS-2

Abstract

A synthesis method of a nano titanium silicalite molecular sieve TS-2 belongs to the field of synthesis of titanium silicalite molecular sieves, aims to improve the content of hexa-coordinated titanium species of the TS-2 molecular sieve and reduce the particle size, and is technically characterized by comprising the following steps: mixing a silicon source, a template agent and water according to a certain proportion, and performing condensation, reflux and stirring to form a seed crystal solution; the method comprises the following steps: mixing a silicon source, a template agent and water according to a certain proportion, and stirring to obtain a first mixed solution; adding a titanium source into isopropanol, and stirring to obtain a second mixed solution; adding the second mixed solution into the first mixed solution, and stirring to remove alcohol to obtain a precursor solution; mixing ammonium salt and deionized water according to a certain proportion, adding the mixture into the precursor solution, and stirring to obtain a first precursor solution; adding the seed crystal solution into the first precursor solution, and stirring to obtain a crystallization solution; crystallizing the crystallized liquid to obtain a crystallized product; and filtering, washing, drying and roasting the crystallized product to obtain the TS-2 molecular sieve which can be used as a catalyst for a macromolecular selective oxidation reaction.

Description

Technical Field

[0001] The invention belongs to the field of molecular sieve synthesis and relates to a method for synthesizing nano titanium silicon molecular sieve TS-2. Background Art

[0002] Titanium silicate TS-2 is a titanium-containing heteroatom molecular sieve with a MEL topology. Its synthesis was first reported by Reddy et al. in the 1990s (Appl. Catal., A 1990, 58, L1-L4). Since then, TS-2 has gained increasing attention as an environmentally friendly catalytic oxidation catalyst. The MEL topology contains straight 10-membered ring channels along both the a- and b-axes, with pore dimensions of 0.54 nm × 0.53 nm. Compared to the MFI topology, which contains one straight channel and one zigzag channel, the MEL structure is generally considered to have superior diffusion properties. Therefore, TS-2 is often used to catalyze the selective oxidation of larger molecules.

[0003] Under typical hydrothermal synthesis conditions, the morphology of TS-2 prepared is typically micron-sized spherical agglomerates ranging from 2 to 12 μm (Microporous Mesoporous Mater. 2004, 69, 197; Catal. Commun. 2004, 5, 359). Larger particle size results in a smaller surface area of TS-2 and longer diffusion paths for reactants and products within the pores, which is detrimental to catalytic performance.

[0004] Chinese patent CN112744831A discloses a method for preparing a titanium-containing molecular sieve. The method comprises mixing titanium silicon oxide, a template, a second silicon source, a seed crystal, a liquid titanium silicon molecular sieve synthesis precursor, water, and an inorganic ammonium source to obtain a second mixture, which is then crystallized. The titanium-containing molecular sieve produced by this method exhibits good activity in the ammoxidation reaction of cyclohexanone.

[0005] Xu et al. synthesized dispersed submicron TS-2 particles by introducing an organic amine ligand, piperidine (Chin. J. Catal. 2020, 41, 1109). Zhang et al. synthesized submicron TS-2 particles with extremely low Ti content by manipulating the Si / Ti molar ratio of the synthetic gel (AIChE J. 2020, 66, e16815).

[0006] The catalytic performance of TS-2 zeolite depends on its diffusion performance and the coordination state of titanium species. There are at least three types of titanium species in TS-2, including tetracoordinated titanium, anatase TiO2, and hexacoordinated titanium (Small 2024, 20, 2406294). Currently, there is little research on the catalytic activity of titanium species in TS-2. However, it can be inferred from the research on TS-1 that the main active center for catalytic oxidation is still tetracoordinated titanium, and hexacoordinated titanium with certain specific structures also has catalytic activity.

[0007] Generally speaking, the MEL straight channels of TS-2 can reduce the diffusion limitation to a certain extent, but its relatively large particle size still has a negative impact on the catalytic performance. Moreover, there are few reports on the methods for regulating the active titanium species in TS-2. Therefore, developing a synthesis method that can reduce the particle size of TS-2 and simultaneously regulate the coordination state of titanium species has important practical significance for the practical application of TS-2.

[0008] Existing technologies have shown that the addition of ammonium salts during the synthesis of TS-1 will inhibit the formation of hexacoordinated titanium (Microporous Mesoporous Mater. 2009, 122, 301). However, the inventors found that for the preparation of TS-2, by adding ammonium salts to the precursor solution and adding seeds to the precursor solution containing ammonium salts, through the combined action of seeds and ammonium salts, not only the content of hexacoordinated titanium species in the molecular sieve is increased, but also the particle size of TS-2 is reduced. Recently, many literature reports have shown that hexacoordinated titanium species have higher catalytic oxidation activity than tetracoordinated titanium (Chem. Eur. J., 2012, 18, 13854, Chem. Commun., 2015, 51, 9010, AIChE J. 2021, e17261, Appl. Cata. B, 2023, 325, 122396).

[0009] CN 115259177 A discloses a hierarchical pore ZSM-5 molecular sieve for VOCs adsorption, its preparation method and application. Specifically, an aluminum source, a silicon source, an alkali source, ZSM-5 molecular sieve seeds and water are mixed uniformly to form a gel; the obtained gel is pre-crystallized in a reaction kettle to obtain a pre-crystallized product; after the obtained pre-crystallized product is cooled, a template agent is added, and after stirring, the temperature is raised for crystallization reaction; the crystallized product after the reaction is subjected to solid-liquid separation, washing, drying, and calcination to obtain a molecular sieve raw powder; the prepared raw material is subjected to acid leaching treatment with an acid solution and then calcined to obtain a molecular sieve precursor; the obtained precursor is placed in an ammonium salt solution for ion exchange to obtain an ammonia-type ZSM-5 molecular sieve, and after calcination, an HZSM-5 molecular sieve is obtained. However, after crystallization, the precursor is placed in an ammonium salt solution for ion exchange to obtain an ammonia-type ZSM-5 molecular sieve, which is ammonium exchange with an ammonium salt to exchange the sodium ions on ZSM-5 into ammonium ions, and then the ammonium ions are turned into hydrogen ions by calcination. The particle size of ZSM-5 is fixed before ammonium exchange, and it does not have the function of adjusting the particle size and increasing the content of six-coordinated titanium species in the molecular sieve. Summary of the Invention

[0010] To solve the problem of increasing the content of six-coordinated titanium species in TS-2 molecular sieve and reducing the particle size, in the first aspect, according to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, it includes: Mix a silicon source, a template agent and water in a certain proportion, and perform condensation reflux stirring to form a seed solution; Mix a silicon source, a template agent and water in a certain proportion, and stir to obtain a first mixed solution; Add a titanium source to isopropyl alcohol and stir to obtain a second mixed solution; Add the second mixed solution to the first mixed solution and stir to remove alcohol to obtain a precursor solution; Mix an ammonium salt and deionized water in a certain proportion, add it to the precursor solution, and stir to obtain a first precursor solution; Add the seed solution to the first precursor solution and stir to obtain a crystallization solution; Crystallize the crystallization solution to obtain a crystallized product; Filter, wash, dry and calcine the crystallized product to prepare the TS-2 molecular sieve.

[0011] According to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, wherein the silicon source is at least one of tetraethyl orthosilicate and silica sol; The template agent is at least one of tetrabutylammonium hydroxide and tetrabutylammonium bromide; The titanium source can be selected from at least one of tetrabutyl titanate, tetraethyl titanate, titanium oxysulfate and titanium tetrachloride; The ammonium salt is at least one of ammonium carbonate, ammonium bicarbonate, ammonium sulfate, ammonium bisulfate, and ammonium chloride.

[0012] According to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, wherein the molar ratio of the silicon source to the template agent in the seed solution is 1:(0.1~0.5); Preferably, the molar ratio of the silicon source to the template agent is 1:(0.2~0.3); Preferably, the molar ratio of the silicon source, the template agent, and water is 1:(0.1~0.5):(10~50).

[0013] According to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, the molar ratio of the silicon source to the template agent in the first mixed solution is 1:(0.1~0.8); Preferably, the molar ratio of the silicon source to the template agent is 1:(0.25~0.4); Preferably, the molar ratio of the silicon source, the template agent, and water is 1:(0.1~0.8):(10~80); Preferably, the molar ratio of the titanium source to isopropanol in the second mixed solution is 1:(5~30); More preferably, the molar ratio of the titanium source to isopropanol is 1:(5~15); Preferably, the molar ratio of the silicon source to the titanium source in the precursor solution is 1:(0.01~0.05); More preferably, the molar ratio of the silicon source to the titanium source is 1:(5~15).

[0014] According to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, in the step of mixing the ammonium salt and deionized water in a certain ratio, the molar ratio of the ammonium salt to deionized water is 1:(20~70); Preferably, the molar ratio of the ammonium salt to deionized water is 1:(30~50); Preferably, the molar ratio of the silicon source to the ammonium salt in the first precursor solution is 1:(0.05~0.15); Preferably, the molar ratio of the silicon source to the ammonium salt is 1:(0.05~0.10).

[0015] According to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, the mass ratio of the seed solution to the first precursor solution is 1:(50~200); Preferably, the mass ratio of the seed solution to the first precursor solution is 1:(100~120).

[0016] According to the synthesis method of nano-TS-2 molecular sieve in some embodiments of the present application, in the step of mixing the silicon source, the template agent, and water in a certain ratio, stirring to obtain the first mixed solution, the stirring temperature is 40°C and the stirring time is 5 h; Preferably, in the step of adding a titanium source into isopropanol and stirring to obtain a second mixed solution, the stirring temperature is room temperature and the stirring time is 0.5 - 2 h; More preferably, the titanium source is added into isopropanol in a dropwise manner.

[0017] Preferably, in the step of adding the second mixed solution into the first mixed solution and stirring to remove alcohol to obtain a precursor solution, the stirring temperature is 60 - 95 °C and the alcohol removal time is 0.5 - 2 h; More preferably, the second mixed solution is added into the first mixed solution in a dropwise manner and under stirring.

[0018] According to the synthesis method of nano - TS - 2 molecular sieve in some embodiments of the present application, in the step of mixing a silicon source, a template agent and water in a certain proportion, and carrying out condensation reflux and stirring to form a seed solution, the condensation reflux stirring temperature is 60 - 80 °C and the condensation reflux stirring time is 48 - 72 h; Preferably, in the step of mixing an ammonium salt and deionized water in a certain proportion, adding them into the precursor solution and stirring to obtain a first precursor solution, the stirring time is 10 - 30 min; Preferably, in the step of adding the seed solution into the first precursor solution and stirring to obtain a crystallization solution, the stirring time is 10 - 30 min.

[0019] Preferably, in the step of crystallizing the crystallization liquid, the crystallization is carried out in a crystallization autoclave, the crystallization temperature is 120 - 180 °C and the crystallization time is 12 - 72 h; In the step of filtering, washing, drying and calcining the crystallization product, the drying temperature is 60 - 120 °C and the drying time is 6 - 24 h; More preferably, the drying temperature is 80 - 100 °C and the drying time is 8 - 12 h; More preferably, the calcining temperature is 540 °C and the calcining time is 6 h.

[0020] In a second aspect, a nano - TS - 2 molecular sieve prepared by the synthesis method of nano - TS - 2 molecular sieve in some embodiments of the present application.

[0021] In a third aspect, the use of the molecular sieve according to some embodiments of the present application as a catalyst.

[0022] The use of the molecular sieve according to some embodiments of the present application as a catalyst in phenol hydroxylation, cyclohexene epoxidation and cyclohexanone ammoxidation reactions.

[0023] The beneficial effects of the present invention are: (1) In the TS-2 synthesis system of the present invention, seeds and ammonium salts are added. Experiments show that it can regulate the active titanium species, change the coordination state of titanium species in TS-2, and form six-coordinate titanium species with high catalytic oxidation activity.

[0024] (2) In the TS-2 synthesis system of the present invention, seeds and ammonium salts are added. Experiments show that it can achieve the regulation of diffusion performance. When only seeds are added to the TS-2 synthesis system, the morphology of small TS-2 crystals does not change, but the aggregates will break; while when seeds and ammonium salts are added to the precursor solution in the present invention, the morphology of TS-2 crystals changes significantly, turning into nanoscale monodisperse rod-like particles and no longer aggregating into micron-sized spherical particles, greatly reducing the particle size and significantly improving the diffusion performance of TS-2.

[0025] (3) Based on the common improvement of the content of the above six-coordinate titanium species and the diffusion performance of the present invention, the TS-2 molecular sieve of the present invention can exhibit excellent catalytic performance for larger molecule reactions such as phenol hydroxylation, cyclohexene epoxidation, cyclohexanone ammoxidation, etc. Description of the Drawings

[0026] Figure 1 are the X-ray diffraction patterns of the TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J samples synthesized in the examples of the present invention, and the TS-2-K and TS-2-L samples synthesized in the comparative examples.

[0027] Figure 2 are the scanning electron microscope photos of the TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J samples synthesized in the examples of the present invention, and the TS-2-K and TS-2-L synthesized in the comparative examples; among them, (a). TS-2-A, (b). TS-2-C, (c). TS-2-E, (d). TS-2-G, (e). TS-2-I, (f). TS-2-J, (g). TS-2-K, (h). TS-2-L.

[0028] Figure 3 are the ultraviolet-visible diffuse reflectance spectra of the TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J samples synthesized in the examples of the present invention, and the TS-2-K and TS-2-L samples synthesized in the comparative examples. Detailed Embodiments

[0029] The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0030] Term Explanation: Titanium silicalite TS-2: A titanium-containing heteroatom molecular sieve with a MEL-type topological structure.

[0031] TS-1 molecular sieve: A molecular sieve with an MFI structure.

[0032] The present invention aims to provide a method for synthesizing nano-TS-2 molecular sieve, which is achieved through the following steps: S1. Preparation of seed solution: Mix a silicon source, a template agent, and water in a certain ratio, and carry out condensation reflux stirring at 60 - 80 °C for 48 - 72 h to form a seed solution; S2. Preparation of precursor solution: Mix a silicon source, a template agent, and water in a certain ratio, and stir at 40 °C for 5 h to form a mixed solution A; Dropwise add a titanium source into isopropanol and stir at room temperature for 0.5 - 2 h to obtain a mixed solution B; Under stirring, dropwise add the mixed solution B into the mixed solution A, and after mixing, stir and heat up to 60 - 95 °C to remove alcohol for 0.5 - 2 h to obtain a precursor solution; S3. Preparation of crystallization solution: Mix an ammonium salt and deionized water to prepare a solution with a certain concentration, and slowly add it to the precursor solution, and stir for 10 - 30 min; Add the seed solution to the precursor solution and stir for 10 - 30 min; Obtain a crystallization solution; S4. Crystallization and post-treatment: Transfer the crystallization solution to a crystallization kettle, crystallize at 120 - 180 °C for 12 - 72 h to obtain a crystallization product, filter, wash, dry, and calcine it to obtain TS-2 molecular sieve.

[0033] Preferably, the silicon source in steps S1 and S2 is at least one of tetraethyl orthosilicate and silica sol; the template agent in steps S1 and S2 is at least one of tetrabutylammonium hydroxide and tetrabutylammonium bromide; the titanium source in step S2 can be selected from at least one of tetrabutyl titanate, tetraethyl titanate, titanium oxysulfate, and titanium tetrachloride; the ammonium salt in step S3 is at least one of ammonium carbonate, ammonium bicarbonate, ammonium sulfate, ammonium bisulfate, and ammonium chloride.

[0034] Preferably, the molar ratio of the silicon source to the template agent in step S1 is 1:(0.1 - 0.5); more preferably, the molar ratio is 1:(0.2 - 0.3).

[0035] Preferably, the molar ratio of the silicon source to water in step S1 is 1:(10 - 50); more preferably, the molar ratio is 1:(15 - 25).

[0036] Preferably, the molar ratio of the silicon source to the titanium source in the mixed solution A in step S2 is 1:(0.01 - 0.05); more preferably, the molar ratio is 1:(0.017 - 0.033).

[0037] Preferably, in step S2, the molar ratio of the silicon source to the template agent in the mixed solution A is 1:(0.1~0.8); more preferably, the molar ratio is 1:(0.25~0.4).

[0038] Preferably, in step S2, the molar ratio of the silicon source to water in the mixed solution A is 1:(10~80); more preferably, the molar ratio is 1:(30~50).

[0039] Preferably, in step S2, the molar ratio of the titanium source to isopropanol in the mixed solution B is 1:(5~30); more preferably, the molar ratio is 1:(5~15).

[0040] Preferably, in step S2, the mass ratio of the mixed solution A to the mixed solution B is 1:(0.5~20); more preferably, the molar ratio is 1:(1.5~4).

[0041] Preferably, in step S3, the molar ratio of the silicon source to the ammonium salt in the precursor solution is 1:(0.05~0.15); more preferably, the molar ratio is 1:(0.05~0.10).

[0042] Preferably, in step S3, the molar ratio of the ammonium salt to water is 1:(20~70); more preferably, the molar ratio is 1:(30~50).

[0043] Preferably, in step S3, the mass ratio of the seed solution to the precursor solution containing the ammonium salt is 1:(50~200); more preferably, the molar ratio is 1:(100~120).

[0044] Preferably, in step S4, the drying temperature is 60~120°C, and the drying time is 6~24 h; more preferably, the drying temperature is 80~100°C, and the drying time is 8~12 h.

[0045] Example 1: Preparation of nano-TS-2-A: Take 5 g of tetraethyl orthosilicate, 7.5 g of tetrabutylammonium hydroxide (25 wt%), and 8.7 g of deionized water, mix them, and condense and reflux with stirring at 80 °C for 72 h to form a seed solution. Take 15 g of tetraethyl orthosilicate, 5.6 g of tetrabutylammonium hydroxide, and 51.9 g of deionized water, mix them, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 0.61 g of tetrabutyl titanate into 10.8 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. While stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.35 g of ammonium carbonate, add it to 13 g of water, stir for 15 min to uniformly prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 24 h. After obtaining the crystallization product, filter to obtain a solid, wash it 3 times with deionized water, dry it at 100 °C for 10 h, and calcine it at 540 °C for 6 h to prepare nano-TS-2-A.

[0046] Example 2: Preparation of nano-TS-2-B: Take 5 g of silica sol (30 wt%), 7.8 g of tetrabutylammonium hydroxide (25 wt%), and 3.2 g of deionized water, mix them, and condense and reflux with stirring at 80 °C for 72 h to form a seed solution. Take 15 g of silica sol (mass fraction 30%), 6.4 g of tetrabutylammonium hydroxide, and 43.1 g of deionized water, mix them, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 0.63 g of tetraethyl titanate into 11.2 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. While stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.40 g of ammonium carbonate, add it to 16 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 36 h. After obtaining the crystallization product, dry it at 110 °C for 9 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-B.

[0047] Example 3: Preparation of nano-TS-2-C: Take 5 g of tetraethyl orthosilicate, 7.5 g of tetrabutylammonium hydroxide (25 wt%), and 8.7 g of deionized water, mix them, and carry out condensation reflux stirring at 80 °C for 72 h to form a seed solution. Take 18 g of tetraethyl orthosilicate, 7.2 g of tetrabutylammonium hydroxide, and 69.1 g of deionized water, mix them, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 0.32 g of titanium oxysulfate into 11.7 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. Under stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.46 g of ammonium chloride, add it to 18 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 72 h. After obtaining the crystallization product, dry it at 90 °C for 11 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-C.

[0048] Example 4: Preparation of nano-TS-2-D: Take 5 g of tetraethyl orthosilicate, 1.9 g of tetrabutylammonium bromide, and 8.7 g of deionized water, mix them, and carry out condensation reflux stirring at 80 °C for 72 h to form a seed solution. Take 16 g of tetraethyl orthosilicate, 6.2 g of tetrabutylammonium bromide, and 48.6 g of deionized water, mix them, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 0.52 g of tetrabutyl titanate into 9.9 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. Under stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.37 g of ammonium carbonate, add it to 12 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 72 h. After obtaining the crystallization product, dry it at 100 °C for 10 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-D.

[0049] Example 5: Preparation of nano-TS-2-E: 5 g of tetraethyl orthosilicate, 7.5 g of tetrabutylammonium hydroxide (25 wt%), and 8.7 g of deionized water were mixed and refluxed with stirring at 80 °C for 72 h to form a seed solution. 20 g of tetraethyl orthosilicate, 10.0 g of tetrabutylammonium hydroxide, and 95.2 g of deionized water were mixed and stirred at 40 °C for 5 h to obtain a mixed solution A. 0.82 g of tetraethyl titanate was added dropwise to 16.2 g of isopropanol and stirred at room temperature for 30 min to obtain a mixed solution B. Under stirring, the mixed solution B was added dropwise to the mixed solution A. After mixing, the temperature was raised to 95 °C with stirring to remove alcohol for 40 min to obtain a precursor solution. 0.65 g of ammonium sulfate was weighed and added to 15 g of water, stirred evenly to prepare a solution, and added to the precursor solution; then the seed solution was added and stirred for 20 min to obtain a crystallization solution. The crystallization solution was transferred to a crystallization kettle and crystallized at 160 °C for 72 h. After obtaining the crystallization product, it was dried at 100 °C for 10 h and calcined at 540 °C for 6 h to prepare nano-TS-2-E.

[0050] Example 6: Preparation of nano-TS-2-F: 5 g of tetraethyl orthosilicate, 2.1 g of tetrabutylammonium bromide, and 9.7 g of deionized water were mixed and refluxed with stirring at 80 °C for 72 h to form a seed solution. 17 g of tetraethyl orthosilicate, 8.7 g of tetrabutylammonium bromide, and 61.1 g of deionized water were mixed and stirred at 40 °C for 5 h to obtain a mixed solution A. 0.32 g of titanium oxysulfate was added dropwise to 12.6 g of isopropanol and stirred at room temperature for 30 min to obtain a mixed solution B. Under stirring, the mixed solution B was added dropwise to the mixed solution A. After mixing, the temperature was raised to 95 °C with stirring to remove alcohol for 40 min to obtain a precursor solution. 0.48 g of ammonium bicarbonate was weighed and added to 18 g of water, stirred evenly to prepare a solution, and added to the precursor solution; then the seed solution was added and stirred for 20 min to obtain a crystallization solution. The crystallization solution was transferred to a crystallization kettle and crystallized at 170 °C for 48 h. After obtaining the crystallization product, it was dried at 80 °C for 10 h and calcined at 540 °C for 6 h to prepare nano-TS-2-F.

[0051] Example 7: Preparation of nano-TS-2-G: Take 5 g of tetraethyl orthosilicate, 9 g of tetrabutylammonium hydroxide (25 wt%), and 10 g of deionized water, mix them, and condense and reflux with stirring at 80 °C for 72 h to form a seed solution. Take 19 g of tetraethyl orthosilicate, 8.6 g of tetrabutylammonium hydroxide, and 78.8 g of deionized water, mix and stir for 5 h to obtain a mixed solution A. Drop 0.82 g of tetrabutyl titanate into 14.4 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. While stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.48 g of ammonium bicarbonate, add it to 18 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 72 h. After obtaining the crystallization product, dry it at 80 °C for 10 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-G.

[0052] Example 8: Preparation of nano-TS-2-H: Take 5 g of tetraethyl orthosilicate, 1.1 g of tetrabutylammonium bromide, and 7.7 g of deionized water, mix them, and condense and reflux with stirring at 80 °C for 72 h to form a seed solution. Mix 20 g of tetraethyl orthosilicate, 9.28 g of tetrabutylammonium bromide, and 77.9 g of deionized water, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 0.77 g of tetraethyl titanate into 13.5 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. While stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 1.1 g of ammonium bicarbonate, add it to 20 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 72 h. After obtaining the crystallization product, dry it at 80 °C for 10 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-H.

[0053] Example 9: Preparation of nano-TS-2-I: Take 5 g of tetraethyl orthosilicate, 7 g of tetrabutylammonium hydroxide (25 wt%), and 9.2 g of deionized water, mix them, and condense and reflux with stirring at 80 °C for 72 h to form a seed solution. Take 18 g of tetraethyl orthosilicate, 7.14 g of tetrabutylammonium hydroxide, and 77.5 g of deionized water, mix them, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 0.68 g of tetrabutyl titanate into 11.7 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. Under stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.16 g of ammonium bicarbonate, add it to 12.6 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 72 h. After obtaining the crystallization product, dry it at 90 °C for 9 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-I.

[0054] Example 10: Preparation of nano-TS-2-J: Take 5 g of tetraethyl orthosilicate, 2.0 g of tetrabutylammonium bromide, and 10.3 g of deionized water, mix them, and condense and reflux with stirring at 80 °C for 72 h to form a seed solution. Take 21 g of tetraethyl orthosilicate, 12.4 g of tetrabutylammonium bromide, and 90 g of deionized water, mix them, and stir at 40 °C for 5 h to obtain a mixed solution A. Drop 1.37 g of tetrabutyl titanate into 15.3 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. Under stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min to obtain a precursor solution. Weigh 0.68 g of ammonium bisulfate, add it to 12.6 g of water, stir evenly to prepare a solution, and add it to the precursor solution; then add the seed solution and stir for 20 min to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 36 h. After obtaining the crystallization product, dry it at 90 °C for 9 h and calcine it at 540 °C for 6 h to prepare nano-TS-2-J.

[0055] Comparative Example 1: Preparation of nano-TS-2-K: Take 22.5 g of tetraethyl orthosilicate and 8.7 g of tetrabutylammonium hydroxide, add 59.8 g of deionized water and mix them, hydrolyze at 40 °C for 5 h to obtain a mixed solution A. Drop 1.26 g of tetrabutyl titanate into 15 g of isopropanol, stir at room temperature for 30 min to obtain a mixed solution B. Under stirring, drop the mixed solution B into the mixed solution A drop by drop. After mixing, stir and heat up to 95 °C to remove alcohol for 40 min, add 14.5 g of water to obtain a crystallization solution. Transfer the crystallization solution to a crystallization kettle and crystallize at 170 °C for 72 h. After obtaining the crystallization product, dry it at 80 °C for 12 h and calcine it at 540 °C for 6 h to prepare a conventional titanium-containing molecular sieve TS-2-K.

[0056] Comparative Example 2: Preparation of nano-TS-2-L: TS-2 was prepared for comparison according to the method disclosed in Chinese Patent Application CN112744831A. Tetrabutyl titanate, tetraethyl orthosilicate, polyacrylic acid (weight average molecular weight of 5000) powder, and 3 g of water were successively added to a 500 mL beaker, mixed evenly on a magnetic stirrer with heating and stirring functions, and stirred at room temperature for 4 hours to obtain a first mixture. In an air atmosphere, the first mixture was burned at 500 °C for 5 hours to obtain a titanium-silicon oxide. The above titanium-silicon oxide, an aqueous solution of tetrabutylammonium hydroxide with a concentration of 25 wt%, cetyltrimethylammonium hydroxide, tetraethyl orthosilicate, seed crystals, a liquid titanium-silicon molecular sieve synthesis precursor, ammonia water with a concentration of 20 wt%, and water were mixed to obtain a second mixture, which was then transferred to a stainless steel sealed reactor and crystallized at a constant temperature of 165 °C for 2 days to obtain a crystallized sample, filtered, washed, dried at 120 °C for 24 hours, and calcined at 550 °C for 6 hours to obtain small crystal stacked TS-2-L.

[0057] Scanning electron microscope photos of each titanium-containing molecular sieve TS-2 are as Figure 2 shown, and the X-ray diffraction patterns are as Figure 1 shown. The ultraviolet-visible spectra are as Figure 3 shown. The performance of the molecular sieve in catalyzing phenol hydroxylation is listed in Table 1.

[0058] Experimental Example: The performance of TS-2 in catalyzing the phenol hydroxylation reaction was evaluated in a round-bottom flask. 8.4 mL of acetone, 4.0 g of phenol, 1.6 g of an aqueous H2O2 solution (30 wt%), and 0.2 g of powdered TS-2 were successively added to the round-bottom flask and stirred evenly; a condensation reflux device was equipped, and the oil bath was heated to 80 °C and reacted for 2 hours. After the reaction, the concentration of H2O2 before and after the reaction was titrated by the iodometric method, and the contents of catechol, hydroquinone, and p-benzoquinone in the reaction products were determined by gas chromatography. The catalytic performance of the TS-2 samples synthesized according to the examples and comparative examples of the present invention is shown in Table 1.

[0059] Table 1 Performance of some samples synthesized in examples and comparative examples Note: X(PHE)=1 - n(PHE) / [n(PHE)+n(CAT)+n(HQ)+n(PBQ)] S(CAT)=n(CAT) / [n(CAT)+n(HQ)+n(PBQ)] S(HQ)=n(HQ) / [n(CAT)+n(HQ)+n(PBQ)] S(PBQ)=n(PBQ) / [n(CAT)+n(HQ)+n(PBQ)] U(H2O2) = 3×X(PHE) / X(H2O2) Samples containing nanoscale monodisperse particles always showed slightly higher phenol conversion (X(PHE)) and H2O2 utilization rate (U(H2O2)). As can be seen from Table 1, the X(PHE) of the TS-2-A sample was the highest, reaching 16.6%, and the U(H2O2) reached 59.6%. The samples TS-2-A to J in each example were significantly higher than the comparative example sample TS-2-K, and the vast majority were higher than the sample TS-2-L. Only the phenol conversion (X(PHE)) of the example sample TS-2-B was basically the same as that of the comparative example sample TS-2-L (14.2%: 14.5%), and only the H2O2 utilization rate (U(H2O2)) of the example sample TS-2-F was basically the same as that of the comparative example sample TS-2-L (49.6%: 49.7%).

[0060] The hydroxylation reaction of phenol produces three main products, namely p-benzoquinone (PBQ), hydroquinone (HQ), and catechol (CAT). Among them, HQ and CAT are the target products, while PBQ is an unwanted by-product. As can be seen from Table 1, the samples containing nanoscale monodisperse particles in the examples had a higher selectivity for CAT (S(CAT)). The S(CAT) of the example sample TS-2-I was the highest, reaching 53.2%, and the example sample TS-2-J was the lowest, reaching 50.2%. Both were higher than 41.1% of the comparative example sample of micron particles TS-2-K and were basically the same as 50.4% of the sample TS-2-L.

[0061] Figure 1 The X-ray diffraction patterns of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J synthesized in the examples of the present invention, and TS-2-K and TS-2-L synthesized in the comparative examples show that the products synthesized by each synthesis method are TS-2 zeolites with a MEL structure.

[0062] Figure 2 Scanning electron microscope photos of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J synthesized in the examples of the present invention, and TS-2-K and TS-2-L synthesized in the comparative examples. From Figure 2 It can be seen that each sample of TS-2-A to J is a monodisperse nanoscale particle (400nm × 200nm), and the particles are composed of rod-like structures (400nm × 40nm) stacked in parallel. The samples of TS-2-K and TS-2-L are large particles of 5 - 10μm. It can be seen that the present invention can reduce the particle size of TS-2-K.

[0063] Figure 3UV-Vis diffuse reflectance spectra of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J synthesized in the embodiments of the present invention, and TS-2-K and TS-2-L synthesized in the comparative examples. There are mainly three absorption bands in the spectra, located at 210-220 nm, 260-280 nm and 310-330 nm respectively, corresponding to tetracoordinated titanium, hexacoordinated titanium and anatase TiO2. It can be seen that TS-2-K obtained without adding seeds and ammonium salts during the synthesis process, and TS-2-L sample obtained without adding ammonium salts mainly contain tetrahedrally coordinated titanium, while the content of hexacoordinated titanium in TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J added with seeds and ammonium salts during the synthesis process increases significantly.

[0064] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for synthesizing nano-TS-2 molecular sieve, characterized in that, Comprising: Mixing a silicon source, a templating agent and water in a certain proportion, and carrying out condensation reflux stirring to form a seed solution; Mixing a silicon source, a templating agent and water in a certain proportion, and stirring to obtain a first mixed solution; Adding a titanium source into isopropanol and stirring to obtain a second mixed solution; Adding the second mixed solution into the first mixed solution, and stirring to remove alcohol to obtain a precursor solution; Mixing an ammonium salt and deionized water in a certain proportion, adding the mixture into the precursor solution, and stirring to obtain a first precursor solution; Adding the seed solution into the first precursor solution and stirring to obtain a crystallization solution; Carrying out crystallization on the crystallization liquid to obtain a crystallization product; Filtering, washing, drying and calcining the crystallization product to obtain the TS-2 molecular sieve.

2. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, wherein Wherein, The silicon source is at least one of tetraethyl orthosilicate and silica sol; The templating agent is at least one of tetrabutylammonium hydroxide and tetrabutylammonium bromide; The titanium source can be selected from at least one of tetrabutyl titanate, tetraethyl titanate, titanium oxysulfate and titanium tetrachloride; The ammonium salt is at least one of ammonium carbonate, ammonium bicarbonate, ammonium sulfate, ammonium bisulfate and ammonium chloride.

3. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, characterized in that, Wherein, The molar ratio of the silicon source to the templating agent in the seed solution is 1:(0.1 - 0.5); Preferably, the molar ratio of the silicon source to the templating agent is 1:(0.2 - 0.3); Preferably, the molar ratio of the silicon source, the templating agent and water is 1:(0.1 - 0.5):(10 - 50).

4. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, characterized in that, The molar ratio of the silicon source to the templating agent in the first mixed solution is 1:(0.1 - 0.8); Preferably, the molar ratio of the silicon source to the templating agent is 1:(0.25 - 0.4); Preferably, the molar ratio of the silicon source, the templating agent and water is 1:(0.1 - 0.8):(10 - 80); Preferably, the molar ratio of the titanium source to isopropanol in the second mixed solution is 1:(5 - 30); More preferably, the molar ratio of the titanium source to isopropanol is 1:(5 - 15); Preferably, the molar ratio of the silicon source to the titanium source in the precursor solution is 1:(0.01 - 0.05); More preferably, the molar ratio of the silicon source to the titanium source is 1:(5 - 15).

5. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, characterized in that, In the step of mixing the ammonium salt and deionized water in a certain proportion, the molar ratio of the ammonium salt to deionized water is 1:(20 - 70); Preferably, the molar ratio of the ammonium salt to deionized water is 1:(30 - 50); Preferably, the molar ratio of the silicon source to the ammonium salt in the first precursor solution is 1:(0.05 - 0.15); Preferably, the molar ratio of the silicon source to the ammonium salt is 1:(0.05 - 0.10).

6. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, wherein The mass ratio of the seed solution to the first precursor solution is 1:(50 - 200); Preferably, the mass ratio of the seed solution to the first precursor solution is 1:(100 - 120).

7. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, characterized in that, In the step of mixing the silicon source, the templating agent and water in a certain proportion and stirring to obtain the first mixed solution, the stirring temperature is 40°C and the stirring time is 5 h; Preferably, in the step of adding the titanium source into isopropanol and stirring to obtain the second mixed solution, the stirring temperature is room temperature and the stirring time is 0.5 - 2 h; More preferably, the titanium source is added dropwise into isopropanol; Preferably, in the step of adding the second mixed solution into the first mixed solution and stirring to remove alcohol to obtain a precursor solution, the stirring temperature is 60-95°C and the alcohol removal time is 0.5-2 h; More preferably, the second mixed solution is added dropwise into the first mixed solution under stirring.

8. The synthesis method of the nano-TS-2 molecular sieve according to claim 1, characterized in that, In the step of mixing a silicon source, a template agent and water in a certain ratio and performing condensation reflux stirring to form a seed solution, the condensation reflux stirring temperature is 60-80°C and the condensation reflux stirring time is 48-72 h; Preferably, in the step of mixing an ammonium salt and deionized water in a certain ratio and adding them into the precursor solution and stirring to obtain a first precursor solution, the stirring time is 10-30 min; Preferably, in the step of adding the seed solution into the first precursor solution and stirring to obtain a crystallization solution, the stirring time is 10-30 min; Preferably, in the step of crystallizing the crystallization liquid, the crystallization is carried out in a crystallization kettle, the crystallization temperature is 120-180°C, and the crystallization time is 12-72 h; In the step of filtering, washing, drying and calcining the crystallization product, the drying temperature is 60-120°C and the drying time is 6-24 h; More preferably, the drying temperature is 80-100°C and the drying time is 8-12 h; More preferably, the calcination temperature is 540°C and the calcination time is 6 h.

9. The nano-TS-2 molecular sieve prepared by the method according to any one of claims 1-8.

10. The use of the molecular sieve according to claim 9 as a catalyst; or The use as a catalyst in phenol hydroxylation, cyclohexene epoxidation, and cyclohexanone ammoxidation reactions.

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