A method for synthesizing nanometer titanium-silicon molecular sieve TS-2

Abstract

The application relates to a synthesis method of a nano titanium-silicon molecular sieve TS-2, and belongs to the field of titanium-silicon molecular sieve synthesis. In order to solve the problems of increasing the content of six-coordinated titanium species of TS-2 molecular sieve and reducing the particle size, the technical points are as follows: a seed liquid is formed by mixing a silicon source, a template agent and water in a certain proportion, condensing, refluxing and stirring; a first mixed solution is obtained by mixing the silicon source, the template agent and water in a certain proportion and stirring; a second mixed solution is obtained by stirring a titanium source in isopropyl alcohol; the second mixed solution is added into the first mixed solution to remove alcohol by stirring; a first precursor liquid is obtained by mixing an ammonium salt and deionized water in a certain proportion and adding into the precursor liquid; a seed liquid is added into the first precursor liquid to obtain a crystallization liquid by stirring; a crystallization product is obtained by crystallizing the crystallization liquid; and the crystallization product is filtered, washed, dried and calcined to prepare the TS-2 molecular sieve, which can be used as a catalyst for macromolecule selective oxidation reaction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of molecular sieve synthesis, and relates to a synthesis method of a nanometer titanium silicate molecular sieve TS-2. BACKGROUND

[0002] Titanium silicate molecular sieve TS-2 is a titanium-containing heteroatomic molecular sieve with MEL topological structure. In the 1990s, Reddy et al. first reported a synthesis method of the molecular sieve (Appl. Catal., A 1990, 58, L1-L4). Since then, TS-2 has gradually attracted attention as an environmentally friendly catalytic oxidation catalyst. The MEL topological structure contains ten-membered straight pores in two directions along the a axis and the b axis, and the pore size is 0.54 nm x 0.53 nm. Compared with the MFI topological structure containing one straight pore and one zigzag pore, the MEL structure is generally considered to have more excellent diffusion performance. Therefore, TS-2 is often used for selective oxidation reactions of larger molecules.

[0003] Under typical hydrothermal synthesis conditions, the morphology of the prepared TS-2 is usually micron-level spherical agglomerates of 2-12 μm (Microporous Mesoporous Mater. 2004, 69, 197, Catal. Commun. 2004, 5, 359). Larger particle size leads to smaller external surface area of TS-2, and longer diffusion path of reactants and products in the pores, which is not conducive to catalytic performance.

[0004] Chinese patent CN112744831A discloses a preparation method of a titanium-containing molecular sieve. The method mixes titanium silicate oxide, a template agent, a second silicon source, seeds, a liquid titanium silicate molecular sieve synthesis precursor, water, and an inorganic ammonium source to obtain a second mixture, and then performs crystallization. The titanium-containing molecular sieve produced by the method exhibits good activity in the cyclohexanone ammoxidation reaction.

[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 by adjusting the Si / Ti molar ratio of the synthesis gel, even at a very low Ti content (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 tetrahedral titanium, anatase TiO2 and hexacoordinated titanium (Small 2024, 20, 2406294). Currently, there are few studies on the catalytic activity of titanium species in TS-2, but from the study of TS-1, it can be inferred that the main active center for catalytic oxidation is still tetrahedral titanium, and some specific structures of hexacoordinated titanium also have catalytic activity.

[0007] In general, the MEL straight channel of TS-2 can reduce the diffusion limitation to some extent, but its large particle size will still have a negative impact on the catalytic performance; moreover, there are few reports on the method of regulating the active titanium species in TS-2. Therefore, developing a synthesis method that can reduce the particle size of TS-2 while regulating the coordination state of titanium species has important practical significance for the practical application of TS-2.

[0008] The prior art shows that the addition of ammonium salt during the synthesis of TS-1 inhibits the formation of hexacoordinated titanium (Microporous Mesoporous Mater. 2009, 122, 301). However, the inventors found that for the preparation of TS-2, the addition of ammonium salt in the precursor solution and the addition of seeds to the precursor solution containing ammonium salt, through the joint action of seeds and ammonium salt, not only increased the content of hexacoordinated titanium species in the molecular sieve, but also reduced the particle size of TS-2. Recently, several papers have reported that hexacoordinated titanium species has higher catalytic oxidation activity than tetrahedral titanium (Chem. Eur. J., 2012, 18, 13854, Chem. Commoun., 2015, 51, 9010, AIChE J. 2021, e17261, Appl. Cata. B, 2023, 325, 122396).

[0009] CN 115259177 A discloses a kind of multistage hole ZSM-5 molecular sieve for VOCs adsorption and its preparation method and application, specifically discloses that aluminum source, silicon source, alkali source, ZSM-5 molecular sieve seed crystal is mixed uniformly with water, forms gel;The obtained gel is pre-crystallized in reaction kettle, and pre-crystallization product is obtained;After the pre-crystallization product is cooled, template agent is added, and after stirring, it is heated to carry out crystallization reaction;After the crystallization product after reaction is separated by solid-liquid, washing, drying, calcination, and the molecular sieve raw powder is obtained;The raw material prepared is treated by acid immersion using acid solution, and the molecular sieve precursor is obtained by calcination;The obtained precursor is placed in ammonium salt solution to carry out ion exchange to obtain ammonia type ZSM-5 molecular sieve, and HZSM-5 molecular sieve is obtained after calcination.However, after crystallization, the precursor is placed in ammonium salt solution to carry out ion exchange to obtain ammonia type ZSM-5 molecular sieve, which is ammonium exchanged with ammonium salt, and sodium ion on ZSM-5 is exchanged into ammonium ion, and then ammonium ion is changed into hydrogen ion by calcination.ZSM-5 has fixed particle size before ammonium exchange, and it does not have the function of adjusting particle size and improving the content of six-coordinated titanium species of molecular sieve. SUMMARY

[0010] In order to solve the problem of improving the content of six-coordinated titanium species of 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 comprises:

[0011] Mixing silicon source, template agent and water in a certain proportion, condensing reflux stirring to form seed crystal solution;

[0012] Mixing silicon source, template agent and water in a certain proportion, stirring to obtain a first mixed solution;

[0013] Add titanium source to isopropyl alcohol, stir to obtain a second mixed solution;

[0014] Add the second mixed solution to the first mixed solution, stir to remove alcohol, and obtain a precursor solution;

[0015] Mixing ammonium salt and deionized water in a certain proportion, adding to the precursor solution, stirring to obtain a first precursor solution;

[0016] Add the seed crystal solution to the first precursor solution, stir to obtain a crystallization solution;

[0017] Crystallize the crystallization solution to obtain a crystallization product;

[0018] Filter, wash, dry and calcine the crystallization product to obtain the TS-2 molecular sieve.

[0019] According to the method for synthesizing the nano TS-2 molecular sieve in some embodiments of the present application, the silicon source is at least one of tetraethyl orthosilicate and silica sol;

[0020] The template agent is at least one of tetrabutylammonium hydroxide and tetrabutylammonium bromide;

[0021] The titanium source can be selected from at least one of tetrabutyl titanate, tetraethyl titanate, titanyl sulfate, and titanium tetrachloride;

[0022] The ammonium salt is at least one of ammonium carbonate, ammonium bicarbonate, ammonium sulfate, ammonium bisulfate, and ammonium chloride.

[0023] According to the method for synthesizing the 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 seed liquid is 1:(0.1-0.5);

[0024] Preferably, the molar ratio of the silicon source to the template agent is 1:(0.2-0.3);

[0025] Preferably, the molar ratio of the silicon source, the template agent, and water is 1:(0.1-0.5):(10-50).

[0026] According to the method for synthesizing the 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);

[0027] Preferably, the molar ratio of the silicon source to the template agent is 1:(0.25-0.4);

[0028] Preferably, the molar ratio of the silicon source, the template agent, and water is 1:(0.1-0.8):(10-80);

[0029] Preferably, the molar ratio of the titanium source to isopropyl alcohol in the second mixed solution is 1:(5-30);

[0030] More preferably, the molar ratio of the titanium source to isopropyl alcohol is 1:(5-15);

[0031] Preferably, the molar ratio of the silicon source to the titanium source in the precursor solution is 1:(0.01-0.05);

[0032] More preferably, the molar ratio of the silicon source to the titanium source is 1:(5-15).

[0033] According to the method for synthesizing the nano TS-2 molecular sieve in some embodiments of the present application, the step of mixing the ammonium salt with deionized water in a certain ratio, wherein the molar ratio of the ammonium salt to the deionized water is 1:(20-70);

[0034] Preferably, the molar ratio of the ammonium salt to the deionized water is 1:(30-50).

[0035] Preferably, the molar ratio of the silicon source and the ammonium salt in the first precursor solution is 1:(0.05-0.15).

[0036] Preferably, the molar ratio of the silicon source and the ammonium salt is 1:(0.05-0.10).

[0037] According to the method for synthesizing the 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).

[0038] Preferably, the mass ratio of the seed solution to the first precursor solution is 1:(100-120).

[0039] According to the method for synthesizing the 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 proportion and stirring to obtain the first mixed solution, the stirring temperature is 40°C and the stirring time is 5h.

[0040] Preferably, in the step of adding the titanium source into isopropyl alcohol and stirring to obtain the second mixed solution, the stirring temperature is room temperature and the stirring time is 0.5-2h.

[0041] More preferably, the titanium source is added into isopropyl alcohol in a dropwise manner.

[0042] Preferably, in the step of adding the second mixed solution into the first mixed solution and stirring to remove alcohol to obtain the precursor solution, the stirring temperature is 60-95°C and the alcohol removal time is 0.5-2h.

[0043] More preferably, the second mixed solution is added into the first mixed solution in a dropwise manner and under stirring.

[0044] According to the method for synthesizing the 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 proportion and stirring to obtain the seed solution, the condensation reflux stirring temperature is 60-80°C and the condensation reflux stirring time is 48-72h.

[0045] Preferably, in the step of mixing the ammonium salt and deionized water in a certain proportion and adding into the precursor solution and stirring to obtain the first precursor solution, the stirring time is 10-30min.

[0046] Preferably, in the step of adding the seed solution into the first precursor solution and stirring to obtain the crystallization solution, the stirring time is 10-30min.

[0047] Preferably, in the step of crystallizing the crystallization solution, the crystallization is performed in a crystallization kettle, the crystallization temperature is 120-180°C and the crystallization time is 12-72h.

[0048] The crystallization product is filtered, washed, dried, and calcined in the steps, wherein the drying temperature is 60-120 DEG C, and the drying time is 6-24h;

[0049] More preferably, the drying temperature is 80-100 DEG C, and the drying time is 8-12h.

[0050] More preferably, the calcination temperature is 540 DEG C, and the calcination time is 6h.

[0051] In a second aspect, the nano TS-2 molecular sieve is prepared according to the method for synthesizing the nano TS-2 molecular sieve in some embodiments of the present application.

[0052] In a third aspect, the molecular sieve is used for a catalyst according to some embodiments of the present application.

[0053] The molecular sieve is used for a catalyst in phenol hydroxylation, cyclohexene epoxidation, and cyclohexanone ammoxidation according to some embodiments of the present application.

[0054] The present application has the following beneficial effects:

[0055] (1) The present application adds seeds and ammonium salt to a TS-2 synthesis system, and experiments show that the active titanium species can be controlled, the coordination state of the titanium species in TS-2 is changed, and six-coordinated titanium species with high catalytic oxidation activity are formed.

[0056] (2) The present application adds seeds and ammonium salt to a TS-2 synthesis system, and experiments show that the diffusion performance can be controlled. When only seeds are added to the TS-2 synthesis system, the morphology of the TS-2 small grains does not change, and only the agglomerates are broken. When seeds and ammonium salt are added to the precursor solution, the morphology of the TS-2 grains changes significantly, and the TS-2 grains are converted into nanoscale monodisperse rod-shaped particles, and no longer agglomerate into micrometer spherical particles, which greatly reduces the particle size, and the diffusion performance of TS-2 is significantly improved.

[0057] (3) Based on the above-mentioned improvement of the content of the six-coordinated titanium species and the diffusion performance, the TS-2 molecular sieve of the present application can exhibit excellent catalytic performance for large molecule reactions such as phenol hydroxylation, cyclohexene epoxidation, and cyclohexanone ammoxidation. BRIEF DESCRIPTION OF DRAWINGS

[0058] 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 by the embodiments of the present application, and TS-2-K and TS-2-L synthesized by the comparative examples are shown in the figure.

[0059] Figure 2are scanning electron microscope photos of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J synthesized by the embodiments of the present application, and TS-2-K and TS-2-L synthesized by the comparative examples; wherein (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.

[0060] Figure 3 are ultraviolet-visible diffuse reflectance spectra of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J samples synthesized by the embodiments of the present application, and TS-2-K and TS-2-L synthesized by the comparative examples. DETAILED DESCRIPTION

[0061] The following non-limiting examples can enable those of ordinary skill in the art to more fully understand the present application, but in no way limit the present application.

[0062] Explanation of terms:

[0063] Titanium silicalite TS-2: titanium-containing heteroatomic molecular sieve with MEL topological structure.

[0064] TS-1 molecular sieve: molecular sieve with MFI structure.

[0065] The present application aims to provide a synthesis method of nano TS-2 molecular sieve, which is realized by the following steps:

[0066] S1, preparation of seed liquid: mix the silicon source, template agent and water in a certain proportion, condense reflux stirring at 60-80℃ for 48-72h, and form a seed liquid;

[0067] S2, preparation of precursor liquid: mix the silicon source, template agent and water in a certain proportion, stir at 40℃ for 5h to form a mixed solution A; add the titanium source dropwise into isopropyl alcohol, stir at room temperature for 0.5-2h to obtain a mixed solution B; under stirring, add the mixed solution B dropwise into the mixed solution A, after mixing, stir and heat to 60-95℃, and remove alcohol for 0.5-2h to obtain a precursor liquid;

[0068] S3, preparation of crystallization liquid: mix the ammonium salt with deionized water to form a solution with a certain concentration, and slowly add it into the precursor liquid, and stir for 10-30min; add the seed liquid into the precursor liquid, and stir for 10-30min; obtain a crystallization liquid;

[0069] S4, crystallization and post-treatment: the crystallization solution is transferred into a crystallization kettle, and crystallized at 120-180℃ for 12-72h to obtain a crystallization product, which is filtered, washed, dried, and calcined to obtain the TS-2 molecular sieve.

[0070] Preferably, the silicon source in steps S1 and S2 is at least one of tetraethyl orthosilicate, silica sol; the template agent in steps S1 and S2 is at least one of tetrabutylammonium hydroxide, tetrabutylammonium bromide; the titanium source in step S2 is at least one of tetrabutyl titanate, tetraethyl titanate, titanyl sulfate, titanium tetrachloride; and the ammonium salt in step S3 is at least one of ammonium carbonate, ammonium bicarbonate, ammonium sulfate, ammonium bisulfate, ammonium chloride.

[0071] 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).

[0072] 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).

[0073] 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).

[0074] Preferably, the molar ratio of the silicon source to the template agent in the mixed solution A in step S2 is 1:(0.1-0.8); more preferably, the molar ratio is 1:(0.25-0.4).

[0075] Preferably, the molar ratio of the silicon source to water in the mixed solution A in step S2 is 1:(10-80); more preferably, the molar ratio is 1:(30-50).

[0076] Preferably, the molar ratio of the titanium source to isopropanol in the mixed solution B in step S2 is 1:(5-30); more preferably, the molar ratio is 1:(5-15).

[0077] Preferably, the mass ratio of the mixed solution A to the mixed solution B in step S2 is 1:(0.5-20); more preferably, the molar ratio is 1:(1.5-4).

[0078] 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).

[0079] 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).

[0080] Preferably, in step S3, the mass ratio of the seed solution to the precursor solution containing ammonium salt is 1:(50-200); more preferably, the molar ratio is 1:(100-120).

[0081] Preferably, in step S4, the drying temperature is 60-120°C, and the drying time is 6-24h; more preferably, the drying temperature is 80-100°C, and the drying time is 8-12h.

[0082] Example 1: Preparation of nano TS-2-A: 5g of tetraethyl orthosilicate, 7.5g of tetrabutylammonium hydroxide (25wt%), and 8.7g of deionized water were mixed, stirred at 80°C under condensation reflux for 72h to form a seed solution. 15g of tetraethyl orthosilicate, 5.6g of tetrabutylammonium hydroxide, and 51.9g of deionized water were mixed, stirred at 40°C for 5h to obtain a mixed solution A. 0.61g of tetrabutyl titanate was added dropwise into 10.8g of isopropyl alcohol, stirred at room temperature for 30min to obtain a mixed solution B. Under stirring, the mixed solution B was added dropwise into the mixed solution A, and after mixing, the temperature was increased to 95°C for alcohol removal for 40min to obtain a precursor solution. 0.35g of ammonium carbonate was weighed into 13g of water, stirred for 15min to uniformly configure into a solution, and then added into the precursor solution; then the seed solution was added, and stirred for 20min to obtain a crystallization solution. The crystallization solution was transferred into a crystallization kettle, and crystallized at 170°C for 24h. After obtaining the crystallization product, the solid was filtered, washed with deionized water for 3 times, dried at 100°C for 10h, and calcined at 540°C for 6h to prepare nano TS-2-A.

[0083] Example 2: Preparation of nano TS-2-B: 5g of silica sol (30wt%), 7.8g of tetrabutylammonium hydroxide (25wt%), and 3.2g of deionized water were mixed, stirred at 80°C under condensation reflux for 72h to form a seed solution. 15g of silica sol (30wt%), 6.4g of tetrabutylammonium hydroxide, and 43.1g of deionized water were mixed, stirred at 40°C for 5h to obtain a mixed solution A. 0.63g of tetrabutyl titanate was added dropwise into 11.2g of isopropyl alcohol, stirred at room temperature for 30min to obtain a mixed solution B. Under stirring, the mixed solution B was added dropwise into the mixed solution A, and after mixing, the temperature was increased to 95°C for alcohol removal for 40min to obtain a precursor solution. 0.40g of ammonium carbonate was weighed into 16g of water, stirred to uniformly configure into a solution, and then added into the precursor solution; then the seed solution was added, and stirred for 20min to obtain a crystallization solution. The crystallization solution was transferred into a crystallization kettle, and crystallized at 170°C for 36h. After obtaining the crystallization product, the solid was dried at 110°C for 9h, and calcined at 540°C for 6h to prepare nano TS-2-B.

[0084] Example 3: Preparation of nano TS-2-C: 5 g of tetraethyl orthosilicate, 7.5 g of tetrabutylammonium hydroxide (25 wt%), and 8.7 g of deionized water were mixed, stirred at 80°C under condensation reflux for 72 h to form a seed solution. 18 g of tetraethyl orthosilicate, 7.2 g of tetrabutylammonium hydroxide, and 69.1 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 sulfate oxide was added dropwise to 11.7 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95°C for 40 min to obtain a precursor solution. 0.46 g of ammonium chloride was weighed into 18 g of water, stirred to obtain 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 72 h. After obtaining the crystallization product, drying was performed at 90°C for 11 h, and calcination was performed at 540°C for 6 h to obtain nano TS-2-C.

[0085] Example 4: Preparation of nano TS-2-D: 5 g of tetraethyl orthosilicate, 1.9 g of tetrabutylammonium bromide, and 8.7 g of deionized water were mixed, stirred at 80°C under condensation reflux for 72 h to form a seed solution. 16 g of tetraethyl orthosilicate, 6.2 g of tetrabutylammonium bromide, and 48.6 g of deionized water were mixed and stirred at 40°C for 5 h to obtain a mixed solution A. 0.52 g of tetrabutyl titanate was added dropwise to 9.9 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95°C for 40 min to obtain a precursor solution. 0.37 g of ammonium carbonate was weighed into 12 g of water, stirred to obtain 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 72 h. After obtaining the crystallization product, drying was performed at 100°C for 10 h, and calcination was performed at 540°C for 6 h to obtain nano TS-2-D.

[0086] 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 stirred at 80°C under reflux condensation 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 isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95°C for 40 min to obtain a precursor solution. 0.65 g of ammonium sulfate was weighed into 15 g of water, stirred to obtain 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 obtain nano TS-2-E.

[0087] 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 stirred at 80°C under reflux condensation 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 titanyl sulfate was added dropwise to 12.6 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95°C for 40 min to obtain a precursor solution. 0.48 g of ammonium bicarbonate was weighed into 18 g of water, stirred to obtain 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 obtain nano TS-2-F.

[0088] Example 7: Preparation of nano TS-2-G: 5 g of tetraethyl orthosilicate, 9 g of tetrabutylammonium hydroxide (25 wt%), and 10 g of deionized water were mixed and stirred at 80°C under condensation reflux for 72 h to form a seed solution. 19 g of tetraethyl orthosilicate, 8.6 g of tetrabutylammonium hydroxide, and 78.8 g of deionized water were mixed and stirred for 5 h to obtain a mixed solution A. 0.82 g of tetrabutyl titanate was added dropwise to 14.4 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95°C for 40 min to obtain a precursor solution. 0.48 g of ammonium bicarbonate was weighed into 18 g of water, stirred to obtain 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 72 h. After obtaining the crystallization product, it was dried at 80°C for 10 h, and calcined at 540°C for 6 h to obtain nano TS-2-G.

[0089] Example 8: Preparation of nano TS-2-H: 5 g of tetraethyl orthosilicate, 1.1 g of tetrabutylammonium bromide, and 7.7 g of deionized water were mixed and stirred at 80°C under condensation reflux for 72 h to form a seed solution. 20 g of tetraethyl orthosilicate, 9.28 g of tetrabutylammonium bromide, and 77.9 g of deionized water were mixed and stirred at 40°C for 5 h to obtain a mixed solution A. 0.77 g of tetrabutyl titanate was added dropwise to 13.5 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95°C for 40 min to obtain a precursor solution. 1.1 g of ammonium bicarbonate was weighed into 20 g of water, stirred to obtain 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 72 h. After obtaining the crystallization product, it was dried at 80°C for 10 h, and calcined at 540°C for 6 h to obtain nano TS-2-H.

[0090] Example 9: Preparation of nano TS-2-I: 5 g of tetraethyl orthosilicate, 7 g of tetrabutylammonium hydroxide (25 wt%), and 9.2 g of deionized water were mixed and stirred at 80 °C under condensation reflux for 72 h to form a seed solution. 18 g of tetraethyl orthosilicate, 7.14 g of tetrabutylammonium hydroxide, and 77.5 g of deionized water were mixed and stirred at 40 °C for 5 h to obtain a mixed solution A. 0.68 g of tetrabutyl titanate was added dropwise to 11.7 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95 °C for 40 min to obtain a precursor solution. 0.16 g of ammonium bicarbonate was weighed into 12.6 g of water, stirred to obtain 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 72 h. After obtaining the crystallization product, drying was performed at 90 °C for 9 h, and calcination was performed at 540 °C for 6 h to obtain nano TS-2-I.

[0091] Example 10: Preparation of nano TS-2-J: 5 g of tetraethyl orthosilicate, 2.0 g of tetrabutylammonium bromide, and 10.3 g of deionized water were mixed and stirred at 80 °C under condensation reflux for 72 h to form a seed solution. 21 g of tetraethyl orthosilicate, 12.4 g of tetrabutylammonium bromide, and 90 g of deionized water were mixed and stirred at 40 °C for 5 h to obtain a mixed solution A. 1.37 g of tetrabutyl titanate was added dropwise to 15.3 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95 °C for 40 min to obtain a precursor solution. 0.68 g of ammonium bisulfate was weighed into 12.6 g of water, stirred to obtain 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 36 h. After obtaining the crystallization product, drying was performed at 90 °C for 9 h, and calcination was performed at 540 °C for 6 h to obtain nano TS-2-J.

[0092] Comparative Example 1: Preparation of nano TS-2-K: 22.5 g of tetraethyl orthosilicate and 8.7 g of tetrabutylammonium hydroxide were mixed, 59.8 g of deionized water was added, and hydrolysis was performed at 40 °C for 5 h to obtain a mixed solution A. 1.26 g of tetrabutyl titanate was added dropwise to 15 g of isopropyl alcohol, 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, and after mixing, the alcohol was removed by increasing the temperature to 95 °C for 40 min, 14.5 g of water was added, and a crystallization solution was obtained. The crystallization solution was transferred to a crystallization kettle, and crystallized at 170 °C for 72 h. After obtaining the crystallization product, drying was performed at 80 °C for 12 h, and calcination was performed at 540 °C for 6 h to obtain conventional titanium-containing molecular sieve TS-2-K.

[0093] Comparative Example 2: Preparation of nano TS-2-L: TS-2 was prepared according to the method disclosed in Chinese patent application CN112744831A. Tetrabutyl titanate, tetraethyl orthosilicate, polyacrylic acid (weight average molecular weight 5000) powder, 3 g of water were sequentially added into a 500 mL beaker, which was placed on a magnetic stirrer with heating and stirring functions to mix uniformly, and stirred at room temperature for 4 hours to obtain a first mixture. The first mixture was burned at 500°C for 5 hours in an air atmosphere to obtain a titanium-silicon oxide. The titanium-silicon oxide, a 25 wt% tetrabutylammonium hydroxide aqueous solution, cetyltrimethylammonium hydroxide, tetraethyl orthosilicate, seed crystals, liquid titanium-silicon molecular sieve synthesis precursor, 20 wt% ammonia water and water were mixed to obtain a second mixture, which was then transferred into a stainless steel sealed reaction kettle, and crystallized at 165°C for 2d to obtain a crystallized sample, which was filtered, washed, dried at 120°C for 24h, and calcined at 550°C for 6h to obtain TS-2-L in the form of small crystal grain stacking.

[0094] The scanning electron microscope photos of each titanium-containing molecular sieve TS-2 are shown in FIG. 1, the X-ray diffraction patterns are shown in FIG. 2, the ultraviolet-visible spectra are shown in FIG. 3, and the performance of the molecular sieve catalyzing phenol hydroxylation is shown in Table 1. Figure 2 Figure 1 The scanning electron microscope photos of each titanium-containing molecular sieve TS-2 are shown in FIG. 1, the X-ray diffraction patterns are shown in FIG. 2, the ultraviolet-visible spectra are shown in FIG. 3, and the performance of the molecular sieve catalyzing phenol hydroxylation is shown in Table 1. Figure 3

[0095] Experimental Example: The performance of TS-2 in catalyzing phenol hydroxylation was evaluated in a round-bottom flask. 8.4 mL of acetone, 4.0 g of phenol, 1.6 g of H2O2 aqueous solution (30 wt%), and 0.2 g of powdered TS-2 were sequentially added into the round-bottom flask and stirred uniformly; a condensation reflux device was prepared, and the oil bath was heated to 80°C; and the reaction was carried out for 2h. After the reaction was completed, the H2O2 concentration before and after the reaction was titrated by iodometric method, and the contents of o-dihydroxybenzene, p-dihydroxybenzene, and p-benzoquinone in the reaction product were determined by gas chromatography. The catalytic performance of TS-2 samples synthesized according to the examples and comparative examples of the present application is shown in Table 1.

[0096] Table 1: Performance of some samples synthesized according to the examples and comparative examples

[0097]

[0098] Explanation:

[0099] X(PHE) = 1 - n(PHE) / [n(PHE) + n(CAT) + n(HQ) + n(PBQ)]

[0100] S(CAT) = n(CAT) / [n(CAT) + n(HQ) + n(PBQ)]

[0101] S(HQ) = n(HQ) / [n(CAT) + n(HQ) + n(PBQ)] ​​

[0102] S(PBQ) = n(PBQ) / [n(CAT) + n(HQ) + n(PBQ)]

[0103] U(H2O2) = 3 x X(PHE) / X(H2O2)

[0104] The samples containing nanoscale monodisperse particles always show slightly higher phenol conversion (X(PHE)) and H2O2 utilization (U(H2O2)). As can be seen from Table 1, the X(PHE) of the sample TS-2-A is the highest, reaching 16.6%, and the U(H2O2) reaches 59.6%, and the samples TS-2-A-J in each example are significantly higher than the sample TS-2-K in the comparative example, and most of them are higher than the sample TS-2-L. Only the phenol conversion (X(PHE)) of the example sample TS-2-B is basically the same as that of the sample TS-2-L in the comparative example (14.2%: 14.5%), and only the H2O2 utilization (U(H2O2)) of the example sample TS-2-F is basically the same as that of the sample TS-2-L in the comparative example (49.6%: 49.7%).

[0105] The phenol hydroxylation reaction produces three main products, namely p-benzoquinone (PBQ), hydroquinone (HQ) and catechol (CAT), among which HQ and CAT are target products, and PBQ is an undesirable by-product. As can be seen from Table 1, the samples containing nanoscale monodisperse particles in the examples have higher selectivity (S(CAT)) for CAT, and the S(CAT) of the example sample TS-2-I is the highest, reaching 53.2%, and the S(CAT) of the example sample TS-2-J is the lowest, reaching 50.2%, both of which are higher than 41.1% of the sample microparticle TS-2-K in the comparative example, and are basically the same as 50.4% of the sample TS-2-L.

[0106] 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 application, and TS-2-K and TS-2-L synthesized in the comparative examples can be seen that the products synthesized by each synthesis method are TS-2 molecular sieves with MEL structure.

[0107] Figure 2 The 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 application, and TS-2-K and TS-2-L synthesized in the comparative examples. From the 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 application, and TS-2-K and TS-2-L synthesized in the comparative examples, it can be seen that the products synthesized by each synthesis method are TS-2 molecular sieves with MEL structure. Figure 2It can be seen that each sample of TS-2-A~J is a single-dispersed nano-particle (400nm×200nm), and the particle is composed of parallel stacked rod-shaped structure (400nm×40nm). The sample of TS-2-K and TS-2-L is a large particle of 5~10μm. It can be seen that the particle size of TS-2-K can be reduced by the present application.

[0108] Figure 3 The UV-Vis diffuse reflectance spectra of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J synthesized by the embodiments of the present application, and TS-2-K and TS-2-L synthesized by the comparative examples are shown in the spectra, and there are three groups of absorption bands, respectively, at 210~220nm, 260~280nm and 310~330nm, which correspond to four-coordinated titanium, six-coordinated titanium and anatase TiO2, respectively. It can be seen that the sample of TS-2-K obtained without adding seed and ammonium salt in the synthesis process, and the sample of TS-2-L obtained without adding ammonium salt, mainly contain tetrahedral coordinated titanium, while the samples of TS-2-A, TS-2-C, TS-2-E, TS-2-G, TS-2-I, TS-2-J obtained by adding seed and ammonium salt in the synthesis process, the content of six-coordinated titanium is obviously increased.

[0109] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art, according to the technical solution and the inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, should be covered in the protection scope of the present application.

Claims

1. A method for synthesizing nano TS-2 molecular sieve, characterized in that, The application relates to a preparation method of TS-2 molecular sieves. The silicon source, the template agent and water are mixed in a certain proportion, and the mixture is condensed and refluxed and stirred to form a seed solution; The silicon source, the template agent and water are mixed in a certain proportion, and the mixture is stirred to obtain a first mixed solution; The titanium source is added into isopropyl alcohol and stirred to obtain a second mixed solution; The second mixed solution is added into the first mixed solution, and alcohol is removed by stirring to obtain a precursor solution; The ammonium salt and deionized water are mixed in a certain proportion, and the mixture is added into the precursor solution and stirred to obtain a first precursor solution; wherein the ammonium salt is at least one of ammonium carbonate, ammonium bicarbonate, ammonium sulfate, bisulfate, and ammonium chloride; The seed solution is added into the first precursor solution and stirred to obtain a crystallization solution; The crystallization solution is crystallized to obtain a crystallization product; The crystallization product is filtered, washed, dried and calcined to obtain the TS-2 molecular sieve.

2. The method of synthesizing nano TS-2 molecular sieve according to claim 1, characterized in that, 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 is at least one of tetrabutyl titanate, tetraethyl titanate, titanyl sulfate and titanium tetrachloride. The molar ratio of the silicon source to the template agent in the seed solution is 1:(0.1-0.5).

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

4. The method of synthesizing nano TS-2 molecular sieve according to claim 3, characterized in that, The molar ratio of the silicon source to the template agent in the first mixed solution is 1:(0.1-0.8). The molar ratio of the silicon source to the template agent in the first mixed solution is 1:(0.25-0.4).

5. The method of synthesizing nano TS-2 molecular sieve according to claim 3, characterized in that, The molar ratio of the silicon source, the template agent and water in the first mixed solution is 1:(0.1-0.8):(10-80). The molar ratio of the titanium source to isopropyl alcohol in the second mixed solution is 1:(5-30).

6. The method of synthesizing nano TS-2 molecular sieve according to claim 1, wherein, The molar ratio of the titanium source to isopropyl alcohol in the second mixed solution is 1:(5-15).

7. The method of synthesizing nano TS-2 molecular sieve according to claim 6, wherein, The molar ratio of the silicon source to the titanium source in the precursor solution is 1:(0.01-0.05).

8. The method of synthesizing nano TS-2 molecular sieve according to claim 6, wherein, 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).

9. The method of synthesizing nano TS-2 molecular sieve according to claim 1, wherein, The molar ratio of the ammonium salt to deionized water is 1:(30-50).

10. The method of synthesizing nano TS-2 molecular sieve according to claim 9, wherein, The molar ratio of the silicon source to the ammonium salt in the first precursor solution is 1:(0.05-0.15).

11. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, The molar ratio of the silicon source to the ammonium salt in the first precursor solution is 1:(0.05-0.10).

12. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, The mass ratio of the seed solution to the first precursor solution is 1:(50-200).

13. The method of claim 12, wherein the method is characterized by: The mass ratio of the seed solution to the first precursor solution is 1:(100-120).

14. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, In the step of mixing the silicon source, the template agent and water in a certain proportion and stirring to obtain the first mixed solution, the stirring temperature is 40 DEG C, and the stirring time is 5 h.

15. The method of claim 14, wherein the method is characterized by: In the step of adding the titanium source into isopropyl alcohol and stirring to obtain the second mixed solution, the stirring temperature is room temperature, and the stirring time is 0.5-2 h.

16. The method of claim 1, wherein the method is characterized by: The titanium source is added into isopropyl alcohol in a dropwise manner.

17. The method of claim 16, wherein the method is characterized by: In the step of adding the second mixed solution into the first mixed solution and removing alcohol by stirring to obtain the precursor solution, the stirring temperature is 60-95 DEG C, and the alcohol removal time is 0.5-2 h.

18. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, ​ 19. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, ​ 20. The method for synthesizing nano-TS-2 molecular sieves according to claim 1, characterized in that, ​ 21. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, ​ 22. The method of claim 1, wherein the method is characterized by: The second mixed solution is added dropwise to the first mixed solution under stirring.

23. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, The silicon source, the template agent and water are mixed in a certain proportion, and the seed solution is formed by condensation reflux stirring at a temperature of 60-80℃ for 48-72h.

24. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, The ammonium salt and deionized water are mixed in a certain proportion, and the first precursor solution is obtained by adding the mixture into the precursor solution and stirring for 10-30min.

25. The method of claim 1, wherein the method is characterized by: The seed solution is added into the first precursor solution, and the crystallization solution is obtained by stirring for 10-30min.

26. The method of claim 1, wherein the method is characterized by: The crystallization is carried out in a crystallization kettle, and the crystallization temperature is 120-180℃ and the crystallization time is 12-72h. The crystallization product is filtered, washed, dried and calcined, and the drying temperature is 60-120℃ and the drying time is 6-24h.

27. The method of claim 26, wherein the method is further defined by: The drying temperature is 80-100℃ and the drying time is 8-12h.

28. The method of synthesizing nano TS-2 molecular sieve of claim 26, wherein, The calcination temperature is 540℃ and the calcination time is 6h.

29. The method of synthesizing nano TS-2 molecular sieve of claim 1, wherein, The nano TS-2 molecular sieve prepared by the method of any one of claims 1-28.

30. The use of the molecular sieve of claim 29 for a catalyst.

31. The use of the molecular sieve of claim 29 for a catalyst in phenol hydroxylation, cyclohexene epoxidation and cyclohexanone ammoxidation reactions.

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