A TS-1 molecular sieve with uniform spatial distribution of Ti atoms and its preparation method

Abstract

The present invention discloses a TS-1 molecular sieve with uniform spatial distribution of Ti atoms and a preparation method thereof, the preparation method of the TS-1 molecular sieve includes: after mixing a silicon source with an inorganic alkaline source and water, hydrothermal reaction is carried out to obtain a silica sol precursor; after mixing a titanium source with the above-mentioned silica sol precursor, ammonium salt is added to precipitate the obtained mixed sol, drying, and after roasting, a silicon-titanium xerogel is obtained; after mixing the above-mentioned silicon-titanium xerogel with ammonium salt and water, heating reaction is carried out to carry out ion exchange, drying, and after roasting, a hydrogen-type silicon-titanium xerogel is obtained; after mixing the above-mentioned hydrogen-type silicon-titanium xerogel with a template, crystallization is carried out, drying, and after roasting, the TS-1 molecular sieve is obtained. A TS-1 molecular sieve with uniform spatial distribution of Ti atoms proposed by the present invention and a preparation method thereof, a TS-1 molecular sieve with uniform spatial distribution of Ti atoms can be synthesized under the premise of using a small amount of template, so the preparation method is green and efficient, has low preparation cost, and is easy to industrial production and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieves, and in particular relates to a TS-1 molecular sieve with uniform spatial distribution of Ti atoms and a preparation method thereof. Background Art

[0002] In 1983, the patent (US4410501A) reported the first generation of titanium silicalite - TS-1. The catalytic oxidation system (TS / H2O2) composed of it as catalyst and hydrogen peroxide as oxidant has the advantages of high atomic utilization, low reaction temperature, and green and pollution-free in the catalytic reaction. It has attracted widespread attention from the scientific and industrial communities as a new generation of green chemical catalyst for selective oxidation.

[0003] The root of the catalytic oxidation ability of TS-1 molecular sieve lies in the Ti active center. Therefore, the properties of the Ti active center (such as the Ti active center content, Ti active center structure, Ti active center distribution, and Ti active center accessibility) directly affect the intrinsic catalytic ability of TS-1 molecular sieve. In particular, the distribution of Ti atoms in the molecular sieve framework has a direct structure-activity relationship with its catalytic ability. At the macroscopic level, the distribution types of framework Ti atoms are mainly divided into three types: surface-poor Ti, surface-rich Ti, and Ti uniformly distributed in the molecular sieve framework. The surface of TS-1 molecular sieve obtained by the classic hydrothermal synthesis method is usually rich in silicon and low in titanium (US4410501A; Appl. Catal. A: Gen., 2013, 453272-279; Angew. Chem. Int. Edit., 2021, 60, 3443-3448). In order to obtain high-performance titanium silicalite molecular sieves, researchers have increased the content of surface Ti active centers as one of the effective strategies. Chemistry Select (Chemistry Select. 2017, 2, 10097-10100) reported a hollow core-shell S-1@TS-1 molecular sieve. This zeolite, with a hollow S-1 core and TS-1 shell, exhibits significantly enhanced catalytic oxidation performance due to the increased accessibility of the tetracoordinated Ti active centers within the framework. Furthermore, surface-Ti-enriched TS-1 molecular sieves can be obtained by acid or organic base modification (Catal. Commun., 2004, 5, 725-728; New J. Chem., 2014, 38, 4229-4234; Chem. Commun., 2018, 54, 6384-6387).

[0004] However, there are very few reports in the existing literature on the synthesis method of molecular sieves with uniform distribution of Ti atoms. Patents (CN113307285A), Materials Chemistry (Chem.Mater., 2021, 33, 4988-5001) and Journal of Catalysis (J.Catal., 2021, 404, 990-998) disclosed for the first time the successful synthesis of a series of molecular sieves with uniform heteroatom distribution by hydrothermal synthesis, including MFI topology (TS-1, Al-MFI, Fe-MFI, Sn-MFI, Nb-MFI), MEL and *BEA topology molecular sieves (TS-2, Ti-Al-Beta). The key to the hydrothermal synthesis is that the all-silicon S-1 molecular sieve is completely dissolved in a high-alkalinity tetrapropylammonium hydroxide TPAOH (TPAOH / SiO2≥1.0) solution to obtain Q 2 and Q 3 The silicon species in the state can condense with heteroatoms like a "grab hand" and enter the framework synchronously with the heteroatoms during the crystallization process, thereby synthesizing a molecular sieve with uniform heteroatom distribution. 2 and Q 3 The key to constructing silicon species in this state lies in the use of a highly basic tetrapropylammonium hydroxide (TPAOH) template (TPAOH / SiO₂ ≥ 1.0). Therefore, the current hydrothermal synthesis technology clearly suffers from the requirement for a large amount of organic template (template / SiO₂ ≥ 1.0). This not only results in high production costs, but also generates a large amount of nitrogen-containing wastewater, limiting its industrial application. Summary of the Invention

[0005] Based on the above technical problems, the present invention proposes a TS-1 molecular sieve with uniform spatial distribution of Ti atoms and a preparation method thereof. A TS-1 molecular sieve with uniform spatial distribution of Ti atoms can be synthesized using a small amount of template agent. Therefore, the preparation method is green and efficient, has low preparation cost, and is easy to industrialize and apply.

[0006] The present invention provides a TS-1 molecular sieve with uniform spatial distribution of Ti atoms, wherein the (Si / Ti ratio of the surface at any thickness): (the overall Si / Ti ratio) of the TS-1 molecular sieve is greater than 0.95 and less than 1.05.

[0007] Furthermore, the present invention also provides a method for preparing the TS-1 molecular sieve having uniform spatial distribution of Ti atoms, comprising the following steps:

[0008] S1. Mixing a silicon source, an inorganic alkali source and water, and performing a hydrothermal reaction to obtain a silica sol precursor;

[0009] S2, mixing the titanium source and the silica sol precursor obtained in step S1, adding ammonium salt to precipitate the obtained mixed sol, drying, and calcining to obtain a silica-titanium xerogel;

[0010] S3, mixing the titanium-silicon xerogel obtained in step S2 with ammonium salt and water, heating the mixture to react for ion exchange, drying, and calcining to obtain hydrogen titanium-silicon xerogel;

[0011] S4, mixing the hydrogenated silicon titanium xerogel obtained in step S3 with the template, crystallizing, drying, and calcining to obtain the TS-1 molecular sieve.

[0012] Preferably, in step S1, SiO2 in the silicon source and OH in the inorganic alkali source are used. - The molar ratio of the silicon source, the inorganic alkali source and the water is 1: (0.4-2): (10-100) based on the molar amount of the silicon source and the water;

[0013] Preferably, the hydrothermal reaction temperature is 100-190° C., and the reaction time is 0.5-24 h.

[0014] Preferably, in step S1, the silicon source is at least one of pure silicon molecular sieve, silica sol, fumed silica gel or water glass; and the inorganic alkali source is at least one of sodium hydroxide or potassium hydroxide.

[0015] In the present invention, in the specific operation of step S1, an inorganic alkali source is first mixed with water, and then a silicon source is added. After mixing evenly, the mixture is hydrothermally treated at 100-190° C. for 0.5-24 h, and the silica sol precursor is obtained after cooling.

[0016] Preferably, in step S2, based on the molar amounts of SiO2 in the silicon source and the titanium source, the molar ratio of the silicon source to the titanium source is 1:(0.01-0.025).

[0017] Preferably, in step S2, the titanium source is at least one of titanium trichloride, titanium tetrachloride, titanyl sulfate or titanium sulfate, and the ammonium salt is at least one of ammonium carbonate, ammonium chloride or ammonium sulfate.

[0018] In the present invention, in the specific operation of step S2, a titanium source is added to the silica sol precursor obtained in step S1 and stirred evenly, an ammonium salt is added to precipitate the obtained mixed sol, and the mixture is filtered, dried, and calcined to obtain the silica-titanium xerogel.

[0019] Preferably, in step S3, the mass ratio of the silicon-titanium xerogel, ammonium salt and water is 1:1:(15-20);

[0020] Preferably, the heating reaction temperature is 70-90° C. and the time is 2-6 hours.

[0021] In the present invention, step S3 is specifically operated to mix the silica-titanium xerogel obtained in step S2 with ammonium salt and water, and then stir the mixture in a water bath at 70-90°C for 2-6 hours, filter, and dry, and repeat the above operation three times to achieve the reaction between ammonium ions and cations (such as Na + ,K + ) is exchanged to obtain the hydrogen-type silicon-titanium dry gel.

[0022] Preferably, in step S4, based on the molar amounts of SiO2 in the silicon source and the template, the molar ratio of the silicon source to the template is 1:(0.05-0.3).

[0023] Preferably, in step S4, the template is at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-butylamine or ethylenediamine.

[0024] Preferably, in step S4, the crystallization is carried out by mixing the hydrogenated titanium-silicon dry gel and the template agent to obtain a crystallized mixed dry gel under a water vapor atmosphere in a crystallization kettle;

[0025] Preferably, the crystallization temperature is 120-190°C and the time is 2-72h;

[0026] Preferably, the mass ratio of the crystallized mixed xerogel obtained by mixing the hydrogenated silicon-titanium xerogel and the template agent and the water corresponding to the water vapor is 1:(1-15).

[0027] In the present invention, in the specific operation of step S4, the hydrogen-type silicon titanium xerogel obtained in step S3 is mixed with a template to obtain a crystallized mixed xerogel; according to the mass ratio of the crystallized mixed xerogel to water being 1:(1-15), the obtained crystallized mixed xerogel is transferred to a hollow barrel tank lined with polytetrafluoroethylene in a crystallization kettle, an appropriate amount of water is placed at the bottom of the crystallization kettle, and the water forms water vapor under heating conditions and enters the hollow barrel tank through the through holes on the hollow barrel tank for crystallization. After static crystallization at 120-190°C for 2-72h, a crystallized product can be obtained; the obtained crystallized product is then subjected to conventional filtration, washing, drying and calcination to obtain the TS-1 molecular sieve with uniform spatial distribution of Ti atoms.

[0028] The present invention uses an inorganic silicon compound, an inorganic titanium compound, a small amount of template and a small amount of water as raw materials, and obtains a TS-1 molecular sieve with uniform spatial distribution of Ti atoms through dry gel crystallization. The Si / Ti ratio of the surface of the molecular sieve at different thicknesses is very close to the overall Si / Ti ratio (only a difference of ±5%).

[0029] Compared with the prior art, the present invention innovatively improves the synthesis route of TS-1 molecular sieve with uniform spatial distribution of Ti atoms, uses inorganic base as alkali source (alkali source / SiO2=~1.0), dissolves / condenses the silicon source, and constructs a Q-like "grab hand" 2 and Q 3 State silicon species, and then using a small amount of organic TPAOH template (template / SiO2 molar ratio = ~0.05) or tetrapropylammonium bromide as a template, TS-1 molecular sieve with uniform Ti spatial distribution can also be synthesized. The entire production process is green and efficient, the preparation cost is greatly reduced, and it is easy to industrialize and apply.

[0030] Compared with the prior art, the present invention has the following significant advantages:

[0031] 1. The TS-1 molecular sieve of the present invention has a TS-1 molecular sieve framework with uniform spatial distribution of Ti atoms, which is conducive to the controllable design of Ti active centers and the synergistic effect of catalysis, and can be used to prepare cyclohexanone oxime, propylene oxide, and catechol using hydrogen peroxide as an oxidant.

[0032] 2. The preparation method of the present invention effectively solves the defect that a large amount of template and water solvent are required to prepare molecular sieves with uniform Ti atomic distribution in the hydrothermal system of the prior art.

[0033] 3. The synthesis process of the present invention is green and efficient, with low preparation cost and easy industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Surface Si / Ti ratios at different depths of the TS-1 molecular sieves obtained in Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0035] Hereinafter, the present invention will describe the technical solution in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0036] Example 1

[0037] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the following method:

[0038] (1) Silica sol precursor:

[0039] According to the SiO2 in pure silicon molecular sieve Silicate-1, OH in NaOH - The molar ratio of NaOH and H2O is 1:1:34. First, NaOH and water are mixed, and then pure silicon molecular sieve Silicate-1 is added. After mixing evenly, the mixture is hydrothermally treated at 170°C for 3 hours, and then cooled to obtain a silica sol precursor.

[0040] (2) Silicon titanium xerogel:

[0041] According to the molar ratio of SiO2 and TiCl3 in pure silicon molecular sieve Silicate-1 being 1:0.017, a TiCl3 solution (15-20 wt.%) is added to the silica sol precursor prepared in step (1) and stirred uniformly to obtain a silica-titanium mixed sol, and then ammonium chloride is added to precipitate the obtained silica-titanium mixed sol, which is then filtered, dried, and calcined at 550°C to obtain a silica-titanium xerogel;

[0042] (3) Hydrogenated silicon titanium xerogel:

[0043] According to the mass ratio of silica-titanium dry gel, ammonium salt and water being 1:1:15, the silica-titanium dry gel (containing cationic Na + ) was mixed with ammonium chloride and water, stirred in a water bath at 80°C for 2 h, filtered, dried, and the above operation was repeated 3 times to obtain ammonium ions NH4 + With the cation Na in the silica-titanium xerogel + After calcination at 550 ° C, the cation-free Na + Hydrogenated silicon-titanium xerogel;

[0044] (4) TS-1 molecular sieve:

[0045] According to the molar ratio of SiO2 in pure silicon molecular sieve Silicate-1 and template agent tetrapropylammonium hydroxide being 1:0.3, the template agent tetrapropylammonium hydroxide is evenly mixed with the hydrogen-type silicon titanium dry gel obtained in step (3) to obtain a crystallized mixed dry gel, and then according to the mass ratio of the crystallized mixed dry gel and water being 1:3, the obtained crystallized mixed dry gel is transferred to the hollow barrel tank in the polytetrafluoroethylene lining of the crystallization kettle, and an appropriate amount of water is placed at the bottom of the crystallization kettle. After the water forms water vapor under heating conditions, it enters the hollow barrel tank through the through hole on the hollow barrel tank for crystallization. Specifically, after static crystallization at 170°C for 48 hours, a crystallized product is obtained. The obtained crystallized product is then filtered, washed, dried, and calcined at 550°C for 8 hours to obtain the TS-1 molecular sieve with uniform spatial distribution of Ti atoms.

[0046] Example 2

[0047] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (4), the template agent tetrapropylammonium hydroxide is uniformly mixed with the hydrogen-type silicon titanium xerogel prepared in step (3) according to the molar ratio of SiO2 in the pure silicon molecular sieve Silicate-1 to the template agent tetrapropylammonium hydroxide being 1:0.2.

[0048] Example 3

[0049] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (1), the SiO2 in pure silicon molecular sieve Silicate-1, the OH in NaOH, - The molar ratio of SiO2 and H2O is 1:1:20, NaOH and water are first mixed, and then pure silicon molecular sieve Silicate-1 is added; in step (4), the molar ratio of SiO2 in pure silicon molecular sieve Silicate-1 and template agent tetrapropylammonium hydroxide is 1:0.1, and the template agent tetrapropylammonium hydroxide is evenly mixed with the hydrogen-type silicon titanium dry gel prepared in step (3).

[0050] Example 4

[0051] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (1), the SiO2 in pure silicon molecular sieve Silicate-1, the OH in KOH - The molar ratio of SiO2 and H2O is 1:1:50, KOH and water are first mixed, and then pure silicon molecular sieve Silicate-1 is added, mixed evenly and then hydrothermally treated at 170°C for 5h; in step (4), the molar ratio of SiO2 in pure silicon molecular sieve Silicate-1 and template agent tetrapropylammonium hydroxide is 1:0.05, and the template agent tetrapropylammonium hydroxide is evenly mixed with the hydrogen-type silicon titanium dry gel prepared in step (3).

[0052] Example 5

[0053] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (4), the molar ratio of SiO2 in the pure silicon molecular sieve Silicate-1 to the template agent tetrapropylammonium bromide is 1:0.2, and the template agent tetrapropylammonium bromide is uniformly mixed with the hydrogen-type silicon titanium xerogel prepared in step (3) to obtain a crystallized mixed xerogel, and the obtained crystallized mixed xerogel is transferred to a hollow barrel tank lined with polytetrafluoroethylene in a crystallization kettle according to a mass ratio of the crystallized mixed xerogel to water of 1:1, and an appropriate amount of water is placed at the bottom of the crystallization kettle. After the water forms water vapor under heating conditions, it enters the hollow barrel tank through the through holes on the hollow barrel tank for crystallization, specifically static crystallization at 150°C for 72 hours.

[0054] Example 6

[0055] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (4), the molar ratio of SiO2 in the pure silicon molecular sieve Silicate-1 to the template agent tetrapropylammonium bromide is 1:0.2, the template agent tetrapropylammonium bromide is uniformly mixed with the hydrogen-type silicon titanium xerogel prepared in step (3) to obtain a crystallized mixed xerogel, and the obtained crystallized mixed xerogel is transferred to a hollow barrel tank in a polytetrafluoroethylene-lined crystallization kettle at a mass ratio of the crystallized mixed xerogel to water of 1:5, and an appropriate amount of water is placed at the bottom of the crystallization kettle.

[0056] Example 7

[0057] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (4), a crystallized mixed xerogel is obtained according to the molar ratio of SiO2 in pure silicon molecular sieve Silicate-1 and template agents tetrapropylammonium bromide and n-butylamine being 1:0.2, and then the obtained crystallized mixed xerogel is transferred to a hollow barrel tank lined with polytetrafluoroethylene in a crystallization kettle according to the mass ratio of the crystallized mixed xerogel to water being 1:10, and an appropriate amount of water is placed at the bottom of the crystallization kettle. After the water forms water vapor under heating conditions, it enters the hollow barrel tank through the through holes on the hollow barrel tank for crystallization, and is specifically statically crystallized at 150°C for 24 hours.

[0058] Example 8

[0059] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (2), a TiCl3 solution (15-20 wt.%) is first added to the silica sol precursor prepared in step (1) and stirred uniformly according to the molar ratio of SiO2 and TiCl3 in the pure silicon molecular sieve Silicate-1 being 1:0.025 to obtain a silicon-titanium mixed sol, and ammonium carbonate is then added to precipitate the obtained silicon-titanium mixed sol; and in step (4), the template agent tetrapropylammonium hydroxide is uniformly mixed with the hydrogen-type silicon-titanium xerogel prepared in step (3) according to the molar ratio of SiO2 in the pure silicon molecular sieve Silicate-1 to the template agent tetrapropylammonium hydroxide being 1:0.2.

[0060] Example 9

[0061] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (2), a TiCl3 solution (15-20 wt.%) is first added to the silica sol precursor prepared in step (1) and stirred uniformly according to the molar ratio of SiO2 and TiCl3 in the pure silica molecular sieve Silicate-1 being 1:0.02 to obtain a silica-titanium mixed sol, and ammonium sulfate is then added to precipitate the obtained silica-titanium mixed sol; and in step (4), the template agent tetrapropylammonium hydroxide is uniformly mixed with the hydrogen-type silica-titanium xerogel prepared in step (3) according to the molar ratio of SiO2 in the pure silica molecular sieve Silicate-1 to the template agent tetrapropylammonium hydroxide being 1:0.2.

[0062] Example 10

[0063] A TS-1 molecular sieve with uniform spatial distribution of Ti atoms is prepared by the method described in Example 1, except that in step (2), a TiCl3 solution (15-20 wt.%) is first added to the silica sol precursor prepared in step (1) and stirred uniformly according to the molar ratio of SiO2 and TiCl3 in the pure silicon molecular sieve Silicate-1 being 1:0.01 to obtain a silicon-titanium mixed sol; and in step (4), the template agent tetrapropylammonium hydroxide is uniformly mixed with the hydrogen-type silicon-titanium xerogel prepared in step (3) according to the molar ratio of SiO2 in the pure silicon molecular sieve Silicate-1 and the template agent tetrapropylammonium hydroxide being 1:0.2.

[0064] Comparative Example 1

[0065] A TS-1 molecular sieve is prepared by the method described in a patent publication (CN113307285A) or materials chemistry (Chem. Mater., 2021, 33, 4988-5001), specifically comprising:

[0066] According to the SiO2 in pure silicon molecular sieve Silicalite-1, OH in tetrapropylammonium hydroxide - The molar ratio of tetrapropylammonium hydroxide to H2O is 1:1:30. A 25% mass concentration of tetrapropylammonium hydroxide solution and water are first mixed, and then pure silicon molecular sieve Silicalite-1 is added. After mixing evenly, the mixture is hydrothermally treated at 170°C for 3 hours and cooled to obtain a silicon species solution.

[0067] TiCl3 solution (15-20 wt.%) was added to the silicon-containing species solution prepared above according to a Si / Ti molar ratio of 60, and stirred to obtain a crystallized mixed solution;

[0068] The crystallization mixed solution prepared above was hydrothermally crystallized at a crystallization temperature of 170° C. for 48 hours to obtain a crystallized product, which was then filtered, washed, dried, and calcined at 550° C. for 8 hours to obtain the TS-1 molecular sieve.

[0069] Comparative Example 2

[0070] A TS-1 molecular sieve is prepared by referring to the classical hydrothermal synthesis method described in the patent publication (US4410501A), specifically comprising:

[0071] The synthetic raw materials are prepared according to a molar ratio of SiO2, TiO2, TPAOH and H2O of 1.0:0.017:0.18:18. Tetraethyl orthosilicate (TEOS) and tetrabutyl titanate (TBOT) are mixed and then slowly added dropwise to a template agent tetrapropylammonium hydroxide (TPAOH) aqueous solution under stirring conditions. The resulting mixture is then placed in a 50°C water bath for hydrolysis into a uniform solution, and then the temperature is raised to 80°C for alcohol removal treatment. Water is continuously added during the alcohol removal process to ensure that the total amount remains basically consistent, and finally a clear and uniform sol is obtained; the sol is charged into a high-pressure reactor and crystallized under static (or dynamic) conditions at 170°C for 48 hours. The obtained product is filtered, dried, and then calcined at 550°C for 8 hours to obtain the TS-1 molecular sieve.

[0072] Comparative Example 3

[0073] A molecular sieve is prepared by the method described in the patent publication (CN113307285A), specifically comprising:

[0074] According to the SiO2 in pure silicon molecular sieve Silicalite-1, OH in alkali source - The molar ratio of alkali source to H2O is 1:1.3:34, and the molar ratio of alkali source to H2O is 1:1.3:34. The molar ratio of alkali source to H2O is 1:0.3. The alkali source and water are first mixed, and then pure silicon molecular sieve Silicalite-1 is added. After mixing evenly, the mixture is hydrothermally treated at 170°C for 3 hours and cooled to obtain a silicon species solution.

[0075] TiCl3 solution (15-20 wt.%) was added to the silicon-containing species solution prepared above according to a Si / Ti molar ratio of 60, and stirred to obtain a crystallized mixed solution;

[0076] The crystallization mixed solution prepared above was hydrothermally crystallized at a crystallization temperature of 170°C for 48 hours to obtain a crystallized product, which was then filtered, washed, dried, and calcined at 550°C for 8 hours. However, TS-1 molecular sieve with uniform spatial distribution of Ti atoms could not be obtained.

[0077] The overall Si / Ti ratio of the TS-1 molecular sieve obtained in Example 1, Comparative Example 1 and Comparative Example 2 was determined by inductively coupled plasma emission spectrometry (ICP); the surface Si / Ti ratio of the TS-1 molecular sieve obtained was determined by X-ray photoelectron spectroscopy (XPS). During the test, under argon ion sputtering (5000 eV), Ta2O5 was used as a standard, and the etching rate was 5 nm / min. That is, as the etching time increased, the detection depth increased, and the surface Si / Ti ratio of the TS-1 molecular sieve at different depths (thickness) obtained was measured; wherein, the surface Si / Ti ratio of the TS-1 molecular sieve at different depths obtained in Example 1, Comparative Example 1 and Comparative Example 2 was referenced. Figure 1 shown.

[0078] Depend on Figure 1 It can be seen that the surface Si / Ti of the TS-1 molecular sieve obtained in Example 1 at different depths is as follows: Figure 1 As shown in Figure B, it can be seen that when the etching time changes from 0s to 300s, the XPS test depth increases, that is, as the etching time increases, the detection depth increases, and the measured surface Si / Ti ratio is very close to the overall Si / Ti ratio (58) (±5%), which shows that the Ti in the TS-1 molecular sieve of the present invention can be evenly distributed on the TS-1 molecular sieve framework; the surface Si / Ti ratios of the TS-1 molecular sieve obtained in Comparative Example 1 at different depths are as follows: Figure 1 As shown in Figure C, it can be seen that when the etching time changes from 0s to 300s, the XPS test depth increases, that is, as the etching time increases, the detection depth increases, and the measured surface Si / Ti and overall Si / Ti ratios (58) are also very close (±5%); this also explains that the Ti in the TS-1 molecular sieve obtained in Comparative Example 1 can be evenly distributed on the TS-1 molecular sieve framework, but in the synthesis process of the comparative example, a large amount of organic template (template / SiO2≥1.0) is required; the surface Si / Ti ratios of the TS-1 molecular sieve obtained in Comparative Example 2 at different depths are as follows: Figure 1 As shown in Figure A, it can be seen that when the etching time changes from 0s to 300s, the XPS test depth increases, that is, as the etching time increases, the detection depth increases, and the measured surface Si / Ti ratio is higher than the overall Si / Ti ratio (57) by at least (+57%-+145%), indicating that the TS-1 molecular sieve obtained in Comparative Example 2 is titanium-rich inside and silicon-rich on the surface.

[0079] At the same time, in other embodiments of the present invention, the XPS graph trends of the obtained TS-1 molecular sieve are consistent with Figure 1 B is similar, and its surface Si / Ti ratio is very close to the bulk Si / Ti ratio (58) (±5%).

[0080] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing TS-1 molecular sieve with uniform spatial distribution of Ti atoms, characterized in that: The steps include: S1. Mixing a silicon source, an inorganic alkali source and water, and performing a hydrothermal reaction to obtain a silica sol precursor; S2, mixing the titanium source and the silica sol precursor obtained in step S1, adding ammonium salt to precipitate the obtained mixed sol, drying, and calcining to obtain a silica-titanium xerogel; S3, mixing the titanium-silicon xerogel obtained in step S2 with ammonium salt and water, heating the mixture to react for ion exchange, drying, and calcining to obtain hydrogen titanium-silicon xerogel; S4, mixing the hydrogenated silicon titanium xerogel obtained in step S3 with the template, crystallizing, drying, and calcining to obtain the TS-1 molecular sieve; The (Si / Ti ratio of the surface at any thickness): (Si / Ti ratio of the whole body) of the TS-1 molecular sieve is greater than 0.95 and less than 1.

05.

2. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to claim 1, characterized in that: In step S1, SiO2 in the silicon source and OH in the inorganic alkali source are used to - Based on the molar amount of silicon source, inorganic alkali source and water, the molar ratio of the silicon source, inorganic alkali source and water is 1:(0.4-2):(10-100).

3. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to claim 1, characterized in that: In step S1, the hydrothermal reaction temperature is 100-190° C., and the reaction time is 0.5-24 h.

4. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, wherein in step S1, the silicon source is at least one of pure silicon molecular sieve, silica sol, fumed silica gel or water glass; and the inorganic alkali source is at least one of sodium hydroxide or potassium hydroxide.

5. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S2, based on the molar amounts of SiO2 in the silicon source and the titanium source, the molar ratio of the silicon source to the titanium source is 1:(0.01-0.025).

6. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S2, the titanium source is at least one of titanium trichloride, titanium tetrachloride, titanyl sulfate or titanium sulfate, and the ammonium salt is at least one of ammonium carbonate, ammonium chloride or ammonium sulfate.

7. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S3, the mass ratio of the silicon-titanium xerogel, ammonium salt and water is 1:1:(15-20).

8. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S3, the heating reaction temperature is 70-90° C. and the time is 2-6 hours.

9. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S4, based on the molar amounts of SiO2 in the silicon source and the template, the molar ratio of the silicon source to the template is 1:(0.05-0.3).

10. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S4, the template agent is at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-butylamine or ethylenediamine.

11. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S4, the crystallization is carried out in a water vapor atmosphere in a crystallization kettle by uniformly mixing the hydrogenated silicon titanium xerogel and the template agent to obtain the crystallized mixed xerogel.

12. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to any one of claims 1 to 3, characterized in that: In step S4, the crystallization temperature is 120-190° C., and the crystallization time is 2-72 hours.

13. The method for preparing the TS-1 molecular sieve with uniform spatial distribution of Ti atoms according to claim 11, characterized in that: In step S4, the mass ratio of the crystallized mixed xerogel obtained by mixing the hydrogenated silicon-titanium xerogel and the template agent and the water corresponding to the water vapor is 1:(1-15).

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