Method for preparing organosilica-modified titanium silicalite molecular sieve and modified titanium silicalite molecular sieve and applications thereof

Abstract

The present application relates to the technical field of molecular sieve, and discloses a method for preparing a silicon-modified titanium-silicon molecular sieve, the modified titanium-silicon molecular sieve and application thereof, the method comprising the following steps: (1) subjecting a mixed solution containing a silicon source, a titanium source, an alkali source, water and a first organosilicon to hydrothermal crystallization; then performing solid-liquid separation, first drying and calcination; (2) contacting the calcination product obtained in step (1) with a second organosilicon, and then performing second drying; wherein the first organosilicon and the second organosilicon are each independently selected from at least one of the organosilicons shown in formula (1); in formula (1), R1, R2, R3 and R4 are each independently selected from H, an alkyl group, an alkoxy group, an aminoalkyl group, an alkylamine group and halogen. The method of the present application can obtain a titanium-silicon molecular sieve with a relatively high oxygen hole content.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a method for preparing organosilicon-modified titanium-silicon molecular sieves, and the modified titanium-silicon molecular sieves and their applications. Background Technology

[0002] Molecular sieves are synthetic zeolites that exhibit molecule sieving, adsorption, ion exchange, and catalytic activities. The catalytic activity of molecular sieves generally occurs within the internal space of the sieve crystal, and their catalytic activity is closely related to their pore size and channel structure. Because molecular sieves possess a regular and uniform intracrystalline channel structure, molecular sieves with suitable channel structures are selected for molecular size sieving based on specific reaction requirements. Therefore, the catalytic performance of molecular sieves is influenced by the kinetic diameters of reactant molecules, product molecules, and reaction intermediates.

[0003] As mentioned earlier, when molecular sieves are used as catalysts or catalyst supports, the selectivity and conversion rate of the target catalytic reaction are influenced by the size and shape of the sieve pores and channels, exhibiting shape-selective catalysis. On the other hand, oxygen vacancies, defects, and step sites on the molecular sieve surface also affect the adsorption-desorption behavior of the reaction process. This is especially true when the molecular sieve is used as a support to load other metal oxides or metal nanoparticles; the influence of these surface oxygen vacancies, defects, and step sites on the catalytic reaction is particularly important. Taking titanium-silicon molecular sieves as an example, they possess a double ten-membered ring intersecting channel structure (MFI) represented by ZSM-5, composed of "Z"-shaped channels and intersecting elliptical through-holes. Ti replaces Al doping into the molecular sieve framework, making it a Pentasil-type heteroatom molecular sieve belonging to the orthorhombic crystal system. The tetracoordinated Ti in the titanium-silicon molecular sieve framework is the active center for selective oxidation reactions. In addition to maintaining the original MFI molecular sieve topology, it has an abundance of active catalytic structures such as oxygen vacancies, which can simultaneously take into account shape-selective catalysis and catalytic oxidation activities. It can be widely used in fields such as olefin epoxidation, cyclohexanone ammoniation, alcohol oxidation, saturated hydrocarbon oxidation, and phenol hydroxylation.

[0004] However, the oxygen vacancy content in existing titanium-silicon molecular sieves is relatively low and needs to be further increased to improve the catalytic performance of titanium-silicon molecular sieves. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem of low oxygen vacancy content in existing titanium-silicon molecular sieves, and to provide a method for preparing organosilicon-modified titanium-silicon molecular sieves, as well as the modified titanium-silicon molecular sieves and their applications.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing organosilicon-modified titanium-silicon molecular sieves, the method comprising the following steps:

[0007] (1) The mixture containing silicon source, titanium source, alkali source, water and first organosilicon is subjected to hydrothermal crystallization; then solid-liquid separation, first drying and calcination are carried out;

[0008] (2) The calcined product obtained in step (1) is contacted with a second organosilicon, and then subjected to a second drying process. The conditions for the second drying process are such that the drying rate of the solid-liquid mixture is 0.015-1.015 g organosilicon / (cm³). 2 h·g roasting product);

[0009] Wherein, the first organosilicon and the second organosilicon are each independently selected from at least one of the organosilicones shown in formula (1);

[0010]

[0011] In formula (1), R1, R2, R3, and R4 are each independently selected from H, alkyl, alkoxy, aminoalkyl, alkylamino, and halogen; wherein the hydrogen atoms in alkyl, alkoxy, aminoalkyl, and alkylamino are either substituted by halogen or not substituted.

[0012] A second aspect of the present invention provides a modified molecular sieve prepared by the method described above.

[0013] A third aspect of the present invention provides a modified titanium-silicon molecular sieve, wherein the content of oxygen vacancies in the modified titanium-silicon molecular sieve is 0.35-5.5 mmol / g.

[0014] The fourth aspect of this invention provides the application of the modified titanium-silicon molecular sieve described above in the preparation of propylene oxide.

[0015] Through the above technical solution, the present invention achieves the following beneficial effects:

[0016] (1) The present invention uses a two-step method to modify titanium silicon molecular sieves with organosilicon and controls the drying rate of solid-liquid mixture to prepare titanium silicon molecular sieves with high oxygen vacancy content.

[0017] (2) The preferred method of the present invention can further reduce the hydroxyl density (acidic sites) in titanium silicon molecular sieve, reduce the average particle size of titanium silicon molecular sieve, and increase the titanium content in titanium silicon molecular sieve.

[0018] (3) The titanium-silicon molecular sieve of the present invention has a high oxygen hole content. On the one hand, this can facilitate the adsorption, migration, and transformation of reactant molecules, providing more catalytic active sites for reactions such as olefin epoxidation, cyclohexanone ammoniation, alcohol oxidation, and saturated hydrocarbon oxidation. On the other hand, it can provide more landing sites for other metal nanoparticles or oxides, facilitating the landing of the second active material in the bifunctional supported catalyst, increasing the number of active sites, and thus improving the overall catalytic performance. The titanium-silicon molecular sieve of the present invention can provide more active sites when used for catalysis, thereby improving the catalytic effect.

[0019] In a preferred embodiment, the titanium-silicon molecular sieve of the present invention has a low average particle size. On the one hand, this allows for a higher specific surface area, reducing the impact of internal diffusion on the catalytic reaction; on the other hand, it provides more surface catalytic active sites, which facilitates the adsorption and desorption processes of the catalytic reaction. For catalytic reactions requiring short residence times, it can achieve better catalytic performance. The titanium-silicon molecular sieve of the present invention has a high hydroxyl density, which helps to improve the surface hydrophilicity of the catalytic material and the placement of the second active component. For catalytic reactions requiring hydrophilicity, this can improve reaction efficiency. For bifunctional catalytic materials loaded with a second active component, it can improve the loading efficiency of metal oxide nanoparticles, thereby increasing the number of active sites and improving the overall catalytic reaction effect. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of this invention provides a method for preparing organosilicon-modified titanium-silicon molecular sieves, the method comprising the following steps:

[0022] (1) The mixture containing silicon source, titanium source, alkali source, water and first organosilicon is subjected to hydrothermal crystallization; then solid-liquid separation, first drying and calcination are carried out;

[0023] (2) The calcined product obtained in step (1) is contacted with a second organosilicon, and then subjected to a second drying process. The conditions for the second drying process are such that the drying rate of the solid-liquid mixture is 0.015-1.015 g organosilicon / (cm³). 2 h·g roasting product);

[0024] Wherein, the first organosilicon and the second organosilicon are each independently selected from at least one of the organosilicones shown in formula (1);

[0025]

[0026] In formula (1), R1, R2, R3, and R4 are each independently selected from H, alkyl, alkoxy, aminoalkyl, alkylamino, and halogen; wherein the hydrogen atoms in alkyl, alkoxy, aminoalkyl, and alkylamino are either substituted by halogen or not substituted.

[0027] According to the present invention, preferably, in formula (1), R1, R2, R3, and R4 are each independently selected from H, C1-C6 alkyl, C1-C6 alkoxy, aminoC1-C6 alkyl, C1-C6 alkylamino, F, Cl, and Br.

[0028] In this invention, the first organosilicon and the second organosilicon can each be independently selected from at least one of the following: CH3-(Si-OR)3, (CH3)2-(Si-OR)2, (CH3)3-(Si-OR), CH3CH2-(Si-OR)3, (CH3CH2)2-(Si-OR)2, (CH3CH2)3-(Si-OR), CH3CH2CH2-(Si-OR)3, (CH3CH2CH2)2-(Si-OR)2, and (CH3CH2CH2)3-(Si-OR); wherein R is selected from H, CH3, CH3CH2, and CH3CH 2CH2, CH3CH2CH2CH2, CH2Cl, CH2ClCH2, CH2ClCH2CH2, CH3CHClCH2, CH2ClCH2CH2CH2, CH3CHClCH2CH2, CH3CH2CHClCH2, CH3CH2CH 2CHCl, CH2NH2, CH2ClCH2, CH2NH2CH2CH2, CH3CHNH2CH2, CH2NH2CH2CH2CH2, CH3CHNH2CH2CH2, CH3CH2CHNH2CH2, CH3CH2CH2CHNH2.

[0029] According to the present invention, preferably, the first organosilicon and the second organosilicon are each independently selected from at least one of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, 3-aminopropyltriethoxysilane, trimethylsilyldiethylamine and tert-butyldimethylchlorosilane.

[0030] According to the present invention, preferably, the first organosilicon is selected from at least one of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, 3-aminopropyltriethoxysilane, trimethylsilyldiethylamine, and tert-butyldimethylchlorosilane.

[0031] According to the present invention, preferably, the second organosilicon is selected from at least one of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, 3-aminopropyltriethoxysilane, and trimethylsilyldiethylamine.

[0032] According to the present invention, preferably, the molar ratio R2 of the silicon source to the first organosilicon is 100:0.5-50; wherein the silicon source is SiO2. More preferably, the molar ratio R2 of the silicon source to the first organosilicon is 100:1-10 (for example, it can be 100:1, 100:2, 100:3, 100:4, 100:4.5, 100:5, 100:5.5, 100:6, 100:7, 100:8, 100:9, 100:10, and any two of the above), and even more preferably 100:1-5; wherein the silicon source is SiO2.

[0033] According to the present invention, preferably, the amount of the second organosilicon is 0.1-2g (e.g., 0.1g, 0.4g, 0.5g, 0.6g, 0.7g, 0.8g, 0.9g, 1g, 1.5g, 2g, and any two of the above) relative to each gram of calcined product, more preferably 0.5-2g, and even more preferably 0.5-1g.

[0034] According to the present invention, preferably, the molar ratio of silicon source, titanium source, alkali source and water in the mixture is R1 of 100:0.005-80:0.5-180:25-900, more preferably 100:0.15-15:15-100:150-750; wherein, the silicon source is calculated as SiO2 and the titanium source is calculated as TiO2.

[0035] According to the present invention, preferably, the silicon source is organosilicon, more preferably an alkyl silicate, more preferably, the alkyl group in the alkyl silicate is a C1-C6 alkyl group, and even more preferably, the silicon source includes at least one of tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetrapentyl silicate.

[0036] According to the present invention, preferably, the titanium source is an organotitanium, more preferably an alkyl titanate, more preferably, the alkyl group in the alkyl titanate is a C1-C6 alkyl group, and even more preferably, the titanium source includes at least one of tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, and tetrapentyl titanate.

[0037] According to the present invention, preferably, the alkali source is an organic ammonium, more preferably an alkyl ammonium hydroxide, more preferably, the alkyl group in the alkyl ammonium hydroxide is a C1-C6 alkyl group, and even more preferably, the alkali source is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapentylammonium hydroxide.

[0038] According to the present invention, preferably, the conditions for hydrothermal crystallization include: a temperature of 135-185°C and a time of 12-64 hours.

[0039] According to the present invention, preferably, the conditions for the first drying include: a temperature of 20-80°C and a time of 6-24 hours.

[0040] According to the present invention, preferably, the calcination conditions include: a temperature of 475-625°C and a time of 6-12 hours.

[0041] According to the present invention, preferably, step (1) further includes: before hydrothermal crystallization, performing a de-alcoholization treatment on an aqueous solution containing a silicon source, a titanium source, and an alkali source, and then mixing the product of the de-alcoholization treatment with a first organosilicon to obtain a mixture.

[0042] According to the present invention, preferably, in step (2), the contact conditions include: a temperature of 20-60°C and a time of 30-70 minutes. The contact method can be a commonly used contact method in the art, such as immersion or wetting.

[0043] According to the present invention, preferably, the second drying conditions result in a drying rate of 0.2-0.6 g organosilicon / (cm³) for the solid-liquid mixture. 2 h·g calcination product), for example, can be 0.2g organosilicon / (cm³). 2 h·g calcination product), 0.3g organosilicon / (cm 2 h·g calcination product), 0.4g organosilicon / (cm) 2 h·g calcination product), 0.5g organosilicon / (cm) 2 h·g calcination product), 0.6g organosilicon / (cm) 2 The drying rate refers to the evaporation rate of water in the solid-liquid mixture, i.e., the weight of volatile organosilicon in the solid-liquid mixture relative to a unit weight of carrier, within a unit time and unit area of ​​a container. The drying rate is tested as follows: the mass of the carrier in the solid-liquid mixture is denoted as M; the solid-liquid mixture is placed in a glass petri dish with a bottom area of ​​S (in cm²). 2 Weigh the glass petri dish containing the solid-liquid mixture before drying, and record the mass as M1 (g). Then, dry the glass petri dish containing the solid-liquid mixture under a certain temperature and humidity environment until constant weight is reached. Stop drying at this point. Record the drying time as T (h). Weigh the glass petri dish containing the solid after drying, and record the mass as M2 (g). The drying rate of the solid-liquid mixture is calculated using the formula: (M1-M2) / (S×T×M).

[0044] According to the present invention, the drying rate can be controlled by adjusting the drying temperature, the relative humidity of the drying environment, and the vacuum degree. Preferably, the conditions for the second drying include: a temperature of 30-70°C, a vacuum degree of ≤40 kPa, preferably 1-35 kPa, and a relative humidity of ≤60%. The relative humidity can be 60%, 50%, 45%, 35%, 25%, 15%, 10%, 5%, or any combination of the above, for example, 5-20%.

[0045] In this invention, the relative humidity is measured using a thermo-hygrometer (model: Alarm-Hygrometer testo 608-H2). Specifically, in this system, relative humidity refers to the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure at the same temperature during the drying process of the solid-liquid mixture.

[0046] According to the present invention, preferably, the fluctuation range of relative humidity during the second drying process is ≤5%. The fluctuation range of relative humidity can be 5%, 4%, 3%, 2%, 1%, 0.5%, or a range consisting of any two of the above points, for example, 2-3%.

[0047] A second aspect of the present invention provides a modified molecular sieve prepared by the method described above.

[0048] A third aspect of the present invention provides a modified titanium-silicon molecular sieve, wherein the content of oxygen vacancies in the modified titanium-silicon molecular sieve is 0.35-5.5 mmol / g.

[0049] According to the present invention, preferably, the content of oxygen vacancies in the modified titanium-silicon molecular sieve is 0.4-0.6 mmol / g.

[0050] According to the present invention, preferably, the ratio of the hydroxyl density Q4 / Q3 of the modified titanium-silicon molecular sieve is 4-10; more preferably, it is 5.2-8. Wherein, Q4 / Q3 represents the hydroxyl density of the modified titanium-silicon molecular sieve. 29 The ratio of peak areas of the peaks with chemical shifts near -113 ppm and -103 ppm in the Si MAS NMR spectrum.

[0051] According to the present invention, preferably, the modified titanium silicate molecular sieve has an L acid content of 0.001-2.5 mmol / g and a B acid / L acid ratio (the acid content ratio of B acid to L acid) of 0.05-2.

[0052] According to the present invention, preferably, the modified titanium-silicon molecular sieve has an average particle size of 60-145 nm.

[0053] According to the present invention, preferably, the molar ratio of silicon to titanium in the modified titanium-silicon molecular sieve is 100:0.05-15.

[0054] According to the present invention, preferably, the mesopore specific surface area of ​​the modified titanium-silicon molecular sieve is 80-225 m². 2 / g, the pore volume of the mesoporous tissue is 0.2-0.65cm³. 3 / g, the specific surface area of ​​the micropores is 150-510m² 2 / g, the pore volume of the micropores is 0.08-0.32cm³. 3 / g, with an average pore size of 0.4-2nm and a crystallinity of 82-98%.

[0055] The fourth aspect of this invention provides the application of the modified titanium-silicon molecular sieve described above in the preparation of propylene oxide.

[0056] The present invention will be described in detail below through embodiments. In the following embodiments,

[0057] The following preparation examples illustrate the preparation method of the modified titanium-silicon molecular sieve in this invention.

[0058] Preparation Example 1

[0059] (1-1) Preparation of a solution containing silicon, titanium, and alkali sources: Weigh tetraethyl silicate and pour it into a beaker equipped with a magnetic stirrer, stirring vigorously. Then, add tetrabutyl titanate dropwise to the beaker containing tetraethyl silicate, maintaining a stirring rate of 400-600 r / min and stirring vigorously for 30 min to mix them thoroughly. The resulting transparent solution is denoted as A1. Slowly add tetrapropylammonium hydroxide solution (the concentration of tetrapropylammonium hydroxide in the solution is 25% by weight) to A1. It initially becomes turbid, gradually turning into a milky white opaque suspension, denoted as A2. Increase the magnetic stirrer speed to 600-800 r / min, add a certain amount of distilled water to A2, and continue stirring for 60 min. The milky white opaque suspension then turns back into a colorless and transparent solution, denoted as A3. In the mixture A3, the molar ratio R1 of tetraethyl silicate, tetrabutyl titanate, tetrapropylammonium hydroxide and water is 100:0.65:80:700.

[0060] (1-2) De-alcoholization treatment: The solution A3 is heated to 80℃ to distill off the ethanol and butanol produced by the hydrolysis of the titanium silica sol. The liquid level of solution A3 in the beaker drops. At this time, the same amount of distilled water is added to maintain the liquid level. After 4-5 hours of alcohol distillation treatment, the liquid level of solution A3 remains basically stable and no longer drops. The solution at this time is recorded as A4.

[0061] (1-3) Pour solution A4 into a high-pressure hydrothermal synthesis reactor, and simultaneously add the first organosilicon (tert-butyldimethylchlorosilane) to the reactor. Start stirring (50 r / min) for hydrothermal crystallization. The molar ratio R2 of the silicon source to the first organosilicon is 100:5. The hydrothermal crystallization conditions are: temperature 170℃ and time 48h. After hydrothermal crystallization is complete, allow the reactor to cool naturally to 30℃. Open the reactor and remove the milky white suspension material, which is recorded as A5. Centrifuge A5 in a high-speed centrifuge, discard the supernatant, and leave the solid material, which is recorded as A6. Wash A6 with distilled water and repeat the centrifugation process 3-4 times until the pH of the supernatant is <8. Discard the supernatant, leaving the solid material A6. Treat A6 in an oven at 50℃ for 20h. At this point, the free water on A6 is basically removed, and A6 appears as irregular clumps, which is recorded as A7. After grinding and pulverizing A7, it was calcined at 550℃ for 6.5 hours to remove crystal water and template agent, thus obtaining the calcined product.

[0062] (2) Place the calcined product obtained in step (1-3) in a container with a bottom area of ​​80 cm². 2 The calcined product was immersed in a glass petri dish for 70 minutes at room temperature (27°C) using a second organosilicon (tert-butyldimethylchlorosilane). The amount of the second organosilicon was 0.5 g per gram of calcined product. After immersion, the product was transferred directly to a vacuum drying oven without solid-liquid separation. The drying conditions were: temperature 30°C, vacuum 2 kPa, relative humidity 15%, with a maximum relative humidity fluctuation of 2%. Drying was stopped after reaching constant weight to obtain modified titanium-silicon molecular sieves. The parameters of the constant temperature and humidity oven resulted in a drying rate of 0.383 g organosilicon / (cm²). 2 h·g roasting product).

[0063] Preparation Example 2-25

[0064] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that the molar ratio R2 of tetraethyl silicate to the first organosilicon in steps (1-3), the time and temperature of hydrothermal crystallization; and the soaking time, drying temperature, relative humidity, maximum fluctuation of relative humidity, vacuum degree and drying rate in step (2) are shown in Table 1.

[0065] Table 1

[0066]

[0067] Note: " / " indicates that the preparation is the same as in Example 1.

[0068] Preparation Example 26

[0069] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that the amount of the second organosilicon was 2g relative to each gram of calcined product.

[0070] Preparation Example 27

[0071] The catalyst was prepared according to the method of Preparation Example 1, except that the first and second organosilicones were both replaced with trimethylsilyldiethylamine.

[0072] Preparation Example 28

[0073] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that the molar ratio R2 of silicon source to first organosilicon was 100:0.4.

[0074] Preparation Example 29

[0075] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that the alcohol removal process in steps (1-2) was not included, and solution A3 was directly poured into the high-pressure hydrothermal synthesis reactor.

[0076] Preparation Example 30

[0077] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that the amount of the second organosilicon was 0.08 g relative to each gram of calcined product.

[0078] Comparative Preparation Example 1

[0079] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that the first organosilicon was not added in steps (1-3); that is, solution A4 was poured into a high-pressure hydrothermal synthesis reactor for hydrothermal crystallization.

[0080] Comparative Preparation Example 2

[0081] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that in step (2), the drying conditions included: a temperature of 100°C, a relative humidity of 65%, and a maximum relative humidity fluctuation of 10%; the parameters of the constant temperature and humidity drying oven were set such that the drying rate was 1.15 g organosilicon / (cm³). 2 h·g roasting product).

[0082] Comparative preparation example 3

[0083] The modified titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1, except that step (2) was not included, that is, the calcined product obtained in steps (1-3) was used as the modified molecular sieve.

[0084] Test case

[0085] (I) The molecular sieves prepared in the above preparation examples and comparative preparation examples were characterized by parameters, and the test results are shown in Table 2.

[0086] The method for testing the hydroxyl density of modified titanium-silicon molecular sieves was as follows: Silicon nuclear magnetic resonance (NMR) was used on a VARIAN VNMRS 400WB NMR spectrometer. The single-pulse method was employed with (CH3)3Si(CH2)3SO3Na as the chemical shift reference, and a rotation rate of 3 kHz and a cycle delay of 60 s were used at a frequency of 79.43 MHz. 29 Si MAS nuclear magnetic resonance spectroscopy measurements. The peak areas near -113 ppm and -103 ppm in the corresponding spectra represent the relative contents of the silicon framework structures Q4:Si(OSi)4 and Q3:Si(OSi)3OH in the molecular sieve, respectively. The ratio Q4 / Q3 represents the relative content of silanol groups in the molecular sieve. The larger the Q4 / Q3 ratio, the lower the hydroxyl content.

[0087] The method for testing the oxygen hole content of modified titanium-silicon molecular sieves is as follows: Electron paramagnetic resonance spectroscopy (EPR) is used to test the unpaired electrons and surrounding chemical environment of the substance. After analyzing the spectral splitting factor (g value) and spectral area, the oxygen hole value of the substance to be tested is quantitatively obtained.

[0088] The method for testing the silicon-titanium molar ratio in modified titanium-silicon molecular sieves is as follows: the content of titanium and silicon elements in the molecular sieves is tested by combining inductively coupled plasma optical emission spectroscopy (ICP-OES) to obtain the overall silicon-titanium ratio of the molecular sieves.

[0089] The method for testing the crystallinity of modified titanium-silicon molecular sieves is as follows: using a JCPDS standard card as the standard sample (whose crystallinity is known, denoted as X). s The XRD diffraction peaks of its crystalline phase in the 2θ = 5–35° range were measured, and several characteristic peaks were obtained, denoted as P. S1 ~P Sn Its corresponding peak height is H S1 ~H Sn The sum of the peak heights is denoted as ΣH. Si The full width at half maximum (FWHM) at 2θ = 24.5° is denoted as W. S XRD analysis revealed a characteristic peak at the position corresponding to the characteristic peak of S-1 in the molecular sieve being tested; this peak is denoted as P. i1 ~P in Its corresponding peak height is H i1 ~H in The sum of the peak heights is denoted as ΣH. ii The full width at half maximum (FWHM) at 2θ = 24.5° is denoted as W. i Crystallinity X of the molecular sieve sample to be tested i The calculation formula is as follows:

[0090] X i =X s *(W i *ΣH ii / (W S *ΣH Si )).

[0091] The method for testing the average particle size of modified titanium-silicon molecular sieve is as follows: The average particle size of the molecular sieve is tested using a laser particle size analyzer. The sample to be tested is diluted to a certain extent to obtain a high degree of dispersion. By setting conditions such as laser wavelength (466nm, 633nm), scattering angle (0.015~144°), and test temperature (room temperature~100℃), the intensity distribution of the scattered light of the particles to the laser is determined, and the average particle size is calculated based on the intensity distribution of the scattered light.

[0092] The pore structure and specific surface area of ​​the modified titanium silicate molecular sieve were tested using a nitrogen physical adsorption instrument. The specific surface area of ​​the molecular sieve was analyzed using the BET (Brunauer-Emmett-Teller) method, and the pore size distribution was calculated using the BJH (Barrett-Joiner-Halenda) model.

[0093] The method for testing the acidity of modified titanium silicate molecular sieves is as follows: pyridine infrared spectroscopy is used. The sample is placed in a vacuum cell and pretreated for 1 h at 500℃ and a vacuum of 0.001 Pa. The temperature is then lowered to 200℃, and pyridine vapor is allowed to flow for 30 min. Excess unadsorbed pyridine vapor is then degassed at 200℃. Subsequently, the temperature is lowered to 100℃, and the desorption peak of pyridine at the corresponding acidic sites is collected. The peak value at 1540 cm⁻¹ in the corresponding spectrum is [missing value]. -1 The peak at 1450 cm⁻¹ is designated as the characteristic peak of Brønsted acid. -1 The peak is denoted as the L acid characteristic peak. Based on the spectrum, the amount of Brønsted acid and L acid is calculated by integrating the peak areas, and the ratio of Brønsted acid to L acid is obtained. The total acid amount is calculated as: Total acid amount = Brønsted acid amount + L acid amount.

[0094] Table 2

[0095]

[0096] Continued from Table 2

[0097]

[0098] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing organosilicon-modified titanium-silicon molecular sieves, characterized in that, The method includes the following steps: (1) The mixture containing silicon source, titanium source, alkali source, water and first organosilicon is subjected to hydrothermal crystallization; then solid-liquid separation, first drying and calcination are carried out; (2) The calcined product obtained in step (1) is contacted with a second organosilicon, and then subjected to a second drying process. The conditions for the second drying process are such that the drying rate of the solid-liquid mixture is 0.015-1.015 g organosilicon / (cm³). 2 h·g roasting product); Wherein, the first organosilicon and the second organosilicon are each independently selected from at least one of the organosilicones shown in formula (1); In formula (1), R1, R2, R3, and R4 are each independently selected from H, alkyl, alkoxy, aminoalkyl, alkylamino, and halogen; wherein the hydrogen atoms in the alkyl, alkoxy, aminoalkyl, and alkylamino groups are either substituted with or unsubstituted by halogens; Preferably, in formula (1), R1, R2, R3, and R4 are each independently selected from H, C1-C6 alkyl, C1-C6 alkoxy, aminoC1-C6 alkyl, C1-C6 alkylamino, F, Cl, and Br.

2. The method according to claim 1, wherein, The first organosilicon and the second organosilicon are each independently selected from at least one of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, 3-aminopropyltriethoxysilane, trimethylsilyldiethylamine, and tert-butyldimethylchlorosilane; And / or, the molar ratio R2 of the silicon source to the first organosilicon is 100:0.5-50; wherein the silicon source is SiO2; And / or, the amount of the second organosilicon is 0.1-2 g relative to each gram of calcined product.

3. The method according to claim 1, wherein, The molar ratio of silicon source, titanium source, alkali source and water in the mixture is R1 of 100:0.005-80:0.5-180:25-900, preferably 100:0.15-15:15-100:150-750; wherein the silicon source is SiO2 and the titanium source is TiO2. And / or, the silicon source is organosilicon, preferably an alkyl silicate, more preferably, the alkyl group in the alkyl silicate is a C1-C6 alkyl group, and even more preferably, the silicon source includes at least one of tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetrapentyl silicate. And / or, the titanium source is organic titanium, preferably an alkyl titanate, more preferably, the alkyl group in the alkyl titanate is a C1-C6 alkyl group, and even more preferably, the titanium source includes at least one of tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, and tetrapentyl titanate. And / or, the alkali source is an organic ammonium, preferably an alkyl ammonium hydroxide, more preferably, the alkyl group in the alkyl ammonium hydroxide is a C1-C6 alkyl group, and even more preferably, the alkali source is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapentylammonium hydroxide.

4. The method according to claim 1, wherein, The conditions for hydrothermal crystallization include: a temperature of 135-185℃ and a time of 12-64h; And / or, the conditions for the first drying include: a temperature of 20-80°C and a time of 6-24 hours; And / or, the calcination conditions include: a temperature of 475-625°C and a time of 6-12 hours.

5. The method according to claim 1, wherein, Step (1) also includes: before hydrothermal crystallization, the aqueous solution containing silicon source, titanium source and alkali source is subjected to alcohol removal treatment, and then the product of alcohol removal treatment is mixed with the first organosilicon to obtain a mixed solution.

6. The method according to claim 1, wherein, In step (2), the contact conditions include: a temperature of 20-60°C and a time of 30-70 min.

7. The method according to claim 1, wherein, The conditions for the second drying include: a temperature of 30-70°C, a vacuum degree of ≤40 kPa, preferably 1-35 kPa, and a relative humidity of ≤60%. Preferably, the relative humidity fluctuation during the second drying process is ≤5%.

8. The modified molecular sieve prepared by the method according to any one of claims 1-7.

9. A modified titanium-silicon molecular sieve, characterized in that, The oxygen vacancy content in this modified titanium-silicon molecular sieve is 0.35-5.5 mmol / g.

10. The modified titanium-silicon molecular sieve according to claim 9, wherein, The modified titanium-silicon molecular sieve has a hydroxyl density Q4 / Q3 ratio of 4-10, where Q4 / Q3 represents the hydroxyl density of the modified titanium-silicon molecular sieve. 29 The ratio of peak areas of the peaks with chemical shifts near -113 ppm and -103 ppm in the Si MAS NMR spectrum; And / or, the modified titanium silicate molecular sieve contains 0.001-2.5 mmol / g of L acid and 0.05-2 of Brønsted acid / L acid, wherein, in the pyridine infrared spectrum, at 1540 cm⁻¹... -1 The integral area of ​​the characteristic peak at that point is the acidity of Brønsted acid, 1450 cm⁻¹. -1 The integral area of ​​the characteristic peak at that location is the acid content of L. And / or, the average particle size of the modified titanium-silicon molecular sieve is 60-145 nm.

11. The modified titanium-silicon molecular sieve according to claim 9, wherein, The silicon-to-titanium molar ratio in the modified titanium-silicon molecular sieve is 100:0.05-15; And / or, the specific surface area of ​​the mesopores in the modified titanium-silicon molecular sieve is 80-225 m². 2 / g, the pore volume of the mesoporous tissue is 0.2-0.65cm³. 3 / g, the specific surface area of ​​the micropores is 150-510m² 2 / g, the pore volume of the micropores is 0.08-0.32cm³. 3 / g, with an average pore size of 0.4-2nm and a crystallinity of 82-98%.

12. The use of the modified titanium silicate molecular sieve according to any one of claims 8-11 in the preparation of propylene oxide.

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