Titanium silical molecular sieve and method for preparing the same

Abstract

The present application relates to the technical field of molecular sieve, and discloses a titanium silicalite molecular sieve and a preparation method thereof, the preparation method comprising the following steps: (1) performing first contact of an aqueous solution containing a silicon source, a titanium source and an alkali source with a solution containing a metal salt; wherein the metal salt comprises a Group VIII and / or Group IB metal salt; (2) performing second contact of the solution obtained through the first contact with a dispersion liquid containing metal particles; wherein the metal particles comprise Group VIII and / or Group IB metal particles; (3) sequentially performing hydrothermal crystallization, solid-liquid separation and calcination on the solution obtained through the second contact. The method of the present application can improve the crystallinity of the titanium silicalite molecular sieve, and can make the doped metal elements enter the framework of the titanium silicalite molecular sieve, thereby avoiding the problem that the doped elements are prone to falling off and improving the catalytic performance of the titanium silicalite molecular sieve.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a titanium-silicon molecular sieve and its preparation method. Background Technology

[0002] Titanium silicate molecular sieves, as an environmentally friendly new catalytic material, offer a new approach to the development of environmentally friendly chemical processes and the production of clean and environmentally friendly chemicals through their industrial applications. Titanium silicate molecular sieves possess the same dual ten-membered ring three-dimensional cross-channel structure (MFI) as ZSM-5 silica-alumina molecular sieves. The presence of titanium active centers in the framework endows titanium silicate molecular sieves with unique selective oxidation properties, enabling them to be widely used in processes such as olefin epoxidation, cyclohexanone ammoniation, phenol hydroxylation, alcohol oxidation, and saturated hydrocarbon oxidation in environmental protection and chemical industries.

[0003] Current research on titanium-silicon molecular sieves at home and abroad mainly focuses on their synthesis, structural modification, catalyst regeneration, and applications in the aforementioned fields. The doping or loading of other active metals into molecular sieves to obtain bifunctional catalytic materials has become a hot topic in industry and academia in recent years. Titanium-silicon molecular sieves doped with other active metal elements can catalyze continuous two- or multi-step reactions: (1) Titanium-silicon molecular sieves loaded with metal nanoparticles can catalyze the in-situ generation of hydrogen peroxide from hydrogen and oxygen. Subsequently, at the titanium active sites of the same molecular sieve, the in-situ generated hydrogen peroxide and propylene undergo an epoxidation reaction to generate propylene oxide. The final continuous catalytic effect is: direct epoxidation of propylene, hydrogen, and oxygen in the gas phase to prepare propylene oxide. (2) Titanium-silicon molecular sieves loaded with metal oxide nanoparticles can catalyze the in-situ hydroxylation of benzene to obtain phenol. Subsequently, at the titanium active sites of the same catalyst, the in-situ generated phenol continues the hydroxylation reaction to obtain hydroquinone. The final continuous catalytic effect is: direct hydroxylation of benzene to obtain hydroquinone in one step. The doping and modification of titanium-silicon molecular sieves yields novel catalytic and environmentally friendly materials that can effectively shorten existing processes and improve reaction efficiency. In subsequent industrial applications, this can significantly reduce equipment layout investment and lower energy consumption.

[0004] However, existing technologies have problems such as the easy shedding of doped or loaded other active metal elements during the doping and modification process of titanium-silicon molecular sieves, the reduction of crystallinity after doping with other metals, and the destruction of the original pore structure, which in turn leads to insufficient catalytic performance for the corresponding reactions. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art where other active metal elements are easily detached during the doping and modification process of titanium-silicon molecular sieves, the crystallinity of the molecular sieve decreases after doping with other metals, and the original pore structure is destroyed. This invention provides a titanium-silicon molecular sieve and its preparation method.

[0006] The inventors of this invention have discovered that by first contacting the solution to be crystallized with Group VIII and / or Group IB metal ions, and then with Group VIII and / or Group IB metal particles, the Group VIII and / or Group IB metals can enter the framework of the titanium-silicon molecular sieve and be uniformly distributed. This effectively prevents the shedding of doped or loaded other active metal elements, maintains the original framework, pore structure, and crystallinity of the molecular sieve, and improves the catalytic performance of the titanium-silicon molecular sieve. To achieve the above objective, the first aspect of this invention provides a method for preparing a titanium-silicon molecular sieve, which includes the following steps:

[0007] (1) The aqueous solution containing silicon source, titanium source and alkali source is brought into first contact with the solution containing metal salt; wherein the metal salt includes Group VIII and / or Group IB metal salt;

[0008] (2) The solution obtained from the first contact is brought into a second contact with a dispersion containing metal particles; wherein the metal particles include Group VIII and / or Group IB metal particles;

[0009] (3) The solution obtained from the second contact is subjected to hydrothermal crystallization, solid-liquid separation and calcination in sequence.

[0010] A second aspect of the present invention provides a titanium-silicon molecular sieve prepared by the method described above.

[0011] A third aspect of the present invention provides a titanium-silicon molecular sieve, wherein the titanium-silicon molecular sieve includes a doped metal element that enters the framework structure of the titanium-silicon molecular sieve, and the bond length between the doped metal element and the O atom in the titanium-silicon molecular sieve framework is 0.02-0.55 nm, preferably 0.15-0.25 nm, wherein the doped metal element includes a Group VIII and / or a Group IB metal element.

[0012] Through the above technical solution, the present invention achieves the following beneficial effects:

[0013] (1) The present invention adopts a two-step method. First, an aqueous solution containing silicon source, titanium source and alkali source is brought into contact with a solution containing metal salt. Then, the solution obtained from the first contact is brought into contact with a dispersion containing metal particles. The solution obtained from the second contact is then subjected to hydrothermal crystallization, solid-liquid separation and calcination in sequence. This can improve the crystallinity of titanium silicon molecular sieve and allow the doped metal elements to enter the framework of titanium silicon molecular sieve, avoiding the problem of easy detachment of doped elements and improving the catalytic performance of titanium silicon molecular sieve in the corresponding catalytic reaction process.

[0014] (2) Preferably, the crystallinity of titanium silicon molecular sieve can be further improved by using the metal particles prepared by the present invention.

[0015] (3) The specific surface area and pore volume of titanium-silicon molecular sieves are further improved, which helps to improve the efficiency of the target reaction. Detailed Implementation

[0016] 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.

[0017] The first aspect of this invention provides a method for preparing titanium-silicon molecular sieves, the method comprising the following steps:

[0018] (1) The aqueous solution containing silicon source, titanium source and alkali source is brought into first contact with the solution containing metal salt; wherein the metal salt includes Group VIII and / or Group IB metal salt;

[0019] (2) The solution obtained from the first contact is brought into a second contact with a dispersion containing metal particles; wherein the metal particles include Group VIII and / or Group IB metal particles;

[0020] (3) The solution obtained from the second contact is subjected to hydrothermal crystallization, solid-liquid separation and calcination in sequence.

[0021] According to the present invention, the molar ratio of the silicon source, titanium source, alkali source and water can be selected within a wide range.

[0022] Preferably, in step (1), the molar ratio R1 of silicon source, titanium source, alkali source and water in the aqueous solution containing silicon source, titanium source and alkali source is 100:0.002-60:1-200:50-1000, more preferably 100:0.1-10:20-120:100-800; wherein, silicon source is calculated as SiO2 and titanium source is calculated as TiO2.

[0023] According to the present invention, the silicon source can be any substance in the field of molecular sieve preparation that can provide silicon. Preferably, the silicon source is organosilicon, more preferably an alkyl silicate, more preferably an alkyl group of C1-C6, and even more preferably, the silicon source includes at least one of tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetrapentyl silicate.

[0024] According to the present invention, the titanium source can be any substance in the field of molecular sieve preparation that can provide titanium. Preferably, the titanium source is organotitanium, more preferably an alkyl titanate, more preferably an alkyl group of C1-C6, and even more preferably, the titanium source includes at least one of tetrabutyl titanate, tetraethyl titanate, tetrapropyl titanate, and tetrapentyl titanate.

[0025] 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 selected from tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapentylammonium hydroxide.

[0026] According to the present invention, preferably, the metal salt comprises a palladium salt and / or a platinum salt. For example, the metal salt can be any metal salt capable of providing Pd ions or Pt ions; preferably, the cation in the metal salt is Pd. 2+ and / or Pt 2+ More preferably, the metal salt includes at least one selected from PdCl2, Pd(NO3)2, PtCl2, and Pt(NO3)2. The inventors have further discovered that when a divalent metal salt (PdCl2) is used… 2+ and / or Pt 2+ This can further improve the uniformity of the loading of active components on the molecular sieve. The inventors speculate that this may be because the divalent metal salt is dicoordinated, and after entering the molecular sieve framework structure, it easily generates oxygen vacancies, thereby promoting the loading of active components. At the same time, the divalent metal salt acts as an electrophilic center to attack the hydroxyl groups on the titanium-silicon molecular sieve, and then the active component (taking Au as an example) couples with the electrophilic center as a nucleophilic center, effectively loading Pd 2+ / Pt 2+ The surrounding area forms PdAu / PtAu alloy clusters, thereby increasing the density and number of active centers. Furthermore, the formation of PdAu / PtAu alloy clusters helps to weaken the titanium-silicon alloy.

[0027] The addition of hydroxyl groups to the molecular sieve reduces the hydroxyl density and effectively decreases the occurrence of the ring-opening isomerization side reaction of propylene oxide.

[0028] According to the present invention, in order to promote the uniform distribution of active components on the molecular sieve and improve the conversion rate of propylene and the selectivity of propylene oxide in the gas-phase preparation of propylene oxide, preferably, the molar ratio R2 of the silicon source to the metal salt is 1000:0.02-5, more preferably 1000:0.1-2, and even more preferably 1000:0.1-0.5; wherein the silicon source is calculated as SiO2 and the metal salt is calculated as a metal element. In the present invention, the molar ratio R2 of the silicon source to the metal salt can be 1000:0.02, 1000:0.2, 1000:0.25, 1000:0.4, 1000:0.5, 1000:1, 1000:2, and any two of the above ranges.

[0029] According to the present invention, preferably, the concentration of the metal salt in the solution containing the metal salt is 0.001-1 mol / L, more preferably 0.01-0.1 mol / L.

[0030] According to the present invention, preferably, the solvent in the solution containing the metal salt is water.

[0031] According to the present invention, the duration of the first contact can be selected within a wide range. However, in order to promote the entry of the metal salt into the molecular sieve framework and the uniform distribution of metal ions within the molecular sieve, the duration of the first contact is preferably 10-120 min, more preferably 40-80 min. Typically, the temperature of the first contact is room temperature. In the present invention, unless otherwise specified, room temperature is typically 15-40°C.

[0032] According to the present invention, in order to promote the uniform distribution of active components on the molecular sieve and improve the conversion rate of propylene and the selectivity of propylene oxide in the gas-phase preparation of propylene oxide, preferably, the molar ratio R3 of the metal salt in step (1) to the metal particles in step (2) is 1:0.001-1, more preferably 1:0.005-0.1, and even more preferably 1:0.005-0.01, where the metal salt and the metal particles are calculated as metal elements. In the present invention, the molar ratio R3 of the metal salt to the metal particles can be 1:0.001, 1:0.005, 1:0.008, 1:0.01, 1:0.015, 1:0.05, 1:0.5, 1:1, and any two of the above ranges.

[0033] According to the present invention, preferably, the metal particles include palladium particles and / or platinum particles.

[0034] According to the present invention, preferably, the concentration of metal particles in the dispersion containing metal particles is 0.001-0.1 mol / L.

[0035] According to the present invention, preferably, the solvent in the dispersion containing metal particles is water.

[0036] According to the present invention, preferably, the particle size of the metal particles in the dispersion containing metal particles is 1-20 nm, more preferably 1-3 nm.

[0037] According to the present invention, preferably, the method for preparing the metal particles is as follows: mixing an aqueous solution of a metal precursor, an aqueous solution of sodium citrate, and an aqueous solution of tannic acid, and then heating at 60-120°C for 2-6 hours to obtain metal particles (colloids), wherein the metal precursor includes a Group VIII metal salt and / or a Group IB metal salt. Preferably, the metal precursor includes a palladium salt and / or a platinum salt. More preferably, the amounts of the aqueous solution of the metal precursor, the aqueous solution of sodium citrate, and the aqueous solution of tannic acid are such that the molar ratio of the metal precursor, sodium citrate, and tannic acid is 1:0.02-0.2:0.025-0.25. The concentration of the aqueous solution of the metal precursor can be 0.005-0.1 mol / L, the concentration of the aqueous solution of sodium citrate can be 0.05-0.5 mol / L, and the concentration of the aqueous solution of tannic acid can be 0.005-0.1 mol / L. In this invention, the amounts of the metal precursor aqueous solution, sodium citrate aqueous solution, and tannic acid aqueous solution are adjusted such that the molar ratio of the metal precursor, sodium citrate, and tannic acid can be 1:0.08-0.12:0.15-0.2.

[0038] According to the present invention, preferably, the second contact time is 20-100 minutes. Typically, the temperature of the second contact is room temperature.

[0039] According to the present invention, preferably, the conditions for hydrothermal crystallization include: a temperature of 120-200°C and a time of 10-80 hours.

[0040] According to the present invention, preferably, the calcination conditions include a temperature of 500-650°C and a time of 4-10 hours. More preferably, the calcination atmosphere is air.

[0041] According to the present invention, preferably, the aqueous solution containing silicon source, titanium source and alkali source is obtained by: first mixing silicon source and titanium source to obtain a first mixture, then mixing the first mixture with alkali source to obtain a second mixture, and then mixing the second mixture with water to obtain the aqueous solution containing silicon source, titanium source and alkali source.

[0042] According to the present invention, preferably, the preparation method further includes: subjecting the product of the first contact to a dealcoholization treatment before performing step (2). The inventors of the present invention have further discovered that, during step...

[0043] (2) Prior to this, the product of the first contact can be treated with alcohol removal to further promote the entry of doped metal into the molecular sieve framework and improve the crystallinity, specific surface area and pore volume of the titanium silicon molecular sieve.

[0044] According to the present invention, preferably, the conditions for the alcohol removal treatment include: a temperature of 70-100°C and a time of 2-8 hours.

[0045] According to the present invention, since some water will evaporate during the de-alcoholization process, it is preferable to replenish water during the de-alcoholization process to maintain the liquid level.

[0046] A second aspect of the present invention provides a titanium-silicon molecular sieve prepared by the method described above.

[0047] A third aspect of the present invention provides a titanium-silicon molecular sieve, wherein the titanium-silicon molecular sieve includes a doped metal element that enters the framework structure of the titanium-silicon molecular sieve, and the bond length between the doped metal element and the O atom in the titanium-silicon molecular sieve framework is 0.02-0.55 nm, preferably 0.15-0.25 nm, wherein the doped metal element includes a Group VIII and / or a Group IB metal element.

[0048] According to the present invention, preferably, the silicon-to-titanium molar ratio in the molecular sieve is 100:0.1-10. In the present invention, the silicon-to-titanium molar ratio in the molecular sieve can be 100:0.1, 100:0.4, 100:0.5, 100:0.6, 100:1, 100:5, 100:10, or any range consisting of any two of the above.

[0049] According to the present invention, preferably, the doped metal element includes Pd and / or Pt.

[0050] According to the present invention, preferably, the content of the doped metal element is 0.01-0.5% by weight, more preferably 0.04-0.06% by weight, based on the total weight of the titanium-silicon molecular sieve.

[0051] According to the present invention, preferably, the molecular sieve has an average particle size of 80-300 nm and a mesopore specific surface area of ​​50-200 m². 2 / g, the pore volume of the mesoporous tissue is 0.2-0.5cm³. 3 / g, the specific surface area of ​​the micropores is 200-500m² 2 / g, the pore volume of the micropores is 0.05-0.25cm³. 3 / g, with a crystallinity of 85-99%.

[0052] The present invention will be described in detail below through embodiments. In the following embodiments,

[0053] Preparation Example 1

[0054] This preparation example illustrates the preparation process of molecular sieves.

[0055] (1-1) Preparation of an aqueous solution containing silicon, titanium and alkali sources: Weigh 41.67 g of tetraethyl silicate and pour it into a beaker containing a magnetic stir bar, and keep stirring vigorously; then add tetrabutyl titanate dropwise to the beaker containing tetraethyl silicate, and keep stirring at a stirring rate of 400 r / min for 30 min to obtain a transparent liquid, which is recorded as mixture A1; then slowly add tetrapropylammonium hydroxide solution (the concentration of tetrapropylammonium hydroxide in the tetrapropylammonium hydroxide solution is 25% by weight) to mixture A1. The solution begins to become turbid and gradually turns into a milky white opaque suspension, which is recorded as mixture A2; adjust the stirring speed to 600 r / min, add distilled water to mixture A2, and continue stirring for 60 min. The milky white opaque suspension turns into a colorless and transparent solution again, which is the aqueous solution containing silicon, titanium and alkali sources, recorded as mixture A3. In the mixture A3, the molar ratio R1 of tetraethyl silicate, tetrabutyl titanate, tetrapropylammonium hydroxide and water is 100:0.5:80:555.

[0056] (1-2) Add 0.1 mol / L PdCl2 solution to mixture A3 and continue stirring at a stirring rate of 600 r / min for 60 min. The resulting solution is denoted as mixture A4. Then, heat mixture A4 to 80℃ for alcohol removal treatment to distill off the ethanol and butanol produced by the hydrolysis of the titanium silica sol. During the alcohol removal treatment, the liquid level in the beaker drops, and the same amount of distilled water needs to be added to maintain the liquid level. After 6 h of alcohol removal treatment, the liquid level of mixture A4 basically stabilizes and no longer drops. The alcohol removal treatment is then ended, and the resulting solution is denoted as mixture A5. The amount of PdCl2 solution added makes the molar ratio R2 of silicon source to metal salt 1000:0.5.

[0057] (2-1) Preparation of nano-sized Pd particles: A 0.003 mol / L PdCl2 aqueous solution was placed in a beaker and heated to 70 °C. Then, a 0.1 mol / L sodium citrate aqueous solution and a 0.05 mol / L tannic acid aqueous solution were added to the beaker. After stirring at 600 r / min for 4 h, palladium nanoparticles were obtained. The Pd nanoparticles in the colloid had a particle size of 1-3 nm. The amounts of PdCl2 aqueous solution, sodium citrate aqueous solution, and tannic acid aqueous solution were such that the molar ratio of PdCl2, sodium citrate, and tannic acid was 1:0.1:0.2.

[0058] (2-2) The palladium nanocolloids prepared in step (2-1) were mixed with water to obtain an aqueous dispersion of Pd nanoparticles with a concentration of 0.01 mol / L. The aqueous dispersion of Pd nanoparticles with a concentration of 0.01 mol / L was added to mixture A5, and stirring was continued at a stirring rate of 600 r / min for 60 min. The resulting solution was denoted as mixture A6. The amount of the nanoparticle dispersion added was such that the molar ratio R3 of the metal salt to the metal particles was 1:0.01.

[0059] (3) The mixture A6 was transferred to a high-pressure hydrothermal reactor and heated to 170°C at a rate of 0.5°C / min for hydrothermal crystallization for 72 hours. After hydrothermal crystallization, the reactor was allowed to cool naturally to 30°C. The milky white suspension was then removed from the reactor and centrifuged in a high-speed centrifuge. The supernatant was discarded, leaving the solid material. The solid material was washed with distilled water and centrifuged repeatedly until the pH of the supernatant was <8. The solid material was then dried in an oven at 50°C for 20 hours to obtain an irregularly shaped agglomerated solid material. The agglomerated solid material was ground and pulverized to obtain a particle size of less than 0.075 mm. The calcined solid material was then calcined at 550°C for 6.5 hours in air to obtain a Pd-modified titanium silicate molecular sieve, designated as molecular sieve-1.

[0060] Preparation Examples 2-6

[0061] The method of preparation example 1 is the same, except that R1, R2, R3, the types of metal salts, and the types of metal particles are shown in Table 1.

[0062] Table 1

[0063] R1 Metal salts R2 Types of metal particles R3 Molecular sieve Preparation Example 2 100:0.5:80:555 <![CDATA[PtCl2]]> 1000:0.5 Pt 1:0.01 Molecular sieve-2 Preparation Example 3 100:0.5:80:555 <![CDATA[PdCl2]]> 1000:0.25 Pd 1:0.005 Molecular sieve-3 Preparation Example 4 100:0.5:80:555 <![CDATA[Pd(NO3)2]]> 1000:0.5 Pd 1:0.01 Molecular sieve-4 Preparation Example 5 100:1:80:555 <![CDATA[PdCl2]]> 1000:0.5 Pd 1:0.01 Molecular sieve-5 Preparation Example 6 100:0.5:40:555 <![CDATA[PdCl2]]> 1000:0.5 Pd 1:0.01 Molecular sieve-6

[0064] Note: The preparation method of Pt metal particles in Preparation Example 2 is the same as that of Pd nanoparticles in Preparation Example 1, except that PdCl2 is replaced with PtCl2. The particle size of Pt metal particles obtained in Preparation Example 2 is 1-3 nm. The preparation methods of Pd metal particles in Preparation Examples 3-6 are the same as those of Pd nanoparticles in Preparation Example 1.

[0065] Preparation Example 7

[0066] The preparation method was the same as in Preparation Example 1, except that the solution containing silicon, titanium, and alkali sources was prepared by directly mixing silicon, titanium, alkali, and water in the same molar ratio as in Preparation Example 1 to obtain mixture A3. The resulting molecular sieve was designated as molecular sieve-7.

[0067] Preparation Example 8

[0068] The preparation method was carried out according to Example 1, except that the dealcoholization step was not included. The resulting molecular sieve is designated as molecular sieve-8.

[0069] Preparation Example 9

[0070] The preparation method was followed as in Example 1, except that tannic acid was not added in step (2-1) when preparing the nano-sized Pd particles. The resulting nano-sized Pd particles had a particle size of 5-10 nm. The resulting molecular sieve is designated as Molecular Sieve-9.

[0071] Preparation Example 10

[0072] The preparation method was followed as in Example 1, except that R3 = 1:0.1. The resulting molecular sieve is designated as Molecular Sieve-10.

[0073] Comparative Preparation Example 1

[0074] The preparation method was carried out according to Example 1, except that steps (1-2), (2-1), and (2-2) were not included. The resulting molecular sieve is denoted as molecular sieve-D1.

[0075] Comparative Preparation Example 2

[0076] The preparation method of Example 1 was followed, except that steps (2-1) and (2-2) were not included; in step (1-2), an aqueous solution of metal salt was added to mixture A3 along with an aqueous dispersion of nano-metal particles (the type, concentration, and amount of the aqueous dispersion of nano-metal particles were the same as in step (2-2) of Example 1). The resulting molecular sieve was designated as molecular sieve-D2.

[0077] Comparative preparation example 3

[0078] The preparation method was carried out according to Example 7, except that step (1-2) did not include the alcohol removal process, and steps (2-1) and (2-2) were not included. The resulting molecular sieve is designated as molecular sieve-D3.

[0079] Test case

[0080] (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.

[0081] The presence of dopants in titanium-silicon molecular sieves was tested using synchrotron X-ray absorption fine structure spectroscopy (XAFS). The atomic nearest-neighbor structures of different elements in the analyte were studied by adjusting the incident X-ray energy. Specifically, the X-ray energy was adjusted to match the inner electron shell of the element under study before being used to probe the sample. The relationship between the number of absorbed X-rays and their energy was then monitored. The obtained spectral structures were analyzed using software to determine the spacing between absorbing atoms and their neighboring atoms, the number and type of atoms, and the oxidation state of the absorbing elements. The Si-O bond length in the titanium-silicon molecular sieve is 0.18-0.19 nm, the Ti-O bond length is 0.19-0.20 nm, and the -O bond lengths of the dopants are shown in Table 2. Specifically, when the bond length between the dopant metal and the O atom is comparable to the Si-O bond length (or Ti-O bond length) (the smaller the difference), it indicates that the dopant element has entered the framework of the titanium-silicon molecular sieve and can maintain the framework structure of the titanium-silicon molecular sieve well. As the difference increases, the dopant element may enter the framework of the titanium-silicon molecular sieve, but it will cause the framework to deform. As the difference further increases (the bond length between the dopant metal and the O atom is greater than 1 nm), the dopant element cannot enter the framework of the titanium-silicon molecular sieve.

[0082] The method for testing the silicon-titanium molar ratio in molecular sieves is as follows: the content of titanium and silicon elements in molecular sieves is tested by combining inductively coupled plasma optical emission spectroscopy (ICP-OES) to obtain the overall silicon-titanium ratio of the molecular sieve.

[0083] The method for determining the Pd / Pt content in molecular sieves is as follows: based on inductively coupled plasma optical emission spectroscopy (ICP-OES), the metal content in the catalytic material is tested. Specifically, after sample digestion, the solution is introduced into the plasma optical emission spectrometer, and the intensity is measured at the corresponding elemental wavelengths. The elemental content in the sample is calculated using the standard curve method. Then, the Pd / Pt content is obtained based on the relevant component data.

[0084] The method for testing the crystallinity of 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:

[0085] X i =X s *(W i *ΣH ii / (W S *ΣH Si )).

[0086] The method for testing the average particle size of molecular sieves is as follows: The average particle size of molecular sieves 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, scattering angle, and test temperature, the intensity distribution of the scattered light of the particles to the laser is determined, and the particle size distribution information is calculated based on the intensity distribution of the scattered light.

[0087] The pore structure and specific surface area of ​​the 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.

[0088] Table 2

[0089]

[0090] 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 a titanium-silicon molecular sieve, characterized in that, The preparation method includes the following steps: (1) The aqueous solution containing silicon source, titanium source and alkali source is brought into first contact with the solution containing metal salt; wherein the metal salt includes Group VIII and / or Group IB metal salt; (2) The solution obtained from the first contact is brought into a second contact with a dispersion containing metal particles; wherein the metal particles include Group VIII and / or Group IB metal particles; (3) The solution obtained from the second contact is subjected to hydrothermal crystallization, solid-liquid separation and calcination in sequence.

2. The preparation method according to claim 1, wherein, In step (1), the metal salt includes palladium salt and / or platinum salt; And / or, the molar ratio R1 of silicon source, titanium source, alkali source and water in the aqueous solution containing silicon source, titanium source and alkali source is 100:0.002-60:1-200:50-1000, preferably 100:0.1-10:20-120:100-800; wherein, the silicon source is calculated as SiO2 and the titanium source is calculated as 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; And / or, the molar ratio R2 of the silicon source to the metal salt is 1000:0.02-5, preferably 1000:0.1-2; wherein the silicon source is calculated as SiO2 and the metal salt is calculated as a metal element; And / or, the metal salt includes at least one of PdCl2, Pd(NO3)2, PtCl2 and Pt(NO3)2; And / or, the concentration of the metal salt in the solution containing the metal salt is 0.001-1 mol / L, preferably 0.01-0.1 mol / L; And / or, the solvent in the metal salt-containing solution is water; And / or, the duration of the first contact is 10-120 min, preferably 40-80 min.

3. The preparation method according to claim 1, wherein, The molar ratio R3 of the metal salt in step (1) to the metal particles in step (2) is 1:0.001-1, preferably 1:0.005-0.1, wherein the metal salt is calculated as a metal element and the metal particles are calculated as a metal element. And / or, in step (2), the metal particles include palladium particles and / or platinum particles; And / or, the concentration of metal particles in the dispersion containing metal particles is 0.001-0.1 mol / L; And / or, the solvent in the dispersion containing metal particles is water; And / or, the particle size of the metal particles in the dispersion containing metal particles is 1-20 nm, preferably 1-3 nm; Preferably, the metal particles are prepared by mixing an aqueous solution of a metal precursor, an aqueous solution of sodium citrate, and an aqueous solution of tannic acid, and then heating the mixture at 60-120°C for 2-6 hours; wherein the metal precursor includes a Group VIII metal salt and / or a Group IB metal salt. More preferably, the amounts of the metal precursor aqueous solution, sodium citrate aqueous solution, and tannic acid aqueous solution are such that the molar ratio of the metal precursor, sodium citrate, and tannic acid is 1:0.02-0.2:0.025-0.25; And / or, the second contact time is 20-100 min.

4. The preparation method according to claim 1, wherein, The conditions for hydrothermal crystallization include: a temperature of 120-200℃ and a time of 10-80h; And / or, the calcination conditions include: a temperature of 500-650°C and a time of 4-10 hours.

5. The preparation method according to claim 1, wherein, The aqueous solution containing silicon source, titanium source and alkali source is obtained by: first mixing silicon source and titanium source to obtain a first mixture, then mixing the first mixture with alkali source to obtain a second mixture, and then mixing the second mixture with water to obtain the aqueous solution containing silicon source, titanium source and alkali source.

6. The preparation method according to claim 1, wherein, The preparation method further includes: before step (2), the product of the first contact is subjected to alcohol removal treatment; Preferably, the conditions for the alcohol removal treatment include: a temperature of 70-100℃ and a time of 2-8 hours.

7. The titanium-silicon molecular sieve prepared by the method according to any one of claims 1-6.

8. A titanium-silicon molecular sieve, characterized in that, The titanium-silicon molecular sieve includes a doped metal element that enters the framework structure of the titanium-silicon molecular sieve. The bond length between the doped metal element and the O atom in the titanium-silicon molecular sieve framework is 0.02-0.55 nm, preferably 0.15-0.25 nm. The doped metal element includes Group VIII and / or Group IB metal elements.

9. The titanium-silicon molecular sieve according to claim 8, wherein, The doped metal element includes Pd and / or Pt; And / or, the silicon-to-titanium molar ratio in the titanium-silicon molecular sieve is 100:0.1-10; And / or, based on the total weight of the titanium-silicon molecular sieve, the content of the doped metal element is 0.01-0.5% by weight.

10. The titanium-silicon molecular sieve according to claim 8, wherein, The titanium-silicon molecular sieve has an average particle size of 80-300 nm and a mesopore specific surface area of ​​50-200 m². 2 / g, the pore volume of the mesoporous tissue is 0.18-0.5cm³. 3 / g, the specific surface area of ​​the micropores is 180-500m² 2 / g, the pore volume of the micropores is 0.05-0.25cm³. 3 / g, with a crystallinity of 85-99%.

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