CN107381592B - Titanium-tin molecular sieve, preparation method thereof and method for catalytic oxidation of cyclohexanone - Google Patents

Titanium-tin molecular sieve, preparation method thereof and method for catalytic oxidation of cyclohexanone Download PDF

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CN107381592B
CN107381592B CN201710535212.3A CN201710535212A CN107381592B CN 107381592 B CN107381592 B CN 107381592B CN 201710535212 A CN201710535212 A CN 201710535212A CN 107381592 B CN107381592 B CN 107381592B
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王宝荣
雷志伟
陈飞彪
谢贤清
郭晓红
廖维林
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Jiangxi Normal University
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Abstract

The invention relates to the technical field of β molecular sieves, and discloses a titanium-tin molecular sieve, a preparation method thereof and a method for catalyzing and oxidizing cyclohexanone, wherein the preparation method of the titanium-tin molecular sieve comprises the following steps of (1) mixing and dissolving a titanium source, polyvinylpyrrolidone and urea in proportion in the presence of an aqueous solvent to obtain a mixture, adding a silicon source, a mineralizer, a structure directing agent and an alkali source into the mixture in proportion, uniformly mixing to obtain a mixed system, (2) adding a tin source into the mixed system obtained in the step (1), and adjusting the pH value of the solution to 9.5-13.6, and (3) transferring the reaction mixture obtained in the step (2) into a reaction kettle, carrying out crystallization reaction at 70-160 ℃ for 0.2-14 days, cooling to room temperature, and then washing, drying and roasting to obtain the titanium-tin molecular sieve.

Description

Titanium-tin molecular sieve, preparation method thereof and method for catalytic oxidation of cyclohexanone
Technical Field
The invention relates to the technical field of β molecular sieves, in particular to a titanium-tin molecular sieve, a preparation method thereof and a method for catalytic oxidation of cyclohexanone.
Background
The heteroatom molecular sieve is a molecular sieve with non-silicon and non-aluminum elements on a framework structure, and the introduction of the heteroatom not only has the function of adjusting the acidity and the surface performance of the zeolite catalyst, but also ensures that the zeolite catalyst has special catalytic performance. The titanium silicalite TS-1 is a molecular sieve with a four-coordinate framework titanium, and the appearance marks the beginning of the synthesis and application research of heteroatom molecular sieves.
β molecular sieve is a three-dimensional twelve-membered ring pore channel structure, in which the pores in the [100] and [010] directions are straight pores with pore diameters of about 0.66 × 0.67nm, and the pores in the [001] direction are sinusoidal pores with pore diameters of about 0.55 × 0.55nm formed by crossing the straight pores in the [100] and [010] directions, and β molecular sieve has a unique pore channel structure, good thermal and hydrothermal stability and acid content, so that it can be widely used as catalytic material in petroleum refining and petrochemical engineering, such as benzene and propylene alkylation, alcohol amination, olefin hydration, toluene disproportionation and methylation, hydrocracking and catalytic dewaxing, etc., and has a wide application prospect.
Ti- β expands the application of TS-1 in macromolecular oxidation reactions, such as the epoxidation of oleic acid and methyl oleate, and Sn- β can effectively catalyze reactions such as Bayer Villiger oxidation, Meerwin-Ponndorf-Verley, Diles-Alder addition and isomerization, so the synthesis of Ti- β and Sn- β is one of the major research directions of heteroatom molecular sieves T.Blasco et al [ Blascot, CamborM, CormaA, et. Chemcomm. 1996, 20: 2367. 2368 ] uses silica as a silicon source, TEAOH as a template and HF as a fluorine source, and synthesizes a non-aluminum Ti- β molecular sieve in a nearly neutral fluorine-containing system, which has the advantages of less defects, good hydrophobicity and thermal stability, etc. they also adopt a silicon source as a template and HF as a fluorine-containing catalyst system, and further use a fluorine-containing catalyst system such as a fluorine-containing molecular sieve for synthesizing fine molecular sieves such as a fluorine-containing catalyst system, which has excellent performances of Ti-alumina, Ti- β, silica, hydrophobic and thermal stability, alumina, and further use of a further as a catalyst system for reactions such as a fluorine-containing catalyst system for reactions such as a chemical engineering molecular sieves No. 8. 9. A, No. 8.
However, HF as a mineralizer brings environmental and safety problems, and can also significantly reduce the alkalinity of the crystallization system, solidify precursor gel, thereby reducing the diffusion rate of the precursor, and affect the nucleation and synthesis stability of the molecular sieve, therefore, Ti- β and Sn- β molecular sieves prepared under the system conditions generally have low heteroatom content [ Corma A., NemethL., RenzM., VacialenS., Nature, 2001, 412, 423-]The particle size is usually above 10 microns and the crystallization time is up to 20 days. Therefore, the method for preparing the catalyst has the advantages of high heteroatom content, small particle size, good synthesis stability and environment-friendly preparation method*Heteroatom molecular sieves of the BEA structure are becoming increasingly important.
Disclosure of Invention
One of the purposes of the invention is to provide a titanium-tin molecular sieve which has the characteristic of small grain size and has good catalytic performance in the oxidation reaction of cyclohexanone.
The invention also aims to provide a preparation method of the titanium-tin molecular sieve, which synthesizes the titanium-tin molecular sieve with small grain size, uniform size and good catalytic performance under the alkaline condition.
The invention also aims to provide a method for catalytically oxidizing cyclohexanone, which has the advantage of high catalytic oxidation efficiency and has higher selectivity to adipic acid.
In order to achieve the purpose, the invention provides a titanium-tin molecular sieve, wherein the molar ratio of silicon to tin to titanium in the molecular sieve is 1: (0.002-0.01): (0.001-0.05), wherein the acid content of the titanium-tin molecular sieve is 36.7-57.9 mu mol/g.
The invention also provides a preparation method of the titanium-tin molecular sieve, which comprises the following steps:
(1) in the presence of an aqueous solvent, mixing and dissolving a titanium source, polyvinylpyrrolidone and urea in proportion to obtain a mixture, adding a silicon source, a mineralizer, a structure directing agent and an alkali source into the mixture in proportion, and uniformly mixing to obtain a mixed system;
(2) adding a tin source into the mixed system obtained in the step (1) to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: water 1: (0.002-0.015): (0.001-0.15): (0.3-3): (0.8-5.0): (10-300) adjusting the pH value of the solution to 9.5-13.6;
(3) and (3) transferring the reaction mixture obtained in the step (2) into a reaction kettle, carrying out crystallization reaction at 70-160 ℃ for 0.2-14 days, cooling to room temperature, and then washing, drying and roasting to obtain the titanium-tin molecular sieve.
In addition, the invention also provides a method for catalytically oxidizing cyclohexanone, which comprises the step of contacting the cyclohexanone with an oxidant in the presence of a catalyst to react, wherein the catalyst contains the titanium-tin molecular sieve;
the reaction conditions are as follows: the molar ratio of the oxidant to the cyclohexanone is (3-12): 1, the pressure is 0.2-3 MPa, the reaction temperature is 50-160 ℃, the reaction time is 0.2-100 h, and the amount of the catalyst is 0.2-20% of the total weight of reactants.
Through the technical scheme, the invention provides a method for synthesizing the titanium-tin molecular sieve through a hydrothermal crystallization method under an alkaline condition, the titanium-tin molecular sieve has smaller grain size and uniform size, the performance of the molecular sieve for catalyzing and oxidizing cyclohexanone is improved through the compounding of titanium and tin, and meanwhile, the selectivity of a catalytic product adipic acid is also high.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is an XRD pattern of the titanium tin molecular sieve of example 1;
FIG. 2 is a chart of the UV-Vis spectra of the titanium tin molecular sieve of example 1;
FIG. 3 is an SEM image of the titanium tin molecular sieve of example 1;
FIG. 4 is a TEM image of the titanium tin molecular sieve in example 1;
FIG. 5 is an SEM image of the titanium tin molecular sieve of example 2.
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a titanium-tin molecular sieve, wherein the molar ratio of silicon to tin to titanium in the molecular sieve is 1: (0.002-0.01): (0.001-0.05).
According to the invention, an important factor influencing the catalytic performance of the molecular sieve is the acidity of the molecular sieve, and in the invention, the acidity of the titanium-tin molecular sieve is 36.7-57.9 mu mol/g, preferably 43.3-57.9 mu mol/g.
According to the invention, one important physical index of the molecular sieve is the specific surface area, and the improvement of the specific surface area can improve the accessibility of active sites in the molecular sieve, thereby improving the catalytic effect of the molecular sieve; further, the specific surface area of the molecular sieve is 568-690 m2The pore volume is 0.37-0.58 cm3/g。
The invention also provides a preparation method of the titanium-tin molecular sieve, which comprises the following steps:
(1) in the presence of an aqueous solvent, mixing and dissolving a titanium source, polyvinylpyrrolidone and urea in proportion to obtain a mixture, adding a silicon source, a mineralizer, a structure directing agent and an alkali source into the mixture in proportion, and uniformly mixing to obtain a mixed system;
(2) to the step of(1) Adding a tin source into the mixed system to obtain the mixture with the molar ratio of SiO2: sn: ti: mineralizing agent: structure directing agent: water 1: (0.002-0.015): (0.001-0.15): (0.3-3): (0.8-5.0): (10-300) adjusting the pH value of the solution to 9.5-13.6;
(3) and (3) transferring the reaction mixture obtained in the step (2) into a reaction kettle, carrying out crystallization reaction at 70-160 ℃ for 0.2-14 days, cooling to room temperature, and then washing, drying and roasting to obtain the titanium-tin molecular sieve.
According to the invention, in the step (1), the silicon source may be at least one of organosilicate, silica gel, white carbon black and silica sol; further, in order to reduce the effect of the hetero atoms in the silicon source on the crystallization product, the silicon source is preferably an organosilicate, and the organosilicate may be at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate and isopropyl silicate.
According to the invention, the mineralizer may be a sodium salt, a potassium salt, more specifically a sodium halide, a potassium halide, a sodium sulfate, a potassium sulfate, a sodium sulfite, a potassium sulfide, a sodium nitrate, a potassium nitrate, a sodium nitrite, a potassium nitrite, a sodium carbonate, a potassium carbonate, or the like; further, the sodium halide is at least one of sodium halide and potassium halide; further, the mineralizer is at least one of sodium fluoride and potassium fluoride.
According to the invention, the structure directing agent has a great influence on the morphological structure of the molecular sieve, and the structure directing agent used in the step (1) of the invention can be at least one of quaternary ammonium base, quaternary ammonium salt and fatty amine, wherein the quaternary ammonium base can be organic quaternary ammonium base, the quaternary ammonium salt can be organic quaternary ammonium salt, and the fatty amine can be NH3Wherein at least one hydrogen is substituted with an aliphatic hydrocarbon group (e.g., an alkyl group).
Specifically, the structure directing agent may be at least one selected from quaternary ammonium bases represented by the general formula II, quaternary ammonium salts represented by the general formula III, and aliphatic amines represented by the general formula iv.
Figure BDA0001340415890000051
In the formula II, R1、R2、R3And R4Each is C1-C4Alkyl of (2) including C1-C4Straight chain alkyl of (2) and C3-C4Branched alkyl groups of (a), for example: r1、R2、R3And R4Each may independently be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl.
Figure BDA0001340415890000061
In the formula III, R1、R2、R3And R4Each is C1-C4Alkyl of (2) including C1-C4Straight chain alkyl of (2) and C3-C4Branched alkyl groups of (a), for example: r1、R2、R3And R4Each may be independently methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; x represents a halogen anion or an acid radical ion, and may be F-、Cl-、Br-、I-Or HSO 4-.
R5(NH2)n(formula IV)
In the formula IV, n is an integer of 1 or 2. When n is 1, R5Is C1-C6Alkyl of (2) including C1-C6Straight chain alkyl of (2) and C3-C6Such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, isopentyl, tert-pentyl and n-hexyl. When n is 2, R5Is C1-C6Alkylene of (2) including C1-C6Linear alkylene of (A) and (C)3-C6Such as methylene, ethylene, n-propylene, n-butylene, n-pentylene or n-hexylene.
Preferably, the structure directing agent in step (1) is at least one of tetraethylammonium hydroxide, tetraethylammonium fluoride, tetraethylammonium chloride, tetraethylammonium bromide, tetraethylammonium iodide, diethylamine and triethylamine; further, the structure directing agent may be tetraethylammonium hydroxide.
In the invention, the alkali source provides enough OH for the crystallization reaction system-In order to ensure smooth completion of the crystallization reaction and improve uniformity of the crystallized product, the alkali source in step (1) may be at least one of alkali metal hydroxide, ammonia water, urea, hydrazine hydrate, sodium carbonate, sodium bicarbonate, aliphatic amine, aliphatic alcohol amine and quaternary ammonium base, preferably at least one of ammonia water, urea, hydrazine hydrate, sodium carbonate, sodium bicarbonate, aliphatic amine, aliphatic alcohol amine and quaternary ammonium base.
According to the invention, a tin source is the most important element influencing the Sn- β molecular sieve, the tin source can be a common tin source known by a person skilled in the art, such as organic tin salt and inorganic tin salt, because the organic tin salt has toxicity and is harmful to human bodies and the environment, the inorganic tin source with lower toxicity is selected by the invention, the inorganic tin source can be at least one of tin halide, stannous sulfate, stannic sulfate, stannate, stannous salt, stannic nitrate, stannic oxide and stannous oxide, in order to ensure that the generated Sn- β molecular sieve has the same crystal form and crystal morphology, ensure the purity of a crystallization product and avoid the generation of various forms of crystallization products, and the tin source in the invention is preferably a single tin source, such as one of tin chloride, stannic nitrate, stannic sulfate and sodium stannate.
According to the present invention, the kind of the titanium source is not particularly limited, the titanium source may be an inorganic titanium source or an organic titanium source, and further the titanium source may be at least one of titanium tetrahalide, titanium sulfate, titanium nitrate, titanium titanate, titanium sulfate, and titanium titanate; preferably a titanate ester, which may be at least one of tetraethyl titanate, tetrapropyl titanate and tetrabutyl titanate.
According to the invention, further, in the step (1), the molar ratio of the titanium source, the polyvinylpyrrolidone and the urea is 1: (5-20): (0.48-2.56).
According to the invention, the temperature of the system is one of important factors influencing the crystallization rate, the crystallization speed is too high, more defects are generated in the crystals, and the crystallinity of the crystals is influenced, the invention adopts a solvent with a lower boiling point as a hydrothermal reaction solvent, and the aqueous medium is a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: (1-4).
According to the invention, further, the molar ratio of each substance in the mixed solution in the step (2) is SiO2: sn: ti: mineralizing agent: structure directing agent: h2O＝1：(0.005～0.01)：(0.003～0.05)：(0.5～2.4)：(1.5～3.6)：(20～100)。。
According to the invention, the temperature and time of the hydrothermal reaction are one of important factors influencing crystal form, crystal size and product morphology of the hydrothermal product, and further, in the step (3), the crystallization temperature is 80-120 ℃, and the crystallization time is 0.5-10 days.
According to the invention, the structure directing agent in the molecular sieve is removed by roasting, the roasting temperature in the step (3) needs to reach the decomposition temperature of the structure directing agent, but the structure of the molecular sieve is not damaged, and further, the roasting temperature of the solid powder in the step (3) is 300-650 ℃, and the roasting time is 2-10 hours; furthermore, the roasting temperature is 400-550 ℃, and the roasting time is 4-8 h.
According to the invention, in the hydrothermal reaction, the pressure of the system is another important factor influencing the crystal form and crystallization rate of the product, the autogenous pressure of the reaction system depends on the volume of the solution in the reaction kettle, and in order to improve the efficiency of the crystallization reaction, the total volume of the mixed solution in the step (1) is further 60-75% of the capacity of the reaction kettle.
In addition, the invention also provides a method for catalytically oxidizing cyclohexanone, which comprises the step of contacting cyclohexanone with an oxidant in the presence of the titanium-tin molecular sieve for reaction, wherein the catalyst is the titanium-tin molecular sieve prepared according to the method, and the reaction conditions of the reaction are as follows: the molar ratio of the oxidant to the cyclohexanone is (3-12): 1, the pressure is 0.2-3 MPa, the reaction temperature is 50-160 ℃, the reaction time is 0.2-100 h, and the amount of the catalyst is 0.2-20% of the total weight of reactants, wherein in the invention, when the reaction conditions are as follows: the molar ratio of hydrogen peroxide to cyclohexanone is 6: 1, the pressure is 2MPa, the reaction temperature is 100 ℃, the reaction time is 30h, the amount of the titanium-tin molecular sieve is 3 percent of the total weight of reactants, and the titanium-tin molecular sieve shows better catalytic performance under the reaction condition.
According to the present invention, further, the oxidizing agent is at least one of hydrogen peroxide, tert-butyl hydroperoxide, peracetic acid, and propionic acid.
In each of the following examples and comparative examples, the crystallographic phase diagram of X-ray diffraction (XRD) was measured using Philips analytical X' pert under the conditions of Cu target, K α radiation, Ni filter, super detector, tube voltage of 30KV and tube current of 40mA, the morphology size of the molecular sieve was measured using Hitachi S4800 type scanning electron microscope and acceleration voltage of 20KV, and the transmission electron microscope diagram of the molecular sieve was measured using FEITecnaiG 220 type high resolution electron microscope with acceleration voltage of 200 kV; the specific surface area and the pore volume of the molecular sieve are tested by adopting a nitrogen adsorption method, a nitrogen adsorption and desorption curve is tested by adopting a specific surface analyzer with a tristar II 3020-M model of Micromeritics, and the specific surface area and the pore volume are obtained by calculating through a BET (BET) method and a t-plot method; the acid content is analyzed by a BIQ-RADFTS3O00 type Fourier infrared spectrometer; the titanium and tin distributions were analyzed by a JASCOUV-visible550 model UV spectrophotometer.
Example 1
Tetrabutyl titanate, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 10: 0.98 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 2, obtaining a mixed system, adding methyl orthosilicate, sodium fluoride, tetraethyl ammonium hydroxide and ammonia water into the mixed system, and uniformly mixing;
adding tin nitrate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O＝1：0.008：0.005: 1: 1.1: 80, adding sodium carbonate to the reaction mixture to adjust the pH value of the solution to be 12.8;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 100 ℃ for 5 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 450 ℃ for 6h to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.007: 0.004, and the acid amount of the molecular sieve is 57.9 mu mol/g.
The specific surface area of the molecular sieve is 690m2Per g, pore volume of 0.58cm3/g。
The titanium tin molecular sieve has an XRD spectrum as shown in figure 1, an ultraviolet-visible spectrum as shown in figure 2, an SEM picture as shown in figure 3 and a TEM spectrum as shown in figure 4. In the XRD spectrum, the peak with 2 theta of 22.4 degrees is a characteristic peak of a BEA structure, in the UV-Vis spectrum, the peak at 210nm is classified into four-coordinate framework tin, and the peak between 250-300nm is a non-framework tin species.
Example 2
Tetraethyl titanate, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 6: 1.95 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 3, adding tetraethoxysilane, potassium sulfide, tetraethyl ammonium fluoride and sodium carbonate into the mixed system according to the proportion, and uniformly mixing;
adding stannous sulfate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.005: 0.05: 0.5: 2.2: 100, adding sodium carbonate to adjust the pH value of the solution to 10.5;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 120 ℃ for 3 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 400 ℃ for 5 hours to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.005: 0.025, the acid amount of the molecular sieve is 48.7 mu mol/g;
the specific surface area of the molecular sieve is 634m2Per g, pore volume of 0.45cm3/g。
The SEM picture of the titanium tin molecular sieve is shown in fig. 5.
Example 3
Titanium sulfate, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 14.8: 0.78 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 3, adding silica sol, potassium fluoride, tetraethyl ammonium iodide and sodium carbonate into the mixed system according to a proportion, and uniformly mixing;
adding tin chloride into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.01: 0.003: 2.4: 3.6: 15, adding tetraethyl ammonium hydroxide to adjust the pH value of the solution to be 13.6;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 80 ℃ for 10 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 550 ℃ for 6 hours to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.006: 0.002, acid amount of the molecular sieve is 43.3 mu mol/g;
the specific surface area of the molecular sieve is 621m2Per g, pore volume of 0.43cm3/g。
Example 4
Titanium tetrachloride, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 5: 2.56 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 1, adding white carbon black, sodium fluoride, tetraethyl ammonium hydroxide and ammonia water into the mixed system according to a certain proportion, and uniformly mixing;
adding sodium stannate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.002: 0.15: 0.3: 0.8: reaction of 30Adding sodium carbonate into the mixture to adjust the pH value of the solution to 9.5;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 70 ℃ for 14 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 300 ℃ for 8h to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.002: 0.05, the acid content of the molecular sieve is 42.9 mu mol/g;
the specific surface area of the molecular sieve is 603m2Per g, pore volume of 0.37cm3/g。
Example 5
Titanium nitrate, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 20: 0.48 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 4, adding silica gel, potassium fluoride, triethylamine and urea into the mixed system according to a proportion, and uniformly mixing;
adding stannous chloride into the mixed system obtained in the step (1) to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.015: 0.001: 3: 5: 300, adding tetraethylammonium hydroxide to adjust the pH value of the solution to be 12.8;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 160 ℃ for 0.2 day, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 650 ℃ for 4h to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.01: 0.001, the acid amount of the molecular sieve is 36.7 mu mol/g;
the specific surface area of the molecular sieve is 568m2Per g, pore volume of 0.58cm3/g。
Comparative example 1
According to the method of the embodiment 2, except that hydrofluoric acid is adopted to adjust the hydrothermal reaction system to be neutral, the specific implementation process is as follows:
tetraethyl titanate, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 6: 1.95 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 3, adding tetraethoxysilane, potassium sulfide, tetraethyl ammonium fluoride and sodium carbonate into the mixed system according to the proportion, and uniformly mixing;
adding stannous sulfate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.005: 0.05: 0.5: 1.5: 100, adding hydrofluoric acid into the reaction mixture, and adjusting the pH value of the solution to 7;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 120 ℃ for 3 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 400 ℃ for 5 hours to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.001: 0.01, the acid amount of the molecular sieve is 29.7 mu mol/g;
the specific surface area of the titanium-tin-silicon composite is 439m2Per g, pore volume of 0.23cm3/g。
Comparative example 2
Following a procedure similar to example 2, except that no titanium source was added, the procedure was as follows:
mixing polyvinylpyrrolidone and urea according to a molar ratio of 6: 1.95 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 3, adding tetraethoxysilane, potassium sulfide, tetraethyl ammonium fluoride and sodium carbonate into the mixed system according to the proportion, and uniformly mixing;
adding stannous sulfate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: mineralizing agent: structure directing agent: h2O is 1: 0.005: 0.5: 1.5: 100, adding sodium carbonate to adjust the pH value of the solution to 10.5;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 120 ℃ for 3 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 400 ℃ for 5 hours to obtain the titanium-tin molecular sieve.
The molar ratio of silicon to tin in the tin-silicon composite prepared by the method is 1: 0.03, the acid content of the molecular sieve is 32.4 mu mol/g;
the specific surface area of the tin-silicon composite is 557m2Per g, pore volume of 0.31cm3/g。
Comparative example 3
Following a procedure similar to example 2, except that no polyvinylpyrrolidone was added, the procedure was as follows:
tetraethyl titanate and urea are mixed according to a molar ratio of 1: 1.95 is dissolved in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 3, adding tetraethoxysilane, potassium sulfide, tetraethyl ammonium fluoride and sodium carbonate into the mixed system according to the proportion, and uniformly mixing;
adding stannous sulfate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.005: 0.05: 0.5: 1.5: 100, adding sodium carbonate to adjust the pH value of the solution to 10.5;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 120 ℃ for 3 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 400 ℃ for 5 hours to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.003: 0.035, acid amount of said molecular sieve is 24.2 μmol/g;
the specific surface area of the molecular sieve is 546m2Per g, pore volume of 0.28cm3/g。
Comparative example 4
Following a procedure similar to example 2, except that no urea was added, the procedure was carried out as follows:
tetraethyl titanate, polyvinylpyrrolidone and urea are mixed according to a molar ratio of 1: 6, dissolving the mixture in a mixed solution of ethanol and water, wherein the volume ratio of the water to the ethanol is 1: 3, adding tetraethoxysilane, potassium sulfide, tetraethyl ammonium fluoride and sodium carbonate into the mixed system according to the proportion, and uniformly mixing;
adding stannous sulfate into the mixed system to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: h2O is 1: 0.005: 0.05: 0.5: 1.5: 100, adding sodium carbonate to adjust the pH value of the solution to 10.5;
transferring the reaction mixture into a reaction kettle, performing crystallization reaction at 120 ℃ for 3 days, cooling to room temperature, and washing and drying the product to obtain a crystallized product;
and roasting the crystallized product at 400 ℃ for 5 hours to obtain the titanium-tin molecular sieve.
The titanium-tin molecular sieve prepared by the method has the following molar ratio of silicon to tin to titanium of 1: 0.002: 0.042, the acid amount of the molecular sieve is 20.1 mu mol/g;
the specific surface area of the molecular sieve is 521m2Per g, pore volume of 0.22cm3/g。
The catalytic results of the Sn- β molecular sieves of examples 1-5 and comparative examples 1-4 in the oxidation reaction of cyclohexanone are shown in Table 1, the reaction conditions include that cyclohexanone and hydrogen peroxide are contacted and reacted in the presence of titanium-tin molecular sieve, the molar ratio of the hydrogen peroxide to the cyclohexanone is 6: 1, the pressure is 2MPa, the reaction temperature is 100 ℃, the reaction time is 30h, and the amount of the titanium-tin molecular sieve is 3% of the total weight of reactants.
Cyclohexanone conversion ═ amount of added reactant-amount of remaining reactant)/amount of added reactant × 100%;
target product selectivity is the amount of reactant consumed for conversion to target product/amount of reactant converted x 100%.
TABLE 1
Example numbering Cyclohexanone conversion (%) Adipic acid selectivity (%)
Example 1 99.8 99.7
Example 2 98.7 98.5
Example 3 92.6 91.2
Example 4 90.2 92.1
Example 5 86.4 83.1
Comparative example 1 57.1 73.5
Comparative example 2 68.5 77.2
Comparative example 3 45.8 47.9
Comparative example 4 38.6 56.8
As can be seen from data in a table and characterization results, the technical scheme of the invention can prepare the titanium-tin molecular sieve by modifying the all-silicon beta molecular sieve under an alkaline condition, the titanium-tin molecular sieve has fewer skeleton defects and uniform particle size, and the molecular sieve has good catalytic performance on oxidation reaction of cyclohexanone.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention. It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims (12)

1. The preparation method of the titanium-tin molecular sieve is characterized by comprising the following steps:
(1) in the presence of an aqueous solvent, mixing and dissolving a titanium source, polyvinylpyrrolidone and urea in proportion to obtain a mixture, adding a silicon source, a mineralizer, a structure directing agent and an alkali source into the mixture in proportion, and uniformly mixing to obtain a mixed system;
(2) adding a tin source into the mixed system obtained in the step (1) to obtain SiO in the molar ratio of each substance2: sn: ti: mineralizing agent: structure directing agent: water 1: (0.002E &0.015): (0.001-0.15): (0.3-3): (0.8-5.0): (10-300) adjusting the pH value of the solution to 9.5-13.6;
(3) and (3) transferring the reaction mixture obtained in the step (2) into a reaction kettle, carrying out crystallization reaction at 70-160 ℃ for 0.2-14 days, cooling to room temperature, and then washing, drying and roasting to obtain the titanium-tin molecular sieve.
2. The method for preparing a titanium-tin molecular sieve according to claim 1, wherein in the step (1), the molar ratio of the titanium source, polyvinylpyrrolidone and urea is 1: (5-20): (0.48-2.56).
3. The method for preparing a titanium-tin molecular sieve according to claim 1 or 2, wherein, in the step (1), the aqueous solvent is a mixed solution of ethanol and water, wherein the volume ratio of water to ethanol is 1: (1-4).
4. The method for preparing the titanium-tin molecular sieve of claim 1 or 2, wherein in the step (2), the molar ratio of each substance in the reaction mixture is SiO 2: sn: ti: mineralizing agent: structure directing agent: H2O ═ 1: (0.005-0.01): (0.003-0.05): (0.5-2.4): (1.5-3.6): (20-100).
5. The method for preparing the titanium-tin molecular sieve of claim 1 or 2, wherein in the step (3), the crystallization temperature is 80-120 ℃; and/or
The crystallization time is 0.5-10 days; and/or
The roasting temperature is 300-650 ℃; and/or
The roasting time is 2-10 h.
6. The method for preparing the titanium-tin molecular sieve of claim 5, wherein in the step (3), the roasting temperature is 400-550 ℃; and/or
The roasting time is 4-8 h.
7. The method of preparing a titanium-tin molecular sieve of claim 1 or 2, wherein the alkali source is at least one of ammonia, urea, hydrazine hydrate, sodium carbonate, sodium bicarbonate, aliphatic amines, aliphatic alcohol amines, and quaternary ammonium bases; and/or
The mineralizer is at least one of sodium halide, potassium halide, sodium sulfate, potassium sulfate, sodium sulfite, potassium sulfide, sodium nitrate, potassium nitrate, sodium nitrite, potassium nitrite, sodium carbonate and potassium carbonate.
8. The method of preparing a titanium-tin molecular sieve of claim 1 or 2, wherein the tin source is at least one of tin halide, stannous sulfate, sodium stannate, potassium stannate, zinc stannate, and tin nitrate.
9. The method of preparing a titanium-tin molecular sieve of claim 8, wherein the tin source is one of tin chloride, tin nitrate, tin sulfate, and sodium stannate.
10. A method for catalytically oxidizing cyclohexanone, which comprises reacting cyclohexanone with an oxidant in the presence of a catalyst, wherein the catalyst contains the titanium-tin molecular sieve prepared by the preparation method according to any one of claims 1 to 9.
11. The process for catalytic oxidation of cyclohexanone according to claim 10, wherein the reaction conditions comprise: the molar ratio of the oxidant to the cyclohexanone is (3-12): 1, the pressure is 0.2-3 MPa, the reaction temperature is 50-160 ℃, the reaction time is 0.2-100 h, and the amount of the catalyst is 0.2-20% of the total weight of reactants.
12. The process for catalytic oxidation of cyclohexanone according to claim 10, wherein the oxidizing agent is at least one of hydrogen peroxide, tert-butyl hydroperoxide, peroxyacetic acid, peroxypropionic acid.
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