CN111348657A - Ultrasonic-assisted titanium-silicon molecular sieve modification method - Google Patents
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Abstract
The invention discloses an ultrasonic-assisted titanium silicalite molecular sieve modification method, which comprises the steps of uniformly mixing a titanium silicalite molecular sieve with a modification reaction solution, then placing the mixture into a crystallization kettle provided with an ultrasonic generator, crystallizing the mixture under the assistance of an ultrasonic field, and then washing, filtering, drying and roasting the mixture to obtain a modified titanium silicalite molecular sieve; wherein the power of the ultrasonic field is 40-160W or the multiple of 40-160W, and the multiple is the mass of the actually used titanium silicalite molecular sieve divided by 20 g; the crystallization time under the assistance of the ultrasonic field is 6-48 hours. The modification method of the titanium silicalite molecular sieve has general applicability, is particularly suitable for alkali-modified TS-1 with more treatment capacity, and the molecular sieve subjected to ultrasonic-assisted modification has good catalytic performance and greatly improved stability.
Description
Technical Field
The invention relates to the technical field of molecular sieve modification, in particular to an ultrasonic-assisted titanium silicalite molecular sieve modification method.
Background
The titanium silicalite molecular sieve (TS-1) is prepared from Ti4+Substituting part of Si4 in full-silicon molecular sieve (Silicalite-1)+A zeolite molecular sieve with MFI type structure is formed. Due to the ion Ti4+Has the characteristic of six coordination and has the potential of accepting electron pairs, so that the TS-1 molecular sieve has the potential of H2O2Or the organic peroxide compound has good adsorption activation performance.
Cyclohexanone oxime is considered as an important chemical production raw material, and is a key intermediate for producing nylon-6 monomer epsilon-Caprolactam (CPL). The company Montedipe S.p.A (EniChem S.p.A) in Italy in the 80 th century succeeded in developing a cyclohexanone ammoximation process from cyclohexanone, ammonia and H2O2The cyclohexanone ammoximation reaction is carried out on the raw material under the catalytic action of a titanium silicalite TS-1 to prepare the cyclohexanone oxime. The production process is simple, mild in condition, environment-friendly, high in reactant conversion rate and product selectivity, and capable of greatly improving industrial benefit, so that the development of the process is of great significance to the industrial production of caprolactam. The titanium silicalite molecular sieve (TS-1) is also applied to other organic oxidation reactions and has wide application potential.
In 1981, Macro Taramasso et al disclose that TS-1 is synthesized by a hydrothermal crystallization method for the first time, and the current synthesis conditions need to be strictly controlled, otherwise, besides four-coordination framework titanium containing active centers, non-framework titanium can be generated, and the catalytic performance of the non-framework titanium is negatively influenced. First, the non-skeleton titanium itself does not have catalytic oxidation activity and also catalytically decomposes the reactant H in the ammoxidation reaction2O2Thereby affecting the conversion rate of the main reaction and the selectivity to the target product, resulting in the reduction of the catalytic performance of TS-1; secondly, the content of non-skeleton titanium is difficult to control, which leads to poor activity stability of the titanium silicalite, thus restricting the industrial application of TS-1.
In recent years, researchers at home and abroad improve the catalytic performance of TS-1 through modification treatment. The modification method of TS-1 mainly comprises the following steps: acid modification, base modification and salt modification. Wherein, the alkali modification can play a role of hole expanding in the TS-1 and form a hollow structure in the crystal, thereby reducing the diffusion limitation of reactant and product molecules and further improving the catalytic performance of the TS-1. Meanwhile, alkali modification can promote the further improvement of the content of framework titanium through the process of dissolution and recrystallization of defect sites.
The patent US6475465B and CN1301599A propose a method for modifying TS-1 by organic base, which is characterized in that a mixture of alcohol amine compounds, quaternary ammonium base, fatty amine and the like, a molecular sieve and water are mixed according to a certain proportion, and the mixture reacts for 3 hours to 3 days at the autogenous pressure of 150 ℃, wherein the used TS-1 can be raw powder or TS-1 modified by acid.
Patent CN101850986A proposes a mixed modification method, which is characterized in that TS-1 is added into a mixed solution of inorganic base and organic base according to a certain proportion, and the mixed solution reacts for 2 to 360 hours at 80 to 200 ℃ and under autogenous pressure, wherein the organic base is quaternary ammonium base and aliphatic amine compounds, and the inorganic base is ammonia water, sodium hydroxide, potassium hydroxide and the like. The patent CN1268400A proposes a method for modifying TS-1 by using an aqueous solution of metal salt or other mixtures, which is characterized in that the aqueous solution of metal salt and TS-1 are mixed according to a certain proportion, reacted at 30-100 ℃ for 6-100h, dried at 110-200 ℃, and then heated to 200-800 ℃ by program, and roasted for 2-20 h.
The invention provides a method for modifying a titanium silicalite molecular sieve, which comprises the steps of uniformly mixing an alkali solution containing an organic chelating agent with the titanium silicalite molecular sieve according to a certain proportion, reacting in a closed reaction kettle, filtering, washing, drying and roasting an obtained product to obtain the TS-1 molecular sieve modified by the alkali solution containing the organic chelating agent.
Patent CN103073022B proposes a modification method of titanium silicalite molecular sieve, which comprises the following steps: (1) primary modification: mixing a titanium silicalite molecular sieve with ammonia water, ammonium nitrate and water, reacting at a certain temperature, and then washing and drying; (2) and (3) secondary modification: mixing the once modified titanium-silicon molecular sieve with sulfur-containing metal salt and water, reacting at a certain temperature, washing with water, and drying; (3) and (4) roasting the secondarily modified titanium silicalite molecular sieve at high temperature. The invention is especially suitable for TS-1 synthesized by a classical system, and the modified molecular sieve has good catalytic performance for cyclohexanone ammoximation.
In the process of modifying the titanium silicalite molecular sieve by using alkali in the prior art, because the molecular sieve and alkali liquor are not uniformly contacted when standing and crystallizing in a hydrothermal synthesis kettle, when the molecular sieve is filled with a large amount, the solid-liquid separation phenomenon is obvious, the modification effect is directly influenced, and the catalytic performance of the molecular sieve is not obviously improved.
Therefore, a modification method of the titanium silicalite molecular sieve is urgently needed to improve the performance of the titanium silicalite molecular sieve.
Disclosure of Invention
One aspect of the present invention is to provide an ultrasonic-assisted method for modifying a titanium silicalite molecular sieve, aiming at the disadvantage of poor effect of the titanium silicalite molecular sieve modification method in the prior art.
The technical scheme provided by the invention is as follows:
an ultrasonic-assisted titanium silicalite molecular sieve modification method comprises the steps of uniformly mixing a titanium silicalite molecular sieve with a modification reaction solution, placing the mixture into a crystallization kettle provided with an ultrasonic generator, crystallizing under the assistance of an ultrasonic field, and then washing, filtering, drying and roasting to obtain a modified titanium silicalite molecular sieve;
wherein the power of the ultrasonic field is 40-160W or the multiple of 40-160W, and the multiple is the mass of the actually used titanium silicalite molecular sieve divided by 20 g; the crystallization time under the assistance of the ultrasonic field is 6-48 hours.
In recent years, ultrasonic waves have been introduced as an auxiliary means for material synthesis and widely used, and ultrasonic waves have a cavitation effect to promote homogenization of precursors and nucleation. The ultrasonic wave has a preliminary research result on the effect caused by the crystallization process, and the crystallization process is controlled by utilizing the energy of the ultrasonic wave, so that the nucleation and growth processes can be promoted, and the crystallization process is optimized. The invention introduces ultrasonic wave as an auxiliary means into the hydrothermal crystallization process, avoids molecular sieve deposition and achieves mesoscopic uniform mixing with alkali modified liquid, and simultaneously utilizes the cavitation of the ultrasonic wave, namely the great energy and the great pressure released at the moment of collapse of countless tiny cavity bubbles generated in a medium, so as to accelerate the dissolution and recrystallization rates of the molecular sieve, greatly improve the catalytic performance of the titanium-silicon molecular sieve, slow down the attenuation of the activity of the molecular sieve and improve the stability of the molecular sieve.
The titanium silicalite molecular sieve used in the present invention may be a titanium silicalite molecular sieve prepared by any method known in the art, for example, a method described in Zeolite, 1992, Vol.12943-950, a method described in J.chem.Soc., Chem Commun, 1992,123-124, or a commercially available titanium silicalite molecular sieve.
The crystallization kettle can be any suitable hydrothermal reaction kettle which can be added with an ultrasonic field in the prior art.
The modification method can be applied to a solid-liquid molecular sieve modification method of an alkaline liquid medium.
Preferably, in one embodiment of the present invention, the modification reaction solution is an aqueous alkali solution.
More preferably, the molar ratio of the titanium silicalite molecular sieve, the base and the water is 1: 0.02-0.6: 3 to 20.
Preferably, in the method for modifying a titanium silicalite molecular sieve, the alkali is organic alkali or inorganic alkali or a mixture of the organic alkali and the inorganic alkali, and the mixing molar ratio is 1: 1-50.
More preferably, in an embodiment of the present invention, the organic base is one or more selected from urea, quaternary ammonium base compounds, alcohol amine compounds or fatty amine compounds; the inorganic alkali is one or more selected from ammonia water, potassium hydroxide, sodium hydroxide or ammonium nitrate.
More specifically, the organic base may be, for example, ethylamine, ethylenediamine, n-butylamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and the like.
In the method for modifying a titanium silicalite molecular sieve of the present invention, the aqueous alkali solution may contain other additives to enhance the performance of the modified molecular sieve, for example, organic chelating agents, such as one or more selected from citric acid, tartaric acid, glutamic acid, ethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, 1, 2-cyclohexanediaminetetraacetic acid, trans-1, 2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, and triethylenetetraminehexaacetic acid.
Preferably, in an embodiment of the present invention, the crystallization temperature is 90 to 200 ℃, and the reaction time is 6 to 48 hours.
Preferably, in an embodiment of the present invention, the water washing is washing with deionized water to neutrality; the drying is carried out at the temperature of 100-150 ℃ for 2-5 hours; the roasting temperature is 500-600 ℃, and the roasting time is 3-10 hours.
Preferably, in an embodiment of the present invention, the addition amount of the titanium silicalite molecular sieve is 10% to 50% of the volume of the crystallization kettle.
In another aspect of the invention, a modified titanium silicalite molecular sieve is provided, which is prepared by the above modification method.
The titanium silicalite molecular sieve catalyst can be used for preparing cyclohexanone oxime by cyclohexanone ammoximation reaction, and can be used as a catalyst in epoxidation of olefin, hydroxylation of phenol, ammoximation of ketone and oxidation reaction of alcohol.
The invention has the beneficial effects that:
the modification method of the titanium silicalite molecular sieve has general applicability, is particularly suitable for alkali-modified TS-1 with more treatment capacity, and the molecular sieve subjected to ultrasonic-assisted modification has good catalytic performance and greatly improved stability.
Drawings
FIG. 1 is a transmission electron microscope image of TS-1 molecular sieve raw powder which is not treated by the method of the present invention;
FIG. 2 is a transmission electron micrograph of a modified TS-1 molecular sieve having a loading of 2 g.
FIG. 3 is a transmission electron microscope image of a TS-1 molecular sieve with a loading of 20g after ultrasonic-assisted modification.
Detailed Description
The invention discloses an ultrasonic-assisted titanium silicalite molecular sieve modification method, which can be realized by appropriately improving process parameters by taking the contents of the titanium silicalite molecular sieve as reference by a person skilled in the art. It is expressly intended that all such alterations and modifications which are obvious to those skilled in the art are deemed to be incorporated herein by reference, and that the techniques of the invention may be practiced and applied by those skilled in the art without departing from the spirit, scope and range of equivalents of the invention.
In the present invention, unless otherwise specified, scientific and technical terms used herein have the meanings that are commonly understood by those skilled in the art.
In order to make those skilled in the art better understand the technical solution of the present invention, the following detailed description of the present invention is provided with reference to specific embodiments.
The TS-1 molecular sieves used in this example were prepared according to the synthetic method set forth in Thangaraj et al (J.chem.Soc., Chem Commun.,1992, 123-124). Adding 20g of ethyl orthosilicate dropwise into 24g of tetrapropyl ammonium hydroxide aqueous solution (the mass fraction is 25%), hydrolyzing at room temperature until the solution is clear, dissolving 1g of tetrabutyl titanate in 6.5g of isopropanol, slowly adding the titanium source mixed solution dropwise into the silicon source hydrolyzed solution under stirring, reacting at 60 ℃ for 1h, heating to 80 ℃ to remove alcohol for 3h, transferring the glue solution to a hydrothermal synthesis kettle, standing and crystallizing for 72h, washing to be neutral, drying for 4h at 120 ℃, and roasting for 6h at 550 ℃.
As shown in FIG. 1, the TS-1 molecular sieve has a uniform microporous structure.
Example 1: modification of titanium silicalite molecular sieves
The preparation method comprises the steps of putting a mixed solution of 20g of TS-1 molecular sieve and 16.8g of tetrapropylammonium hydroxide aqueous solution (the mass fraction is 25%) and 18g of water into a reaction kettle, carrying out hydrothermal treatment for 24 hours at a self-generating pressure and a reaction temperature of 180 ℃, an ultrasonic field power of 60W and an ultrasonic time of 12 hours, then washing the mixture with deionized water to a pH value of 7-8, drying the mixture for 4 hours at a temperature of 120 ℃, and roasting the mixture for 5 hours at a temperature of 550 ℃.
The transmission electron micrograph is shown in FIG. 3.
Example 2: modification of titanium silicalite molecular sieves
The method comprises the steps of putting a mixed solution of 20g of TS-1 molecular sieve and 12.9g of tetrabutylammonium hydroxide aqueous solution (the mass fraction is 40%) and 38g of water into a reaction kettle, carrying out hydrothermal treatment for 36h at the reaction temperature of 160 ℃ and the ultrasonic field power of 50W under the self-generating pressure, then washing with deionized water to the pH value of 7-8, drying at 120 ℃ for 5h, and roasting at 550 ℃ for 8 h.
Example 3: modification of titanium silicalite molecular sieves
20g of TS-1 molecular sieve and 14.5g of tetramethylammonium hydroxide aqueous solution (the mass fraction is 25 percent) are mixed,
and (2) putting 40g of water mixed solution into a reaction kettle, carrying out hydrothermal treatment for 30h at the reaction temperature of 190 ℃ and the ultrasonic field power of 40W under the autogenous generation pressure for 10h, then washing the solution with deionized water to the pH value of 7-8, drying the solution for 4h at 120 ℃, and roasting the solution for 4h at 550 ℃.
Example 4: modification of titanium silicalite molecular sieves
The preparation method comprises the steps of putting a mixed solution of 20g of TS-1 molecular sieve, 12.5g of ammonia water solution and 52g of water into a reaction kettle, carrying out hydrothermal treatment for 36h at the reaction temperature of 170 ℃ and the ultrasonic field power of 55W under the self-generating pressure, washing with deionized water until the pH value is 7-8, drying at 120 ℃ for 3h, and roasting at 550 ℃ for 4 h.
Example 5: modification of titanium silicalite molecular sieves
The preparation method comprises the steps of putting a mixed solution of 20g of TS-1 molecular sieve, 1.1g of potassium hydroxide and 60g of water into a reaction kettle, carrying out hydrothermal treatment for 40h at the reaction temperature of 160 ℃ and the ultrasonic field power of 100W under the self-generating pressure, washing with deionized water to the pH value of 7-8, drying at 120 ℃ for 3h, and roasting at 550 ℃ for 6 h.
Example 6: modification of titanium silicalite molecular sieves
The preparation method comprises the steps of putting a mixed solution of 20g of TS-1 molecular sieve, 2.3g of potassium hydroxide and 80g of water into a reaction kettle, carrying out hydrothermal treatment for 48 hours at a reaction temperature of 170 ℃ and an ultrasonic field power of 50W under a self-generating pressure, washing with deionized water to a pH value of 7-8, drying at 120 ℃ for 3 hours, and roasting at 550 ℃ for 8 hours.
Comparative example 1: preparation of unmodified molecular sieves
TS-1 molecular sieves were prepared according to the synthetic procedure proposed by Thangaraj et al (J.chem.Soc., Chem Commun.,1992, 123-124). Adding 20g of ethyl orthosilicate dropwise into 24g of tetrapropyl ammonium hydroxide aqueous solution (the mass fraction is 25%), hydrolyzing at room temperature until the solution is clear, dissolving 1g of tetrabutyl titanate in 6.5g of isopropanol, slowly adding the titanium source mixed solution dropwise into the silicon source hydrolyzed solution under stirring, reacting at 60 ℃ for 1h, heating to 80 ℃ to remove alcohol for 3h, transferring the glue solution to a hydrothermal synthesis kettle, standing and crystallizing for 72h, washing to be neutral, drying for 4h at 120 ℃, and roasting for 6h at 550 ℃.
As shown in FIG. 1, the transmission electron microscope shows that the TS-1 molecular sieve has a uniform micropore structure.
Comparative example 2: alkali modification of small amounts of molecular sieves
A mixed solution of 2g of TS-1 molecular sieve and 1.68g of tetrapropylammonium hydroxide aqueous solution (the mass fraction is 25%) and 1.8g of water is put into a reaction kettle, treated for 48 hours at the reaction temperature of 180 ℃ under the self-generating pressure, washed to the pH value of 7-8 by deionized water, dried for 4 hours at the temperature of 120 ℃ and roasted for 3 hours at the temperature of 550 ℃.
As shown in a transmission electron microscope figure 2, a large number of cavities and depressions with different sizes of 10-80nm appear in the modified molecular sieve, and the cavities and depressions reduce the diffusion resistance of the reaction and the product, thereby being beneficial to improving the catalytic activity and prolonging the service life of the molecular sieve.
Comparative example 3: base modification of bulk molecular sieves
A mixed solution of 20g of TS-1 molecular sieve and 16.8g of tetrapropylammonium hydroxide aqueous solution (the mass fraction is 25%) and 18g of water is filled into a reaction kettle, the mixed solution is treated for 48 hours at the reaction temperature of 180 ℃ under the self-generating pressure, then the mixed solution is washed by deionized water to the pH value of 7-8, dried for 4 hours at the temperature of 120 ℃ and roasted for 3 hours at the temperature of 550 ℃.
Experimental example: evaluation of catalytic performances of titanium silicalite TS-1 before and after modification
The catalytic performance of the sample was evaluated using the cyclohexanone ammoximation reaction as a probe reaction. Carrying out continuous raw material liquid sample injection reaction in a three-neck flask with a condensing tube in a constant-temperature water bath at 80 ℃. The reaction solution was taken once per hour and analyzed by Agilent7890B gas chromatograph, and the catalytic activity of the TS-1 molecular sieve was expressed as the conversion of cyclohexanone.
Reaction conditions are as follows: hydrogen peroxide (H)2O2) Molar ratio of/Cyclohexanone 1.2, Ammonia (NH)3) /Cyclohexanone (C)6H10O) molar ratio of 2.2, tert-butanol (C)4H9OH)/Cyclohexanone (C)6H10O) mass ratio of 2.5, tert-butanol (C)4H9OH)/deionized Water (H)2O) mass ratio is 1, the dosage of the TS-1 molecular sieve is 0.5-1% of the mass of the reaction liquid, and the liquid inlet amount of the raw material is 90 g/h.
Chromatographic conditions are as follows: the chromatographic column adopts HP-5 type capillary column (0.32mm x 30mx 0.25 μm), FID detector, carrier gas is nitrogen, FID detector temperature is 270 deg.C, injection port temperature is 240 deg.C, column temperature is 120 deg.C, and is maintained for 4min, and then temperature is raised to 190 deg.C at 20 deg.C min-1 rate, and is maintained for 11 min.
The conversion rate of cyclohexanone is calculated by a normalization method, and the conversion rate calculation formula is as follows:
wherein n isOxime compoundsRepresenting the amount of material reacted to form cyclohexanone oxime, nKetonesRepresenting the amount of unreacted cyclohexanone material.
The results of the experiment are shown in tables 1 and 2.
TABLE 1 catalytic Activity of Cyclohexanone oximation reaction catalysts
TABLE 2 tabulation of specific surface area, pore volume and pore size for the samples
Comparing the BET data of different samples, it is obvious that the number of mesopores of the molecular sieve after alkali modification is increased, the average pore diameter is increased, and the number and size of the mesopores influence the diffusion rate of reactants and products, which determines the service life of the molecular sieve. When the alkali modification treatment amount is large, the modification effect is poor due to uneven contact between the modification liquid and the molecular sieve, and the ultrasonic wave is introduced in the crystallization stage, so that the layering effect can be improved, the catalytic activity of the molecular sieve can be improved, and the service life of the molecular sieve can be prolonged.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. An ultrasonic-assisted titanium silicalite molecular sieve modification method is characterized in that a titanium silicalite molecular sieve and a modification reaction solution are uniformly mixed and then are placed in a crystallization kettle provided with an ultrasonic generator, crystallization is carried out under the assistance of an ultrasonic field, and then the modified titanium silicalite molecular sieve is obtained through water washing, filtering, drying and roasting;
wherein the power of the ultrasonic field is 40-160W or the multiple of 40-160W, and the multiple is the mass of the actually used titanium silicalite molecular sieve divided by 20 g;
the crystallization time under the assistance of the ultrasonic field is 6-48 hours.
2. The method of claim 1, wherein the modification reaction solution is an alkali solution.
3. The method of claim 2, wherein the modification reaction solution is an aqueous alkali solution.
4. The method of claim 3, wherein the molar ratio of the titanium silicalite molecular sieve to the base to the water is 1: 0.02-0.6: 3 to 20.
5. The method of any of claims 2 to 4, wherein the base is an organic base or an inorganic base, or a mixture thereof.
6. The method for modifying a titanium silicalite molecular sieve according to claim 5, wherein the organic base is one or more selected from urea, quaternary ammonium base compounds, alcohol amine compounds or fatty amine compounds; the inorganic alkali is one or more selected from ammonia water, potassium hydroxide, sodium hydroxide or ammonium nitrate.
7. The method for modifying a titanium silicalite molecular sieve according to claim 1, wherein the crystallization temperature is 90 to 200 ℃ and the reaction time is 6 to 48 hours.
8. The method for modifying a titanium silicalite molecular sieve according to claim 1, wherein the water washing is performed to neutrality by deionized water; the drying is carried out at the temperature of 100-150 ℃ for 2-5 hours; the roasting temperature is 500-600 ℃, and the roasting time is 3-10 hours.
9. The method for modifying titanium silicalite molecular sieves according to claim 1, wherein the amount of the titanium silicalite molecular sieves added is 10-50% of the volume of the crystallization kettle.
10. A modified titanium silicalite molecular sieve produced by the modification process of any one of claims 1 to 9.
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| CN112591762A (en) * | 2020-12-14 | 2021-04-02 | 湖南化工职业技术学院（湖南工业高级技工学校） | Ultrasonic-assisted titanium-silicon molecular sieve modification method |
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| CN101837988A (en) * | 2010-03-12 | 2010-09-22 | 重庆理工大学 | Method for preparing iron modified SBA-15 mesoporous molecular sieve |
| CN103551192A (en) * | 2013-11-22 | 2014-02-05 | 东北石油大学 | Preparation method of rare-earth modified MCM-48 loaded double-function catalyst |
| CN104028300A (en) * | 2014-06-06 | 2014-09-10 | 郑州大学 | Modified TS-1 molecular sieve as well as preparation method and application thereof |
| CN107999125A (en) * | 2017-12-14 | 2018-05-08 | 中触媒新材料股份有限公司 | A kind of core shell structure Ti-MWW system with molecular sieve for preparing containing micropore-mesopore is standby and applies |
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| CN101837988A (en) * | 2010-03-12 | 2010-09-22 | 重庆理工大学 | Method for preparing iron modified SBA-15 mesoporous molecular sieve |
| CN103551192A (en) * | 2013-11-22 | 2014-02-05 | 东北石油大学 | Preparation method of rare-earth modified MCM-48 loaded double-function catalyst |
| CN104028300A (en) * | 2014-06-06 | 2014-09-10 | 郑州大学 | Modified TS-1 molecular sieve as well as preparation method and application thereof |
| CN107999125A (en) * | 2017-12-14 | 2018-05-08 | 中触媒新材料股份有限公司 | A kind of core shell structure Ti-MWW system with molecular sieve for preparing containing micropore-mesopore is standby and applies |
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| CN112591762A (en) * | 2020-12-14 | 2021-04-02 | 湖南化工职业技术学院（湖南工业高级技工学校） | Ultrasonic-assisted titanium-silicon molecular sieve modification method |
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