Method for simply preparing high skeleton titanium SPP structure TS-1 molecular sieve and application

Abstract

The application discloses a method for simply preparing TS-1 molecular sieve with high skeleton titanium SPP structure and application, and the TS-1 molecular sieve is obtained by adding a template agent and a crystallization regulator and changing a crystallization mode in a synthetic glue solution, has an interlaced support SPP structure, high skeleton titanium content and a mesoporous structure. The crystallization regulator promotes titanium into the molecular sieve skeleton through hydrogen bond action, a first-stage crystallization process is introduced after the glue preparation is completed, sufficient growth time is given to the SPP structure, and the SPP structure can still retain a "card house" structure in a second-stage crystallization process with high temperature. Compared with a conventional hydrothermal synthesis TS-1 molecular sieve method, the TS-1 prepared by using the method has high skeleton titanium content, the SPP structure is interlaced and supported, rich mesoporous structures are introduced, and catalytic activity and selectivity are obviously improved, mainly in macromolecular olefin epoxidation, aromatic hydrocarbons hydroxylation, benzene hydroxylation, ketone amine oximation and alkane oxidation and the like.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis technology, and relates to a simple method for preparing TS-1 molecular sieves with high framework titanium SPP structure and its application. Background Technology

[0002] Titanium silicate molecular sieve (TS-1) exhibits excellent selectivity and high catalytic activity in a mild reaction system using H2O2 as the oxidant for olefin epoxidation, aromatic hydrocarbon hydroxylation, phenol hydroxylation, ketone ammoniumization, and alkane oxidation. Furthermore, its only byproduct is water, making it environmentally friendly.

[0003] After nearly forty years of research, titanium silicate molecular sieves have played a crucial role in selective oxidation reactions. However, with the increasing scope of applications, the limitations of this catalytic material are becoming increasingly apparent. For example, limited by the small pore size (<1 nm) of the molecular sieve material, titanium silicate molecular sieves exhibit very low catalytic activity in the selective oxidation of long-chain or cyclic macromolecular substrates, which are often important steps in the production of high-value-added fine chemicals or pharmaceuticals. Increasing mesopores and macropores in natural microporous molecular sieves is one way to eliminate or mitigate these problems.

[0004] Over the past decade, significant efforts have been devoted to preparing molecular sieves with enhanced microporous accessibility. Many new approaches to preparing hierarchical porous molecular sieves have been discovered, such as (1) post-synthesis modification via desilication, dealumination, or steam treatment; (2) hydrothermal crystallization synthesis using specific organosilane surfactants as mesoporous templates; and (3) synthesis of small-crystal nanoscale molecular sieve crystals. Post-treatment methods, such as alkali and acid treatments, are common, but they inevitably lead to problems such as reduced zeolite crystallinity, loss of catalyst materials, numerous defects, uneven chemical composition, and difficulty in controlling the mesoporous structure. Furthermore, small-crystal molecular sieve crystals present difficulties in separation during the reaction process.

[0005] Therefore, the preparation of a hierarchical porous TS-1 molecular sieve with a large specific surface area and high framework titanium content remains a research focus. Summary of the Invention

[0006] The purpose of this invention is to provide a simple method for preparing TS-1 molecular sieves with a high framework titanium SPP structure and its application. The TS-1 synthesized by this method has an interlaced supported SPP structure. The synthesis process is simple, with a high framework titanium content and abundant mesoporous structure. The synthesized sample exhibits high activity and stability in catalytic oxidation reactions.

[0007] This invention provides a simple method for preparing a high-framework titanium SPP structure TS-1 molecular sieve, comprising adding a crystallization regulator to a mixed solution of a silicon source hydrolysis solution and a titanium source hydrolysis solution to obtain a synthetic solution, and carrying out a crystallization reaction, including: a first-stage crystallization: crystallization at 40-100℃ for 3-48 hours, a second-stage crystallization: crystallization at 110-170℃ for 24-72 hours, and separating, drying, and calcining the crystallization product to obtain a high-framework titanium SPP structure TS-1 molecular sieve; The crystallization regulator is selected from one or more of biuret, ethylenediamine, urea, ammonium acetate, and ammonium carbonate; the molar ratio of the crystallization regulator to the silicon source in the synthetic adhesive is 1:(3.3-13.3); the silicon source is SiO2; the preparation of the hydrolysis solution of the silicon source is as follows: the silicon source, template agent, and H2O are mixed evenly in a molar ratio of 1:(0.2-0.9):(10-30), and hydrolyzed at room temperature for 1-3 hours; the template agent includes one or more of tetrabutylphosphine hydroxide and tetrabutylammonium hydroxide.

[0008] Adding a crystallization regulator to the TS-1 synthetic adhesive solution promotes the entry of titanium into the molecular sieve framework through hydrogen bonding. After the adhesive preparation is completed, the first crystallization process is introduced to give the SPP structure sufficient growth time so that it can still retain the "House of Cards" structure in the second crystallization process at a high temperature.

[0009] The template agent also includes one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide.

[0010] The crystallization temperature of the second stage is 150-170℃.

[0011] The molar ratio of silicon source: titanium source: H2O in the synthetic adhesive solution is 1:(0.005-0.035):(10-30), and the silicon source and titanium source are calculated as SiO2 and TiO2, respectively.

[0012] The preparation of the hydrolysis solution of the titanium source involves mixing the titanium source, IPA (isopropanol), or ethanol at a molar ratio of 1:(5-15) until homogeneous, and then dissolving the mixture at room temperature. The dissolution time is 0-1 h.

[0013] The silicon source is selected from tetraethyl orthosilicate, and the titanium source is selected from tetrabutyl titanate.

[0014] The roasting temperature is 500-580℃, and the roasting time is 6-8h.

[0015] The present invention further provides the application of the high-framework titanium SPP structure TS-1 molecular sieve obtained by the above preparation method in olefin epoxidation using H2O2 as an oxidant.

[0016] Beneficial effects of the invention

[0017] 1. The synthesis process of this invention is simple, requires no alcohol removal during the synthesis process, has a short crystallization time, and improves the synthesis efficiency;

[0018] 2. The TS-1 sample synthesized in this invention has an interleaved supported SPP structure, a high titanium content in the framework, and abundant mesoporous structure, exhibiting high catalytic oxidation activity and selectivity. Attached Figure Description

[0019] Figure 1 UV-vis spectra of TS-1 molecular sieves prepared in Comparative Examples 1-3 and Examples 1-2.

[0020] Figure 2 Scanning electron microscopy of the TS-1 molecular sieves prepared in Comparative Examples 1-3 and Examples 1-3. Detailed Implementation

[0021] The specific embodiments of the present invention are described in detail below.

[0022] Comparative Example 1

[0023] 12.50 g of TEOS was added to a three-necked flask, and 12.44 g of TBPOH aqueous solution (25 wt.%) and 3.34 g of deionized water were added at 25 °C with magnetic stirring. Hydrolysis was carried out for 2 h to obtain a silicon source hydrolysis solution. 0.51 g of TBOT (tetrabutyl titanate) was dispersed in 1.19 g of IPA and hydrolyzed at room temperature for 0.5 h to obtain a titanium hydrolysis solution. The titanium hydrolysis solution was mixed with the silicon hydrolysis solution and stirred for 12 h. The synthesized gel solution was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner and crystallized at 170 °C for 72 h. The reactor was cooled, and the crystallized product was washed, dried, and calcined. The resulting TS-1 sample was labeled B1.

[0024] Comparative Example 2

[0025] 12.50 g of TEOS was added to a three-necked flask, and 12.44 g of TBPOH aqueous solution (25 wt.%) and 3.34 g of deionized water were added at 25 °C with magnetic stirring. Hydrolysis was carried out for 2 h to obtain a silicon source hydrolysis solution. 0.51 g of TBOT was dispersed in 1.19 g of IPA and hydrolyzed at room temperature for 0.5 h to obtain a titanium hydrolysis solution. The titanium hydrolysis solution was mixed with the silicon hydrolysis solution and stirred for 1 h. The synthesized solution was then transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner and crystallized (aged) at 80 °C under autogenous pressure for 72 h, followed by crystallization at 170 °C for 24 h. The reactor was cooled, and the crystallized product was washed, dried, and calcined. The resulting TS-1 sample was designated as B1.

[0026] Comparative Example 3

[0027] 12.50 g of TEOS was added to a three-necked flask, and 12.44 g of TBPOH aqueous solution (25 wt.%) and 3.34 g of deionized water were added at 25 °C with magnetic stirring. Hydrolysis was carried out for 2 h to obtain a silicon source hydrolysis solution. 0.51 g of TBOT was dispersed in 1.19 g of IPA and hydrolyzed at room temperature for 0.5 h to obtain a titanium hydrolysis solution. The titanium hydrolysis solution was mixed with the silicon hydrolysis solution, and 0.18 g of urea was added. After stirring for 12 h, the synthetic solution was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner and crystallized at 130 °C under autogenous pressure for 72 h. The reactor was cooled, and the crystallized product was washed, dried, and calcined. The resulting TS-1 sample was numbered B3.

[0028] Example 1

[0029] 12.50 g of TEOS was added to a three-necked flask, and 12.44 g of TBPOH aqueous solution (25 wt.%) and 3.34 g of deionized water were added at 25 °C with magnetic stirring. Hydrolysis was carried out for 2 h to obtain a silicon source hydrolysis solution. 0.51 g of TBOT was dispersed in 1.19 g of IPA and hydrolyzed at room temperature for 0.5 h to obtain a titanium hydrolysis solution. The titanium hydrolysis solution was mixed with the silicon hydrolysis solution, and then 0.18 g of urea was added. After stirring for 1 h, the synthetic solution was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner and crystallized at 80 °C under autogenous pressure for 72 h, followed by crystallization at 170 °C for 24 h. The reactor was cooled, and the crystallized product was washed, dried, and calcined. The resulting TS-1 sample was numbered A1.

[0030] Example 2

[0031] 12.50 g of TEOS was added to a three-necked flask, and 12.44 g of TBPOH aqueous solution (25 wt.%) and 3.34 g of deionized water were added at 25 °C with magnetic stirring. Hydrolysis was carried out for 2 h to obtain a silicon source hydrolysis solution. 0.51 g of TBOT was dispersed in 1.19 g of IPA and hydrolyzed at room temperature for 0.5 h to obtain a titanium hydrolysis solution. The titanium hydrolysis solution was mixed with the silicon hydrolysis solution, and then 0.36 g of urea was added. After stirring for 1 h, the synthetic solution was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner and crystallized at 80 °C under autogenous pressure for 72 h, followed by crystallization at 170 °C for 24 h. The reactor was cooled, and the crystallized product was washed, dried, and calcined. The resulting TS-1 sample was designated A2.

[0032] Example 3

[0033] 12.50 g of TEOS was added to a three-necked flask, and 12.44 g of TBPOH aqueous solution (25 wt.%) and 3.34 g of deionized water were added at 25 °C with magnetic stirring. Hydrolysis was carried out for 2 h to obtain a silicon source hydrolysis solution. 0.51 g of TBOT was dispersed in 1.19 g of IPA and hydrolyzed at room temperature for 0.5 h to obtain a titanium hydrolysis solution. The titanium hydrolysis solution was mixed with the silicon hydrolysis solution, and 0.18 g of urea was added. After stirring for 1 h, the synthetic solution was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner and crystallized at 80 °C under autogenous pressure for 48 h. Then, it was crystallized at 150 °C for 48 h. The reactor was cooled, and the crystallized product was washed, dried, and calcined. The resulting TS-1 sample was numbered A3.

[0034] Example 4

[0035] The samples prepared in the above embodiments and comparative examples were analyzed by UV-Vis spectrophotometry. In the UV-Vis spectra, the characteristic peak at 210 nm was the absorption peak of framework Ti, and the absorption peak at 330 nm was the absorption peak of non-framework anatase. Figure 1 It can be seen that TS-1, obtained by adding a crystallization regulator to the synthetic adhesive solution, exhibits a strong absorption peak at 210 nm. This indicates that the addition of a crystallization regulator to the synthetic adhesive solution can significantly increase the titanium content of the framework.

[0036] Example 5

[0037] The samples prepared in the above examples and comparative examples were characterized by nitrogen physical adsorption and X-ray fluorescence spectroscopy. Table 1 shows that the mesoporous pore volume increased significantly after the introduction of the 80℃ high-temperature aging process, and the silicon-to-titanium ratio decreased significantly after the addition of a crystallization regulator and an increase in the crystallization temperature. This indicates that the aging process facilitates the formation of the SPP structure, while increasing the crystallization temperature and adding a crystallization regulator helps increase the titanium content.

[0038] Table 1 Characterization results of different TS-1 molecular sieve catalysts

[0039]

[0040] Example 6

[0041] The samples prepared in the above embodiments and comparative examples were characterized by scanning electron microscopy. Figure 2 It can be seen that the sample has an interlaced SPP structure, which gives the sample a large specific surface area and mesoporous volume.

[0042] Example 7

[0043] Using hexene, hydrogen peroxide, acetonitrile, and methanol as reaction substrates, the activity and selectivity of the catalysts prepared in the above examples in the epoxidation of hexene were investigated. The reaction conditions were as follows: 5.89 g of hexene, 22 ml of methanol, and 7.94 g of 30 wt.% H₂O₂ were added to a 50 ml round-bottom flask, and the reaction was carried out at 60 °C with magnetic stirring for 2 h. The composition of the product was analyzed by gas chromatography. The catalytic effect is shown in the table below. As can be seen from Table 2, the high-framework titanium SPP structure hierarchical porous TS-1 (A1 and A2) provided by this invention exhibits high catalytic performance in the epoxidation of hexene. This is because the high mesoporous surface area is retained after the introduction of an aging process and a crystallization regulator, increasing the framework titanium content, resulting in more active sites and improved accessibility of the active sites.

[0044] Table 2. Test results of different TS-1 molecular sieve catalysts in the epoxidation of n-hexene.

[0045] B1 16.55 77.89 A1 33.75 80.93 A2 49.78 82.69

Claims

1. A simple method for preparing TS-1 molecular sieves with a high framework titanium SPP structure, characterized in that: The process involves adding a crystallization regulator to a mixed solution of hydrolyzed solutions from a silicon source and a titanium source to obtain a synthetic solution, followed by a crystallization reaction. The reaction includes: a first-stage crystallization at 40-100℃ for 3-48 hours, and a second-stage crystallization at 110-170℃ for 24-72 hours. The crystallized product is then separated, dried, and calcined to obtain a high-framework titanium SPP structure TS-1 molecular sieve. The crystallization regulator is selected from one or more of biuret, ethylenediamine, urea, ammonium acetate, and ammonium carbonate. The crystallization regulator in the synthetic solution reacts with the silicon source... The molar ratio is 1:(3.3-13.3), and the silicon source is calculated as SiO2; the preparation of the hydrolysis solution of the silicon source is as follows: the silicon source, template agent and H2O are mixed evenly in a molar ratio of 1:(0.2-0.9):(10-30), and hydrolyzed at room temperature for 1-3 hours; the template agent includes one or more of tetrabutylphosphine hydroxide and tetrabutylammonium hydroxide; the molar ratio of silicon source:titanium source:H2O in the synthetic adhesive solution is 1:(0.005-0.035):(10-30), and the silicon source and titanium source are calculated as SiO2 and TiO2, respectively.

2. The method for simple preparation of high-framework titanium SPP structure TS-1 molecular sieve as described in claim 1, characterized in that: The template agent also includes one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide.

3. The method for simply preparing high-framework titanium SPP structure TS-1 molecular sieve as described in claim 1, characterized in that: The crystallization temperature of the second stage is 150-170℃.

4. The method for simply preparing high-framework titanium SPP structure TS-1 molecular sieve as described in claim 1, characterized in that: The preparation of the hydrolysis solution of the titanium source involves mixing the titanium source, isopropanol, or ethanol at a molar ratio of 1:(5-15) until homogeneous, and then dissolving the mixture at room temperature.

5. The method for simply preparing high-framework titanium SPP structure TS-1 molecular sieve as described in claim 1, characterized in that: The silicon source is selected from tetraethyl orthosilicate, and the titanium source is selected from tetrabutyl titanate.

6. The method for simply preparing high-framework titanium SPP structure TS-1 molecular sieve as described in claim 1, characterized in that: The roasting temperature is 500-580℃, and the roasting time is 6-8h.

7. The application of the high-framework titanium SPP structure TS-1 molecular sieve obtained by the method of claim 1 in olefin epoxidation using H2O2 as an oxidant.

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