A method for synthesizing nanoscale sheet-like ts-1 titanium silicalite molecular sieve

Abstract

The application discloses a synthesis method of nanoscale sheet TS-1 titanium silicate molecular sieve. Tetraethyl orthosilicate is used as a silicon source, tetrabutyl titanate is used as a titanium source, tetrapropyl ammonium hydroxide is used as a template agent, and an ammonium salt is added as an assistant for limiting particle growth along a b axis. After hydrothermal reaction, the obtained product is washed, baked and calcined, so that the nanoscale sheet TS-1 titanium silicate molecular sieve with a b axis size of 20-50 nm and a axis and c axis size of 80-150 nm is synthesized. The method has the advantages of simple operation, repeatability, small template agent consumption, low cost, easy industrial production and application, etc. The sheet nanoscale TS-1 titanium silicate molecular sieve synthesized by the method has small particle size, thin b axis thickness, large specific surface area, more exposed Ti active sites, shortened transmission path of reactants and products, reduced diffusion resistance, and higher catalytic activity for oxidation reactions of toluene and cyclohexene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and particularly relates to a synthesis method of nanoscale sheet-shaped TS-1 titanium-silicon molecular sieve. BACKGROUND

[0002] Titanium-silicon molecular sieve has a microporous structure and is a green and environmentally friendly catalyst. In 1981, Taramasso et al. of Enichem Company in Italy first introduced a transition metal element Ti into a pure silicon zeolite, successfully synthesizing TS-1 titanium-silicon molecular sieve. It has the same MFI topological structure as ZSM-5 molecular sieve and belongs to the orthorhombic system. Compared with other molecular sieves, it has good hydrothermal stability and can be applied to various catalytic oxidation reactions, especially a series of selective oxidation reactions of organic matter with H2O2 as an oxidant, such as propylene epoxidation and phenol hydroxylation, and exhibits excellent catalytic oxidation performance.

[0003] The classical synthesis method of TS-1 titanium-silicon molecular sieve is to use tetraethyl orthosilicate as a silicon source, tetrapropylammonium hydroxide as a template agent, and tetrabutyl titanate as a titanium source. First, tetraethyl orthosilicate is mixed with tetrapropylammonium hydroxide to obtain a silicon ester hydrolysate; tetrabutyl titanate is dissolved in isopropyl alcohol to prevent it from rapidly hydrolyzing to form anatase TiO2; then it is added dropwise to the silicon ester hydrolysate; after alcohol removal by heating, hydrothermal crystallization, filtration and washing, drying and calcination, the target product TS-1 titanium-silicon molecular sieve is finally obtained.

[0004] TS-1 titanium-silicon molecular sieve has two-dimensional ten-membered ring channels, one of which is a straight channel parallel to the b-axis direction, with a pore size of The other is a zigzag type ten-membered ring channel with a pore size of The molecular diffusion path along the b-axis is the shortest and the transmission is the fastest, so synthesizing TS-1 titanium-silicon molecular sieve with b-axis directional growth is an effective strategy to improve its catalytic activity. Most of the currently reported nanoscale TS-1 titanium-silicon molecular sieves are ellipsoidal or cubic in shape, which has a large steric hindrance and hinders the diffusion of molecules. Patent CN 112978757 A prepared short-b-axis micrometer-scale flake TS-1 titanium-silicon molecular sieve by adding sulfate, and the molecular sieve has a size of 1-10 μm x 0.05-0.8 μm x 0.1-2 μm. Literature [Chem. Commun., 2011, 47, 1048-1050, NanoResearch 2023, 16(5):6278-6289] prepared short-b-axis nanosheet TS-1 titanium-silicon molecular sieve by adding urea, but the b-axis is still thick, with a size of about 100 nm, and the a-axis and c-axis sizes are still large, about 200-300 nm. SUMMARY

[0005] The present application aims to provide a synthesis method of nano-scale flaky TS-1 titanium-silicon molecular sieve with a b-axis size of 20-40 nm and a-axis and c-axis size of 80-150 nm, which has smaller particle size and thinner thickness along the straight channel b-axis, shortens the molecular transmission path, improves the diffusion performance, and shows high activity in catalyzing reactions such as direct hydroxylation of toluene to produce cresol and catalyzing cyclohexene to produce cyclohexane oxide.

[0006] To achieve the above object, the technical solution adopted by the present application comprises the following steps:

[0007] Step 1: uniformly mix tetraethyl orthosilicate, tetrapropylammonium hydroxide and deionized water according to a molar ratio of 1:0.10-0.35:15-60 to obtain a clear solution A;

[0008] Step 2: uniformly mix tetrabutyl titanate and isopropanol according to a molar ratio of 1:30-80 to obtain a clear solution B;

[0009] Step 3: slowly add the solution B obtained in Step 2 into the solution A of Step 1, and remove isopropanol by heating to 82-90°C under stirring, and then supplement deionized water to keep the solution volume unchanged;

[0010] Step 4: add an ammonium salt into the solution obtained in Step 3 to obtain a crystallization slurry, and the molar ratio of components in the crystallization slurry is SiO2:TiO2:TPAOH:A:H2O=1:0.01-0.04:0.10-0.35:0.10-0.80:15-60, wherein A represents the ammonium salt, and the ammonium salt is any one of ammonium chloride, ammonium carbonate, ammonium sulfate and ammonium nitrate; TPAOH represents tetrapropylammonium hydroxide;

[0011] Step 5: place the crystallization slurry obtained in Step 4 in a reaction kettle, and hydrothermally react at 160-180°C for 36-72 hours, then wash and dry the obtained product, and calcine it in a muffle furnace at 550°C for 4-10 hours to obtain nano-scale flaky TS-1 titanium-silicon molecular sieve; the a-axis and c-axis size of the nano-scale flaky TS-1 titanium-silicon molecular sieve is 80-150 nm, and the b-axis size is 20-50 nm.

[0012] In Step 1, preferably, tetraethyl orthosilicate, tetrapropylammonium hydroxide and deionized water are mixed according to a molar ratio of 1:0.10-0.35:15-60, and stirred for 30-120 minutes to obtain a clear solution A.

[0013] In Step 2, preferably, tetrabutyl titanate and isopropanol are mixed according to a molar ratio of 1:30-80, and stirred for 30-60 minutes to obtain a clear solution B.

[0014] In the above step 3, the solution B obtained in step 2 is preferably slowly added into the solution A of step 1, and heated to 82-90°C under stirring, and kept constant temperature for 3-6 hours to remove the isopropyl alcohol.

[0015] In the above step 4, the ammonium salt is preferably added into the solution obtained in step 3, and stirred for 30-120 minutes to obtain the crystallization slurry.

[0016] In the above step 4, the molar ratio of the components in the crystallization slurry is preferably SiO2:TiO2:TPAOH:A:H2O = 1:0.02-0.03:0.20-0.30:0.20-0.40:35-50.

[0017] In the above step 5, the crystallization slurry obtained in step 4 is preferably placed in a reaction kettle, and hydrothermally reacted at 170-180°C for 48-60 hours.

[0018] The beneficial effects of the present application are as follows:

[0019] The present application uses tetraethyl orthosilicate as the silicon source, tetrabutyl titanate as the titanium source, and tetrapropyl ammonium hydroxide as the template agent, and adds ammonium salt as an auxiliary agent for limiting the growth of particles along the b axis. After hydrothermal reaction, the obtained product is washed, baked and calcined to synthesize the small-size nanoscale TS-1 titanium silicate molecular sieve with the b axis size of 20-50 nm and the a axis and c axis size of 80-150 nm. The method is simple in operation, reproducible, low in template agent consumption and cost, and easy for industrial production and application. The small-size nanoscale TS-1 titanium silicate molecular sieve synthesized by the method has high four-coordination framework titanium content, almost no anatase, small particle size and thin b axis thickness, uniform particle size, good dispersibility, good crystallinity, large specific surface area, more exposed Ti active sites, shortened transport path of reactants and products, reduced diffusion resistance, good diffusion efficiency, and is suitable for catalyzing the oxidation reaction of toluene and cyclohexene, etc., showing higher catalytic activity, high selectivity and conversion rate. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the SEM image of sample S1 prepared in Example 1.

[0021] Figure 2 is the XRD image of sample S1 prepared in Example 1.

[0022] Figure 3 is the SEM image of sample S1 prepared in Example 2.

[0023] Figure 4is the XRD pattern of sample S1 prepared in Example 2.

[0024] Figure 5 is the SEM pattern of sample S1 prepared in Example 3.

[0025] Figure 6 is the XRD pattern of sample S1 prepared in Example 3. DETAILED DESCRIPTION

[0026] The application will be further described in conjunction with the accompanying drawings and examples, but the scope of protection of the application is not limited to these examples.

[0027] Example 1

[0028] Step 1: 75.20 g (4.1742 mol) of deionized water was added into a beaker at room temperature, and then 6.90 g (0.0243 mol) of a 25 wt% aqueous solution of tetrapropylammonium hydroxide was added, and stirred for 15 minutes. Then, 22.92 g (0.1100 mol) of tetraethyl orthosilicate was slowly added dropwise into the solution under stirring, and stirred for 1 hour to form a clear solution A.

[0029] Step 2: 1.01 g (0.0030 mol) of tetrabutyl titanate was added into 10.5 g (0.1747 mol) of isopropanol at room temperature, and stirred for 30 minutes to obtain a clear solution B.

[0030] Step 3: Solution B was slowly added into solution A under strong stirring, and after the dropwise addition was completed, the temperature was increased to 85°C, and constant temperature stirring was performed for 4 hours to remove isopropanol, and deionized water was added to keep the solution volume unchanged.

[0031] Step 4: 3.45 g (0.0261 mol) of ammonium sulfate was added into the solution obtained in Step 3, and stirred for 2 hours to obtain a crystallization slurry, and the molar ratio of the components in the crystallization slurry was SiO2:TiO2:TPAOH:A:H2O = 1:0.0270:0.2213:0.2373:40.5520, and A represented ammonium sulfate.

[0032] Step 5: The crystallization slurry obtained in Step 4 was transferred into a 100 mL reaction kettle, and hydrothermal reaction was performed at 170°C for 72 hours, and the white suspension was filtered, washed with water for 3 times, and dried at 100°C for 12 hours, and then ground, and the obtained sample was placed in a muffle furnace, and heated to 550°C at a heating rate of 3°C / min, and constant temperature calcination was performed for 6 hours to remove tetrapropylammonium hydroxide, and nanoscale flaky TS-1 titanium silicalite molecular sieve (denoted as S1) was obtained. Figure 1 It can be seen that the b-axis size of the obtained molecular sieve particles was 20-50 nm, and the a-axis and c-axis sizes were about 80-150 nm.Figure 2 It can be seen that the sample has good crystallinity.

[0033] Example 2

[0034] Step 1: 30.41 g (1.6875 mol) of deionized water was added into a beaker at room temperature, and then 29.6 g (0.2611 mol) of a 25 wt% tetrapropylammonium hydroxide aqueous solution was added, stirred for 15 minutes, and then 20.64 g (0.0991 mol) of tetraethyl orthosilicate was slowly added dropwise into the solution under stirring, and a clear solution A was formed after stirring for 1 hour.

[0035] Step 2: 1.12 g (0.0033 mol) of tetrabutyl titanate was added into 8.00 g (0.1331 mol) of isopropanol at room temperature, stirred for 30 minutes, and a clear solution B was obtained.

[0036] Step 3: Solution B was slowly added into solution A under strong stirring, and after the dropwise addition was completed, the temperature was increased to 82°C, and constant temperature stirring was performed for 4 hours to remove isopropanol, and deionized water was added to keep the solution volume unchanged.

[0037] Step 4: 1.25 g (0.0233 mol) of ammonium chloride was added into the solution obtained in Step 3, and stirred for 2 hours to obtain a crystallization slurry, and the molar ratio of the components in the crystallization slurry was SiO2:TiO2:TPAOH:A:H2O = 1:0.0332:0.2635:0.2358:26.7024, wherein A represents ammonium chloride.

[0038] Step 5: The crystallization slurry obtained in Step 4 was transferred into a 100 mL reaction kettle, and hydrothermal reaction was performed at 180°C for 36 hours, and the white suspension was filtered, washed with water for 3 times, and dried at 100°C for 12 hours, and then ground, and the obtained sample was placed in a muffle furnace, and heated to 550°C at a heating rate of 3°C / min, and constant temperature calcination was performed for 6 hours to remove tetrapropylammonium hydroxide, and nanoscale flaky TS-1 titanium silicalite molecular sieve (denoted as S2) was obtained. Figure 3 It can be seen that the b-axis size of the obtained molecular sieve particles is 20-50 nm, and the a-axis and c-axis sizes are about 80-150 nm. Figure 4 It can be seen that the sample has good crystallinity.

[0039] Example 3

[0040] Step 1: 39.15 g (2.1732 mol) of deionized water was added into a beaker at room temperature, and then 25.50 g (0.0225 mol) of a 25 wt% aqueous solution of tetrapropylammonium hydroxide was added, and stirred for 15 minutes. Then, 22.92 g (0.1100 mol) of tetraethyl orthosilicate was slowly added dropwise into the solution under stirring, and stirred for 1 hour to form a clear solution A.

[0041] Step 2: 0.89 g (0.0026 mol) of tetrabutyl titanate was added into 12.40 g (0.2063 mol) of isopropanol at room temperature, and stirred for 30 minutes to obtain a clear solution B.

[0042] Step 3: Solution B was slowly added into solution A under strong stirring, and after the dropwise addition was completed, the temperature was increased to 85°C, and constant temperature stirring was performed for 5 hours to remove isopropanol, and deionized water was added to keep the solution volume unchanged.

[0043] Step 4: 2.86 g (0.0461 mol) of ammonium carbonate was added into the solution obtained in Step 3, and stirred for 2 hours to obtain a crystallization slurry, and the molar ratio of the components in the crystallization slurry was SiO2:TiO2:TPAOH:A:H2O = 1:0.0238:0.2044:0.4191:22.1649.

[0044] Step 5: The crystallization slurry obtained in Step 4 was transferred into a 100 mL reaction kettle, and hydrothermal reaction was performed at 160°C for 48 hours. After the reaction kettle was naturally cooled to room temperature, the white suspension was filtered, washed with water for 3 times, and dried at 100°C for 12 hours. Then, the sample was ground, and heated to 550°C at a heating rate of 3°C / min in a muffle furnace, and calcined at constant temperature for 6 hours to remove residual tetrapropylammonium hydroxide, to obtain nanoscale flaky TS-1 titanium silicalite (denoted as S3). Figure 5 It can be seen that the b-axis size of the obtained molecular sieve particles was 20-50 nm, and the a-axis and c-axis sizes were about 80-150 nm. Figure 6 It can be seen that the sample had good crystallinity.

[0045] The nanoscale flaky TS-1 titanium silicalite obtained in Examples 1-3 above was used for catalytic oxidation reaction, and the specific method was as follows:

[0046] 1. Catalytic oxidation reaction of toluene

[0047] In a 500 mL round bottom flask, 9.2 mmol of toluene, 156.8 mmol of hydrogen peroxide (30 wt%), 2 g of nanoscale flaky TS-1 titanium silicalite molecular sieve and 120 mL of deionized water were added, and under the conditions of magnetic stirring, heating at 60°C, and reflux condensation, a sample was taken after 2 hours of reaction, and the selectivity and yield of the target product cresol were detected by gas chromatography (GC, Bruker 450-GC). The test results are shown in Table 1.

[0048] Table 1 Reaction performance of TS-1 titanium silicalite molecular sieve for catalyzing direct hydroxylation of toluene to produce cresol

[0049] Sample name Conversion / % Selectivity / % S1 75.8％ 99.2％ S2 72.5％ 98.5％ S3 73.4％ 99.0％

[0050] 2. Catalyzing oxidation of cyclohexene

[0051] In a 500 mL three-necked flask, 1 g of nanoscale flaky TS-1 titanium silicalite molecular sieve was added, and then 10 mL of cyclohexene, 4.4 mL of 30% mass concentration hydrogen peroxide aqueous solution and 100 mL of acetonitrile were added. Under the conditions of magnetic stirring, heating at 60°C and reflux condensation, a sample was taken after 5 hours of reaction, and the yield of the target product cyclohexene oxide was detected by gas chromatography (GC, Bruker 450-GC). The test data are shown in Table 2.

[0052] Table 2 Reaction performance of TS-1 titanium silicalite molecular sieve for catalyzing cyclohexene to produce cyclohexene oxide

[0053] Sample name Conversion / % Selectivity / % S1 35.6％ 99.9％ S2 32.7％ 99.1％ S3 31.9％ 98.5％

[0054] As can be seen from the results in Tables 1 and 2, the nanoscale flaky TS-1 titanium silicalite molecular sieve synthesized by the method of the present application has the highest catalytic oxidation activity.

Claims

1. A method for synthesizing nanosheet TS-1 titanium silical molecular sieve, characterized in that The method comprises the following steps: Step 1: uniformly mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and deionized water according to a molar ratio of 1:0.10-0.35:15-60 to obtain a clear solution A; Step 2: uniformly mixing tetrabutyl titanate and isopropyl alcohol according to a molar ratio of 1:30-80 to obtain a clear solution B; Step 3: slowly adding the solution B obtained in Step 2 into the solution A in Step 1, and removing isopropyl alcohol by heating to 82-90°C under stirring, and then supplementing deionized water to keep the solution volume unchanged; Step 4: adding an ammonium salt into the solution obtained in Step 3 to obtain a crystallization slurry, wherein the molar ratio of components in the crystallization slurry is SiO2:TiO2:TPAOH:A:H2O=1:0.01-0.04:0.10-0.35:0.10-0.80:15-60, wherein A represents the ammonium salt, and the ammonium salt is any one of ammonium chloride, ammonium carbonate, ammonium sulfate and ammonium nitrate; and TPAOH represents tetrapropylammonium hydroxide; Step 5: placing the crystallization slurry obtained in Step 4 in a reaction kettle, and hydrothermally reacting at 160-180°C for 36-72 hours, and then washing, drying and calcining at 550°C for 4-10 hours in a muffle furnace to obtain a nanoscale flaky TS-1 titanium silicate molecular sieve. The nanoscale flaky TS-1 titanium silicate molecular sieve has an a-axis and c-axis size of 80-150nm and a b-axis size of 20-50nm.

2. The method of synthesizing nanosheet-like TS-1 titanosilicate zeolite according to claim 1, characterized by: In Step 1, tetraethyl orthosilicate, tetrapropylammonium hydroxide and deionized water are mixed according to a molar ratio of 1:0.10-0.35:15-60, and stirred for 30-120 minutes to obtain a clear solution A.

3. The method of synthesizing nanosheet-shaped TS-1 titanium silical molecular sieve according to claim 1, characterized in that: In Step 2, tetrabutyl titanate and isopropyl alcohol are mixed according to a molar ratio of 1:30-80, and stirred for 30-60 minutes to obtain a clear solution B.

4. The method of synthesizing nanosheet-shaped TS-1 titanium silical zeolite according to claim 1, characterized in that: In Step 3, the solution B obtained in Step 2 is slowly added into the solution A in Step 1, and isopropyl alcohol is removed by heating to 82-90°C under stirring for 3-6 hours.

5. The method of synthesizing nanosheet-shaped TS-1 titanium silical molecular sieve according to claim 1, characterized in that: In Step 4, an ammonium salt is added into the solution obtained in Step 3, and stirred for 30-120 minutes to obtain a crystallization slurry.

6. The method of synthesizing nanosheet-like TS-1 titanium silical molecular sieve according to claim 1 or 5, characterized in that: In Step 4, the molar ratio of components in the crystallization slurry is SiO2:TiO2:TPAOH:A:H2O=1:0.02-0.03:0.20-0.30:0.20-0.40:35-50.

7. The method of synthesizing nanosheet-shaped TS-1 titanium silical zeolite according to claim 1, characterized in that: In Step 5, the crystallization slurry obtained in Step 4 is placed in a reaction kettle, and hydrothermally reacted at 170-180°C for 48-60 hours.

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