High-stability hierarchical pore fer-type titanosilicate molecular sieve, and preparation method and application thereof
By activating the silicon source with fluorosilicic acid and modifying it with tetraethyl orthosilicate, combined with composite template agent and ammonium dihydrogen phosphate treatment, a highly stable hierarchical porous FER-type titanium-silicon molecular sieve was prepared. This solved the problems of low silicon source reactivity and poor framework stability in the preparation of traditional FER-type titanium-silicon molecular sieves, and achieved high-efficiency catalytic performance and industrial application.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIHUA UNIV
- Filing Date
- 2026-03-11
- Publication Date
- 2026-06-05
AI Technical Summary
Traditional FER-type titanium-silicon molecular sieves suffer from problems such as low silicon source reactivity, poor framework structure stability, uneven titanium species dispersion, simple pore structure, and insufficient hydrothermal stability during preparation, resulting in low catalytic efficiency and limiting their industrial-scale application.
A multi-level porous structure was constructed by using fluorosilicic acid activation and tetraethyl orthosilicate-modified silicon source, combined with tetraethylammonium chloride and polyethylene glycol composite template agent. A composite titanium source and silane coupling agent were used to promote uniform dispersion of titanium species, and the framework stability was enhanced by ammonium dihydrogen phosphate treatment.
It significantly improves the crystallinity and hydrothermal stability of molecular sieves, enhances catalytic efficiency, conversion rate and selectivity in the cyclohexanone ammonium oxime reaction, and the preparation process is mild and easy to industrialize, which is in line with the concept of green chemical development.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of molecular sieve material preparation technology, and in particular to a highly stable hierarchical porous FER-type titanium-silicon molecular sieve, its preparation method, and its application. Background Technology
[0002] Titanium silicate molecular sieves are a type of heteroatom molecular sieve formed by introducing titanium elements into the molecular sieve framework. They combine the shape-selective catalytic properties of molecular sieves with the oxidative catalytic activity of titanium species. They have broad application prospects in catalytic reactions such as olefin epoxidation, ketone ammoniation, and aromatic hydroxylation. Especially in the field of biomass catalytic conversion, they can efficiently catalyze reactions such as oxidation and isomerization of biomass derivatives, thus contributing to the development of the green chemical industry.
[0003] FER-type molecular sieves are molecular sieves with a two-dimensional ten-membered ring pore structure. Their pore size is moderate, exhibiting excellent shape selectivity. Introducing titanium into the FER-type molecular sieve framework can prepare FER-type titanium-silicon molecular sieves that possess both shape selectivity and oxidation activity. However, the traditional preparation process of FER-type titanium-silicon molecular sieves suffers from problems such as low silicon source reactivity, poor framework structural stability, uneven titanium species dispersion, and a single pore structure (mostly micropores). This leads to low catalytic efficiency, poor hydrothermal stability, and a tendency for framework collapse after high-temperature steam treatment, resulting in a significant decrease in crystallinity and a shortened service life, thus limiting their widespread industrial application.
[0004] To address the aforementioned issues, existing technologies have attempted to improve the preparation process by modifying silicon sources and optimizing template agents, but many shortcomings remain: for example, the modification effect of silicon sources is not good, resulting in limited improvement in the crystallinity and framework stability of molecular sieves; single template agents are difficult to construct uniform hierarchical porous structures, resulting in large diffusion resistance and affecting catalytic efficiency; titanium species are prone to agglomeration to form non-framework titanium, reducing catalytic activity and selectivity; and hydrothermal stability still cannot meet the requirements of harsh industrial reaction conditions, etc.
[0005] Therefore, this study yielded a preparation method that can significantly improve the crystallinity, framework stability, hierarchical pore structure uniformity, and catalytic performance of FER-type titanium-silicon molecular sieves. This method is mild and easy to scale up industrially, and has significant practical implications and industrial application value. Summary of the Invention
[0006] The purpose of this invention is to provide a high-stability hierarchical porous FER-type titanium-silicon molecular sieve, its preparation method and application, thereby solving the problems of low crystallinity, poor framework stability, uneven hierarchical pore structure, poor catalytic performance and insufficient hydrothermal stability in the existing technology.
[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a highly stable hierarchical porous FER-type titanium-silicon molecular sieve, the method comprising the following steps: 1) Potassium silicate is activated by immersing it in a fluorosilicic acid solution, and then the activated potassium silicate is modified with tetraethyl orthosilicate to obtain a modified silicon source. 2) The modified silicon source, titanium source, composite template agent, seed crystal, silane coupling agent and water are mixed to obtain a gel, which is then crystallized to obtain the precursor; 3) The precursor was calcined and then acid-modified to obtain the FER topology; 4) The FER topology is immersed in ammonium dihydrogen phosphate solution for reaction, followed by drying and calcination to obtain FER-type titanium-silicon molecular sieve.
[0008] Preferably, in step 1), the mass fraction of the fluorosilicic acid solution is 5-8%, the activation temperature is 40-50°C, and the activation time is 2-3 hours. The mass ratio of activated potassium silicate to tetraethyl orthosilicate is 1:0.3~0.5, the modification temperature is 60~70℃, and the modification time is 1~2h.
[0009] Preferably, in step 2), the titanium source is tetrabutyl titanate and / or isopropyl titanate; The composite template agent is a mixture of tetraethylammonium chloride and polyethylene glycol, with a molar ratio of tetraethylammonium chloride to polyethylene glycol of 8~9.5:0.5~2; The seed crystal is PLS-3; The silane coupling agent is γ-glycidoxypropyltrimethoxysilane; The molar ratio of the modified silicon source, titanium source, composite template agent, seed crystal, silane coupling agent and water is 1:30~80:0.15~0.2:0.2~0.3:0.02~0.06:7~9.
[0010] Preferably, in step 2), the crystallization temperature is 180~190℃ and the crystallization time is 36~48h.
[0011] Preferably, in step 3), calcination includes a first calcination and a second calcination; In the first calcination, the calcination atmosphere is nitrogen atmosphere, the calcination temperature is 245~255℃, and the calcination time is 2~3h; In the second calcination, the calcination atmosphere is air, the calcination temperature is 570~590℃, and the calcination time is 10~12h.
[0012] Preferably, in step 3), the acid used for acid modification includes one or more of oxalic acid, citric acid, formic acid, acetic acid and malonic acid, the concentration of the acid is 0.08~0.12mol / L, and the solid-liquid ratio of the calcined product to the acid is 1g:10~15mL; Acid modification is carried out under microwave conditions. The acid modification temperature is 70~80℃, the acid modification time is 1~2h, and the microwave power is 300~400W.
[0013] Preferably, in step 4), the concentration of the ammonium dihydrogen phosphate solution is 0.05~0.1mol / L, the reaction temperature is 100~110℃, and the reaction time is 3~4h.
[0014] Preferably, in step 4), the drying temperature is 90~100℃, the drying time is 6~8h, the calcination temperature is 540~560℃, and the calcination time is 6~8h.
[0015] The present invention also provides a method for preparing a highly stable multi-level porous FER type titanium-silicon molecular sieve, which yields the FER type titanium-silicon molecular sieve.
[0016] This invention also provides the application of the FER-type titanium-silicon molecular sieve in the field of biomass catalytic conversion.
[0017] The beneficial effects of this invention are: This invention significantly improves the reactivity of the silicon source by activating it with fluorosilicic acid and grafting it with tetraethyl orthosilicate, thereby increasing the crystallinity of the prepared molecular sieve to over 90%. At the same time, the modified silicon source constructs a more compact framework structure, laying the foundation for the excellent hydrothermal stability of the molecular sieve.
[0018] In this invention, a composite template agent of tetraethylammonium chloride and polyethylene glycol-6000 is used. Tetraethylammonium chloride induces the formation of FER topology, while polyethylene glycol-6000 acts as a mesoporous directing agent to form mesopores of 2-5 nm in the framework, successfully constructing a microporous-mesoporous hierarchical pore structure. The specific surface area is increased to 450-500 m² / g, and the pore volume is increased to 0.40-0.45 cm³ / g, effectively reducing diffusion resistance and improving catalytic efficiency.
[0019] The synergistic effect of the composite titanium source and silane coupling agent in this invention promotes the uniform dispersion of titanium species in the molecular sieve framework, reducing the content of non-framework titanium to below 3%. In the cyclohexanone ammonium oxime reaction, the cyclohexanone conversion rate can reach over 95%, and the oxime selectivity exceeds 98%. Compared with samples prepared by traditional methods, the conversion rate and selectivity are improved by more than 20% and 15%, respectively.
[0020] In this invention, the lanthanum element in the modified seed crystal and the phosphorus element in the stabilization treatment work synergistically to form a multi-element bonded structure in the molecular sieve framework. After hydrothermal treatment at 873K and 100% water vapor atmosphere for 24 hours, the crystallinity retention rate is still over 90%, which is far superior to traditional samples (crystallinity retention rate is less than 65%), and the service life is significantly extended.
[0021] The preparation process parameters of this invention are mild, and each step is synergistic and controllable. It does not require special and expensive equipment and is easy to scale up for industrial production. Moreover, there is no harmful gas emission during the preparation process, and the washing wastewater can be recycled after simple treatment, which is in line with the concept of green chemical development. Detailed Implementation
[0022] This invention provides a method for preparing a highly stable hierarchical porous FER-type titanium-silicon molecular sieve, the method comprising the following steps: 1) Potassium silicate is activated by immersing it in a fluorosilicic acid solution, and then the activated potassium silicate is modified with tetraethyl orthosilicate to obtain a modified silicon source. 2) The modified silicon source, titanium source, composite template agent, seed crystal, silane coupling agent and water are mixed to obtain a gel, which is then crystallized to obtain the precursor; 3) The precursor was calcined and then acid-modified to obtain the FER topology; 4) The FER topology is immersed in ammonium dihydrogen phosphate solution for reaction, followed by drying and calcination to obtain FER-type titanium-silicon molecular sieve.
[0023] In this invention, in step 1), the mass fraction of the fluorosilicic acid solution is preferably 5-8%, more preferably 5.5-7.5%, and even more preferably 6-7%. The activation temperature is preferably 40-50°C, more preferably 42-48°C, and even more preferably 45-46°C. The activation time is preferably 2-3 hours, and even more preferably 2.5 hours. The preferred mass ratio of activated potassium silicate to tetraethyl orthosilicate is 1:0.3~0.5, more preferably 1:0.35~0.45, and even more preferably 1:0.4~0.42. The preferred modification temperature is 60~70℃, more preferably 62~68℃, and even more preferably 65~66℃. The preferred modification time is 1~2h, and even more preferably 1.5h.
[0024] In this invention, in step 1), the particle size of potassium silicate is preferably 100-200 mesh, more preferably 120-180 mesh, and even more preferably 140-160 mesh. This particle size can enhance the activation and modification effect. The activation is preferably carried out under stirring, and the stirring speed is preferably 200~300 rpm, more preferably 220~280 rpm, and even more preferably 240~260 rpm. The modification is preferably carried out under stirring, and the stirring speed is preferably 150~200 rpm, more preferably 160~190 rpm, and even more preferably 170~180 rpm. The modified material is preferably filtered, washed, and dried sequentially. The drying temperature is preferably 80-90°C, more preferably 82-88°C, and even more preferably 84-86°C. The drying time is preferably 4-6 hours, more preferably 4.5-5.5 hours, and even more preferably 5 hours.
[0025] In this invention, in step 2), the titanium source is preferably tetrabutyl titanate and / or isopropyl titanate; The composite template agent is preferably a mixture of tetraethylammonium chloride and polyethylene glycol. The molar ratio of tetraethylammonium chloride to polyethylene glycol is preferably 8~9.5:0.5~2, more preferably 8.2~9.2:0.8~1.8, and even more preferably 8.5~8.8:1~1.5. The polyethylene glycol is preferably polyethylene glycol-6000, which has a moderate molecular weight and can play a role in guiding mesoporous structures and constructing a uniform mesoporous structure. The seed crystal is preferably PLS-3 seed crystal, and the particle size of the PLS-3 seed crystal is preferably 50~100nm, more preferably 60~90nm, and even more preferably 70~80nm. The PLS-3 seed crystal is preferably dried before use. The drying temperature is preferably 110~120℃, more preferably 112~118℃, and even more preferably 114~116℃. The drying time is preferably 2~3h, and even more preferably 2.5h. The purpose of drying is to remove moisture from the seed crystal, thereby improving the activity of the seed crystal. The preferred silane coupling agent is γ-glycidoxypropyltrimethoxysilane; The preferred molar ratio of the modified silicon source, titanium source, composite template agent, seed crystal, silane coupling agent, and water is 1:30~80:0.15~0.2:0.2~0.3:0.02~0.06:7~9, more preferably 1:40~70:0.16~0.19:0.22~0.28:0.03~0.05:7.5~8.5, and even more preferably 1:50~60:0.17~0.18:0.24~0.26:0.04~0.045:8~8.2.
[0026] In this invention, in step 2), the crystallization temperature is preferably 180~190℃, more preferably 182~188℃, and even more preferably 184~186℃; the crystallization time is preferably 36~48h, more preferably 38~46h, and even more preferably 40~42h; and the crystallization pressure is preferably 0.3~0.5MPa, more preferably 0.35~0.45MPa, and even more preferably 0.4~0.42MPa.
[0027] In this invention, in step 2), the mixing speed is preferably 300-400 rpm, more preferably 320-380 rpm, and even more preferably 340-360 rpm; the mixing time is preferably 2-3 hours, and even more preferably 2.5 hours.
[0028] In this invention, step 3) includes a first calcination and a second calcination; In the first calcination, the calcination atmosphere is preferably a nitrogen atmosphere, the calcination temperature is preferably 245~255℃, more preferably 247~253℃, more preferably 248~250℃, and the calcination time is preferably 2~3h, more preferably 2.5h; In the second calcination, the calcination atmosphere is preferably an air atmosphere, the calcination temperature is preferably 570~590℃, more preferably 575~585℃, more preferably 580~582℃, and the calcination time is preferably 10~12h, more preferably 10.5~11.5h, and more preferably 11h.
[0029] In this invention, in step 3), the acid used for acid modification preferably includes one or more of oxalic acid, citric acid, formic acid, acetic acid, and malonic acid. The concentration of the acid is preferably 0.08~0.12 mol / L, more preferably 0.09~0.11 mol / L, and even more preferably 0.1 mol / L. The solid-liquid ratio of the calcined product to the acid is preferably 1g:10~15mL, more preferably 1g:11~14mL, and even more preferably 1g:12~13mL. Acid modification is preferably carried out under microwave conditions. The acid modification temperature is preferably 70~80℃, more preferably 72~78℃, and even more preferably 74~76℃. The acid modification time is preferably 1~2h, more preferably 1.5h. The microwave power is preferably 300~400W, more preferably 320~380W, and even more preferably 340~360W.
[0030] In this invention, in step 4), the concentration of the ammonium dihydrogen phosphate solution is preferably 0.05~0.1 mol / L, more preferably 0.06~0.09 mol / L, and even more preferably 0.07~0.08 mol / L; the reaction temperature is preferably 100~110℃, more preferably 102~108℃, and even more preferably 104~106℃; and the reaction time is preferably 3~4 h, and even more preferably 3.5 h.
[0031] In this invention, in step 4), the drying temperature is preferably 90~100℃, more preferably 92~98℃, and even more preferably 95~96℃; the drying time is preferably 6~8h, more preferably 6.5~7.5h, and even more preferably 7h; the calcination temperature is preferably 540~560℃, more preferably 545~555℃, and even more preferably 548~550℃; and the calcination time is preferably 6~8h, more preferably 6.5~7.5h, and even more preferably 7h.
[0032] In this invention, in step 4), the heating rate from room temperature to calcination temperature is preferably 5~10℃ / min, more preferably 6~9℃ / min, and even more preferably 7~8℃ / min; The calcined product is preferably cooled, pulverized, and sieved. The cooling is preferably natural cooling, and the cooling temperature is preferably room temperature. The particle size of the sieved product is preferably 80-120 mesh, more preferably 90-110 mesh, and even more preferably 100 mesh.
[0033] The present invention also provides a method for preparing a highly stable multi-level porous FER type titanium-silicon molecular sieve, which yields the FER type titanium-silicon molecular sieve.
[0034] In this invention, the FER-type titanium-silicon molecular sieve has a typical FER topology, which is a microporous-mesoporous hierarchical structure, wherein the mesopore size is 2~5nm and the specific surface area is 450~500m². 2 / g, pore volume 0.40~0.45cm³ 3 / g; In the cyclohexanone amination reaction, the cyclohexanone conversion rate is ≥95%, the oxime selectivity is ≥98%, and the catalytic performance is excellent.
[0035] This invention also provides the application of the FER-type titanium-silicon molecular sieve in the field of biomass catalytic conversion.
[0036] In this invention, the specific application is to catalyze the oxidation, isomerization, epoxidation and other reactions of biomass derivatives (such as cellulose, hemicellulose, lignin, etc.), and is particularly suitable for catalyzing the oximeation of cyclohexanone and the oxidation of glucose to prepare gluconic acid. It can significantly improve the reaction conversion rate and product selectivity, shorten the reaction time, and the molecular sieve has a long service life and can be reused many times while maintaining high catalytic activity.
[0037] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0038] Example 1
[0039] Take 150-mesh potassium silicate powder, immerse it in a 5% (w / w) fluorosilicic acid solution, and activate it for 2 hours at 40℃ and 200 rpm stirring. After activation, filter and wash until neutral to obtain activated potassium silicate. Mix the activated potassium silicate with tetraethyl orthosilicate at a mass ratio of 1:0.3, add it to a constant temperature water bath, and modify it for 1 hour at 60℃ and 150 rpm stirring. After modification, filter and wash until neutral, dry at 80℃ for 4 hours, and pulverize to obtain modified silicon source powder. Modified silicon source powder, tetrabutyl titanate, composite template agent (molar ratio of tetraethylammonium chloride to polyethylene glycol-6000 is 8:0.5), PLS-3 seed crystals (particle size 80 nm, pre-dried at 110℃ for 2 h), γ-glycidyl etheroxypropyltrimethoxysilane, and water were added sequentially to a reaction vessel in a molar ratio of 1:30:0.15:0.2:0.02:7. The mixture was stirred at 300 rpm for 2 h to form a gel. The gel was then transferred to a high-pressure reaction vessel and crystallized at 180℃ and 0.3 MPa for 36 h. After crystallization, the mixture was allowed to cool naturally to room temperature, filtered, and washed until neutral to obtain the precursor. The precursor was placed in a muffle furnace and calcined at 245°C for 2 hours under a nitrogen atmosphere. Then, the atmosphere was switched to air, and the temperature was raised to 570°C for 10 hours. After calcination, the product was allowed to cool naturally to room temperature to obtain the calcined product. The calcined product was immersed in a 0.08 mol / L oxalic acid solution with a solid-liquid ratio of 1 g:10 mL. The product was then acid-modified at 70°C for 1 hour under microwave conditions (300 W power). After acid modification, the product was filtered and washed until neutral to obtain the FER topology. The FER topological structure was immersed in a 0.05 mol / L ammonium dihydrogen phosphate solution and transferred to a reflux apparatus. The reaction was carried out at 100℃ and 150 rpm for 3 hours. After the reaction was completed, the product was filtered and washed until neutral. The washed product was placed in an oven and dried at 90℃ for 6 hours. After drying, the product was transferred to a muffle furnace and calcined at 540℃ for 6 hours at a heating rate of 5℃ / min. After calcination, the product was naturally cooled to room temperature, crushed, and sieved to obtain the FER type titanium-silicon molecular sieve product with a particle size of 80~120 mesh.
[0040] Example 2
[0041] Take 150-mesh potassium silicate powder, immerse it in a 6.5% (w / w) fluorosilicic acid solution, and activate it for 2.5 h at 45℃ and 250 rpm stirring. After activation, filter and wash until neutral to obtain activated potassium silicate. Mix the activated potassium silicate with tetraethyl orthosilicate at a mass ratio of 1:0.4, add it to a constant temperature water bath, and modify it for 1.5 h at 65℃ and 175 rpm stirring. After modification, filter and wash until neutral, dry at 85℃ for 5 h, and pulverize to obtain modified silicon source powder. Modified silicon source powder, isopropyl titanate, composite template agent (molar ratio of tetraethylammonium chloride to polyethylene glycol-6000 of 8.75:1.25), PLS-3 seed crystals (particle size 80 nm, pre-dried at 115℃ for 2.5 h), γ-glycidyl etheroxypropyltrimethoxysilane, and water were added sequentially to a reaction vessel in a molar ratio of 1:55:0.175:0.25:0.04:8. The mixture was stirred at 350 rpm for 2.5 h to form a gel. The gel was then transferred to a high-pressure reaction vessel and crystallized at 185℃ and 0.4 MPa for 42 h. After crystallization, the mixture was allowed to cool naturally to room temperature, filtered, and washed until neutral to obtain the precursor. The precursor was placed in a muffle furnace and calcined at 250°C for 2.5 h under a nitrogen atmosphere. Then, the atmosphere was switched to air, and the temperature was raised to 580°C for 11 h. After calcination, the product was naturally cooled to room temperature to obtain the calcined product. The calcined product was immersed in a 0.1 mol / L citric acid solution with a solid-liquid ratio of 1 g:12.5 mL. The product was then acid-modified at 75°C for 1.5 h under microwave conditions (350 W). After acid modification, the product was filtered and washed until neutral to obtain the FER topology. The FER topological structure was immersed in a 0.075 mol / L ammonium dihydrogen phosphate solution and transferred to a reflux apparatus. The reaction was carried out at 105℃ and 175 rpm for 3.5 h. After the reaction was completed, the product was filtered and washed until neutral. The washed product was placed in an oven and dried at 95℃ for 7 h. After drying, the product was transferred to a muffle furnace and calcined at 550℃ at a heating rate of 7.5℃ / min for 7 h. After calcination, the product was naturally cooled to room temperature, crushed, and sieved to obtain the FER type titanium-silicon molecular sieve product with a particle size of 80~120 mesh.
[0042] Example 3
[0043] Take 150-mesh potassium silicate powder, immerse it in an 8% (w / w) fluorosilicic acid solution, and activate it for 3 hours at 50℃ and 300 rpm stirring. After activation, filter and wash until neutral to obtain activated potassium silicate. Mix the activated potassium silicate with tetraethyl orthosilicate at a mass ratio of 1:0.5, add it to a constant temperature water bath, and modify it for 2 hours at 70℃ and 200 rpm stirring. After modification, filter and wash until neutral, dry at 90℃ for 6 hours, and pulverize to obtain modified silicon source powder. In a molar ratio of 1:80:0.2:0.3:0.06:9, modified silicon source powder, a mixture of tetrabutyl titanate and isopropyl titanate (molar ratio 1:1), a composite template agent (molar ratio of tetraethylammonium chloride to polyethylene glycol-6000 of 9.5:2), PLS-3 seed crystals (particle size 80 nm, pre-dried at 120℃ for 3 h), γ-glycidyl etheroxypropyltrimethoxysilane, and water were added sequentially to a reaction vessel and stirred at 400 rpm for 3 h to form a gel. The gel was then transferred to a high-pressure reaction vessel and crystallized at 190℃ and 0.5 MPa for 48 h. After crystallization, the mixture was allowed to cool naturally to room temperature, filtered, and washed until neutral to obtain the precursor. The precursor was placed in a muffle furnace and calcined at 255°C for 3 hours under a nitrogen atmosphere. Then, the atmosphere was switched to air, and the temperature was raised to 590°C for 12 hours. After calcination, the product was naturally cooled to room temperature to obtain the calcined product. The calcined product was immersed in a 0.12 mol / L oxalic acid solution with a solid-liquid ratio of 1 g:15 mL. The product was then acid-modified at 80°C for 2 hours under microwave conditions (400 W power). After acid modification, the product was filtered and washed until neutral to obtain the FER topology. The FER topological structure was immersed in a 0.1 mol / L ammonium dihydrogen phosphate solution and transferred to a reflux apparatus. The reaction was carried out at 110℃ and 200 rpm for 4 hours. After the reaction was completed, the product was filtered and washed until neutral. The washed product was placed in an oven and dried at 100℃ for 8 hours. After drying, the product was transferred to a muffle furnace and calcined at 560℃ at a heating rate of 10℃ / min for 8 hours. After calcination, the product was naturally cooled to room temperature, crushed, and sieved to obtain the FER type titanium-silicon molecular sieve product with a particle size of 80~120 mesh.
[0044] Comparative Example 1
[0045] Compared with Example 2, the potassium silicate was not activated with fluorosilicic acid or modified with tetraethyl orthosilicate. The unmodified potassium silicate was used directly as the silicon source, and the other steps were the same as in Example 2.
[0046] Comparative Example 2
[0047] Compared with Example 2, the composite template agent in Example 2 was replaced with a single tetraethylammonium chloride, and the other steps were the same as in Example 2.
[0048] Comparative Example 3
[0049] Compared with Example 2, γ-glycidoxypropyltrimethoxysilane was removed from Example 2, and the other steps were the same as in Example 2.
[0050] Comparative Example 4
[0051] Tetrabutyl tetrasilicate, tetrapropylammonium hydroxide, and water were mixed in a molar ratio of 1:40:0.2:8 and stirred for 2 hours to form a gel. The gel was transferred into a high-pressure reactor and crystallized at 180°C for 48 hours. After cooling, filtration, and washing, the precursor was obtained. The precursor was calcined at 550°C for 10 hours in air and then cooled to obtain FER-type titanium-silicon molecular sieve.
[0052] The molecular sieves obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to the following performance tests: Pore structure parameter detection: Nitrogen adsorption-desorption test was performed on the molecular sieve samples using a nitrogen adsorption-desorption instrument. Before the test, the samples were degassed at 300℃ for 4 hours. The specific surface area of the samples was calculated according to the BET model. The mesopore volume and mesopore size of the samples were calculated according to the BJH model. The test results are shown in Table 1.
[0053] Table 1. Detection results of molecular sieve pore structure parameters obtained in Examples 1-3 and Comparative Examples 1-4
[0054] As shown in Table 1, the FER-type titanium-silicon molecular sieves prepared in Examples 1-3 of this invention have a specific surface area of 450-500 m² / g and a pore volume of 0.40-0.45 cm³. 3 / g, with a mesopore size of 2~5nm, and all performance characteristics are superior to comparative examples 1~4; among them, example 2 has the best performance, with a specific surface area of 478.6m². 2 / g, pore volume 0.427cm 3 / g. Comparative Example 1, without modification of the silicon source, resulted in a significant decrease in specific surface area and pore volume, indicating that fluorosilicic acid activation and tetraethyl orthosilicate modification of the silicon source can effectively enhance its reactivity and improve the crystallinity and pore structure of the molecular sieve. Comparative Example 2, using a single template agent, did not form a significant mesoporous structure, resulting in low specific surface area and pore volume, indicating that the synergistic effect of the composite template agent can effectively construct a microporous-mesoporous hierarchical pore structure and improve pore structure parameters. The molecular sieve obtained in Comparative Example 4 had the worst performance in all aspects, with a crystallinity of only 68.9% and a specific surface area of 289.7 m². 2 / g, with a non-framework titanium content of 8.2%, further demonstrates the significant advantages of the preparation method of the present invention.
[0055] Catalytic performance testing: The catalytic performance of molecular sieve samples was evaluated using the cyclohexanone amination oxime reaction as a probe reaction. The reaction conditions were: 0.1 mol cyclohexanone, 0.12 mol hydrogen peroxide (30% by mass), 0.15 mol ammonia (25% by mass), 0.5 g molecular sieve catalyst, 50 mL tert-butanol as the reaction solvent, 80 °C at the reaction temperature, and 4 h at the reaction time. After the reaction was completed, the composition of the reaction products was detected by gas chromatography, and the conversion rate of cyclohexanone and the oxime selectivity were calculated. The detection results are shown in Table 2.
[0056] Cyclohexanone conversion rate = (Amount of cyclohexanone reacted / Initial amount of cyclohexanone) × 100%
[0057] Oxime selectivity = (Amount of oxime formed / Amount of cyclohexanone reacted) × 100%
[0058] Table 2. Results of molecular sieve catalytic performance testing obtained in Examples 1-3 and Comparative Examples 1-4
[0059] As shown in Table 2, the molecular sieves prepared in Examples 1-3 all achieved a cyclohexanone conversion rate of over 95% and an oxime selectivity of over 98% in the cyclohexanone ammonium oxime reaction. Compared with Comparative Example 4, the conversion rate and selectivity were improved by more than 20% and 15%, respectively. The catalytic performance of Comparative Examples 1-3 was poor, further verifying the synergistic effect of the preparation steps and parameters of this invention on improving catalytic performance.
[0060] Reusability performance testing: Using the molecular sieve sample prepared in Example 2 as the object, the above-mentioned cyclohexanone amination oxime reaction was repeated. After each reaction, the catalyst was filtered, washed, and dried (95°C, 7h) and then directly used in the next reaction. The catalyst was used continuously for 5 times. The cyclohexanone conversion rate and oxime selectivity of each reaction were detected to evaluate the reusability of the catalyst. The test results are shown in Table 3.
[0061] Table 3. Results of the test on the reusability of the molecular sieve obtained in Example 2
[0062] As shown in Table 3, the molecular sieve prepared in Example 2 still maintains a cyclohexanone conversion rate of over 96% and an oxime selectivity of over 98% after five consecutive uses. This indicates that the molecular sieve has excellent reusability, a long service life, and is suitable for industrial-scale applications.
[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing a highly stable hierarchical porous FER-type titanium-silica molecular sieve, characterized in that, The preparation method includes the following steps: 1) Potassium silicate is activated by immersing it in a fluorosilicic acid solution, and then the activated potassium silicate is modified with tetraethyl orthosilicate to obtain a modified silicon source. 2) The modified silicon source, titanium source, composite template agent, seed crystal, silane coupling agent and water are mixed to obtain a gel, which is then crystallized to obtain the precursor; 3) The precursor was calcined and then acid-modified to obtain the FER topology; 4) The FER topology is immersed in ammonium dihydrogen phosphate solution for reaction, followed by drying and calcination to obtain FER-type titanium-silicon molecular sieve.
2. The method for preparing a high-stability hierarchical porous FER-type titanium-silicon molecular sieve according to claim 1, characterized in that, In step 1), the mass fraction of the fluorosilicic acid solution is 5-8%, the activation temperature is 40-50℃, and the activation time is 2-3 hours. The mass ratio of activated potassium silicate to tetraethyl orthosilicate is 1:0.3~0.5, the modification temperature is 60~70℃, and the modification time is 1~2h.
3. The method for preparing a high-stability hierarchical porous FER-type titanium-silica molecular sieve according to claim 1, characterized in that, In step 2), the titanium source is tetrabutyl titanate and / or isopropyl titanate; The composite template agent is a mixture of tetraethylammonium chloride and polyethylene glycol, with a molar ratio of tetraethylammonium chloride to polyethylene glycol of 8~9.5:0.5~2; The seed crystal is PLS-3; The silane coupling agent is γ-glycidoxypropyltrimethoxysilane; The molar ratio of the modified silicon source, titanium source, composite template agent, seed crystal, silane coupling agent and water is 1:30~80:0.15~0.2:0.2~0.3:0.02~0.06:7~9.
4. The method for preparing a high-stability hierarchical porous FER-type titanium-silicon molecular sieve according to claim 1 or 3, characterized in that, In step 2), the crystallization temperature is 180~190℃ and the crystallization time is 36~48h.
5. The method for preparing a high-stability hierarchical porous FER-type titanium-silicon molecular sieve according to claim 1, characterized in that, In step 3), calcination includes a first calcination and a second calcination; In the first calcination, the calcination atmosphere is a nitrogen atmosphere, the calcination temperature is 245~255℃, and the calcination time is 2~3h; In the second calcination, the calcination atmosphere is air, the calcination temperature is 570~590℃, and the calcination time is 10~12h.
6. The method for preparing a high-stability hierarchical porous FER-type titanium-silicon molecular sieve according to claim 5, characterized in that, In step 3), the acid used for acid modification includes one or more of oxalic acid, citric acid, formic acid, acetic acid and malonic acid, the concentration of the acid is 0.08~0.12mol / L, and the solid-liquid ratio of the calcined product to the acid is 1g:10~15mL; Acid modification is carried out under microwave conditions. The acid modification temperature is 70~80℃, the acid modification time is 1~2h, and the microwave power is 300~400W.
7. The method for preparing a high-stability hierarchical porous FER-type titanium-silicon molecular sieve according to claim 5 or 6, characterized in that, In step 4), the concentration of the ammonium dihydrogen phosphate solution is 0.05~0.1mol / L, the reaction temperature is 100~110℃, and the reaction time is 3~4h.
8. The method for preparing a high-stability hierarchical porous FER-type titanium-silica molecular sieve according to claim 7, characterized in that, In step 4), the drying temperature is 90~100℃, the drying time is 6~8h, the calcination temperature is 540~560℃, and the calcination time is 6~8h.
9. The FER-type titanium-silicon molecular sieve prepared by the preparation method of the high-stability multi-level porous FER-type titanium-silicon molecular sieve according to claims 1 to 8.
10. The application of the FER-type titanium-silicon molecular sieve according to claim 9 in the field of biomass catalytic conversion.