Preparation method and application of a catalyst based on pyridine ionic liquid

Abstract

The application discloses a preparation method of a catalyst based on a pyridine ionic liquid and application thereof, and belongs to the technical field of catalyst preparation. The catalyst based on the pyridine ionic liquid is prepared by utilizing the hydrolysis reaction of a silane coupling agent to obtain silica nanotubes containing a pyridine unit, and then through a quaternary ammonium reaction. The catalyst has a high specific surface area and a rich pore structure, is favorable for exposure of active sites and contact of the active sites with reactants, and improves a catalytic rate. Meanwhile, the silica nanotubes contain hydroxyl groups, can synergistically catalyze a carbon dioxide cycloaddition reaction with pyridine ionic liquid sites, and can catalyze a reaction of carbon dioxide and an epoxide compound to prepare a cyclic carbonate under a solvent-free and metal-free condition. The catalyst is easy to recycle, product purification is simple, and the catalyst has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing a catalyst based on pyridine ionic liquid and its application. Background Technology

[0002] The reaction of carbon dioxide with epoxides to prepare cyclic carbonates produces no byproducts and boasts 100% atom utilization, making it one of the ideal methods for the resource utilization of carbon dioxide. Furthermore, the resulting cyclic carbonates can be widely applied in emerging fields such as biodegradable plastics and lithium-ion battery electrolytes. Due to the thermodynamic stability and kinetic inertness of carbon dioxide, developing highly efficient catalysts is crucial for the resource utilization of carbon dioxide in the preparation of cyclic carbonates.

[0003] Ionic liquids possess advantages such as stable physicochemical properties, low volatility, and tunable structure and function, making them widely used in carbon dioxide cycloaddition reactions. Pyridine ionic liquids are among the most commonly used. Norouzi et al., in their article "CO2 conversion into carbonate using pyridinium-based ionic liquids under mild conditions" (Fuel, 2023, 334, 126641), prepared a series of bifunctional pyridinium-based acidic ionic liquids that can efficiently catalyze carbon dioxide cycloaddition reactions under metal-free and solvent-free conditions. However, the catalyst requires extraction and separation, making product purification difficult and unsuitable for industrial production. Chinese invention patent document CN116920939A discloses a core-shell catalyst prepared by grafting 1-vinylimidazole onto the surface of spherical silica and then using a free radical copolymerization method to obtain a polyionic liquid supported on the spherical silica surface. This catalyst can catalyze the reaction of carbon dioxide with epoxides to prepare cyclic carbonates at 1–3 MPa and 80–120 °C. However, using spherical silica as a support is not conducive to the exposure of active sites in polyionic liquids, thus limiting their catalytic activity. Chinese invention patent document CN115960326A discloses a heterogeneous catalyst containing pyridine ionic liquids, prepared via alkylation using a covalent organic framework material containing bipyridine units as a precursor. This catalyst can catalyze the cycloaddition reaction of carbon dioxide at 0.1 MPa–2 MPa and 25–150 °C. However, the synthesis of traditional covalent organic framework materials usually relies on strict inert atmosphere protection and high-purity organic solvents, making large-scale production difficult. Hoon et al., in their article "Pyridinium-Functionalized Ionic Metal-Organic Frameworks Designed as Bifunctional Catalysts for CO2Fixation into Cyclic Carbonates" (ACS Appl. Mater. Interfaces 2020, 12, 24868), reported a metal-organic framework material catalyst containing pyridine ionic liquids prepared via a post-modification method, which can catalyze the cycloaddition reaction of carbon dioxide at 5 bar and 100 °C. However, metal-organic frameworks are formed by coordination bonds, which result in poor stability and easy structural collapse, making them difficult to apply in actual production. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a catalyst based on pyridine ionic liquid. Pyridine units are introduced into silica nanotubes via hydrolysis, followed by quaternization to obtain the catalyst based on the pyridine ionic liquid. The catalyst prepared by this method possesses a high specific surface area and abundant pore structure, which is beneficial for the exposure of active sites and their contact with reactants, promoting mass transfer efficiency and thus improving its catalytic activity. The catalyst can efficiently catalyze the reaction of carbon dioxide with epoxides under solvent-free and metal-free conditions.

[0005] To achieve the objective of this invention, the present invention provides a technical solution for preparing a catalyst based on pyridine ionic liquid, comprising the following steps:

[0006] (1) Dissolve the triblock copolymer P123 and potassium chloride in hydrochloric acid solution to form solution 1;

[0007] Silane coupling agent A was added to solution 1 and stirred to form solution 2; silane coupling agent B was added to solution 2 and stirred to form solution 3; solution 3 was subjected to hydrothermal reaction at 90-110℃ for 12-48h; after the reaction was completed, the product was subjected to solid-liquid separation, washing, extraction and drying to obtain silica nanotubes containing bipyridine units.

[0008] (2) Silica nanotubes containing bipyridine units and haloalkanes were dispersed in toluene and reacted at 80-120℃ for 8-24h under an inert atmosphere. After the reaction was completed, the reactants were separated into solid and liquid components. The solid was washed and dried to obtain a catalyst based on pyridine ionic liquid.

[0009] Furthermore, the silane coupling agent A in step (1) includes A1 or A2, with the following structural formula:

[0010] .

[0011] The silane coupling agent B is a silane coupling agent containing a bipyridine unit, including B1 or B2, with the following structural formula:

[0012] .

[0013] Further, in step (1), the concentration of hydrochloric acid solution is 1.0-2.0M; the concentration of triblock copolymer P123 in solution 1 is 3.1-3.7g / L; the concentration of potassium chloride in solution 1 is 9.7-11.7g / L; the concentration of silane coupling agent A in solution 2 is 5-15.6mmol / L; the concentration of silane coupling agent B in solution 3 is 3.9-14.4mmol / L; and the extraction is a Soxhlet extraction using ethanol.

[0014] Furthermore, in step (2), the general chemical formula of the haloalkane is CH3(CH2)nX, where X is one of Cl, Br, and I; n = 1, 2, or 3; and the inert atmosphere is argon, helium, or nitrogen.

[0015] Furthermore, in step (2), the amount of silica nanotubes containing bipyridine units and haloalkanes is 1g:6-10mmol, and the drying is carried out under vacuum conditions at 60-100℃ for 8-24h.

[0016] Another object of the present invention is to provide an application of the pyridine ionic liquid-based catalyst prepared by the above method in the reaction of carbon dioxide with epoxides to prepare cyclic carbonates.

[0017] The advantages of this invention over the prior art are as follows:

[0018] 1. The technical solution of the catalyst preparation method based on pyridine ionic liquid provided by this invention involves hydrolyzing a silane coupling agent containing bipyridine units under the conditions of 1.0-2.0 M hydrochloric acid, 3.1-3.7 g / L triblock copolymer P123, and 9.7-11.7 g / L potassium chloride. Following this hydrothermal reaction at 90-110 °C for 12-48 h, silica nanotubes containing bipyridine units are obtained. Quaternization modification is then performed to ionize the bipyridine units in the silica nanotubes, successfully immobilizing the homogeneous pyridine ionic liquid onto the silica nanotube framework, thereby achieving the transformation of the catalyst from homogeneous to heterogeneous. The resulting catalyst has a specific surface area of ​​366-485 m². 2 / g, total pore volume 0.86-1.75cm³ 3 The high specific surface area and abundant pore structure of the pyridine ion liquid sites in the framework facilitate better contact with the reactants, resulting in excellent catalytic activity. At 120℃ and 2MPa, the conversion rate of propylene carbonate can reach 88%–96% after 12 hours of reaction. Furthermore, the obtained catalyst can be efficiently recovered and recycled through simple centrifugation or filtration, solving the problems of difficult separation of homogeneous ionic liquid catalysts from the reaction system and complex product purification, making it suitable for industrial applications.

[0019] 2. The technical solution of the catalyst preparation method based on pyridine ionic liquid provided by this invention selects triblock copolymer P123 as a template agent through numerous experiments, enabling self-assembly to form a micelle structure and regulate the pore structure; hydrochloric acid plays a catalytic and intermediate ion role, promoting the ordered arrangement of micelles and the hydrolysis of silane coupling agents; potassium chloride can synergistically form an ordered mesoporous structure with the template agent, stabilizing the reaction system. Ultimately, the successful synthesis of silica nanotubes containing bipyridine units was achieved.

[0020] 3. The technical solution of the catalyst preparation method based on pyridine ionic liquid provided by the present invention, through numerous experiments to select silane coupling agents containing bipyridine units, can realize the introduction of bipyridine units into the silica nanotube framework, thereby achieving the controllable synthesis of silica nanotubes containing bipyridine units with high specific surface area and abundant pore structure. Using these as a support, through quaternization, the active sites are highly dispersed and fully exposed, effectively promoting the mass transfer efficiency between reactants and products. This solves the problem of insufficient exposure of active sites and limited mass transfer when using traditional spherical silica as a support to load active components, thus significantly improving the activity of the catalyst.

[0021] 4. The technical solution of the catalyst preparation method based on pyridine ionic liquid provided by the present invention uses silane coupling agent A and silane coupling agent B for hydrolysis, thereby forming silica nanotubes containing bipyridine units with -Si-O-Si- covalent bonds as the framework. Using these nanotubes as a carrier, the high stability of the catalyst framework structure is achieved, which solves the problem of easy collapse of the structure when using metal framework materials as carriers in the prior art through coordination bonds.

[0022] 5. The technical solution of the catalyst preparation method based on pyridine ionic liquid provided by this invention utilizes a green hydrolysis route with water as a solvent to prepare silica nanotubes containing bipyridine units, achieving large-scale catalyst preparation without the need for inert gas protection and avoiding the use of organic solvents. This preparation method is simple to operate, safe, and environmentally friendly, solving the problem of complex precursor preparation processes in existing technologies when using covalent organic framework materials and metal-organic framework materials as precursors. For example, covalent organic framework materials often require preparation in inert gas protection and organic solvents, while metal-organic framework materials often require high-temperature crystallization.

[0023] 6. The technical solution for the application of pyridine ionic liquid-based catalysts provided by this invention enables the catalyst to efficiently catalyze the cycloaddition reaction of CO2 with epoxides under mild conditions without solvents or metal co-catalysts. It not only achieves a propylene carbonate yield of 88% to 96%, but is also recyclable. The inventors found that the activity does not decrease after being recycled more than 5 times. At the same time, it solves the key problems of difficult recovery of homogeneous catalysts and the complex preparation and poor stability of traditional heterogeneous catalysts, providing a new development path for the resource utilization of CO2. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation process of Cat1 in Example 1;

[0025] Figure 2 This is the nitrogen adsorption-desorption isotherm curve of Cat2 obtained in Example 2 at 77 K;

[0026] Figure 3This is a transmission electron microscope image of Cat2 obtained in Example 2. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. However, the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention. The reagents used in the embodiments of the present invention are all obtained through commercial channels. Among them, the triblock copolymer P123 refers to polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (foreign name: polyethylene oxide–polypropylene oxide–polyethylene oxide), chemical formula PEO-PPO-PEO (EO 20 PO 70 EO 20 ). Example 1

[0028] (1) 1.10 g of triblock copolymer P123 and 3.5 g of potassium chloride were dissolved in 360 mL of 1 M hydrochloric acid solution to form solution 1; 1.8 mmol of silane coupling agent A1 was added to solution 1 and stirred for 6 h to form solution 2; then 5.2 mmol of silane coupling agent B1 was added to solution 2 and stirred for 12 h to form solution 3; solution 3 was transferred to a 90 °C oven for hydrothermal reaction for 48 h; after the reaction was completed, the reaction solution was filtered, washed three times with deionized water, and then extracted with ethanol at 80 °C using a Soxhlet method. The obtained solid was dried at 80 °C for 12 h to obtain silica nanotubes (bp-SNTs) containing bipyridine units.

[0029] (2) Take 1g of bp-SNTs and 10mmol of chloroethane and disperse them in 20mL of toluene. Then, under helium protection, control the temperature at 80℃ for 24h and react. Filter the reaction product and wash it with ethanol three times. Dry the obtained solid in a vacuum oven at 60℃ for 24h to obtain a catalyst based on pyridine ionic liquid (bp-SNTs-ILs), named Cat1.

[0030] The catalytic performance of the obtained pyridine ionic liquid-based catalysts was evaluated:

[0031] 10 mmol of propylene oxide and 80 mg of Cat1 were placed in a 15 mL stainless steel reactor, sealed, and purged with 2 MPa of carbon dioxide. The reactor was then transferred to a 120 °C oil bath and stirred for 12 h. After the reaction, the reactor was cooled with an ice-water bath. Unreacted carbon dioxide was then released, and the resulting liquid was transferred to a centrifuge tube containing a certain amount of internal standard (biphenyl). After centrifugation, the supernatant was analyzed by gas chromatography. The yield of propylene carbonate was 92%. Example 2

[0032] (1) 1.23 g of triblock copolymer P123 and 3.85 g of potassium chloride were dissolved in 360 mL of 1.5 M hydrochloric acid solution to form solution 1; 2.81 mmol of silane coupling agent A1 was added to solution 1 and stirred for 9 h to form solution 2; then 4.19 mmol of silane coupling agent B2 was added to solution 2 and stirred for 18 h to form solution 3; solution 3 was transferred to an oven at 100 °C for hydrothermal reaction for 24 h; after the reaction was completed, the reaction solution was filtered, washed three times with deionized water, and then extracted with ethanol at 80 °C using a Soxhlet method. The obtained solid was dried at 80 °C for 12 h to obtain bp-SNTs.

[0033] (2) Take 1g of bp-SNTs and 8mmol of bromopropane and disperse them in 20mL of toluene. Then, under argon protection, control the reaction temperature at 100℃ and react for 16h. Filter the reaction product and wash it three times with ethanol. Dry the obtained solid in a vacuum oven at 80℃ for 16h to obtain bp-SNTs-ILs, named Cat2.

[0034] The catalytic performance of the obtained Cat2 was evaluated: the yield of propylene carbonate was 96%. The catalytic performance evaluation method was the same as that in Example 1. Example 3

[0035] (1) 1.26 g of triblock copolymer P123 and 3.96 g of potassium chloride were dissolved in 360 mL of 1.8 M hydrochloric acid solution to form solution 1; 4.2 mmol of silane coupling agent A2 was added to solution 1 and stirred for 10 h to form solution 2; then 2.8 mmol of silane coupling agent B1 was added to solution 2 and stirred for 20 h to form solution 3; solution 3 was transferred to an oven at 105 °C and reacted for 18 h; after the reaction was completed, the reaction solution was filtered, washed three times with deionized water, and then extracted with ethanol at 80 °C using a Soxhlet method. After drying, bp-SNTs were obtained.

[0036] (2) Take 1g of bp-SNTs and 7mmol of iodopropane and disperse them in 20mL of toluene. Then, under argon protection, control the temperature at 110℃ and react for 12h. Filter the reaction product and wash it three times with ethanol. Dry the obtained solid in a vacuum oven at 90℃ for 14h to obtain bp-SNTs-ILs, which is named Cat3.

[0037] The catalytic performance of the obtained Cat3 was evaluated: the yield of propylene carbonate was 90%. The catalytic performance evaluation method was the same as that in Example 1. Example 4

[0038] (1) Dissolve 1.33 g of triblock copolymer P123 and 4.21 g of potassium chloride in 360 mL of 2 M hydrochloric acid solution to form solution 1; add 5.6 mmol of silane coupling agent A2 to solution 1 and stir for 12 h to form solution 2; then add 1.4 mmol of silane coupling agent B2 to solution 2 and stir for 24 h to form solution 3; transfer solution 3 to an oven at 110 °C and react for 12 h; after the reaction is completed, filter the reaction solution, wash it three times with deionized water, and then extract it with ethanol at 80 °C using a Soxhlet method. After drying, bp-SNTs are obtained.

[0039] (2) Take 1g of bp-SNTs and 6mmol of iodobutane and disperse them in 20mL of toluene. Then, under nitrogen protection, control the temperature at 120℃ for 8h. Filter the reaction product and wash it three times with ethanol. Dry the obtained solid in a vacuum oven at 100℃ for 12h to obtain bp-SNTs-ILs, named Cat4.

[0040] The catalytic performance of the obtained Cat4 was evaluated: the yield of propylene carbonate was 88%. The catalytic performance evaluation method was the same as that in Example 1. Comparative Example 1

[0041] The amount of silane coupling agent A1 in Example 2 was adjusted to 0.36 mmol, and the amount of silane coupling agent B2 was adjusted to 6.62 mmol. The other conditions were the same as in Example 2, and the catalyst was obtained and named Cat5.

[0042] The catalytic performance of the obtained Cat5 was evaluated: the yield of propylene carbonate was 67%. The catalytic performance evaluation method was the same as that in Example 1. Comparative Example 2

[0043] The amount of silane coupling agent A1 in Example 2 was adjusted to 6.62 mmol, and the amount of silane coupling agent B2 was adjusted to 0.36 mmol. The other conditions were the same as in Example 2, and the catalyst was obtained and named Cat6.

[0044] The catalytic performance of the obtained Cat6 was evaluated: the yield of propylene carbonate was 43%. The catalytic performance evaluation method was the same as that in Example 1. Comparative Example 3

[0045] The catalyst was obtained by replacing silane coupling agent B2 in Example 2 (1) with silane coupling agent tetraethoxysilane (TEOS) and keeping the other conditions the same as in Example 2. It was named Cat7.

[0046] The catalytic performance of the obtained Cat7 was evaluated: the yield of propylene carbonate was 2%. The catalytic performance evaluation method was the same as that in Example 1. Comparative Example 4

[0047] The catalyst was obtained by replacing 1.23g of triblock copolymer P123 in Example 2 (1) with 3g of triblock copolymer P123, while the other conditions were the same as in Example 2. The catalyst was named Cat8. Electron microscopy characterization showed that the catalyst was in the form of nanofibers.

[0048] The catalytic performance of the obtained Cat8 was evaluated: the yield of propylene carbonate was 56%. The catalytic performance evaluation method was the same as that in Example 1. Comparative Example 5

[0049] The catalyst was obtained by replacing the bromopropane in Example 2 (2) with n-propane, and the other conditions were the same as in Example 2. It was named Cat9.

[0050] The catalytic performance of the obtained Cat9 was evaluated: the yield of propylene carbonate was 1%. The catalytic performance evaluation method was the same as that in Example 1.

[0051] Application Example 1

[0052] To test the universality of catalyst Cat2: epichlorohydrin, 1,2-epoxyhexane, and 2-phenyl-epoxyethylene were used as reaction substrates to replace propylene oxide used in the catalyst evaluation, while keeping other parameters unchanged. The conversion rates of the substrates used are shown in Table 1 below.

[0053]

[0054] As shown in Table 1, the Cat1 catalyst prepared in this invention can efficiently catalyze the cycloaddition reactions of various epoxides with carbon dioxide to obtain the corresponding cyclic carbonate products, demonstrating a certain degree of universality. The catalytic performance evaluation method is the same as that in Example 1.

[0055] Application Example 2

[0056] The specific surface area and total pore volume of catalysts Cat1-Cat4 were tested using a Micromeritics ASAP 2020 physical adsorption analyzer. 100 mg of catalyst was placed in a sample tube and pretreated under vacuum at 100 °C for 8 h. Subsequently, N2 adsorption-desorption experiments were conducted at liquid nitrogen temperature (77 K). Based on the obtained adsorption-desorption isotherms, the specific surface area of ​​the catalyst sample was calculated using the Brunauer-Emmett-Teller (BET) theory, and the total pore volume was determined by the single-point adsorption capacity at P / P0 = 0.99.

[0057] Cyclic stability testing of catalysts Cat1-Cat4: Similar to the catalytic performance evaluation in Example 1, the catalysts after the reaction were washed three times with ethanol, dried in a vacuum oven, and used for the next catalytic reaction, with other parameters remaining unchanged. The yields of propylene carbonate at different cycle numbers are shown in the table below.

[0058]

[0059] As shown in Table 2, the catalyst prepared in this invention uses silica nanotubes containing bipyridine units as a support. A heterogeneous catalyst containing pyridine ionic liquid is obtained through a quaternization reaction, achieving immobilization of the pyridine ionic liquid and solving the problem of the difficulty in separating homogeneous pyridine ionic liquids from the catalytic system. Silica nanotubes not only possess their own channels, but the interlacing of the tubes also forms a channel structure, resulting in catalysts with high specific surface areas and abundant channel structures. The specific surface area is 366-485 m². 2 / g, total pore volume 0.86-1.75cm³ 3 / g. This facilitates the exposure of active sites in the catalyst and their contact with reactants, promoting mass transfer rates and enabling the catalyst to exhibit excellent catalytic activity. Under conditions of 120℃ and 2 MPa, the yield of propylene carbonate reaches 88-96% after 12 h of reaction. Furthermore, by using silane coupling agents A and B for hydrolysis to form silica nanotubes connected by -Si-O-Si- covalent bonds and containing bipyridine units, the preparation process is not only simple but also exhibits excellent stability. This results in excellent cyclic stability in the catalytic reaction of carbon dioxide and propylene oxide to prepare propylene carbonate. After 5 cycles, the catalytic performance of Cat1, Cat2, Cat3, and Cat4 remains well maintained, with a propylene carbonate yield of 86%-90%.

[0060] Figure 1The diagram below illustrates the preparation process of Example 1, Cat1. Under specific solution conditions, a silane coupling agent is sequentially added and hydrolyzed, followed by a reaction at 90-110°C to obtain silica nanotubes with a framework containing bipyridine units. The bipyridine units in the silica nanotubes undergo a quaternization reaction with ethane chloride to obtain a catalyst containing pyridine ionic liquid.

[0061] Figure 2 The figure shows the nitrogen adsorption-desorption isotherm curve of Cat2 obtained in Example 2 at 77 K. The figure contains two hysteresis loops, indicating that the material not only has its own tube-like channels, but also pores formed by the interlacing of tubes, exhibiting a multi-level porous structure. The BET specific surface area is 485 m². 2 / g, total pore volume is 1.75cm³ 3 / g.

[0062] Figure 3 The transmission electron microscope (TEM) image of Cat2 obtained in Example 2 shows that it is composed of 7-10 nm nanotubes, possessing both the nanotubes' own channels and mesopores formed by the interlacing of nanotubes. This abundant channel structure facilitates the exposure of active sites, promotes mass transfer efficiency, and thus contributes to the catalyst's excellent catalytic performance. Furthermore, the silica nanotubes are linked by Si-O-Si covalent bonds, achieving high stability of the catalyst framework structure and solving the problem of structural collapse in existing technologies using metal framework materials as precursors, where the links are coordinated.

[0063] Comparing Comparative Examples 1 and 2 with Example 2, it can be seen that the ratio of silane coupling agents A and B directly affects the bipyridine unit content, thereby regulating the number of active sites and specific surface area of ​​the catalyst. An optimal concentration range exists to achieve high catalytic activity. In Comparative Example 1, compared to Example 2, the amount of silane coupling agent A1 was reduced and silane coupling agent B2 was increased, resulting in a significant increase in the bipyridine unit content in the obtained silica nanotubes. Through quaternization, a catalyst with high pyridine ion liquid site content was obtained. However, the higher pyridine ion liquid site content led to enhanced intermolecular forces, significantly reducing the catalyst's specific surface area. This limited the exposure of active sites and resulted in insufficient contact with reactants, leading to decreased catalytic activity. In Comparative Example 2, compared to Example 2, the amount of silane coupling agent A1 was increased and silane coupling agent B2 was reduced, resulting in a significant decrease in the bipyridine unit content in the obtained silica nanotubes. Through quaternization, a catalyst with lower pyridine ion liquid site content was obtained. During the catalytic reaction, insufficient active sites led to decreased catalytic activity. Therefore, the concentration of silane coupling agent A in solution 2 needs to be controlled at 5-15.6 mol / L, and the concentration of silane coupling agent B in solution 3 needs to be controlled at 3.9-14.4 mol / L, in order to obtain a catalyst with high specific surface area, abundant active sites and excellent catalytic activity.

[0064] Comparing Comparative Example 3 with Example 2, it can be seen that the silane coupling agent containing bipyridine units is a key component in constructing active sites, and its absence will prevent the catalyst from forming effective active centers. Comparative Example 3 used the silane coupling agent tetraethoxysilane (TEOS) to replace the silane coupling agent B2 containing bipyridine units in Example 2 (1). The resulting material did not contain bipyridine units and could not react with haloalkanes. The resulting catalyst did not contain pyridine ionic liquid sites, i.e., active sites, and exhibited extremely low catalytic activity. This indicates that the use of silane coupling agents containing bipyridine units is key to introducing ionizable functional groups—bipyridine units—into silica nanotubes. Silica nanotubes containing bipyridine units can be converted into pyridine ionic liquid sites through quaternization reactions, thereby obtaining catalysts that exhibit excellent catalytic activity.

[0065] Comparing Comparative Example 4 with Example 2, it can be seen that the concentration of triblock copolymer P123 is crucial to the morphology of silica nanotubes. A suitable concentration range helps form a high specific surface area structure, promoting catalytic activity. Comparative Example 4 increased the concentration of triblock copolymer P123, affecting the hydrolysis of the silane coupling agent and its self-assembly with the triblock copolymer P123. This resulted in a nanofiber-like material, which is less conducive to the exposure of active sites than silica nanotubes, leading to a significant decrease in the catalytic activity of the resulting catalyst, although it still possesses some catalytic activity. This indicates that the concentration of triblock copolymer P123 plays a key role in the formation of silica nanotubes. In this invention, the concentration of triblock copolymer P123 is selected as 3.1-3.7 g / L, enabling silane coupling agents A and B to hydrolyze and self-assemble into silica nanotubes with high specific surface area and abundant pore structure. This allows the prepared catalyst to effectively expose active sites, significantly promoting the mass transfer efficiency between reactants and products, and thus exhibiting excellent catalytic activity.

[0066] Comparing Comparative Example 5 with Example 2, it can be seen that haloalkanes are essential reactants for forming active pyridine ionic liquid sites; the heterogeneous design greatly improves the catalyst recovery and industrial application. Comparative Example 5, using n-propane instead of haloalkanes, could not react with the bipyridine units in the silica nanotubes, and the resulting catalyst did not contain pyridine ionic liquid sites, i.e., active sites, exhibiting extremely low catalytic activity. This indicates that the reaction of haloalkanes with the bipyridine units in silica nanotubes to generate pyridine ionic liquid sites is key to the catalyst's activity. Simultaneously, the transformation of the pyridine ionic liquid catalyst from homogeneous to heterogeneous phases was achieved. The obtained catalyst can be efficiently recovered and recycled through simple centrifugation or filtration, solving the problems of difficult separation of homogeneous ionic liquid catalysts from the reaction system and complex product purification, significantly improving the feasibility of industrial applications.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a catalyst based on pyridine ionic liquid, characterized in that, Includes the following steps: (1) Dissolve the triblock copolymer P123 and potassium chloride in hydrochloric acid solution to form solution 1; Silane coupling agent A is added to solution 1, and the mixture is stirred to react, forming solution 2; Add silane coupling agent B to solution 2, stir to react, and form solution 3; Solution 3 was subjected to a hydrothermal reaction at 90-110℃ for 12-48 h; after the reaction was completed, the product was subjected to solid-liquid separation, washing, extraction and drying to obtain silica nanotubes containing bipyridine units. (2) Silica nanotubes containing bipyridine units and haloalkanes were dispersed in toluene and reacted at 80-120℃ for 8-24h under an inert atmosphere. After the reaction was completed, the reaction product was separated into solid and liquid components. The obtained solid was washed and dried to obtain a catalyst based on pyridine ionic liquid. In step (1), the silane coupling agent A includes A1 or A2, with the following structural formula: The silane coupling agent B is a silane coupling agent containing a bipyridine unit, including B1 or B2, with the following structural formula: ； The concentration of triblock copolymer P123 in solution 1 is 3.1-3.7 g / L; the concentration of silane coupling agent A in solution 2 is 5-15.6 mmol / L; and the concentration of silane coupling agent B in solution 3 is 3.9-14.4 mmol / L.

2. The method for preparing the catalyst based on pyridine ionic liquid according to claim 1, characterized in that, In step (1), the concentration of hydrochloric acid solution is 1.0-2.0M; the concentration of potassium chloride in solution 1 is 9.7-11.7g / L; and the extraction is a Soxhlet extraction with ethanol.

3. The method for preparing the catalyst based on pyridine ionic liquid according to claim 1, characterized in that, In step (2), the general chemical formula of the haloalkane is CH3(CH2)nX, where X is one of Cl, Br, and I; n = 1, 2, or 3; and the inert atmosphere is argon, helium, or nitrogen.

4. The method for preparing the catalyst based on pyridine ionic liquid according to claim 1, characterized in that, In step (2), the amount of silica nanotubes containing bipyridine units and haloalkanes is 1g:6-10mmol, and the drying is carried out under vacuum conditions at 60-100℃ for 8-24h.

5. The application of a catalyst based on a pyridine ionic liquid prepared by the method according to any one of claims 1-4, characterized in that, A pyridine ionic liquid-based catalyst was used in the reaction of CO2 with epoxides to prepare cyclic carbonates.

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