Ionic liquid in-situ self-assembly in covalent organic frameworks catalysts, methods of making and uses thereof

Abstract

The present application relates to a kind of ionic liquid in-situ self-assembly in covalent organic framework catalyst and its preparation method and application, it is characterized in that by in-situ self-assembly method, basic choline ionic liquid is encapsulated in triazole group covalent organic framework, catalyst [ChVOH] 10 The specific surface area of the COF is 150-230 m 2 / g;The [ChVOH] x COF catalyst provided by the present application has simple synthesis method, convenient operation, mild condition, compared with existing catalyst, does not need cocatalyst such as TBAB, reduces production cost, is convenient to recover, is more beneficial to industrial production.The [ChVOH] 10 COF catalyst provided by the present application is used for one-pot step coupling preparation of dimethyl carbonate under normal pressure CO2, and has higher cyclic propylene ester yield and dimethyl carbonate yield.

Description

Technical Field

[0001] This invention relates to an in-situ self-assembly of ionic liquids in covalent organic framework catalysts, their preparation methods and applications, particularly in the stepwise coupled preparation of dimethyl carbonate using a one-pot method with atmospheric pressure carbon dioxide. Background Technology

[0002] To address the impact of greenhouse gases on the human environment, the conversion of CO2 into valuable green chemicals has attracted considerable attention in recent years. Industrially, CO2, as a non-toxic, abundant, and inexpensive renewable C1 resource, can replace toxic and harmful raw materials such as phosgene, isocyanates, and carbon monoxide, transforming it into high-value-added chemicals such as methane, methanol, acetic acid, urea, organic carbonates, polycarbonates, and polyurethanes. Organic carbonates can be classified into cyclic carbonates and chain carbonates based on their molecular structure. Cyclic carbonates possess characteristics such as high boiling points, structural stability, and environmental biodegradability, making them widely used in lithium-ion battery electrolytes, pharmaceutical intermediates, and polycarbonate raw materials. Chain carbonates, due to their superior physicochemical properties compared to cyclic carbonates, have a wider range of applications. For example, dimethyl carbonate (DMC) is suitable for use as a food flavoring agent, fuel additive, and low-temperature electrolyte, demonstrating significant development potential from both environmental and energy perspectives. However, the CO2 coupling reaction route requires the effective series connection of CO2 cycloaddition and CH3OH transesterification reactions, thus placing higher demands on the design of the catalytic system. Overcoming the high thermodynamic stability and kinetic inertia of CO2 often requires harsh reaction conditions such as high temperature and high pressure. Therefore, a key issue is how to capture and convert CO2 under mild conditions. To date, many homogeneous and heterogeneous catalysts have been developed for the production of dimethyl carbonate from CO2, such as ionic liquids, polyionic liquids, metal halides, metal oxides, organic amine liquid bases, metal-organic frameworks, and covalent organic frameworks. However, most reported catalysts require stringent reaction conditions. For example, adding homogeneous co-catalysts such as tetrabutylammonium halide (TBAX, X = Br, Cl, I) or metal sites to the system to synergistically catalyze the conversion of CO2 inevitably increases costs.

[0003] Ionic liquids (ILs) are salts composed of organic cations and organic or inorganic anions. They are molten salts that exist in a liquid state below 100 °C. As "green solvents," ILs possess structural designability, strong solubility, and good chemical and thermal stability. They have been widely used and researched in surface processing, microelectronic device development, fine chemical processing, and new materials research, and have shown significant advantages in the CO2-to-carbonate conversion reaction. However, in reaction systems, the difficulty in separating ILs as homogeneous catalysts can lead to catalyst decomposition or byproduct formation. Therefore, easy catalyst separation in reaction systems is also a significant advantage. Covalent organic frameworks (COFs) possess numerous advantages, including the designability of organic monomers, the order and regularity of crystalline materials, and the diversity of covalent bond forms. Furthermore, compared to other porous materials, COFs have advantages such as low density, high porosity, large specific surface area, good stability, ease of modification, and functionalization. Most importantly, some COFs can be reused continuously while maintaining good CO2 capture performance, thus holding promise for practical applications in CO2 adsorption and conversion. Using COFs as supports for ILs can overcome the challenge of complex modification of basic active sites in COFs. Therefore, the functionalization design and structural framework modification of covalent organic framework materials using ionic liquids to effectively construct basic functional sites is imperative. Ionic liquids are used to prepare ILs-COFs composites via physical impregnation; however, ionic liquids are prone to leaching from the host COF, leading to decreased catalyst activity and poor stability. Furthermore, the organic connection of ILs before or after COF synthesis often requires complex synthetic steps or makes it difficult to prepare active groups. Therefore, the preparation of ILs-COFs composite catalysts remains a significant challenge. To address this, a simple method is proposed to develop ILs-COFs composite catalysts that exhibit both good catalytic activity and stability. Summary of the Invention

[0004] The purpose of this invention is to improve upon the problems and deficiencies of the prior art by providing a catalyst in which a basic ionic liquid is self-assembled in situ within a triazole covalent organic framework. Another purpose of this invention is to provide a method for preparing the above-mentioned catalyst. A further purpose of this invention is to provide applications of the above-mentioned catalyst.

[0005] The technical solution of this invention is: a catalyst in which an ionic liquid is in situ self-assembled within a covalent organic framework, characterized in that a basic choline ionic liquid is encapsulated within a triazole covalent organic framework using an in-situ self-assembly method, and the specific surface area of ​​the catalyst is 150~230 m² / g; wherein, the basic choline ionic liquid [ChH + ][ -O2MVIm + ][OH - The structures of the triazole covalent organic framework are shown in Formulas 1 and 2, respectively;

[0006]

[0007] Formula 1 Alkaline choline ionic liquid [ChH] + ][ - O2MVIm + ][OH - Structural diagram

[0008]

[0009] Formula 2. Triazolyl covalent organic framework structure diagram.

[0010] The present invention also provides a method for preparing the above-mentioned catalyst, the specific steps of which are as follows:

[0011] (1) Ionic liquids [ChH] + ][ - O2MVIm + ][OH - Preparation of [ChH]: Bromoacetic acid and N-vinylimidazole were dissolved in an organic solution, heated to react, cooled, and then alkali solution and choline chloride were added. The mixture was reacted, washed, and dried to obtain [ChH]. + ][ - O2MVIm + ][OH - ];

[0012] (2) Preparation of catalysts for in-situ self-assembly of ionic liquids in covalent organic frameworks: 1,3,5-tricarboxymethyl phloroglucinol, 3,5-diamino-1,2,4-triazole and [ChH + ][ - O2MVIm + ][OH - The ionic liquid was dissolved in a mixed solution, sonicated, frozen, thawed, degassed, heated to react, washed, and dried to obtain a catalyst in situ self-assembled in a covalent organic framework; wherein the mixed solution was a mixture of 1,4-dioxane, dimethylacetamide, acetic acid solution, and mesitylene in a volume ratio of (2.5~3.2):1:(0.5~1.5):(2.5~3.5), and the concentration of the acetic acid solution was 3~12 M;

[0013] In step (1), the preferred mass ratio of N-vinylimidazolium, bromoacetic acid, choline chloride and alkaline solution is 1:(1.3~1.5):(1.3~1.5):(0.8~1.5).

[0014] In preferred step (1), the organic solution is ethanol or acetonitrile; the alkaline solution is KOH or NaOH; the heating temperature is 70~90 ℃ and the heating time is 20~30 h.

[0015] In preferred step (2), 1,3,5-tricarboxymethyl phloroglucinol, 3,5-diamino-1,2,4-triazole and [ChH] + ][ - O2MVIm + ][OH - The mass ratio of the reactants is (5.5~6.5):3:(1~10); the temperature for heating the reaction is 110~140 ℃, and the reaction time is 2~4 days.

[0016] The application of the catalyst described in this invention in the stepwise coupled one-pot process of catalytic atmospheric pressure carbon dioxide to prepare dimethyl carbonate is as follows: the catalyst prepared above and propylene oxide are added sequentially to the reactor. After replacing the air in the reactor with CO2, the reactor is pressurized and heated to the reaction temperature to start the reaction. After the reaction is completed, the reactor is rapidly cooled and the gas is exhausted. Methanol is added to the system, and the reactor is heated to the reaction temperature to start the reaction. After the reaction is completed, the catalyst is separated by centrifugation.

[0017] During the CO2 addition process, the mass ratio of catalyst to propylene oxide is 1:(12~16), the reaction temperature is 80~90℃, the reaction time is 8~12 h, and the carbon dioxide pressure is 0.08~0.13 MPa; the mass ratio of propylene oxide to methanol is 1:(8~11); after adding methanol, the reaction temperature is 140~150 ℃, and the reaction time is 2~3 h.

[0018] Beneficial effects:

[0019] (1) The method for synthesizing catalysts in situ self-assembled ionic liquids in covalent organic frameworks provided by the present invention is simple, convenient to operate, and has mild conditions. The method for preparing porous nanowire materials with abundant basic sites has the advantages of specific surface area of ​​150~230 m² / g, rich pore structure, and the catalyst can be recycled and used 3~7 times.

[0020] (2) The catalyst provided by the present invention is a heterogeneous composite catalyst of covalent organic framework material modified with ionic liquid. Compared with existing catalysts, it does not require a co-catalyst such as TBAB, which reduces production costs, is easy to recycle, and is more conducive to industrial production.

[0021] (3) The catalyst provided by the present invention is used for one-pot stepwise coupling of CO2 under normal pressure to prepare dimethyl carbonate, with a high yield of cyclic propylene ester of 43.1% and a yield of dimethyl carbonate of 56.7%, which is better than the reaction conditions reported in the existing literature. Attached Figure Description

[0022] Figure 1 The images show the FT-IR spectra of the catalyst prepared in Example 1 and the TT-COF and corresponding monomers prepared in Comparative Example 1.

[0023] Figure 2 This is a SEM image of the catalyst prepared in Example 1.

[0024] Figure 3 The attached diagram shows the N2 adsorption-desorption process of the catalyst prepared in Example 1.

[0025] Figure 4 This is a thermogravimetric diagram of the catalyst prepared in Example 1.

[0026] Figure 5 These are catalytic performance graphs of the catalysts prepared in Examples 1-5.

[0027] Figure 6 The catalyst prepared in Example 1 and the TT-COF prepared in Comparative Example 1, [ChH + ][ - O2MVIm + ][OH - ] and [ChH + ][ - O2MVIm + ][OH - Catalytic performance diagram of ]+TT-COF. Detailed Implementation

[0028] The present invention will now be described in more detail using comparative examples and embodiments. These comparative examples and embodiments are merely descriptions of the best comparative and implementation methods of the present invention and do not limit the scope of protection of the present invention in any way.

[0029] Example 1

[0030] Step 1: In a flask, 283 mg of N-vinylimidazole was dissolved in 10 mL of ethanol, and 420 mg of bromoacetic acid was added. The mixture was reacted at 80 °C for 24 h under N2 protection. After cooling, 400 mg of KOH aqueous solution and 420 mg of choline chloride were added, and the reaction was allowed to proceed at room temperature. The mixture was washed several times with ethyl acetate and dried under vacuum at 60 °C for 24 h to obtain the ionic liquid [ChH]. + ][ - O2MVIm + ][OH - ].

[0031] Step 2: In a Pyrex tube, sequentially add 30 mg of 1,3,5-tricarboxymethyl phloroglucinol, 15 mg of 3,5-diamino-1,2,4-triazole, and 10 mg of [ChH] + ][- O2MVIm + ][OH - The catalyst was dissolved in a mixed solvent (2.66 mL, 1,4-dioxane / dimethylacetamide / 6M acetic acid / trimethylbenzene = 3 / 1 / 1 / 3, volume ratio), sonicated for 30 min, frozen at 77 K, thawed, degassed, and subjected to three cycles. Afterward, the catalyst was sealed and reacted at 120 °C for 4 days. After the reaction was completed and cooled to room temperature, the catalyst was washed sequentially with DMF, methanol, and acetone, and then dried under vacuum at 80 °C overnight to obtain the catalyst.

[0032] FT-IR characterization of catalysts, such as Figure 1 As shown in the FT-IR plots, the contractile vibrations of C=C, C=N, and CN are at 1598 cm⁻¹. -1 1400 cm -1 1241 cm -1 The appearance of [ChH] indicates successful synthesis. Simultaneously, [ChH] + ][ - O2MVIm + ][OH - The incorporation of [ ] does not cause structural changes in COF. SEM characterization of the catalyst is as follows: Figure 2 As shown in the figure, SEM images reveal that the prepared catalyst exhibits a uniform nanowire structure. N2 adsorption-desorption experiments are also performed as follows: Figure 3 As shown, the catalyst has a specific surface area of ​​170.2614 m² / g and exhibits a type II isotherm curve. Under higher pressures, the adsorption capacity for nitrogen increases significantly, making it a typical mesoporous material. Figure 4 Thermogravimetric analysis (TGA) curves demonstrate the thermal stability of the catalyst. The initial mass reduction up to 150 °C is due to the evaporation and removal of moisture and organic solvents. The mass decrease in the 170–270 °C range is attributed to [ChH]. + ][ - O2MVIm + ][OH - The catalyst begins to collapse and decompose at 310 °C.

[0033] 580 mg of propylene oxide and 45 mg of catalyst were weighed sequentially and added to a high-pressure reactor. The air inside the reactor was replaced three times with carbon dioxide. Carbon dioxide was then introduced into the reactor until the pressure reached 0.1 MPa. The stirring speed was adjusted to 300 r / min, and the temperature was raised to the reaction temperature of 80 °C to initiate the reaction. The reaction was allowed to proceed for 10 h. After the reaction was completed, the system was rapidly cooled. 4.8 g of methanol was added to the system, and the temperature was raised to the reaction temperature of 140 °C. The reaction was allowed to proceed for 2 h. After the reaction was completed, the catalyst was separated by centrifugation. Gas chromatography analysis of the resulting liquid showed a cyclic propylene ester yield of 43.1% with a selectivity of 99%, and a dimethyl carbonate selectivity of 99% with a dimethyl carbonate yield of 56.7%.

[0034] Comparative Example 1

[0035] Step 1: In a flask, 283 mg of N-vinylimidazole was dissolved in 10 mL of acetonitrile, and 396 mg of bromoacetic acid was added. The reaction was carried out at 80 °C for 24 h under N2 protection. After cooling, 393 mg of KOH and 400 mg of choline chloride were added, and the reaction was carried out at room temperature. The mixture was washed several times with ethyl acetate and dried under vacuum at 60 °C for 24 h to obtain the ionic liquid [ChH]. + ][ - O2MVIm + ][OH - ].

[0036] Step 2: The preparation method of TT-COF is consistent with that in the published paper (XUE Q, WANG P, CHENG L, et al. Triazole-based COF tightly hugging ionic liquids through interactions of hydrogen bonds for enhanced atmospheric CO2 conversion [J]. Sep PurifTechnol, 2025, 352.).

[0037] Step 3: In a mortar, combine 30 mg of TT-COF and 10 mg of [ChH] in sequence. + ][ - O2MVIm + ][OH - Add the mixture and grind it together until completely homogeneous to obtain a physically mixed TT-COF+IL.

[0038] FT-IR characterization of TT-COF catalyst as follows Figure 1As shown in the FT-IR spectrum of TT-COF, the characteristic peaks of the monomers required for TT-COF synthesis have disappeared, and the contraction vibrations of the synthesized C=C, C=N, and CN are at 1598 cm⁻¹. -1 1400 cm -1 and 1241cm -1 The appearance of COF indicates its successful synthesis.

[0039] Dimethyl carbonate was prepared by a one-pot, stepwise coupled process using catalyst-catalyzed atmospheric pressure carbon dioxide.

[0040] Weigh out 567 mg of propylene oxide and 43 mg of catalyst (to test [ChH] separately). + ][ - O2MVIm + ][OH - [ ], TT-COF and TT-COF+IL), were added to a high-pressure reactor. The air in the reactor was replaced with carbon dioxide three times. Carbon dioxide was then introduced into the reactor until the pressure reached 0.12 MPa. The stirring speed was adjusted to 300 r / min, and the temperature was raised to the reaction temperature of 81 ℃ to start the reaction. The reaction was carried out for 11 h. After the reaction was completed, the system was rapidly cooled. 4.85 g of methanol was added to the system, and the temperature was raised to the reaction temperature of 142 ℃. The reaction was carried out for 2.2 h. After the reaction was completed, the catalyst was separated by centrifugation. The liquid obtained from the reaction was analyzed by gas chromatography. [ChH + ][ - O2MVIm + ][OH - Catalytic results: cyclic propylene ester yield was 61.6%, cyclic propylene ester selectivity was 99%, dimethyl carbonate selectivity was 99%, and dimethyl carbonate yield was 37.9%; TT-COF catalytic results: cyclic propylene ester yield was 58.9%, cyclic propylene ester selectivity was 99%, dimethyl carbonate selectivity was 30.4%, and dimethyl carbonate yield was trace; TT-COF+IL catalytic results: cyclic propylene ester yield was 64.2%, cyclic propylene ester selectivity was 99%, dimethyl carbonate selectivity was 99%, and dimethyl carbonate yield was 34.9%.

[0041] The catalyst prepared in Example 1 and the TT-COF prepared in Comparative Example 1, [ChH + ][ - O2MVIm + ][OH - ] and [ChH + ][ - O2MVIm + ][OH - The catalytic performance of ]+TT-COF is shown in the figure below. Figure 6 As shown.

[0042] Example 2

[0043] Step 1: In a flask, 280 mg of N-vinylimidazolium was dissolved in 10 mL of acetonitrile, and 410 mg of bromoacetic acid was added. The mixture was reacted at 70 °C for 24 h under N2 protection. After cooling, 420 mg of KOH and 405 mg of choline chloride were added, and the mixture was reacted at room temperature for 12 h. The mixture was washed several times with ethyl acetate and dried under vacuum at 60 °C for 24 h to obtain the ionic liquid [ChH]. + ][ - O2MVIm + ][OH - ].

[0044] Step 2: In a Pyrex tube, sequentially add 32 mg of 1,3,5-tricarboxymethyl phloroglucinol, 15 mg of 3,5-diamino-1,2,4-triazole, and 5 mg of [ChH] + ][ - O2MVIm + ][OH - The catalyst was dissolved in a mixed solvent (2.66 mL, 1,4-dioxane / dimethylacetamide / 12M acetic acid / trimethylbenzene = 3.2 / 1 / 0.6 / 3.2, volume ratio), sonicated for 30 min, frozen at 77 K, thawed, degassed, and subjected to three cycles. Afterward, the catalyst was sealed and reacted at 130 °C for 4 days. After the reaction was completed and cooled to room temperature, the catalyst was washed sequentially with DMF, methanol, and acetone, and then dried under vacuum overnight at 80 °C to obtain the catalyst.

[0045] Dimethyl carbonate was prepared in a one-pot stepwise coupling process using a catalyst to catalyze the production of carbon dioxide at atmospheric pressure.

[0046] 580 mg of propylene oxide and 45 mg of catalyst were weighed sequentially and added to a high-pressure reactor. The air inside the reactor was replaced three times with carbon dioxide. Carbon dioxide was then introduced into the reactor until the pressure reached 0.13 MPa. The stirring speed was adjusted to 300 r / min, and the temperature was raised to the reaction temperature of 80 °C to initiate the reaction. The reaction was allowed to proceed for 10 h. After the reaction was completed, the system was rapidly cooled. 4.81 g of methanol was added to the system, and the temperature was raised to the reaction temperature of 145 °C. The reaction was allowed to proceed for 2.1 h. After the reaction was completed, the catalyst was separated by centrifugation. Gas chromatography analysis of the resulting liquid showed a cyclic propylene ester yield of 61.1% with a selectivity of 99%, and a dimethyl carbonate selectivity of 99% with a dimethyl carbonate yield of 39.7%.

[0047] Example 3

[0048] Step 1: In a flask, 290 mg of N-vinylimidazole was dissolved in 10 mL of ethanol, and 380 mg of bromoacetic acid was added. The mixture was reacted at 75 °C for 30 h under N2 protection. After cooling, 435 mg of NaOH and 406 mg of choline chloride were added, and the reaction was allowed to proceed at room temperature. The mixture was washed several times with ethyl acetate and dried under vacuum at 60 °C for 24 h to obtain the ionic liquid [ChH]. + ][ - O2MVIm + ][OH - ].

[0049] Step 2: In a Pyrex tube, sequentially add 33 mg of 1,3,5-tricarboxymethyl phloroglucinol, 17 mg of 3,5-diamino-1,2,4-triazole, and 15 mg of [ChH] + ][ - O2MVIm + ][OH - The catalyst was dissolved in a mixed solvent (2.0 mL, 1,4-dioxane / dimethylacetamide / 6M acetic acid / trimethylbenzene = 2.5 / 1 / 1 / 2.5, volume ratio), sonicated for 30 min, frozen at 77 K, thawed, degassed, and subjected to three cycles. Afterward, the catalyst was sealed and reacted at 120 °C for 3 days. After the reaction was completed and cooled to room temperature, the catalyst was washed sequentially with DMF, methanol, and acetone, and then dried under vacuum at 80 °C overnight to obtain the catalyst.

[0050] Dimethyl carbonate was prepared by a one-pot, stepwise coupled process using catalyst-catalyzed atmospheric pressure carbon dioxide.

[0051] 581 mg of propylene oxide and 40 mg of catalyst were weighed sequentially and added to a high-pressure reactor. The air inside the reactor was replaced three times with carbon dioxide. Carbon dioxide was then introduced into the reactor until the pressure reached 0.09 MPa. The stirring speed was adjusted to 300 r / min, and the temperature was raised to the reaction temperature of 80 °C to initiate the reaction. The reaction was carried out for 12 h. After the reaction was completed, the system was rapidly cooled. 4850 mg of methanol was added to the system, and the temperature was raised to the reaction temperature of 140 °C. The reaction was carried out for 2.5 h. After the reaction was completed, the catalyst was separated by centrifugation. Gas chromatography analysis of the resulting liquid showed a cyclic propylene ester yield of 48.2% and a cyclic propylene ester selectivity of 99%, as well as a dimethyl carbonate selectivity of 99% and a dimethyl carbonate yield of 51.2%.

[0052] Example 4

[0053] Step 1: In a flask, 290 mg of N-vinylimidazole was dissolved in 10 mL of ethanol, and 435 mg of bromoacetic acid was added. The mixture was reacted at 85 °C for 30 h under N2 protection. After cooling, 310 mg of NaOH and 435 mg of choline chloride were added, and the reaction was allowed to proceed at room temperature. The mixture was washed several times with ethyl acetate and dried under vacuum at 60 °C for 24 h to obtain the ionic liquid [ChH]. + ][ - O2MVIm + ][OH - ].

[0054] Step 2: In a Pyrex tube, sequentially add 40 mg of 1,3,5-tricarboxymethyl phloroglucinol, 20 mg of 3,5-diamino-1,2,4-triazole, and 32 mg of [ChH] + ][ - O2MVIm + ][OH - The catalyst was dissolved in a mixed solvent (2.83 mL, 1,4-dioxane / dimethylacetamide / 3M acetic acid / trimethylbenzene = 3 / 1 / 1.5 / 3, volume ratio), sonicated for 30 min, frozen at 77 K, thawed, degassed, and subjected to three cycles. Afterward, the catalyst was sealed and reacted at 120 °C for 4 days. After the reaction was completed and cooled to room temperature, the catalyst was washed sequentially with DMF, methanol, and acetone, and then dried under vacuum at 80 °C overnight to obtain the catalyst.

[0055] Dimethyl carbonate was prepared by a one-pot, stepwise coupled process using catalyst-catalyzed atmospheric pressure carbon dioxide.

[0056] 590 mg of propylene oxide and 48 mg of catalyst were weighed sequentially and added to a high-pressure reactor. The air inside the reactor was replaced three times with carbon dioxide. Carbon dioxide was then introduced into the reactor until the pressure reached 0.11 MPa. The stirring speed was adjusted to 300 r / min, and the temperature was raised to the reaction temperature of 80 °C to initiate the reaction. The reaction was allowed to proceed for 10 h. After the reaction was completed, the system was rapidly cooled. 4.806 g of methanol was added to the system, and the temperature was raised to the reaction temperature of 140 °C. The reaction was allowed to proceed for 2 h. After the reaction was completed, the catalyst was separated by centrifugation. Gas chromatography analysis of the resulting liquid showed a cyclic propylene ester yield of 48.6% with a selectivity of 99%, and a dimethyl carbonate selectivity of 99% with a dimethyl carbonate yield of 51.3%.

[0057] Example 5

[0058] Step 1: In a flask, 285 mg of N-vinylimidazole was dissolved in 10 mL of acetonitrile, and 375 mg of bromoacetic acid was added. The mixture was reacted at 70 °C for 24 h under N2 protection. After cooling, 390 mg of KOH and 380 mg of choline chloride were added, and the mixture was reacted at room temperature for 12 h. The mixture was washed several times with ethyl acetate and dried under vacuum at 60 °C for 24 h to obtain the ionic liquid [ChH]. + ][ - O2MVIm + ][OH - ].

[0059] Step 2: In a Pyrex tube, sequentially add 32 mg of 1,3,5-tricarboxymethyl phloroglucinol, 15 mg of 3,5-diamino-1,2,4-triazole, and 50 mg of [ChH] + ][ - O2MVIm + ][OH - The catalyst was dissolved in a mixed solvent (2.66 mL, 1,4-dioxane / dimethylacetamide / 6M acetic acid / trimethylbenzene = 3 / 1 / 1 / 3, volume ratio), sonicated for 30 min, frozen at 77 K, thawed, degassed, and subjected to three cycles. Afterward, the catalyst was sealed and reacted at 120 °C for 3 days. After the reaction was completed and cooled to room temperature, the catalyst was washed sequentially with DMF, methanol, and acetone, and then dried under vacuum at 80 °C overnight to obtain the catalyst.

[0060] Dimethyl carbonate was prepared by a one-pot, stepwise coupled process using catalyst-catalyzed atmospheric pressure carbon dioxide.

[0061] 575 mg of propylene oxide and 45 mg of catalyst were weighed sequentially and added to a high-pressure reactor. The air inside the reactor was replaced three times with carbon dioxide. Carbon dioxide was then introduced into the reactor until the pressure reached 0.12 MPa. The stirring speed was adjusted to 300 r / min, and the temperature was raised to the reaction temperature of 85 °C to start the reaction. The reaction was carried out for 10 h. After the reaction was completed, the system was rapidly cooled. 5.75 g of methanol was added to the system, and the temperature was raised to the reaction temperature of 150 °C. The reaction was carried out for 2 h. After the reaction was completed, the catalyst was separated by centrifugation. Gas chromatography analysis of the resulting liquid showed that the yield of cyclic propylene ester was 46.9%, the selectivity of cyclic propylene ester was 99%, the selectivity of dimethyl carbonate was 99%, and the yield of dimethyl carbonate was 52.8%.

[0062] The catalytic performance of the catalysts prepared in Examples 1-5 above is shown in the figure. Figure 5 As shown.

[0063] The experimental results of the catalysts prepared in Examples 1-5 in the stepwise coupled one-pot preparation of dimethyl carbonate using atmospheric pressure carbon dioxide are shown in Table 1.

[0064] Table 1. Results of the application experiment

[0065]

Claims

1. A catalyst in which an ionic liquid self-assembles in situ within a covalent organic framework, characterized in that... A basic choline ionic liquid was encapsulated within a triazole covalent organic framework using an in-situ self-assembly method, resulting in a catalyst with a specific surface area of ​​150–230 m² / g; wherein the basic choline ionic liquid [ChH]... + ][ - O2MVIm + ][OH - The structures of the triazole covalent organic framework are shown in Formulas 1 and 2, respectively; Formula 1 Alkaline choline ionic liquid [ChH] + ][ - O2MVIm + ][OH - Structural diagram Formula 2. Triazolyl covalent organic framework structure diagram.

2. A method for preparing the catalyst as described in claim 1, comprising the following specific steps: (1) Ionic liquids [ChH] + ][ - O2MVIm + ][OH - Preparation of [ChH]: Bromoacetic acid and N-vinylimidazole were dissolved in an organic solution, heated to react, cooled, and then alkali solution and choline chloride were added. The mixture was reacted, washed, and dried to obtain [ChH]. + ][ - O2MVIm + ][OH - ]; (2) Preparation of catalysts for in-situ self-assembly of ionic liquids in covalent organic frameworks: 1,3,5-tricarboxymethyl phloroglucinol, 3,5-diamino-1,2,4-triazole and [ChH + ][ - O2MVIm + ][OH - The catalyst is dissolved in a mixed solution, sonicated, frozen, thawed, degassed, heated to react, washed, and dried to obtain an ionic liquid catalyst that is self-assembled in situ on a covalent organic framework; wherein the mixed solution is a mixture of 1,4-dioxane, dimethylacetamide, acetic acid solution, and mesitylene in a volume ratio of (2.5~3.2):1:(0.5~1.5):(2.5~3.5), wherein the concentration of the acetic acid solution is 3~12 M.

3. The method according to claim 2, characterized in that, In step (1), the mass ratio of N-vinylimidazole, bromoacetic acid, choline chloride and alkaline solution is 1:(1.3~1.5):(1.3~1.5):(0.8~1.5).

4. The method according to claim 2, characterized in that, In step (1), the organic solution is ethanol or acetonitrile; the alkaline solution is KOH or NaOH; the heating temperature is 70~90 ℃, and the heating time is 20~30 h.

5. The method according to claim 2, characterized in that... In step (2), 1,3,5-tricarboxymethyl phloroglucinol, 3,5-diamino-1,2,4-triazole and [ChH + ][ - O2MVIm + ][OH - The mass ratio of the reactants is (5.5~6.5):3:(1~10); the temperature for heating the reaction is 110~140 ℃, and the reaction time is 2~4 days.

6. The application of the catalyst as described in claim 1 in the stepwise coupled one-pot preparation of dimethyl carbonate using atmospheric pressure carbon dioxide is as follows: the catalyst prepared above and propylene oxide are added sequentially to the reactor. After replacing the air in the reactor with CO2, the reactor is pressurized and heated to the reaction temperature to start the reaction. After the reaction is completed, the reactor is rapidly cooled and the exhaust is vented. Methanol is added to the system, and the reactor is heated to the reaction temperature to start the reaction. After the reaction is completed, the catalyst is separated by centrifugation.

7. The application according to claim 6, characterized in that: During the CO2 addition process, the mass ratio of catalyst to propylene oxide is 1:(12~16), the reaction temperature is 80~90 ℃, the reaction time is 8~12 h, and the carbon dioxide pressure is 0.08~0.13 MPa; the mass ratio of propylene oxide to methanol is 1:(8~11); after adding methanol, the reaction temperature is 140~150 ℃, and the reaction time is 2~3 h.

Images