A heterogeneous catalyst, a method of preparation and its use for catalyzing carbon dioxide conversion

Abstract

The application provides a kind of heterogeneous catalyst, preparation method and its method for catalyzing carbon dioxide conversion, belong to the technical field of catalyst containing organic complex.The heterogeneous catalyst is recorded as TAPPM-PTBAR n It is bifunctional metal porphyrin / quaternary phosphonium salt ionic liquid containing Lewis acid metal site and halide ion, wherein M is Co 3+ , Co 2+ , Mn, Zn, X is halogen, R n (CH2)2H, (CH2)4H, (CH2)6H, (CH2)2OH, CH2COOH, (CH2)2N H2Any one of.The present heterogeneous catalyst contains double active centers with synergistic effect between each other, and has the advantages of good universality, high selectivity and high conversion rate when used in the coupling reaction of epoxy substrate and carbon dioxide.

Description

Technical Field

[0001] This application relates to a heterogeneous catalyst, its preparation method, and its application in catalytic carbon dioxide conversion, belonging to the field of catalyst technology containing organic complexes. Background Technology

[0002] The rapid increase in atmospheric carbon dioxide levels is a major cause of global climate change. Given that carbon dioxide is widely distributed in nature, abundant, and inexpensive (C1) resources, and is also a major greenhouse gas in the atmosphere, reducing atmospheric CO2 levels is urgently needed. Utilizing simple organic solvents to react with CO2 to convert it into high-value-added chemicals is one of the most promising methods currently under research. The formation of cyclic carbonates from CO2 and epoxides is a highly attractive 100% atom-economic reaction. It represents a more environmentally friendly and safer alternative to the traditional synthesis of cyclic carbonates from glycols and toxic phosgene.

[0003] Polymers, due to their tunable composition, are often used as a platform for synthesizing bifunctional catalysts for CO2 cycloaddition reactions. Synthetic methods for bifunctional polymers used in CO2 cycloaddition reactions mainly include: forming ionic polymers from porphyrin / pyridine / imidazolium-functionalized metal complexes and bromides; polymerization of two different types of monomers containing Lewis acids and nucleophilic sites; and post-modification of polymers with Lewis acid / nucleophilic sites. Metalloporphyrin polymers are frequently used for CO2 cycloaddition reactions at Lewis acid sites.

[0004] Today, cyclic carbonates have found numerous applications as intermediates in fine chemical synthesis, electrolytes and polar aprotic solvents in lithium-ion batteries, and in the synthesis of important polymers such as polycarbonates and polyurethanes. Considering the thermodynamic stability and kinetic inertness of CO2, it is essential to design and develop advanced catalysts to facilitate its conversion into other high-value-added chemicals under mild conditions. Although the preparation of cyclic carbonates on homogeneous catalysts such as tetrabutylammonium bromide (TBAB) and potassium iodide (KI) has been industrialized, the reaction process requires high temperatures (T>200℃) and carbon dioxide pressures (P>6.0MPa). Furthermore, the limited availability of raw materials and the cumbersome operation of the catalysts are unavoidable challenges. Summary of the Invention

[0005] In view of this, this application first provides a heterogeneous catalyst having a highly cross-linked polymer backbone, abundant Lewis acid metal centers and nucleophilic active sites, and phosphonium-containing functional cations, which endow the synthetic catalyst with the expected ability to fix carbon dioxide under mild, solvent-free catalytic conditions.

[0006] Specifically, this application is implemented through the following scheme: A heterogeneous catalyst is a bifunctional metalporphyrin / quaternary phosphonium salt ionic liquid containing Lewis acid metal sites and halide ions, with the following structural formula: , denoted as TAPPM-PTBAR n Where: M is Co 3+ Co 2+ Any one of Mn, Zn, where X is a halogen and R is a halogen. n It can be any one of (CH2)2H, (CH2)4H, (CH2)6H, (CH2)2OH, CH2COOH, or (CH2)2NH2. The optimal configuration is when X is Br and M is Co3+ / Co2+.

[0007] Meanwhile, the applicant's second objective is to provide a method for preparing the aforementioned heterogeneous catalyst, the steps of which are as follows: Step 1: Using tetraaminophenylporphyrin (TAPP) and tris(4-benzaldehyde)phosphine (PTBA) as raw materials, tetraaminophenylporphyrin is dissolved in anhydrous DMF, acetic acid and tris(4-benzaldehyde)phosphine are added under N2, and the reaction is stirred to obtain TAPP-PTBA.

[0008] Step 2, mix TAPP-PTBA and hydrogen halide ammonium salt XR n After being added to DMF and stirred under vacuum with N2, the mixture was cooled to room temperature and filtered to obtain a solid. The solid was dispersed in triethylamine and stirred, then filtered, washed several times with ethyl acetate, and dried under vacuum overnight to obtain the porphyrin / quaternary phosphonium salt ionic liquid TAPP-PTBAR. n .

[0009] Step 3: Apply the porphyrin / quaternary phosphonium salt ionic liquid TAPP-PTBAR n Dispersed in DMF, vacuumed and charged with N2, MCl added under N2 atmosphere x The reaction mixture was stirred overnight in an nH₂O solution. After cooling to room temperature, HCl was added and the reaction was stirred again. The mixture was then filtered, washed three times, and dried under vacuum to obtain the finished metal porphyrin / quaternary phosphonium salt heterogeneous catalyst TAPPM-PTBAR. n .

[0010] The heterogeneous catalyst formed by the above scheme contains both a metal center and a nucleophile center, and there is a synergistic effect between the two active centers, which makes it have very high catalytic activity.

[0011] Furthermore, as a preferred option: In step one, 4-nitrobenzaldehyde and pyrrole are used as raw materials. The raw materials are added to acetic anhydride and refluxed. The precipitate obtained from the reaction is washed, dried under vacuum, dissolved in concentrated hydrochloric acid, and then added to a concentrated hydrochloric acid solution of SnCl2. The reaction is stirred to obtain tetraaminophenylporphyrin.

[0012] In step one, a hexane solution of n-butyllithium was added dropwise to an anhydrous tetrahydrofuran solution of 4-bromobenzaldehyde diethyl acetal. The mixture was stirred at -78℃ to -65℃. Phosphorus trichloride was then added to the mixture and the stirring continued. The mixture was then heated to room temperature, the reaction mixture was quenched with hydrochloric acid aqueous solution, extracted, dried, and column filtered to obtain tris(4-benzaldehyde)phosphine.

[0013] In step two, the hydrogen halide ammonium salt XR n It is the ammonium hydrobromide BrR n .

[0014] In step two, the R n It is any one of (CH2)2H, (CH2)4H, (CH2)6H, (CH2)2OH, CH2COOH, and (CH2)2NH2.

[0015] In step three, the MCI x ·nH2O solution is MCl x DMF solution containing nH2O.

[0016] In step three, the MCI x The nH2O solution is any one of CoCl2·6H2O, ZnCl2, or MnCl2·4H2O.

[0017] The applicant's third objective is to provide the aforementioned heterogeneous catalyst TAPPM-PTBAR. n Applications, namely the heterogeneous catalyst TAPPM-PTBAR n The method applied to catalytic carbon dioxide conversion involves adding the heterogeneous catalyst TAPPM-PTBAR to the reaction system of an epoxy substrate and carbon dioxide under atmospheric pressure, solvent-free, and co-catalyst-free conditions. n After the coupling reaction is completed, the catalyst is filtered to separate, washed, and vacuum dried before proceeding to the next catalytic cycle.

[0018] In the above reaction, the epoxy substrate is Any one of them.

[0019] In the above reaction, metal M acts as a Lewis acid site, and halide anion X acts as a nucleophile. Together, they form a bifunctional active site with a synergistic effect, endowing the heterogeneous catalyst TAPPM-PTBAR with a unique characteristic. nIn coupling reactions, it exhibits superior catalytic performance, demonstrating not only high versatility, applicable to most epoxides with different functional groups, but also high conversion and selectivity. The selectivity of all cyclic carbonate products remains almost constant (>99%), and the conversion rate remains above 60%. The conversion rate of some epoxides can be maintained around 75-95%, and almost no byproducts are observed in this reaction. Attached Figure Description

[0020] Figure 1 The XRD patterns of TAPP, PTBA, and TAPP-PTBA are shown in the example. Figure 2 In the examples, TAPP, PTBA, TAPP-PTBA, TAPP-PTBAR6, and TAPPCo are used. 3+ -Infrared spectrum of PTBAR6; Figure 3 In the examples, TAPP-PTBA, TAPP-PTBAR6, and TAPPCo are used. 3+ -Thermogravimetric analysis spectrum of PTBAR6. Detailed Implementation

[0021] The instruments and reagents used in the following examples are shown in Table 1 and Table 2, respectively.

[0022] Table 1: Summary of instruments used in the embodiments .

[0023] Table 2: Summary of reagents used in the examples .

[0024] Example 1: Preparation of heterogeneous catalyst TAPPM-PTBAR n This embodiment uses the heterogeneous catalyst TAPPCo 3+ Taking PTBAR6 as an example, the structure and preparation method of the heterogeneous catalyst in this case are explained as follows: (1) Preparation of tetraaminophenylporphyrin (TAPP) 4-Nitrobenzaldehyde (11.1235 g, 73.6 mol, 1 eq) was dissolved in propionic acid (300 mL), and acetic anhydride (12 mL) was added. The mixture was heated to 120 °C in a three-necked round-bottom flask. Pyrrole (5.0423 mL, 75.15 mmol, 1 eq) was added dropwise using a syringe. The mixture was refluxed for 1 h, cooled to room temperature, and allowed to stand overnight. The precipitate was obtained by filtration, washed with water and methanol until the filtrate was colorless, and dried under vacuum. The solid was dissolved in pyridine (80 mL), refluxed at 80 °C for 1 h, and the mixture was placed in a refrigerator overnight. The precipitate was collected by filtration, washed three times with acetone, and dried under vacuum to give TNPP (4.7125 g, yield: 32.22%).

[0025] The obtained TNPP (2.0972 g, 2.638 mmol, 1 eq) was dissolved in 200 mL of concentrated HCl. A concentrated HCl solution (250 mL) of SnCl2 (10.6223 g, 56.01 mmol, 20 eq) was added to the reaction system. The solution was heated to 70 °C in a water bath and stirred continuously for 2 h. The hot water bath was removed, and a cold water bath and then an ice water bath were used. The reaction mixture was neutralized with concentrated NaOH to pH 7.0. The filter cake was obtained by filtration and washed twice with water. It was dried under vacuum at room temperature, and extracted with acetone using a Soxhlet extraction for 5 days. The solvent was removed under reduced pressure, and the product was dried under vacuum to obtain TAPP (1.6012 g, yield: 89.8%).

[0026] The above process is described as shown in reaction formula (1).

[0027] (1)

[0028] 1 H NMR (400MHz, DMSO-d6) δ8.90 (pyrrole ring, 4H), 9.90 (-CHO, 1H), 7.59-7.00 (Ar-H, 8H), 5.58 (-NH2, 4H), -2.71 (pyrrole NH, 2H).

[0029] (2) Preparation of tris(4-benzaldehyde)phosphine (PTBA) Under nitrogen protection, a hexane solution of n-butyllithium (10 mL, 2.5 M, 3 eq) was added dropwise to an anhydrous tetrahydrofuran solution of 4-bromobenzaldehyde diethyl acetal (13.22 g, 2.5 mmol, 3 eq) over 40 min. The mixture was stirred for 1 h while maintaining the temperature below -78 °C. Freshly distilled phosphorus trichloride (1.16 g, 0.85 mmol, 1 eq) was added dropwise to anhydrous tetrahydrofuran (10 mL). The mixture was stirred for another 1 h. The system was then heated to room temperature. The mixture was allowed to react overnight. The reaction mixture was quenched with 60 mL of 2N HCl aqueous solution. The mixture was extracted with ethyl acetate and water. The solution was dried over anhydrous sodium sulfate. After filtration, the solution was concentrated under reduced pressure. The crude liquid was hydrolyzed in a THF / 2N HCl solution (120 mL, 1:1, v / v). The mixture was refluxed under nitrogen for 2 h and then cooled to room temperature. The mixture was poured into 60 mL of saturated sodium carbonate solution. Extracted with 150 mL of diethyl ether and dried. The mixture was concentrated. The mixture was purified by column chromatography (ethyl acetate / petroleum ether, 1:3) to give tris(4-benzaldehyde)phosphine (0.923 g, 31.99%).

[0030] The above process is described as shown in reaction formula (2).

[0031] (2)

[0032] 1 H NMR (400MHz, Chloroform-d) δ 10.08 (CHO, 3H), 7.36-8.93 (Ar-H, 8H) ppm.

[0033] (3) Synthesis of porphyrin / quaternary phosphonium salt ionic liquid (TAPP-PTBAR6) TAPP (0.8765 g, 1.298 mmol, 3 eq) was dissolved in anhydrous DMF (20 ml), sonicated for 5 minutes, and one drop of acetic acid was added under N2. Then, PTBA (0.5942 g, 1.715 mmol, 4 eq) was added, and the mixture was stirred at 120 °C for 5 days. After the reaction was complete, the mixture was washed with anhydrous DMF and dichloromethane, and dried under vacuum to obtain TAPP-PTBA (1.3117 g, yield: 89.72%).

[0034] TAPP-PTBA (1.0389 g) and 2-bromoethylamine hydrobromide (0.1029 g) were added to a flask containing DMF (30 ml). The mixture was evacuated and purged with N2 at 100 °C with stirring for 12 h. After cooling to room temperature, the solid was obtained by filtration. The solid was dispersed in triethylamine (40 ml) and stirred at room temperature for 5 h. After stopping the reaction, the mixture was filtered, washed several times with ethyl acetate, and dried under vacuum overnight.

[0035] The product obtained, TAPP-PTBAR6, was a dark purple solid (1.0174 g, yield: 94.92%).

[0036] (4) Metalporphyrin / quaternary phosphonium salt ionic liquid (TAPPCo) 3+ Synthesis of -PTBAR6 TAPP-PTBAR6 (1.0174 g) was dispersed in DMF (20 ml) under vacuum and N2 atmosphere. A solution of CoCl2·6H2O (0.2 g, 0.8405 mmol) (DMF, 10 ml) was added to a round-bottom flask under N2 atmosphere. The mixture was stirred overnight at 100 °C. After cooling to room temperature, it was filtered and washed three times with dichloromethane, then dried under vacuum for 10 h. The resulting product, TAPPCo... 2+ -PTBAR6 is a black solid (1.0798 g, yield: 92.76%).

[0037] The above-mentioned TAPPCo 2+ -PTBAR6 (1.0798 g) sample was added with HCl (30 ml, 2 M) and stirred at room temperature for 5 h. After the reaction was complete, the mixture was filtered, washed with dichloromethane, and dried under vacuum for 10 h. The resulting product, TAPPCo... 3+ -PTBAR6 is a black solid (1.0723 g, yield: 91.56%).

[0038] The above process is described in reaction formula (3).

[0039] (3) The products of the above steps were characterized by NMR, TGA, IR, XRD and other methods.

[0040] (1) X-ray polycrystalline powder diffraction results: The crystal structures of TAPP, PTBA and TAPP-PTBA are as follows Figure 1 As shown, the TAPP-PTBA sample only exhibits a diffuse peak generated by the amorphous SiO2 on the glass slide (background) at 20.5° to 21.7°, while no sharp strong peaks appear at other positions, indicating that TAPP-PTBA has an amorphous structure.

[0041] (2) FT-IR characterization results: The obtained catalyst TAPPCo 3+ The structure of -PTBAR6 was characterized, such as Figure 2 As shown, the precursors TAPP, PTBA, the quaternary phosphonium salt TAPP-PTBAR6, and the metalloporphyrin quaternary phosphine salt TAPPCo were compared. 3+ The structures of compounds such as -PTBAR6 were analyzed by infrared spectroscopy. TAPP-PTBA was obtained by the Schiff base reaction of TAPP and PTBA, and the results were obtained at 1650 cm⁻¹.-1 Peaks formed by strong tensile vibrations of -C=N were observed at 3200–3500 cm⁻¹ and 1680 cm⁻¹. -1 The disappearance of the characteristic NH2 and -C=O stretching vibrations indicates that the reaction has been almost completely completed. The disappearance of the aldehyde vibration peak and the appearance of the imine bond vibration peak prove the successful formation of TAPP-PTBA. TAPP-PTBAR6 and TAPPCo 3+ -PTBAR6 at 3200~3500cm -1 The appearance of a broad peak at the site proves that the phosphonium site has been successfully functionalized.

[0042] (3) Thermogravimetric analysis results: for TAPP-PTBA, TAPP-PTBAR6 and TAPPCo 3+ The thermal stability of -PTBAR6 was studied, and the results are as follows: Figure 3 As shown, within the temperature range of room temperature to 100°C, the weight loss due to the evaporation of absorbed water is approximately <5%. This indicates that under the cycloaddition reaction conditions of this case, TAPPCo... 3+ -PTBAR6 catalyst is stable.

[0043] Example 2: Application Case This embodiment uses the cycloaddition reaction of epichlorohydrin (ECH) with CO2 as a model to study the heterogeneous catalyst TAPPM-PTBAR in this case. n The catalytic performance is as follows: Under solvent-free conditions, a certain amount of the heterogeneous catalyst TAPPM-PTBARn was added to a 25 ml Schlenk tube equipped with a magnetic magnet. A fixed amount of epichlorohydrin (ECH) was then added to the Schlenk tube as the epoxy substrate for the cycloaddition reaction with carbon dioxide. After the reaction, the catalyst was separated by filtration, washed with dichloromethane, and dried under vacuum at 60 °C before proceeding to the next catalytic cycle. The substrate selectivity and conversion were determined by 1H NMR, and the results are shown in Table 3.

[0044] Table 3: Effect of different catalysts on the cycloaddition reaction of CO2 and ECH .

[0045] The highest conversion rate of ECH for the control catalyst was less than 70% (Entries 1–3, Table 3). TAPPCo... 3+-PTBA quaternized different alkyl chain lengths, achieving ECH conversion rates of 75.28%–84.69% (Entries 4–6, Table 3), with a significant increase in conversion rate as the alkyl chain length increased. This is because longer carbon chains in alkyl groups have greater steric hindrance, weakening the electrostatic interaction between halide anions and phosphonium cations. Therefore, it enhances the leaving ability of halide cations, which is beneficial for improving ECH conversion.

[0046] Furthermore, the electron-donating ability of alkyl groups increases with the number of carbon atoms. (TAPPCo...) 3+ After quaternizing different functional chains with -PTBA, the conversion rate of ECH reached 80.17% to 94.89% (Entries 7 to 9, Table 3), indicating that the synergistic effect of the metal center and the multi-active center of the nucleophile is beneficial to catalyzing the cycloaddition reaction of CO2 with epoxide.

[0047] Different metal-coordinated porphyrin / quaternary phosphonium salt bifunctional heterogeneous catalysts also exhibit different catalytic activities (Entries 9-12, Table 3). The stronger the Lewis acidity of the metal, the stronger its catalytic activity.

[0048] Example 3: Universality Experiment of Heterogeneous Catalysts This embodiment investigated the substrate range for the synthesis of various cyclic carbonates using the selected metalloporphyrin / quaternary phosphonium salt bifunctional heterogeneous catalyst under ambient pressure, solvent-free, and co-catalyst-free conditions. The results are shown in Table 4.

[0049] As can be seen from Table 4: TAPPCo 3+ Taking PTBAR6 as an example, using the catalyst in this study for carbon dioxide conversion, most epoxides substituted with different functional groups can be efficiently converted into the corresponding cyclic carbonates with considerable conversion rates and high selectivity. The selectivity of all cyclic carbonate products remains almost constant (>99%), and almost no byproducts are observed in this reaction.

[0050] Table 4: TAPPCo 3+ - The universal applicability of PTBAR6 catalysts .

[0051] In this embodiment, a metalloporphyrin / quaternary phosphine salt ionic liquid (TAPPCo) was prepared via Schiff base reaction and metal coordination. 3+ Cobalt (PTBAR6) can be used as a heterogeneous catalyst for the coupling reaction of CO2 and epoxides, effectively catalyzing most epoxides. The synergistic effect of cobalt as a Lewis acid site and the halide anion as a nucleophile as a bifunctional active site promotes the catalytic reaction.

Claims

1. A heterogeneous catalyst, characterized in that, Its structural formula is: , denoted as TAPPM-PTBAR n Where: M is any one of Co(II), Mn, and Zn, X is a halogen, and R n It is any one of (CH2)2H, (CH2)4H, (CH2)6H, (CH2)2OH, CH2COOH, and (CH2)2NH2.

2. The heterogeneous catalyst according to claim 1, characterized in that: X is Br, and M is Co(II).

3. A method for preparing the heterogeneous catalyst according to claim 1, characterized in that, The steps are as follows: Step 1: Using tetraaminophenylporphyrin and tris(4-benzaldehyde)phosphine as raw materials, tetraaminophenylporphyrin is dissolved in anhydrous DMF. Acetic acid and tris(4-benzaldehyde)phosphine are added under N2, and the reaction is stirred to obtain TAPP-PTBA, whose structural formula is: ; Step 2, mix TAPP-PTBA and ammonium hydrobromide BrR n Added to DMF, the mixture was stirred under vacuum with N2, cooled to room temperature, and filtered to obtain a solid. The solid was dispersed in triethylamine and stirred, then filtered, washed several times with ethyl acetate, and dried under vacuum overnight to obtain TAPP-PTBAR. n Its structural formula is: ; Step 3: Disperse TAPP-PTBARn in DMF, evacuate and fill with N2 atmosphere, then add MCl under N2 atmosphere. x The reaction mixture was stirred overnight in an nH₂O solution. After cooling to room temperature, HCl was added and the reaction was stirred again. The mixture was then filtered, washed three times, and dried under vacuum to obtain the heterogeneous catalyst TAPPM-PTBAR. n The MCI x The nH2O solution is either CoCl2·6H2O or MnCl2·4H2O.

4. The method for preparing a heterogeneous catalyst according to claim 3, characterized in that: In step one, 4-nitrobenzaldehyde and pyrrole are used as raw materials. The raw materials are added to acetic anhydride and refluxed. The precipitate obtained from the reaction is washed, dried under vacuum, dissolved in concentrated hydrochloric acid, and then added to a concentrated hydrochloric acid solution of SnCl2. The reaction is stirred to obtain tetraaminophenylporphyrin.

5. The method for preparing a heterogeneous catalyst according to claim 3, characterized in that: In step one, a hexane solution of n-butyllithium was added dropwise to an anhydrous tetrahydrofuran solution of 4-bromobenzaldehyde diethyl acetal. The mixture was stirred at -78℃ to -65℃. Phosphorus trichloride was then added to the mixture and the stirring continued. The mixture was then heated to room temperature, the reaction mixture was quenched with hydrochloric acid aqueous solution, extracted, dried, and column filtered to obtain tris(4-benzaldehyde)phosphine.

6. A method for applying the heterogeneous catalyst of claim 1 to the catalytic conversion of carbon dioxide, characterized in that: Under normal pressure, solvent-free, and co-catalyst-free conditions, the heterogeneous catalyst TAPPM-PTBAR was added to the reaction system of epoxy substrate and carbon dioxide. n The coupling reaction is carried out. After the reaction is complete, the catalyst is filtered and separated, washed, and vacuum dried before proceeding to the next catalytic cycle. The epoxy substrate is... Any one of them.

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