A highly efficient heterogeneous catalyst for the CO2 cycloaddition to prepare cyclic carbonates, its preparation method and application

Abstract

The application discloses a kind of high-efficiency heterogeneous catalyst for CO2 ring addition preparation cyclic carbonate and its preparation method and application, belong to catalyst technical field.The high-efficiency heterogeneous catalyst is transition metal doped polyoxometalate coordination polymer, chemical general formula is C 16 H 58 M2N2Na2O 48 V 10 Wherein, M is selected from Co 2+ , Ni 2+ , Cu 2+ Or Zn 2+ Its preparation method is: sodium vanadate, transition metal acetate and bis (2-hydroxyethyl) amino (trihydroxymethyl) methane ligand are dissolved in water with pH being 1~3, stirring reaction, after filtration, crystallization is stationary, and is obtained.In the ring addition reaction of CO2 and epoxide, the catalyst and cocatalyst tetrabutylammonium bromide synergistic effect, catalytic yield can be up to 98.2%, selectivity is more than 99%, and catalytic activity still remains at 88% after recycling five times.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and more specifically relates to a highly efficient heterogeneous catalyst for the cycloaddition of CO2 to prepare cyclic carbonates, its preparation method, and its application. Background Technology

[0002] Capturing CO2 efficiently and converting it into high-value resources is an effective means of solving environmental problems. CO2, as an abundant, non-toxic, and renewable C1 resource, can be converted into chemical intermediates such as cyclic carbonates and amides through catalytic technology. However, the thermodynamic stability and kinetic inertness of CO2 hinder its efficient activation. Furthermore, current catalysts, such as quaternary phosphonium salts, quaternary ammonium salts, and ionic liquids, generally suffer from low activity, insufficient stability, and difficulty in recycling. Therefore, designing catalysts that combine high activity, high stability, and recyclability is of great significance.

[0003] Polymetallic vanadates are classic metal clusters that exhibit excellent catalytic activity due to the high redox properties of metal V, making them highly efficient catalysts for CO2 conversion. However, the synthesis of novel vanadium polyacids currently being prepared still suffers from insufficient structural controllability and poor thermal stability. While classic homovanadium vanadates are structurally stable and easy to synthesize, they lack sufficient catalytic active sites. This hinders their application as CO2 catalysts. Therefore, how to increase the number of catalytic active sites while maintaining the structural stability of vanadium polyacids has become a key factor in the synthesis of catalysts capable of catalyzing CO2 conversion.

[0004] One approach is to increase the catalytic sites of vanadium polyacids by adding transition metals. The introduction of transition metals mainly falls into three categories. The first is to introduce them into the polyacid anion structure to form a heteropolyacid anion. While this method yields polyacids with high stability, the transition metal heteroatoms are often surrounded, thus reducing their catalytic activity. The second method involves the transition metal acting as a cation, coordinating with the vanadium polyacid anion. Although this structure exposes the transition metal and enhances its catalytic activity, it is often structurally unstable. The third method involves introducing ligands to form coordination polymers with the transition metal, which then connect to the polyacid anion via electrostatic attraction or chemical bonding. This method preserves the stability of the homopolyvanadate while introducing transition metal active sites. Therefore, the third method is one of the effective means to prepare highly efficient catalysts for CO2 conversion.

[0005] However, there is still a lack of heterogeneous catalysts based on ligand modification strategies that can effectively separate and synergistically catalyze transition metal active centers and vanadium polyacid anions. In particular, there is an urgent need to develop new catalytic materials with better performance for achieving efficient, highly selective and recyclable CO2 cycloaddition reactions under mild conditions.

[0006] Based on this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a highly efficient heterogeneous catalyst for the cycloaddition of CO2 to prepare cyclic carbonates, its preparation method and application, so as to solve the problems existing in the prior art, achieve efficient and highly selective conversion of CO2, and endow the catalyst with excellent stability and recyclability.

[0008] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a highly efficient heterogeneous catalyst for the cycloaddition of CO2 to prepare cyclic carbonates. The highly efficient heterogeneous catalyst is a transition metal-doped polyvanadate coordination polymer with the general chemical formula: C 16 H 58 M2N2Na2O 48 V 10 Where M is selected from Co 2+ Ni 2+ Cu 2+ or Zn 2+ .

[0009] Preferably, the highly efficient heterogeneous catalyst has a triclinic P-1 space group structure, and its asymmetric unit contains a {V} 10 O 28} 6- Anions, two Na+ + Cations, two transition metals M 2+ Ions, two BisTris ligands, and ten coordinated water molecules.

[0010] Preferably, the BisTris ligand is bis(2-hydroxyethyl)amino(tris(hydroxymethyl)methane), which reacts with the transition metal M 2+ The ion coordinates with a coordinated water molecule to form an M-BisTris coordinated cation.

[0011] Preferably, the Na + Cations and from two {V 10 O 28} 6- The terminal oxygen of the anion coordinates with four water molecules to form a one-dimensional chain structure.

[0012] Preferably, the V 10 O 28 6- The anion and the M-BisTris coordinated cation form a three-dimensional network structure through hydrogen bonding interactions.

[0013] The second technical solution of the present invention provides a method for preparing the above-mentioned highly efficient heterogeneous catalyst for the cycloaddition of CO2 to prepare cyclic carbonates, comprising the following steps: Sodium vanadate, transition metal acetate and BisTris ligand were dissolved in water with a pH of 1-3, stirred and reacted, filtered and allowed to stand to crystallize, to obtain the highly efficient heterogeneous catalyst for the preparation of cyclic carbonates by CO2 cycloaddition.

[0014] Preferably, the transition metal acetate is (CH3COO)2Co, Ni(CH3COO)2, Cu(CH3COO)2 or Zn(CH3COO)2.

[0015] Preferably, the reaction time is 6-8 hours; the static crystallization time is 7-14 days.

[0016] The third technical solution of the present invention provides the application of the above-mentioned highly efficient heterogeneous catalyst for the preparation of cyclic carbonates by CO2 cycloaddition in the preparation of cyclic carbonates by CO2 cycloaddition, wherein the highly efficient heterogeneous catalyst and the co-catalyst are used together to catalyze the cycloaddition reaction of epoxides and CO2 to generate cyclic carbonates. The co-catalyst includes tetrabutylammonium bromide; The highly efficient heterogeneous catalyst is recovered by filtration and separation after the cycloaddition reaction is completed, so as to be recycled.

[0017] Preferably, the epoxide comprises epichlorohydrin; the conditions for the cycloaddition reaction are: the molar amount of the high-efficiency heterogeneous catalyst is 0.3% of the molar amount of the epoxide, the molar ratio of the high-efficiency heterogeneous catalyst to the co-catalyst is 0.15:2, the reaction temperature is 50~60℃, the reaction time is 10~12h, and the CO2 pressure is 1 atm.

[0018] The technical mechanism of this invention is as follows: The transition metal-doped polyvanadate coordination polymer catalyst prepared in this invention exhibits a catalytic mechanism for the cycloaddition reaction of CO2 with epoxides, primarily involving a synergistic catalytic effect. Specifically, the catalyst structure contains two key active centers: one is {V 10 O 28} 6- The vanadium (V) center in the polyvanadate anion, and the transition metal (M=Co) in the M-BisTris coordinated cation. 2+ Ni 2+ Cu 2+ or Zn 2+ The vanadium center in the catalyst, along with the transition metal center, interacts with oxygen in the epoxide during the catalytic reaction, altering the electron distribution of oxygen and thus activating the carbon-oxygen bond. Simultaneously, the bromide ions (Br₂) released from the co-catalyst tetrabutylammonium bromide (TBABr)...- The catalyst attacks the less sterically hindered carbon atoms in the epoxide, causing the epoxide to open and form an intermediate. Subsequently, the carbon atoms of CO2 attack the oxygen atoms of the ring-opening intermediate, forming a carbonate intermediate. Finally, the intermediate undergoes an intramolecular cyclization reaction, the bromide ion leaves, and a cyclic carbonate product is generated, allowing the catalyst to be regenerated and enter the next catalytic cycle. Compared with the undoped transition metal compound 1, the synergistic catalytic effect between the vanadium center and the transition metal center in the transition metal-doped polyvanadate coordination polymer catalysts (compounds 2-5) significantly enhances the activation ability of the substrate, thereby greatly improving the catalytic efficiency. In addition, the three-dimensional network structure formed by hydrogen bonding and electrostatic interactions endows the catalyst with excellent heterogeneous catalytic properties and structural stability, allowing it to be separated and recycled through simple filtration.

[0019] The present invention discloses the following technical effects: This invention provides a novel transition metal-doped polyvanadate coordination polymer catalyst. By introducing bis(2-hydroxyethyl)amino(tris(hydroxymethyl)methane) (BisTris) as a multifunctional ligand, a transition metal (Co) catalyst is successfully incorporated. 2+ Ni 2 + Cu 2+ Zn 2+ Introduced as a coordinating cation (M-BisTris) into the classic {V} 10 O 28 In polyvanadate systems, this structural design not only preserves {V} 10 O 28 The stability of anions is further enhanced by the effective separation and exposure of transition metal active centers through ligands, forming a unique "anion-cation" synergistic catalytic system.

[0020] Experiments have shown that this type of catalyst, under mild conditions (50–60 °C, 1 atm CO2), with tetrabutylammonium bromide (TBABr) as a co-catalyst, can efficiently catalyze the cycloaddition reaction of epoxides with CO2 to generate cyclic carbonates, achieving a yield of up to 98.2% and a selectivity exceeding 99%. Compared with similar materials without transition metal doping, its catalytic activity is significantly enhanced, demonstrating that {V 10 O 28 A significant synergistic catalytic effect exists between the vanadium center in the anion and the transition metal center in the M-BisTris cation. Furthermore, this catalyst is a heterogeneous catalyst with excellent structural and thermal stability. It can be separated by simple filtration after reaction, and its catalytic activity remains above 88% after five cycles, demonstrating good recyclability and application prospects. This invention provides a new approach and strategy for designing efficient, stable, and recyclable heterogeneous CO2 conversion catalysts. Attached Figure Description

[0021] Figure 1 Here are schematic diagrams of the structure of compound 1, where (a) is a schematic diagram of the structure of compound 1 along the b-axis, (b) is a schematic diagram of the structure of compound 1 along the BisTris coordination polymer, and (c) is a simplified schematic diagram of the structure of compound 1. Figure 2 This is a schematic diagram of the structure of compound 1, where (a) is an asymmetric unit and (b) is a {V 10 O 28} 6- The anion, (c) is NaH(BisTris) 2+ The one-dimensional structure of the cation, (d) is a protonated BisTris molecule, (e) is {V 10 O 28} 6- Hydrogen bonds with BisTris ligands; Figure 3 This is a schematic diagram of the structure of compound 2, where (a) is a one-dimensional chain-like coordination polymer structure, (b) is a Co-BisTris cation, and (c) is a {V 10 O 28} 6- Hydrogen bonds between the Co-BisTris cation and the Co-BisTris cation, (d) is a schematic diagram of the structure of a molecule; Figure 4 Here are schematic diagrams of the structures of compounds 2, 3, 4, and 5; Figure 5 Fourier transform infrared (FT-IR) spectra of compound 1 (black), compound 2 (red), compound 3 (blue), compound 4 (pink), and compound 5 (green); Figure 6 The PXRD spectrum of compound 1 is shown below. Figure 7 The PXRD spectra of compounds 2 (red), 3 (blue), 4 (pink), and 5 (green) are shown. Figure 8 The TGA-DSC spectrum of compound 1 is shown below. Figure 9 The TGA-DSC spectrum of compound 2; Figure 10 The TGA-DSC spectrum of compound 3 is shown below. Figure 11 The TGA-DSC spectrum of compound 4 is shown below. Figure 12 The TGA-DSC spectrum of compound 5 is shown below. Figure 13Time-tracking experiments were conducted on compound 5 as a catalyst under optimal conditions. Figure 14 Thermal filtration experiments were conducted on compound 5 as a catalyst under optimal conditions. Figure 15 The images show the FT-IR spectra of compound 1 before (black) and after (red) catalytic reaction. Figure 16 The FT-IR spectra of compound 2 before catalysis (black), compound 2 after catalysis (red), compound 3 after catalysis (blue), compound 4 after catalysis (pink), and compound 5 after catalysis (green) are shown. Figure 17 The PXRD spectra of compound 1 before the reaction (red) and after the reaction (black) are shown. Figure 18 The PXRD spectra of compound 2 before catalysis (black), compound 2 after catalysis (red), compound 3 after catalysis (blue), compound 4 after catalysis (pink), and compound 5 after catalysis (green) are shown. Figure 19 The yield of cyclic carbonates for compound 5 after 5 repetitions; Figure 20 This is a schematic diagram of the mechanism of the CO2 cycloaddition reaction. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0028] All chemical reagents used in the following examples and comparative examples of this invention are commercially available products (the source of commercially available products does not affect the technical effect of this invention), and unless otherwise specified, they are used directly without further purification.

[0029] 1 1H nuclear magnetic resonance (NMR) spectra were acquired using a Bruker Avance 400 MHz spectrometer, with deuterated solvent as the test medium and tetramethylsilane (TMS) as the internal standard.

[0030] Fourier transform infrared (FT-IR) spectroscopy measurements were performed on an Alpha Centauri FT-IR spectrometer, with a wavenumber range of 400 to 4000 cm⁻¹. -1 All samples were prepared using the standard KBr tableting method.

[0031] Thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) was performed on a PerkinElmer TGA7 analyzer under a dynamic argon atmosphere, with a temperature range of 40 to 800 °C, a constant heating rate of 10 °C / min, and an argon flow rate of 25 mL / min.

[0032] Powder X-ray diffraction (PXRD) patterns were recorded using Cu Kα radiation with a 2θ scan range of 10° to 50° and a continuous scan rate of 10° per minute.

[0033] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0034] Example 1 Compound 2 (C 16 H 58 Co2N2Na2O 48 V 10 Synthesis of ) 0.2 g Na3VO4, 0.1 g Co(CH3COO)2·4H2O, and 0.1 g bis(2-hydroxyethyl)amino(trishydroxymethyl)methane (BisTris) were added to 10 mL of H2O at pH=2. The mixture was stirred at room temperature for 6 hours. After the reaction, the mixture was filtered, and the filtrate was allowed to stand at room temperature for one week to obtain orange blocky crystals, which is compound 2.

[0035] The yield (calculated based on V) was 47%. ICP-OES (elemental analysis, %): V, 25.8 (theoretical value 26.9); Co, 6.6 (theoretical value 6.2). Elemental analysis: C, 10.5 (theoretical value 10.1); N, 1.3 (theoretical value 1.5).

[0036] The results above show that the target compound 2 was successfully synthesized in this embodiment. The results also indicate that the content of each element is very close to the theoretical values ​​calculated from the chemical formula, suggesting that the product has high purity and is free of impurities.

[0037] Example 2 Compound 3 (C 16 H 58 N2Na2Ni2O 48 V 10 Synthesis of ) The synthesis steps are similar to those for compound 2, except that Co(CH3COO)2·4H2O is replaced with an equimolar amount of Ni(CH3COO)2·4H2O. Orange blocky crystals are obtained, which is compound 3.

[0038] The yield (calculated based on V) was 40%. ICP-OES (elemental analysis, %): V, 26.3 (theoretical value 26.9); Ni, 6.1 (theoretical value 6.2). Elemental analysis: C, 10.4 (theoretical value 10.1); N, 1.6 (theoretical value 1.5).

[0039] The results above show that the target compound 3 was successfully synthesized in this embodiment. The results also indicate that the content of each element is very close to the theoretical values ​​calculated from the chemical formula, suggesting that the product has high purity and is free of impurities.

[0040] Example 3 Compound 4 (C 16 H 58 Cu2N2Na2O 48 V 10 Synthesis of ) The synthesis steps are similar to those for compound 2, except that Co(CH3COO)2·4H2O is replaced with an equimolar amount of Cu(CH3COO)2. Orange blocky crystals are obtained, which is compound 4.

[0041] The yield (calculated based on V) was 44%. ICP-OES (elemental analysis, %): V, 27.3 (theoretical value 26.8); Cu, 6.8 (theoretical value 6.7). Elemental analysis: C, 10.2 (theoretical value 10.1); N, 1.7 (theoretical value 1.5).

[0042] The results above show that the target compound 4 was successfully synthesized in this embodiment. The results also indicate that the content of each element is very close to the theoretical values ​​calculated from the chemical formula, suggesting that the product has high purity and is free of impurities.

[0043] Example 4 Compound 5 (C 16 H 58 N2Na2O 48 V 10 Synthesis of Zn2): The synthesis steps were similar to those for compound 2, except that Co(CH3COO)2·4H2O was replaced with an equimolar amount of Zn(CH3COO)2. Orange blocky crystals were obtained, which is compound 5.

[0044] The yield (calculated based on V) was 41%. ICP-OES (elemental analysis, %): V, 26.5 (theoretical value 26.8); Zn, 7.2 (theoretical value 6.9). Elemental analysis: C, 10.3 (theoretical value 10.1); N, 1.7 (theoretical value 1.5).

[0045] The results above show that the target compound 5 was successfully synthesized in this embodiment. The results indicate that the content of each element is very close to the theoretical values ​​calculated from the chemical formula, suggesting that the product has high purity and is free of impurities.

[0046] Comparative Example 1 Compound 1 (C 32 H 80 N4Na2O 48 V 10 Synthesis of ·8H2O: 0.2 g Na3VO4 and 0.1 g bis(2-hydroxyethyl)amino(tris(hydroxymethyl)methane) (BisTris) were added to 10 mL of H2O at pH=2. The mixture was stirred at room temperature for 6 hours. After the reaction, the mixture was filtered, and the filtrate was allowed to stand at room temperature for one week to obtain orange blocky crystals, which was compound 1.

[0047] The yield (calculated based on V) was 59%. ICP-OES (elemental analysis, %): V, 25.1 (theoretical value 25.6). Elemental analysis: C, 20.2 (theoretical value 19.3); N, 2.4 (theoretical value 2.8).

[0048] Figure 1 Here are schematic diagrams of the structure of compound 1, where (a) is a schematic diagram of compound 1 along the b-axis, (b) is a schematic diagram of compound 1 along the BisTris coordination polymer, and (c) is a simplified schematic diagram of the structure of compound 1. Figure 1 In (a), light green represents V; red represents O; light blue represents Na; gray represents H; orange represents N; and black represents C. Figure 1 In (b), light green represents V; red represents O; light blue represents Na; gray represents H; orange represents N; and black represents C. Figure 1 In (c), light green represents {V} 10 O 28 Clusters; light blue indicates Na; pink indicates BisTris. For clarity, Figure 1 The H atom portion has been omitted.

[0049] Comparative Example 2 Synthesis of Co-BisTris complexes: 0.02 mol of CoCl2 was added to deionized water containing 0.02 mol of bis(2-hydroxyethyl)amino(tris(hydroxymethyl)methane) (BisTris). The solution was stirred at 60 °C. The product was collected by evaporating the solution under reduced pressure to obtain the Co-BisTris complex.

[0050] Comparative Example 3 (C 16 H 36 N)3[H3V 10 O 28 ] (containing only the center of V) 10 O 28 Synthesis of compounds: 15g Na₃VO₄ was dissolved in 110mL H₂O. 71mL of 3mol / L HCl solution was added dropwise at a rate of two drops per second with rapid stirring, during which the solution changed from colorless to orange. Then, 60mL of an aqueous solution containing 60g TBABr was added in 2mL portions, and the mixture was stirred for another 15 minutes. The orange precipitate was collected by filtration, washed successively with H₂O, ethanol, and diethyl ether, and dried for 12 hours. The solid was dissolved in 150mL acetonitrile, stirred, filtered, and slowly evaporated to obtain 1.8g of orange crystals, which is (C₂O₃VO₄). 16 H 36 N)3[H3V10 O 28 ] (containing only the center of V) 10 O 28} compounds).

[0051] The calculated yield is 86%.

[0052] Experimental Example 1: Crystal Structure Characterization The structures of compounds 1-5 prepared in Examples 1-4 and Comparative Example 1 were determined by single-crystal X-ray diffraction (SCXRD). The results are as follows: Figures 1-4 As shown in Table 1.

[0053] Figure 2 This is a schematic diagram of the structure of compound 1, where (a) is an asymmetric unit and (b) is a {V 10 O 28} 6- The anion, (c) is NaH(BisTris) 2+ The one-dimensional structure of the cation, (d) is a protonated BisTris molecule, (e) is {V 10 O 28} 6- Hydrogen bonds with BisTris ligands. Figure 2 In the color spectrum, light green represents V; red represents O; pale blue represents Na; gray represents H; orange represents N; and black represents C. For clarity, some H atoms have been omitted.

[0054] Figure 3 This is a schematic diagram of the structure of compound 2, where (a) is a one-dimensional chain-like coordination polymer structure, (b) is a Co-BisTris cation, and (c) is a {V 10 O 28} 6- Hydrogen bonds between the Co-BisTris cation and the Co-BisTris cation, (d) is a schematic diagram of the structure of a molecule. Figure 3 Medium, light green, V; red, O; light blue, Na; gray, H; orange, N; black, C; blue, Co. For clarity, some H atoms have been omitted.

[0055] Figure 4 This is a schematic diagram of the structures of compounds 2, 3, 4, and 5. Figure 4 Medium, light green, V; red, O; light blue, Na; gray, H; orange, N; black, C; blue, Co; dark green, Ni; green, Cu; blue-green, Zn. For clarity, some H atoms have been omitted. Single-crystal X-ray diffraction analysis showed that compound 1 crystallizes in the orthorhombic crystal system, space group Cmce. Its asymmetric unit contains a classical {V} 10 O 28}6- Anions, two Na+ + Cations and four BisTris ligands ( Figure 2 a and 2b). Na + The cation coordinates to six oxygen atoms from three BisTris ligands, each BisTris ligand being associated with Na. + Cationic coordination leads to the formation of a one-dimensional chain-like coordination polymer structure. Figure 2 c). It is worth mentioning that in the BisTris ligand, the hydrogen atom of the hydroxyl functional group interacts with Na. + During coordination, it remains in an undissociated state, while the nitrogen atom undergoes protonation. Figure 2 d). This process achieves charge balance regulation by introducing protons to compensate for charge differences within compound 1. Furthermore, the Na-BisTris complex cation with {V 10 O 28} 6- Anions are linked not only by charge but also by hydrogen bonds. The hydroxyl hydrogen atom in BisTris is bonded to {V... 10 O 28} 6- The bridging μ2-O and the terminal Ot group in the middle form hydrogen bonds ( Figure 2 e), with bond lengths of 1.813, 1.841, 1.958, and 2.081 Å, respectively. Furthermore, under hydrogen bonding, {V 10 O 28} 6- The anion and the Na-BisTris complex cation formed a three-dimensional structure ( Figure 2 ).

[0056] SCXRD analysis showed that compound 2 crystallizes in the triclinic P-1 space group, and its asymmetric unit contains a {V} 10 O 28} 6- Anions, two Na+ + Two Co 2+ It contains two BisTris ligands and eight coordinated water molecules. Unlike compound 1, Na... + No longer coordinated with BisTris, but with two {V 10 O 28} 6- The two terminal oxygen groups (Ot) of the anion form a six-coordinate mode with four water molecules. Each {V 10 O 28} 6- Anion connects four adjacent Na groups + This forms a one-dimensional chain-like coordination polymer structure. Figure 3 a). Furthermore, BisTris ligands and Co2+ Instead of Na + Coordination. Each Co 2+ It coordinates with four hydroxyl groups, one nitrogen atom, and one water molecule from a BisTris ligand to form a distorted octahedral configuration. Figure 3 b). Unlike compound 1, the nitrogen atom in the BisTris ligand of compound 2 does not have a bonded proton. Additionally, {V 10 O 28} 6- The bridging oxygen (μ2-O) and terminal oxygen (Ot) in the anion also form hydrogen bonds with the four surrounding Co-BisTris cations, with bond lengths of 1.782, 1.809, 1.844, 1.872, 1.928, and 2.211 Å, respectively. Figure 3 c). The structures of compounds 3-5 are similar to those of compound 2, the only difference being the transition metal ion; the composition of the remaining parts and the coordination mode of the metal are the same.

[0057] Table 1. Summary of single-crystal X-ray diffraction (SCXRD) crystallographic data for compounds 1–5

[0058]

[0059] The above results indicate that, compared to compound 1, compounds 2–5 all crystallize in the triclinic crystal system, space group P-1, and their asymmetric units, except for {V 10 O 28} 6- anions and Na + In addition to cations, two transition metal ions (Co) were also introduced. 2+ Ni 2+ Cu 2+ or Zn 2+ Unlike compound 1, compounds 2-5 contain Na. + It no longer coordinates with BisTris ligands, but instead with ligands from two {V} 10 O 28} 6- The terminal oxygen of the anion coordinates with four water molecules to form a one-dimensional chain structure. Simultaneously, the BisTris ligand coordinates with transition metal ions to form M-BisTris coordinated cations. Furthermore, in compounds 2–5, the nitrogen atom of the BisTris ligand does not have a proton bond; instead, it participates in coordination as a neutral ligand. 10 O 28} 6-The anion and the M-BisTris coordinated cation interact via hydrogen bonds, further assembling into a three-dimensional network structure. This structural difference allows for the effective separation and exposure of the vanadium center and the transition metal center in compounds 2–5, laying the structural foundation for synergistic catalytic effects in subsequent catalytic reactions.

[0060] Experimental Example 2: Characterization of Physicochemical Properties Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), and thermogravimetric-differential scanning calorimetry (TGA-DSC) were performed on compounds 1-4 prepared in Examples 1-4 and Comparative Example 1. The results are as follows: Figures 5-12 As shown.

[0061] Figure 5 Fourier transform infrared (FT-IR) spectra of compounds 1 (black), 2 (red), 3 (blue), 4 (pink), and 5 (green). Figure 6 The image shows the PXRD pattern of compound 1. Figure 7 The PXRD spectra of compounds 2 (red), 3 (blue), 4 (pink), and 5 (green) are shown. Figure 8 The image shows the TGA-DSC spectrum of compound 1. Figure 9 The image shows the TGA-DSC spectrum of compound 2. Figure 10 The image shows the TGA-DSC spectrum of compound 3. Figure 11 The image shows the TGA-DSC spectrum of compound 4. Figure 12 The image shows the TGA-DSC spectrum of compound 5.

[0062] FT-IR spectroscopy ( Figure 5 Compounds 1–5 were recorded at 400–4000 cm⁻¹. -1 Fourier transform infrared spectra within the range. For example... Figure 5 As shown, compounds 2-5 exhibit similar spectral peaks due to their structural similarities. (400-1000 cm⁻¹) -1 The peaks within this range are attributed to stretching vibrations of VOV, V=O, and VO, 800~1600 cm⁻¹ -1 The peaks within the range are attributed to the stretching vibrations of the BisTris ligand.

[0063] Powder X-ray diffraction analysis was used. Figure 6 and Figure 7 The purity of compounds 1-5 was characterized using [a certain method]. Figure 6 and Figure 7As can be seen, the experimentally obtained PXRD peaks agree well with the simulated peaks, indicating that the solid phases of compounds 1-5 are pure and therefore suitable for subsequent catalytic performance studies. Furthermore, the PXRD patterns of compounds 2-5 are highly similar, indicating that their structures are very similar, consistent with the results obtained from SCXRD testing.

[0064] The stability and molecular formula of compounds 1–5 were studied using a combination of thermogravimetric analysis and differential scanning calorimetry. Figures 8-12 As shown, all compounds 1-5 exhibited weight loss at approximately 100°C, and their structures remained unchanged below 100°C. This indicates that when these compounds are used as catalysts at temperatures below 100°C to study their catalytic performance, they do not decompose. TGA-DSC analysis ( Figures 8-12 The results show that all compounds are structurally stable below 100°C and have good thermal stability for catalytic reactions.

[0065] Experimental Example 3: Catalytic Performance Test Using epichlorohydrin as a substrate and tetrabutylammonium bromide (TBABr) as a cocatalyst, the performance of compounds 1-5 prepared in Examples 1-4 and Comparative Example 1 in the CO2 cycloaddition reaction was evaluated.

[0066] The reaction equation for the cycloaddition reaction of epichlorohydrin with CO2 is as follows: .

[0067] Table 2. Performance of compounds 1-5 in CO2 cycloaddition reaction under different conditions.

[0068] In Table 2, the catalyst dosage was 0.3% of the molar amount of epichlorohydrin; the molar ratio of catalyst to co-catalyst was 0.15:2. The yield (%) and selectivity (%) of cyclic carbonates were determined by... 1 Determined by H NMR spectroscopy.

[0069] Table 2 shows that the reaction can proceed even without a catalyst, but the catalytic yield is quite low, only 6.2%. However, the reaction is almost impossible without a co-catalyst, indicating that the co-catalyst plays a crucial role in the reaction process. Furthermore, CO2 pressure is also a key factor in the reaction. If the reaction is carried out in air, almost no products are detected. Considering economic factors, atmospheric pressure was chosen as the reaction pressure condition. Reaction temperature also has a significant impact on the reaction. When the reaction is carried out at 20℃ and 40℃, the yield of cyclic carbonates only reaches 49.3% and 86.5%, respectively. In contrast, when the reaction temperature is increased to 60℃, the yield of cyclic carbonates can be increased to 98.2%.

[0070] Optimization of reaction conditions (taking compound 5 as an example): Under a CO2 pressure of 1 atm and a reaction time of 12 hours, the yield can reach 98.2% when the reaction temperature is 60℃ (see Table 1).

[0071] Figure 13 Time-tracking experiments were conducted under optimal conditions using compound 5 as a catalyst. (Time-tracking experiment) Figure 13 The data shows that the cycloaddition reaction is basically completed within 8 to 12 hours.

[0072] Figure 14 Hot filtration experiments were conducted using compound 5 as a catalyst under optimal conditions. The procedures were as follows: using compound 5 as a catalyst and epichlorohydrin as the substrate (catalyst amount was 0.3% of the molar amount of epichlorohydrin), the reaction was carried out at 1 atm CO2 pressure and 60°C for 4 hours, after which the reaction was stopped. The solution was then filtered under reduced pressure while hot. After filtration, the filtrate was further reacted at 1 atm CO2 pressure and 60°C for 8 hours, with samples taken every 2 hours. 1 1H NMR analysis was performed to calculate yield and selectivity. Thermal filtration experiments ( Figure 14 This study confirmed that the yield of cyclic carbonates no longer changed significantly with increasing reaction time, indicating that the reaction follows a heterogeneous catalytic mechanism.

[0073] Catalyst performance comparison: Under optimal reaction conditions (60℃, 1 atm CO2, 12 h), the catalytic activities of compounds 1–5 are shown in Table 2. The catalytic activities of compounds 2–5 doped with transition metals (cyclic carbonate yield 91.5–96.3%) were significantly higher than those of undoped compound 1 (cyclic carbonate yield 82.1%). Among them, compound 5 (Zn doped) performed best, achieving a cyclic carbonate yield of 98.2% and selectivity exceeding 99%.

[0074] Catalyst stability: The FT-IR and PXRD spectra before and after catalysis were compared (e.g., Figures 15-18 (As shown) to demonstrate the stability of compounds 1-5 during the catalytic process.

[0075] Figure 15 The images show the FT-IR spectra of compound 1 before (black) and after (red) catalytic reaction. Figure 16 The FT-IR spectra of compound 2 before catalysis (black), compound 2 after catalysis (red), compound 3 after catalysis (blue), compound 4 after catalysis (pink), and compound 5 after catalysis (green) are shown. Figure 17 The images show the PXRD patterns of compound 1 before (red) and after (black) the reaction. Figure 18The images show the PXRD patterns of compound 2 before catalysis (black), compound 2 after catalysis (red), compound 3 after catalysis (blue), compound 4 after catalysis (pink), and compound 5 after catalysis (green). Figures 15-18 As can be seen, almost no changes were observed in either the infrared absorption peak or the PXRD peak, indicating that compounds 1-5 exhibit excellent stability as catalysts during the catalytic process.

[0076] Cyclic stability test: Compound 5 was subjected to five cycles under optimal reaction conditions (60℃, 1 atm CO2, 12 h), and recovered by filtration after each cycle. Results are as follows: Figure 19 As shown.

[0077] Figure 19 The yield of cyclic carbonates after compound 5 was obtained by repeating the process 5 times. Figure 19 It can be seen that the yield of cyclic carbonates after compound 5 was still above 88% after being reused 5 times, indicating that it has good cycling stability.

[0078] In summary, the high-efficiency heterogeneous catalyst prepared by this invention can achieve efficient and highly selective conversion of CO2, while also possessing excellent stability and recyclability.

[0079] Experimental Example 4: Verification of the Synergistic Catalytic Mechanism As can be seen from Table 2, both the co-catalyst and the catalyst play crucial roles in the reaction process. The introduction of the co-catalyst further indicates that bromide ions (Br) play a key role. - This plays a crucial role in the reaction. Based on this, the reaction mechanism of this reaction is proposed, such as... Figure 20 As shown. Taking compound 2 as an example, to verify the synergistic catalytic effect of vanadium (V) and the transition metal cobalt (Co) in compound 2, Co-BisTris complexes (Comparative Example 2) and (C) were synthesized, respectively. 16 H 36 N)3[H3V 10 O 28 ] (containing only the center of V) 10 O 28 (Comparative Example 3). Under the same optimal reaction conditions, the catalytic yield of the Co-BisTris complex was 32.6%, (C 16 H 36 N)3[H3V 10 O 28 ] (containing only the center of V) 10 O 28The catalytic yield of compounds 3-5 was 38.1%, significantly lower than that of compound 2 (92.9%). This result indicates that integrating the vanadium center and the transition metal center into the same catalyst via ligands can produce a significant synergistic catalytic effect, thereby greatly improving catalytic efficiency. The mechanisms of compounds 3-5 are similar to those of compound 2, differing only in the transition metal ion; the remaining composition and metal coordination modes are identical.

[0080] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A highly efficient heterogeneous catalyst for the CO2 cycloaddition to prepare cyclic carbonates, characterized in that, The highly efficient heterogeneous catalyst is a transition metal-doped polyvanadate coordination polymer with the general chemical formula: C 16 H 58 M2N2Na2O 48 V 10 Where M is selected from Co 2+ Ni 2+ Cu 2+ or Zn 2+ .

2. The highly efficient heterogeneous catalyst for the CO2 cycloaddition to prepare cyclic carbonates according to claim 1, characterized in that, The highly efficient heterogeneous catalyst has a triclinic P-1 space group structure, and its asymmetric unit contains a {V} 10 O 28 } 6- Anions, two Na+ + Cations, two transition metals M 2+ Ions, two BisTris ligands, and ten coordinated water molecules.

3. The highly efficient heterogeneous catalyst for the CO2 cycloaddition to prepare cyclic carbonates according to claim 2, characterized in that, The BisTris ligand is bis(2-hydroxyethyl)amino(tris(hydroxymethyl)methane), which reacts with transition metal M 2+ The ion coordinates with a coordinated water molecule to form an M-BisTris coordinated cation.

4. The highly efficient heterogeneous catalyst for the CO2 cycloaddition to prepare cyclic carbonates according to claim 2, characterized in that, The Na + Cations and from two {V 10 O 28 } 6- The terminal oxygen of the anion coordinates with four water molecules to form a one-dimensional chain structure.

5. The highly efficient heterogeneous catalyst for the CO2 cycloaddition to prepare cyclic carbonates according to claim 3, characterized in that, The V 10 O 28 6- The anion and the M-BisTris coordinated cation form a three-dimensional network structure through hydrogen bonding interactions.

6. The method for preparing the highly efficient heterogeneous catalyst for the cycloaddition of CO2 to cyclic carbonates according to any one of claims 1 to 5, characterized in that, Includes the following steps: Sodium vanadate, transition metal acetate and BisTris ligand were dissolved in water with a pH of 1-3, stirred and reacted, filtered and allowed to stand to crystallize, to obtain the highly efficient heterogeneous catalyst for the preparation of cyclic carbonates by CO2 cycloaddition.

7. The preparation method according to claim 6, characterized in that, The transition metal acetate is (CH3COO)2Co, Ni(CH3COO)2, Cu(CH3COO)2 or Zn(CH3COO)2.

8. The preparation method according to claim 6, characterized in that, The reaction time is 6-8 hours; the static crystallization time is 7-14 days.

9. The application of the highly efficient heterogeneous catalyst according to any one of claims 1 to 5 for the preparation of cyclic carbonates by CO2 cycloaddition, characterized in that, The highly efficient heterogeneous catalyst and the co-catalyst are used together to catalyze the cycloaddition reaction of epoxides and CO2 to generate cyclic carbonates. The co-catalyst includes tetrabutylammonium bromide; The highly efficient heterogeneous catalyst is recovered by filtration and separation after the cycloaddition reaction is completed, so as to be recycled.

10. The application according to claim 9, characterized in that, The epoxide includes epichlorohydrin; the conditions for the cycloaddition reaction are: the molar amount of the high-efficiency heterogeneous catalyst is 0.3% of the molar amount of the epoxide, the molar ratio of the high-efficiency heterogeneous catalyst to the co-catalyst is 0.15:2, the reaction temperature is 50~60℃, the reaction time is 10~12h, and the CO2 pressure is 1 atm.

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