Preparation method of rare-earth-based composite catalyst and application of rare-earth-based composite catalyst in synthesis of polycarbonate

Abstract

The invention relates to a preparation method of a rare-earth-based composite catalyst and application of the rare-earth-based composite catalyst in synthesis of polycarbonate, and belongs to the technical field of chemical synthesis. According to the preparation method disclosed by the invention, phytic acid modified graphene oxide is used for preparing a carbon foam carrier, the carbon foam carrier is used for loading rare earth borohydride and diethyl zinc to prepare a rare earth-based composite catalyst, and the rare earth-based composite catalyst is used for preparing polycarbonate through copolymerization of carbon dioxide and epoxide; diethylzinc is fixed through rich oxygen-enriched functional groups on the surface of a carbon foam carrier, and further complexation with rare earth borohydride is performed to obtain an efficient polycarbonate synthesis catalyst, the rare earth-based composite catalyst is high in catalytic efficiency and easy to separate after the reaction is finished, and polycarbonate prepared through catalysis is high in molecular weight and high in carbonate chain link content.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a method for preparing a rare earth-based composite catalyst and its application in the synthesis of polycarbonate. Background Technology

[0002] Currently, the global use of fossil fuels leads to a net increase of 9 billion tons of carbon dioxide in the atmosphere annually. CO2 contributes to the greenhouse effect, including global warming. However, CO2 is also an important C1 resource, widely distributed, abundant, non-flammable, non-toxic, and inexpensive, and can be used to prepare various organic chemicals, materials, and fuels. Polycarbonate, as an important engineering plastic, is widely used in the electronics, automotive, and construction industries. Polycarbonate can be copolymerized from CO2 and epoxides under the action of a catalyst. Currently, the main industrialized polycarbonate is aromatic polycarbonate, but its environmental degradation rate is slow, easily causing white pollution. Aliphatic polycarbonate, on the other hand, is biodegradable, avoids environmental pollution, and has a very broad development prospect. With the increasing demand for environmentally friendly materials, developing an efficient, low-cost, and easily recyclable polycarbonate synthesis method is of great significance.

[0003] Since Professor Xiangping first prepared carbon dioxide / epoxide copolymers using the ZnEt2 / H2O catalytic system in 1969, over 50 years of development have led to the formation of a relatively complete catalytic system in the field of carbon dioxide polymerization, with progress made in product selectivity and polymer structure regulation. Catalysts mainly include homogeneous systems represented by metalloporphyrins, zinc phenoxyphosphates, and β-diimine zinc, as well as heterogeneous systems represented by diethylzinc (ZnEt2) / multi-active hydrogen compounds, zinc carboxylate, bimetallic cyanides, and rare earth ternary catalysts. Compared to homogeneous catalytic systems, heterogeneous catalysts have advantages such as simpler synthesis methods, relatively lower prices, and higher molecular weight copolymers. Compared to other heterogeneous catalysts, rare earth ternary catalysts can simultaneously prepare high molecular weight, highly alternating aliphatic polycarbonates; however, they still suffer from low catalytic efficiency and difficulty in catalyst separation after the reaction. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a rare earth-based composite catalyst and its application in the synthesis of polycarbonate.

[0005] This invention proposes a novel method for preparing rare earth-based composite catalysts and their application in the preparation of polycarbonate by introducing rare earth elements and carbon foam carriers. This method is expected to improve the synthesis efficiency and product quality of polycarbonate while reducing environmental impact.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a rare earth-based composite catalyst, comprising the following steps: S1. Mix the aqueous dispersion of graphene oxide with the aqueous solution of phytic acid to obtain a mixed solution and place it in a high-pressure reactor for a full hydrothermal reaction; after the reaction is completed, cool to room temperature, wash and freeze-dry, and calcine to obtain a carbon foam carrier; S2. Under the protection of an inert gas, the carbon foam support obtained in step S1 is dispersed in a solvent with rare earth borohydride and diethyl zinc, and the reaction is carried out. The solvent is then removed by distillation to obtain a rare earth-based composite catalyst.

[0007] This invention utilizes carbon foam as a support to support rare earth borohydride and diethylzinc to prepare a rare earth-based composite catalyst, which is then used in the copolymerization of carbon dioxide and epoxides to prepare polycarbonate. Phytic acid-modified graphene-derived carbon foam (graphene oxide), with its large specific surface area and abundant porous structure, is used as the support. Diethylzinc is fixed by the abundant oxygen-rich functional groups on the surface of the carbon foam support, and further complexed with rare earth borohydride to obtain a highly efficient polycarbonate synthesis catalyst. This overcomes the problems of insufficient catalytic efficiency and difficulty in separation of existing catalysts. The rare earth-based composite catalyst of this invention features high catalytic efficiency, high polycarbonate molecular weight, high carbonate chain segment content, and easy separation after the catalyst reaction.

[0008] In a preferred embodiment of the preparation method described in this invention, in step S1, the ratio of graphene oxide to phytic acid in the mixed solution is 1g:5~30mL; In step S2, the mass ratio of the carbon foam carrier to rare earth borohydride and diethyl zinc is 0.5~1.5:0.02:0.2.

[0009] In a preferred embodiment of the preparation method described in this invention, in step S1, the ratio of graphene oxide to phytic acid in the mixed solution is 1 g: 12.5~30 mL. Within this ratio range, the rare earth-based composite catalyst exhibits higher catalytic efficiency.

[0010] In a preferred embodiment of the preparation method described in this invention, in step S1, the ratio of graphene oxide to phytic acid in the mixed solution is 1 g: 25~30 mL. Within this ratio range, the rare earth-based composite catalyst exhibits higher catalytic efficiency.

[0011] In a preferred embodiment of the preparation method described in this invention, in step S1, the ratio of graphene oxide to phytic acid in the mixed solution is 1 g: 25 mL. Within this ratio range, the rare earth-based composite catalyst exhibits the best catalytic efficiency.

[0012] In a preferred embodiment of the preparation method described in this invention, in step S1, the ratio of graphene oxide to water in the aqueous dispersion of graphene oxide is 1g:180~220mL; the volume percentage of phytic acid in the aqueous solution of phytic acid is 40~60%. If the aqueous dispersion of graphene oxide or the aqueous solution of phytic acid is too concentrated or too dilute, it will affect the preparation of the carbon foam carrier and prevent the successful synthesis of the target carrier.

[0013] In a preferred embodiment of the preparation method of the present invention, in step S1, the ratio of graphene oxide to water in the aqueous dispersion of graphene oxide is 1g:200mL; and the volume percentage of phytic acid in the aqueous solution of phytic acid is 50%.

[0014] In a preferred embodiment of the preparation method described in this invention, in step S1, the hydrothermal reaction is carried out at 200-250°C for 10-16 hours. If the time is too short, the reaction will be insufficient, and the graphene cannot be completely converted into a carbon foam carrier.

[0015] In a preferred embodiment of the preparation method of the present invention, in step S1, the washing is performed using ethanol and water.

[0016] In a preferred embodiment of the preparation method described in this invention, the calcination conditions in step S1 are 550~650℃ for 1.5~2.5h. If the temperature or time is too low, the phytic acid will not decompose completely; if it is too high, the structure will collapse, both of which will affect the preparation of the carbon foam carrier.

[0017] In a preferred embodiment of the preparation method described in this invention, in step S1, the calcination conditions are calcination at 600°C for 2 hours.

[0018] In a preferred embodiment of the preparation method described in this invention, in step S2, the mass ratio of the carbon foam support to rare earth borohydride and diethylzinc is 0.8~1.5:0.02:0.2. Within this ratio range, the rare earth-based composite catalyst exhibits higher catalytic efficiency.

[0019] In a preferred embodiment of the preparation method described in this invention, in step S2, the mass ratio of the carbon foam support to rare earth borohydride and diethylzinc is 1~1.5:0.02:0.2. Within this ratio range, the rare earth-based composite catalyst exhibits higher catalytic efficiency.

[0020] In a preferred embodiment of the preparation method described in this invention, in step S2, the mass ratio of the carbon foam support to rare earth borohydride and diethylzinc is 1:0.02:0.2. Within this ratio range, the rare earth-based composite catalyst exhibits the best catalytic efficiency.

[0021] In a preferred embodiment of the preparation method described in this invention, in step S2, the rare earth borohydride includes Y(BH4)3˙3THF, Ln(BH4)3˙3THF or Nd(BH4)3˙3THF.

[0022] In a preferred embodiment of the preparation method of the present invention, in step S2, the solvent includes tetrahydrofuran, toluene, n-hexane or n-heptane.

[0023] Secondly, the present invention provides a rare earth-based composite catalyst prepared using the above-described preparation method.

[0024] The rare earth-based composite catalyst of this invention exhibits a catalytic efficiency (TON) exceeding 20,000 g / mol, demonstrating high catalytic efficiency. When used as a catalyst in the preparation of polycarbonate, the polycarbonate prepared can achieve a carbonate repeating unit content of over 88% and a weight-average molecular weight of over 30,000, resulting in a high molecular weight. The polycarbonate also possesses good mechanical properties and thermal stability.

[0025] Thirdly, the present invention provides the application of the above-mentioned rare earth-based composite catalyst in the preparation of polycarbonate.

[0026] Fourthly, the present invention provides a method for preparing polycarbonate, wherein propylene oxide, cyclohexene oxide, the above-mentioned rare earth-based composite catalyst and solvent are mixed and placed in a batch reactor, carbon dioxide is introduced, and the reaction is carried out to obtain polycarbonate.

[0027] In a preferred embodiment of the method for preparing polycarbonate according to the present invention, the molar ratio of propylene oxide, cyclohexene oxide and diethylzinc in the above rare earth-based composite catalyst is 2:10:0.1~1.

[0028] In a preferred embodiment of the method for preparing polycarbonate according to the present invention, the reaction pressure for a complete reaction is 1~4 MPa; and the reaction temperature for a complete reaction is 70~100℃.

[0029] In a preferred embodiment of the polycarbonate preparation method of the present invention, the reaction pressure for complete reaction is 2-3 MPa. Within this range, the rare earth-based composite catalyst exhibits higher catalytic efficiency and a higher carbonate repeating content.

[0030] In a preferred embodiment of the polycarbonate preparation method of the present invention, the reaction pressure for complete reaction is 3 MPa. Within this range, the rare earth-based composite catalyst exhibits the highest catalytic efficiency and also a relatively high carbonate repeating content.

[0031] In a preferred embodiment of the method for preparing polycarbonate according to the present invention, the reaction temperature for complete reaction is 80-90°C. Within this range, the rare earth-based composite catalyst exhibits higher catalytic efficiency and a higher carbonate repeating content.

[0032] In a preferred embodiment of the polycarbonate preparation method of the present invention, the reaction temperature for complete reaction is 90°C. Within this range, the rare earth-based composite catalyst exhibits the highest catalytic efficiency and also a relatively high carbonate repeating content.

[0033] In a preferred embodiment of the method for preparing polycarbonate according to the present invention, the solvent is tetrahydrofuran.

[0034] Fifthly, the present invention provides a polycarbonate prepared using the above-described preparation method.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes phytic acid-modified graphene oxide to prepare a carbon foam support. Rare earth borohydride and diethylzinc are then supported on this carbon foam support to prepare a rare earth-based composite catalyst, which is used in the copolymerization of carbon dioxide and epoxides to prepare polycarbonate. The carbon foam, with its large specific surface area and abundant porous structure, serves as the support. Diethylzinc is fixed by the abundant oxygen-rich functional groups on the surface of the carbon foam support, and further complexed with rare earth borohydride to obtain a highly efficient polycarbonate synthesis catalyst. The rare earth-based composite catalyst of this invention exhibits high catalytic efficiency, is easily separated after the reaction, and produces polycarbonate with high molecular weight and high carbonate chain segment content. It also boasts high weight-average molecular weight, excellent mechanical properties, high carbonate chain segment content, a regular polymer backbone structure, few impurities (such as chain segments generated by side reactions like ether bonds and ketone bonds), and good thermal stability. Detailed Implementation

[0036] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0038] Example 1 A rare earth-based composite catalyst and polycarbonate prepared therefrom, wherein the preparation method of the rare earth-based composite catalyst includes the following steps: S1. Disperse 1g of graphene oxide in 200mL of water, add 50mL of 50% phytic acid aqueous solution and mix well to obtain a mixed solution. Transfer the solution to a high-pressure reactor and react at 200℃ for 16h. After the reaction is completed, cool to room temperature, wash several times with ethanol and water, freeze dry, and calcine at 600℃ in an inert gas atmosphere for 2h to obtain a carbon foam support. S2. Under inert gas protection, 1g of carbon foam support obtained in step S1, 0.02g of rare earth borohydride (Y(BH4)3·3THF) and 0.2g of diethylzinc are dispersed in 10mL of tetrahydrofuran, stirred overnight, and the tetrahydrofuran is removed by distillation to obtain rare earth-based composite catalyst.

[0039] Polycarbonate was prepared using the rare earth-based composite catalyst of this embodiment. The preparation method was as follows: a batch reactor was used, with propylene oxide and cyclohexene oxide as raw materials, the rare earth-based composite catalyst of this embodiment as the catalyst, tetrahydrofuran as the solvent, and carbon dioxide was introduced to maintain the pressure inside the reactor at 3 MPa. The reactor was stirred at 800 r / min for 12 h at 90 °C to obtain polycarbonate. The molar ratio of propylene oxide, cyclohexene oxide, and diethylzinc in the rare earth-based composite catalyst was 2:10:0.1. The prepared polycarbonate was named polycarbonate one.

[0040] Examples 2-4 Three examples of rare earth-based composite catalysts and polycarbonates prepared therefrom are presented. The rare earth-based composite catalysts in Examples 2-4 differ from those in Example 1 only in the mass ratio of carbon foam support to rare earth borohydride (Y(BH4)3·3THF) and diethylzinc in step S2. Specifically, Example 2: The mass ratio of carbon foam support to rare earth borohydride (Y(BH4)3··3THF) and diethylzinc in step S2 of Example 1 was adjusted from 1:0.02:0.2 to 0.5:0.02:0.2 to obtain a rare earth-based composite catalyst. Following the preparation method of polycarbonate one in Example 1, polycarbonate was prepared using the rare earth-based composite catalyst of this example and named polycarbonate two.

[0041] Example 3: The mass ratio of carbon foam support to rare earth borohydride (Y(BH4)3·3THF) and diethylzinc in step S2 of Example 1 was adjusted from 1:0.02:0.2 to 0.8:0.02:0.2 to obtain a rare earth-based composite catalyst. Following the preparation method of polycarbonate one in Example 1, polycarbonate was prepared using the rare earth-based composite catalyst of this example and named polycarbonate three.

[0042] Example 4: The mass ratio of carbon foam support to rare earth borohydride (Y(BH4)3·3THF) and diethylzinc in step S2 of Example 1 was adjusted from 1:0.02:0.2 to 1.5:0.02:0.2 to obtain a rare earth-based composite catalyst. Following the preparation method of polycarbonate one in Example 1, polycarbonate was prepared using the rare earth-based composite catalyst of this example and named polycarbonate four.

[0043] Examples 5-7 Three examples of rare earth-based composite catalysts and polycarbonates prepared therefrom are provided. The rare earth-based composite catalysts in Examples 5-7 differ from those in Example 1 only in the volume of the phytic acid aqueous solution in step S1. Specifically, Example 5: The volume of the phytic acid aqueous solution in step S1 of Example 1 was adjusted from 50 mL to 10 mL to obtain a rare earth-based composite catalyst. Following the preparation method of polycarbonate one in Example 1, polycarbonate was prepared using the rare earth-based composite catalyst of this example and named polycarbonate five.

[0044] Example 6: The volume of the phytic acid aqueous solution in step S1 of Example 1 was adjusted from 50 mL to 25 mL to obtain a rare earth-based composite catalyst. Following the preparation method of polycarbonate I in Example 1, polycarbonate was prepared using the rare earth-based composite catalyst of this example and named polycarbonate VI.

[0045] Example 7: The volume of the phytic acid aqueous solution in step S1 of Example 1 was adjusted from 50 mL to 60 mL to obtain a rare earth-based composite catalyst. Following the preparation method of polycarbonate one in Example 1, polycarbonate was prepared using the rare earth-based composite catalyst of this example and named polycarbonate seven.

[0046] Examples 8-10 A rare earth-based composite catalyst and polycarbonate prepared therefrom, the polycarbonate of Examples 8-10 differs from that of Example 1 only in the reaction temperature during the polycarbonate preparation method, specifically, Example 8: The reaction temperature in the polycarbonate preparation method of Example 1 was adjusted from 90°C to 70°C to obtain polycarbonate, which was named polycarbonate VIII.

[0047] Example 9: The reaction temperature in the polycarbonate preparation method of Example 1 was adjusted from 90°C to 80°C to obtain polycarbonate, which was named polycarbonate nine.

[0048] Example 10: The reaction temperature in the polycarbonate preparation method of Example 1 was adjusted from 90°C to 100°C to obtain polycarbonate, which was named polycarbonate 10.

[0049] Examples 11-13 A rare earth-based composite catalyst and polycarbonate prepared therefrom, the polycarbonate of Examples 11-13 differs from that of Example 1 only in the reaction pressure during the polycarbonate preparation method, specifically, Example 11: The reaction pressure in the polycarbonate preparation method of Example 1 was adjusted from 3 MPa to 1 MPa to obtain polycarbonate, which was named polycarbonate eleven.

[0050] Example 12: The reaction pressure in the polycarbonate preparation method of Example 1 was adjusted from 3 MPa to 2 MPa to obtain polycarbonate, which was named polycarbonate twelve.

[0051] Example 13: The reaction pressure in the polycarbonate preparation method of Example 1 was adjusted from 3 MPa to 4 MPa to obtain polycarbonate, which was named polycarbonate thirteen.

[0052] Comparative Example A rare earth-based composite catalyst and polycarbonate prepared therefrom are disclosed. The difference between the rare earth-based composite catalyst in this comparative example and that in Example 1 is that the carbon foam support is not calcined in step S1. The preparation method of the rare earth-based composite catalyst in this comparative example includes the following steps: S1. Disperse 1g of graphene oxide in 200mL of water, add 50mL of 50% phytic acid aqueous solution and mix well to obtain a mixed solution. Transfer the solution to a high-pressure reactor and react at 200℃ for 16h. After the reaction is completed, cool to room temperature, wash several times with ethanol and water, freeze dry to obtain carbon foam carrier. S2, the same as step S2 in Example 1, yields a rare earth-based composite catalyst.

[0053] Following the preparation method of polycarbonate 1 in Example 1, polycarbonates were prepared using comparative rare earth-based composite catalysts and named comparative polycarbonates respectively.

[0054] Test case The catalytic efficiency (TON) of the rare earth-based composite catalysts used in the examples and comparative examples as catalysts for the preparation of polycarbonate was tested respectively. The weight-average molecular weight and carbonate repeating unit content of the polycarbonate prepared by the rare earth-based composite catalysts in the examples and comparative examples were determined.

[0055] Weight-average molecular weight determination method: The molecular weight of polycarbonate samples was determined by gel permeation chromatography. The specific steps are as follows: 5.0 mg of sample was accurately weighed and dissolved in 1 mL of tetrahydrofuran to prepare the test solution, which was then filtered through a 0.4 μm polytetrafluoroethylene (PTFE) membrane. Subsequently, analysis was performed using a Shimadzu LC-20AD GPC system with an injection volume of 20 μL. The analytical conditions were: column temperature 40 ℃, tetrahydrofuran as the mobile phase, flow rate set to 0.6 mL / min, and detection using a RID-10A differential refractive index detector. The system was calibrated using polystyrene standards, with a molecular weight range covering 2000 to 500000.

[0056] Method for determining the chain structure of polycarbonate: The chain structure of polycarbonate was characterized using 1H NMR spectroscopy. The test was conducted on a Bruker AVANCE III 500MHz spectrometer with a magnetic field strength of 9.4 T. The instrument is equipped with a positive broadband liquid probe for detection.1 H, 15 N to 31 P-core, its 1 H and 13 The sensitivities of C were no less than 300:1 (0.1% EB) and 170:1 (ASTM standard), respectively. In the experiment, the sample was dissolved in deuterated chloroform, and the content of ester segments in the copolymer was determined by integrating and calculating the characteristic peak areas.

[0057] The catalytic efficiency (TON), weight-average molecular weight of polycarbonate, and carbonate repeating unit content of the rare earth-based composite catalysts in Examples 1-13 and the comparative examples are shown in Table 1. Table 1 As shown in Table 1, Example 1, and the comparative example, the preparation of the carbon foam support in the rare earth-based composite catalyst must involve calcination. The absence of calcination leads to a decrease in the catalytic efficiency of the obtained rare earth-based composite catalyst. The high concentration of phytic acid used in the carbon foam support preparation process can clog the pores of the carbon foam support to some extent, hindering the incorporation of rare earth active components. The calcination step solves the pore clogging problem while retaining a large number of phosphate groups on the carbon foam surface, providing binding sites for the subsequent loading of active components.

[0058] As shown in Table 1, Examples 1 and 5-7, the catalytic efficiency of the rare earth-based composite catalyst gradually increases with the increase of phytic acid content, and then remains basically unchanged after exceeding 50 mL. With the increase of phytic acid usage, the phosphate binding sites on the carbon foam support increase, and the three-dimensional foam structure also increases, both of which are beneficial for the subsequent loading of rare earth elements, thereby improving the catalytic activity of the catalyst. Considering cost factors, a phytic acid usage of 50 mL is more optimal.

[0059] As shown in Table 1, Examples 1 and 2-4, the catalytic efficiency of the rare earth-based composite catalyst first gradually increases and then decreases with the increase of carbon foam support. Increasing the carbon foam support increases the number of linking sites for the active components; however, excessive carbon foam support can lead to the coating of active sites. A mass ratio of carbon foam support to rare earth borohydride (Y(BH4)3∙3THF) and diethylzinc of 1:0.02:0.2 is more optimal.

[0060] As shown in Table 1, Examples 1 and 8-10, the reaction temperature for polycarbonate preparation has a certain impact on the catalytic efficiency of the rare earth-based composite catalyst, the weight-average molecular weight of polycarbonate, and the carbonate repeating unit content. Both excessively high and low temperatures will cause a decrease in catalytic efficiency. The catalyst exhibits optimal catalytic efficiency at 90℃. Furthermore, the carbonate repeating unit content gradually decreases with increasing temperature. At a reaction temperature of 90℃, the carbonate repeating unit content is relatively high; therefore, a reaction temperature of 90℃ is more optimal.

[0061] As shown in Table 1, Examples 1 and 11-13, the reaction pressure during polycarbonate preparation has a certain impact on the catalytic efficiency of the rare earth-based composite catalyst, the weight-average molecular weight of the polycarbonate, and the carbonate repeating unit content. Both excessively high and low pressures can lead to a decrease in catalytic efficiency. Too low a pressure results in a low carbon dioxide concentration in the system, leading to reduced catalytic efficiency; too high a pressure results in a high carbon dioxide concentration in the system, causing a decrease in the solubility of the copolymer, thus reducing catalytic efficiency. The rare earth-based composite catalyst exhibits higher catalytic efficiency and a higher carbonate repeating unit content at a reaction pressure of 3 MPa; therefore, a reaction pressure of 3 MPa is optimal.

[0062] In addition, the present invention also replaces the solvent tetrahydrofuran with toluene, n-hexane or n-heptane to prepare rare earth-based composite catalysts, and the catalytic efficiency of the obtained rare earth-based composite catalysts is basically the same.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A process for the preparation of a rare earth based composite catalyst, characterized in that, The method comprises the following steps: S1, mixing the aqueous dispersion of graphene oxide and the aqueous solution of phytic acid uniformly to obtain a mixed solution and placing the mixed solution in a high-pressure reaction kettle for hydrothermal reaction; after the reaction is completed, the mixed solution is cooled to room temperature, washed, freeze-dried, and calcined to obtain a carbon foam carrier; S2, dispersing the carbon foam carrier obtained in step S1, a rare earth borohydride, and diethyl zinc into a solvent under inert gas protection, fully reacting, and distilling the solvent to obtain a rare earth-based composite catalyst.

2. The production method according to claim 1, wherein In step S1, the ratio of graphene oxide to phytic acid in the mixed solution is 1 g:5-30 mL; In step S1, the ratio of graphene oxide to water in the aqueous dispersion of graphene oxide is 1 g:180-220 mL; In step S1, the volume percentage of phytic acid in the aqueous solution of phytic acid is 40-60%.

3. The production method according to claim 1, wherein In step S1, the hydrothermal reaction is performed at 200-250°C for 10-16h; In step S1, the calcination is performed at 550-650°C for 1.5-2.5h.

4. The production method according to claim 1, wherein In step S2, the mass ratio of the carbon foam carrier to the rare earth borohydride and diethyl zinc is 0.5-1.5:0.02:0.2; In step S2, the rare earth borohydride comprises Y(BH4)3·3THF, Ln(BH4)3·3THF, or Nd(BH4)3·3THF; In step S2, the solvent comprises tetrahydrofuran, toluene, n-hexane, or n-heptane.

5. A rare earth-based composite catalyst prepared by the method of any one of claims 1-4.

6. Use of the rare earth-based composite catalyst of claim 5 in the preparation of polycarbonates.

7. A process for the preparation of polycarbonate, characterized by, The propylene oxide, cyclohexene oxide, the rare earth-based composite catalyst of claim 5, and a solvent are mixed and placed in a batch kettle type reaction device, carbon dioxide is introduced, and the mixture is fully reacted to obtain a polycarbonate.

8. The production method according to claim 7, wherein The molar ratio of the propylene oxide, cyclohexene oxide, and diethyl zinc in the rare earth-based composite catalyst is 2:10:0.1-1; In step S2, the reaction pressure for the full reaction is 1-4 MPa; In step S2, the reaction temperature for the full reaction is 70-100°C.

9. The production method according to claim 7, wherein The solvent is tetrahydrofuran.

10. A polycarbonate prepared by the method of any one of claims 7-9.

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