SiO2at-Al2O3 loaded rare earth three-way catalyst, preparation method of catalyst and application of catalyst in synthesis of polycarbonate

Abstract

The invention relates to a SiO2-coated Al2O3 loaded rare earth three-way catalyst, a preparation method thereof and application of the catalyst in polycarbonate synthesis, and belongs to the technical field of polymer synthesis. According to the catalyst, SiO2-coated Al2O3 serves as a carrier to load a rare earth three-way catalyst, SiO2-coated Al2O3 is of a double-layer structure, the inner layer of SiO2-coated Al2O3 is SiO2, the outer layer of SiO2-coated Al2O3 is Al2O3, and the rare earth three-way catalyst contains yttrium trichloroacetate, glycerin and diethyl zinc. The SiO2-coated Al2O3 carrier with a double-layer structure is prepared, and the rare earth three-way catalyst is loaded by utilizing the characteristics of large specific surface area, abundant radial pore structures and abundant contactable active surfaces of the SiO2-coated Al2O3 carrier, so that the efficient polycarbonate synthesis catalyst is obtained; the catalyst has the characteristics of high catalytic efficiency (TON), high polycarbonate molecular weight, high carbonate chain link content, easiness in separation after the reaction is finished, and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, and in particular to SiO2@Al2O3 supported rare earth ternary catalysts, their preparation methods, and their applications 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 CO2 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 produce various organic chemicals, materials, and fuels. Polycarbonate can be produced by copolymerizing CO2 and epoxides under the action of a catalyst. Currently, the main industrialized variety of 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.

[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 aliphatic polycarbonates with high molecular weight and highly alternating structures; however, they still suffer from low catalytic efficiency.

[0004] Although some researchers have used metal oxides such as Al2O3 as supports to support rare earth ternary catalysts, bulk metal oxides have problems such as small specific surface area, insufficient binding sites for immobilizing active components, and easy agglomeration of catalysts, which cannot further improve their catalytic activity. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a SiO2@Al2O3 supported rare earth ternary catalyst, its preparation method, and its application in the synthesis of polycarbonate.

[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 catalyst for supporting a rare earth ternary catalyst using SiO2@Al2O3 as a support. The catalyst uses SiO2@Al2O3 as a support to support a rare earth ternary catalyst. The SiO2@Al2O3 has a bilayer structure, with an inner layer of SiO2 and an outer layer of Al2O3. The rare earth ternary catalyst contains yttrium trichloroacetate, glycerol, and diethylzinc.

[0007] This invention uses SiO2@Al2O3 as a support. The SiO2@Al2O3 support has a bilayer structure. The inner SiO2 layer provides a special morphological structure, including a radially porous structure, a large specific surface area, and a large contact surface. The outer Al2O3 layer provides surface adsorption and catalytic reaction centers for catalytically active substances. The overall flower-like morphology can reduce catalyst aggregation and prevent potential active centers from being buried. This catalyst is not prone to aggregation, has high catalytic efficiency, and has the potential to replace traditional rare earth ternary catalysts in the synthesis and production of polycarbonate.

[0008] In a preferred embodiment of the catalyst described in this invention, the rare earth ternary catalyst is loaded onto the SiO2@Al2O3 surface via the interaction of diethylzinc and the hydroxyl groups of alumina.

[0009] In a preferred embodiment of the catalyst described in this invention, the catalyst has a specific surface area of ​​140~160 m². 2 ·g -1 The pore size is 6~7.5 nm.

[0010] Furthermore, the catalyst has a specific surface area of ​​159.1 m². 2 ·g -1 The pore size is 7.2 nm.

[0011] In a preferred embodiment of the catalyst described in this invention, the content of Al2O3 in SiO2@Al2O3 is 9wt%~67wt%.

[0012] Preferably, the Al2O3 content in SiO2@Al2O3 is 50 wt%. As the Al2O3 content in the SiO2@Al2O3 support increases, the efficiency of catalytic synthesis of polycarbonate gradually increases and then decreases. This is because when the Al2O3 content is low, there are fewer linking sites for the active components, while excessive Al2O3 may lead to a reduction in the specific surface area of ​​the SiO2@Al2O3 support and pore blockage, reducing the binding efficiency of the rare earth ternary catalyst and decreasing the reaction mass transfer effect.

[0013] In a preferred embodiment of the catalyst described in this invention, the content of SiO2@Al2O3 is 65.22wt%~78.95wt%.

[0014] Preferably, the SiO2@Al2O3 content is 75.76 wt%. As the amount of flower-shaped SiO2@Al2O3 support increases, the efficiency of catalytic synthesis of polycarbonate gradually increases and then decreases. This is because when there is less flower-shaped SiO2@Al2O3 support, there are fewer linking sites for the active ingredients, while too much support will lead to the encapsulation of active sites.

[0015] In a preferred embodiment of the catalyst described in this invention, the mass ratio of yttrium trichloroacetate, glycerol, and diethylzinc in the rare earth ternary catalyst is (0.018~0.022):(0.09~0.11):(0.18~0.22).

[0016] Preferably, in the rare earth ternary catalyst, the mass ratio of yttrium trichloroacetate, glycerol and diethylzinc is 0.02:0.1:0.2.

[0017] Secondly, the present invention provides a method for preparing SiO2@Al2O3 in the catalyst, comprising the following steps: S1: Hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, cyclohexane and tetraethoxysilane were mixed with an aqueous ethanol solution for 1.5-2.5 h, ammonia was added, and stirring was continued for 7.5-8.5 h to obtain a suspension. The suspension was reacted at 140-160℃ for 11-13 h, and reaction product 1 was collected, washed, and calcined at 500-700℃ for 3.5-4.5 h to obtain flower-like SiO2. S2: Mix aluminum chloride solution, dopamine hydrochloride and the flower-like SiO2 prepared in step S11, stir and react for 11-13 h, collect reaction product 2, wash, and calcine at 400-500℃ for 1.5-2.5 h to obtain flower-like SiO2@Al2O3.

[0018] As a preferred embodiment of the preparation method of the present invention, in step S1, hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, cyclohexane and tetraethoxysilane are stirred and mixed with an aqueous ethanol solution for 2 h.

[0019] In a preferred embodiment of the preparation method described in this invention, in step S1, ammonia water is added and stirring is continued for 8 hours.

[0020] In a preferred embodiment of the preparation method described in this invention, in step S1, the reaction is carried out at 150°C for 12 h.

[0021] In a preferred embodiment of the preparation method described in this invention, in step S1, calcination is performed at 600°C for 4 hours.

[0022] In a preferred embodiment of the preparation method described in this invention, in step S1, the volume ratio of ethanol to water in the ethanol aqueous solution is 1:(1.5~2.5).

[0023] More preferably, in step S1, the volume ratio of ethanol to water in the ethanol-water solution is 1:2.

[0024] In a preferred embodiment of the preparation method described in this invention, in step S1, the ratio of hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, cyclohexane, tetraethoxysilane, aqueous ethanol solution and ammonia is: (0.9~1.1) g : (3.9~4.1) g : (45~55) mL : (4.9~5.1) g : (195~205) mL : (4.9~5.1) mL.

[0025] More preferably, in step S1, the ratio of hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, cyclohexane, tetraethoxysilane, aqueous ethanol solution and ammonia is 1 g: 4 g: 50 mL: 5 g: 200 mL: 5 mL.

[0026] In a preferred embodiment of the preparation method described in this invention, in step S1, the sample is washed with ethanol and water.

[0027] In a preferred embodiment of the preparation method described in this invention, in step S1, the sample is calcined in air.

[0028] In a preferred embodiment of the preparation method described in this invention, in step S1, the mixture is stirred at 400~600 r / min.

[0029] As a more preferred embodiment of the preparation method of the present invention, in step S1, the mixture is stirred at 500 r / min.

[0030] In a preferred embodiment of the preparation method described in this invention, in step S2, the reaction is stirred for 12 h.

[0031] In a preferred embodiment of the preparation method described in this invention, in step S2, the speed is 700~900 r / min.

[0032] In a more preferred embodiment of the preparation method described in this invention, in step S2, the speed is 800 r / min.

[0033] In a preferred embodiment of the preparation method described in this invention, in step S2, the sample is calcined at 500°C for 2 hours.

[0034] In a preferred embodiment of the preparation method described in this invention, in step S2, the product is dried at 70-90°C for 20-30 h and then calcined.

[0035] More preferably, in step S2, the product is dried at 80°C for 24 hours and then calcined.

[0036] In a preferred embodiment of the preparation method described in this invention, step S2 involves calcination in air.

[0037] In a preferred embodiment of the preparation method described in this invention, in step S2, the concentration of the aluminum chloride solution is 18%~22% w / v.

[0038] More preferably, in step S2, the concentration of the aluminum chloride solution is 20% w / v.

[0039] In a preferred embodiment of the preparation method of the present invention, in step S2, AlCl3•6H2O is dissolved in water to prepare an aluminum chloride solution, wherein the mass ratio of AlCl3•6H2O, PDA and flower-shaped SiO2 is (2~48):1:10.

[0040] More preferably, in step S2, the mass ratio of AlCl3•6H2O, PDA and flower-shaped SiO2 is 24:1:10.

[0041] Thirdly, the present invention provides a method for preparing the catalyst, wherein yttrium trichloroacetate and glycerol are mixed under an inert gas atmosphere, and diethylzinc is added under ice-water bath conditions to obtain a rare earth ternary catalyst, and then flower-shaped SiO2@Al2O3 prepared by the above preparation method is added, and the mixture is stirred for 0.8~1.5 h to obtain the catalyst.

[0042] As a preferred embodiment of the preparation method described in this invention, stirring is performed for 1 hour.

[0043] In a preferred embodiment of the preparation method described in this invention, the mass ratio of yttrium trichloroacetate, glycerol, and diethylzinc is (0.018~0.022):(0.09~0.11):(0.18~0.22).

[0044] More preferably, the mass ratio of yttrium trichloroacetate, glycerol and diethylzinc is 0.02:0.1:0.2.

[0045] In a preferred embodiment of the preparation method described in this invention, the mass ratio of the flower-like SiO2@Al2O3 to diethylzinc is (3~6):1.

[0046] More preferably, the mass ratio of the flower-shaped SiO2@Al2O3 to diethylzinc is 5:1.

[0047] Fourthly, the present invention provides the application of the catalyst in the synthesis of polycarbonate.

[0048] Fifthly, the present invention provides a method for synthesizing polycarbonate, wherein the catalyst, propylene oxide, cyclohexene oxide and tetrahydrofuran are mixed, CO2 is introduced to maintain a pressure of 2-5 MPa, and the mixture is stirred at 70-100°C for 10-14 h to prepare polycarbonate.

[0049] In a preferred embodiment of the preparation method described in this invention, the pressure is 4 MPa. Pressure has a significant impact on catalytic efficiency. At low CO2 pressure, the reduced system concentration leads to decreased catalytic efficiency, while high pressure and high CO2 concentration cause a decrease in the solubility of the copolymer, thereby reducing catalytic efficiency.

[0050] In a preferred embodiment of the preparation method described in this invention, the temperature is 90°C. The reaction temperature has a certain impact on catalytic efficiency, weight-average molecular weight, and ester unit content; excessively high or low temperatures will cause a decrease in catalytic efficiency.

[0051] As a preferred embodiment of the preparation method described in this invention, the reaction is stirred for 12 h.

[0052] In a preferred embodiment of the preparation method described in this invention, the ratio of the catalyst, propylene oxide, cyclohexene oxide and tetrahydrofuran is (0.1~5) g : (9.8~10.2) mL : (1.4~1.6) mL : (9.8~10.2) mL.

[0053] More preferably, the ratio of the catalyst, propylene oxide, cyclohexene oxide and tetrahydrofuran is 4 g: 10 mL: 1.5 mL: 10 mL.

[0054] In a preferred embodiment of the preparation method described in this invention, the stirring parameters are 800~1200 r / min.

[0055] More preferably, the stirring parameter is 1000 r / min.

[0056] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a catalyst for the copolymerization of carbon dioxide and epoxides into polycarbonate using a flower-like SiO2@Al2O3 support and a method for its application. The invention prepares a SiO2@Al2O3 support with a bilayer structure. Utilizing its large specific surface area, abundant radial pore structure, and abundant contactable active surfaces, a rare-earth ternary catalyst is supported to obtain a highly efficient polycarbonate synthesis catalyst, thus overcoming the problems of insufficient catalytic efficiency and difficulty in separation of existing catalysts. The catalyst prepared by this invention features high catalytic efficiency (TON), high polycarbonate molecular weight, high ester segment content, and easy separation after the reaction. The catalytic efficiency can reach over 30,000 g / mol, the ester segment content is greater than 92%, and the weight-average molecular weight exceeds 40,000. Detailed Implementation

[0057] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Unless otherwise specified, other materials and reagents used in the embodiments are commercially available.

[0058] Example 1: Preparation method of SiO2@Al2O3 supported rare earth ternary catalyst 1. Dissolve 2 g CTAB (hexadecyltrimethylammonium bromide) and 8 g PVP (polyvinylpyrrolidone) in a 400 mL mixture of water and ethanol (water:ethanol = 2:1, volume ratio). Add 100 mL cyclohexane and 10 g TEOS (tetraethoxysilane) while stirring at 500 r / min. After stirring for 2 h, add 10 mL ammonia and continue stirring for 8 h to obtain a suspension. Transfer the suspension to a high-pressure reactor and react overnight (12 h) at 150 °C to obtain the reaction product. Centrifuge the reaction product at 8000 r / min for 10 min, collect the solid product, wash twice with ethanol and twice with water, freeze-dry, and calcine in air at 600 °C for 4 h to obtain flower-like SiO2.

[0059] 2. Weigh 24 g of AlCl3•6H2O and dissolve it in water to prepare a 20% (w / v) aluminum chloride solution. Add 1 g of DA (dopamine hydrochloride) and 10 g of flower-shaped SiO2, mix well, and stir vigorously (800 r / min) overnight (12 h) to obtain the reaction product. Centrifuge at 8000 r / min for 10 min to collect the precipitate, wash with water to remove excess soluble salts, collect the precipitate, dry it at 80℃ for 24 h, crush it, and calcine it in air atmosphere for 2 h at a calcination temperature of 500℃ to obtain flower-shaped SiO2@Al2O3, which can be used as a carrier.

[0060] 3. Add 0.02 g of yttrium trichloroacetate and 0.1 g of glycerol to a closed container under an inert atmosphere (N2) to form a clear solution. Then, add 0.2 g of diethylzinc under ice-water bath conditions to form a rare earth ternary catalyst. Stir at 150 r / min, add 1 g of flower-shaped SiO2@Al2O3, and stir for 1 h to obtain the SiO2@Al2O3 supported rare earth ternary catalyst.

[0061] Example 2: Effect of different reaction temperatures on the results of catalytic polymerization The catalytic properties of the SiO2@Al2O3 supported rare earth ternary catalyst prepared in Example 1 were investigated using an intermittent batch reactor.

[0062] 4 g of SiO2@Al2O3 supported rare earth ternary catalyst, 10 mL of propylene oxide, 1.5 mL of cyclohexene oxide and 10 mL of tetrahydrofuran were weighed and added to a 150 mL high-pressure reactor. CO2 was introduced to maintain the pressure inside the reactor at 4 MPa. The reactor was stirred at 1000 r / min for 12 h at different temperatures (70℃, 80℃, 90℃ and 100℃) to prepare polycarbonate.

[0063] Molecular weight analysis of polycarbonates prepared under different temperature conditions was performed by liquid chromatography. The instrument used was an Agilent 1260 high-performance liquid chromatograph (HPLC), with an injection volume of 15 μL (sample dissolved in tetrahydrofuran). Chromatographic separation conditions: mobile phase: tetrahydrofuran; flow rate: 0.8 mL / min; column temperature: 35℃; detector: RID-10A; molecular weight quantification was performed using the external standard method.

[0064] Table 1 The effects of different reaction temperatures on the catalytic polymerization results are shown in Table 1. It can be seen that the reaction temperature has a certain impact on the catalytic efficiency, weight-average molecular weight, and carbonate repeating unit content. Both excessively high and low temperatures will cause a decrease in catalytic efficiency. The catalyst exhibits the best catalytic efficiency at 90℃. Furthermore, as the temperature increases, the ester repeating unit content gradually decreases, which can be attributed to the fact that high temperatures favor the homopolymerization of epoxides and the formation of byproducts.

[0065] Example 3: Effect of different reaction pressures on the results of catalytic polymerization In Example 2, the reaction temperature was set at 90°C, and the pressures inside the reactor were 2 MPa, 3 MPa, 4 MPa, and 5 MPa, respectively. Other preparation and detection methods were the same as in Example 2. Polycarbonate was prepared and tested. The effect of different reaction pressures on the catalytic polymerization results was investigated.

[0066] Table 2 The effects of different reaction pressures on the catalytic polymerization results are shown in Table 2. The results indicate that pressure has a significant impact on catalytic efficiency. This is because at low CO2 pressures, the reduced system concentration leads to decreased catalytic efficiency, while high pressure and high CO2 concentrations reduce the solubility of the copolymer, thus decreasing catalytic efficiency. Therefore, a higher catalytic efficiency is observed at 4 MPa.

[0067] Example 4 Effect of SiO2@Al2O3 support content on catalytic polymerization results In Example 1, the content of flower-like SiO2@Al2O3 supported rare earth ternary catalyst was set up with 0.6 g, 0.8 g, 1 g, and 1.2 g of the catalyst, respectively. The resulting SiO2@Al2O3 supported rare earth ternary catalyst was then prepared and tested according to the method in Example 2. The effect of the flower-like SiO2@Al2O3 content in different composite catalysts on the catalytic polymerization results was investigated.

[0068] Table 3 The effects of different flower-shaped SiO2@Al2O3 support contents on the catalytic polymerization results are shown in Table 3. The catalytic efficiency gradually increases with increasing flower-shaped SiO2@Al2O3 support content, then decreases. This is because a smaller amount of flower-shaped SiO2@Al2O3 support results in fewer linking sites for the active components, while excessive support leads to the encapsulation of active sites. Therefore, the optimal flower-shaped SiO2@Al2O3 support content is 1 g.

[0069] Example 5 Effect of Al2O3 content on catalytic polymerization results In Example 1, during the preparation of flower-like SiO2@Al2O3, the AlCl3•6H2O content used in the step of preparing the 20% (w / v) aluminum chloride solution was 2.4 g, 12 g, 24 g, and 48 g, respectively, to prepare flower-like SiO2@Al2O3 with different Al2O3 contents and catalysts with SiO2@Al2O3 supported on rare earth ternary catalysts with different Al2O3 contents. Polycarbonate was then prepared and tested according to the method in Example 2. The effect of the flower-like SiO2@Al2O3 content in different composite catalysts on the catalytic polymerization results was investigated.

[0070] Table 4 The effects of different Al2O3 contents on the catalytic polymerization results are shown in Table 4. The results show that the catalytic efficiency gradually increases and then decreases with increasing Al2O3 content in the SiO2@Al2O3 support. This is because a lower Al2O3 content results in fewer linking sites for the active components, while excessive Al2O3 may reduce the specific surface area and pore blockage of the SiO2@Al2O3 support, thus reducing the binding efficiency of the rare earth ternary catalyst and decreasing the mass transfer effect. Therefore, the optimal Al2O3 content in the SiO2@Al2O3 support is 50 wt%.

[0071] Effect of flower-shaped SiO2 in the support on the catalyst in Comparative Example 1 Using Al2O3 without a flower-like SiO2 substrate as a support to support a rare earth ternary catalyst as a comparative example, the preparation method of the rare earth ternary catalyst with Al2O3 support is as follows: 1. Weigh 24 g of AlCl3•6H2O and dissolve it in water to prepare a 20% aluminum chloride solution. Add 50 mL of 5% (w / v) dopamine hydrochloride solution and 1 mL of ammonia water, mix well, and stir vigorously (800 r / min) overnight (12 h) to obtain the reaction product. Centrifuge at 8000 r / min to collect the precipitate, wash with water to remove excess soluble salts, collect the precipitate, dry it at 80℃ for 24 h, crush it, and calcine it in air atmosphere for 2 h at 500℃ to obtain Al2O3 as a support.

[0072] 2. Add 0.02 g of yttrium trichloroacetate and glycerol to a closed container under an inert atmosphere to form a clear solution. Then, add 0.2 g of diethylzinc under ice-water bath conditions to form a rare earth ternary catalyst. Add 1 g of Al2O3 and stir for 1 h to obtain a rare earth ternary catalyst with Al2O3 as the support.

[0073] The catalytic effects of the two supported catalysts in Example 1 and Comparative Example 1 were investigated according to the method of Example 2. The specific surface area and pore size of Brunauer-Emmett-Teller (BET) were characterized by an ASAP 2020 V4.02 (V4.02J) physical adsorption analyzer (Micromeritics, USA).

[0074] Table 5 Table 5 shows that the supported catalyst prepared using flower-shaped SiO2 as a substrate and subsequently the SiO2@Al2O3 support has a larger specific surface area and mesoporous structure. In contrast, the specific surface area of ​​Al2O3 directly used as the support in Comparative Example 1 is significantly reduced, which is detrimental to mass transfer and the loading of rare earth ternary catalysts, resulting in insufficient catalytic performance. These results demonstrate that the single supported catalyst in Comparative Example 1 has limited performance and needs to be combined with the large specific surface area composite support constructed in Example 1 to achieve better catalytic performance.

[0075] Comparative Example 2: Effect of different metal oxides in the support on the catalyst In the catalyst preparation step of Example 1, 24 g AlCl3•6H2O was replaced with 43.4 g Ce(NO3)3·6H2O or 29.7 g Zn(NO3)2·6H2O, respectively, to obtain rare earth ternary catalysts with SiO2@Ce2O3 as support or rare earth ternary catalysts with SiO2@ZnO as support.

[0076] Table 6 As shown in Table 6, the catalytic activity of the supported catalysts is significantly dependent on the support. The catalysts with SiO2@Al2O3 as the support have better catalytic performance than those with SiO2@Ce2O3 or SiO2@ZnO as the support.

[0077] 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 catalyst for a SiO2@Al2O3 supported rare earth ternary catalyst, characterized in that, The catalyst is a rare earth ternary catalyst supported on SiO2@Al2O3. SiO2@Al2O3 has a double-layer structure, with SiO2 as the inner layer and Al2O3 as the outer layer. The rare earth ternary catalyst contains yttrium trichloroacetate, glycerol and diethylzinc.

2. The catalyst according to claim 1, characterized in that, The catalyst has a specific surface area of ​​140~160 m². 2 ·g -1 The pore size is 6~7.5 nm.

3. The catalyst according to claim 1, characterized in that, The content of Al2O3 in SiO2@Al2O3 is 9wt%~67wt%.

4. The catalyst according to claim 1, characterized in that, The catalyst contains 65.22 wt% to 78.95 wt% SiO2@Al2O3.

5. The catalyst according to claim 1, characterized in that, In the rare earth ternary catalyst, the mass ratio of yttrium trichloroacetate, glycerol, and diethylzinc is (0.018~0.022):(0.09~0.11):(0.18~0.22).

6. A method for preparing SiO2@Al2O3 in the catalyst according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Cetyltrimethylammonium bromide, polyvinylpyrrolidone, cyclohexane and tetraethoxysilane are mixed with an aqueous ethanol solution and stirred for 1.5-2.5 h. Ammonia water is added and stirring is continued for 7.5-8.5 h to obtain a suspension. The suspension is reacted at 140-160℃ for 11-13 h. The reaction product 1 is collected, washed, and calcined at 500-700℃ for 3.5-4.5 h to obtain flower-like SiO2. S2: Mix aluminum chloride solution, dopamine hydrochloride and the flower-like SiO2 prepared in step S11, stir and react for 11-13 h, collect reaction product 2, wash, and calcine at 400-500℃ for 1.5-2.5 h to obtain flower-like SiO2@Al2O3.

7. A method for preparing the catalyst according to any one of claims 1 to 5, characterized in that, Yttrium trichloroacetate and glycerol were mixed under an inert gas atmosphere, and diethylzinc was added under ice-water bath conditions to obtain a rare earth ternary catalyst. Then, flower-shaped SiO2@Al2O3 prepared by the preparation method described in claim 6 was added, and the mixture was stirred for 0.8 to 1.5 h to obtain the catalyst.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the flower-like SiO2@Al2O3 to diethylzinc is (3~6):

1.

9. The use of the catalyst according to any one of claims 1 to 5 in the synthesis of polycarbonate.

10. A method for synthesizing polycarbonate, characterized in that, The catalyst described in any one of claims 1 to 5, propylene oxide, cyclohexene oxide, and tetrahydrofuran are mixed, and CO2 is introduced to maintain a pressure of 2 to 5 MPa. The mixture is stirred at 70 to 100°C for 10 to 14 h to prepare polycarbonate.

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