SiO2 nanoparticle loaded metal catalyst with core-shell structure as well as preparation and application of SiO2 nanoparticle loaded metal catalyst

Abstract

The invention belongs to the technical field of preparation of metal catalysts, and particularly relates to a core-shell structure SiO2 nanoparticle supported metal catalyst and preparation and application thereof, and the core-shell structure SiO2 nanoparticle supported metal catalyst is characterized by comprising preparation of core-shell structure SiO2 nanoparticles and preparation of a supported metal catalyst; a reduction system composed of the core-shell structure SiO2 nanoparticle loaded metal catalyst and hydroboron is used for reducing a liquid carboxyl-terminated fluorine-containing polymer. Compared with the prior art. The method has the beneficial effects that (1) the SiO2 nanoparticles (YSNPs) are of a core-shell mesoporous structure and are of great significance when being used as a carrier of a metal catalyst to reduce the liquid carboxyl-terminated fluorine-containing polymer, the liquid carboxyl-terminated fluorine-containing polymer is efficiently reduced at a low temperature within a short time, the optimal reduction rate reaches 85%, and the secondary utilization reduction rate still can reach 75%; the metal catalyst not only can be used as a functional fluorine-containing polymer key raw material, but also can be directly applied to the fields of gluing, sealing, surface coating, material modification and the like.

Description

Technical Field

[0001] This invention belongs to the field of metal catalyst preparation technology, and particularly relates to a core-shell structured SiO2 nanoparticle-supported metal catalyst and its preparation and application. Background Technology

[0002] Liquid-terminated functionalized fluoropolymers not only share similar main-chain structures and monomer compositions with solid fluoropolymers, exhibiting excellent thermal stability, oil resistance, and chemical resistance, but also possess unparalleled flowability and plasticity compared to solid fluoropolymers. This makes them easier to process, mold, and cure, making them indispensable and irreplaceable high-performance materials for vehicles such as automobiles, locomotives, ships, and aircraft. The oxidative degradation method for preparing liquid-terminated functionalized fluoropolymers involves oxidatively degrading high-molecular-weight fluoropolymers into low-molecular-weight liquid-terminated functionalized fluoropolymers with active functional groups. This method offers advantages such as readily available raw materials (which can be production waste), simple processing, high yield, low cost, and greater economic and environmental benefits, making it suitable for the recycling of fluoropolymers. However, the oxidative degradation method often only produces liquid-terminated functionalized fluoropolymers containing terminal carboxyl unsaturated groups. Due to the influence of these terminal carboxyl unsaturated groups, the curing, heat resistance, and aging resistance of liquid-terminated carboxyl fluoropolymers are inferior. Related studies have shown that reducing terminal carboxyl groups to terminal hydroxyl groups can significantly improve the curing, heat resistance, and aging resistance properties of fluoropolymers. Currently, the application of NaBH4 / metal chloride reduction systems in the reduction of liquid terminal carboxyl fluoropolymers has been reported, such as NaBH4 / CeCl3, NaBH4 / AlCl3, and NaBH4 / SmCl3 systems. However, these reduction systems are all heterogeneous catalytic reduction systems, with high reduction reaction temperatures (90 °C), long reaction times (6 h), and problems such as residual catalyst in the product that are difficult to separate and recover. Therefore, developing a supported, highly active catalyst provides a feasible solution to these problems and is of great significance for the preparation of high-purity, low-molecular-weight terminal hydroxyl fluoropolymers. Summary of the Invention

[0003] The purpose of this invention is to provide a core-shell structured SiO2 nanoparticle-supported metal catalyst and its preparation and application, overcoming the shortcomings of existing technologies. It utilizes a reduction system composed of YSNPs-M and borohydrides, prepares YSNPs using a microwave-assisted method, and uses the YSNPs to support the metal catalyst to obtain YSNPs-M. Liquid-terminated carboxyl-containing fluorinated polymers are then reduced to liquid-terminated hydroxyl-containing fluorinated polymers under the action of the borohydride / YSNPs-M reduction system. This achieves effective catalyst recovery and reuse, improves the purity of the reduction product, reduces costs, and simultaneously lowers reaction time and temperature.

[0004] To achieve the above objectives, the present invention provides the following technical solution: One technical solution: A method for preparing a metal catalyst supported on core-shell structured SiO2 nanoparticles, characterized by comprising the preparation of core-shell structured SiO2 nanoparticles and the preparation of the supported metal catalyst, specifically including the following steps: The preparation of core-shell structured SiO2 nanoparticles involved adding water, ethanol, ammonia, and 3-aminophenol into a container, controlling the microwave power, and stirring under microwave conditions for the first time. Then, tetraethyl orthosilicate and formaldehyde solution were added dropwise, and stirring was carried out a second time with the same microwave power and speed. The reaction solids were collected by centrifugation, and the reaction solids were dried and calcined to obtain core-shell structured SiO2 nanoparticles. To prepare the supported metal catalyst, core-shell SiO2 nanoparticles and metal chlorides were dissolved in methanol. After stirring at room temperature for 2 h, the mixture was placed in a vacuum environment for 2 h to allow the metal chloride methanol solution to fully penetrate the core-shell SiO2 nanoparticles. Then, the mixture was stirred at 100 °C until the methanol was completely evaporated. Tetrahydrofuran and diisobutylaluminum hydride were added sequentially at room temperature to react with the metal chloride inside the core-shell SiO2 nanoparticles. After stirring at room temperature for 5 minutes, the reaction solid was collected by centrifugation, which is the core-shell SiO2 nanoparticle supported metal catalyst.

[0005] In step 1), the microwave power is 20-100 W; the ratio of water:ethanol:ammonia:3-aminophenol:ethyl orthosilicate:formaldehyde solution is 90 ml:45 ml:0.4 ml:1 g:2-8 ml:1.5 ml; the first stirring time is 2-6 min, and the second stirring time is 2-6 min; the calcination conditions are 500-600℃ and calcination time is 4-6 h; the water is deionized water, and the ethanol, ammonia, 3-aminophenol, ethyl orthosilicate, and formaldehyde solution are all analytical grade reagents.

[0006] In step 2), the metal chloride is any one of lanthanum chloride, neodymium chloride, cerium chloride, or samarium chloride; in step 2), the core-shell structured SiO2 nanoparticles and the metal chloride are in a mass ratio of 1:2; the amount of tetrahydrofuran is 15 ml; the amount of diisobutylaluminum hydride is 15 mmol; the metal chloride, diisobutylaluminum hydride, and tetrahydrofuran are all analytical grade reagents.

[0007] Technical Solution 2: A core-shell structured SiO2 nanoparticle-supported metal catalyst, characterized in that the core-shell structured SiO2 nanoparticle-supported metal catalyst is prepared by the preparation method according to any one of claims 1-3.

[0008] Technical Solution 3: Application of a core-shell structured SiO2 nanoparticle-supported metal catalyst, characterized in that the core-shell structured SiO2 nanoparticle-supported metal catalyst and borohydride form a reduction system for reducing liquid-terminated carboxyl fluorinated polymers.

[0009] The borohydride is any one of sodium borohydride, potassium borohydride, or lithium borohydride; the molar ratio of the borohydride to the carboxyl group in the liquid-terminated carboxyl-containing fluoropolymer is 1:1-5:1; the ratio of the metal catalyst supported on the core-shell structured SiO2 nanoparticles to the borohydride is 1 g:2-8 mmol; all borohydrides are analytical grade reagents.

[0010] The number average molecular weight of the liquid-terminated carboxyl-containing fluoropolymer is 0.5 × 10⁻⁶. 3 -5×10 4 Polymers containing fluorine atoms on the carbon atoms of the main chain or side chain and containing carboxyl groups at the chain ends.

[0011] The liquid carboxyl-terminated fluoropolymer is a binary copolymer of fluoroolefins containing carboxyl-terminated groups or a terpolymer of fluoroolefins containing carboxyl-terminated groups.

[0012] The fluoroolefin binary copolymer containing a terminal carboxyl group is any one of vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-monochlorotrifluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, or vinylidene fluoride-perfluoroethyl vinyl ether copolymer; the fluoroolefin terpolymer containing a terminal carboxyl group includes any one of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, vinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer, or vinylidene fluoride-tetrafluoroethylene-perfluoroethyl vinyl ether terpolymer.

[0013] The reaction principle of this invention is as follows: Microwave-controlled reaction rates of 3-aminophenol and formaldehyde solution, as well as the hydrolysis rate of tetraethyl orthosilicate, are used to prepare SiO2 nanoparticles (YSNPs). Simultaneously, the unique core-shell structure of YSNPs provides more anchoring sites and active sites for the loading of metal catalysts, which is beneficial for catalyst loading and the progress of the reduction reaction. Furthermore, the YSNPs have a particle size of approximately 250 nm, and after the reaction, they can be separated from the liquid product through conventional operations such as filtration, sedimentation, or centrifugation.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes a microwave-assisted method to prepare core-shell mesoporous SiO2 nanoparticles (YSNPs) in a relatively short reaction time. YSNPs possess advantages such as large specific surface area, heat resistance, and dimensional stability. Using them as a support for metal catalysts is of great significance for the reduction of liquid-terminated carboxyl-containing fluoropolymers, enabling highly efficient reduction of these polymers at low temperatures and in a short time, with an optimal reduction rate reaching 85%, and a secondary utilization reduction rate still achieving 75%. 2) Core-shell structured SiO2 nanoparticles supporting metal catalysts can be easily recovered and reused, improving the purity of reduction products and reducing production costs; 3) The low molecular weight hydroxyl-terminated fluoropolymer prepared by the core-shell structure SiO2 nanoparticles supported by the metal catalyst of this invention has stable chemical properties and wide applications. It can not only be used as a key raw material for functional fluoropolymers, but also be directly applied to adhesives, sealants, surface coatings and material modification. Attached Figure Description

[0015] Figure 1 The images show scanning electron microscope (SEM) images (a) and transmission electron microscope (TEM) images (b) of YSNPs prepared in Example 1 of the present invention, TEM images (c) of nanoparticles prepared in Comparative Example 3, and TEM images (d) of composite nanoparticles prepared in Comparative Example 2. Figure 2 The infrared spectrum of the reduction product in Example 1 of this invention is shown. Detailed Implementation

[0016] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0017] To more clearly illustrate the technical solutions in the specific embodiments of the present invention or the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The components of the embodiments of the present invention described and shown in the accompanying drawings can typically be arranged and designed in many different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention.

[0018] In the following examples, the ratio of water:ethanol:ammonia:3-aminophenol:tetraethyl orthosilicate:formaldehyde solution was 90 ml:45 ml:0.4 ml:1 g:2-8 ml:1.5 ml; the first stirring time was 2-6 min, and the second stirring time was 2-6 min; the calcination conditions were 500-600℃ for 4-6 h; the water was deionized water, and the ethanol, ammonia, 3-aminophenol, tetraethyl orthosilicate, and formaldehyde solution were all analytical grade reagents. The core-shell structured SiO2 nanoparticles and metal chloride were used in a mass ratio of 1:2; the amount of tetrahydrofuran was 15 ml; the amount of diisobutylaluminum hydride was 15 mmol; the metal chloride, diisobutylaluminum hydride, and tetrahydrofuran were all analytical grade reagents.

[0019] This core-shell structured SiO2 nanoparticle-supported metal catalyst, along with borohydride, forms a reduction system for reducing liquid-terminated carboxyl-containing fluoropolymers. The borohydride is any one of sodium borohydride, potassium borohydride, or lithium borohydride; the molar ratio of borohydride to carboxyl groups in the liquid-terminated carboxyl-containing fluoropolymer is 1:1-5:1; the molar ratio of the core-shell structured SiO2 nanoparticle-supported metal catalyst to borohydride is 1 g:2-8 mmol; all borohydrides are analytical grade reagents. The number average molecular weight of the liquid-terminated carboxyl-containing fluoropolymer is 0.5 × 10⁻⁶. 3 -5×10 4 Within this range, polymers containing fluorine atoms on the carbon atoms of the main chain or side chain and containing carboxyl groups at the chain ends. The liquid carboxyl-terminated fluoropolymer is a binary copolymer of fluoroolefins containing carboxyl groups or a terpolymer of fluoroolefins containing carboxyl groups.

[0020] Example 1 A method for preparing a metal catalyst supported on core-shell SiO2 nanoparticles includes the preparation of core-shell SiO2 nanoparticles and the preparation of the supported metal catalyst, specifically including the following steps: To prepare core-shell structured SiO2 nanoparticles, 90 ml of water, 45 ml of ethanol, 400 μl of ammonia, and 1 g of 3-aminophenol were poured into a 500 ml beaker. The mixture was stirred for 5 min under microwave conditions at 50 W. Then, 4 ml of tetraethyl orthosilicate and 1.5 ml of formaldehyde solution were added dropwise, and the mixture was stirred a second time for 5 min at the same microwave power and speed. The reaction solids were collected by centrifugation, dried in a forced-air drying oven at 60 °C, and then calcined in a muffle furnace at 550 °C for 6 h to obtain core-shell structured SiO2 nanoparticles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images are shown below. Figure 1 (a) and Figure 1 (b) It can be observed that the nanoparticles have a core-shell structure; To prepare the supported metal catalyst, 2 g of core-shell SiO2 nanoparticles and 4 g of cerium chloride were dissolved in 20 ml of methanol. After stirring at room temperature for 2 h, the solution was placed in a vacuum environment for 2 h to allow the metal chloride methanol solution to fully penetrate the core-shell SiO2 nanoparticles. Then, the mixture was stirred at 100 °C until the methanol was completely evaporated. 20 ml of tetrahydrofuran and 15 mmol of diisobutylaluminum hydride were added sequentially at room temperature to react with the metal chloride inside the core-shell SiO2 nanoparticles. After stirring at room temperature for 5 minutes, the reaction solid was collected by centrifugation, which is the core-shell SiO2 nanoparticle supported metal catalyst (abbreviated as YSNPs-M). Five g of a liquid carboxyl-terminated fluoropolymer (vinylidene fluoride-hexafluoropropylene copolymer, carboxyl content 2.5% by mass, number average molecular weight 3600, carboxyl content 2.8 mmol) was dissolved in 15 ml of a mixed solution of tetrahydrofuran and 15 ml of diethylene glycol dimethyl ether. At 0 °C, 0.5 g of sodium borohydride reducing agent was added, and the mixture was stirred for 1 h. Then, 3 g of YSNPs-M prepared in Example 1 was added, and the temperature was raised to 40 °C. Stirring was continued for 2 h. After the reaction was complete, the reaction was quenched with hydrochloric acid until the solution pH was neutral. YSNPs-M was recovered from the solution by centrifugation. Deionized water was then added to the solution, and the liquid fluoropolymer precipitated. The precipitate was collected and vacuum dried at 60 °C to constant weight. Chemical titration determined that the reduction rate of the liquid carboxyl-terminated fluoropolymer was 85%. Figure 2 In the diagram, line a represents the infrared spectrum of the liquid-terminated carboxyl-terminated fluorinated polymer, and line b represents the infrared spectrum of the reduction product. Compared to line a, line b has a higher infrared spectrum at 1769 cm⁻¹. -1 The characteristic peak of the carbon-oxygen double bond (carbonyl group) in the corresponding carboxyl group is significantly weakened, indicating that the carboxyl group has been successfully reduced.

[0021] Example 2 The preparation and testing were carried out according to Example 1, the difference being that the amount of tetraethyl orthosilicate used in step 1) of Example 1 was different, the amount of tetraethyl orthosilicate used was 7 ml. The results showed that a core-shell structured SiO2 nanoparticle-supported metal catalyst could be obtained, and the reduction rate of the liquid-terminal carboxyl fluorinated polymer was 82%.

[0022] Example 3 The preparation and testing were carried out according to Example 1, except that the microwave power of step 1) of Example 1 was different, and the microwave power was 80 W. The results showed that a core-shell structured SiO2 nanoparticle-supported metal catalyst could be obtained, and the liquid end carboxyl fluorinated polymer rate was 82%.

[0023] Example 4 The preparation and testing were carried out according to Example 1, the difference being that the type of metal chloride loaded in step 2) of Example 1 was different, and lanthanum chloride catalyst was loaded, with a reduction rate of 83%.

[0024] Example 5 The preparation and testing were carried out according to Example 1, except that the type of borohydride in step 3) of Example 1 was different, potassium borohydride was used, and the reduction rate was 84%.

[0025] Example 6 The preparation and testing were carried out according to Application Example 1, except that the YSNPs-M separated and recovered after the reduction reaction in Application Example 1 was applied again to the reduction reaction of the liquid-terminated carboxyl fluoropolymer, and the reduction rate was 75%.

[0026] Example 7 The preparation and testing were carried out according to Example 1, except that the liquid-terminal carboxyl-containing fluoropolymer in step 3) of Example 1 was different. Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (carboxyl mass percentage 2.5%, number average molecular weight 3650, carboxyl content 2.8 mmol) was used, and the reduction rate was 84%.

[0027] Comparative Example 1 Five g of a liquid carboxyl-terminated fluoropolymer (vinylidene fluoride-hexafluoropropylene copolymer, carboxyl content 2.5% by mass, number average molecular weight 3600, carboxyl content 2.8 mmol) was dissolved in a mixed solution of 15 ml tetrahydrofuran and 15 ml diethylene glycol dimethyl ether. At 0 °C, 0.5 g of sodium borohydride reducing agent was added, and the mixture was stirred for 1 h. Then, 2 g of cerium chloride was added, and the temperature was raised to 40 °C for 6 h. After the reaction was complete, the reaction was quenched with hydrochloric acid until the solution pH was neutral. The solution was repeatedly washed with deionized water until the liquid fluoropolymer precipitated. The precipitate was collected and dried under vacuum at 60 °C to constant weight. The reduction rate of the liquid carboxyl-terminated fluoropolymer was determined to be 55% by chemical titration.

[0028] Comparative Example 2 To prepare core-shell structured SiO2 nanoparticles, 90 ml of water, 45 ml of ethanol, 400 μl of ammonia, and 1 g of 3-aminophenol were poured into a 500 ml beaker. The mixture was stirred for 5 min under microwave conditions at 200 W. Then, 4 ml of tetraethyl orthosilicate and 1.5 ml of formaldehyde solution were added dropwise, and the mixture was stirred a second time for 5 min at the same microwave power and speed. The reaction solids were collected by centrifugation, dried in a forced-air drying oven at 60 °C, and then calcined in a muffle furnace at 550 °C for 6 h to obtain core-shell structured SiO2 nanoparticles. Transmission electron microscopy (TEM) images are shown below. Figure 1 As shown in d, it can be observed that the outer shell of the prepared nanoparticles is mostly broken and no mesoporous core is formed.

[0029] To prepare the supported metal catalyst, 2 g of core-shell SiO2 nanoparticles and 4 g of cerium chloride were dissolved in 20 ml of methanol. After stirring at room temperature for 2 h, the solution was placed in a vacuum environment for 2 h to allow the metal chloride methanol solution to fully penetrate the core-shell SiO2 nanoparticles. Then, the mixture was stirred at 100 °C until the methanol was completely evaporated. 20 ml of tetrahydrofuran and 15 mmol of diisobutylaluminum hydride were added sequentially at room temperature to react with the metal chloride inside the core-shell SiO2 nanoparticles. After stirring at room temperature for 5 minutes, the reaction solid was collected by centrifugation, which is the core-shell SiO2 nanoparticle supported metal catalyst (abbreviated as YSNPs-M). Five g of a liquid carboxyl-terminated fluoropolymer (vinylidene fluoride-hexafluoropropylene copolymer, carboxyl content 2.5% by mass, number average molecular weight 3600, carboxyl content 2.8 mmol) was dissolved in a mixed solution of 15 ml tetrahydrofuran and 15 ml diethylene glycol dimethyl ether. At 0 °C, 0.5 g of sodium borohydride reducing agent was added, and the mixture was stirred for 1 h. Then, 3 g of YSNPs-M prepared in Example 1 was added, and the temperature was raised to 40 °C. Stirring was continued for 2 h. After the reaction was complete, the reaction was quenched with hydrochloric acid until the solution pH was neutral. YSNPs-M was recovered from the solution by centrifugation. Deionized water was then added to the solution, and the liquid fluoropolymer precipitated. The precipitate was collected and vacuum dried at 60 °C to constant weight. The reduction rate of the liquid carboxyl-terminated fluoropolymer was determined to be 61% by chemical titration.

[0030] Comparative Example 3 The preparation and testing were performed according to Comparative Example 2, the difference being that microwave assistance was not used in step 1) of Comparative Example 2, and the reduction rate was 64%. Transmission electron microscopy images are shown below. Figure 1 As shown in Figure c, it can be observed that the prepared nanoparticles have a hollow structure and no mesoporous core is formed.

[0031] Comparative Example 4 The nanoparticles were prepared and tested according to Comparative Example 2. The difference was that in step 1) of Comparative Example 2, the microwave power was 50W and the second stirring was 20 minutes. As a result, the prepared nanoparticle shells were more broken and no mesoporous cores were formed, with a reduction rate of 60%.

[0032] This invention employs a microwave-assisted method to prepare YSNPs, significantly shortening the reaction time. Simultaneously, by utilizing YSNPs to support a metal catalyst and form a reduction system with borohydrides, low molecular weight terminal carboxyl-containing fluoropolymers are reduced. Under conditions of a reaction temperature of 40 °C and a reaction time of 2 h, highly efficient reduction of low molecular weight terminal carboxyl-containing fluoropolymers is achieved, with a maximum reduction rate reaching 85%, representing a significant improvement in performance compared to existing products.

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a core-shell structured SiO2 nanoparticle supported metal catalyst, characterized by, The preparation of core-shell structure SiO2 nanoparticles and the preparation of metal catalyst loaded thereon, specifically comprising the following steps: 1) Preparation of core-shell structure SiO2 nanoparticles, water, ethanol, ammonia and 3-amino phenol are added into a container, and a certain microwave power is controlled, and the first stirring is carried out under microwave conditions; then the tetraethyl orthosilicate and formaldehyde solution are added drop by drop, and the second stirring is carried out at the same microwave power and speed; the reaction solid is collected by centrifugal separation, and the reaction solid is dried and calcined to obtain the core-shell structure SiO2 nanoparticles; 2) Preparation of metal catalyst loaded on the core-shell structure SiO2 nanoparticles, the core-shell structure SiO2 nanoparticles and metal chloride are dissolved in methanol, stirred at room temperature for 2 h, and then placed in a vacuum environment for 2 h, so that the metal chloride methanol solution is fully immersed into the core-shell structure SiO2 nanoparticles; then after stirring at 100 DEG C until the methanol is completely volatilized, tetrahydrofuran and diisobutylaluminum hydride are added at room temperature, and the metal chloride in the core-shell structure SiO2 nanoparticles is reacted, and after stirring at room temperature for 5 minutes, the reaction solid is collected by centrifugal separation, which is the core-shell structure SiO2 nanoparticles loaded with metal catalyst.

2. The method for preparing a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 1, characterized in that, In the step 1), the microwave power is 20-100 W; the ratio of water:ethanol:ammonia:3-amino phenol: tetraethyl orthosilicate:formaldehyde solution is 90 ml:45 ml:0.4 ml:1 g:2-8 ml:1.5 ml; the first stirring time is 2-6 min, and the second stirring time is 2-6 min; the calcination condition is 500-600 DEG C, and the calcination time is 4-6 h; the water is deionized water, and the ethanol, ammonia, 3-amino phenol, tetraethyl orthosilicate and formaldehyde solution are all analytical reagents.

3. The method for preparing a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 1, characterized in that, In the step 2), the metal chloride is any one of lanthanum chloride, neodymium chloride, cerium chloride or samarium chloride; the mass ratio of the core-shell structure SiO2 nanoparticles and the metal chloride in step 2) is 1:2; the amount of tetrahydrofuran is 15 ml; the amount of diisobutylaluminum hydride is 15 mmol; the metal chloride, diisobutylaluminum hydride and tetrahydrofuran are all analytical reagents.

4. A core-shell structured Si02 nanoparticle supported metal catalyst, characterized in that, The core-shell structure SiO2 nanoparticles loaded with metal catalyst is prepared by the preparation method according to any one of claims 1-3.

5. The use of a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 4, wherein the metal catalyst is selected from the group consisting of platinum, palladium, rhodium, ruthenium, gold, silver, copper, iron, cobalt, nickel, and combinations thereof. The core-shell structure SiO2 nanoparticles loaded with metal catalyst is used in a reduction system with borohydride for reducing liquid carboxyl-terminated fluoropolymer.

6. The use of a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 5, wherein the metal catalyst is selected from the group consisting of platinum, palladium, rhodium, ruthenium, gold, silver, copper, iron, cobalt, nickel, and combinations thereof. The borohydride is any one of sodium borohydride, potassium borohydride or lithium borohydride; the molar ratio of borohydride to carboxyl in the liquid carboxyl-terminated fluoropolymer is 1:1-5:1; the amount ratio of the core-shell structure SiO2 nanoparticles loaded with metal catalyst to borohydride is 1 g:2-8 mmol; the borohydride is all analytical reagent.

7. The use of a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 5, wherein the metal catalyst is selected from the group consisting of platinum, palladium, rhodium, ruthenium, gold, silver, copper, iron, cobalt, nickel, and combinations thereof. The number average molecular weight of the liquid carboxyl-terminated fluoropolymer is in the range of 0.5 x 10 3 -5 x 10 4 The polymer contains fluorine atoms on the main chain or side chain carbon atoms and carboxyl groups at the chain ends.

8. The use of a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 5, wherein the metal catalyst is selected from the group consisting of platinum, palladium, rhodium, ruthenium, gold, silver, copper, iron, cobalt, nickel, and combinations thereof. The liquid carboxyl-terminated fluoropolymer is fluorine-containing olefin binary copolymer containing carboxyl terminal or fluorine-containing olefin ternary copolymer containing carboxyl terminal.

9. The use of a core-shell structured SiO2 nanoparticle supported metal catalyst according to claim 8, characterized in that, The fluorine-containing olefin-based copolymer containing terminal carboxyl groups is any one of a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-monochlorotrifluoroethylene copolymer, a vinylidene fluoride-perfluoromethyl vinyl ether copolymer, a vinylidene fluoride-hexafluoropropylene copolymer, or a vinylidene fluoride-perfluoroethyl vinyl ether copolymer; and the fluorine-containing olefin-based terpolymer containing terminal carboxyl groups includes any one of a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a vinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer, or a vinylidene fluoride-tetrafluoroethylene-perfluoroethyl vinyl ether terpolymer.

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