A core-shell type Cu-mo based catalyst with halogen resistance and its application in pet / pc mixed polyester cascade depolymerization

Abstract

The application discloses a kind of core-shell type Cu-Mo-based catalyst with halogen resistance and its application in PET / PC mixed polyester cascade depolymerization.The catalyst takes Fe3O4@SiO2 magnetic composite carrier as core, ZrO2-TiO2 composite oxide as resistance shell, and loads Cu-Mo bimetallic active component on the shell.The resistance shell can physically block the diffusion of halogen ions to the inside, and chemisorb and fix halogen ions through lattice oxygen vacancies, avoiding active site poisoning;Cu-Mo bifunctional active site cooperates with the core-shell structure, and can realize the cascade depolymerization of PC and PET at different temperature windows in turn, respectively obtaining high yield of bisphenol A and phthalic acid.The catalyst of the application does not need complex sorting pretreatment for mixed polyester raw materials containing PVC and other halogen impurities, and still maintains more than 85% activity retention rate in a system with PVC content up to 10 wt%.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, and relates to a Cu-Mo based catalyst, specifically a halogen-resistant core-shell Cu-Mo based catalyst and its application in the stepwise depolymerization of PET / PC blended polyester. Background Technology

[0002] Polyethylene terephthalate (PET) and polycarbonate (PC) are engineering plastics produced in large quantities and are widely used in packaging fibers, electronics, automotive parts, and other fields. With the continuous growth in the consumption of plastic products, the volume of waste PET and PC is increasing year by year. How to achieve efficient recycling and high-value utilization of these two types of polyester plastics has become a key focus in the field of resource recycling.

[0003] In actual recycling processes, PET and PC plastics are often mixed together. Efficient recycling of waste PET / PC mixed plastics faces two major challenges: First, the ester bond chemical environments of PET and PC differ significantly. PC's carbonate bonds have low steric hindrance and high nucleophilic reactivity, while PET's aromatic ester bonds have high electron cloud density and relatively weak reactivity. Their optimal depolymerization temperature windows do not overlap, making it difficult to achieve highly selective monomer recovery simultaneously through a single process. Second, waste plastics commonly contain halogen-containing polymers such as polyvinyl chloride (PVC). Halogen ions released during depolymerization can severely corrode equipment and poison catalysts, leading to rapid catalyst deactivation. To avoid halogen interference with the depolymerization process, existing technologies typically require strict sorting and removal of PVC through pretreatment processes such as flotation and solvent extraction, significantly increasing process costs and energy consumption, and limiting the economic viability of mixed waste plastic recycling processes.

[0004] Furthermore, existing catalytic systems suffer from a third problem: homogeneous catalytic systems are prone to separation difficulties, equipment corrosion, and secondary pollution, while heterogeneous catalysts generally suffer from the drawbacks of easy loss of active sites and poor cycle stability. In current technologies, catalysts used for polyester depolymerization are mostly homogeneous metal salts (such as zinc acetate) or conventional metal oxides. These catalysts are not only unable to resist halogen corrosion but are also difficult to separate and recover from the products. Some supported solid acids or hydrogenation catalysts exhibit activity in single polyester depolymerization, but they have poor adaptability to mixed feedstocks containing PVC, and the product distribution is complex, making it impossible to simultaneously achieve the co-production of multiple high-value-added monomers such as terephthalic acid (PTA) and bisphenol A (BPA).

[0005] Therefore, there is an urgent need to develop a heterogeneous catalyst that not only has the ability to depolymerize PET / PC mixtures in stages, but also has excellent resistance to interference and stability with chloride ions, and can be recycled multiple times, in order to reduce the sorting and pretreatment costs in the recycling process of mixed waste plastics and improve the yield and quality of target monomers. Summary of the Invention

[0006] To address the problems in existing technologies, such as the difficulty in simultaneously recovering PET / PC blended polyesters at high value through a single process, the easy corrosion of equipment and poisoning of catalysts by halogen-containing impurities, and the easy loss of active sites and poor cycle stability of heterogeneous catalysts, this invention provides a core-shell Cu-Mo based catalyst with halogen resistance, its preparation method, and its application.

[0007] The technical solution adopted in this invention is: a core-shell Cu-Mo based catalyst with halogen resistance, wherein the catalyst has a core-shell structure, the core is a Fe3O4@SiO2 magnetic composite support, and the shell is a ZrO2-TiO2 composite oxide resistant shell coated on the surface of the core; the resistant shell is loaded with metal active components Cu and Mo; based on the total mass of the catalyst, the loading of Cu is 4~6 wt%, and the loading of Mo is 4~6 wt%; the molar ratio of Zr to Ti in the resistant shell is 1:2~2:1.

[0008] The efficient recycling of PET / PC mixed plastics is challenging due to several factors. Firstly, PC exhibits low steric hindrance and high nucleophilic reactivity in its carbonate bonds, while PET has high electron cloud density and relatively weak reactivity in its aromatic ester bonds. Their optimal depolymerization temperature windows do not overlap, making it difficult for conventional single-active-site catalysts to activate both types of bonds in a controllable sequence within the same system. Secondly, halogen ions released by PVC mixed in with waste plastics upon heating can directly attack the active metal sites on the catalyst surface, causing irreversible poisoning. To address this, the catalyst of this invention employs a three-layer core-shell structure: a core support, a resistant outer shell, and surface active sites. The outer layer is a dense ZrO2-TiO2 composite oxide resistant shell, which physically blocks the diffusion of halogen ions into the interior. Simultaneously, oxygen vacancies in the outer shell lattice chemically adsorb and fix halogen ions, preventing poisoning of active sites. This allows the catalyst to maintain over 90% of its initial activity even in mixed raw materials with a PVC content as high as 5 wt%. Furthermore, through the synergy between the copper-molybdenum bifunctional active sites on the catalyst and the core-shell structure, PC and PET can be depolymerized sequentially at different temperature windows. The catalyst preferentially hydrolyzes PC at 100–140 °C to produce bisphenol A, and then raises the temperature to 160–200 °C to hydrolyze PET to obtain terephthalic acid, achieving a stepwise conversion of mixed raw materials into two high-value monomers. Simultaneously, the catalyst exhibits high tolerance to the composition ratio and impurity content of the mixed polyester raw materials, eliminating the need for complex sorting and impurity removal pretreatment. Its heterogeneous structure facilitates magnetic separation and recovery, achieving an activity retention rate of over 85% after 10 consecutive cycles. The catalyst uses an Fe3O4@SiO2 composite support as its core, allowing for simple separation using an external magnetic field while maintaining structural and activity stability during multiple cycles, making it suitable for the depolymerization of practical mixed waste plastics.

[0009] Preferably, the Cu loading is 6 wt%, the Mo loading is 4 wt%, and the molar ratio of Zr to Ti is 1:1.

[0010] Preferably, the resistant shell has a dense structure and the shell lattice contains oxygen vacancies for chemical adsorption and fixation of halide ions.

[0011] Preferably, the catalyst is magnetically separated and recovered under the action of an external magnetic field.

[0012] This invention also provides a method for preparing the core-shell Cu-Mo based catalyst, comprising the following steps:

[0013] (1) Fe3O4 nanoparticles were prepared by a solvothermal method;

[0014] (2) A SiO2 layer is coated on the surface of the Fe3O4 nanoparticles to obtain a Fe3O4@SiO2 magnetic composite carrier;

[0015] (3) Using zirconium source and titanium source as raw materials, a ZrO2-TiO2 composite oxide shell is hydrothermally grown on the surface of the Fe3O4@SiO2 magnetic composite carrier. The hydrothermal growth temperature is 160~180 ℃ and the time is 12~18 h. The product is calcined to obtain a core-shell carrier.

[0016] (4) The copper source and molybdenum source are loaded on the core-shell support by impregnation, and after drying and calcination, they are reduced in a hydrogen atmosphere to obtain the core-shell Cu-Mo based catalyst.

[0017] As a preferred embodiment, in step (1), iron salt is dissolved in ethylene glycol, sodium acetate and polyethylene glycol are added, and the mixture is reacted at 180~220℃ for 6~10 h. The product is collected by magnetic separation, washed and dried to obtain Fe3O4 nanoparticles.

[0018] Preferably, the Fe3O4 nanoparticles have a particle size of 3~5 μm.

[0019] Preferably, in step (2), Fe3O4 nanoparticles are dispersed in an ethanol-water mixture, ultrasonically dispersed, and then ammonia is added. Then, tetraethyl orthosilicate is added dropwise to carry out a hydrolysis-condensation reaction, so that SiO2 is uniformly coated on the surface of Fe3O4 nanoparticles. After magnetic separation, washing, and drying, Fe3O4@SiO2 magnetic composite carrier is obtained. The volume ratio of ethanol to water in the ethanol-water mixture is 3:1 to 5:1. The drying temperature is 50 to 70 °C.

[0020] Preferably, in step (3), the zirconium source is zirconium oxychloride and the titanium source is tetrabutyl titanate; the Fe3O4@SiO2 magnetic composite carrier is dispersed with the zirconium source and the titanium source in ethanol, diluted ammonia is added to adjust the pH to 7-9 and then hydrothermal reaction is carried out. The product is washed, dried and then calcined at 400-600 °C for 2-4 h to obtain the core-shell carrier.

[0021] Preferably, in step (4), the copper source is copper nitrate and the molybdenum source is ammonium molybdate; after impregnation by equal volume impregnation, the catalyst is allowed to stand for 8-16 h, dried at 80-120 ℃, calcined at 400-500 ℃ for 1-3 h, and then reduced at 300-400 ℃ for 1-3 h under a hydrogen atmosphere to obtain the core-shell Cu-Mo based catalyst.

[0022] Preferably, the core-shell Cu-Mo based catalyst has a particle size of 4~6 μm.

[0023] This invention also provides the application of the core-shell Cu-Mo based catalyst in the stepwise depolymerization of PET / PC blended polyester containing halogen impurities. The method is characterized by adding the PET / PC blended polyester, the catalyst, and water to a reactor and carrying out the depolymerization reaction in two stages under an inert atmosphere: the first stage is carried out at 100-140 °C to hydrolyze PC into bisphenol A; the second stage is carried out at 160-200 °C to hydrolyze PET into terephthalic acid; the polyvinyl chloride content in the PET / PC blended polyester is not higher than 10 wt%; after the reaction, the catalyst is recovered by magnetic separation and recycled.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention introduces ZrO2-TiO2 composite oxide as a halogen-resistant shell into the polyester depolymerization catalyst through a core-shell structure design, which significantly improves the catalyst's tolerance to halogen-containing impurities. It maintains more than 90% of the initial activity in mixed raw materials with a PVC content of up to 5 wt%, and greatly reduces the pretreatment cost of mixed plastic raw materials.

[0026] 2. The synergistic effect of Cu-Mo bimetallic active sites enables the stepwise depolymerization of PET and PC, with high product selectivity, and can simultaneously obtain high-value chemicals such as PTA and BPA, with good atom economy.

[0027] 3. The magnetic core facilitates rapid magnetic separation and recovery of the catalyst. After 10 consecutive cycles, the activity retention rate reaches over 85%, demonstrating excellent cycle stability and promising prospects for industrial application. Attached Figure Description

[0028] Figure 1Scanning electron microscope (SEM) images of the Fe3O4@SiO2 magnetic support (a, b) and catalyst Cat-1 (c, d) prepared in Example 1 of this invention. Detailed Implementation

[0029] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0030] Example 1:

[0031] Step 1: Preparation of Fe3O4 core: 5.4 g FeCl3·6H2O was dissolved in 100 mL ethylene glycol, 3.6 g anhydrous sodium acetate and 1.0 g polyethylene glycol were added, and the mixture was stirred until homogeneous. The mixture was then transferred to a hydrothermal reactor and reacted at 200 ℃ for 8 h. The product was collected by magnetic separation, washed three times with ethanol, and dried under vacuum at 60 ℃ to obtain Fe3O4 nanoparticles.

[0032] Step 2: SiO2 coating: Disperse 2.0 g Fe3O4 in 200 mL of ethanol-water mixture (volume ratio 4:1), sonicate for 30 min, add 5 mL of concentrated ammonia, and add 3 mL of tetraethyl orthosilicate dropwise. Stir at room temperature for 6 h. Magnetic separation and washing, dry at 60 ℃ to obtain Fe3O4@SiO2.

[0033] Step 3: ZrO2-TiO2 shell growth: 1.5 g Fe3O4@SiO2 was dispersed in 150 mL ethanol, 0.6 g zirconium oxychloride and 0.6 g tetrabutyl titanate were added, and the mixture was stirred for 30 min. Diluted ammonia was added to adjust the pH to 8, and the mixture was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h. After washing and drying, the product was calcined at 500 °C for 3 h to obtain the core-shell support.

[0034] Step 4: Cu-Mo Support: Weigh 1.0 g of core-shell support and impregnate it in a mixed solution containing 0.228 g of copper nitrate and 0.073 g of ammonium molybdate using an equal-volume impregnation method. Let it stand for 12 h, dry at 100 ℃, calcine at 450 ℃ for 2 h, and reduce at 350 ℃ for 2 h under a hydrogen atmosphere to obtain catalyst Cat-1. The Zr / Ti molar ratio is 1:1, the Cu loading is 6 wt%, and the Mo loading is 4 wt%.

[0035] Example 2:

[0036] The preparation method is the same as in Example 1, except that in step 3, the amount of zirconium oxychloride is 1.2 g, the amount of tetrabutyl titanate is 0.6 g, and the Zr / Ti molar ratio is 2:1, thus obtaining catalyst Cat-2.

[0037] Example 3:

[0038] The preparation method is the same as in Example 1, except that in step 3, the amount of zirconium oxychloride is 0.6 g, the amount of tetrabutyl titanate is 1.2 g, and the Zr / Ti molar ratio is 1:2, thus obtaining catalyst Cat-3.

[0039] Example 4:

[0040] The preparation method is the same as in Example 1, except that in step 4, the amount of copper nitrate is 0.152 g, the amount of ammonium molybdate is 0.110 g, the Cu loading is 4 wt%, and the Mo loading is 6 wt%, thus obtaining catalyst Cat-4.

[0041] Example 5:

[0042] The preparation method is the same as in Example 1, except that the hydrothermal reaction temperature in step 3 is 160 °C, the reaction time is 18 h, and the shell thickness is increased by about 30%, thus obtaining the catalyst Cat-5.

[0043] Comparative Example 1:

[0044] Instead of preparing a ZrO2-TiO2 resistant shell, Cu-Mo bimetal was directly loaded onto the Fe3O4@SiO2 surface, and the remaining steps were the same as in Example 1, to obtain the comparative catalyst Ref-1.

[0045] Comparative Example 2:

[0046] Only Cu monometal was loaded, without adding molybdenum components, and the remaining steps were the same as in Example 1 to obtain the comparative catalyst Ref-2.

[0047] Comparative Example 3:

[0048] Only Mo monometal was loaded, without adding copper components, and the remaining steps were the same as in Example 1 to obtain the comparative catalyst Ref-3.

[0049] Comparative Example 4:

[0050] Using commercial TiO2 as a support to support Cu-Mo, without a core-shell structure and a resistant outer shell, and with the same loading amount as in Example 1, a comparative catalyst Ref-4 was obtained.

[0051] The Fe3O4@SiO2 magnetic support and Cat-1 catalyst prepared in Example 1 were characterized by scanning electron microscopy, and the results are as follows: Figure 1As shown in the SEM images, the Fe3O4@SiO2 magnetic support exhibits a spindle-shaped structure with consistent structure and uniform particle size. The Cat-1 catalyst prepared by loading Cu and Mo metals exhibits a relatively rough surface structure due to the aggregation of the loaded metal particles, but the particle size does not change significantly.

[0052] Catalyst performance testing

[0053] Depolymerization experiments were conducted using a 100 mL high-pressure reactor. Standard reaction conditions included: 2.0 g of a 7:3 PET / PC mixture (crushed to less than 2 mm), 0.2 g of catalyst, 40 mL of deionized water, initial N2 pressure of 2 MPa, and a two-stage reaction: the first stage was at 140 °C for 3 h (PC preferentially depolymerized), and the second stage was at 180 °C for 3 h (PET deeply depolymerized). After the reaction, the mixture was cooled, and the liquid phase products were separated by centrifugation. The solid residue was washed repeatedly with 0.5 mol / L NaOH solution, and the combined liquid phase fraction was analyzed by high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The solid residue was dried, weighed, and placed in centrifuge tubes. Sufficient dichloromethane (DCM) was added, and the mixture was stirred at room temperature for 30 minutes to dissolve the PC. The insoluble solids were collected by centrifugation, washed twice with fresh DCM, and dried under vacuum at 80 °C to constant weight. This weight was recorded as the sum of the masses of PET and catalyst; subtracting the catalyst mass yielded the weight of unreacted PET. The weight of unreacted PC is obtained by subtracting the weight of PET and catalyst from the total weight of solid residue, and the conversion rate and monomer yield are calculated accordingly. The BPA monomer yield is quantitatively calculated by gas chromatography-mass spectrometry (GC-MS), and the PTA monomer yield is quantitatively calculated by high performance liquid chromatography (HPLC).

[0054] Halogen resistance test: Add 5-10 wt% PVC powder to the above raw materials and compare the changes in catalyst activity before and after the reaction.

[0055] Cyclic stability test: After the reaction, the catalyst is recovered by magnetic separation, washed with ethanol, dried and directly used in the next reaction, and continuously cycled 10 times.

[0056] Catalyst activity test results

[0057] The catalysts in the embodiments of this invention all exhibited excellent synergistic depolymerization performance of the two polyesters, and the catalytic activity test results are shown in Table 1. PC conversion rates were all above 95%, BPA yields above 88%, PET conversion rates above 93%, and PTA yields above 84%, significantly better than the comparative examples. The PC depolymerization activity of Comparative Example 2 (Cu only) decreased significantly, and the PET depolymerization activity of Comparative Example 3 (Mo only) decreased significantly, proving that Cu-Mo bimetallic synergy is key to achieving efficient stepwise depolymerization of mixed polyesters. Comparative Examples 1 and 4 lacked a resistant shell; although their initial activity was acceptable, the amount of byproducts (benzoic acid, cycloalkanes) generated was high, indicating that excessive exposure of active sites led to over-reaction.

[0058] As shown in Table 2, in a system containing 5 wt% PVC, the core-shell catalyst of this invention exhibited a PC and PET depolymerization activity retention rate exceeding 90%, demonstrating excellent halogen resistance. The ZrO2-TiO2 shell not only reduces the contact between halide ions and active sites through physical barriers but also immobilizes a large amount of Cl through lattice defect chemisorption. - The comparative catalyst without a resistant outer shell showed significant activity degradation and severe metal leaching. Further testing showed that even with the PVC content increased to 10 wt% (Table 3), the activity retention rate of Cat-1 could still reach over 85%.

[0059] Table 1. Data on the co-catalytic depolymerization reaction of dual polyesters Cat-1 98.2 94.0 96.6 92.1 Cat-2 96.2 90.3 94.3 88.6 Cat-3 95.9 92.1 93.1 87.4 Cat-4 95.2 89.9 95.3 89.6 Cat-5 96.1 90.6 93.7 84.2 Ref-1 93.4 68.7 90.6 59.7 Ref-2 66.8 45.4 88.9 84.5 Ref-3 90.6 82.1 56.4 42.3 Ref-4 92.6 64.3 91.3 60.2

[0060] Table 2. Data on the co-catalytic depolymerization of dipolyesters containing PVC (5 wt%) Cat-1 94.7 90.2 92.7 88.2 Cat-2 92.6 87.3 91.1 84.4 Cat-3 91.3 88.1 91.6 85.1 Cat-4 92.2 84.9 89.7 84.7 Cat-5 93.7 88.9 92.2 82.5 Ref-1 27.4 16.6 21.7 14.2 Ref-2 54.2 47.8 79.7 68.1 Ref-3 84.1 91.1 33.6 24.7 Ref-4 19.3 9.3 14.2 7.3

[0061] Table 3. Data on the co-catalytic depolymerization of dipolyesters containing PVC (10 wt%) Cat-1 91.1 88.4 90.4 88.1 Cat-2 89.6 86.8 88.2 86.6 Cat-3 88.7 86.5 87.9 86.5 Cat-4 90.5 87.6 88.9 86.2 Cat-5 89.1 86.9 86.9 85.9

[0062] Cyclic stability test results

[0063] Ten cycles of experiments were conducted using Cat-1 as a representative catalyst, and the results are shown in Table 4. The PC conversion rate was 98.2% in the first cycle and remained at 92.6% in the tenth cycle, with an activity retention rate of 94.3%. The BPA yield decreased from 94.0% to 87.2%, with a retention rate of 92.8%. The PET conversion rate decreased from 96.6% to 91.1%, with a retention rate of 94.3%. The PTA yield decreased from 92.1% to 84.7%, with a retention rate of 92.0%. The PC and PET conversion rates maintained a relatively low rate of decrease after the fifth reaction. There were no significant changes in the catalyst phase before and after the reaction, and the total dissolution of Cu and Mo was less than 5 ppm, demonstrating that the catalyst possesses excellent structural stability and recyclability.

[0064] Table 4 Results of Cyclic Tests for Synergistic Catalytic Depolymerization of Dipolyester 1 98.2 94.0 96.6 92.1 2 96.9 92.6 95.2 89.1 3 95.4 91.1 94.3 88.4 4 94.6 89.3 93.2 87.5 5 94.1 88.6 91.9 86.6 6 93.7 87.9 91.7 86.0 7 93.3 87.7 91.6 85.6 8 93.1 87.6 91.5 85.2 9 92.8 87.4 91.3 84.9 10 92.6 87.2 91.1 84.7

[0065] Verification of the step-by-step depolymerization process

[0066] Using Cat-1 as a representative catalyst, the depolymerization process was analyzed by temperature-programmed sampling, and the results are shown in Table 5. Within the first 2 hours at 140 °C, the PC conversion rate reached over 90%, while the PET conversion rate was less than 20%, with BPA being the main product. After heating to 180 °C, PET began to depolymerize rapidly, and the conversion rate exceeded 95% within 3 hours, with PTA becoming the main product. This result confirms that the catalyst can achieve stepwise depolymerization of PC and PET through temperature control, facilitating the stepwise separation and purification of products.

[0067] Table 5. Time-product distribution results of the synergistic depolymerization reaction of the dipolyester 140 1 69.1 63.5 12.4 4.7 140 2 90.6 85.3 18.2 11.3 140 3 94.2 91.1 19.0 14.1 180 1 95.7 92.8 55.3 46.2 180 2 97.9 93.6 79.7 74.2 180 3 98.2 94.0 96.6 92.1

[0068] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope of the present invention.

Claims

1. A core-shell Cu-Mo based catalyst with halogen resistance, characterized in that, The catalyst has a core-shell structure, wherein the core is a Fe3O4@SiO2 magnetic composite support, and the shell is a ZrO2-TiO2 composite oxide resistant shell covering the surface of the core; The resistant shell is loaded with metallic active components Cu and Mo; based on the total mass of the catalyst, the loading of Cu is 4-6 wt% and the loading of Mo is 4-6 wt%. The molar ratio of Zr to Ti in the resistant shell is 1:2 to 2:

1.

2. The core-shell Cu-Mo based catalyst according to claim 1, characterized in that, The Cu loading was 6 wt%, and the Mo loading was 4 wt%. The molar ratio of Zr to Ti is 1:

1.

3. The core-shell Cu-Mo based catalyst according to claim 1, characterized in that, The lattice of the resistant shell contains oxygen vacancies for the chemical adsorption and fixation of halide ions.

4. The method for preparing the core-shell Cu-Mo based catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Fe3O4 nanoparticles were prepared by a solvothermal method; (2) A SiO2 layer is coated on the surface of the Fe3O4 nanoparticles to obtain a Fe3O4@SiO2 magnetic composite carrier; (3) Using zirconium source and titanium source as raw materials, a ZrO2-TiO2 composite oxide shell is hydrothermally grown on the surface of the Fe3O4@SiO2 magnetic composite carrier. The hydrothermal growth temperature is 160~180 ℃ and the time is 12~18 h. The product is calcined to obtain a core-shell carrier. (4) The copper source and molybdenum source are loaded on the core-shell support by impregnation, and after drying and calcination, they are reduced in a hydrogen atmosphere to obtain the core-shell Cu-Mo based catalyst.

5. The preparation method according to claim 4, characterized in that, In step (1), iron salt is dissolved in ethylene glycol, sodium acetate and polyethylene glycol are added, and the mixture is reacted at 180~220 ℃ for 6~10 h. The product is collected by magnetic separation, washed and dried to obtain Fe3O4 nanoparticles.

6. The preparation method according to claim 4, characterized in that, In step (2), Fe3O4 nanoparticles are dispersed in an ethanol-water mixture, ultrasonically dispersed, and then ammonia is added. Tetraethyl orthosilicate is then added dropwise to carry out a hydrolysis-condensation reaction, so that SiO2 is uniformly coated on the surface of Fe3O4 nanoparticles. After magnetic separation, washing, and drying, Fe3O4@SiO2 magnetic composite carrier is obtained. The volume ratio of ethanol to water in the ethanol-water mixture is 3:1 to 5:

1. The drying temperature is 50 to 70 °C.

7. The preparation method according to claim 4, characterized in that, In step (3), the zirconium source is zirconium oxychloride and the titanium source is tetrabutyl titanate. The Fe3O4@SiO2 magnetic composite carrier is dispersed with the zirconium source and the titanium source in ethanol. After adjusting the pH to 7-9, a hydrothermal reaction is carried out. The product is washed, dried and then calcined at 400-600 °C for 2-4 h to obtain the core-shell carrier.

8. The preparation method according to claim 4, characterized in that, In step (4), the copper source is copper nitrate and the molybdenum source is ammonium molybdate. After impregnation by equal volume impregnation method, the catalyst is allowed to stand for 8-16 h, dried at 80-120 ℃, calcined at 400-500 ℃ for 1-3 h, and then reduced at 300-400 ℃ for 1-3 h under hydrogen atmosphere to obtain the core-shell Cu-Mo based catalyst.

9. The application of the core-shell Cu-Mo based catalyst according to any one of claims 1 to 3 in the stepwise depolymerization of PET / PC blended polyesters containing halogen impurities, characterized in that, The PET / PC blended polyester, the catalyst, and water are added to the reactor, and the depolymerization reaction is carried out in two stages under an inert atmosphere: the first stage is carried out at 100~140 °C to hydrolyze the PC; the second stage is carried out at 160~200 °C to hydrolyze the PET; after the reaction is completed, the catalyst is recovered by magnetic separation and recycled.

10. The application according to claim 9, characterized in that, The PC is hydrolyzed to generate bisphenol A, and the PET is hydrolyzed to generate terephthalic acid.

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