Preparation method of low-noble-metal pd supported nickel-based composite metal catalyst and application thereof in plastic waste recycling

Abstract

The application provides a preparation method of a low-noble-metal Pd-loaded nickel-based composite metal catalyst and application of the catalyst in plastic waste recycling, and belongs to the technical field of preparation of noble-metal nanometer catalytic materials.The preparation method of the composite metal catalyst comprises the following steps: S1, pretreating foam nickel (NF); S2, weighing sodium chloride and pouring the sodium chloride into a centrifugal tube, then pouring potassium chloropalladate solution and iron chloride hexahydrate solution into the centrifugal tube, and stirring to form a uniform solution; S3, vertically and suspending the pretreated NF in the uniform solution in step S2 to perform a corrosion reaction, and after the corrosion reaction is completed, washing and drying are performed to obtain the composite metal catalyst.The synthesis strategy of the nickel-based catalyst has the advantages of simple operation, low cost, environmental friendliness and the like, the raw materials used are easy to obtain and meet the green chemistry principle, and the synthesis strategy has the feasibility of large-scale production, and has a wide application prospect in the fields of clean energy conversion and polymer plastic waste resourceization.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of noble metal nanocatalytic material preparation, and particularly relates to a preparation method of a low-noble-metal-Pd-loaded nickel-based composite metal catalyst and application thereof in plastic waste recycling. BACKGROUND

[0002] Plastics, as an important basic material, have been widely used in various fields due to their excellent physical properties, convenient processing technology and significant cost advantage. The industrialized production and extensive use of plastic products have not only improved the convenience of social life, but also brought about ecological challenges that cannot be ignored. The increasing plastic waste not only aggravates the problem of white pollution, but also leads to the continuous accumulation of environmental risks, posing a major hidden danger to soil and water safety and public health. It is worth noting that if synthetic plastics made of petroleum as raw materials lack a scientific and effective recycling mechanism, it will also cause a huge loss of non-renewable petroleum resources.

[0003] Polyethylene terephthalate (PET) is a representative of polyester materials and ranks second in the global production of thermoplastic polymer materials, of which China occupies a leading position in global polyester production. PET materials are widely favored due to their excellent comprehensive performance, not only having excellent mechanical strength, electrical insulation, wear resistance and dimensional stability, but also becoming the core raw material for synthetic polyester, accounting for more than 80% of the total synthetic fiber output. In addition, PET materials are non-toxic and odorless, meeting the food contact safety standards, and are therefore widely used in food packaging and catering containers.

[0004] However, most current PET products are still mainly used once and are difficult to degrade in the natural environment after being discarded, causing serious environmental burden. For the recycling of PET, currently, two ways of physical regeneration and chemical recycling are mainly used. Physical regeneration treats waste through heat melting and mechanical processing, but this process can cause a decrease in molecular weight, resulting in performance degradation of the regenerated material, which can usually only be used in a degraded manner and is difficult to achieve multiple cycles, and has limited processing capacity for complex waste fibers. In contrast, chemical recycling technology can depolymerize PET long-chain molecules into monomers or crack them into small-molecule organic matter under specific chemical or biological catalytic conditions, and then obtain high-value raw materials through purification or refining processes. In theory, chemical recycling can realize the closed-loop regeneration of waste plastics, and therefore has been continuously concerned in the scientific research and industrial fields in recent years and has become a key technical direction for promoting the sustainable development of plastics.

[0005] The molecular formula of PET is (C 10 H8O4) nThe hydrolysis reaction can occur under alkaline conditions to generate terephthalic acid (PTA) and ethylene glycol (EG), but there is a problem of difficult product separation in the process. In recent years, researchers have found that through special chemical means such as photocatalysis and electrocatalysis, EG can be further converted into high-value and easily separated chemicals such as formic acid (FA) under the action of catalysts, which provides a new idea for the high-value recycling of PET.

[0006] As disclosed in Chinese patent CN118910641A, a palladium-doped cobalt-nickel phosphorus-based electrocatalyst and its preparation method and application are disclosed. The palladium-doped cobalt-nickel phosphorus-based electrocomposite material is Pd-CoNiP@M, and the spore-shaped cobalt-nickel phosphorus substrate beads are uniformly loaded on the surface of the foam substrate. The cobalt-nickel phosphorus substrate is doped with palladium atoms. The catalytic material is prepared by chemical plating method. Only by placing the pretreated metal foam material in the chemical plating solution, the palladium-doped cobalt-nickel phosphorus-based catalyst can be quickly synthesized. The palladium-doped cobalt-nickel phosphorus-based catalyst material is used as a catalyst for alcohol oxidation reaction on the anode, and ethylene glycol is reformed into formic acid or other high-value chemicals, and hydrogen gas is generated by hydrogen evolution reaction on the cathode. The invention overcomes the problem of high temperature and high pressure limitation in the synthesis of traditional catalysts, and the catalyst can be quickly prepared by chemical plating method and applied to degrade waste plastics to generate high-value products. However, although this method has made some progress, it still faces technical bottlenecks such as high cost of catalyst, low reaction efficiency, and insufficient selectivity of target oxidation products, which need to be further optimized.

[0007] To solve the above technical problems, a preparation method of a low-noble metal Pd-loaded nickel-based composite metal catalyst and its application in plastic waste recycling are designed. SUMMARY

[0008] Based on the deficiencies in the prior art, the present application provides a preparation method of a low-noble metal Pd-loaded nickel-based composite metal catalyst and its application in plastic waste recycling, aiming to solve the technical bottlenecks of high cost and low utilization efficiency of existing catalysts, and low selectivity of target oxidation products.

[0009] To achieve the above purpose, the present application adopts the following technical solutions:

[0010] On the one hand, the present application provides a preparation method of a low-noble metal Pd-loaded nickel-based composite metal catalyst, which comprises the following steps:

[0011] S1, placing the foam nickel (NF) in a hydrochloric acid solution and ultrasonic treating, then rinsing with deionized water and drying to obtain pretreated NF;

[0012] S2, weighing sodium chloride into a centrifuge tube, then pouring the prepared potassium chloropalladate solution and ferric chloride hexahydrate solution into the centrifuge tube containing sodium chloride, and stirring to form a uniform solution;

[0013] S3, the pretreated NF in step S1 is vertically and suspendedly immersed in the uniform solution in step S2, and the etching reaction is carried out under the condition of high-speed stirring, and after the reaction is completed, it is taken out, washed and dried to obtain the low-noble metal Pd loaded nickel-based composite metal catalyst, named PdFe-Ni(OH)2 / NF.

[0014] The thickness of the NF in step S1 is 3-5 mm, and the area is 2.5 cm x 3 cm.

[0015] The concentration of the hydrochloric acid solution in step S1 is 3 mol / L; the ultrasonic time is 40 min; and the drying temperature is 60°C.

[0016] The mass ratio of sodium chloride, potassium chloropalladate and ferric chloride hexahydrate in step S2 is 610-1074:1-2:1-5;

[0017] Preferably, the mass ratio of sodium chloride, potassium chloropalladate and ferric chloride hexahydrate is 887.4:1:2.4786.

[0018] The concentration of potassium chloropalladate in step S2 is 0.5-3 mmol / L, and the addition amount of the potassium chloropalladate solution is 40-50 ml;

[0019] Preferably, the concentration of potassium chloropalladate in step S2 is 1 mmol / L, and the addition amount of the potassium chloropalladate solution is 40 ml.

[0020] The concentration of ferric chloride hexahydrate in step S2 is 5-30 mmol / L, and the addition amount of the ferric chloride hexahydrate solution is 10-50 μl.

[0021] Preferably, the concentration of ferric chloride hexahydrate in step S2 is 5-30 mmol / L, and the addition amount of the ferric chloride hexahydrate solution is 10-30 μl.

[0022] More preferably, the concentration of ferric chloride hexahydrate in step S2 is 10 mmol / L, and the addition amount of the ferric chloride hexahydrate solution is 30 μl.

[0023] The etching reaction in step S3 is 1-5 h, and the rotation speed of high-speed stirring is 1000-1500 r.

[0024] Preferably, the etching reaction in step S3 is 3 h, and the rotation speed of high-speed stirring is 1200 r.

[0025] In another aspect, the present application provides a low noble metal Pd supported nickel-based composite metal catalyst prepared by the above preparation method.

[0026] In still another aspect, the present application also provides the use of the low noble metal Pd supported nickel-based composite metal catalyst prepared by the above preparation method in degrading plastic waste.

[0027] In still another aspect, the present application provides a method for degrading plastic waste by using a low noble metal Pd supported nickel-based composite metal catalyst, comprising the following steps:

[0028] (1) Washing and drying PET waste plastic powder, then dissolving in an alkaline solution at high temperature, cooling to room temperature, and removing impurities by suction filtration to obtain an alkaline solution containing terephthalate and ethylene glycol, i.e. PET hydrolysis product;

[0029] (2) Assembling a flow-type electrolytic cell in a two-electrode form, wherein the anode electrode is the low noble metal Pd supported nickel-based composite metal catalyst prepared by the above preparation method, and the cathode electrode is Pt / C; the electrolyte in the anode zone and the cathode zone is the PET hydrolysis product, and the cathode zone and the anode zone are separated by an anion exchange membrane;

[0030] (3) Heating the flow-type electrolytic cell, applying voltage to the electrolytic cell, and performing electrocatalytic oxidation reaction of the PET hydrolysis product as the electrolyte, and obtaining potassium formate and potassium terephthalate after the reaction is completed.

[0031] The alkaline solution in the above step (1) is potassium hydroxide solution or sodium hydroxide solution; the concentration of the alkaline solution is 2-5 mol / L, the temperature of the dissolution is 25-80℃, and the time of the dissolution is 12-72 h; the concentration of the alkaline solution needs to be adjusted to 1-2.5 mol / L after suction filtration.

[0032] Preferably, the concentration of the alkaline solution is 3 mol / L, the temperature of the dissolution is 80℃, and the time of the dissolution is 24 h; the concentration of the alkaline solution needs to be adjusted to 1.5 mol / L after suction filtration.

[0033] The cathode electrode in the above step (2) is Pt / C sprayed on NF, the thickness of NF is 3-5 mm, the size is 2 cm x 2 cm, and the content of Pt / C is 1-3 mg / cm 2 ; the concentration of potassium hydroxide solution in the electrolyte is 1-2.5 mol / L.

[0034] Preferably, the content of Pt / C is 1.0 mg / cm 2 ; the concentration of potassium hydroxide solution in the electrolyte is 1.5 mol / L.

[0035] The heating temperature in the step (3) is 25-60℃, the applied voltage range is 1.4-1.6V, and the electrocatalytic oxidation reaction time is 48h-300h.

[0036] Preferably, the heating temperature is 60℃, and the applied voltage range is 1.5V.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] (1) The present application synthesizes an ultra-micro noble metal palladium loaded non-noble metal Ni, Fe composite catalyst PdFe-Ni(OH)2 / NF with oxygen affinity by a simple controllable method. The catalyst takes the nickel-iron bimetallic with oxygen affinity as the substrate, realizes the ultra-micro loading of noble metal Pd, and exhibits excellent electrocatalytic oxidation performance. The unique ultrathin nanosheet structure can significantly increase the exposure degree of active sites and optimize the catalyst-reactant interface contact, thereby greatly improving the intrinsic catalytic activity, providing a high-activity and low-cost electrocatalyst for the electrocatalytic oxidation process of PET.

[0039] (2) The PdFe-Ni(OH)2 / NF catalyst prepared by the present application effectively regulates the electronic structure of the Pd active center by introducing the Ni-Fe bimetallic oxygen affinity component, optimizes the adsorption behavior of the catalyst surface to the carbonyl intermediate (C=O*), and at the same time, the presence of Ni and Fe components promotes the in-situ generation of hydroxyl radicals (*OH). The synergistic effect of the two not only significantly improves the reaction selectivity of the catalytic system, but also enhances the anti-poisoning ability of the catalyst, thereby greatly accelerating the electrocatalytic oxidation reaction kinetics of PET.

[0040] (3) The catalyst synthesis strategy proposed by the present application has the advantages of simple operation, low cost, environmental friendliness, and the like. The raw materials used are easy to obtain and meet the principles of green chemistry. In the field of PET electrocatalytic oxidation, the preparation method exhibits excellent industrial adaptability and feasibility for large-scale production, and has broad application prospects in the fields of clean energy conversion and polymer waste resourceization. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only one embodiment of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0042] Figure 1is a flow chart of the preparation method of the PdFe-Ni(OH)2 / NF composite metal catalyst provided by the present application;

[0043] Figure 2 is a flow chart of the method of electrocatalyzing PET plastic waste by the PdFe-Ni(OH)2 / NF composite metal catalyst provided by the present application;

[0044] Figure 3 is an inductively coupled plasma spectrum of the PdFe-Ni(OH)2 / NF prepared in Example 1 of the present application;

[0045] Figure 4 is a scanning electron microscope image of the PdFe-Ni(OH)2 / NF prepared in Example 1 of the present application;

[0046] Figure 5 is an atomic force microscope image of the PdFe-Ni(OH)2 scraped from the catalyst in Example 1 of the present application

[0047] Figure 6 is a current density curve of the PdFe-Ni(OH)2 / NF catalyst with different iron contents prepared in Examples 1-4 of the present application in the EG oxidation process;

[0048] Figure 7 is a linear sweep voltammetry characteristic curve of the PdFe3-Ni(OH)2 / NF catalyst in Example 5 and Comparative Example 1 of the present application in the EG oxidation process and the conventional oxygen evolution reaction, respectively;

[0049] Figure 8 is a faraday efficiency column chart of formic acid through the PdFe3-Ni(OH)2 / NF catalyst in Example 5 of the present application at different voltages;

[0050] Figure 9 is a nuclear magnetic resonance hydrogen spectrum of formic acid through the PdFe3-Ni(OH)2 / NF catalyst in Example 5 of the present application at different voltages;

[0051] Figure 10 is an X-ray diffraction chart of the product obtained by electrocatalyzing PET hydrolysis by the PdFe3-Ni(OH )2 / NF catalyst in Example 6 of the present application. DETAILED DESCRIPTION

[0052] The present application will be further described below in conjunction with the drawings and examples:

[0053] Embodiments of the present application are described in detail below with reference to the attached drawing figures, wherein like or similar constituent elements or features may be denoted by like reference characters throughout the drawing figures and the description. The embodiments described below are exemplary only and are not intended to be limiting of the present application.

[0054] In the description of the present application, it is necessary to point out that, unless explicitly defined and limited otherwise, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0055] In the description of the present application, it is necessary to understand that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0056] The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available unless otherwise specified.

[0057] Example 1

[0058] As shown in the following steps: Figure 1

[0059] S1, place the foam nickel (NF) with a size of 2.5 cm x 3 cm x 5 mm in a 3 mol / L hydrochloric acid solution for ultrasonic treatment for 40 min, then rinse several times with deionized water and place in a vacuum drying oven at 60°C for drying to obtain the pretreated NF;

[0060] S2, weigh 1.16 g of sodium chloride into a centrifuge tube, dissolve 5 mg of potassium chloropalladate in 153 ml of deionized water, and then weigh 108 mg of iron chloride hexahydrate into 1 ml of deionized water; finally, pour 40 ml of potassium chloropalladate solution and 30 μl of iron chloride hexahydrate solution into the centrifuge tube containing sodium chloride, and stir to form a uniform solution;

[0061] ​S3, the pretreated NF is vertically and suspendedly immersed in the uniform solution prepared in S2, and after the corrosion reaction is carried out for 3 h under the condition of high-speed stirring at 1200 r, the NF is taken out and washed with deionized water and anhydrous ethanol for 3 times respectively, and then is placed in a vacuum drying box for drying at 60°C for 12-24 h, to obtain a PdFe3-Ni(OH)2 / NF composite metal catalyst.

[0062] Example 2

[0063] The difference from Example 1 is only that the volume of the added ferric chloride hexahydrate solution in step S2 is 10 μl, and the others are the same as those in Example 1, to obtain a PdFe1-Ni(OH)2 / NF composite metal catalyst.

[0064] Example 3

[0065] The difference from Example 1 is only that the volume of the added ferric chloride hexahydrate solution in step S2 is 50 μl, and the others are the same as those in Example 1, to obtain a PdFe5-Ni(OH)2 / NF composite metal catalyst.

[0066] Comparative Example 1

[0067] The difference from Example 1 is only that the volume of the added ferric chloride hexahydrate solution in step S2 is 0 μl, i.e. no ferric chloride hexahydrate is added, and the others are the same as those in Example 1, to obtain a Pd-Ni(OH)2 / NF composite metal catalyst.

[0068] Comparative Example 2

[0069] The difference from Example 1 is only that the volume of the added ferric chloride hexahydrate solution in step S2 is 100 μl, and the others are the same as those in Example 1, to obtain a PdFe10-Ni(OH)2 / NF composite metal catalyst.

[0070] Application Example 1

[0071] A three-electrode system is adopted to perform catalytic oxidation in an electrolytic cell, the PdFe3-Ni(OH)2 / NF catalyst prepared in Example 1 is used as a working electrode, Ag / AgCl is used as a reference electrode, and a platinum sheet is used as a counter electrode, and a mixed solution of 1 mol / L potassium hydroxide solution and 0.1 mol / L ethylene glycol solution in a volume ratio of 175:1 is used as an electrolyte, to jointly constitute an electrocatalytic reactor. Linear sweep voltammetry characteristic curve test is performed at room temperature and normal pressure under the condition of 1.32-1.48 V vs. RHE, and continuous stirring reaction is performed at a constant voltage of 1.40 V vs. RHE.

[0072] Application Comparative Example 1:

[0073] The difference from application example 1 is that the electrolyte is 1M potassium hydroxide solution, and the voltage interval is 1.0-1.55V vs. RHE, and the others are the same as application example 1.

[0074] Application example 2 A method for degrading waste plastics by using a PdFe-Ni(OH)2 / NF composite metal catalyst

[0075] As shown in Figure 2 , the following steps are included:

[0076] 1. 10g of PET plastic was washed and dried, then placed in a 3mol / L potassium hydroxide alkaline solution, heated to 80℃ by oil bath reflux, after heating for 24h, cooled to room temperature, impurities were removed by suction filtration, to obtain an alkaline solution containing terephthalate and ethylene glycol, as the PET hydrolyzate;

[0077] 2. A flow-type electrolytic cell was assembled, using a two-electrode form, the working electrode was the composite metal catalyst PdFe3-Ni(OH)2 / NF prepared in example 1, the cathode electrode was Pt / C sprayed on NF, the thickness of NF was 5mm, the size was 2cm x 2cm, and its content was 1.0mg / cm 2 . The electrolyte in the anode and cathode zones was the PET hydrolyzate and the concentration of the alkaline solution was 1.5mol / L, the cathode zone and the anode zone were separated by an anion exchange membrane;

[0078] 3. The flow-type electrolytic cell was heated at 60℃, and a voltage of 1.5V was applied to the electrolytic cell, the anode zone electrolyte PET hydrolyzate was subjected to electrocatalytic oxidation reaction for 200h, and after the reaction was completed, potassium formate and potassium terephthalate were obtained.

[0079] As can be seen from Figure 3 , the mass fraction of Pd in the composite metal catalyst PdFe3-Ni(OH)2 / NF prepared in example 1 is only 0.174%, which indicates that this catalyst has a super-low noble metal loading, greatly reducing the cost.

[0080] As can be seen from Figure 4 , the composite metal catalyst PdFe3-Ni(OH)2 / NF prepared in example 1 has obvious ultrathin nanosheets, and has good contact with the substrate, which provides the possibility of increasing the conductivity and exposing more active sites.

[0081] As can be seen from Figure 5 , the composite catalyst PdFe3-Ni(OH)2 / NF prepared in example 1 is composed of ultrathin nanosheets, and the thickness of its nanosheets is only 1.55nm, the ultrathin material surface can expose more active sites, improving the catalytic activity of the material.

[0082] By Figure 6 It can be seen that the electrocatalytic oxidation performance of the composite metal catalysts PdFe-Ni(OH)2 / NF with different Fe contents prepared in Examples 1-3 and Comparative Examples 1-2 is obviously different, and it can be obviously seen that the PdFe-Ni(OH)2 / NF catalyst has the best EG electrocatalytic oxidation performance when the Fe-containing solution is 30 μl.

[0083] By Figure 7 It can be seen that the PdFe3-Ni(OH)2 / NF catalyst needs a lower potential and has a faster kinetics in the EG oxidation process at the same current density compared with Application Example 1 and Application Comparative Example 1.

[0084] By Figure 8 It can be seen that in Application Example 1, the Faraday efficiency of formic acid presents a trend of first increasing and then decreasing with the increase of voltage in the whole electrocatalytic process, which indicates that the OER reaction is enhanced and the EGOR reaction is weakened with the increase of voltage, so the Faraday efficiency of formic acid is reduced. When the voltage is 1.4 V vs. RHE, the Faraday efficiency of formic acid is as high as 97.4%, which is the best voltage. This indicates that the PdFe3-Ni(OH)2 / NF catalyst has very high catalytic activity.

[0085] By Figure 9 It can be seen that the nuclear magnetic resonance hydrogen spectrum of the PdFe3-Ni(OH)2 / NF composite metal catalyst in Application Example 1 at different charge passes, and the results describe the dynamic process of EG to FA oxidation, and it can be found that the content of EG gradually decreases and the content of FA gradually increases with the increase of charge.

[0086] By Figure 10 It can be seen that in Application Example 2, the PdFe3-Ni(OH)2 / NF catalyst is used for electrocatalytic reaction of PET hydrolysis products by using the constant voltage method, and under the condition of 1.5 V voltage, the electrolyte flow rate of the anode and cathode is 40 ml / min, the PET hydrolysis products are completely electrolyzed to obtain an alkaline solution containing potassium terephthalate and potassium formate, and terephthalic acid and KDF are obtained by acidification and rotary evaporation. The phase analysis of the obtained KDF powder shows that the KDF crystal powder is successfully prepared by comparing with the standard PDF card.

[0087] The above has described the present application by way of examples, but the present application is not limited to the above specific examples, and any modification or change made on the basis of the present application is within the scope of the present application.

Claims

1. A method for preparing a nickel-based composite metal catalyst supported on low-noble-metal Pd for degrading plastic waste, characterized in that: Includes the following steps: S1. After ultrasonic treatment of the nickel foam in hydrochloric acid solution, it is rinsed with deionized water and dried to obtain the pretreated NF. S2. Weigh out sodium chloride and pour it into a centrifuge tube. Then pour 40-50 mL of the prepared 0.5-3 mmol / L potassium chloropalladate solution and 10-50 μL of 5-30 mmol / L ferric chloride hexahydrate solution into the centrifuge tube containing sodium chloride and stir to form a homogeneous solution. S3. The pretreated NF from step S1 is vertically and suspended in the homogeneous solution from step S2. The corrosion reaction is carried out under high-speed stirring. After the reaction is completed, the catalyst is removed, washed, and dried to obtain the nickel-based composite metal catalyst supported by the low-noble metal Pd.

2. The method for preparing a low-noble-metal Pd-supported nickel-based composite metal catalyst for degrading plastic waste according to claim 1, characterized in that: The concentration of the hydrochloric acid solution in step S1 is 3 mol / L; the ultrasonic time is 40 min; and the drying temperature is 60℃.

3. The method for preparing a low-noble-metal Pd-supported nickel-based composite metal catalyst for degrading plastic waste according to claim 1, characterized in that: The concentration of potassium chloropalladium in step S2 is 1 mmol / L, and the amount of potassium chloropalladium solution added is 40 mL.

4. The method for preparing a low-noble-metal Pd-supported nickel-based composite metal catalyst for degrading plastic waste according to claim 1, characterized in that: The concentration of ferric chloride hexahydrate in step S2 is 10 mmol / L, and the amount of ferric chloride hexahydrate solution added is 30 μL.

5. A nickel-based composite metal catalyst supported on low-noble metal Pd, prepared by the preparation method according to any one of claims 1-4.

6. The application of the nickel-based composite metal catalyst supported on low-noble metal Pd prepared by the preparation method according to any one of claims 1-4 in the degradation of plastic waste.

7. A method for degrading plastic waste using a nickel-based composite metal catalyst supported on low-noble-metal Pd prepared by the preparation method according to any one of claims 1-4, characterized in that: Includes the following steps: (1) Wash and dry the PET waste plastic powder, then dissolve it in an alkaline solution at high temperature, cool it to room temperature, filter it to remove impurities, and obtain an alkaline solution containing terephthalate and ethylene glycol, which is the PET hydrolysis product; (2) Assemble a flow electrolytic cell with two electrodes. The anode electrode is a nickel-based composite metal catalyst supported on low-noble metal Pd prepared by the preparation method described in any one of claims 1-4, and the cathode electrode is Pt / C. The electrolyte in both the anode and cathode regions is PET hydrolysis product, and the cathode and anode regions are separated by an anion exchange membrane. (3) The flow electrolytic cell is heated and a voltage is applied to the electrolytic cell. The PET hydrolysis product is used as the electrolyte for electrocatalytic oxidation reaction. After the reaction is completed, potassium formate and potassium terephthalate are obtained.

8. The method according to claim 7, characterized in that: The alkaline solution mentioned in step (1) is a potassium hydroxide solution or a sodium hydroxide solution; the concentration of the alkaline solution is 2-5 mol / L; after filtration, the concentration of the alkaline solution needs to be adjusted to 1-2.5 mol / L; The cathode electrode mentioned in step (2) is Pt / C sprayed onto NF; the content of Pt / C is 1-3 mg / cm³. 2 ; The heating temperature in step (3) is 25-60℃, the applied voltage range is 1.4-1.6V, and the electrocatalytic oxidation reaction time is 48h-300h.

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