Preparation method of nickel-based composite metal catalyst loaded with low noble metal Pd and application of nickel-based composite metal catalyst in plastic waste recycling

Abstract

The invention provides a preparation method of a low-precious metal Pd-loaded nickel-based composite metal catalyst and application of the low-precious metal Pd-loaded nickel-based composite metal catalyst in plastic waste recycling, and belongs to the technical field of precious metal nano catalytic material preparation. The preparation method of the composite metal catalyst comprises the following steps: S1, pretreating foamed nickel (NF); s2, weighing sodium chloride, pouring the sodium chloride into a centrifugal tube, then pouring the potassium chloropalladate solution and the ferric chloride hexahydrate solution into the centrifugal tube, and stirring to form a uniform solution; and S3, vertically immersing the pretreated NF in the uniform solution in the step S2 in a suspended manner, carrying out a corrosion reaction, and washing and drying after the corrosion reaction is ended, so as to obtain the composite metal catalyst. The synthesis strategy of the nickel-based catalyst has the advantages of being easy and convenient to operate, low in cost, environmentally friendly and the like, the adopted raw materials are easy to obtain and accord with the green chemistry principle, the feasibility of large-scale production is achieved, and the nickel-based catalyst has wide application prospects in the fields of clean energy conversion, macromolecule plastic waste recycling and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of precious metal nanocatalytic material preparation, and particularly relates to a method for preparing a low-precious metal Pd-loaded nickel-based composite metal catalyst and its application in the recycling of plastic waste. Background Art

[0002] As an important basic material, plastics are widely used in many fields due to their excellent physical properties, convenient processing technology, and significant cost advantages. While the industrial production and widespread use of plastic products have improved the convenience of social life, they have also brought about significant ecological challenges. The growing amount of plastic waste not only exacerbates the problem of white pollution, but also leads to the continuous accumulation of environmental risks, posing a major threat to soil, water safety, and public health. It is worth noting that if synthetic plastics made from petroleum as raw materials lack a scientific and effective recycling and reuse mechanism, they will also cause a huge loss of non-renewable petroleum resources.

[0003] Polyethylene terephthalate (PET), a representative polyester material, ranks second in global thermoplastic polymer production, with China leading the global polyester market. PET is widely favored for its exceptional overall performance, including excellent mechanical strength, electrical insulation, abrasion resistance, and dimensional stability. It is also the core raw material for synthetic polyester, accounting for over 80% of total synthetic fiber production. Furthermore, PET is non-toxic and odorless, meeting food contact safety standards, making it widely used in food packaging and catering containers.

[0004] However, most PET products are still used once and are difficult to degrade in the natural environment after being discarded, which brings a serious environmental burden. For the recycling of PET, there are currently two main methods: physical regeneration and chemical recycling. Physical regeneration processes waste materials through hot melting and mechanical processing, but this process will cause the molecular weight to decrease, which will deteriorate the performance of the recycled materials. Usually, they can only be downgraded for use, and it is difficult to achieve multiple cycles. The processing capacity of waste fibers with complex components is limited. In contrast, chemical recycling technology uses specific chemical or biological catalytic conditions to depolymerize PET long-chain molecules into monomers or crack them into small molecular organic matter, and then through purification or refining processes, high-value raw materials are recovered. In theory, chemical recycling can achieve closed-loop regeneration of waste plastics. Therefore, it has received continuous attention in 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) nUnder alkaline conditions, PET can undergo hydrolysis to produce terephthalic acid (PTA) and ethylene glycol (EG), but this process is difficult to separate. In recent years, researchers have discovered that through special chemical methods such as photocatalysis and electrocatalysis, EG can be further converted into high-value-added and easily separable chemicals such as formic acid (FA) under the action of catalysts. This provides new ideas for the high-value recycling of PET.

[0006] For example, Chinese patent CN118910641A discloses a palladium-doped cobalt-nickel-phosphorus-based electrocatalyst, its preparation method, and its application. This invention describes a palladium-doped cobalt-nickel-phosphorus-based electrocatalyst, Pd-CoNiP@M, composed of spore-shaped cobalt-nickel-phosphorus matrix spheres uniformly loaded on the surface of a foam substrate. The cobalt-nickel-phosphorus matrix is doped with palladium atoms. The catalytic material is prepared using an electroless plating method. Simply placing the pretreated metal foam in an electroless plating bath allows for rapid synthesis of the palladium-doped cobalt-nickel-phosphorus-based catalyst. The palladium-doped cobalt-nickel-phosphorus-based catalyst then acts as a catalyst for alcohol oxidation at the anode, reforming ethylene glycol into formic acid or other high-value chemicals. A hydrogen evolution reaction then occurs at the cathode to generate hydrogen. This invention overcomes the high-temperature and high-pressure limitations of traditional catalyst synthesis, enabling rapid catalyst preparation using electroless plating for the degradation of waste plastics into high-value products. However, despite some progress, this method still faces technical bottlenecks such as high catalyst cost, low reaction efficiency, and insufficient selectivity for the target oxidation product, requiring further optimization.

[0007] In order to solve the above technical problems, the present invention designs a preparation method of a low-noble metal Pd-loaded nickel-based composite metal catalyst and its application in the recycling of plastic waste. Summary of the Invention

[0008] Based on the deficiencies in the prior art, the present invention provides a method for preparing a nickel-based composite metal catalyst with low noble metal Pd loading and its application in the recycling of plastic waste, aiming to solve the technical bottlenecks of the existing catalysts, such as high cost and insufficient utilization efficiency, as well as low selectivity of the target oxidation product.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] In one aspect, the present invention provides a method for preparing a low-noble metal Pd-loaded nickel-based composite metal catalyst, comprising the following steps:

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

[0012] S2. Weigh sodium chloride and pour it into a centrifuge tube. Then pour the prepared potassium chloropalladate solution and ferric chloride hexahydrate solution into the centrifuge tube containing sodium chloride and stir to form a homogeneous solution.

[0013] S3. The NF pretreated in step S1 is vertically and suspended and immersed in the uniform solution of step S2, and a corrosion reaction is carried out under high-speed stirring. 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 the above step S1 is 3-5 mm and the area is 2.5 cm×3 cm.

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

[0016] The mass ratio of sodium chloride, potassium chloropalladate and ferric chloride hexahydrate described in the above 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 amount of potassium chloropalladate solution added is 40-50 ml;

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

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

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

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

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

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

[0025] On the other hand, the present invention provides a low-noble metal Pd-loaded nickel-based composite metal catalyst prepared by the above preparation method.

[0026] On the other hand, the present invention also provides the use of the low-noble metal Pd-loaded nickel-based composite metal catalyst prepared by the above preparation method in the degradation of plastic waste.

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

[0028] (1) washing and drying the PET waste plastic powder, then dissolving it in an alkaline solution at high temperature, cooling it to room temperature, and filtering it to remove impurities, thereby obtaining an alkaline solution containing terephthalate and ethylene glycol, i.e., a PET hydrolyzate;

[0029] (2) Assembling a flow-type electrolytic cell in a two-electrode form, wherein the anode electrode is a nickel-based composite metal catalyst loaded with low-noble metal Pd obtained by the above-mentioned preparation method, and the cathode electrode is Pt / C; the electrolytes in the anode region and the cathode region are both PET hydrolyzates, and the cathode region and the anode region are separated by an anion exchange membrane;

[0030] (3) The flow-type electrolytic cell is heated and voltage is applied to the electrolytic cell, and the PET hydrolysis product is used as an electrolyte to perform an electrocatalytic oxidation reaction, and potassium formate and potassium terephthalate are obtained after the reaction is completed.

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

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

[0033] The cathode electrode in step (2) is Pt / C sprayed on NF, the thickness of NF is 3-5mm, the size is 2cm×2cm, and the content of Pt / C is 1-3mg / 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 above step (3) is 25-60° C., the applied voltage range is 1.4-1.6 V, and the electrocatalytic oxidation reaction time is 48 h-300 h.

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

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

[0038] (1) The present invention adopts a simple and controllable method to synthesize an ultra-trace precious metal palladium-loaded non-precious metal Ni and Fe composite catalyst PdFe-Ni(OH)2 / NF with oxygen-affinity properties. The catalyst uses the oxygen-affinity nickel-iron bimetallic as the substrate to achieve ultra-trace loading of precious metal Pd; and the catalytic system exhibits excellent electrocatalytic oxidation performance. Its unique ultra-thin nanosheet structure can significantly increase the exposure of active sites and optimize the catalyst-reactant interface contact, thereby greatly improving the intrinsic catalytic activity, providing a high-activity, low-cost electrocatalyst for the electrocatalytic oxidation process of PET.

[0039] (2) The PdFe-Ni(OH)2 / NF catalyst prepared by the present invention effectively regulates the electronic structure of the Pd active center by introducing the Ni-Fe bimetallic oxyphilic component, and optimizes the adsorption behavior of the catalyst surface to the carbonyl intermediate (C=O*); 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 in this invention has the advantages of being simple to operate, low-cost, and environmentally friendly. The raw materials used are readily available and conform to the principles of green chemistry. In the field of PET electrocatalytic oxidation, this preparation method demonstrates excellent industrial adaptability and feasibility for large-scale production. It has broad application prospects in fields such as clean energy conversion and polymer waste resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only one embodiment of the present invention. Those skilled in the art can also derive other implementation drawings based on the provided drawings without inventive effort.

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

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

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

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

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

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

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

[0049] Figure 8 is a bar graph of the Faradaic efficiency of formic acid at different voltages for the PdFe3-Ni(OH)2 / NF catalyst in Example 5 of the present invention;

[0050] Figure 9 1 is a hydrogen nuclear magnetic resonance spectrum of the PdFe3-Ni(OH)2 / NF catalyst in Example 5 of the present invention under different charge passages;

[0051] Figure 10 The PdFe3-Ni(OH )2 X-ray diffraction pattern of the product obtained by electrocatalytic hydrolysis of PET using the / NF catalyst. DETAILED DESCRIPTION

[0052] The present invention will be further described below with reference to the accompanying drawings and examples:

[0053] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0054] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0055] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0056] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0057] Example 1

[0058] like Figure 1 As shown, the following steps are included:

[0059] S1. Place nickel foam (NF) with a size of 2.5 cm × 3 cm × 5 mm in a 3 mol / L hydrochloric acid solution and ultrasonicate for 40 min. Then rinse with deionized water several times and dry in a vacuum drying oven at 60°C to obtain 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 ferric chloride hexahydrate and dissolve it in 1 ml of deionized water; finally, pour 40 ml of the potassium chloropalladate solution and 30 μl of the ferric chloride hexahydrate solution into the centrifuge tube containing sodium chloride and stir to form a homogeneous solution;

[0061] S3. The pretreated NF was vertically and suspended and immersed in the uniform solution prepared in S2. Under the condition of high-speed stirring at 1200r, the corrosion reaction was carried out for 3 hours. After that, it was taken out and washed with deionized water and anhydrous ethanol three times respectively. Then, it was placed in a vacuum drying oven at 60°C and dried for 12-24 hours to obtain PdFe3-Ni(OH)2 / NF composite metal catalyst.

[0062] Example 2

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

[0064] Example 3

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

[0066] Comparative Example 1

[0067] The only difference from Example 1 is that the volume of the ferric chloride hexahydrate solution added in step S2 is 0 μl. That is, ferric chloride hexahydrate is not added. The other steps are the same as in Example 1 to obtain a Pd-Ni(OH)2 / NF composite metal catalyst.

[0068] Comparative Example 2

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

[0070] Application Example 1

[0071] Catalytic oxidation was carried out in an electrolytic cell using a three-electrode system. The PdFe3-Ni(OH)2 / NF catalyst prepared in Example 1 served as the working electrode, Ag / AgCl served as the reference electrode, and a platinum sheet served as the counter electrode. 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 served as the electrolyte, forming the electrocatalytic reactor. Linear sweep voltammetric curves were measured at 1.32-1.48 V vs. RHE at room temperature and pressure, with continuous stirring 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 range is 1.0-1.55V vs. RHE. Other aspects are the same as Application Example 1.

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

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

[0076] 1. Wash and dry 10 g of PET plastic, then place it in a 3 mol / L potassium hydroxide alkaline solution, heat it to 80°C in an oil bath reflux, heat it for 24 hours, cool it to room temperature, and remove impurities by suction filtration to obtain an alkaline solution containing terephthalate and ethylene glycol as the PET hydrolyzate;

[0077] 2. Assemble a flow-type electrolytic cell with two electrodes. The working electrode is the composite metal catalyst PdFe3-Ni(OH)2 / NF prepared in Example 1, and the cathode electrode is Pt / C sprayed on NF. The NF is 5 mm thick and 2 cm × 2 cm in size, and its content is 1.0 mg / cm 2 The electrolytes in both the anode and cathode regions are PET hydrolysis products, and the concentration of the alkaline solution is 1.5 mol / L. The cathode and anode regions are separated by an anion exchange membrane.

[0078] 3. The flow-type electrolytic cell was heated at 60° C. and a voltage of 1.5 V was applied to the electrolytic cell. The PET hydrolysis product in the anode electrolyte was subjected to an electrocatalytic oxidation reaction for 200 hours. After the reaction, potassium formate and potassium terephthalate were obtained.

[0079] Depend on Figure 3 It can be seen that the mass fraction of Pd in the composite metal catalyst PdFe3-Ni(OH)2 / NF prepared in Example 1 is only 0.174%, which shows that this catalyst has an ultra-low precious metal loading, which greatly reduces the cost.

[0080] Depend on Figure 4 It can be seen that the composite metal catalyst PdFe3-Ni(OH)2 / NF prepared in Example 1 has obvious ultra-thin nanosheets and has good contact with the substrate, which provides a possibility for increasing conductivity and exposing more active sites.

[0081] Depend on Figure 5 It can be seen that the catalyst PdFe3-Ni(OH)2 / NF prepared in Example 1 is composed of ultra-thin nanosheets, and the thickness of the nanosheets is only 1.55 nm. The ultra-thin material surface can expose more active sites, thereby improving the catalytic activity of the material.

[0082] Depend on 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 are significantly different. It can be clearly seen that the electrocatalytic oxidation performance of EG is best when the Fe-containing solution of PdFe-Ni(OH)2 / NF catalyst is 30 μl.

[0083] Depend on Figure 7 It can be seen that compared with Application Example 1 and Comparative Example 1, the PdFe3-Ni(OH)2 / NF catalyst requires a lower potential during the EG oxidation process at the same current density and its kinetics is faster.

[0084] Depend on Figure 8 As can be seen in Application Example 1, throughout the electrocatalytic process, the Faradaic efficiency of formic acid increases first and then decreases with increasing voltage. This indicates that as the voltage rises, the OER reaction strengthens while the EGOR reaction weakens, resulting in a decrease in the Faradaic efficiency of formic acid. At 1.4 V vs. RHE, the Faradaic efficiency of formic acid reaches 97.4%, the optimal voltage. This demonstrates the high catalytic activity of the PdFe₃-Ni(OH)₂ / NF catalyst.

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

[0086] Depend on Figure 10 It can be seen that in Application Example 2, when the PdFe3-Ni(OH)2 / NF catalyst electrocatalyzes the PET hydrolyzate, a constant voltage method is used to carry out an electrocatalytic reaction on the PET hydrolyzate. Under the condition of a voltage of 1.5 V, the electrolyte flow rate in the anode and cathode regions is 40 ml / min, and the PET hydrolyzate is completely electrolyzed to obtain an alkaline solution containing potassium terephthalate and potassium formate. Terephthalic acid and KDF are obtained by acidification and rotary evaporation. The obtained KDF powder is subjected to phase analysis and compared with the standard PDF card. It can be seen that KDF crystal powder is finally successfully prepared.

[0087] The present invention has been described above by way of examples, but the present invention is not limited to the above specific embodiments. Any changes or modifications based on the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a low-noble metal Pd-loaded nickel-based composite metal catalyst, characterized in that: The steps include: S1, placing nickel foam in a hydrochloric acid solution for ultrasonic treatment, then rinsing with deionized water, and drying to obtain pretreated NF; S2. Weigh sodium chloride and pour it into a centrifuge tube. Then pour the prepared potassium chloropalladate solution and ferric chloride hexahydrate solution into the centrifuge tube containing sodium chloride and stir to form a homogeneous solution. S3. Vertically and suspendedly immerse the NF pretreated in step S1 in the uniform solution of step S2, and carry out corrosion reaction under high-speed stirring. After the reaction is completed, take out, wash, and dry to obtain the low-noble metal Pd-loaded nickel-based composite metal catalyst.

2. The preparation method according to claim 1, wherein: The concentration of the hydrochloric acid solution in step S1 is 3 mol / L; the ultrasonication time is 40 min; and the drying temperature is 60°C.

3. The preparation method according to claim 1, wherein: The concentration of the potassium chloropalladate in step S2 is 0.5-3 mmol / L, and the amount of the potassium chloropalladate solution added is 40-50 ml.

4. The preparation method according to claim 3, wherein: The concentration of the potassium chloropalladate described in step S2 is 1 mmol / L, and the amount of the potassium chloropalladate solution added is 40 ml.

5. The preparation method according to claim 1, wherein: The concentration of the ferric chloride hexahydrate in step S2 is 5-30 mmol / L, and the amount of the ferric chloride hexahydrate solution added is 10-50 μl.

6. The preparation method according to claim 5, characterized in that: The concentration of the ferric chloride hexahydrate in step S2 is 10 mmol / L, and the amount of the ferric chloride hexahydrate solution added is 30 μl.

7. A nickel-based composite metal catalyst loaded with low-noble metal Pd prepared by the preparation method according to any one of claims 1 to 6.

8. Use of a low-noble metal Pd-loaded nickel-based composite metal catalyst prepared by the preparation method according to any one of claims 1 to 6 in the degradation of plastic waste.

9. A method for degrading plastic waste using a nickel-based composite metal catalyst loaded with low-noble metal Pd prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The steps include: (1) washing and drying the PET waste plastic powder, then dissolving it in an alkaline solution at high temperature, cooling it to room temperature, and filtering it to remove impurities, thereby obtaining an alkaline solution containing terephthalate and ethylene glycol, i.e., a PET hydrolyzate; (2) Assembling a flow-type electrolytic cell in a two-electrode form, wherein the anode electrode is a nickel-based composite metal catalyst loaded with low-noble metal Pd prepared by the preparation method according to any one of claims 1 to 6, and the cathode electrode is Pt / C; the electrolytes in the anode region and the cathode region are both PET hydrolyzates, and the cathode region and the anode region are separated by an anion exchange membrane; (3) The flow-type electrolytic cell is heated and voltage is applied to the electrolytic cell, and the PET hydrolysis product is used as an electrolyte to perform an electrocatalytic oxidation reaction, and potassium formate and potassium terephthalate are obtained after the reaction is completed.

10. The method according to claim 9, characterized in that: The alkaline solution described 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 in step (2) is Pt / C sprayed on NF; the content of Pt / C is 1-3 mg / cm 2 ; The heating temperature in step (3) is 25-60° C., the applied voltage range is 1.4-1.6 V, and the electrocatalytic oxidation reaction time is 48 h to 300 h.

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