Small-size high-entropy catalyst for plastic depolymerization as well as preparation method and application of small-size high-entropy catalyst
By preparing small-sized high-entropy catalysts, the problems of low plastic depolymerization efficiency and complex high-entropy alloy synthesis were solved, achieving efficient and selective low-temperature depolymerization of polyethylene with low catalyst metal content and mild reaction conditions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-17
- Publication Date
- 2026-03-13
AI Technical Summary
Existing technologies suffer from low plastic depolymerization efficiency, stringent reaction conditions, a lack of efficient, highly selective, and environmentally friendly catalysts, and complex high-entropy alloy synthesis methods, which limit their widespread application.
A method for preparing small-sized high-entropy catalysts was adopted. Solvents and citric acid were added to the catalyst support and metal salt. After filtration and drying, the catalyst was calcined in a mixed atmosphere of carbon dioxide, hydrogen and nitrogen. Ruthenium salt was added, the catalyst was shaken and washed, and then calcined again to form ultra-small high-entropy alloy nanoparticles with an average particle size of less than 2 nm. These nanoparticles were used for the low-temperature depolymerization of polyethylene.
It provides a highly active catalyst with strong anti-sintering ability and good selectivity, realizing efficient low-temperature depolymerization of polyethylene. The catalyst has low metal content, mild reaction conditions, and good product selectivity.
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Figure CN121648959A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalysts and plastic conversion and utilization, and specifically relates to a small-sized high-entropy catalyst for plastic depolymerization, its preparation method and application. Background Technology
[0002] The widespread application of petroleum-based synthetic plastics has greatly improved the quality of life in modern society. Statistics show that in 2019 alone, global plastic production reached a staggering 460 million tons. However, less than 20% of plastic waste is effectively recycled, which not only wastes resources but also causes increasingly serious environmental pollution. To address this problem, the hydrogenation depolymerization of waste plastics has become an excellent recycling method. However, for plastics, especially polyethylene, depolymerization is often limited by low efficiency and strict reaction conditions. Therefore, synthesizing highly efficient, highly selective, environmentally friendly, and highly catalytically active catalysts is a crucial step.
[0003] High-entropy alloys have shown great catalytic potential as a novel type of metallic material. They have attracted widespread attention due to their multimetallic sites composed of five or more elements, their heat resistance, and their corrosion resistance. Currently, the main methods for synthesizing high-entropy alloys include arc melting, thermal carbon impaction, aerosol spray pyrolysis, melt spinning, ball milling, and solvothermal methods. These methods require strict synthesis conditions, limiting the further promotion of high-entropy alloys. Therefore, developing new synthesis methods for high-entropy alloys is crucial, and reducing the amount of metal used is also an important step. Summary of the Invention
[0004] The primary objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a method for preparing a small-sized high-entropy catalyst for low-temperature hydrogenation depolymerization of plastics.
[0005] Another object of the present invention is to provide a small-sized high-entropy catalyst for low-temperature depolymerization of plastics prepared by the method.
[0006] Another object of the present invention is to provide the application of the small-sized high-entropy catalyst for low-temperature depolymerization of plastics.
[0007] The objective of this invention is achieved through the following technical solution: A method for preparing a small-sized, high-entropy catalyst for low-temperature depolymerization of plastics includes the following steps: (1) Add solvent to catalyst support and metal salt, then add citric acid, stir and mix well, filter, dry to obtain catalyst precursor; (2) The catalyst precursor obtained in step (1) is heated to 800°C in a mixed gas atmosphere of carbon dioxide, hydrogen and nitrogen and then cooled to room temperature after calcination to obtain HEA catalyst. (3) Add solvent and ruthenium salt to the HEA catalyst obtained in step (2), shake, filter, wash, dry and then calcine in a reducing gas atmosphere. After calcine is completed, cool to room temperature to obtain small-sized high-entropy catalyst HEA-Ru-R.
[0008] Furthermore, the catalyst support described in step (1) is a mesoporous molecular sieve; even further, it is MCM-41.
[0009] Furthermore, the catalyst support is added at a rate of 0.2 g of catalyst support per 0.01 mol of metal salt; Further, the metal salt mentioned in step (1) includes at least one of iron salt, cobalt salt, nickel salt, copper salt and zinc salt; Furthermore, the iron salt mentioned in step (1) is a soluble iron salt; even further, it is ferric nitrate.
[0010] Furthermore, the cobalt salt mentioned in step (1) is a soluble cobalt salt; even further, it is cobalt acetate.
[0011] Furthermore, the nickel salt mentioned in step (1) is a soluble nickel salt; even further, it is nickel acetate.
[0012] Furthermore, the copper salt mentioned in step (1) is a soluble copper salt; even further, it is copper acetate.
[0013] Furthermore, the zinc salt mentioned in step (1) is a soluble zinc salt; even further, it is zinc acetate.
[0014] Further, the metal salt mentioned in step (1) is iron salt, cobalt salt, nickel salt, copper salt and zinc salt, and the molar ratio of iron salt, cobalt salt, nickel salt, copper salt and zinc salt mentioned in step (1) is 0~1:0~1:0~1:0~1:0~1; even further, it is 1:1:1:1:1.
[0015] Furthermore, the citric acid mentioned in step (1) is preferably citric acid monohydrate.
[0016] Furthermore, the total molar amount of the metal salt in step (1) is in a molar ratio of 1:1 to that of citric acid.
[0017] Further, the solvent mentioned in step (1) is a mixed solution of water and ethylene glycol; Furthermore, the ratio of water to ethylene glycol is 1:1 to 2; even further, it is 1:1.5. Furthermore, the water is preferably deionized water.
[0018] Further, the amount of solvent added in step (1) is 20-30 mL for each metal; even further, it is 24 mL for each metal.
[0019] Furthermore, the stirring conditions described in step (1) are: stirring at 300-600 r / min for 4-12 hours; and even further, stirring at 450 r / min for 8 hours.
[0020] Furthermore, the drying time described in step (1) is 6 to 12 hours; even further, it is 8 hours.
[0021] Furthermore, in step (2), the volume ratio of CO2, H2, and N2 in the mixed gas of carbon dioxide, hydrogen, and nitrogen is 1:1:8, and the flow rate of the mixed gas is 150 mL / min.
[0022] Furthermore, the heating rate described in step (2) is 5°C / min.
[0023] Furthermore, the calcination temperature mentioned in step (2) is 800°C.
[0024] Furthermore, the calcination time in step (2) is 1 to 6 hours; preferably 3 hours.
[0025] Furthermore, the mass ratio of ruthenium salt to HEA in step (3) is 1:50 to 150; even further, it is 1:100.
[0026] Further, the solvent mentioned in step (3) is a mixture of ethylene glycol and water; the ratio of ethylene glycol to water is 1.5:1; the amount added is 10 to 30 mL of solvent per 300 mg HEA; even further, the amount added is 20 mL of solvent per 300 mg HEA.
[0027] Furthermore, the oscillation conditions described in step (3) are: rotation speed of 100-300 r / min, oscillation for 0-4 h (excluding 0); even further, the rotation speed is 200 r / min, oscillation for 2 h.
[0028] Furthermore, the drying conditions described in step (3) are: temperature of 80-120℃, drying time of 2-6 hours; even further, the drying conditions are: temperature of 105℃, drying time of 4 hours.
[0029] Furthermore, the calcination conditions described in step (3) are: a temperature of 200 to 900°C and a calcination time of 0 to 3 hours (excluding 0); even further, the conditions are: a temperature of 400°C and a calcination time of 1 hour.
[0030] Further, the cooling in step (3) is cooling in a reducing gas atmosphere; the reducing gas is a mixture of N2 and H2 or H2; even further, the reducing gas is a reducing gas obtained by mixing H2 and N2 in a volume ratio of 1:9.
[0031] An ultra-small high-entropy catalyst for low-temperature depolymerization of polyethylene was prepared by the above method.
[0032] The ultra-small high-entropy catalyst for low-temperature depolymerization of polyethylene is used in the preparation of high-value compounds from depolymerized polyethylene.
[0033] Furthermore, the application includes the following steps: The above-mentioned ultra-small high-entropy catalyst for low-temperature depolymerization of polyethylene was mixed with low-density polyethylene and subjected to a catalytic reaction at 210℃~260℃ with hydrogen gas introduced to obtain a high-value compound.
[0034] Furthermore, the high-value compound is an oil with different C-chain distribution and a gaseous product (C1-C4) with low carbon chains; preferably an oil product.
[0035] Furthermore, the temperature of the catalytic reaction is preferably 210~260℃; even more preferably 210℃.
[0036] Furthermore, the hydrogen pressure introduced is 0.5 MPa to 3 MPa; even further, it is 3 MPa.
[0037] Furthermore, the rotational speed of the catalytic reaction is 0–400 r / min; even further, it is 200 r / min.
[0038] Furthermore, the catalytic reaction time is 0–20 h; even further, it is 20 h.
[0039] The present invention has the following advantages and effects compared with the prior art: The ultra-small high-entropy catalyst of this invention is prepared by impregnating and reducing five different metals, followed by ruthenium ion replacement. During the replacement process, ruthenium ions disintegrate the high-entropy alloy due to the redox potential. After the large high-entropy alloy particles are disintegrated, hydroxy-iron bonds are formed between water and iron during the replacement process, etching the support. Finally, ethylene glycol anchors to the etched support and forms special silicon-oxygen-iron bonds, forming a high-entropy alloy-ethylene glycol complex. After reduction with reducing gas, ultra-small high-entropy alloy nanoparticles with an average particle size of less than 2 nm are formed on the support. These ultra-small high-entropy alloy nanoparticles provide more active sites for the depolymerization of polyethylene in plastics. The catalyst prepared by this method has a metal content of no more than 3 wt% and a ruthenium content of no more than 0.5 wt%. It also provides high activity and excellent anti-sintering ability, and exhibits good selectivity for target oil products. Attached Figure Description
[0040] Figure 1 This is a flowchart illustrating the preparation process of the catalyst in this invention.
[0041] Figure 2 This is the XRD pattern of the HEA-Ru-R catalyst prepared in Example 1.
[0042] Figure 3 This is a TEM image of the HEA-Ru-R catalyst prepared in Example 1.
[0043] Figure 4 This is a TEM image of HEA+Ru prepared in Comparative Example 1.
[0044] Figure 5 This is a graph showing the effect of calcination temperature of different catalysts on the depolymerization of polyethylene plastic in Example 2.
[0045] Figure 6 This is a graph showing the depolymerization and conversion effect of polyethylene plastic at different rotation speeds in Example 3.
[0046] Figure 7 This is a graph showing the effect of different reaction temperatures on the depolymerization of polyethylene plastic in Example 4. Detailed Implementation
[0047] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed according to conventional experimental conditions or experimental conditions recommended by the manufacturer. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.
[0048] The molecular sieve involved in the embodiments of the present invention is MCM-41, pure silicon, purchased from the catalyst factory of Nankai University.
[0049] Example 1: Preparation of Ultrasmall High Entropy Catalyst The preparation of the ultrasmall high-entropy alloy HEA-Ru-R includes the following steps: (preparation process as follows) Figure 1 (As shown) (1) Weigh 1 g of MCM-41 in beaker 1 and place it in an oven overnight. Weigh 4.04 g of ferric nitrate, 2.49 g of cobalt acetate, 2.48 g of nickel acetate, 1.99 g of copper acetate, and 2.19 g of zinc acetate. Add 80 mL of a mixed solution of ethylene glycol and water (volume ratio of ethylene glycol to water is 1.5:1). At the same time, take out beaker 2, weigh 10.5 g of citric acid monohydrate, and add 40 mL of a mixed solution of ethylene glycol and water (volume ratio of ethylene glycol to water is 1.5:1). Stir each solution at room temperature (450 r / min, stirring for 2 h). Then pour the solution from beaker 2 into beaker 1 and stir at room temperature (450 r / min, stirring for 6 h). Filter the solution and dry it in an oven at 105 °C for 8 h to obtain the catalyst precursor. (2) The catalyst precursor was placed in a pyrolysis furnace with a mixed atmosphere of CO2, H2, and N2 (volume ratio of CO2, H2, and N2 1:1:8, flow rate 150 mL / min) and calcined. During calcination, the temperature was increased to 800 °C at a heating rate of 5 °C / min, and calcined at 800 °C for 3 h. After cooling to room temperature, HEA was obtained. (3) Add 300 mg HEA to a 50 mL Erlenmeyer flask, add 20 mL of a mixed solution of ethylene glycol and water (the volume ratio of ethylene glycol to water is 1.5:1), add 8.1 mg of ruthenium trichloride, place in a shaker and shake (200 r / min, 2 h), then filter, wash, and place in an oven at 105 °C to dry for 4 h to obtain HEA-Ru.
[0050] (4) HEA-Ru was placed in a pyrolysis furnace at 400℃ under a mixed atmosphere of N2 and H2 (volume ratio of H2 to N2 1:9, flow rate 150 mL / min) and calcined for 1 h. It was then cooled to room temperature to obtain the ultra-small high-entropy catalyst HEA-Ru-R.
[0051] Figure 2 This is an ultra-small high-entropy transmission electron microscope (TEM) image. As can be seen from the image, the ultra-small high-entropy alloy is uniformly distributed on the molecular sieve, and the average particle size is maintained at about 2 nm.
[0052] Figure 3The image shows an ultra-small high-entropy X-ray diffraction (XRD) pattern. The peaks at 44.5°, 50.7°, and 74.3° indicate a standard face-centered cubic structure for high-entropy alloys. This demonstrates that a pure-phase high-entropy alloy was synthesized.
[0053] Comparative Example 1: Preparation of Hexa-Element High-Entropy Alloy The purpose of Comparative Example 1 is to compare whether the same ultra-small high-entropy catalyst can be obtained by directly synthesizing ruthenium into a high-entropy alloy.
[0054] The metal addition amounts were basically the same as described above. Ferric nitrate (4.04 g), cobalt acetate (2.49 g), nickel acetate (2.48 g), copper acetate (1.99 g), and zinc acetate (2.19 g) were weighed. The difference was the addition of ruthenium trichloride (27 mg), and 80 mL of a mixed solution of ethylene glycol and water (ethylene glycol to water volume ratio 1.5:1) was added. Simultaneously, beaker #2 was taken out, citric acid (10.5 g) was weighed, and 40 mL of the mixed solution of ethylene glycol and water (ethylene glycol to water volume ratio 1.5:1) was added. Both were stirred at room temperature (450 r / min, stirring for 2 h). The solution from beaker #2 was then poured into beaker #1, and stirred at room temperature (450 r / min, stirring for 6 h). After filtration, the mixture was dried in a 105℃ oven for 8 h to obtain the catalyst precursor.
[0055] The catalyst precursor was placed in a pyrolysis furnace with a mixed atmosphere of CO2, H2, and N2 (volume ratio of CO2, H2, and N2 1:1:8, flow rate 150 mL / min) and calcined at a temperature of 800 °C, a heating rate of 5 °C / min, and a calcination time of 3 h. After cooling to room temperature, HEA+Ru was obtained.
[0056] Figure 4 This is a transmission electron microscope (TEM) image of a six-element high-entropy alloy. As can be seen from the image, the particle size of the synthesized six-element high-entropy alloy is very uneven, with a particle size distribution between 5 and 15 nm.
[0057] Comparative Example 2: Individual Ru Load The purpose of Comparative Example 2 is to compare whether the same ultrasmall metal catalyst can be obtained by directly synthesizing ruthenium into the catalyst.
[0058] Weigh 1g of MCM-41 into beaker 1 and place it in an oven overnight. Weigh 27mg of ruthenium acetate and add 80mL of a mixture of ethylene glycol and water. At the same time, take out beaker 2, weigh 56.3mg of citric acid monohydrate, and add 40mL of a mixture of ethylene glycol and water. Stir each beaker at room temperature (450r / min, for 2h). Then pour the solution from beaker 2 into beaker 1 and stir at room temperature (450r / min, for 6h). After filtration, dry the solution in an oven at 105℃ for 8h to obtain the catalyst precursor.
[0059] The catalyst precursor was placed in a pyrolysis furnace with a mixed atmosphere of CO2, H2, and N2 (volume ratio of CO2, H2, and N2 1:1:8, flow rate 150 mL / min) and calcined at a temperature of 800 °C, a heating rate of 5 °C / min, and a calcination time of 3 h. After cooling to room temperature, MCM-41-Ru was obtained.
[0060] Comparative Example 3: Quaternary Medium Entropy Alloy (1) The preparation steps (2) to (4) of Comparative Example 3 are the same as those of Example 1. The difference is that in the preparation of the metal precursor solution in step (1) of Comparative Example 3, only four metals are added, each metal amount is 0.0125 mol, and 80 ml of a mixed solution of ethylene glycol and water is added to beaker No. 1. 10.5 g of citric acid monohydrate is weighed in beaker No. 2 and 40 ml of a mixed solution of ethylene glycol and water is added. After stirring for 2 h, beaker No. 2 is poured into beaker No. 1 and stirred for 6 h. After filtration, it is placed in an oven at 105 ℃ and dried for 8 h to obtain the corresponding quaternary medium entropy alloy precursor.
[0061] (2) The corresponding quaternary medium-entropy alloy precursor was placed in a pyrolysis furnace for calcination at a temperature of 800℃, a heating rate of 5℃ / min, and a calcination time of 3h. After cooling to room temperature, (noA, A=Fe,Co,Ni,Cu,Zn)HEA was obtained. (3) Add 300 mg HEA to a 50 ml Erlenmeyer flask, add 20 ml of a mixture of ethylene glycol and water, add 8.1 mg of ruthenium trichloride, shake in a shaker (200 r / min, 2 h), filter, wash, and dry in an oven at 105 °C for 4 h to obtain (noA, A=Fe, Co, Ni, Cu, Zn)HEA-Ru.
[0062] (4) HEA-Ru was placed in a N2 and H2 mixed atmosphere (H2 and N2 volume ratio 1:9, flow rate 150 mL / min) pyrolysis furnace at 400℃ and calcined for 1 h, and then cooled to room temperature to obtain an ultra-small high entropy catalyst (noA, A=Fe, Co, Ni, Cu, Zn) HEA-Ru-R. The purpose was to compare the effects of medium entropy alloy and high entropy alloy catalysts on the reaction.
[0063] Comparative Example 4: Different calcination temperatures The purpose of Comparative Example 4 is to investigate the anti-sintering ability and catalytic activity of the obtained ultra-small high-entropy catalyst at different reduction temperatures.
[0064] The preparation steps of Comparative Example 4 were the same as those of Example 1, except that in step (4) of Comparative Example 4, the calcination temperature was changed to 200℃, 600℃, 800℃, and 900℃, respectively, and the calcination time was 1h under a mixed atmosphere of N2 and H2 (volume ratio of H2 to N2 1:9, flow rate 150mL / min). After the calcination, the mixture was cooled to room temperature. HEA-Ru-R (a, a=200℃, 600℃, 800℃, 900℃) was obtained.
[0065] Example 2 Evaluation of the catalyst-catalyzed hydrogenation conversion reaction of polyethylene The following samples were used for polyethylene hydrogenation conversion: HEA, HEA-Ru, HEA-Ru-R prepared in Example 1, HEA+Ru prepared in Comparative Example 1, MCM-41-Ru prepared in Comparative Example 2, (noA, A=Fe, Co, Ni, Cu, Zn)HEA-Ru-R prepared in Comparative Example 3, and HEA-Ru-R (a, a=200℃, 600℃, 800℃, 900℃) prepared in Comparative Example 4. The specific steps are as follows: (1) Weigh 250 mg of sample and 500 mg of polyethylene separately using a balance, add them to the quartz liner, and weigh the total mass before the reaction. Place the liner into the mechanical reactor, seal it, and purge with hydrogen gas (hydrogen pressure of 2 MPa) 2-3 times. Set the reaction program. The reaction conditions are: at a hydrogen pressure of 3 MPa, set the rotation speed to 200 r / min, start timing from the temperature rise from room temperature to 210℃, and react for 20 h.
[0066] (2) After the reaction is complete, allow it to cool naturally to room temperature and weigh the total mass after the reaction to determine the gas conversion rate. Collect the remaining residual product and catalyst with 30 mL of dichloromethane liquid, shake with a shaker for 10 min, filter using an organic 13 mm * 0.22 μm filter, and test and analyze the liquid product types using a gas chromatograph-mass spectrometer (Thermo Trace 1300-ISQ) equipped with a TG-5MS column (30 m × 0.25 mm × 0.25 μm). Quantitatively test the liquid product distribution using a gas chromatograph (Agilent 8860) equipped with an HP-5 column (30 m × 0.32 mm × 0.25 μm, Agilent 19091J-413), with an instrument injection port vaporization temperature of 280 °C and a pre-detector FID temperature of 300 °C. The column oven temperature program was as follows: hold at 60℃ for 3 min, then increase to 280℃ at a rate of 10℃ / min and hold for 3 min. The experiment was repeated three times. The remaining product was dried in a 120℃ oven for 8 h, and the conversion rate was calculated.
[0067] The conversion rate is calculated using the following formula.
[0068] ; ; ; The experimental results are shown in Table 1. The results demonstrate that the HEA-Ru-R catalyst exhibits optimal activity for the hydrogenation conversion of polyethylene to liquid products under the designed conditions. Comparison with HEA+Ru and MCM-41-Ru shows that neither direct synthesis of the hexa-membered high-entropy alloy nor direct support of Ru resulted in good activity, proving that the synthesis of ultra-small high-entropy alloys can improve catalyst activity. Comparison of different calcination temperatures with HEA-Ru-R demonstrates the need for a suitable temperature-dependent reduction catalyst (results at different calcination temperatures are shown in Table 1). Figure 5 (As shown). By comparing the quaternary medium-entropy alloy and HEA-Ru-R, it was demonstrated that although the method is the same, the effect is not as good as that of the high-entropy alloy because it is not a high-entropy alloy, which further verifies the superiority of the catalyst.
[0069] Table 1. Conversion effect of different catalysts on plastic depolymerization
[0070] Example 3: Effect of rotational speed on the depolymerization of polyethylene into oil products Using HEA-Ru-R prepared in Example 1 as the core, the effect of different rotation speeds on the depolymerization of polyethylene into oil products was investigated.
[0071] The specific operating steps are the same as in Example 2: 0 r / min, 200 r / min, and 400 r / min. The difference is that three sets of experiments are changed, and the "set the rotation speed to 200 r / min" in step (1) of Example 2 is changed to "set it to 0 r / min, 200 r / min, and 400 r / min respectively". The reaction results are as follows: Figure 6 As shown.
[0072] Rotation speed affects the yield of the three states of reactants. When the rotation speed is too high, the active sites of the catalyst cannot effectively contact the reactants, resulting in a reduction of liquid products. When the rotation speed is too low, the catalyst contacts the reactants for too long, causing the already broken polyethylene bonds to break further, resulting in the formation of more gaseous products. Example 4: Effect of Temperature Conditions on the Depolymerization of Polyethylene into Oil-Based Products Using HEA-Ru-R prepared in Example 1 as the core, the effect of different temperature conditions on the depolymerization of polyethylene into oil products was investigated. The specific operation steps were the same as in Example 2, except that four sets of experiments were changed, and the "heating from room temperature to 210℃" in step (1) of Example 2 was changed to "heating from room temperature to 190℃, 210℃, 230℃ and 260℃ respectively". The reaction results are as follows: Figure 7 As shown.
[0073] The activity of the HEA-Ru-R reaction for polyethylene conversion changes with increasing temperature, and the product distribution of polyethylene also changes. At low temperatures (190℃), there is virtually no effect because the temperature does not reach the activation energy for breaking the C-C bonds. At high temperatures (260℃), the products are primarily gaseous, because the high activity leads to an excessively strong ability to break the C-C bonds, causing the reaction to proceed towards gaseous products. This temperature-based investigation not only illustrates the relationship between catalyst activity and temperature but also provides a method for the targeted selection of products.
[0074] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.
Claims
1. A method for preparing a small-sized, high-entropy catalyst for low-temperature depolymerization of plastics, characterized in that, Includes the following steps: (1) Add solvent to catalyst support and metal salt, then add citric acid, stir and mix well, filter, dry to obtain catalyst precursor; (2) The catalyst precursor obtained in step (1) is heated to 800°C in a mixed gas atmosphere of carbon dioxide, hydrogen and nitrogen and then cooled to room temperature after calcination to obtain HEA catalyst. (3) Add solvent and ruthenium salt to the HEA catalyst obtained in step (2), shake, filter, wash, dry and then calcine in a reducing gas atmosphere. After calcine is completed, cool to room temperature to obtain a small-sized high-entropy catalyst.
2. The preparation method according to claim 1, characterized in that, The catalyst support mentioned in step (1) is a mesoporous molecular sieve; The amount of catalyst support added in step (1) is 0.2g of catalyst support for every 0.01mol of metal salt.
3. The preparation method according to claim 1, characterized in that, The metal salt mentioned in step (1) includes at least one of iron salt, cobalt salt, nickel salt, copper salt and zinc salt; the iron salt is a soluble iron salt; the cobalt salt is a soluble cobalt salt; the nickel salt is a soluble nickel salt; the copper salt is a soluble copper salt; and the zinc salt mentioned in step (1) is a soluble zinc salt.
4. The preparation method according to claim 3, characterized in that, The metal salts mentioned in step (1) are iron salts, cobalt salts, nickel salts, copper salts and zinc salts, and the molar ratio of the iron salts, cobalt salts, nickel salts, copper salts and zinc salts mentioned in step (1) is 0~1:0~1:0~1:0~1:0~1.
5. The preparation method according to claim 1, characterized in that, The citric acid mentioned in step (1) is citric acid monohydrate; The total molar amount of the metal salt mentioned in step (1) is in a molar ratio of 1:1 to that of citric acid; The solvent mentioned in step (1) is a mixed solution of water and ethylene glycol; the ratio of water to ethylene glycol is 1:1 to 2. The solvent addition amount mentioned in step (1) is 20-30 mL for each metal; The stirring conditions described in step (1) are: stirring at 300-600 r / min for 4-12 hours; The drying time mentioned in step (1) is 6 to 12 hours.
6. The preparation method according to claim 1, characterized in that, In step (2), the volume ratio of CO2, H2, and N2 in the mixed gas of carbon dioxide, hydrogen, and nitrogen is 1:1:8, and the flow rate of the mixed gas is 150 mL / min. The heating rate mentioned in step (2) is 5℃ / min; The calcination time mentioned in step (2) is 1 to 6 hours.
7. The preparation method according to claim 1, characterized in that, The mass ratio of ruthenium salt to HEA in step (3) is 1:50 to 150; The solvent mentioned in step (3) is a mixture of ethylene glycol and water; the ratio of ethylene glycol to water is 1 to 2:1; the amount of solvent added is 10 to 30 mL per 300 mg HEA; The oscillation conditions described in step (3) are: rotation speed of 100-300 r / min, oscillation time of 0-4 h, excluding 0 h; The drying conditions described in step (3) are: temperature of 80-120℃, drying time of 2-6 hours.
8. The preparation method according to claim 1, characterized in that, The calcination conditions described in step (3) are: temperature of 200-900℃, calcination time of 0-3h, excluding 0h; The cooling described in step (3) is cooling in a reducing gas atmosphere; the reducing gas is a mixture of N2 and H2 or H2.
9. An ultra-small high-entropy catalyst for low-temperature depolymerization of polyethylene, prepared by the method described in any one of claims 1 to 8.
10. The application of the ultra-small high-entropy catalyst for low-temperature depolymerization of polyethylene as described in claim 9 in the preparation of high-value compounds from depolymerized polyethylene.