A high-entropy alloy catalyst, a preparation method and application thereof

Abstract

This invention belongs to the field of catalyst technology, specifically relating to a high-entropy alloy catalyst, its preparation method, and its application. The high-entropy alloy catalyst is composed of five metallic elements—Pt, Ir, Fe, Mo, and Bi—in a molar ratio of (0.05-0.3):(0.05-0.3):(0.1-0.4):(0.1-0.4):(0.05-0.3), and the catalyst is supported on carbon nanotubes. The catalyst of this invention exhibits good thermal stability and resistance to carbon deposition, retaining over 90% of its activity after five cycles.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a high-entropy alloy catalyst, its preparation method, and its application. Background Technology

[0002] With the continuous growth in the consumption of plastic products, the pollution problem caused by waste plastics is becoming increasingly serious. General-purpose plastics such as PET, PP, and PE, due to their strong chemical stability and difficulty in recycling, cause severe environmental pollution when large quantities are stockpiled or incinerated. Existing plastic degradation technologies mainly include thermal pyrolysis, chemical catalytic degradation, and biodegradation, but these have many drawbacks: thermal pyrolysis requires high temperature and pressure conditions, resulting in high energy consumption and complex products; traditional chemical catalysts (such as platinum-carbon and metal oxides) are mostly single-component or two-component, with single active sites, leading to poor degradation selectivity and easy catalyst deactivation; biodegradation efficiency is extremely low, making industrial application difficult.

[0003] High-entropy alloys, as a novel material composed of five or more metallic elements, exhibit unique advantages in the field of catalysis due to their multiple active sites and synergistic effects. However, research on the application of existing high-entropy alloy catalysts in the field of plastic degradation is limited.

[0004] Existing high-entropy alloy catalysts suffer from the following technical bottlenecks: 1) Inappropriate selection of support materials, often using ordinary carbon materials, leading to easy agglomeration and detachment of catalyst particles, affecting catalytic stability; 2) Lack of targeted design in the metal element ratio, failing to optimize for the dual requirements of "CC bond breaking and O atom activation" in plastic degradation, resulting in difficulty in achieving both activity and selectivity; 3) Cumbersome preparation methods, relying heavily on high-temperature melting, sputtering, and other technologies, making it difficult to achieve uniform dispersion and loading of nanoscale particles; 4) Low specific surface area and insufficient exposure of active sites in unsupported high-entropy alloy catalysts, limiting catalytic efficiency.

[0005] Carbon nanotubes, as a carrier material with high specific surface area, excellent conductivity, and mechanical stability, can effectively disperse nanocatalyst particles and prevent agglomeration. However, in current technologies, the application of carbon nanotube-supported high-entropy alloys is mostly concentrated in electrocatalytic oxygen reduction and hydrogen evolution, without addressing the degradation of waste plastics. Furthermore, the inert surface of carbon nanotubes results in weak interactions with metal ions, leading to insufficient catalyst loading stability. Simultaneously, the synergistic effect of the five metal elements Pt, Ir, Fe, Mo, and Bi in the field of plastic degradation has not yet been developed, and targeted formulation design and simplified preparation methods for this pentagonal system have not been reported.

[0006] Therefore, developing a carbon nanotube-supported, optimized PtIrFeMoBi high-entropy alloy catalyst is of great significance for achieving efficient resource utilization of waste plastics. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a high-entropy alloy catalyst, its preparation method, and its applications. By optimizing the metal element ratio and solvothermal preparation process, uniform dispersion and robust loading of the catalyst are achieved, enabling its application in the directional degradation of waste plastics under mild conditions, while simultaneously improving degradation efficiency and catalyst stability.

[0008] To achieve the above-mentioned objectives of this invention, the specific technical solution adopted by this invention is as follows:

[0009] A high-entropy alloy catalyst is composed of five metallic elements, Pt, Ir, Fe, Mo and Bi, in a molar ratio of (0.05-0.3):(0.05-0.3):(0.1-0.4):(0.1-0.4):(0.05-0.3), and the high-entropy alloy catalyst is supported on a carbon nanotube carrier.

[0010] Preferably, the molar ratio of the five metallic elements Pt, Ir, Fe, Mo, and Bi is 0.15:0.15:0.25:0.25:0.20.

[0011] Preferably, the high-entropy alloy catalyst has a particle size of 2-10 nm.

[0012] Preferably, the carbon nanotubes have a diameter of 5-20 nm, a length of 1-5 μm, and a purity of ≥98 wt.%, and the carbon nanotubes are pretreated with nitric acid acidification.

[0013] More preferably, the pretreatment process of carbon nanotubes is as follows: add carbon nanotubes to a 6 mol / L nitric acid solution, reflux at 80°C for 2 hours, filter and wash until the filtrate is neutral, and vacuum dry at 60°C for 8 hours to obtain the final product.

[0014] This invention also relates to a method for preparing the above-mentioned high-entropy alloy catalyst, comprising the following steps:

[0015] (1) PtCl2, IrCl3, Fe(NO3)3, MoCl5, and Bi(NO3)3 were dissolved in ethylene glycol, carbon nanotubes were added, and the mixture was ultrasonically dispersed to obtain a homogeneous mixture A.

[0016] (2) Add a surfactant and a reduction accelerator to mixture A to obtain mixture B;

[0017] (3) Mixture B is prepared by using programmed temperature control for solvothermal reaction. After the reaction is completed, it is centrifuged, washed and dried to obtain the final product.

[0018] Preferably, the total metal concentration of PtCl2, IrCl3, Fe(NO3)3, MoCl5, and Bi(NO3)3 in step (1) is 0.01-0.1 mol / L, and the mass ratio of carbon nanotubes to total metals is 5-10:1.

[0019] Preferably, the surfactant in step (2) is polyvinylpyrrolidone, the amount of surfactant is 5%-10% of the total metal mass, the reduction promoter is ascorbic acid, and the molar ratio of the reduction promoter to the total metal ions is 1-2:1.

[0020] Preferably, the conditions for the programmed temperature control in step (3) are: first, increase the temperature to 110-130℃ at 1-3℃ / min and hold for 0.8-1.2h, then increase the temperature to 180-250℃ at 0.5-1.5℃ / min and hold for 6-24h.

[0021] Preferably, the solvent for washing in step (3) is ethanol, the number of washings is 3-5, the drying is vacuum drying, the drying temperature is 60-80℃, and the drying time is 10-14h.

[0022] This invention also relates to the application of the above-mentioned high-entropy alloy catalyst in the degradation of waste plastics.

[0023] Preferably, the mass ratio of the catalyst to the plastic is 1:50-100.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Through a unique five-element metal combination design, each metal component plays a synergistic catalytic role in the degradation of plastics: Pt and Ir provide excellent C-C bond breaking ability; Fe and Mo promote hydrogen transfer reaction; Bi regulates surface acidity and inhibits carbon deposition.

[0026] (2) The catalyst in this invention has good thermal stability and anti-carbon deposition ability, and its activity retention rate is still above 90% after 5 cycles. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are not intended to limit the present invention, but only to illustrate the present invention. Unless otherwise specified, the experimental methods used in the following embodiments are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0028] Carbon nanotube pretreatment: Add 5g of carbon nanotubes to 100mL of 6mol / L nitric acid solution, reflux at 80℃ for 2h, filter, wash with deionized water until the filtrate is neutral, and vacuum dry at 60℃ for 8h to obtain the final product.

[0029] Example 1

[0030] A method for preparing a high-entropy alloy catalyst, comprising the following steps:

[0031] (1) Weigh 0.15 mmol of PtCl2, 0.15 mmol of IrCl3, 0.25 mmol of Fe(NO3)3, 0.25 mmol of MoCl5, and 0.20 mmol of Bi(NO3)3, dissolve them in 50 mL of ethylene glycol, and stir for 15 min until completely dissolved; add 1.2 g of pretreated carbon nanotubes, and ultrasonically disperse for 40 min to obtain a homogeneous mixture A.

[0032] (2) Add 10 mg of polyvinylpyrrolidone and 1.0 mmol of ascorbic acid to the above mixture A, stir evenly to obtain mixture B, and transfer it to a 100 mL high-pressure reactor.

[0033] (3) The solvothermal reaction was controlled by a programmed temperature rise. The programmed temperature rise was as follows: the temperature was increased to 120℃ at 2℃ / min and held for 1 hour, then increased to 220℃ at 1℃ / min and held for 12 hours. After the reaction was completed, the temperature was cooled to room temperature, centrifuged at 9000r / min, washed with ethanol 4 times, and dried under vacuum at 70℃ for 12 hours to obtain the high entropy alloy catalyst.

[0034] The catalyst has a particle size of 4.5 nm and five metal elements are evenly distributed.

[0035] Example 2

[0036] A method for preparing a high-entropy alloy catalyst, comprising the following steps:

[0037] (1) Weigh 0.10 mmol of PtCl2, 0.20 mmol of IrCl3, 0.30 mmol of Fe(NO3)3, 0.25 mmol of MoCl5, and 0.15 mmol of Bi(NO3)3, dissolve them in 50 mL of ethylene glycol, and stir for 15 min until completely dissolved; add 1.3 g of pretreated carbon nanotubes, and ultrasonically disperse for 40 min to obtain a homogeneous mixture A.

[0038] (2) Add 10 mg of polyvinylpyrrolidone and 1.0 mmol of ascorbic acid to the above mixture A, stir evenly to obtain mixture B, and transfer it to a 100 mL high-pressure reactor.

[0039] (3) The solvothermal reaction was controlled by a programmed temperature rise. The programmed temperature rise was as follows: the temperature was increased to 115℃ at 1.5℃ / min and held for 1 hour, then increased to 200℃ at 1.2℃ / min and held for 10 hours. After the reaction was completed, the temperature was cooled to room temperature, centrifuged at 9000r / min, washed with ethanol 4 times, and dried under vacuum at 70℃ for 12 hours to obtain the high-entropy alloy catalyst.

[0040] The catalyst has a particle size of 5.2 nm and five metal elements are evenly distributed.

[0041] Example 3

[0042] A method for preparing a high-entropy alloy catalyst, comprising the following steps:

[0043] (1) Weigh 0.20 mmol of PtCl2, 0.10 mmol of IrCl3, 0.20 mmol of Fe(NO3)3, 0.30 mmol of MoCl5, and 0.20 mmol of Bi(NO3)3, dissolve them in 50 mL of ethylene glycol, and stir for 15 min until completely dissolved; add 1.0 g of pretreated carbon nanotubes, and ultrasonically disperse for 40 min to obtain a homogeneous mixture A.

[0044] (2) Add 10 mg of polyvinylpyrrolidone and 1.0 mmol of ascorbic acid to the above mixture A, stir evenly to obtain mixture B, and transfer it to a 100 mL high-pressure reactor.

[0045] (3) The solvothermal reaction was controlled by a programmed temperature increase. The programmed temperature increase was as follows: the temperature was increased to 125℃ at 2.5℃ / min and held for 1 hour, then increased to 240℃ at 0.8℃ / min and held for 8 hours. After the reaction was completed, the temperature was cooled to room temperature, centrifuged at 9000r / min, washed with ethanol 4 times, and dried under vacuum at 70℃ for 12 hours to obtain the high-entropy alloy catalyst.

[0046] The catalyst has a particle size of 6.8 nm and five metal elements are evenly distributed.

[0047] Comparative Example 1

[0048] The only difference between this comparative example and Example 1 is the proportion of the five-element high-entropy alloy. Specifically, in step (1), PtCl2 0.4 mmol, IrCl3 0.4 mmol, Fe(NO3)3 0.1 mmol, MoCl5 0.05 mmol, and Bi(NO3)3 0.05 mmol are used, and the other conditions are the same as in Example 1.

[0049] Comparative Example 2

[0050] The only difference between this comparative example and Example 1 is that Mo and Bi are not added. Specifically, in step (1), PtCl2 0.3 mmol, IrCl3 0.3 mmol, and Fe(NO3)3 0.4 mmol are used, and the other conditions are the same as in Example 1.

[0051] Comparative Example 3

[0052] The only difference between this comparative example and Example 1 is that Bi is not added. Specifically, in step (1), PtCl2 0.19 mmol, IrCl3 0.19 mmol, Fe(NO3)3 0.31 mmol, and MoCl5 0.31 mmol are used, and the other conditions are the same as in Example 1.

[0053] Comparative Example 4

[0054] The only difference between this comparative example and Example 1 is that the polyvinylpyrrolidone (PVP) in step (2) is replaced with an equal mass of hexadecyltrimethylammonium bromide (CTAB), while the other preparation conditions are exactly the same as in Example 1.

[0055] Comparative Example 5

[0056] The only difference between this comparative example and Example 1 is that the ascorbic acid in step (2) is replaced with an equimolar amount of sodium borohydride (NaBH4), while the other preparation conditions are exactly the same as in Example 1.

[0057] Comparative Example 6

[0058] The only difference between this comparative example and Example 1 is that Fe(NO3)3 in step (1) is replaced with an equimolar amount of FeCl3, while the other preparation conditions are exactly the same as in Example 1.

[0059] Comparative Example 7

[0060] The only difference between this comparative example and Example 1 is that in step (1), the metal precursor is replaced with only 1.0 mmol of PtCl2, and IrCl3, Fe(NO3)3, MoCl5 and Bi(NO3)3 are not added. The rest of the preparation steps and conditions are exactly the same as in Example 1.

[0061] Effect test

[0062] Test Example 1: Plastic Degradation Performance Test

[0063] Waste plastics: Low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET) (all industrial-grade waste recycled materials, crushed to 100 mesh powder).

[0064] A fixed-bed reactor was used under a nitrogen atmosphere (flow rate 50 mL / min) at a reaction temperature of 380℃ for 2 hours. The catalyst-to-plastic mass ratio was 1:50. Specifically, 0.5 g of catalyst was uniformly packed into the isothermal section of the reactor, and the top and bottom ends were filled with quartz wool for fixation. 25 g of pretreated plastic powder was weighed and placed in the feeding device, and fed into the reactor at a constant rate. Nitrogen gas (purity ≥99.99%) was introduced to replace the air in the reactor for 30 minutes, with the nitrogen flow rate controlled at 50 mL / min. The temperature was increased to 380℃ at a rate of 5℃ / min and maintained at this temperature for 2 hours. During the reaction, gaseous and liquid products were collected separately using a condenser, and the residual solids remained in the reactor.

[0065] Test metrics:

[0066] Plastic conversion rate (%) = (mass of plastic before reaction - mass of residual solids after reaction) / mass of plastic before reaction × 100%;

[0067] Liquid hydrocarbon yield (%) = mass of liquid product / mass of plastic before reaction × 100% (liquid hydrocarbons are defined as C5-C64) 20 Alkanes / olefins);

[0068] Olefin selectivity (%) = (molar amount of olefins (C2-C4) in gaseous products / total molar amount of gaseous products) × 100%;

[0069] Product purity (%): Gas chromatography-mass spectrometry (GC-MS) was used to analyze the percentage of target hydrocarbons (without heterocyclic and oxygen-containing impurities) in the liquid product.

[0070] The results of catalytic degradation of low-density polyethylene (LDPE) using the catalysts in Examples 1-3 and Comparative Examples 1-7 are shown in Table 1.

[0071]

[0072] The catalyst in Example 1 was used to catalytically degrade polypropylene (PP) and polyethylene terephthalate (PET), and the results are shown in Table 2.

[0073]

[0074] Test Example 2: Catalyst Stability Test

[0075] Under the aforementioned fixed-bed reactor and conditions, LDPE degradation reactions were carried out five times consecutively. After each reaction, the catalyst was removed from the reactor, placed in a centrifuge tube, ethanol was added, and the mixture was centrifuged at 9000 r / min for 10 min. The supernatant was discarded, and the reaction was washed four times. Subsequently, the catalyst was dried in a vacuum drying oven at 70℃ for 12 h, and the recovered catalyst was used for the next reaction. The plastic conversion rate of the first and fifth reactions was tested separately, and the activity retention rate (%) was calculated as: (Fifth conversion rate / First conversion rate) × 100%.

[0076] Carbon deposition test: The carbon deposition of the catalyst after 5 cycles was tested using a thermogravimetric analyzer (TGA). 10 mg of the recovered catalyst sample was placed in an alumina crucible and heated from room temperature to 800℃ at a rate of 10℃ / min under air atmosphere (flow rate 20 mL / min). The weight loss rate within the temperature range of 300-800℃ was recorded, and this weight loss rate is the carbon deposition of the catalyst (wt%).

[0077] The test results are shown in Table 3.

[0078]

[0079] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. The application of a high-entropy alloy catalyst in the thermocatalytic degradation of waste plastics, characterized in that, The waste plastic material is low-density polyethylene, polypropylene, or polyethylene terephthalate. The high-entropy alloy catalyst is composed of carbon nanotubes pretreated with nitric acid and five metallic elements, Pt, Ir, Fe, Mo, and Bi, supported thereon in a molar ratio of (0.05-0.3):(0.05-0.3):(0.1-0.4):(0.1-0.4):(0.05-0.3). The preparation method of the high-entropy alloy catalyst includes the following steps: (1) PtCl2, IrCl3, Fe(NO3)3, MoCl5, and Bi(NO3)3 were dissolved in ethylene glycol, and carbon nanotubes pretreated with nitric acid were added and ultrasonically dispersed to obtain mixture A; (2) Add a surfactant and a reduction accelerator to mixture A to obtain mixture B; (3) Mixture B is subjected to a solvothermal reaction controlled by programmed temperature rise. After the reaction is completed, it is centrifuged, washed and dried to obtain the high-entropy alloy catalyst. The surfactant is polyvinylpyrrolidone, and the reduction accelerator is ascorbic acid.

2. The application according to claim 1, characterized in that, The high-entropy alloy catalyst has a particle size of 2-10 nm.

3. The application according to claim 1, characterized in that, The carbon nanotubes have a diameter of 5-20 nm, a length of 1-5 μm, and a purity of ≥98 wt.%.

4. The application according to any one of claims 1-3, characterized in that, The total metal concentration of PtCl2, IrCl3, Fe(NO3)3, MoCl5 and Bi(NO3)3 in step (1) is 0.01-0.1 mol / L, and the mass ratio of carbon nanotubes to total metals is 5-10:

1.

5. The application according to any one of claims 1-3, characterized in that, The amount of surfactant used in step (2) is 5%-10% of the total metal mass, and the molar ratio of the reduction promoter to the total metal ions is 1-2:

1.

6. The application according to any one of claims 1-3, characterized in that, The conditions for the programmed temperature control in step (3) are as follows: first, increase the temperature to 110-130℃ at 1-3℃ / min and hold for 0.8-1.2h, then increase the temperature to 180-250℃ at 0.5-1.5℃ / min and hold for 6-24h.

7. The application according to any one of claims 1-3, characterized in that, The solvent for washing in step (3) is ethanol, and the number of washing cycles is 3-5. The drying is vacuum drying, the drying temperature is 60-80℃, and the drying time is 10-14h.

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