Coated SiC-coated ZnFe-MMO microwave catalyst as well as preparation method and application thereof

Abstract

The invention discloses a coated SiC-coated ZnFe-MMO microwave catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalyst preparation and plastic chemical recovery. The catalyst takes silicon carbide particles as an inner core, and the surface is coated with a zinc-iron composite metal oxide catalyst layer. The preparation method comprises the following steps: coating silicon carbide particles with ZnFe-gel through a sol-gel method to prepare a precursor, and roasting to obtain the ZnFe-based silicon carbide composite material. The catalyst can realize rapid conversion of polyolefin plastic in a CO2 atmosphere, synergistically fix CO2, eliminate carbon deposition and generate synthesis gas with high selectivity. Compared with the prior art, the method has the advantages of high reaction rate, high product selectivity, low energy consumption and the like, the catalyst synthesis method is simple, the wave-absorbing performance is excellent, the stability is good, a new way is provided for plastic green recovery and CO2 resource utilization, and the wide practical application value is shown.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and plastic chemical recycling technology, and particularly relates to a coated SiC@ZnFe-MMO microwave catalyst, its preparation method and application. Background Technology

[0002] Plastics, as one of the most important synthetic materials of the 20th century, have been widely adopted in packaging, agriculture, medicine, electronics, and daily life due to their outstanding characteristics such as lightweight, durability, and low cost. Among them, polyolefin plastics (such as polyethylene PE and polypropylene PP) are the largest and most widely used plastic category in the world, accounting for more than half of the total global plastic production. These materials possess excellent mechanical properties and chemical stability, and can serve for a long time in a variety of complex environments, bringing great convenience to modern industrial production and daily life. However, it is precisely this strong stability that makes polyolefin plastics extremely difficult to degrade in the natural environment. A large amount of waste plastic enters the ecosystem through landfill, incineration, or indiscriminate disposal, causing a serious "white pollution" problem. Polyolefin molecules are mainly composed of C-C bonds and lack active functional groups. Their natural degradation cycle can take hundreds of years. This not only continuously occupies valuable land resources, but also gradually breaks down into microplastics, which accumulate through the food chain, posing a potential and lasting threat to the balance of the ecosystem and human health.

[0003] Traditional methods for treating polyolefin waste primarily involve landfilling and incineration, both of which have significant drawbacks. Landfilling not only consumes vast amounts of land resources, but its leachate can also pollute soil and groundwater, causing secondary environmental hazards. While incineration can reduce volume and recover some energy, it easily generates toxic and harmful pollutants such as dioxins and heavy metal fly ash, and emits large amounts of CO2, further exacerbating the greenhouse effect. These methods are essentially "downgraded recycling," failing to fully exploit the carbon resource value of plastics and contradicting the concept of sustainable development. In recent years, chemical recycling methods, represented by pyrolysis and catalytic cracking, have received widespread attention and research. Their core objective is to convert polyolefins into fuels or high-value-added chemicals, achieving "upgraded recycling." However, traditional thermocatalytic processes often rely on high-temperature heating, which is not only energy-intensive and requires harsh reaction conditions, but also suffers from bottlenecks such as catalyst deactivation due to carbon buildup and low product selectivity, severely restricting their large-scale application.

[0004] Against this backdrop, microwave catalysis technology, as an emerging energy conversion pathway, exhibits irreplaceable and unique advantages. Unlike traditional heating methods, microwaves can directly act on catalysts and reactant molecules, achieving molecular-level "internal heating." This significantly improves energy utilization efficiency and induces a "hot spot" effect at relatively low bulk temperatures, efficiently promoting the breaking and recombination of C-C bonds. Combining microwave technology with CO2 as a mild oxidant to construct a microwave-CO2 synergistic catalytic system not only utilizes CO2 as a carbon source to regulate product distribution but also converts CO2 into high-value-added chemicals such as CO through a reduction pathway, truly realizing a green development model of "treating waste with waste."

[0005] Although some research has attempted to apply microwave technology to plastic pyrolysis, developing catalytic materials that combine high microwave absorption performance with excellent catalytic activity and good stability remains a core challenge in this field. Current microwave catalysts generally suffer from drawbacks such as easy sintering of active components, poor microwave response performance, and insufficient cycle stability. Therefore, designing a catalyst that can strongly couple microwave energy, achieve directional conversion of polyolefins under mild conditions, and efficiently synergistically react with CO2 has become a core research direction for promoting the practical application of this technology. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a coated SiC@ZnFe-MMO microwave catalyst, its preparation method, and its application, in order to achieve efficient and highly selective conversion of polyolefin plastics in a microwave-CO2 field, providing new materials and pathways for the resource utilization of plastic waste.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A coated SiC@ZnFe-MMO microwave catalyst has a silicon carbide particle core and a zinc-iron composite metal oxide (ZnFe-MMO) catalyst layer coated on the surface.

[0008] The coated SiC@ZnFe-MMO microwave catalyst of this invention features a unique core-shell structure design. The core silicon carbide is an excellent microwave absorber, capable of efficiently and rapidly converting microwave energy into heat energy, serving as an "internal heat source" for the catalyst and enabling rapid heating of the entire catalyst. The outer shell, a zinc-iron composite metal oxide coating, is the catalytic active center, but its own microwave absorption capacity is relatively weak. Through the coating structure, it can directly obtain heat energy from the silicon carbide core and be efficiently activated, overcoming the bottleneck of "slow heating and low efficiency" in traditional catalysts in microwave fields. This avoids the heat conduction process from the outside to the inside in traditional heating methods, resulting in minimal energy loss and overall energy saving.

[0009] This invention also provides a method for preparing a coated SiC@ZnFe-MMO microwave catalyst, comprising the following steps: Zinc source, iron source and complexing agent are dissolved in solvent, and the precursor sol is prepared by stirring and aging. Silicon carbide particles were immersed in the precursor sol, dried at 100°C to obtain a gel precursor, and then calcined to obtain the coated SiC@ZnFe-MMO microwave catalyst.

[0010] This invention first coats silicon carbide particles with ZnFe gel using a sol-gel method, followed by calcination to obtain the coated SiC@ZnFe-MMO microwave catalyst. The sol-gel method combined with calcination is simple, controllable, and allows for uniform coating of the ZnFe-MMO layer on the SiC surface, facilitating the formation of a stable core-shell structure and improving the overall performance of the catalyst.

[0011] Further, the molar ratio of the zinc source to the solvent is 1:120; the molar ratio of the zinc source to the complexing agent is 1:1; and the molar ratio of the zinc source to the iron source is 1:(1.5-3.5).

[0012] This invention optimizes the molar ratio of zinc source, iron source and complexing agent, regulates the composition and structure of metal oxide, enhances the synergistic catalytic effect of catalyst, and improves its dual function of chain scission and CO2 activation of polyolefin.

[0013] Furthermore, the zinc source is zinc acetate dihydrate; the iron source is ferric nitrate; the complexing agent is triethanolamine; and the solvent is anhydrous ethanol.

[0014] This invention uses zinc acetate dihydrate, ferric nitrate, triethanolamine and anhydrous ethanol as raw materials, which are widely available, inexpensive and easy to form stable precursor sols, which is beneficial to the smooth progress of subsequent coating processes.

[0015] Furthermore, the stirring temperature is 60°C, and the stirring time is 2 hours.

[0016] This stirring condition facilitates the full dissolution and mixing of raw materials, promotes the complexation reaction, and improves the uniformity and stability of the precursor sol.

[0017] Furthermore, the aging time is 24 hours.

[0018] Aging for 24 hours can promote the aging and structural stability of the sol, avoid uneven coating caused by excessively rapid gelation, and facilitate the formation of a dense and continuous ZnFe-MMO coating layer.

[0019] Furthermore, the calcination temperature is 400-600℃, preferably 550℃, the heating rate is 2-10℃ / min, preferably 5℃ / min, and the time is 1-3h, preferably 2h.

[0020] By controlling the calcination temperature, heating rate, and time, the crystal form and surface properties of metal oxides can be regulated to avoid over-sintering and maintain a high specific surface area and active site density.

[0021] This invention also provides an application of a coated SiC@ZnFe-MMO microwave catalyst in the microwave-CO2 synergistic catalytic conversion of polyolefin plastics.

[0022] When this catalyst is applied in a CO2 atmosphere, the synergistic conversion of polyolefin plastics and CO2 can be achieved, which not only eliminates catalyst carbon deposits, but also converts CO2 into CO with high selectivity, realizing the resource utilization of "waste treatment".

[0023] Further, the polyolefin plastic is polyethylene (PE) and / or polypropylene (PP); the conditions for the microwave catalytic conversion are: reaction temperature of 450-650℃, microwave power of 200-800W (preferably 600W), gas environment of CO2, gas flow rate of 0.5L / min, purging time of 15min, and microwave frequency of 2.45GHz.

[0024] Furthermore, the mass ratio of the coated SiC@ZnFe-MMO microwave catalyst to the polyolefin plastic is 15:1.

[0025] This invention also provides the application of a coated SiC@ZnFe-MMO microwave catalyst in the microwave catalytic conversion of polyolefin plastics under a nitrogen atmosphere.

[0026] The microwave catalyst of this invention can still efficiently catalyze the conversion of polyolefins under a nitrogen atmosphere, mainly generating high-value-added gases such as hydrogen, demonstrating that the catalyst also has good catalytic performance and applicability in an inert atmosphere.

[0027] Further, the polyolefin plastic is polyethylene (PE) and / or polypropylene (PP); the catalytic conversion conditions are: reaction temperature of 450-650℃, microwave power of 200-800W (preferably 600W), gas environment of N2, gas flow rate of 0.5L / min, purging time of 15min, and microwave frequency of 2.45GHz.

[0028] For common polyolefin plastics such as polyethylene and polypropylene, high conversion rate and high selectivity can be achieved under optimized reaction conditions. The catalyst has strong adaptability and is suitable for the resource-based treatment of various plastic wastes.

[0029] Furthermore, the mass ratio of the coated SiC@ZnFe-MMO microwave catalyst to the polyolefin plastic is 15:1.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects: To simultaneously achieve the high-value conversion of waste plastics and the greenhouse gas CO2, this invention constructs a core-shell structured coated SiC@ZnFe-MMO microwave catalyst and uses it to drive a microwave-CO2 synergistic catalytic degradation reaction system for polyolefin plastics. The catalyst's core is composed of SiC, a strong microwave absorber, responsible for efficiently converting microwave energy into heat energy; the outer shell is composed of zinc-iron composite metal oxides, which has the dual function of catalyzing the dehydrogenation of plastic chains and activating CO2. This ingenious design ensures close synergy between energy transfer and catalytic reaction, laying a solid foundation for subsequent efficient conversion.

[0031] In this invention, carbon dioxide is efficiently activated at the ZnFe-MMO shell of the SiC@ZnFe-MMO catalyst and participates in the reaction as a mild oxidant: it removes carbon deposits on the catalyst through a gasification reaction to extend its lifespan, and the carbon atoms in the activated CO2 molecules are fully reduced, so that the main gaseous products of the reaction are directionally converted into carbon monoxide (CO), realizing the high-value conversion of greenhouse gases into chemical raw materials.

[0032] The coated SiC@ZnFe-MMO microwave catalyst of this invention achieves precise division of labor and efficient synergy between microwave absorption and catalytic activity due to its unique core-shell structure. Thus, in the microwave-CO2 synergistic strategy, it simultaneously realizes the high-value conversion of two pollutants, waste plastics and greenhouse gas CO2, into syngas. It has outstanding advantages such as high energy efficiency, long catalyst life and high product value, providing a novel and promising technical path for the recycling of waste carbon resources. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 Digital photograph of SiC particles; Figure 2 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Digital photograph of the MMO microwave catalyst; Figure 3 X-ray powder diffraction patterns of the coated SiC@ZnFe-MMO microwave catalysts prepared in Examples 1, 2 and 3; Figure 4The coated SiC@Zn1Fe prepared in Example 2 2.5 - Scanning electron microscope image of the MMO microwave catalyst; Figure 5 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Transmission electron microscope image of MMO microwave catalyst; Figure 6 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Transmission electron microscopy energy dispersive spectroscopy of MMO microwave catalyst; Figure 7 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Product composition distribution diagram of microwave catalytic upgrading and recovery of PE using MMO microwave catalyst at different reaction temperatures; Figure 8 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Selectivity of gaseous products for microwave catalytic upgrading and recovery of PE using MMO microwave catalyst at different reaction temperatures; Figure 9 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution of gaseous products from microwave catalytic upgrading and recovery of PE using MMO microwave catalyst at different reaction temperatures; Figure 10 SiC@Zn1Fe in Example 1 1.5 -MMO, SiC@Zn1Fe in Example 2 2.5 -MMO and SiC@Zn1Fe in Example 3 3.5 - Product composition distribution diagram of PE recovery via microwave catalysis at 550℃ using MMO microwave catalyst. Figure 11 The coated SiC@Zn1Fe prepared in Example 2 2.5 -Graph showing the change of gaseous products of PE recovery via microwave catalysis at 550℃ using MMO microwave catalyst over time. Figure 12 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Comparison of gaseous product distribution of MMO microwave catalyst for microwave catalytic upgrading and recovery of PE at 550℃ under CO2 and N2 atmospheres; Figure 13 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution of gaseous products from the microwave catalytic upgrading and recovery of different plastics (PP, LDPE, HDPE and PS) using MMO microwave catalyst; Figure 14The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution map of gaseous products from the microwave catalytic upgrading and recycling of waste plastics in daily life using MMO microwave catalyst. Figure 15 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution diagram of gaseous products from the recovery of PE via 10 cycles of microwave catalysis using MMO microwave catalyst. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] This invention provides a method for preparing a coated SiC@ZnFe-MMO microwave catalyst, comprising the following steps: I. Preparation of Coated SiC@ZnFe-MMO Microwave Catalyst (a) Experimental materials Zinc source: Zinc acetate dihydrate; Iron source: ferric nitrate; Complexing agent: triethanolamine; Solvent: Anhydrous ethanol; Carrier: Silicon carbide particles.

[0040] (II) Preparation steps 1) Preparation of precursor sol: Weigh an appropriate amount of zinc acetate dihydrate and dissolve it in anhydrous ethanol according to the molar ratio of zinc source (zinc acetate dihydrate) to solvent (anhydrous ethanol) of 1:120, and stir until completely dissolved.

[0041] 2) Add triethanolamine (zinc source to complexing agent molar ratio 1:1) and ferric nitrate (zinc source to iron source molar ratio 1:(1.5-3.5), such as 1:1.5, 1:2.5 or 1:3.5) to the above solution and stir until a mixed solution is obtained.

[0042] 3) The mixed solution was stirred at 60°C for 2 hours, and then aged at room temperature for 24 hours to obtain a stable precursor sol.

[0043] 4) Preparation of gel precursor: The silicon carbide particles were completely immersed in the above precursor sol and dried at 100°C to obtain the precursor.

[0044] 5) Calcination and shaping: The precursor is placed in a calcination device and heated to 400-600℃ (preferably 550℃) at a heating rate of 2-10℃ / min (preferably 5℃ / min). It is calcined at this temperature for 1-3h (preferably 2h) and then naturally cooled to obtain the coated SiC@ZnFe-MMO microwave catalyst.

[0045] II. Application Experiments of Coated SiC@ZnFe-MMO Microwave Catalysts (I) Common Experimental Preparations 1) Weigh the prepared coated SiC@ZnFe-MMO microwave catalyst and polyolefin plastic (polyethylene PE and / or polypropylene PP), mix them evenly at a mass ratio of catalyst:plastic = 15:1, and place the mixture in the reaction vessel of the microwave reactor.

[0046] 2) Check the sealing of the microwave reactor and the control functions of various parameters to ensure that the equipment is operating normally; prepare product collection and analysis equipment (such as gas chromatograph).

[0047] (II) Application 1: Microwave-CO2 synergistic catalytic conversion of polyolefin plastics 1) Introduce CO2 gas into the microwave reactor, control the gas flow rate to be 0.5 L / min, and continue purging for 15 min to completely remove residual air from the reaction vessel.

[0048] 2) Set the microwave reactor parameters: microwave frequency 2.45GHz, microwave power 200-800W (preferably 600W), reaction temperature 450-650℃ (e.g., 450℃, 550℃ or 650℃), and maintain CO2 gas flow rate of 0.5L / min.

[0049] 3) Start the microwave reactor and carry out the catalytic conversion reaction according to the set parameters (reaction time 30 min). Monitor the reaction status in real time during the reaction.

[0050] 4) After the reaction is complete, turn off the microwave reactor and CO2 gas supply, collect the gaseous products generated by the reaction, and analyze the composition and content of the products by gas chromatography.

[0051] (III) Application 2: Microwave catalytic conversion of polyolefin plastics under nitrogen atmosphere 1) Introduce N2 gas into the microwave reactor, control the gas flow rate to be 0.5 L / min, and continue purging for 15 min to completely remove residual air from the reaction vessel.

[0052] 2) Set the microwave reactor parameters: microwave frequency 2.45GHz, microwave power 200-800W (preferably 600W), reaction temperature 450-650℃, and maintain N2 gas flow rate 0.5L / min.

[0053] 3) Start the microwave reactor and carry out the catalytic conversion reaction according to the set parameters (reaction time 30 min). During the reaction, continuously monitor the equipment operation and reaction progress.

[0054] 4) After the reaction is complete, turn off the microwave reactor and the N2 gas supply, collect the generated gaseous products, and analyze the composition and content of the products by gas chromatography.

[0055] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0056] All raw materials used in this invention were purchased from the market.

[0057] The technical solution of the present invention will be further illustrated by the following embodiments.

[0058] Example 1 A method for preparing a coated SiC@ZnFe-MMO microwave catalyst, comprising the following steps: 1) Dissolve 4.4 g of zinc acetate dihydrate in 140 mL of anhydrous ethanol, add 2.7 mL of triethanolamine and 12.1 g of ferric nitrate nonahydrate (molar ratio of zinc acetate dihydrate to ferric nitrate nonahydrate is 1:1.5), and dissolve completely. Transfer the resulting mixed solution to a three-necked flask, stir at 60 °C for 2 h, and age at room temperature for 24 h to obtain a stable precursor sol. Immerse silicon carbide particles in the precursor sol and dry at 100 °C to obtain SiC@Zn1Fe with a loading of 5%. 1.5 - Gel precursor; 2) SiC@Zn1Fe 1.5 The gel precursor was calcined at 550℃ in air for 2 hours, with a heating rate controlled at 5℃ / min, to obtain coated SiC@Zn1Fe. 1.5 -MMO microwave catalyst.

[0059] Example 2 A method for preparing a coated SiC@ZnFe-MMO microwave catalyst, comprising the following steps: 1) Dissolve 4.4 g of zinc acetate dihydrate in 140 mL of anhydrous ethanol, add 2.7 mL of triethanolamine and 20.2 g of ferric nitrate nonahydrate (molar ratio of zinc acetate dihydrate to ferric nitrate nonahydrate is 1:2.5), and dissolve completely. Transfer the resulting mixed solution to a three-necked flask, stir at 60 °C for 2 h, and age at room temperature for 24 h to obtain a stable precursor sol. Immerse silicon carbide particles in the precursor sol and dry at 100 °C to obtain SiC@Zn1Fe 2.5 - Gel precursor; 2) SiC@Zn1Fe 2.5 The gel precursor was calcined at 550℃ in air for 2 hours, with a heating rate controlled at 5℃ / min, to obtain coated SiC@Zn1Fe. 2.5 -MMO microwave catalyst.

[0060] Example 3 A method for preparing a coated SiC@ZnFe-MMO microwave catalyst, comprising the following steps: 1) Dissolve 4.4 g of zinc acetate dihydrate in 140 mL of anhydrous ethanol, add 2.7 mL of triethanolamine and 28.3 g of ferric nitrate nonahydrate (molar ratio of zinc acetate dihydrate to ferric nitrate nonahydrate is 1:3.5), and dissolve completely. Transfer the resulting mixed solution to a three-necked flask, stir at 60 °C for 2 h, and age at room temperature for 24 h to obtain a stable precursor sol. Immerse silicon carbide particles in the precursor sol and dry at 100 °C to obtain SiC@Zn1Fe 3.5 - Gel precursor; 2) SiC@Zn1Fe 3.5The gel precursor was calcined at 550℃ in air for 2 hours, with a heating rate controlled at 5℃ / min, to obtain coated SiC@Zn1Fe. 3.5 -MMO microwave catalyst.

[0061] Figure 1 Digital photographs of the silicon carbide particles in Examples 1-3.

[0062] Figure 2 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Digital photograph of the MMO microwave catalyst.

[0063] Figure 3 X-ray powder diffraction patterns of the coated SiC@ZnFex-MMO microwave catalysts prepared in Examples 1, 2 and 3.

[0064] Figure 4 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Scanning electron microscope image of MMO microwave catalyst.

[0065] Figure 5 The coated SiC@Zn1Fe prepared in Example 2 2.5 Transmission electron microscope image of MMO microwave catalyst.

[0066] Figure 6 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Transmission electron microscopy energy dispersive spectroscopy of MMO microwave catalyst.

[0067] from Figures 1-6 As can be seen, the SiC@ZnFe-MMO microwave catalyst was successfully prepared, with ZnFe catalytic sites (i.e., ZnFe composite metal oxides) uniformly coated on the surface of SiC particles to form a ZnFe composite metal oxide catalyst layer. The mass percentage of the ZnFe composite metal oxide catalyst layer in the coated SiC@ZnFe-MMO microwave catalyst was determined to be 5%.

[0068] Performance characterization of microwave catalysts: 1. Catalytic performance testing of microwave catalysts at different reaction temperatures 1) Mix the microwave catalyst (45g) prepared in Example 2 with PE (3g) evenly and place it in a microwave reactor. Before activating microwave irradiation, introduce CO2 gas at a flow rate of 0.5L / min for 15min to eliminate residual air. Turn off the gas until the reaction is complete. 2) A microwave reactor with a frequency of 2.45 GHz was used as the energy source for the microwave catalysis experiment. The power of the microwave reactor was controlled at 600 W (referring to the power during the heating stage). The reaction temperatures were 450℃, 550℃, and 650℃, and the microwave reaction was carried out (the microwave reaction time was 30 min). The gases produced by the reaction were collected and the composition of the products was analyzed by gas chromatography.

[0069] Figure 7 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Composition distribution of products recovered from PE by microwave catalysis using MMO microwave catalyst at different reaction temperatures.

[0070] Figure 8 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Selectivity of gaseous products for microwave catalytic upgrading and recovery of PE using MMO microwave catalyst at different reaction temperatures.

[0071] Figure 9 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution of gaseous products from the microwave catalytic upgrading and recovery of PE using MMO microwave catalyst at different temperatures.

[0072] Depend on Figure 7 It can be seen that above 550℃, the products are mainly gases; Figure 8 , Figure 9 It can be seen that the gaseous products are mainly syngas.

[0073] 2. Catalytic performance test of microwave catalyst at 550℃ (1) Gas selection: CO2 1) Mix the microwave catalyst (45g) prepared in Examples 1-3 with PE (3g) evenly and place them in a microwave reactor. Before activating microwave irradiation, introduce CO2 gas at a flow rate of 0.5L / min for 15min to eliminate residual air. Turn off the gas until the reaction is complete. 2) A microwave reactor with a frequency of 2.45 GHz was used as the energy source for the microwave catalysis experiment. The power of the microwave reactor was controlled at 600 W (referring to the power during the heating stage), and the reaction temperature was 550 °C. The microwave reaction was carried out (the microwave reaction time was 30 min). The gases produced by the reaction were collected and the composition of the products was analyzed by gas chromatography.

[0074] Figure 10 SiC@Zn1Fe in Example 1 1.5 -MMO, SiC@Zn1Fe in Example 2 2.5 -MMO and SiC@Zn1Fe in Example 3 3.5- Product composition distribution diagram of PE recovery via microwave catalysis using MMO microwave catalyst at 550℃.

[0075] Depend on Figure 10 It can be seen that the CO yield is highest when the molar ratio of Zn to Fe is 1:2.5, that is, the CO2 conversion rate is highest.

[0076] Figure 11 The coated SiC@Zn1Fe prepared in Example 2 2.5 -Graph showing the change of gaseous products of PE recovery via microwave catalysis at 550℃ using MMO microwave catalyst over time.

[0077] Depend on Figure 11 It can be seen that the concentrations of H2 and CO increased continuously with time before 30 minutes, and then tended to stabilize after 30 minutes.

[0078] (2) Gas selection: N2 1) Mix the microwave catalyst (45g) prepared in Example 2 with PE (3g) evenly and place it in a microwave reactor. Before activating microwave irradiation, introduce N2 gas at a flow rate of 0.5L / min for 15min to eliminate residual air. Turn off the gas until the reaction is complete. 2) A microwave reactor with a frequency of 2.45 GHz was used as the energy source for the microwave catalysis experiment. The power of the microwave reactor was controlled at 600 W (referring to the power during the heating stage), and the reaction temperature was 550 °C. The microwave reaction was carried out (the microwave reaction time was 30 min). The gases produced by the reaction were collected and the composition of the products was analyzed by gas chromatography.

[0079] Figure 12 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Comparison of gaseous product distribution of MMO microwave catalyst for microwave catalytic upgrading and recovery of PE at 550℃ under CO2 and N2 atmospheres.

[0080] Depend on Figure 12 It can be seen that the coated SiC@Zn1Fe 2.5 The main gaseous product of the -MMO microwave catalyst under N2 atmosphere is H2, and CO is almost negligible. However, the yield of CO increases significantly under CO2 atmosphere, indicating that CO2 participates in the reaction and generates CO.

[0081] (3) Replacement of plastic sources 1) Mix the microwave catalyst (45g) prepared in Example 2 with 3g of plastic (LDPE, PP, HDPE, PS and waste plastics from daily life) evenly and place it in a microwave reactor. Before activating microwave irradiation, introduce CO2 gas at a flow rate of 0.5L / min for 15min to eliminate residual air. Turn off the gas until the reaction is complete. 2) A microwave reactor with a frequency of 2.45 GHz was used as the energy source for the microwave catalysis experiment. The power of the microwave reactor was controlled at 600 W (referring to the power during the heating stage), and the reaction temperature was 550 °C. The microwave reaction was carried out (the microwave reaction time was 30 min). The gases produced by the reaction were collected and the composition of the products was analyzed by gas chromatography.

[0082] Figure 13 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution diagram of gaseous products for the microwave catalytic upgrading and recovery of different plastics (PP, LDPE, HDPE and PS) using MMO microwave catalyst.

[0083] Figure 14 The coated SiC@Zn1Fe prepared in Example 2 2.5 -MMO microwave catalyst microwave catalysis upgrade recycling of waste plastics in daily life (a mixture of food containers (PP), reagent barrels (HDPE), droppers (PP), bubble wrap (LDPE), disposable spoons (PP), plastic bags (HDPE), and cling film (LDPE) etc.) gaseous product distribution map.

[0084] Depend on Figure 13 , Figure 14 It can be seen that the coated SiC@Zn1Fe 2.5 -MMO microwave catalysts can convert a variety of different plastics, including waste plastics from everyday life.

[0085] (4) Cyclic performance test 1) Mix the microwave catalyst (45g) prepared in Example 2 with PE (3g) evenly and place them in a microwave reactor. Before activating microwave irradiation, introduce CO2 gas at a flow rate of 0.5L / min for 15min to eliminate residual air. Turn off the gas until the reaction is complete. 2) A microwave reactor with a frequency of 2.45 GHz was used as the energy source for the microwave catalysis experiment. The power of the microwave reactor was controlled at 600 W (referring to the power during the heating stage), and the reaction temperature was 550 °C. The microwave reaction was carried out (the microwave reaction time was 30 min). The gases produced by the reaction were collected and the composition of the products was analyzed by gas chromatography.

[0086] The above test method was used in a cyclic operation, that is, PE was recycled by microwave catalysis in cycles (the amount of PE used in each cycle was 3g).

[0087] Figure 15 The coated SiC@Zn1Fe prepared in Example 2 2.5 - Distribution diagram of gaseous products from the recovery of PE via 10 cycles of microwave catalysis using MMO microwave catalyst.

[0088] Depend on Figure 15 It can be seen that the coated SiC@Zn1Fe 2.5 -MMO microwave catalysts maintain good syngas yields even after multiple cycles of plastic conversion.

[0089] In summary, this invention discloses a coated SiC@ZnFe-MMO microwave catalyst, its preparation method, and its applications, relating to the fields of catalyst preparation and plastic chemical recycling. The catalyst employs a core-shell structure, with silicon carbide particles as the core (for efficient microwave absorption and heat generation), and a zinc-iron composite metal oxide catalytic layer coated on the surface (responsible for catalytic reaction). This catalyst can catalyze the conversion of polyolefin plastics (PE, PP, etc., and household waste plastics) under a microwave-CO2 atmosphere, effectively removing catalyst carbon deposits and selectively generating syngas, achieving synergistic resource utilization of plastics and CO2. It possesses advantages such as fast reaction rate, low energy consumption, good stability, and simple synthesis process, providing a new pathway for green plastic recycling and high-value utilization of CO2, with broad application prospects.

[0090] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A coated SiC@ZnFe-MMO microwave catalyst, characterized in that, It has silicon carbide particles as the core and a zinc-iron composite metal oxide catalyst layer on the surface.

2. A method for preparing the coated SiC@ZnFe-MMO microwave catalyst as described in claim 1, characterized in that, Includes the following steps: Zinc source, iron source and complexing agent are dissolved in solvent, and the precursor sol is prepared by stirring and aging. Silicon carbide particles were immersed in the precursor sol, dried to obtain a gel precursor, and then calcined to obtain the coated SiC@ZnFe-MMO microwave catalyst.

3. The preparation method of the coated SiC@ZnFe-MMO microwave catalyst according to claim 2, characterized in that, The molar ratio of the zinc source to the solvent is 1:120; the molar ratio of the zinc source to the complexing agent is 1:1; and the molar ratio of the zinc source to the iron source is 1:(1.5-3.5).

4. The preparation method of the coated SiC@ZnFe-MMO microwave catalyst according to claim 3, characterized in that, The zinc source is zinc acetate dihydrate; the iron source is ferric nitrate; the complexing agent is triethanolamine; and the solvent is anhydrous ethanol.

5. The preparation method of the coated SiC@ZnFe-MMO microwave catalyst according to claim 2, characterized in that, The stirring temperature was 60℃ and the stirring time was 2 hours.

6. The preparation method of the coated SiC@ZnFe-MMO microwave catalyst according to claim 2, characterized in that, The aging time is 24 hours.

7. The preparation method of the coated SiC@ZnFe-MMO microwave catalyst according to claim 2, characterized in that, The calcination temperature is 400-600℃, the heating rate is 2-10℃ / min, and the time is 1-3h.

8. The application of the coated SiC@ZnFe-MMO microwave catalyst as described in claim 1 in the microwave-CO2 synergistic catalytic conversion of polyolefin plastics.

9. The application of the coated SiC@ZnFe-MMO microwave catalyst as described in claim 1 in the microwave catalytic conversion of polyolefin plastics under a nitrogen atmosphere.

10. The application according to claim 8 or 9, characterized in that, The polyolefin plastic is polyethylene and / or polypropylene; the catalytic conversion conditions are: reaction temperature of 450-650℃, microwave power of 200-800W, gas environment of CO2 or N2, and gas flow rate of 0.5L / min.

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