Coated SiC-coated NiFe microwave catalyst as well as preparation method and application thereof in catalytic conversion of polyolefin plastic

Abstract

The invention discloses a coated SiC-coated NiFe microwave catalyst, a preparation method thereof and an application of the coated SiC-coated NiFe microwave catalyst in catalytic conversion of polyolefin plastics, and relates to the technical field of preparation of catalysts and chemical recovery of plastics. The coated SiC-coated NiFe microwave catalyst comprises a porous silicon carbide round rod and a nickel-iron alloy catalyst layer coated on the surface of the porous silicon carbide round rod. According to the coated SiC-coated NiFe microwave catalyst, a porous SiC rod is coated with NiFe-gel through a sol-gel method, a precursor is prepared, and then thermal reduction treatment is performed, so that the coated SiC-coated NiFe microwave catalyst is obtained. According to the coated SiC-coated NiFe microwave catalyst disclosed by the invention, polyolefin plastic can be quickly and highly selectively converted into hydrogen and carbon nanotubes. Compared with the traditional chemical recovery technology, the method has the characteristics of rapid reaction, high selectivity and environmental protection. And the coated SiC-coated NiFe microwave catalyst has the advantages of simple synthesis method, excellent wave absorbing performance, low energy consumption, stable performance and the like, is a recycled material which is more energy-saving and lower in cost, and shows wide practical application value.

Description

Technical Field

[0001] The present invention relates to the technical fields of the preparation of catalysts and the chemical recycling of plastics, and particularly relates to a coated SiC@NiFe microwave catalyst, a preparation method thereof, and an application thereof in catalytic conversion of polyolefin plastics. Background Art

[0002] Polyolefin plastics such as polyethylene (PE) and polypropylene (PP) are widely used due to their stability and durability. However, due to their characteristics of being difficult to degrade naturally, they have caused serious environmental pollution and waste of resources. Therefore, it is of great significance to find a method for efficiently recycling and effectively utilizing the rich hydrocarbon resources contained therein.

[0003] Traditional mechanical recycling is the most common method for recycling polyolefin plastics. However, this method requires classifying plastics into single plastics for effective recycling, and the recovery rate is extremely low. Therefore, this method has obvious deficiencies. The chemical recycling method is a process of converting plastic waste into high-value-added chemicals through a series of chemical reactions such as pyrolysis, photoreforming, electrocatalysis, and biocatalysis. It has attracted much attention due to its unique advantages in reducing environmental pollution, reducing carbon emissions, and economy.

[0004] Due to the rich C and H elements contained in polyolefin plastics, the pyrolysis products are mainly hydrogen, hydrocarbons, and carbon materials, which have obvious economic advantages. However, at the same time, due to the fact that the chemical bonds in its molecules are mainly extremely stable C-C and C-H, the main recycling method is thermal pyrolysis, which has the deficiencies of low conversion rate and high energy consumption. Compared with the traditional thermal pyrolysis method, the microwave catalytic pyrolysis method can effectively reduce energy consumption due to its characteristics of fast heating and high energy, and is thus widely used in the treatment of polyolefin plastics. However, when the microwave catalytic pyrolysis method is used to treat polyolefin plastics, a sufficient amount of microwave absorbent and catalyst are required to catalyze the reaction. During the microwave reaction process, the heat transfer and mass transfer between the plastic, the microwave absorbent, and the catalyst are disordered and random. An excessive proportion of the microwave absorbent causes more plastic molecules to only undergo pyrolysis reactions on the surface of the microwave absorbent without catalytic reactions, thereby greatly reducing the selectivity and yield of hydrogen and carbon materials in the products. Even in this case, a reaction temperature of more than 600°C and a microwave power of 600 W are still required to fully react. Therefore, it is of great significance to design a catalyst with a high proportion of microwave absorbent and capable of achieving directional heat transfer and mass transfer during the reaction. Summary of the Invention

[0005] The purpose of the present invention is to provide a coated SiC@NiFe microwave catalyst, a preparation method thereof, and an application thereof in catalytic conversion of polyolefin plastics, so as to solve the problems existing in the above-mentioned prior art and achieve efficient, low-energy-consuming, and low-cost conversion of waste polyolefin plastics.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention: A coated SiC@NiFe microwave catalyst, comprising a porous silicon carbide (SiC) rod and a nickel-iron alloy (NiFe) catalyst layer coated on the surface of the porous silicon carbide rod.

[0008] The coated SiC@NiFe microwave catalyst of the present invention uses a porous SiC rod as the skeleton, and the active substance nickel-iron alloy is uniformly coated on the surface of the porous SiC rod. This catalyst structure retains the porous structure and excellent microwave absorption and heat generation performance of the SiC skeleton, which not only promotes the diffusion of the substrate (plastic), but also enables the reaction to proceed efficiently at a lower temperature. In addition, since the nickel-iron alloy catalyst layer is tightly coated on the SiC skeleton, the substrate can only directly contact the active sites in the catalyst layer, effectively avoiding the inefficient pyrolysis reaction between the substrate and the SiC skeleton, and realizing the directivity of mass transfer. At the same time, the microwave energy absorbed by SiC is first transferred to the active sites of the coating layer (nickel-iron alloy catalyst layer), and then to the substrate, realizing the directivity of heat transfer. In contrast, the NiFe-SiC mixed powder microwave catalyst has significantly insufficient catalytic efficiency and activity due to the randomness of the mass transfer and heat transfer processes.

[0009] The coated SiC@NiFe microwave catalyst of the present invention presents a coated structure and has good microwave absorption performance, which promotes the cleavage of C-C bonds and C-H bonds in plastic molecules, enables the reaction to proceed rapidly, and thus enables the rapid and efficient conversion of waste polyolefin plastics into high-added-value industrial raw materials (such as H2, solid carbon materials, etc.), and finally realizes the efficient chemical recycling of waste polyolefin plastics.

[0010] Further, the nickel-iron alloy in the nickel-iron alloy catalyst layer exists in the form of nanoparticles.

[0011] Further, the mass ratio of the nickel-iron alloy catalyst layer in the coated SiC@NiFe microwave catalyst is 3-8%.

[0012] Another technical solution of the present invention: A preparation method of the above-mentioned coated SiC@NiFe microwave catalyst, comprising the following steps:

[0013] Mix a nickel source, an iron source, a gel source and water to obtain a precursor solution; immerse the porous silicon carbide rod in the precursor solution, and then dry it to obtain a precursor; perform a thermal reduction treatment on the precursor in a reducing atmosphere to obtain the coated SiC@NiFe microwave catalyst.

[0014] The above method first uses the sol-gel method to coat porous SiC rods with NiFe-gel to obtain a precursor, and then performs a reduction treatment to obtain a coated SiC@NiFe microwave catalyst.

[0015] Further, the nickel source is a water-soluble nickel salt.

[0016] Further, the water-soluble nickel salt includes nickel nitrate.

[0017] Further, the iron salt is a water-soluble iron salt.

[0018] Further, the water-soluble iron salt includes iron nitrate.

[0019] Further, the gel source includes citric acid (CA).

[0020] Further, the reducing atmosphere includes a hydrogen atmosphere.

[0021] Further, the temperature of the reduction heat treatment (i.e., reduction roasting) is 400 - 800 °C, and the time is 1 - 4 h.

[0022] Further, the temperature of the reduction heat treatment is preferably 650 °C, and the time is preferably 3 h.

[0023] Further, the heating rate of the reduction heat treatment is 2 - 10 °C / min -1 , preferably 5 °C / min -1 .

[0024] Further, the mixing of the nickel source, iron source, gel source and water to obtain a precursor solution includes: dissolving the nickel source, iron source and gel source in water, and stirring at 80 °C for 1 - 4 h to obtain a precursor solution.

[0025] Further, the stirring time is preferably 2 h.

[0026] Further, the drying temperature is 60 - 100 °C, and the time is 12 - 36 h.

[0027] Further, the drying temperature is preferably 80 °C, and the time is preferably 24 h.

[0028] Further, the concentration of nickel ions in the precursor solution is 0.1 - 0.3 M, the concentration of iron ions is 0.1 - 0.3 M, and the concentration of the gel source is 0.6 M.

[0029] Further, the pore density of the porous silicon carbide round rod is 60 - 100 PPI, preferably 100 PPI.

[0030] The third technical solution of the present invention: Application of the above-mentioned coated SiC@NiFe microwave catalyst in the microwave catalytic conversion of plastics.

[0031] Further, the plastic is a polyolefin plastic.

[0032] Further, the polyolefin plastic is waste polyolefin plastic.

[0033] Further, the polyolefin plastic includes polyethylene (PE) and / or polypropylene (PP).

[0034] The fourth technical solution of the present invention: Application of the above-mentioned coated SiC@NiFe microwave catalyst in the microwave catalytic conversion of polyolefin plastics to selectively produce H2 and carbon nanotubes.

[0035] Further, the conditions for the microwave catalytic conversion include: the reaction temperature is 300 - 600 °C, the microwave power is 200 - 800 W, the gas environment is N2, and the gas flow rate is 0.5 L / min.

[0036] Optionally, the conditions for the microwave catalytic conversion further include: the microwave frequency is 2.45 GHz.

[0037] Further, the microwave power (the power in the heating-up stage) is preferably 400 W.

[0038] Further, the mass ratio of the coated SiC@NiFe microwave catalyst to the polyolefin plastic is catalyst: plastic = 5:1.

[0039] The present invention discloses the following technical effects:

[0040] In order to design and develop a microwave catalyst with high performance, stable structure, low energy consumption, and low cost for the rapid, efficient, and highly selective chemical recycling of plastics, the present invention constructs a coated SiC@NiFe microwave catalyst and uses this catalyst to rapidly catalytically convert polyolefin plastics to produce hydrogen and carbon nanotubes.

[0041] The coated SiC@NiFe microwave catalyst developed in the present invention shows a significant improvement in absorbing and converting microwave energy compared with the NiFe-SiC mixed powder microwave catalyst, and its heating rate is significantly enhanced. Thanks to the unique coated structure design, the catalyst realizes the directional mass transfer and heat transfer among the microwave absorber SiC, the catalytic active sites NiFe, and the substrate plastic during the catalytic process, so that the conversion process of waste polyolefin plastics to hydrogen and carbon nanotubes is more efficient, rapid, energy-saving, and stable.

[0042] The coated SiC@NiFe microwave catalyst of the present invention can rapidly and highly selectively convert polyolefin plastics into hydrogen and carbon nanotubes. Compared with traditional chemical recycling technologies, this method features rapid reaction, high selectivity, and environmental friendliness. Moreover, the coated SiC@NiFe microwave catalyst has advantages such as simple synthesis method, excellent microwave absorption performance, low energy consumption, and stable performance. It is a more energy-efficient and cost-effective recycling material, showing broad practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0044] Figure 1 Digital photo of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0045] Figure 2 X-ray powder diffraction pattern of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0046] Figure 3 Scanning electron microscope image of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0047] Figure 4 Scanning electron microscope energy spectrum of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0048] Figure 5 Transmission electron microscope image of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0049] Figure 6 Graph of the surface and internal temperature change over time of the coated SiC@NiFe microwave catalyst prepared in Example 1 under microwave irradiation at 2.45 GHz and 400 W.

[0050] Figure 7 Comparison graph of the surface and internal temperature change over time under different microwave power irradiations of the coated SiC@NiFe microwave catalyst prepared in Example 1 and the NiFe-SiC mixed powder microwave catalyst prepared in Comparative Example 1 under the same mass and 2.45 GHz conditions.

[0051] Figure 8 Product composition distribution graph of the microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1 at different reaction temperatures.

[0052] Figure 9 Product composition distribution diagram of microwave catalytic upgrading and recycling of PE by catalyst-free porous SiC rods at different reaction temperatures.

[0053] Figure 10 Gas product selectivity diagram of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1 at different reaction temperatures.

[0054] Figure 11 Scanning electron microscope image of the solid product of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0055] Figure 12 Transmission electron microscope image of the solid product of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0056] Figure 13 Raman spectrum of the solid product of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0057] Figure 14 Product composition distribution diagram of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1 and the NiFe-SiC mixed powder microwave catalyst prepared in Comparative Example 1 at 450 °C.

[0058] Figure 15 Gas product selectivity diagram of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1 and the NiFe-SiC mixed powder microwave catalyst prepared in Comparative Example 1 at 450 °C.

[0059] Figure 16 Gas product selectivity diagram of microwave catalytic upgrading and recycling of different polyolefin plastics (PE, PP, mixture of PE and PP) by the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0060] Figure 17 Gas product selectivity diagram of microwave catalytic upgrading and recycling of waste plastics in life by the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0061] Figure 18 Gas product selectivity diagram of microwave catalytic upgrading and recycling of PE 5 times by the coated SiC@NiFe microwave catalyst prepared in Example 1. Detailed implementation mode

[0062] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be construed as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0063] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0064] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0065] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are merely exemplary.

[0066] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0067] It should be noted that the aspects not described in detail in the present invention are all conventional operating means in the art and are not the focus of the present invention.

[0068] In the following examples, comparative examples, and test examples of the present invention, if room temperature is involved, it specifically refers to 20 - 30 °C.

[0069] Unless otherwise specified, each raw material used in the following examples, comparative examples, and test examples of the present invention is a common commercially available product. Among them, the pore density of the cylindrical porous SiC rod is 100 PPI.

[0070] Example 1

[0071] A coated SiC@NiFe microwave catalyst is prepared according to the following steps:

[0072] (1) Dissolve 0.01 mol of nickel nitrate hexahydrate, 0.02 mol of iron nitrate nonahydrate, and 0.06 mol of citric acid in 100 mL of deionized water. Transfer the mixed solution to a three-necked flask and stir at 80 °C for 2 h until evenly dispersed to obtain a NiFe-CA solution (i.e., the precursor solution). Vertically immerse a cylindrical porous SiC rod with a diameter of 25 mm and a height of 50 mm (i.e., the porous SiC round rod) in the NiFe-CA solution and dry it at a constant temperature of 80 °C for 24 h to obtain a SiC@NiFe-CA precursor.

[0073] (2) Heat the SiC@NiFe-CA precursor to 650 °C in a 10 vol% hydrogen atmosphere (balanced gas is nitrogen) and reduce it for 3 h, controlling the heating rate at 5 °C / min -1 to obtain a coated SiC@NiFe microwave catalyst.

[0074] Figure 1 Digital photo of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0075] Figure 2 X-ray powder diffraction pattern of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0076] Figure 3 Scanning electron microscope image of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0077] Figure 4 Energy-dispersive X-ray spectroscopy of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0078] Figure 5 Transmission electron microscope image of the coated SiC@NiFe microwave catalyst prepared in Example 1.

[0079] From Figures 1-5 it can be seen that the SiC@NiFe microwave catalyst was successfully prepared, and the NiFe catalytic sites (i.e., NiFe alloy) were evenly coated on the surface of the porous SiC round rod to form a NiFe alloy catalyst layer, while retaining the porous structure of SiC. After testing, the mass ratio of the nickel-iron alloy catalyst layer in the coated SiC@NiFe microwave catalyst is 5%.

[0080] Comparative Example 1

[0081] A NiFe-SiC mixed powder microwave catalyst is prepared as follows:

[0082] (1) Dissolve 0.01 mol of nickel nitrate hexahydrate, 0.02 mol of iron nitrate nonahydrate and 0.06 mol of citric acid in 100 mL of deionized water. Transfer the mixed solution to a three-necked flask and stir at 80 °C for 4 h until evenly dispersed to obtain a NiFe-CA solution. Dry the NiFe-CA solution at 80 °C for 24 h to obtain a NiFe-CA precursor.

[0083] (2) Heat the NiFe-CA precursor to 650 °C in a 10 vol% hydrogen atmosphere (balanced gas is nitrogen) and reduce it for 3 h, controlling the heating rate at 5 °C min -1 , to obtain a NiFe alloy microwave catalyst. Physically mix the obtained NiFe alloy microwave catalyst with SiC powder of the same mass as the cylindrical porous SiC rod used in Example 1 evenly to obtain a NiFe-SiC mixed powder microwave catalyst (the mass ratio of the NiFe alloy in the NiFe-SiC mixed powder microwave catalyst is 5%).

[0084] Test Example 1

[0085] Temperature rise of the microwave catalyst under microwave irradiation

[0086] Figure 6 It is a graph showing the change of surface and internal temperature with time of the coated SiC@NiFe microwave catalyst prepared in Example 1 under microwave irradiation at 2.45 GHz (microwave frequency) and 400 W (microwave power);

[0087] From Figure 6 it can be seen that the internal temperature of the coated SiC@NiFe microwave catalyst is higher than the external temperature, that is, the thermal energy is directionally transferred from the silicon carbide rod to the nickel-iron alloy catalytic site, realizing the directional transfer of thermal energy.

[0088] Figure 7 It is a comparison chart of the change of surface and internal temperature with time of the coated SiC@NiFe microwave catalyst prepared in Example 1 and the NiFe-SiC mixed powder microwave catalyst (i.e., SiC-NiFe Mix) prepared in Comparative Example 1 under the same mass (i.e., the same mass of the microwave catalyst) and at 2.45 GHz under irradiation with different microwave powers;

[0089] From Figure 7 it can be seen that the coated SiC@NiFe microwave catalyst has a stronger ability to absorb microwaves and increase temperature, and can achieve rapid temperature rise at a lower power, that is, this microwave catalyst has the characteristics of energy saving and low cost.

[0090] Test Example 2

[0091] Characterization of the catalytic performance of the microwave catalyst

[0092] (1) Catalytic performance test of microwave catalyst at different reaction temperatures

[0093] Mix 25 g of microwave catalyst with 5 g of PE evenly and place them in a microwave reactor. Before activating microwave irradiation, introduce inert gas (N2) at a flow rate of 0.5 L / min for 30 min to eliminate residual air, and continuously introduce N2 at the same flow rate until the reaction ends during the reaction.

[0094] Use a microwave reactor with a frequency of 2.45 GHz as the energy source for microwave catalytic experiments. Control the power of the microwave reactor to be 400 W (referring to the power during the heating stage), and the reaction temperatures are 300 - 600 °C. Conduct microwave reactions (the microwave reaction time is 10 min), collect the gases generated by the reactions respectively, and analyze the product composition using gas chromatography; collect the solid reaction products respectively and characterize them using methods such as Raman spectroscopy.

[0095] Figure 8 Product composition distribution diagram of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1 at different reaction temperatures (where Gas represents gas, Wax represents waxes, and Char represents carbon residue);

[0096] Figure 9 Product composition distribution diagram of microwave catalytic upgrading and recycling of PE by the catalyst-free porous SiC rod (i.e., the carrier raw material in Example 1: a cylindrical porous SiC rod with a diameter of 25 mm and a height of 50 mm) at different reaction temperatures;

[0097] From Figure 8 , Figure 9 It can be seen that only non-catalytic pyrolysis reactions occur in the porous SiC rod, with more by-products (waxes) and incomplete reactions; while in the coated SiC@NiFe microwave catalyst, due to the presence of NiFe catalytic sites, catalytic pyrolysis reactions occur, improving the conversion rate and selectivity of the products (gas and carbon residue).

[0098] Figure 10 Gas product selectivity diagram of microwave catalytic upgrading and recycling of PE by the coated SiC@NiFe microwave catalyst prepared in Example 1 at different reaction temperatures;

[0099] From Figure 10 It can be seen that the coated SiC@NiFe microwave catalyst effectively realizes the rapid and efficient upgrading and recycling of PE plastics at a lower temperature (450 °C). The gas products are mainly H2, with the characteristics of low cost, low energy consumption, and high efficiency; where C1 is methane, C2 is ethane and / or ethylene, and C 3+ represents hydrocarbons with higher carbon content.

[0100] Figure 11 Scanning electron microscope image of the solid product obtained by microwave catalytic upgrading and recycling of PE using the coated SiC@NiFe microwave catalyst prepared in Example 1;

[0101] Figure 12 Transmission electron microscope image of the solid product obtained by microwave catalytic upgrading and recycling of PE using the coated SiC@NiFe microwave catalyst prepared in Example 1;

[0102] Figure 13 Raman spectrum of the solid product obtained by microwave catalytic upgrading and recycling of PE using the coated SiC@NiFe microwave catalyst prepared in Example 1;

[0103] From Figure 11 , Figure 12 , Figure 13 it can be seen that the solid product of upgrading and recycling PE plastic with the coated SiC@NiFe microwave catalyst is carbon nanotubes.

[0104] (2) Catalytic performance test of the microwave catalyst at 450 °C

[0105] Mix the microwave catalyst (25 g) and PE (5 g) evenly and place them in a microwave reactor. Before activating the microwave irradiation, pass an inert gas (N2) at a flow rate of 0.5 L / min for 30 min to eliminate the residual air, and continuously pass N2 at the same flow rate until the reaction ends during the reaction.

[0106] Use a microwave reactor with a frequency of 2.45 GHz as the energy source for the microwave catalytic experiment, control the power of the microwave reactor to 400 W (referring to the power during the heating stage), the reaction temperature to 450 °C, carry out the microwave reaction (the microwave reaction time is 10 min), collect the gases generated by the reaction respectively, and analyze the product composition using gas chromatography; collect the solid products of the reaction respectively, and characterize them using methods such as Raman spectroscopy.

[0107] Figure 14 Product composition distribution diagram of microwave catalytic upgrading and recycling of PE at 450 °C using the coated SiC@NiFe microwave catalyst prepared in Example 1 and the NiFe-SiC mixed powder microwave catalyst prepared in Comparative Example 1;

[0108] Figure 15 Gas product selectivity diagram of microwave catalytic upgrading and recycling of PE at 450 °C using the coated SiC@NiFe microwave catalyst prepared in Example 1 and the NiFe-SiC mixed powder microwave catalyst prepared in Comparative Example 1;

[0109] From Figure 14 , 15It can be seen that due to the unique directional mass transfer and heat transfer characteristics of the coated SiC@NiFe microwave catalyst, it has higher catalytic activity, with the carbon and gas conversion rates reaching as high as 42.8 wt% and 56.2 wt% respectively, and the hydrogen selectivity being 96.0 vol%. In contrast, due to the random and non-directional mass transfer and heat transfer during the reaction process, the NiFe-SiC mixed powder microwave catalyst has significantly insufficient catalytic ability and activity (the carbon and gas conversion rates are 44.4 wt% and 41.4 wt% respectively, and the hydrogen selectivity is 64.0 vol%).

[0110] Replace PE with PP, a mixture of PE and PP (equal mass mixture), or waste plastics in life for the above-mentioned catalytic performance test at 450 °C.

[0111] Figure 16 Selectivity diagram of gas products for the coated SiC@NiFe microwave catalyst prepared in Example 1 for microwave catalytic upgrading and recycling of different polyolefin plastics (PE, PP, and a mixture of PE and PP).

[0112] Figure 17 Selectivity diagram of gas products for the coated SiC@NiFe microwave catalyst prepared in Example 1 for microwave catalytic upgrading and recycling of waste plastics in life (EPE (PE), disposable gloves (PE), reagent barrels (PP), straws (PP), lunch boxes (PS), and mixed plastics (equal mass mixture of the above-mentioned waste plastics)).

[0113] From Figure 16 、 Figure 17 It can be seen that the coated SiC@NiFe microwave catalyst can convert a variety of different plastics, including waste plastics in life.

[0114] Use the above test method to conduct cyclic microwave catalytic recycling of PE at 450 °C for the coated SiC@NiFe microwave catalyst prepared in Example 1 (the amount of PE used in each cycle is 5 g).

[0115] Figure 18 Selectivity diagram of gas products for the coated SiC@NiFe microwave catalyst prepared in Example 1 for 5 - cycle microwave catalytic upgrading and recycling of PE.

[0116] From Figure 18 It can be seen that the selectivity of the coated SiC@NiFe microwave catalyst for converting plastics remains good after multiple cycles.

[0117] In summary, it can be seen that the coated SiC@NiFe microwave catalyst prepared by the method of the present invention can still rapidly heat up at a relatively low microwave power due to the high mass ratio of the SiC rod skeleton (95 wt%), promoting the activation and cleavage of C-C and C-H bonds in polyolefin plastics; at the same time, the NiFe catalyst layer is coated on the surface of the SiC skeleton, realizing directional mass transfer and heat transfer, and effectively avoiding the inefficient non-catalytic pyrolysis reaction caused by the direct contact between the plastic and the SiC skeleton. Compared with the non-coated microwave catalyst (NiFe-SiC mixed powder microwave catalyst) with random and disordered mass transfer and heat transfer, the coated SiC@NiFe microwave catalyst has the advantages of high efficiency, rapidity and low energy consumption, and is a more environmentally friendly method for upgrading and recycling waste plastics.

[0118] The embodiments described above are only used to describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A coated SiC@NiFe microwave catalyst, characterized in that, It includes a porous silicon carbide round rod and a nickel-iron alloy catalyst layer coated on the surface of the porous silicon carbide round rod.

2. The coated SiC@NiFe microwave catalyst according to claim 1, characterized in that, The mass ratio of the nickel-iron alloy catalyst layer in the coated SiC@NiFe microwave catalyst is 3-8%.

3. The preparation method of the coated SiC@NiFe microwave catalyst according to claim 1, characterized in that, It includes the following steps: Mix a nickel source, an iron source, a gel source and water to obtain a precursor solution; Immerse the porous silicon carbide round rod in the precursor solution, and then dry it to obtain a precursor; perform thermal reduction treatment on the precursor in a reducing atmosphere to obtain the coated SiC@NiFe microwave catalyst.

4. The preparation method according to claim 3, characterized in that, The nickel source is a water-soluble nickel salt; And / or, the iron salt is a water-soluble iron salt; And / or, the gel source includes citric acid.

5. The preparation method according to claim 4, characterized in that, The water-soluble nickel salt includes nickel nitrate; And / or, the water-soluble iron salt includes iron nitrate.

6. The preparation method according to claim 3, characterized in that, The reducing atmosphere includes a hydrogen atmosphere; And / or, the temperature of the thermal reduction treatment is 400-800 °C, and the time is 1-4 h.

7. The preparation method according to claim 3, characterized in that, The step of mixing a nickel source, an iron source, a gel source and water to obtain a precursor solution includes: dissolving the nickel source, the iron source and the gel source in water, and stirring at 80 °C for 1-4 h to obtain a precursor solution.

8. Application of the coated SiC@NiFe microwave catalyst according to any one of claims 1-2 in microwave catalytic conversion of plastics.

9. Application of the coated SiC@NiFe microwave catalyst according to any one of claims 1-2 in microwave catalytic conversion of polyolefin plastics to selectively generate H2 and carbon nanotubes.

10. The application according to claim 8 or claim 9, characterized in that The conditions for the microwave catalytic conversion include: the reaction temperature is 300-600 °C, the microwave power is 200-800 W, the gas environment is N2, and the gas flow rate is 0.5 L / min.

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