Preparation method of a dual-atom catalyst and catalytic reforming method of tar

Abstract

The present invention discloses a preparation method of a dual-atom catalyst and a method for catalytic reforming of tar; the preparation method is as follows: First, prepare rod-shaped Fe2O3. Second, react on the surface of the rod-shaped Fe2O3 to form a polydopamine layer. Third, remove the rod-shaped Fe2O3 after pyrolytic carbonization to obtain a rod-shell-shaped nitrogen-carbon material. Fourth, deposit nickel in an atomically dispersed manner on the nitrogen-carbon material by chemical vapor deposition to obtain a nickel-based catalyst. Fifth, load ruthenium atoms on the nickel atoms of the nickel-based catalyst by microwave plasma chemical vapor deposition to obtain a dual-atom catalyst. The present invention constructs a nitrogen-doped mesoporous carbon material with a rod-shell structure as a carrier by preparing rod-shaped Fe2O3 as a template and then performing calcination and etching after forming a PDA film on the surface of the template; this rod-shell structure helps to increase the loading amount of bimetallic atoms and form a pore structure more favorable for catalysis, thereby improving the catalytic activity of the catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysis, and particularly relates to a preparation method of a dual-atom catalyst for catalytic reforming of tar. By using this catalyst in combination with plasma catalysis for degradation, the anti-sintering and anti-poisoning capabilities of the catalyst are enhanced, and the catalytic reforming of tar is promoted. Background Art

[0002] Energy is the foundation and driving force for the progress of human civilization, crucial for national economy and people's livelihood, national security, and human survival and development. It is of great significance for promoting economic and social development and enhancing people's well-being. China has made significant progress in major renewable energy projects and is at the global leading level. The exploitable resources of clean energy containing solar energy in China are 2.148 billion tons of standard coal, among which biomass energy accounts for 54.5%, which is twice that of hydropower and 3.5 times that of wind power. Among new energies, biomass energy is the only renewable carbon source and can be converted into solid, liquid, and gaseous fuels.

[0003] Biomass energy is the most promising renewable energy. Biomass gasification power generation technology can achieve a relatively high utilization rate on a smaller scale. However, the tar by-product in the gasification process may cause secondary pollution to water. Only by solving the problem of secondary pollution can biomass gasification power generation technology compete equally with other technologies. At the same time, the condensation and polymerization of tar are likely to cause pollution and blockage of downstream equipment, affecting the operation of the gasification system and the safety of gas-using devices. Therefore, the removal and conversion of tar are urgently needed for the popularization and application of biomass energy, and have important research value and practical significance.

[0004] Currently, the main methods for reducing the tar yield include filtration, thermal cracking, and catalytic cracking. Catalytic cracking is an economically feasible method with high tar removal efficiency and high energy utilization rate. Tar undergoes reactions such as thermal cracking, steam reforming, dry reforming, carbon formation, and water-gas shift on the active sites of the catalyst, and decomposes into small-molecule tar, H2, CO, and CO2 and other products. The key lies in the catalyst, and the activity and properties of the catalyst are the core of tar catalytic reforming. Commonly used catalysts for tar reforming include natural ore catalysts, alkali metal catalysts, non-nickel metal catalysts, and nickel-based metal catalysts. Nickel-based catalysts have a relatively low cost and good activity, can promote the conversion of tar by activating CO and CO2, and at the same time, nickel-based catalysts have the ability to reverse the ammonia reaction and can reduce NOx emissions, so they are widely used.

[0005] The use of nickel-based catalysts usually involves the use of supports, which can effectively improve the dispersion of metals, inhibit the aggregation of metal particles, and control the particle size of metal particles. However, single-atom catalysts are prone to sintering and deactivation of metal particles at high temperatures, and carbon deposition may also occur, affecting the activity of the catalyst. Therefore, after selecting a suitable support, metal promoters are often added to prepare bimetallic or multi-metallic catalysts to improve the catalytic performance of the catalyst and extend its service life.

[0006] According to the different supports, non-natural catalysts can be divided into zeolite catalysts, silicon-based catalysts, hydrotalcite catalysts, perovskite catalysts, and carbon-based catalysts. Due to their good pore structure or other characteristics, these catalysts have good dispersion of the supported metals and strong metal-support interactions. On the other hand, adding appropriate metal promoters to these catalysts can make them more active and stable.

[0007] The chemical vapor deposition method utilizes the dispersion of organometallic ligands on metal components, their reactivity with surface acid sites, and the easy control of the partial pressure of metal precursors to deposit organometallic precursors on suitable supports, thereby preparing catalysts with a more ordered structure and higher dispersion of active metal components.

[0008] At the same time, tar steam reforming is a typical energy-intensive reaction (ΔH>0), often requiring temperatures above 600 °C, which is prone to catalyst sintering and deactivation. Low-temperature plasma can generate active substances such as highly excited molecules, atoms, free radicals, reactive ions, and high-energy electrons at lower reaction temperatures, promoting the progress of thermodynamically unfavorable reactions and enabling catalytic reactions to occur at low temperatures. Constructing a low-temperature plasma-assisted Ni-Ru dual-atom catalytic system can overcome the problems of carbon deposition and sintering caused by high-temperature reaction conditions and achieve efficient and stable hydrogen-rich conversion of biomass tar. Summary of the Invention

[0009] The purpose of the present invention is to provide a dual-atom catalyst for tar catalytic reforming and its preparation method, and to construct a low-temperature plasma-assisted Ni-Ru bimetallic catalytic system to improve the efficiency of the catalyst in degrading tar while enhancing the anti-sintering and anti-poisoning capabilities of the catalyst.

[0010] In the first aspect, the present invention provides a method for preparing a dual-atom catalyst, which includes the following steps:

[0011] Step 1: Add an FeCl3 solution dropwise to an NaOH solution, then add an Na2SO4 solution, react to form an Fe(OH)3 sol, and calcine to obtain rod-shaped Fe2O3. The length of the rod-shaped Fe2O3 is 20 nm to 60 nm, and the diameter is 3 nm to 10 nm.

[0012] Step 2: Add the rod-shaped Fe2O3 and dopamine hydrochloride obtained in Step 1 to the buffer solution successively and mix and stir to form a polydopamine layer on the surface of the rod-shaped Fe2O3.

[0013] Step 3: Pyrolytic carbonize the product obtained in Step 2 to carbonize the polydopamine layer; then, etch the obtained product under acidic conditions to remove the rod-shaped Fe2O3 to obtain a rod-shell-shaped nitrogen-carbon material.

[0014] Step 4: Deposit nickel in an atomically dispersed manner on the nitrogen-carbon material by chemical vapor deposition; obtain the nickel-based catalyst Ni-NC.

[0015] Step 5: Load ruthenium atoms on the nickel atoms of the nickel-based catalyst Ni-NC by microwave plasma chemical vapor deposition to obtain a dual-atom catalyst.

[0016] Preferably, in Step 1, the concentration of the FeCl3 solution is 2M; the concentration of the NaOH solution is 5.4M; the condition for dropping the FeCl3 solution into the NaOH solution is: under continuous stirring, drop it at a rate of 10 mL / min for 10 - 15 min; the concentration of the Na2SO4 solution is 0.6M; the reaction condition when adding the Na2SO4 solution is oil bath stirring reaction at 75°C for 5 min.

[0017] Preferably, the calcination condition in Step 1 is: calcine the Fe(OH)3 gel at 100°C for 70 - 100 h, wash it with water and ethanol more than ten times until it is clear, and then dry the obtained rod-shaped Fe2O3 at 70°C for 10 h.

[0018] Preferably, the buffer solution described in Step 2 uses a 10 mM Tris-HCl buffer solution;

[0019] Preferably, in Step 2, after adding the rod-shaped Fe2O3 to the buffer solution and stirring for 15 - 25 min, then add dopamine hydrochloride and continue stirring for 8 h. The obtained product is centrifuged and washed and then dried at 70°C.

[0020] Preferably, the condition for pyrolytic carbonization in Step 3 is to anneal the product obtained in Step 2 at 350 - 450°C for 1 h in an N2 atmosphere, and control the heating rate at 1°C / min.

[0021] Preferably, in Step 3, the etching condition is: mix the product obtained by carbonizing the polydopamine layer with a 12M hydrochloric acid solution, react and then take out the solid product, and react the obtained solid product with a 1M hydrochloric acid solution at 180°C for 8 - 10 h. The obtained product is washed with ethanol and then dried.

[0022] Preferably, the chemical vapor deposition process in step 4 is as follows: after uniformly mixing the Ni(NO3)2 solution and the NaOH solution with the nitrogen-carbon material obtained in step 3, the pH value is adjusted to 10.5 using NaOH; after stirring at 60°C for 30-45 minutes, the solid product is filtered and washed with distilled water until neutral, and dried at 60°C. The obtained solid product is heated to 500-600°C at a heating rate of 10°C / min for calcination, and the calcination time is 12 hours.

[0023] Preferably, in step 5, the process of microwave plasma vapor deposition is as follows: the product obtained in step 4 is heated to 550-750°C in a microwave plasma device at a heating rate of 3°C / min and a carrier gas is introduced; after cooling, ruthenium carbonate vapor enters the microwave plasma device with the carrier gas and is heated to 400-500°C at 2.5°C / min, and reduced for 1 hour; after cooling, a diatomic catalyst is obtained. The carrier gas is H2, and its gas flow rate is 30-50ml / min.

[0024] In a second aspect, the present invention provides a diatomic catalyst prepared by the aforementioned method; wherein the loading amount of ruthenium is 1 wt% to 12 wt%.

[0025] In a third aspect, the present invention provides a tar catalytic reforming method, the specific process is: the treated tar is gasified and then introduced into a low-temperature plasma reaction system equipped with a diatomic catalyst prepared by the above method. The low-temperature plasma reaction system is started, the voltage is set to 78kV to 82kV, the frequency is 2kHz to 3kHz, the gas preheating temperature is 200℃ to 400℃, the carrier gas atmosphere is N2 / H2O=(8000~15000):1, and the gas flow rate is 6L / min to 10L / min.

[0026] Preferably, the low-temperature plasma synergistic catalytic system used in the tar catalytic reforming method includes a gas distribution system and a low-temperature plasma reaction system. The gas distribution system uses high-purity air as a carrier gas to evaporate liquid tar into a gaseous state and input it into the low-temperature plasma reaction system. The low-temperature plasma reaction system includes a power supply and one or more dielectric barrier discharge reactors. The power supply supplies power to each dielectric barrier discharge reactor. There is a discharge reaction chamber in the dielectric barrier discharge reactor. The diatomic catalyst is placed in the discharge reaction chamber. The input port of the discharge reaction chamber is connected to the output port of the gas distribution system.

[0027] Preferably, the dielectric barrier discharge reactor comprises a quartz outer tube, a quartz inner tube, an electrode rod and a metal mesh. The quartz outer tube is coaxially arranged with the quartz inner tube, and the quartz outer tube is sleeved on the outer side of the quartz inner tube. The electrode rod is arranged in the quartz inner tube as a high-voltage electrode; the metal mesh is wrapped on the outer side of the quartz outer tube as a grounding electrode. A discharge reaction chamber is formed between the inner side of the quartz outer tube and the outer side of the quartz inner tube.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The present invention constructs a nitrogen-doped mesoporous carbon material with a rod-shell structure as a carrier by preparing rod-shaped Fe2O3 as a template, followed by calcination and etching after forming a PDA film on the template surface; this rod-shell structure helps to increase the loading amount of bimetallic atoms and form a pore structure more conducive to catalysis, thereby enhancing the catalytic activity of the catalyst.

[0030] 2. The present invention deposits two different metal atoms on the nitrided mesoporous carbon by combining chemical vapor deposition and microwave plasma deposition, significantly improving the dispersion of nickel single atoms in the catalyst, effectively improving the particle size of metal particles, enhancing the anti-sintering and anti-poisoning abilities of the catalyst, and improving the intrinsic activity of the catalyst.

[0031] 3. By depositing Ru atoms into the nickel-based catalyst, the present invention effectively improves the aggregation of metal particles, increases the number of active sites by activating adjacent active sites, promotes the electron transfer on the catalyst surface, promotes the oxidative conversion of carbonaceous compounds on the catalyst surface, and enhances the anti-coking ability of the catalyst.

[0032] 4. The present invention introduces the synergistic effect of low-temperature plasma discharge and catalytic decomposition in tar reforming, which helps to inhibit the aggregation of metal atoms on the catalyst and improve the service life of the catalyst. Brief Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the surface structure of the catalyst provided in Embodiment 1 of the present invention.

[0034] Figure 2 It is a schematic diagram of the structure of the low-temperature plasma synergistic catalytic system provided in Embodiment 2 of the present invention. Detailed Embodiments

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] Embodiment 1

[0037] A dual-atom catalyst for tar catalytic reforming has a rod-shell-like rod structure, uses nitrogen-doped mesoporous carbon as a carrier, and is precipitated and impregnated by a chemical method. A large number of Ni single atoms are loaded on the carrier, enabling the Ni single atoms to coordinate with the active sites on the rod-shell carrier, thereby anchoring the Ni single atoms on the nitrided carbon carrier to form a rod structure, obtaining a nickel-based catalyst with Ni single atoms highly dispersed on the nitrogen-doped mesoporous carbon carrier. Then, Ru atoms are anchored on the Ni atoms by chemical vapor deposition, further realizing the dispersion and coordination of a large number of single atoms, improving the dispersion of nickel particles, and preparing a dual-metal catalyst for catalytic reforming.

[0038] During the tar reforming process, the active sites of nickel single atoms have reaction selectivity. The anchoring of Ru atoms enables the activation of the adjacent active sites of nickel atoms, making them more likely to participate in the methyl dehydrogenation reaction and inhibiting the C-C bond cleavage reaction that leads to carbon deposition, thereby suppressing carbon deposition. On the other hand, the increased dispersion of metal particles in the single-atom catalyst increases the number of coordinatively unsaturated atoms, promotes the mobility of lattice oxygen, and thus improves the intrinsic catalytic activity. Therefore, in this application, by dispersing and anchoring nickel atoms and ruthenium atoms on nitrogen-doped mesoporous carbon, the catalytic decomposition of tar molecular chains containing a large number of methyl groups can be achieved.

[0039] The preparation process of the dual-atom catalyst for tar catalytic reforming is as follows:

[0040] Step 1: The ferric chloride solution is subjected to an oil bath and slowly added dropwise to the sodium hydroxide solution, and then sodium sulfate is slowly added to synthesize iron hydroxide sol, which is calcined and washed to obtain rod-shaped iron oxide solids. The concentration of the FeCl3 solution is 2M; the concentration of the NaOH solution is 5.4M; the condition for dropping the FeCl3 solution into the NaOH solution is: under continuous stirring, it is dropped at a rate of 10 mL / min for 15 min; the calcination condition is: the Fe(OH)3 gel is calcined at 100 °C for 96 h and then washed with water and ethanol more than ten times until it is clear, and the obtained rod-shaped Fe2O3 is dried at 70 °C for 10 h. The concentration of the Na2SO4 solution is 0.6M; the reaction condition when adding the Na2SO4 solution is an oil bath stirring reaction at 75 °C for 5 min. The rod-shaped iron oxide is added to 10 mM Tris-HCl buffer solution and stirred for 25 min, and then dopamine hydrochloride is added and stirred continuously for 8 h. The obtained product is centrifuged and washed and then dried at 70 °C. A layer of PDA film is loaded on the surface of the rod-shaped iron oxide solid. The length of the rod-shaped iron oxide is 20 nm to 60 nm, and the diameter is 3 nm to 10 nm.

[0041] Step 2: The rod-shaped iron oxide solid loaded with the PDA film obtained in Step 1 is pyrolytically carbonized at 450 °C, and the carbon film on the surface is pyrolyzed to generate nitrogen-doped carbon materials. The pyrolytic carbonization condition is: the product obtained in Step 2 is annealed at 450 °C for 1 h in an N2 atmosphere, and the heating rate is controlled at 1 °C / min. Then it is mixed and reacted with a high-concentration hydrochloric acid solution for 10 h, and then hydrothermally reacted with a low-concentration hydrochloric acid solution at 180 °C for 10 h to etch the iron oxide from the nitrogen-doped carbon materials, and after washing and drying, a rod-shell-shaped nitrogen-doped carbon material carrier is obtained. The etching condition is: the Fe2O3@NC material obtained by carbonizing the polydopamine layer is mixed with 12M hydrochloric acid solution for 10 h, then the solid product is taken out, and it is thermally reacted with 1M hydrochloric acid solution at 180 °C for 10 h. The obtained product is washed with ethanol and then dried.

[0042] Step 3: Mix the prepared nitrogen-doped mesoporous carbon with nickel nitrate, adjust the pH value to 10.5 with sodium hydroxide, stir at 60 °C for 45 min, filter and wash the solid product with distilled water until neutral, and dry at 60 °C. Heat the obtained sample to 600 °C at a heating rate of 10 °C / min and calcine for 12 h. Nickel is deposited on the nitrogen-carbon material atomically by chemical vapor deposition; a nickel-based catalyst Ni-NC supported by nitrogen-doped mesoporous carbon is prepared.

[0043] Step 4: Place the prepared nickel-based catalyst in a microwave plasma chemical vapor deposition device, start the microwave plasma chemical vapor deposition device, with a power of 20 W - 60 W, and set the internal pressure to 0.1 atmospheres; introduce a hydrogen gas flow of 50 ml / min into the microwave plasma chemical vapor deposition device, heat it to 750 °C at a heating rate of 3 °C / min, and reduce it for 12 h to complete the pretreatment; maintain the operation of the microwave plasma chemical vapor deposition device, and start cooling inside; after cooling to room temperature, inject the ruthenium carbonate solution into the microwave plasma chemical vapor deposition device; the ruthenium carbonate solution entering the microwave plasma chemical vapor deposition device turns from liquid to gas to form ruthenium vapor; heat it to 500 °C at a heating rate of 2.5 °C / min and reduce it for 1 h to load the ruthenium vapor onto the nickel-based catalyst; then, introduce a hydrogen gas flow of 50 ml / min at a constant temperature of 500 °C and reduce it for 1 h; cool the obtained product in an argon gas flow to obtain a dual-atom catalyst for tar catalytic reforming.

[0044] The surface structure of the obtained dual-atom catalyst is as Figure 1 shown; it can be seen from Figure 1 that: from the bright spots (marked with circles) in the image, it can be seen that single atoms are evenly dispersed on the nitrogen-doped carbon material support.

[0045] Example 2

[0046] A low-temperature plasma synergistic catalytic system for catalytic degradation of tar pollutants, which includes a gas distribution system 1, a low-temperature plasma reaction system, and an analysis and detection system.

[0047] The gas distribution system 1 uses high-purity air as the carrier gas, evaporates the liquid tar into gas, controls the gas flow rate with a mass flow meter, adjusts the ratio of high-purity air to gaseous tar according to experimental conditions, and adjusts the tar concentration by adjusting the gas flow rate to control the tar content in the low-temperature plasma reaction system.

[0048] The low-temperature plasma reaction system includes a power supply 2 and multiple dielectric barrier discharge reactors 3. The power supply 2 supplies power to each dielectric barrier discharge reactor 3, with a frequency range of 5 kHz - 20 kHz, a power range of 0 - 500 W, and an output voltage range of 0 - 30 kV.

[0049] The dielectric barrier discharge reactor 3 includes a quartz outer tube, a quartz inner tube, a stainless steel rod and a copper mesh. The quartz outer tube is coaxially arranged with the quartz inner tube, and the quartz outer tube is sleeved on the outside of the quartz inner tube. The stainless steel rod is arranged in the quartz inner tube as a high-voltage electrode; the copper mesh is wrapped on the outside of the quartz outer tube as a grounding electrode. The length of the quartz outer tube is 400 mm, the outer diameter is 25 mm, and the inner diameter is 17 mm; the length of the quartz inner tube is 485 mm, the outer diameter is 12 mm, and the inner diameter is 8 mm; the diameter of the stainless steel rod is 5.6 mm. The length of the copper mesh is 200 mm and the thickness is 0.05 mm.

[0050] A discharge reaction chamber is formed between the inner side of the quartz outer tube and the outer side of the quartz inner tube. The catalyst is placed in the discharge reaction chamber between the quartz outer tube and the quartz inner tube. One end of the reaction chamber is filled with an appropriate amount of quartz wool to prevent the catalyst from being blown away from the discharge reaction chamber with the airflow.

[0051] The analysis and detection system includes an oscilloscope 4, a spectrometer 5, a gas chromatograph 6, a nitrogen oxide analyzer 7, an ozone detector 8 and a gas chromatography-mass spectrometer 9, which are used to detect various parameters in the reaction process.

[0052] During the operation of the low-temperature plasma synergistic catalytic system, the stainless steel rod and the copper mesh form a stable discharge space; air and the gaseous tar to be processed are continuously input into the discharge reaction chamber; low-temperature plasma is generated in the discharge reaction chamber, and the gaseous tar is decomposed under the synergistic effect of plasma catalysis. The catalytic performance (specific tar conversion rate and H2 selectivity) of the final catalyst is adjusted by adjusting the discharge power, frequency, gas preheating temperature, carrier gas atmosphere and gas flow rate and nickel single atom loading during the low-temperature plasma discharge process.

[0053] The low-temperature plasma synergistic catalytic system is used to treat tar pollutants. In this example, toluene is used as a typical tar simulant to test the treatment effect of the catalytic system, as follows:

[0054] The initial toluene concentration is maintained at 1000±10ppm; the operating voltage of the low-temperature plasma device is 220V; the catalyst is the bimetallic catalyst prepared in Example 1, fixed in the dielectric barrier discharge device with quartz wool. The range of each process parameter is set, the discharge voltage is 20kV~80kV, the frequency is 1kHz~10kHz, the carrier gas atmosphere (high-purity air atmosphere), the gas flow rate is 2L / min~10L / min, and the Ru catalyst loading is 5wt.%~12wt.%. Among them, the carrier gas atmosphere is adjusted by a flow controller that controls the mixing ratio of high-purity air and H2O injection pump. Tests are carried out within the setting range of the above variables to obtain the toluene conversion rate and H2 selectivity in the catalytic system under the conditions of synchronous changes of multiple variables (discharge voltage, frequency, gas preheating temperature, carrier gas atmosphere and gas flow rate).

[0055] The results show that when the ozone and toluene concentrations at the outlet of the low-temperature plasma reaction system are 64ppm and 160ppm respectively, the toluene conversion rate at the outlet of the low-temperature plasma reaction system reaches a maximum value of 84%, and the H2 selectivity at this time is 36.1%. The corresponding discharge voltage, frequency, gas preheating temperature, carrier gas atmosphere, and gas flow rate are 70kV, 10kHZ, N2 / H2O=10000:1, and 8L / min respectively; when the ozone concentration, toluene concentration, and catalyst nickel loading at the outlet of the plasma device are 71ppm, 76ppm, and 4% respectively, the H2 selectivity at the outlet of the low-temperature plasma reaction system reaches a maximum value of 56.5%, and the toluene conversion rate at this time is 92.4%.

[0056] When comprehensively considering the toluene conversion rate and H2 selectivity, the voltage is set to 78kV~82kV, the frequency is 2kHz~3kHz, the gas preheating temperature is 200℃~400℃, the carrier gas atmosphere is N2 / H2O=(8000~15000):1, the gas flow rate is 6L / min~10L / min, and the Ru loading amount is 1-12wt%. Under these optimized conditions, the toluene conversion rate can reach 82%~91%, the H2 selectivity can reach 27.3%~62.1%, and the stable working time can reach more than 24h.

[0057] Compared with the diatomic catalyst prepared by the same method, the toluene reforming hydrogen production was carried out at 800℃. After 6 hours, the toluene conversion rate of the catalyst was obviously observed to drop from 90% to 78%, and the H2 selectivity dropped from 45% to 32%. Through analysis, the catalyst clustering phenomenon was obvious, the active sites were sintered and deactivated, and the performance was reduced.

Claims

1. A preparation method of a dual-atom catalyst, characterized in that: It includes the following steps: Step 1: After dropping FeCl3 solution into NaOH solution, add Na2SO4 solution, react to form Fe(OH)3 sol, and calcine to obtain rod-shaped Fe2O3; the length of the rod-shaped Fe2O3 is 20 nm to 60 nm, and the diameter is 3 nm to 10 nm; Step 2: Add the rod-shaped Fe2O3 obtained in Step 1 and dopamine hydrochloride into a buffer solution successively and mix and stir to form a polydopamine layer on the surface of the rod-shaped Fe2O3; Step 3: Pyrolyze and carbonize the product obtained in Step 2 to carbonize the polydopamine layer; then, etch the obtained product under acidic conditions to remove the rod-shaped Fe2O3 to obtain a rod-shell-shaped nitrogen-carbon material; Step 4: Deposit nickel at the atomic level on the nitrogen-carbon material by chemical vapor deposition; obtain a nickel-based catalyst Ni-NC; Step 5: Load ruthenium atoms on the nickel atoms of the nickel-based catalyst Ni-NC by microwave plasma chemical vapor deposition to obtain a dual-atom catalyst.

2. The preparation method of a dual-atom catalyst according to claim 1, characterized in that: In Step 2, after adding the rod-shaped Fe2O3 to the buffer solution and stirring for 15 - 25 min, add dopamine hydrochloride and continue stirring. The obtained product is centrifuged, washed, and dried.

3. The preparation method of a dual-atom catalyst according to claim 1, characterized in that: The conditions for pyrolysis and carbonization in Step 3 are to anneal the product obtained in Step 2 at 350 - 450 °C in an N2 atmosphere.

4. The preparation method of a dual-atom catalyst according to claim 1, characterized in that: In Step 3, the etching conditions are: mix and react the product obtained by carbonizing the polydopamine layer with 12 M hydrochloric acid solution, take out the solid product, and react the obtained solid product with 1 M hydrochloric acid solution at 180 °C for 8 - 10 h. The obtained product is washed with ethanol and dried.

5. The preparation method of a dual-atom catalyst according to claim 1, characterized in that: The process of chemical vapor deposition in Step 4 is: uniformly mix Ni(NO3)2 solution and NaOH solution with the nitrogen-carbon material obtained in Step 3, stir and react. The obtained solid product is filtered, washed with distilled water until neutral, and dried; The obtained solid product is calcined by heating to 500 - 600 °C.

6. The preparation method of a dual-atom catalyst according to claim 1, characterized in that: In Step 5, the process of microwave plasma chemical vapor deposition is: heat the product obtained in Step 4 to 550 - 750 °C in a microwave plasma device and introduce a carrier gas; after cooling, ruthenium carbonate vapor enters the microwave plasma device with the carrier gas and reacts at 400 - 500 °C; after cooling, a dual-atom catalyst is obtained; the carrier gas is H2, and its gas flow rate is 30 - 50 ml / min.

7. A dual-atom catalyst, characterized in that: It is prepared by the preparation method described in any one of claims 1 - 6; the ruthenium loading is 1 wt% to 12 wt%.

8. A method for catalytic reforming of tar, characterized in that: The specific process is: vaporize the tar to be treated and introduce it into a low-temperature plasma reaction system equipped with the dual-atom catalyst described in claim 7; start the low-temperature plasma reaction system, set the voltage to 78 kV to 82 kV, the frequency to 2 kHz to 3 kHz, the gas preheating temperature to 200 °C to 400 °C, the carrier gas atmosphere to N2 / H2O = (8000 - 15000):1, and the gas flow rate to 6 L / min to 10 L / min.

9. A method for catalytic reforming of tar according to claim 8, characterized in that: The low-temperature plasma synergistic catalytic system used in the tar catalytic reforming method includes a gas distribution system (1) and a low-temperature plasma reaction system; the gas distribution system (1) uses high-purity air as a carrier gas to evaporate liquid tar into gas and input it into the low-temperature plasma reaction system; the low-temperature plasma reaction system includes a power supply (2) and one or more dielectric barrier discharge reactors (3); the power supply (2) supplies power to each dielectric barrier discharge reactor (3); a discharge reaction chamber is provided in the dielectric barrier discharge reactor; a diatomic catalyst is placed in the discharge reaction chamber; the input port of the discharge reaction chamber is communicated with the output port of the gas distribution system.

10. A method for catalytic reforming of tar according to claim 9, characterized in that: The dielectric barrier discharge reactor (3) includes a quartz outer tube, a quartz inner tube, an electrode rod, and a metal mesh; the quartz outer tube and the quartz inner tube are coaxially arranged, and the quartz outer tube is sleeved outside the quartz inner tube; the electrode rod is arranged inside the quartz inner tube and serves as a high-voltage electrode; the metal mesh is wrapped outside the quartz outer tube and serves as a grounding electrode; a discharge reaction chamber is formed between the inner side surface of the quartz outer tube and the outer side surface of the quartz inner tube.

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