A copper-based radio frequency plasma-assisted synthesis ammonia catalyst, a preparation method and application thereof

Abstract

This invention relates to a copper-based radio frequency plasma-assisted ammonia synthesis catalyst, its preparation method, and its application, belonging to the field of plasma ammonia synthesis technology. The invention first cleanses a pure copper support using an organic solvent and pure water, then places the cleaned copper support in pure water. Next, an aqueous solution of an active metal precursor is added dropwise to the system. After stirring and reacting, the resulting copper-based catalyst precursor is placed in a quartz reaction tube of a non-thermal radio frequency plasma reactor. A hydrogen-argon mixture is introduced, and the reactor is reduced using the generated plasma at 100–200°C and 250 Pa–1000 Pa for 0.5–2 hours, thereby obtaining a highly stable and active copper-based radio frequency plasma-assisted ammonia synthesis catalyst. With the assistance of radio frequency plasma, this catalyst can achieve low-temperature, low-pressure catalytic reaction of nitrogen and hydrogen to synthesize ammonia. This invention achieves efficient nitrogen fixation while effectively reducing energy consumption and environmental pollution.

Description

Technical Field

[0001] This invention belongs to the field of plasma ammonia synthesis technology, specifically relating to a copper-based radio frequency plasma-assisted ammonia synthesis catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is a widely used bulk chemical with broad applications in agriculture, chemicals, and the energy industry. One of its most important uses is as a key component of nitrogen fertilizers, promoting the sustainability of global food production. Synthetic ammonia is also used in the production of other chemicals, such as important chemical feedstocks like nitrates and amines, and as a promising hydrogen carrier (with a hydrogen mass fraction of up to 17.75 wt%). Furthermore, ammonia can be used as a fuel, considered to have decarbonization potential in power generation and heavy transportation. It can participate directly in combustion or be mixed with other fuels for power generation, reconstructing clean, carbon-free power systems; it can also be used as engine fuel, with pure, carbon-free products upon complete combustion, helping to address carbon emissions in the transportation sector. Therefore, ammonia, as a strategically valuable high-power, renewable, and clean energy source, provides a new option for rapidly adjusting my country's energy structure.

[0003] The International Energy Agency (IEA) projects that global demand for green and blue hydrogen will reach 7.5 × 10⁻⁶ tons by 2040. 7 Currently, the main method for synthesizing ammonia is the Haber-Bosch process, which was industrialized in 1913. This method relies on iron or ruthenium-based catalysts to directly dissociate inert nitrogen-nitrogen triple bonds (945 kJ / mol) under high temperature and high pressure conditions (450–600 °C, 10–30 MPa). However, its harsh operating conditions require a large amount of energy consumption, accounting for approximately 1% to 2% of global energy consumption, and are accompanied by significant carbon dioxide emissions, accounting for 1.4% of global carbon dioxide emissions, placing enormous pressure on the world's energy and environment. Furthermore, large-scale Haber-Bosch chemical plants face the challenge of integrating and utilizing renewable energy sources such as wind and solar power. Therefore, in order to reduce the conditions and energy consumption of catalytic ammonia synthesis while meeting the huge global demand for ammonia, exploring more environmentally friendly, easy-to-operate, and green sustainable ammonia synthesis methods has become a key research focus for contemporary scientists.

[0004] Nonthermal plasma-assisted catalysis is a simple and environmentally friendly application technology. This technology can excite and activate inert gas molecules, such as carbon dioxide, methane, and nitrogen, under low-temperature and low-pressure conditions. Unlike traditional thermal catalysis methods, the bulk temperature of nonthermal plasma technology remains low, while the electrons generated in the plasma have an exceptionally high electron temperature of 10⁻⁶. 4 ~10 5K, equivalent to 1–10 eV, is a high-energy electron that can excite and activate inert reactant molecules into highly reactive species, including free radicals, vibrationally excited molecules, and ions. This is crucial for initiating chemical reactions under mild conditions and helps overcome the thermodynamic limitations of reactions. This technology has reportedly been successfully applied to various chemical reactions with significant progress, such as methane reforming, nitrogen fixation, carbon monoxide conversion, carbon dioxide reduction, and pollutant removal. However, most related work focuses on dielectric barrier discharge plasma, with few reports on radio frequency (RF) plasma. RF plasma is an application technology excited by a high-frequency (typically 13.56 MHz) AC power supply, capable of operating under low temperature and negative pressure conditions. This technology is widely used in the semiconductor processing industry due to its ease of scale-up, low radiation hazard, and long service life because the RF coil does not directly contact the plasma, thus avoiding corrosion. It also produces more uniform plasma. Therefore, utilizing RF non-thermal plasma as an auxiliary catalyst to achieve low-temperature, low-pressure, controllable ammonia synthesis is a very promising catalytic technology. Summary of the Invention

[0005] To achieve efficient radio frequency plasma-assisted catalytic nitrogen fixation and ammonia synthesis, this invention aims to provide a copper-based radio frequency plasma-assisted ammonia synthesis catalyst, its preparation method, and its applications. The copper-based radio frequency plasma-assisted ammonia synthesis catalyst prepared by this invention enhances the absorption of electromagnetic wave energy in the system, and through the regulation of the loading of surface-active metals, it exhibits a significantly enhanced catalytic effect on radio frequency plasma-assisted nitrogen fixation and ammonia synthesis.

[0006] The solution to this problem is as follows: Elements such as copper, silver, ruthenium, gold, and palladium are respectively loaded onto the surface of a copper-based catalyst that enhances electromagnetic wave absorption, or metal-copper alloys (such as gold-copper alloys, palladium-copper alloys, etc.) are directly formed on the surface of the copper-based catalyst, resulting in a copper-based radio frequency plasma-assisted ammonia synthesis catalyst with high stability and high activity. This copper-based radio frequency plasma-assisted ammonia synthesis catalyst, with the assistance of radio frequency plasma, can achieve low-temperature, low-pressure catalytic reaction of nitrogen and hydrogen to synthesize ammonia.

[0007] The preparation method of a copper-based radio frequency plasma-assisted ammonia synthesis catalyst according to the present invention comprises the following steps:

[0008] (1) The pure copper carrier is washed with organic solvent and pure water in sequence, and then the washed copper carrier is placed in pure water; the pure copper carrier is copper wire, copper foam, copper mesh or copper foil, with a length of 5 to 20 cm and a width or diameter of no more than 4 cm; the organic solvent is ethyl acetate, acetone and anhydrous ethanol;

[0009] (2) Weigh the active metal precursor to prepare an aqueous solution, and then add it dropwise to the system in step (1). Stir the reaction magnetically at 20-70℃ for 0.5-3 hours. Wash and dry the obtained copper support to obtain a copper-based catalyst precursor. The active metal in the active metal precursor is 0.006-0.120% of the mass of the copper support. The active metal precursor is one or more of copper chloride, silver nitrate, sodium chloropalladium, chloroauric acid, and ruthenium chloride.

[0010] (3) The copper-based catalyst precursor obtained in step (2) is placed in the quartz reaction tube of a non-thermal radio frequency plasma reactor (4-6 cm in diameter and 55-65 cm in length), and a hydrogen-argon mixture with a flow rate of 5-50 sccm is introduced, wherein the volume of hydrogen is 1-5% of the volume of argon; at 100-200℃ and 250-1000 Pa, the generated plasma is used for reduction treatment for 0.5-2 h to obtain a copper-based radio frequency plasma-assisted ammonia synthesis catalyst.

[0011] The non-thermal radio frequency plasma reactor consists of a quartz reaction tube, a radio frequency coil (made of 20-30 turns of copper wire with a diameter of 0.6 cm, a coil diameter of 8-12 cm, and an axial length of 20-30 cm), and a radio frequency power supply. The quartz reaction tube and the radio frequency coil are coaxially arranged. The radio frequency coil is connected to the radio frequency power supply (input power of 20-200 W, frequency of 13.56 MHz). Under the action of the radio frequency power supply, the radio frequency coil generates a high-frequency electromagnetic field. A mixture of argon and hydrogen gas is introduced into the quartz reaction tube, and the mixture generates plasma under the action of the high-frequency electromagnetic field.

[0012] The active metal component precursor added in step (2) is copper chloride, silver nitrate, sodium chloropalladium, chloroauric acid or ruthenium chloride. When the copper support is a copper mesh (CM), the catalysts obtained in step (3) are named Cu / CM, Ag / CM, PdCu3 / CM, AuCu3 / CM and Ru / CM according to their respective structures. Taking the loaded metal gold as an example, when gold accounts for 0.03% of the total mass of the catalyst, AuCu3 alloy nanoparticles are formed on the surface of the copper support. The highly uniformly dispersed nanoparticles have a particle size of 90 to 140 nm.

[0013] (4) Radio frequency plasma-assisted ammonia synthesis: The copper-based radio frequency plasma-assisted ammonia synthesis catalyst obtained in step (3) is used to catalyze the reaction of nitrogen and hydrogen mixture under low temperature and low pressure radio frequency plasma-assisted conditions to synthesize ammonia.

[0014] The aforementioned low temperature range is 20℃~200℃;

[0015] The low-pressure range is 250 Pa to 1000 Pa;

[0016] The flow rate of the nitrogen-hydrogen mixture is 10-100 sccm, the volume ratio of nitrogen to hydrogen is 1:2-4, and the reaction time is 0.5-5 h.

[0017] Before the plasma reaction begins, a copper-based radio frequency plasma-assisted ammonia synthesis catalyst is placed in a quartz reaction tube of a non-thermal radio frequency plasma reactor. The quartz reaction tube is then pre-evacuated to negative pressure using a vacuum pump and cleaned multiple times with nitrogen and hydrogen reaction gases to remove impurities. During the initial reaction, a heating band wrapped around the outer wall of the quartz reaction tube controls the reaction temperature. A mixture of nitrogen and hydrogen is introduced into the front end of the quartz reaction tube, and a glass cold trap is added to the rear end of the quartz reaction tube and placed in a liquid nitrogen Dewar flask to collect the ammonia product. After the reaction is completed, dilute sulfuric acid solution is injected into the glass cold trap to react with the ammonia product to generate ammonium ions. The amount of ammonium ions in the solution is determined by titration colorimetry and ion chromatography, and then converted into the ammonia outlet volume ratio to measure the ammonia production rate.

[0018] This invention utilizes a copper-based support that enhances electromagnetic wave absorption to construct a copper-based catalyst with metal or alloy nanoparticles loaded on its surface. This catalyst is then applied to radio frequency plasma-assisted ammonia synthesis. Radio frequency plasma technology activates the strong nitrogen-nitrogen triple bonds in nitrogen gas, offering a simple, environmentally friendly, and sustainable solution. The copper-based catalyst designed and constructed in this invention achieves highly efficient nitrogen fixation under mild conditions, while reducing energy consumption and environmental pollution, thus contributing to the rapid adjustment of my country's energy structure. Attached Figure Description

[0019] Figure 1 (a)~ Figure 1 (c) are scanning electron microscope images of AuCu3 / CM prepared in Example 1 at different magnifications. It can be seen from the images that the prepared AuCu3 nanoparticles have a relatively uniform morphology. Figure 1 (d)~ Figure 1 (f) is the elemental distribution diagram of AuCu3 / CM, which shows that the gold element in AuCu3 / CM is only distributed on the nanoparticles on the surface of the copper mesh and is very uniform.

[0020] Figure 2 Example 1: Particle size distribution of AuCu3 nanoparticles (Au loading of 0.03 wt%) loaded on the surface of a copper mesh; indicating that the AuCu3 nanoparticles on the surface of the prepared copper-based catalyst have a uniform particle size distribution of 114 ± 21 nm.

[0021] Figure 3 (a): XRD diffraction patterns of Cu / CM, AuCu3 / CM and Ru / CM prepared in Example 1 and comparison with corresponding standard PDF cards; Figure 3(b): XRD diffraction patterns of Ag / CM and PdCu3 / CM prepared in Example 1 and corresponding standard PDF cards; indicating that the nanoparticles loaded on the copper mesh surface are pure phases without impurities.

[0022] Figure 4 The graph shows a comparison of the catalytic rates exhibited by different metal wires of the same specification under the same radio frequency plasma-assisted ammonia synthesis catalytic reaction conditions. The inset is a simplified experimental setup diagram. The metal wires were 10 cm long, 1 mm in diameter, and 99.999% pure. The radio frequency plasma-assisted catalytic reaction conditions were: radio frequency input power 100 W, temperature 200 °C, pressure 300 Pa, and reaction time 1 h. Corresponding to Example 1, the copper wire was observed to have the best catalytic activity, with an ammonia outlet volume percentage of 1.14%, nearly five times higher than the blank (0.24%).

[0023] Figure 5 A comparison of ammonia synthesis rates of a series of prepared copper-based catalysts is shown. The catalysts are Cu / CM, Ag / CM, PdCu3 / CM, AuCu3 / CM, and Ru / CM, with a catalyst dosage of 0.80 g and a metal loading of 0.03 wt%. The RF plasma-assisted catalysis reaction conditions were: input power 100 W, temperature 200 °C, pressure 300 Pa, and reaction time 1 h. Corresponding to Example 2, AuCu3 / CM showed the best performance, with an ammonia outlet volume percentage of 1.71%. The TOF axis represents the conversion frequency of NH3 produced per hour per active site for Cu, Ag, Pd, Au, and Ru catalysts. It can be seen that AuCu3 active sites exhibit the fastest NH3 conversion frequency, at 175 h. -1 ;

[0024] Figure 6 Comparison of the ammonia synthesis activities of a series of AuCu3 / CM catalysts with different gold loadings. The gold loading ranges from 0.006% to 0.120%. The reaction conditions for radio frequency plasma-assisted catalysis are: input power 100W, temperature 200℃, pressure 300Pa, and reaction time 1h. It can be seen that when the gold loading accounts for 0.03wt% of the catalyst, the catalyst activity is high, and the gold atom utilization rate is the highest, resulting in the best effect, corresponding to Examples 2-6.

[0025] Figure 7 Stability cycle test curves of AuCu3 / CM catalyst under the conditions of input power 100W, temperature 200℃, and pressure 300Pa; continuous testing for fifty hours shows that AuCu3 / CM catalyst has excellent stability. Detailed Implementation

[0026] The non-thermal radio frequency plasma reactor used in this embodiment consists of a quartz reaction tube (5 cm in diameter and 50 cm in length), a radio frequency coil (made of 25 turns of copper wire with a diameter of 0.6 cm, a coil diameter of 10 cm, and an axial length of 25 cm), and a radio frequency power supply. The quartz reaction tube and the radio frequency coil are coaxially arranged, and the radio frequency coil is connected to the radio frequency power supply (input power of 100 W and frequency of 13.56 MHz). Under the action of the radio frequency power supply, the radio frequency coil generates a high-frequency electromagnetic field. An argon-hydrogen mixture (for catalyst preparation) or a nitrogen-hydrogen mixture (for ammonia synthesis) is introduced into the quartz reaction tube. The argon-hydrogen mixture or the nitrogen-hydrogen mixture generates plasma under the action of the high-frequency electromagnetic field. With the assistance of the plasma, the catalyst is prepared or ammonia is synthesized.

[0027] Example 1: Application of different metal wires as catalysts in radio frequency plasma-assisted ammonia synthesis reaction

[0028] The activity of radio frequency plasma-assisted catalytic synthesis of ammonia was tested using different metal wires as reaction catalysts. High-purity (99.999%) metal wires with a diameter of 1 mm (including aluminum, titanium, iron, cobalt, nickel, copper, zinc, molybdenum, silver, and tungsten wires) with a length of 10 cm were cut. The surface of the metal wires was cleaned with organic solvents ethyl acetate, acetone, and anhydrous ethanol, and then placed in a quartz reaction tube 5 cm from the end of the radio frequency coil.

[0029] Before the reaction began, a metal wire was placed in the quartz reaction tube of a non-thermal radio frequency plasma reactor. The quartz reaction tube was first evacuated (approximately 50 Pa) using a vacuum pump, and then repeatedly cleaned with a nitrogen-hydrogen mixed reaction gas (nitrogen-hydrogen volume ratio 1:3) to remove impurities. Next, a nitrogen-hydrogen reaction gas (nitrogen-hydrogen volume ratio 1:3) was introduced at a flow rate of 18 sccm, and the system pressure reached a stable value of 300 Pa. A glass cold trap was added to the end of the quartz reaction tube and placed inside a liquid nitrogen Dewar flask to collect the ammonia product. When the temperature near the metal wire catalyst reached 200°C, the radio frequency power supply was activated to generate plasma. At this point, the metal wire catalyst was completely covered by plasma, and the ammonia synthesis reaction time was 1 hour. After the reaction, dilute sulfuric acid solution was injected into the glass cold trap to react with the ammonia product, generating ammonium ions. The amount of ammonium ions in the solution was determined using titration colorimetry and ion chromatography, and then converted into the ammonia outlet volume percentage to measure the ammonia production rate. The experimental results are as follows: Figure 4 As shown.

[0030] Example 2: Preparation and application of copper-based radio frequency plasma-assisted ammonia synthesis catalyst

[0031] (1) The 40-mesh copper mesh carrier was washed with ethyl acetate, acetone, anhydrous ethanol and pure water in sequence, then cut into a shape of 2cm*10cm with a weight of 0.80g and placed in 150mL of pure water.

[0032] (2) Weigh 3 mL of an aqueous solution containing 0.24 mg of active metal precursor and add it dropwise to the solution in step (1). After stirring magnetically at 20 °C for 1.5 h, remove the copper mesh support, wash and dry it to obtain a black catalyst precursor. Then place the catalyst precursor in the quartz reaction tube of the non-thermal radio frequency plasma reactor, located 5 cm from the end of the radio frequency coil, and introduce a hydrogen-argon mixture with a flow rate of 18 sccm, wherein the volume of hydrogen is 3% of the volume of argon. At 200 °C and 300 Pa, reduce the catalyst using the generated plasma for 1.5 h to obtain a copper-based radio frequency plasma-assisted ammonia synthesis catalyst. The active metal precursors used are copper chloride (0.24 mg is the mass of copper in copper chloride), silver nitrate, sodium chloropalladate, chloroauric acid or ruthenium chloride. When the copper support is a copper mesh (CM), the resulting catalysts are named Cu / CM, Ag / CM, PdCu3 / CM, AuCu3 / CM and Ru / CM respectively according to their structures.

[0033] (3) Radio frequency plasma-assisted ammonia synthesis:

[0034] Before the reaction begins, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor. The quartz reaction tube is first evacuated (approximately 50 Pa) using a vacuum pump, and then the quartz reaction tube is repeatedly cleaned with a nitrogen-hydrogen mixed reaction gas (nitrogen-hydrogen volume ratio of 1:3) to remove impurity gases. Then, a nitrogen-hydrogen reaction gas (nitrogen-hydrogen volume ratio of 1:3) is introduced, with a flow rate of 18 sccm. The system pressure is 300 Pa when stable. A glass cold trap is added to the tail end of the quartz reaction tube and placed in a liquid nitrogen Dewar flask to collect the ammonia product by freezing. When the temperature near the copper-based radio frequency plasma-assisted ammonia synthesis catalyst rises to 200°C, the radio frequency power supply is started to generate plasma. At this time, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is completely covered by the generated plasma, and the ammonia synthesis reaction time is 1 hour. After the reaction was complete, dilute sulfuric acid solution was introduced into a glass cold trap to react with the ammonia gas produced, generating ammonium ions. The amount of ammonium ions in the solution was determined using titration colorimetry and ion chromatography, and then converted into the proportion of ammonia gas at the outlet volume to measure the ammonia production rate. The experimental results are as follows: Figure 5As shown, the outlet volume percentages of ammonia produced after catalytic reactions by five catalysts—Cu / CM, Ag / CM, PdCu3 / CM, AuCu3 / CM, and Ru / CM—were 1.26%, 1.61%, 1.40%, 1.71%, and 1.41%, respectively. AuCu3 / CM exhibited the best catalytic activity and excellent stability, enabling continuous and stable catalytic synthesis of ammonia for up to 50 hours without activity decay. Figure 7 As shown.

[0035] Example 3: Preparation and Application of Copper-Based Radio Frequency Plasma-Assisted Ammonia Synthesis Catalyst

[0036] (1) The pretreatment of the copper mesh is the same as in Example 2.

[0037] (2) Preparation of low-loaded gold catalyst (0.006 wt% compared to the copper mesh support): 3 mL of chloroauric acid solution containing 0.05 mg of gold was added dropwise to the solution in step (1). After reacting at 20 °C for 1.5 h, the copper mesh support was removed, washed, and dried to obtain a black catalyst precursor on the copper mesh support. The catalyst precursor was then placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor, located 5 cm from the end of the radio frequency coil. A hydrogen-argon mixture with a flow rate of 18 sccm was introduced, wherein the volume of hydrogen was 3% of the volume of argon. The catalyst was reduced by the generated plasma at 200 °C and 300 Pa for 1.5 h to obtain a copper-based radio frequency plasma-assisted ammonia synthesis catalyst with low-loaded gold (0.006 wt%).

[0038] (3) Radio frequency plasma-assisted ammonia synthesis: Before the reaction begins, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor. The quartz reaction tube is first evacuated (about 50 Pa) using a vacuum pump. Then, the quartz reaction tube is repeatedly cleaned with a nitrogen-hydrogen mixed reaction gas (nitrogen-hydrogen volume ratio of 1:3) to remove impurity gases. Then, nitrogen-hydrogen reaction gas (nitrogen-hydrogen volume ratio of 1:3) is introduced, and the flow rate is set to 18 sccm. The system pressure is 300 Pa when it is stable. A glass cold trap is added to the tail end of the quartz reaction tube and placed in a liquid nitrogen Dewar flask to collect the ammonia product by freezing. When the temperature near the copper-based radio frequency plasma-assisted ammonia synthesis catalyst rises to 200℃, the radio frequency power supply is started to generate plasma. At this time, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is completely covered by the generated plasma. The ammonia synthesis reaction time is 1 h. After the reaction was complete, dilute sulfuric acid solution was introduced into a glass cold trap to react with the ammonia product, generating ammonium ions. The amount of ammonium ions in the solution was determined by titration colorimetry and ion chromatography, and then converted into the ammonia outlet volume percentage to measure the ammonia production rate. The results showed that the ammonia outlet volume percentage could reach 1.28%.

[0039] Example 4: Preparation and Application of Copper-Based Radio Frequency Plasma-Assisted Ammonia Synthesis Catalyst

[0040] (1) The pretreatment of the copper mesh is the same as in Example 2.

[0041] (2) Preparation of 0.012wt% gold-supported catalyst: A chloroauric acid solution containing 0.10 mg of gold was measured and added dropwise to the solution in step (1). After reacting at 20℃ for 1.5 h, the copper mesh support was removed, washed, and dried to obtain a copper-based black catalyst precursor. The catalyst precursor was then placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor, located 5 cm from the tail of the radio frequency coil. A hydrogen-argon mixture with a flow rate of 18 sccm was introduced, wherein the volume of hydrogen was 3% of the volume of argon. The catalyst was reduced by the generated plasma at 200℃ and 300 Pa for 1.5 h to obtain a 0.012wt% gold-supported copper-based radio frequency plasma-assisted ammonia synthesis catalyst.

[0042] (3) Radio frequency plasma-assisted ammonia synthesis: Before the reaction begins, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor. The quartz reaction tube is first evacuated (about 50 Pa) using a vacuum pump. Then, the quartz reaction tube is repeatedly cleaned with a nitrogen-hydrogen mixed reaction gas (nitrogen-hydrogen volume ratio of 1:3) to remove impurity gases. Then, nitrogen-hydrogen reaction gas (nitrogen-hydrogen volume ratio of 1:3) is introduced, and the flow rate is set to 18 sccm. The system pressure is 300 Pa when it is stable. A glass cold trap is added to the tail end of the quartz reaction tube and placed in a liquid nitrogen Dewar flask to collect the ammonia product by freezing. When the temperature near the copper-based radio frequency plasma-assisted ammonia synthesis catalyst rises to 200℃, the radio frequency power supply is started to generate plasma. At this time, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is completely covered by the generated plasma. The ammonia synthesis reaction time is 1 h. After the reaction was complete, dilute sulfuric acid solution was introduced into a glass cold trap to react with the ammonia product, generating ammonium ions. The amount of ammonium ions in the solution was determined by titration colorimetry and ion chromatography, and then converted into the ammonia outlet volume percentage to measure the ammonia production rate. The results showed that the ammonia outlet volume percentage could reach 1.35%.

[0043] Example 5: Preparation and application of copper-based radio frequency plasma-assisted ammonia synthesis catalyst

[0044] (1) The pretreatment of the copper mesh is the same as in Example 2.

[0045] (2) Preparation of 0.060wt% gold-supported catalyst: A chloroauric acid solution containing 0.48mg of gold was measured and added dropwise to the solution in step (1). After reacting at 20℃ for 1.5h, the copper mesh support was removed, washed, and dried to obtain a copper-based black catalyst precursor. The catalyst precursor was then placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor, located 5cm from the tail of the radio frequency coil. A hydrogen-argon mixture with a flow rate of 18sccm was introduced, wherein the volume of hydrogen was 3% of the volume of argon. The catalyst was reduced by the generated plasma at 200℃ and 300Pa for 1.5h to obtain a 0.060wt% gold-supported copper-based radio frequency plasma-assisted ammonia synthesis catalyst.

[0046] (3) Radio frequency plasma-assisted ammonia synthesis: Before the reaction begins, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor. The quartz reaction tube is first evacuated (about 50 Pa) using a vacuum pump. Then, the quartz reaction tube is repeatedly cleaned with a nitrogen-hydrogen mixed reaction gas (nitrogen-hydrogen volume ratio of 1:3) to remove impurity gases. Then, nitrogen-hydrogen reaction gas (nitrogen-hydrogen volume ratio of 1:3) is introduced, and the flow rate is set to 18 sccm. The system pressure is 300 Pa when it is stable. A glass cold trap is added to the tail end of the quartz reaction tube and placed in a liquid nitrogen Dewar flask to collect the ammonia product by freezing. When the temperature near the copper-based radio frequency plasma-assisted ammonia synthesis catalyst rises to 200℃, the radio frequency power supply is started to generate plasma. At this time, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is completely covered by the generated plasma. The ammonia synthesis reaction time is 1 h. After the reaction was complete, dilute sulfuric acid solution was introduced into a glass cold trap to react with the ammonia product, generating ammonium ions. The amount of ammonium ions in the solution was determined by titration colorimetry and ion chromatography, and then converted into the ammonia outlet volume percentage to measure the ammonia production rate. The results showed that the ammonia outlet volume percentage could reach 1.88%.

[0047] Example 6: Preparation and Application of Copper-Based Radio Frequency Plasma-Assisted Ammonia Synthesis Catalyst

[0048] (1) The pretreatment of the copper mesh is the same as in Example 2.

[0049] (2) Preparation of high-loaded gold (0.120wt%) catalyst: A chloroauric acid solution containing 0.96 mg of gold was measured and added dropwise to the solution in step (1). After reacting at 20℃ for 1.5 h, the copper mesh support was removed, washed, and dried to obtain a copper-based black catalyst precursor. The catalyst precursor was then placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor, located 5 cm from the end of the radio frequency coil. A hydrogen-argon mixture with a flow rate of 18 sccm was introduced, wherein the volume of hydrogen was 3% of the volume of argon. The catalyst was reduced by the generated plasma at 200℃ and 300 Pa for 1.5 h to obtain a 0.120wt% gold-loaded copper-based radio frequency plasma-assisted ammonia synthesis catalyst.

[0050] (3) Radio frequency plasma-assisted ammonia synthesis: Before the reaction begins, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor. The quartz reaction tube is first evacuated (about 50 Pa) using a vacuum pump. Then, the quartz reaction tube is repeatedly cleaned with a nitrogen-hydrogen mixed reaction gas (nitrogen-hydrogen volume ratio of 1:3) to remove impurity gases. Then, nitrogen-hydrogen reaction gas (nitrogen-hydrogen volume ratio of 1:3) is introduced, and the flow rate is set to 18 sccm. The system pressure is 300 Pa when it is stable. A glass cold trap is added to the tail end of the quartz reaction tube and placed in a liquid nitrogen Dewar flask to collect the ammonia product by freezing. When the temperature near the copper-based radio frequency plasma-assisted ammonia synthesis catalyst rises to 200℃, the radio frequency power supply is started to generate plasma. At this time, the copper-based radio frequency plasma-assisted ammonia synthesis catalyst is completely covered by the generated plasma. The ammonia synthesis reaction time is 1 h. After the reaction was complete, dilute sulfuric acid solution was introduced into a glass cold trap to react with the ammonia product, generating ammonium ions. The amount of ammonium ions in the solution was determined by titration colorimetry and ion chromatography, and then converted into the ammonia outlet volume percentage to measure the ammonia production rate. The results showed that the ammonia outlet volume percentage could reach 2.24%.

[0051] The above examples demonstrate that the prepared copper-based radio frequency plasma-assisted ammonia synthesis catalyst has high catalytic activity and can efficiently catalyze the reaction of nitrogen and hydrogen to synthesize ammonia under radio frequency plasma assistance.

Claims

1. A method for preparing a copper-based radio frequency plasma-assisted ammonia synthesis catalyst, comprising the following steps: (1) The pure copper carrier was washed with organic solvent and pure water in sequence, and then the washed copper carrier was placed in pure water; (2) Weigh the active metal precursor to prepare an aqueous solution, and then add it dropwise to the system in step (1). Stir the reaction magnetically at 20~70 °C for 0.5~3 h. Wash and dry the obtained copper support to obtain the copper-based catalyst precursor; the mass of the active metal in the active metal precursor is 0.006~0.120% of the mass of the copper support. (3) The copper-based catalyst precursor obtained in step (2) is placed in the quartz reaction tube of the non-thermal radio frequency plasma reactor and a hydrogen-argon mixture with a flow rate of 5-50 sccm is introduced, wherein the volume of hydrogen is 1-5% of the volume of argon; at 100-200℃ and 250 Pa-1000 Pa, the generated plasma is used for reduction treatment for 0.5-2 h to obtain the copper-based radio frequency plasma-assisted ammonia synthesis catalyst.

2. A process for the preparation of a copper-based RF-PA synthesis catalyst as claimed in claim 1, characterized in that: The pure copper carrier in step (1) is copper wire, copper foam, copper mesh or copper foil, with a length of 5~20 cm and a width or diameter of no more than 4 cm; the organic solvent is ethyl acetate, acetone and anhydrous ethanol.

3. The method of making a copper-based RF-PA ammonia synthesis catalyst of claim 1, wherein: The active metal precursor in step (2) is one or more of copper chloride, silver nitrate, sodium chloropalladium, chloroauric acid, and ruthenium chloride.

4. The preparation method of a copper-based radio frequency plasma-assisted ammonia synthesis catalyst as described in claim 1, characterized in that: The non-thermal radio frequency plasma reactor in step (3) consists of a quartz reaction tube, a radio frequency coil, and a radio frequency power supply. The quartz reaction tube and the radio frequency coil are coaxially arranged, and the radio frequency coil is connected to the radio frequency power supply. Under the action of the radio frequency power supply, the radio frequency coil generates a high-frequency electromagnetic field. The argon and hydrogen mixture introduced into the quartz reaction tube generates plasma under the action of the high-frequency electromagnetic field.

5. The preparation method of a copper-based radio frequency plasma-assisted ammonia synthesis catalyst as described in claim 4, characterized in that: The RF coil is made of 20-30 turns of copper wire with a diameter of 0.6 cm, the coil diameter is 8-12 cm, and the axial length of the coil is 20-30 cm; the RF power input power is 20-200 W, and the frequency is 13.56 MHz; The diameter of the quartz reaction tube is 4-6 cm and the length is 55-65 cm.

6. A copper-based radio frequency plasma-assisted ammonia synthesis catalyst, characterized in that: It is prepared by the method described in any one of claims 1 to 5.

7. The application of the copper-based radio frequency plasma-assisted ammonia synthesis catalyst according to claim 6 in the synthesis of ammonia from a nitrogen-hydrogen mixture under low temperature and low pressure radio frequency plasma-assisted conditions.

8. The application of the copper-based radio frequency plasma-assisted ammonia synthesis catalyst as described in claim 7 in the catalytic reaction of a nitrogen-hydrogen mixture to synthesize ammonia, characterized in that: The low temperature range is 20 ℃~200 ℃, the low pressure range is 250Pa~1000 Pa; the flow rate of the nitrogen-hydrogen mixture is 10~100 sccm, the volume ratio of nitrogen to hydrogen is 1:2~4, and the reaction time is 0.5~5 h.

Images