WO2021077730A1 - Nitrogen fixation device and method using low-temperature jet flow plasma coupled with monatomic catalysis - Google Patents

Abstract

Disclosed are a nitrogen fixation device and method using low-temperature jet flow plasma coupled with monatomic catalysis. The nitrogen fixation device comprises an electrochemical workstation, a plasma power supply, an H-type electrolytic cell and a jet flow plasma reactor. The method involves firstly preparing a transition metal monatomic catalyst, and thus preparing a working electrode of the H-type electrolytic cell; directly introducing air, nitrogen, or a mixed gas of oxygen and nitrogen into the jet flow plasma reactor, turning on the plasma power supply to achieve a stable discharge of jet flow plasma, and after the jet flow plasma reactor is discharged for 10 minutes, turning off the plasma power supply; and transferring the reaction liquid after discharge into the H-type electrolytic cell, finally turning on the electrochemical workstation to perform an electrochemical catalytic process for 30 min, and collecting a solution containing NH₄ ⁺ after the reaction in the H-type electrolytic cell. The present invention is high in efficiency and environmentally friendly, and combines plasma discharge and an electrochemical catalytic reaction, wherein a monatomic catalyst is beneficial to the improvement of the yield and reaction rate of ammonia synthesis.

Description

Low-temperature jet plasma coupling single atom catalysis nitrogen fixing device and method Technical field

The invention belongs to the technical fields of low-temperature jet plasma activation catalysis and single-atom catalysts in the synthesis of ammonia and energy storage, and particularly relates to a method that uses low-temperature jet plasma to activate air, nitrogen, and water, and couples single-atom electrocatalysis to achieve online/offline distributed Technical methods for the synthesis of ammonia, nitric acid, nitrogen oxides and other chemicals.

Background technique

Nitrogen fixation refers to the conversion of abundant nitrogen molecules in the atmosphere into nitrogen-containing compounds (such as ammonia, nitrate, nitrogen dioxide, etc.). It is one of the most basic biochemical reactions in nature, maintaining the global nitrogen cycle and the survival of plants and animals. . The free nitrogen in nature has a stable electronic structure (N≡N,948kJ/mol), which is difficult to be used directly. It can only fix nitrogen through the nitrogen fixation of a few microorganisms and the high-energy action of lightning. However, the population explosion and the rapid development of industry and agriculture in the past 100 years have sharply spawned the demand for nitrogen fixation, thus driving the continuous innovation of artificial nitrogen fixation technology. At present, the mainstream industrial nitrogen fixation technology is still the Haber process developed in the last century.

It accounts for about 40% of the total amount of artificial nitrogen fixation; its nitrogen fixed in the form of ammonia is widely used in agriculture, animal husbandry, chemical and pharmaceutical industries, and meets the nitrogen demand of 40% of the world's population. However, this technology uses high-purity hydrogen as a raw material, and requires harsh catalytic conditions (450-600°C, 148-350 atm) to achieve nitrogen fixation. The huge energy consumption and serious environmental pollution have caused it to be controversial. According to statistics, the Haber process directly consumes nearly 1 to 2% of the world’s energy and nearly 3 to 5% of natural gas, and emits nearly 300 million tons of CO2 (about 3% of the total global CO2 emissions). The large amount of wastewater with high ammonia nitrogen and poor biodegradability produced in the process is extremely difficult to dispose of. Therefore, with the increasingly prominent energy and environmental issues and the rapid increase in nitrogen demand today, the development of alternative low-carbon, high-efficiency, and clean new artificial nitrogen fixation technologies is urgently needed. The electrochemically catalyzed nitrogen reduction (NRR) ammonia synthesis technology is inspired by the participation of protons and electrons in biological enzymes in the nitrogen fixation reaction. It uses cheap nitrogen (air) and water as raw materials. The electrode voltage can be flexibly controlled to achieve normal temperature and pressure. Nitrogen fixation has gradually become a research hotspot in the field of nitrogen fixation. Compared with the Haber process, which has complex facilities, severe reaction conditions, and huge energy consumption pollution, electrocatalytic ammonia synthesis technology is more flexible and convenient, and can be compatible with local renewable energy sources (including intermittent energy such as wind, solar, and tidal energy) according to local conditions The power supply to realize the miniaturization and distributed new nitrogen fixation concept, to provide clean nitrogen fixation guarantee for remote and backward areas or developing countries that do not have the basis for the application of synthetic ammonia industry.

At present, only a few transition metals, transition metal oxides, carbon materials and enzyme catalysts have been used in the research of ammonia synthesis reaction, but the effect is not satisfactory. In recent years, the development of "single-atom catalysts" has been proposed. With the characteristics of "isolated active sites", "unsaturated coordination environment" and "100% metal atom utilization", it has been used in many fields such as _{electrolysis of water, fuel cells, CO 2 reduction, etc.} Significant results have been achieved, so it can provide new options for the field of nitrogen fixation with new high-efficiency electrocatalysis. However, the hydrogen evolution potential and nitrogen reduction potential in conventional aqueous systems are very close. Hydrogen evolution as a competitive reaction will seriously affect the efficiency of electrocatalytic ammonia synthesis. It is also a key technical difficulty that restricts the industrialization of electrocatalytic nitrogen fixation. Plasma is divided into high-temperature plasma and low-temperature plasma. Low-temperature plasma generally refers to plasma with a macroscopic temperature below 100,000K. Low-temperature plasma technology is well compatible with new energy sources such as solar energy and wind energy, and can be efficiently activated under normal temperature and pressure conditions. Nitrogen molecules in the air realize nitrogen fixation. Low-temperature plasma, as another potential nitrogen fixation technology, can rely on vibrationally excited nitrogen molecules, free radicals and other active nitrogen-containing ions to significantly optimize the catalytic environment and interaction mechanism on the electrocatalyst surface, reduce the N ₂ activation energy, and strengthen Single atom electrocatalytic nitrogen fixation effect. At the same time, the low-temperature plasma can react with the electrocatalytic nitrogen fixation by-products hydrogen, water, etc., to form activated water rich in reactive nitrogen, oxygen and other components as a new type of electrolyte, and use ammonia, nitric acid and ammonium nitrate (NH ₃ +HNO ₃ → NH ₄ NO ₃ ) realizes secondary nitrogen fixation, which improves the overall economy of the system.

Therefore, based on the overall consideration of the electrocatalytic nitrogen fixation reaction system (covering electrocatalysts, electrolytes, and corresponding electronic proton transfer and ion diffusion processes), innovatively develop and apply low-temperature plasma-based synergistic single-atom electrocatalytic coupling systems and equipment For nitrogen fixation, it can solve the problems of low yield of traditional electrocatalysis and difficult activation, and finally realize efficient, clean, distributed green nitrogen fixation, and improve the overall economic and social benefits of the new type of nitrogen fixation.

Summary of the invention

The purpose of the present invention is to solve the problems of low ammonia yield, poor selectivity, and high comprehensive cost in the existing electrocatalytic nitrogen fixation process in order to solve the problems of low ammonia yield, poor selectivity and high comprehensive cost in the existing electrocatalytic nitrogen fixation process. Jet plasma technology activates air, nitrogen and water to produce active electrolyte, and then single-atom catalytic active electrolyte is reduced to produce synthetic ammonia. This method has the advantages of simple process, high disposal efficiency, wide application range, flexible adjustability, high product value and high product value. Good compatibility with renewable energy.

The purpose of the present invention is achieved through the following technical solutions: a low-temperature jet plasma coupled single-atom catalyzed nitrogen fixation device, which includes an electrochemical workstation, a plasma power supply, an H-type electrolytic cell and a jet plasma reactor;

The electrochemical workstation includes a reference electrode clamp, a working electrode clamp, and a counter electrode clamp; the plasma power supply includes a power supply positive electrode and a power supply negative electrode;

The H-type electrolytic cell includes a first argon gas inlet, a first argon gas outlet, a proton exchange membrane, a second argon gas inlet, and a second argon gas outlet; the reference electrode and electrochemical cell of the H-type electrolytic cell The reference electrode clamp in the workstation is connected, the working electrode of the H-type electrolytic cell is connected with the working electrode clamp in the electrochemical workstation, and the counter electrode of the H-type electrolytic cell is connected with the counter electrode in the electrochemical workstation. Clip phase connection to form a loop of electrocatalytic process;

The jet plasma reactor includes an inner electrode, an outer electrode, and a gas channel. The inner electrode is connected to the positive electrode of the plasma power source, and the outer electrode is connected to the negative electrode of the plasma power source. The gas channel is used for communication. Enter the gas to discharge the jet plasma in the jet plasma reactor;

The proton exchange membrane is between the two H-type electrolytic cells to prevent gas diffusion from affecting the progress of the positive and negative reactions.

A low-temperature jet plasma coupled single-atom catalysis nitrogen fixation method. The nitrogen fixation method is an off-line operation mode and includes the following steps:

(1) The precursor of the transition metal catalyst is calcined at a high temperature in a tube furnace at a calcination temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare the transition metal monoatomic catalyst. The precursor of the transition metal catalyst includes Cu, Fe, Ni, Co metal particles grown on a carbon substrate;

(2) After mixing the transition metal monoatomic catalyst prepared in step (1), the naphthol solution with a mass fraction of 5% and anhydrous ethanol, brush on carbon paper and dry to obtain the working electrode of the H-type electrolytic cell , Wherein the volume ratio of naphthol solution and absolute ethanol is 7:10000, and the loading amount of transition metal monoatomic catalyst is 0.57mg/cm ² ～0.86mg/cm ² ;

(3) Directly pass air, nitrogen or a mixed gas of oxygen and nitrogen into the incident flow plasma reactor; and use a mass flow meter to adjust the flow rate and proportion of the gas entering the jet plasma reactor. The oxygen in the oxygen and nitrogen mixed gas is The volume ratio with nitrogen is 4:6～1:9; the gas flow rate is adjusted to 4L/min～8L/min; the plasma power is turned on, and the plasma power is used to adjust the power input to both ends of the jet plasma reactor to achieve jet plasma Stable discharge, adjust the distance between the discharge end of the jet plasma reactor and the liquid surface in the reaction vessel between 1cm-5cm; turn off the plasma power supply after 10 minutes of discharge in the jet plasma reactor;

(4) Transfer 50ml of the reaction solution after discharge into the two reaction cells of the H-shaped electrolytic cell, and pass argon into the electrolyte in the H-shaped electrolytic cell through the first argon inlet and the second argon inlet at the same time Argon gas to achieve deoxygenation; argon gas flows out from the first argon gas outlet and the second argon gas outlet;

(5) After the electrochemical workstation is turned on, the CV stabilizes the current and performs an electrochemical catalysis process at different applied voltages (1.1V-1.6V) for 30 minutes, and collects the reacted NH ₄ ⁺ solution in the H-type electrolytic cell.

Further, the nitrogen fixation method is an online operation mode; in the online operation mode, the jet plasma reactor is fixed in the H-type electrolytic cell, and the discharge end directly reacts with the solution in the H-type electrolytic cell; H- After the working electrode of the type electrolytic cell, adjust the parameters to be consistent with the offline operation, and turn on the plasma power supply and electrochemical workstation at the same time, and perform denutrition. The oxygen removal method is consistent with offline operation. The working time of the plasma power supply and electrochemical workstation In addition, the voltage applied by the electrochemical workstation is consistent with the offline operation to realize the ammonia synthesis reaction, and collect the NH ₄ ⁺ -containing solution after the reaction in the H-type electrolytic cell.

Further, during the operation, the gas products of the H-type electrolytic cell are collected, and the concentration of the gaseous nitrogen fixation products produced is analyzed and tested by gas chromatography;

_{Further, take 4 ml of the NH 4} ⁺ solution after reaction in the H-type electrolytic cell, add the indophenol blue coloring solution and let it stand for two hours to obtain green solutions of different depths; the results are obtained by UV-spectrophotometer test Solution, obtain the yield of synthetic ammonia.

The beneficial effects of the present invention:

(1) High efficiency; using the characteristics of high energy density and uniform energy distribution of low-temperature plasma, it can effectively activate air, nitrogen, and oxygen, break the corresponding chemical bonds, and form relatively simple free radicals, which can be used for subsequent electrochemistry. Catalytic synthesis of ammonia provides required raw materials. The single-atom catalyst has high catalytic utilization and selectivity, which is beneficial to increase the yield and reaction rate of synthetic ammonia.

(2) The value of the product is high; compared with the traditional ammonia synthesis reaction, the present invention can also produce high concentration nitrogen oxides based on plasma activation, which can also be used as a chemical product through collection; in addition, there is high purity oxygen at the anode of the electrolytic cell Produced are all conducive to improving the overall economy.

(3) Environmentally friendly; the combined mode of electrochemistry and plasma discharge provides a very high energy density, and its products are mainly nitrogen-containing compounds, all of which have high utility value, and the overall system is comparable to the traditional Hubble Compared with synthetic ammonia, it is green and environmentally friendly; there is no emission of carbon dioxide and other greenhouse gases.

(4) Strong tunability; each reaction parameter under this method, including plasma discharge power, gas flow, electrode applied potential, etc., can be flexibly adjusted. It can achieve the target results by flexibly changing the operating conditions for different components, different disposal amounts, target products and other conditions.

(5) The design of the device is reasonable; the device integrates the characteristics of a jet low-temperature plasma reaction device and an electrochemical electrolysis device, and combines the advantages of high power density of plasma equipment, strong processing capacity, strong selectivity of electrochemical equipment, and high product purity. The advantages of low energy consumption, easy control, flexible adjustment, and outstanding effects.

Description of the drawings

Figure 1 is a diagram of an apparatus for coupling monoatomic electrocatalytic nitrogen fixation using low-temperature plasma jets in offline mode;

Figure 2 is a diagram of an apparatus for coupling monoatomic electrocatalytic nitrogen fixation using low-temperature plasma jets in online mode;

Figure 3 is the standard curve of the experiment for calculating the yield of synthetic ammonia;

In the figure: 1. Electrochemical platform; 2. Plasma power supply; 3. Reference electrode; 4. Working electrode; 5. Counter electrode; 6. H-type electrolytic cell; 7. First argon inlet; 8. Section An argon outlet; 9. Proton exchange membrane; 10. The second argon inlet; 11. The second argon outlet; 12. Power supply positive electrode; 13. Power supply negative electrode; 14. Jet plasma reactor.

Detailed ways

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

The invention utilizes the principle of low-temperature plasma jet coupling single-atom electrocatalytic nitrogen fixation. The jet low-temperature plasma generates abundant ions, electrons, active molecules, free radicals, etc., which can activate molecules such as air, nitrogen, water, and oxygen, and pass them The collision and dissociation between them breaks chemical bonds such as OO, H-OH, NN, etc., forming raw materials required for electrocatalysis. In the potential range applied by the electrochemical platform, the active electrolyte formed by the plasma will be converted into synthetic ammonia.

As shown in Figure 1, a low-temperature jet plasma coupled single-atom catalysis nitrogen fixation device, the device includes an electrochemical workstation 1, a plasma power source 2, an H-type electrolytic cell 6 and a jet plasma reactor 14;

The electrochemical workstation 1 includes a reference electrode clamp 3, a working electrode clamp 4, and a counter electrode clamp 5; the plasma power source 2 includes a power supply positive electrode 12 and a power supply negative electrode 13;

The H-shaped electrolytic cell 6 includes a first argon gas inlet 7, a first argon gas outlet 8, a proton exchange membrane 9, a second argon gas inlet 10, and a second argon gas outlet 11; the H-shaped electrolytic cell 6 The reference electrode is connected to the reference electrode clamp 3 in the electrochemical workstation 1, the working electrode of the H-type electrolytic cell 6 is connected to the working electrode clamp 4 in the electrochemical workstation 1, and the H-type electrolytic cell The counter electrode of the cell 6 is connected with the counter electrode clamp 5 in the electrochemical workstation 1 to form a loop of the electrocatalytic process;

The jet plasma reactor 14 includes an inner electrode, an outer electrode, and a gas channel. The inner electrode is connected to the positive electrode 12 of the plasma power source 2 and the outer electrode is connected to the negative electrode 13 of the plasma power source 2; The gas channel is used to pass in gas to discharge the jet plasma in the jet plasma reactor 14;

The proton exchange membrane 9 is between the two H-type electrolytic cells 6 to prevent gas diffusion from affecting the progress of the positive and negative reactions.

A low-temperature jet plasma coupled single-atom catalysis nitrogen fixation method, the nitrogen fixation method is an off-line operation mode, and includes the following steps:

(1) The precursor of the transition metal catalyst is calcined at a high temperature in a tube furnace at a calcination temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare the transition metal monoatomic catalyst. The precursor of the transition metal catalyst includes Cu, Fe, Ni, Co metal particles grown on a carbon substrate;

(2) After mixing the transition metal monoatom catalyst prepared in step (1), the naphthol solution with a mass fraction of 5% and absolute ethanol, brush on carbon paper and dry to obtain the work of the H-type electrolytic cell 6 An electrode, wherein the volume ratio of the naphthol solution and the absolute ethanol is 7:10000, and the loading amount of the transition metal monoatomic catalyst is 0.57 mg/cm ² to 0.86 mg/cm ² ;

(3) Directly pass air, nitrogen, or a mixed gas of oxygen and nitrogen into the incident flow plasma reactor 14; and use a mass flow meter to adjust the flow rate and proportion of the gas entering the jet plasma reactor 14. The oxygen and nitrogen mixed gas The volume ratio of oxygen and nitrogen is 4:6～1:9; the gas flow rate is adjusted to 4L/min～8L/min; the plasma power supply 2 is turned on, and the plasma power supply 2 is used to adjust the power input to both ends of the jet plasma reactor 14 , To realize the stable discharge of the jet plasma, adjust the distance between the discharge end of the jet plasma reactor 14 and the liquid surface in the reaction vessel between 1cm-5cm; after the jet plasma reactor 14 discharges for 10 minutes, turn off the plasma power supply 2 ；

(4) Transfer 50ml of the reaction solution after discharge into the two reaction cells of the H-shaped electrolytic cell 6, and at the same time pass through the first argon gas inlet 7 and the second argon gas inlet 10 to the electrolyte in the H-shaped electrolytic cell 6 Argon gas is passed through to achieve deoxygenation; argon gas flows out from the first argon gas outlet 8 and the second argon gas outlet 11;

(5) After the electrochemical workstation 1 is turned on, the CV stabilizes the current, and the electrochemical catalysis process is carried out at different applied voltages (1.1V-1.6V) for 30 minutes to collect the reacted NH ₄ ⁺ solution in the H-type electrolytic cell 6 .

As shown in Figure 2, a low-temperature jet plasma coupled single atom catalysis nitrogen fixation method also has an online operation mode; in the online operation mode, the jet plasma reactor 14 is fixed in the H-type electrolytic cell 6, and the discharge end Directly react with the solution in the H-type electrolytic cell 6; after the working electrode of the H-type electrolytic cell 6 is prepared, and adjust the parameters to be consistent with the offline operation, turn on the plasma power supply 2 and electrochemical workstation 1 at the same time, and perform the removal The maintenance and removal methods are the same as offline operation. The working hours of plasma power supply 2 and electrochemical workstation 1 and the voltage applied by electrochemical workstation 1 are consistent with offline operation to realize the synthesis of ammonia reaction and collect the H-type electrolytic cell 6 The reacted solution _{contains NH 4} ^+.

During offline or online operation, collect the gas products of the H-type electrolytic cell 6, and use gas chromatography to analyze and test the concentration of the gaseous nitrogen fixation products produced;

_{Take 4ml of the NH 4} ⁺ solution after the reaction in the H-type electrolytic cell 6, add the indophenol blue coloring solution and let it stand for two hours to obtain green solutions of different depths; use the UV-spectrophotometer to test the obtained solution, The yield of synthetic ammonia is obtained.

In the existing methods for obtaining synthetic ammonia through electrocatalysis by preparing a single-atom catalyst, the resulting synthetic ammonia yield is very small. The method of the present invention can greatly increase the yield of electrocatalytic ammonia synthesis. A comparative example and the present invention are given below.的实施例。 Example.

Comparative example 1

First dissolve 144mg of glucose (C6H12O6) in 40ml of absolute ethanol, then 40ml of metal salt solution, including 7.75mg of ammonium molybdate ((NH4)6Mo7O24) and 690mg of hydroxylamine hydrochloride ((NH3OH)Cl), Add dropwise to the previous mixed solution, then stir at 70°C for 16 hours to evaporate the alcohol and water in the solution, and grind the final product into a powder.

Then, the obtained powder was placed in a crucible and heated to 650° C. at a heating rate of 5° C./min under an argon atmosphere and kept for four hours to obtain a monoatomic Mo catalyst SA-Mo/NPC.

Finally, the monoatomic Mo catalyst SA-Mo/NPC was painted on a carbon cloth as a working electrode for the electrocatalytic reaction of nitrogen fixation, and the resulting synthetic ammonia yield was 34 μg/h.

Example 1-5

A tube furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcining temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare a Co monoatomic catalyst. The prepared Co single-atom catalyst with a load of 0.7 mg/cm ² , 0.7 μL of DuPont D520 (5% wt) nafion solution and 1 mL of absolute ethanol were dropped on the carbon paper and dried to prepare an H-type electrolytic cell 6 Working electrode;

Take 160ml of 0.1M KOH into the reaction vessel, place the reaction vessel on a magnetic stirrer, set the speed to 240rpm, and adjust the distance between the discharge end of the jet plasma reactor 14 and the reaction liquid surface in the reaction vessel to 1, 2, 3, 4, 5cm, connect the positive pole 12 of the plasma power supply 2 and the negative pole 13 of the power supply to the jet plasma reactor 14, pass air into the jet plasma reactor 14, and adjust the flow to 7L/min through the mass flow controller, and turn it on Plasma power supply 2, adjust the voltage to 10KV, that is, plasma liquid surface discharge reaction occurs, and the reaction time is 10min;

After the reaction is over, transfer 50ml of the discharged reaction solution into the two reaction cells of the H-type electrolytic cell 6 respectively; combine the prepared working electrode, silver chloride electrode and platinum electrode with the electrochemical workstation 1 The working electrode clamp 4, the reference electrode clamp 3 and the counter electrode clamp 5 are connected. After the CV stabilizes the loop current, a voltage of 1.3V is applied for electrochemical catalytic reaction. After half an hour of reaction, the reaction solution is absorbed 4ml and the indophenol blue developer After mixing and standing for 2 hours, the standard curve of synthetic ammonia yield calculated according to the experiment shown in Figure 3 (the abscissa is x represents the _{concentration of NH 4} ⁺ , the ordinate is y represents the absorbance, and R is the linear correlation of the fitted curve ℃), use an ultraviolet spectrophotometer to detect the concentration _{of NH 4} ^{+ in the reaction solution.}

The following table shows the comparison data of the response effect of different discharge distances:

It can be seen from the results of the examples that the smaller the discharge distance, the more thorough the treatment of the liquid surface, and the higher the yield. Even if the discharge distance is 5 cm, the resulting synthetic ammonia yield is close to twice that of the comparative example.

Example 6-10

A tube furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcining temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare a Co monoatomic catalyst. The prepared Co single-atom catalyst with a load of 0.7 mg/cm ² , 0.7 μL of DuPont D520 (5% wt) nafion solution and 1 mL of absolute ethanol were dropped on the carbon paper and dried to prepare an H-type electrolytic cell 6 Working electrode;

Take 160ml of 0.1M KOH into the reaction vessel, place the reaction vessel on a magnetic stirrer, set the speed to 240rpm, adjust the distance between the discharge end of the jet plasma reactor 14 and the reaction liquid surface in the reaction vessel to 1cm, and set the plasma power supply 2 The positive pole 12 of the power supply and the negative pole 13 of the power supply 13 are connected to the jet plasma reactor 14, and air is introduced into the jet plasma reactor 14 and the flow is adjusted to 4, 5, 6, 7, 8 L/min through the mass flow control meter, and then turned on. Plasma power supply 2, adjust the voltage to 10KV, that is, plasma liquid surface discharge reaction occurs, and the reaction time is 10min;

After the reaction is over, transfer 50ml of the discharged reaction solution into the two reaction cells of the H-type electrolytic cell 6 respectively; combine the prepared working electrode, silver chloride electrode and platinum electrode with the electrochemical workstation 1 The working electrode clamp 4, the reference electrode clamp 3 and the counter electrode clamp 5 are connected. After the CV stabilizes the loop current, a voltage of 1.3V is applied for electrochemical catalytic reaction. After half an hour of reaction, the reaction solution is absorbed 4ml and the indophenol blue developer After mixing and standing for 2 hours, the standard curve of synthetic ammonia yield calculated according to the experiment shown in Figure 3 (the abscissa is x represents the _{concentration of NH 4} ⁺ , the ordinate is y represents the absorbance, and R is the linear correlation of the fitted curve ℃), use an ultraviolet spectrophotometer to detect the concentration _{of NH 4} ^{+ in the reaction solution.}

The following table shows the comparison data of the reaction effect of different air flow rates:

It can be seen from the results of the examples that the effect is best when the gas flow rate is 7L/min. This result is mainly because the gas flow rate will affect the discharge effect of the plasma reactor. A larger gas flow rate will push the plasma arc outwards, thus The area of the discharge area is increased, and when the gas flow is further increased, the gas will take away a large amount of energy, and the area of the discharge area will be reduced, so that the discharge effect will be reduced.

Examples 11-15

A tube furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcining temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare a Co monoatomic catalyst. The prepared Co single-atom catalyst with a load of 0.7 mg/cm ² , 0.7 μL of DuPont D520 (5% wt) nafion solution and 1 mL of absolute ethanol were dropped on the carbon paper and dried to prepare an H-type electrolytic cell 6 Working electrode;

Take 160ml of 0.1M KOH into the reaction vessel, place the reaction vessel on a magnetic stirrer, set the rotation speed to 240rpm, adjust the distance between the discharge end of the jet plasma reactor 14 and the reaction liquid surface in the reaction vessel to 1cm, and set the plasma power supply 2 The positive pole 12 and negative pole 13 of the power supply are connected to the jet plasma reactor 14, and the jet plasma reactor 14 is fed with pure nitrogen, air, N ₂ ：O ₂ ＝9:1, N ₂ ：O ₂ ＝7:3 , N ₂ ：O ₂ ＝6:4 and adjust the total flow to 7L/min through the mass flow control meter, turn on the plasma power supply 2, and adjust the voltage to 10KV, that is, plasma surface discharge reaction occurs, and the reaction time is 10min;

After the reaction is over, transfer 50ml of the discharged reaction solution into the two reaction cells of the H-type electrolytic cell 6 respectively; combine the prepared working electrode, silver chloride electrode and platinum electrode with the electrochemical workstation 1 The working electrode clamp 4, the reference electrode clamp 3 and the counter electrode clamp 5 are connected. After the CV stabilizes the loop current, a voltage of 1.3V is applied to carry out the electrochemical catalytic reaction. After half an hour of reaction, the reaction solution is absorbed 4ml and the indophenol blue developer After mixing and standing for 2 hours, the standard curve of synthetic ammonia yield calculated according to the experiment shown in Figure 3 (the abscissa is x represents the _{concentration of NH 4} ⁺ , the ordinate is y represents the absorbance, and R is the linear correlation of the fitted curve ℃), use an ultraviolet spectrophotometer to detect the concentration _{of NH 4} ^{+ in the reaction solution.}

The following table shows the comparison data of the reaction effect of different gas ratios:

According to the experimental results, when oxygen is involved in the plasma discharge, the yield of synthetic ammonia is higher. This is because oxygen can increase the concentration of nitrite in the solution after the reaction. The source of nitrogen in synthetic ammonia is mainly nitrite. .

Examples 16-19

A tubular furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcination temperature of 800 degrees, and ammonia gas is introduced into the tubular furnace to prepare different transition metal monoatomic catalysts. The prepared Cu different loading 0.7mg / cm ² of, Fe, Ni, Co monatomic catalyst, 0.7μL DuPont D520 (5% wt) nafion solution dropwise 1mL of anhydrous ethanol in carbon paper, and drying to obtain Working electrode of H-type electrolytic cell 6;

Take 160ml of 0.1M KOH into the reaction vessel, place the reaction vessel on a magnetic stirrer, set the speed to 240rpm, adjust the distance between the discharge end of the jet plasma reactor 14 and the reaction liquid surface in the reaction vessel to 1cm, and set the plasma power supply 2 The positive pole 12 of the power supply and the negative pole 13 of the power supply are connected to the jet plasma reactor 14, and air is introduced into the jet plasma reactor 14 and the flow rate is adjusted to 7L/min through the mass flow control meter. The plasma power supply is turned on and the voltage is adjusted to 10KV. , That is, plasma liquid surface discharge reaction occurs, and the reaction time is 10 minutes;

After the reaction is over, transfer 50ml of the discharged reaction solution into the two reaction cells of the H-type electrolytic cell 6 respectively; combine the prepared working electrode, silver chloride electrode and platinum electrode with the electrochemical workstation 1 The working electrode clamp 4, the reference electrode clamp 3 and the counter electrode clamp 5 are connected. After the CV stabilizes the loop current, a voltage of 1.3V is applied for electrochemical catalytic reaction. After half an hour of reaction, the reaction solution is absorbed 4ml and the indophenol blue developer After mixing and standing for 2 hours, according to the standard curve calculated for the synthetic ammonia yield in the experiment shown in Figure 3 (the abscissa is the _{concentration of NH 4} ⁺ , the ordinate is the absorbance), the NH ₄ ^{+ in the reaction solution is detected by an ultraviolet spectrophotometer.} concentration.

The following table shows the comparison data of the reaction effects of different transition metal single-atom catalysts:

According to the results of the examples, it can be known that using Co atoms to prepare the working electrode has a higher yield of synthetic ammonia.

Examples 20-25

A tube furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcining temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare a Co monoatomic catalyst. The prepared Co single-atom catalysts with different loadings of 0.7 mg/cm ² , 0.7 μL of DuPont D520 (5% wt) nafion solution and 1 mL of absolute ethanol were dropped on the carbon paper and dried to prepare an H-type electrolytic cell 6 Working electrode;

Take 160ml of 0.1M KOH into the reaction vessel, place the reaction vessel on a magnetic stirrer, set the speed to 240rpm, adjust the distance between the discharge end of the jet plasma reactor 14 and the reaction liquid surface in the reaction vessel to 1cm, and set the plasma power supply 2 The positive pole 12 of the power supply and the negative pole 13 of the power supply are connected to the jet plasma reactor 14, and air is introduced into the jet plasma reactor 14 and the flow is adjusted to 7L/min through the mass flow control meter. The power is turned on and the voltage is adjusted to 10KV, namely The plasma liquid surface discharge reaction occurs, and the reaction time is 10 minutes;

After the reaction is over, transfer 50ml of the discharged reaction solution into the two reaction cells of the H-type electrolytic cell 6 respectively; combine the prepared working electrode, silver chloride electrode and platinum electrode with the electrochemical workstation 1 The working electrode clamp 4, the reference electrode clamp 3 and the counter electrode clamp 5 are connected. After the CV stabilizes the loop current, different voltages (1.1V-1.6V) are applied to carry out the electrochemical catalytic reaction. After half an hour of reaction, the reaction solution is absorbed 4ml and The indophenol blue developer was mixed, and after standing for 2 hours, the standard curve for the yield of synthetic ammonia was calculated according to the experiment shown in Figure 3 (the abscissa is x represents the _{concentration of NH 4} ⁺ , the ordinate is y represents the absorbance, and R is the The linear correlation degree of the fitted curve), and the NH ₄ ⁺ concentration in the reaction solution was detected with an ultraviolet spectrophotometer.

The following table is the comparison data of the reaction effect of different applied potentials in the electrocatalytic process:

According to the results of the examples, it can be seen that the overall trend of the yield of synthetic ammonia increases with the increase of the electrocatalytic applied potential.

Examples 26-28

A tube furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcining temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare a Co monoatomic catalyst. Different loading produced ^{0.57mg / cm 2, 0.7mg / cm} 2, 0.86mg / cm Co monoatomic catalyst ^2, 0.7μL DuPont D520 (5% wt) nafion solution and 1mL of anhydrous ethanol dropwise carbon paper On top, the working electrode of the H-shaped electrolytic cell 6 is obtained by drying;

Take 160ml of 0.1M KOH into the reaction vessel, place the reaction vessel on a magnetic stirrer, set the speed to 240rpm, adjust the distance between the discharge end of the jet plasma reactor 14 and the reaction liquid surface in the reaction vessel to 1cm, and set the plasma power supply 2 The positive electrode 12 of the power supply and the negative electrode 13 of the power supply are connected to the jet plasma reactor 14. Air is introduced into the jet plasma reactor 14 and the flow rate is adjusted to 7L/min through the mass flow control meter. The plasma power supply 2 is turned on and the voltage is adjusted to 10KV, that is, plasma liquid surface discharge reaction occurs, and the reaction time is 10min;

After the reaction is over, transfer 50ml of the discharged reaction solution into the two reaction cells of the H-type electrolytic cell 6 respectively; combine the prepared working electrode, silver chloride electrode and platinum electrode with the electrochemical workstation 1 The working electrode clamp 4, the reference electrode clamp 3 and the counter electrode clamp 5 are connected. After the CV stabilizes the loop current, a voltage of 1.3V is applied for electrochemical catalytic reaction. After half an hour of reaction, the reaction solution is absorbed 4ml and the indophenol blue developer After mixing and standing for 2 hours, the standard curve of synthetic ammonia yield calculated according to the experiment shown in Figure 3 (the abscissa is x represents the _{concentration of NH 4} ⁺ , the ordinate is y represents the absorbance, and R is the linear correlation of the fitted curve ℃), use an ultraviolet spectrophotometer to detect the concentration _{of NH 4} ^{+ in the reaction solution.}

The following table shows the comparison data of the reaction effect of different catalyst loadings:

According to the results of the examples, when the catalyst loading is 0.86 mg/cm ² , the yield of synthetic ammonia obtained is the highest.

By adopting the method of the present invention, the yield of obtained synthetic ammonia is much higher than the existing conventional yield of synthetic ammonia obtained by electrocatalysis.

Example 30

A tube furnace is used to calcinate the precursor of the transition metal catalyst at a high temperature with a calcining temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare a Co monoatomic catalyst. The prepared Co single-atom catalysts with different loadings of 0.7 mg/cm ² , 0.7 μL of DuPont D520 (5% wt) nafion solution and 1 mL of absolute ethanol were dropped on the carbon paper and dried to prepare an H-type electrolytic cell 6 Working electrode;

Take 50ml of 0.1M KOH solution into the two reaction cells of the H-shaped electrolytic cell, place the H-shaped electrolytic cell on a magnetic stirrer, set the speed to 240 rpm, and adjust the discharge end of the jet plasma reactor 14 to react with the H-shaped electrolytic cell. The distance of the liquid surface is 1cm, the power supply positive electrode 12 and the power supply negative electrode 13 of the plasma power supply 2 are connected to the jet plasma reactor 14, and air is introduced into the jet plasma reactor 14 and the flow rate is adjusted to 7L through the mass flow controller. /min, turn on the power supply, adjust the voltage to 10KV, and then the plasma level discharge reaction will occur. The reaction time can be adjusted within 5-30 minutes. At the same time as the plasma discharge reaction starts, turn on the electrochemical workstation to remove the prepared working electrode and chlorine. The silver electrode and the platinum sheet electrode are respectively connected to the working electrode holder 4, the reference electrode holder 3 and the counter electrode holder 5 of the electrochemical workstation 1. After the CV stabilizes the loop current, a voltage of 1.3V is applied to carry out the electrochemical catalytic reaction. After hours, 4 ml of the reaction solution was absorbed and mixed with the indophenol blue developer, and after standing for 2 hours, the NH ₄ ⁺ concentration in the reaction solution was detected by an ultraviolet spectrophotometer.

This mode is an online detection mode. Compared with the offline mode, this method can continuously provide nitrogen-containing substances by treating the liquid surface for a long time. At the same time, the two devices of the H-type electrolytic cell and the jet plasma reactor are combined in Together, the operation is more convenient and the control is more flexible.

The method of the present invention, while ammonia, along with the oxidation product prepared nitrogenase NO _x, and nitric acid. The two treatment processes of coupling low-temperature plasma and single-atom catalyst not only ensure the high-efficiency activation of nitrogen, but also ensure the selectivity of ammonia synthesis, and realize high-efficiency economy based on the production of oxidized nitrogen fixation products. Compared with the current synthetic ammonia effect, it has achieved a great improvement, and the current experimental equipment is continuously improved, and it is expected to achieve better results in the future.

The above-mentioned embodiments are used to explain the present invention, not to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall into the protection scope of the present invention.

Claims (6)

1. A low-temperature jet plasma coupled single-atom catalysis nitrogen fixing device, characterized in that the device includes an electrochemical workstation (1), a plasma power supply (2), an H-type electrolytic cell (6) and a jet plasma reactor ( 14);

   The electrochemical workstation (1) includes a reference electrode clamp (3), a working electrode clamp (4), a counter electrode clamp (5), etc.; the plasma power source (2) includes a positive electrode (12) and a negative electrode ( 13).

   The H-type electrolytic cell (6) includes a first argon gas inlet (7), a first argon gas outlet (8), a proton exchange membrane (9), a second argon gas inlet (10) and a second argon gas outlet (11) etc.; the reference electrode of the H-type electrolytic cell (6) is connected with the reference electrode clamp (3) in the electrochemical workstation (1), and the work of the H-type electrolytic cell (6) The electrode is connected with the working electrode clamp (4) in the electrochemical workstation (1), and the counter electrode of the H-type electrolytic cell (6) is connected with the counter electrode clamp (5) in the electrochemical workstation (1), Form the circuit of the electrocatalytic process.

   The jet plasma reactor (14) includes an inner electrode, an outer electrode, and a gas channel. The inner electrode is connected to the positive electrode (12) of the plasma power source (2), and the outer electrode is connected to the plasma power source (2). The negative electrode (13) of the power supply is connected; the gas channel is used to pass in gas to discharge the jet plasma in the jet plasma reactor (14).

   The proton exchange membrane (9) is between the two H-type electrolytic cells (6) to prevent gas diffusion from affecting the progress of the positive and negative reactions.
2. A low-temperature jet plasma coupled single-atom catalysis nitrogen fixation method is characterized in that the nitrogen fixation method is an offline operation mode and includes the following steps:

   (1) The precursor of the transition metal catalyst is calcined at a high temperature in a tube furnace at a calcination temperature of 800 degrees, and ammonia gas is introduced into the tube furnace to prepare the transition metal monoatomic catalyst. The precursor of the transition metal catalyst includes Cu, Fe, Ni, Co metal particles grown on a carbon substrate;

   (2) After mixing the transition metal monoatomic catalyst prepared in step (1), the naphthol solution with a mass fraction of 5% and anhydrous ethanol, brush on carbon paper and dry to obtain an H-type electrolytic cell (6) In the working electrode, the volume ratio of naphthol solution and absolute ethanol is 7:10000, and the loading amount of transition metal monoatomic catalyst is 0.57mg/cm ² ～0.86mg/cm ² ;

   (3) Directly pass air, nitrogen or a mixed gas of oxygen and nitrogen into the incident flow plasma reactor (14); and use a mass flow meter to adjust the flow rate and proportion of the gas entering the jet plasma reactor (14), the oxygen The volume ratio of oxygen and nitrogen in the mixed gas with nitrogen is 4:6～1:9; the gas flow is adjusted to 4L/min～8L/min; the plasma power supply (2) is turned on, and the plasma power supply (2) is used to adjust the input jet The power at both ends of the plasma reactor (14) realizes the stable discharge of jet plasma. Adjust the distance between the discharge end of the jet plasma reactor (14) and the liquid surface in the reaction vessel to be between 1cm-5cm; jet plasma reaction After the device (14) is discharged for 10 minutes, turn off the plasma power supply (2);

   (4) Transfer 50ml of the reaction solution after discharge into the two reaction cells of the H-type electrolysis cell (6), and at the same time pass through the first argon inlet (7) and the second argon inlet (10) to the H-type electrolysis Argon gas is passed into the electrolyte in the cell (6) to achieve deoxygenation; the argon gas flows out from the first argon gas outlet (8) and the second argon gas outlet (11);

   (5) Turn on the electrochemical workstation (1) and run the CV to make the current stable, perform an electrochemical catalysis process at an applied voltage of 1.1V-1.6V for 30 minutes, and collect the reacted content in the H-type electrolytic cell (6) NH ₄ ⁺ solution.
3. The method for nitrogen fixation with low-temperature jet plasma coupled with single atom catalysis according to claim 2, wherein the nitrogen fixation method is an online operation mode; in the online operation mode, the jet plasma reactor (14) is fixed at In the H-type electrolytic cell (6), the discharge end directly reacts with the solution in the H-type electrolytic cell (6); after the working electrode of the H-type electrolytic cell (6) is prepared, the adjustment parameters are consistent with those in offline operation , Turn on the plasma power supply (2) and electrochemical workstation (1) at the same time, and perform deoxygenation. The deoxygenation method is the same as offline operation. The working time of the plasma power supply (2) and electrochemical workstation (1) and the electrochemical workstation (1) The applied voltage is consistent with the offline operation mode to realize the synthesis of ammonia reaction, and collect the reacted NH ₄ ⁺ solution in the H-type electrolytic cell (6).
4. The method for fixing nitrogen with low temperature jet plasma coupled single atom catalysis according to claim 3, characterized in that the solution in the reaction vessel in the offline operation mode is equal to the solution in the H-type electrolytic cell (6) in the online operation mode. It is a 0.1MKOH solution.
5. The method of applying low-temperature jet plasma coupled monoatomic catalysis nitrogen fixation device according to claim 2, characterized in that, during operation, the gas products of the H-type electrolytic cell (6) are collected and analyzed and tested by gas chromatography The concentration of gaseous nitrogen fixation products produced.
6. The method of applying low-temperature jet plasma coupled monoatomic catalysis nitrogen fixation device according to claim 2, characterized in that 4ml of the NH ₄ ⁺ solution after the reaction in the H-type electrolytic cell (6) is taken and added After the indophenol blue coloring solution was allowed to stand for two hours, green solutions with different color depths were obtained; the obtained solution was tested with an ultraviolet-spectrophotometer, and the yield of synthetic ammonia was obtained.

Images