An ammonia synthesis system coupling a supported metal catalyst with a plasma reactor

Abstract

The application discloses a synthesis ammonia system coupled with a supported metal catalyst and a plasma reactor, and the system comprises a double dielectric barrier discharge reactor and a supported metal catalyst filled in the double dielectric barrier discharge reactor. The reactor is in a concentric tube structure, and a cooling water jacket, an outer quartz glass tube and an inner quartz glass tube are coaxially nested in sequence from outside to inside. The general formula of the supported metal catalyst is xCu-yNi-zCa-(1-x-y-z)C, 5%<=x<=20%, 5%<=y<=15%, 1%<=z<=5%. The system is reacted under mild conditions of 20-50 DEG C and 0.1-0.3 MPa. Through the synergistic effect of the catalyst and the plasma, the ammonia decomposition is reduced, the ammonia yield is improved, and the ammonia synthesis energy efficiency is up to 5.14 g NH3 / kWh.

Description

Technical Field

[0001] This invention belongs to the field of plasma ammonia synthesis technology, and relates to an ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor. Background Technology

[0002] Ammonia (NH3) is an important chemical raw material and a crucial precursor for the synthesis of many products, including fertilizers, plastics, resins, explosives, and synthetic fibers. Due to its high calorific value, lack of greenhouse gas emissions during combustion, and high hydrogen content, ammonia is considered a carbon-free hydrogen energy carrier.

[0003] Currently, the Haber-Bosch process is the main industrial method for large-scale production of NH3. This process is carried out at 450–600 °C and 150–300 bar, resulting in high energy consumption and large CO2 emissions. Therefore, developing a mild, green, and efficient ammonia synthesis technology is of significant research importance.

[0004] Nitrogen gas is chemically stable, and under normal conditions, its strong triple bond structure is difficult to break. Triple bond dissociation is crucial for ammonia synthesis. Plasma ammonia synthesis involves applying a high-energy electric field within the reaction zone. Electrons move at high speed under the influence of this field, colliding with nitrogen molecules and weakening their strong bonds. This breaks the bonds in the nitrogen molecules, causing inelastic collisions with the electrons. The resulting nitrogen or hydrogen molecules ionize or dissociate, generating numerous excited-state nitrogen- and hydrogen-containing active groups, which ultimately react to form ammonia.

[0005] Plasma technology can overcome the limitations of traditional ammonia synthesis methods, accelerating the reaction rate and promoting ammonia synthesis under ambient temperature and pressure. It is a promising alternative to thermocatalytic ammonia synthesis. However, in the presence of plasma alone, while increasing the input power improves the reaction conversion rate, it also accelerates the decomposition of ammonia in the reverse reaction. Introducing transition metals or metal oxides as catalysts can reduce ammonia decomposition to some extent. For example, the article "Efficient synthesis of ammonia from N2 and H2 alone in a ferroelectric packed-bed DBDreactor" studied the use of PZT and BaTiO3 as ferroelectric materials in a ferroelectric-regulated dual-dielectric barrier plasma reactor for ammonia synthesis. This study provides an effective method for ammonia synthesis under ambient temperature and pressure conditions. However, in a large electrode gap, the energy efficiency of PZT as a ferroelectric material is only 0.9 gNH3 / kWh, indicating low ammonia synthesis efficiency. The article "Non-thermal plasma synergistic Ni / Al2O3 for ammonia synthesis: Configuration and optimization of a double dielectric barrier discharge reactor" optimizes the structure of a dielectric barrier discharge reactor, using stainless steel rods as high-voltage electrodes and a tubular furnace for heating in the discharge zone. Plasma discharge begins after the reaction zone reaches a predetermined temperature, with a heating range of 100–800 °C. The reaction zone is filled with Ni / Al2O3 catalyst, achieving an energy efficiency of 1.19 g / kWh at an output voltage of 16 kV. The optimized reactor structure results in more uniform discharge within the reaction zone. The presence of nickel improves the energy efficiency of the ammonia synthesis reaction; however, the synergistic effect between the single-metal supported catalyst and plasma is poor, leading to low ammonia synthesis efficiency. Furthermore, the presence of the tubular furnace increases the energy consumption of the ammonia synthesis reaction, and the reaction temperature is relatively demanding.

[0006] Therefore, developing a novel catalyst that exhibits high activity and stability under mild conditions is of great significance for promoting the further development of plasma-catalyzed ammonia synthesis technology. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention aims to provide an ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor. This system comprises a dual-dielectric barrier discharge reactor and a supported metal catalyst filled within the reactor. The reactor has a concentric tubular structure, with a cooling water jacket, an outer quartz glass tube, and an inner quartz glass tube coaxially nested from the outside in. The supported metal catalyst has the general formula xCu-yNi-zCa-(1-xyz)C, where 5%≤x≤20%, 5%≤y≤15%, and 1%≤z≤5%. The system reacts under mild conditions of 20–50 °C and 0.1–0.3 MPa. Through the synergistic effect of the catalyst and plasma, ammonia decomposition is reduced, and ammonia yield is increased, achieving a maximum ammonia synthesis energy efficiency of 5.14 g NH3 / kWh.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor, the system comprising a dual dielectric barrier discharge reactor and a supported metal catalyst filled within the dual dielectric barrier discharge reactor; The dual-dielectric barrier discharge reactor includes an inner quartz glass tube, with an outer quartz glass tube coaxially nested around it. A high-voltage copper wire is inserted inside the inner quartz glass tube, and the other end of the high-voltage copper wire is electrically connected to a power source. The high-voltage copper wire is also electrically connected to the high-voltage output terminal of the power source. The grounding terminal of the power source is electrically connected to a grounding copper wire, and the other end of the grounding copper wire is grounded. A sieve plate is provided at the bottom inside the outer quartz glass tube, and an air inlet is provided on the upper side wall of the outer quartz glass tube. An air outlet is connected to the lower end of the outer quartz glass tube. A cooling water jacket is tightly fitted to the outer wall of the outer quartz glass tube. A cooling water inlet is provided on one side of the lower part of the cooling water jacket, and a cooling water outlet is provided on the other side of the upper part of the cooling water jacket. The general chemical formula for the supported metal catalyst is: xCu-yNi-zCa-(1-xyz)C, where: Cu and Ni are active components, Ca is an active additive, C is a support, x and y represent the mass percentages of the active metal components Cu and Ni, respectively, z represents the mass percentage of the active additive Ca, and 5%≤x≤20%, 5%≤y≤15%, 1%≤z≤5%; Nitrogen and hydrogen are introduced into the plasma reactor, where molecular bonds are broken in the plasma discharge reaction zone to form the intermediate product ·NH₃. x It adsorbs onto the active sites of the catalyst and undergoes a hydrogenation reaction to generate ammonia; As a limitation of the present invention, the sieve plate is filled with an insulating medium and a supported metal catalyst from bottom to top; the insulating medium is quartz sand or glass beads.

[0009] As another limitation of the present invention, a plasma discharge region is formed between the inner quartz glass tube (1) and the outer quartz glass tube (2), and the electrode spacing of the plasma discharge region is 3~7 mm.

[0010] As a third limitation of the present invention, the reaction temperature of the ammonia synthesis system is 20~50℃, the reaction pressure is 0.1~0.3 MPa, the discharge frequency is 8~15 kHz, and the discharge voltage is 10~20 kV; the feed gas is nitrogen and hydrogen, with nitrogen and hydrogen fed in a molar ratio of (1:4)~(2:1), and the space velocity of nitrogen and hydrogen in the plasma discharge region is 600~6000 h⁻¹. -1 .

[0011] In this invention, when the voltage is 10~20 kV, the discharge intensity and energy in the reaction zone can excite the dissociation of nitrogen and hydrogen and promote the combination of free radicals to generate ammonia; when the voltage is below 10 kV, the discharge intensity is low, the dissociation efficiency of the raw material gas is low, and the ammonia synthesis reaction efficiency is low; when the voltage is above 20 kV, the discharge intensity is high, the ammonia is in a high-energy environment, which easily causes the decomposition of the product.

[0012] In this invention, the nitrogen to hydrogen feed ratio is (1:4) to (2:1) and the space velocity is 600 to 6000 h⁻¹. -1 At that time, the feed gas in the reaction zone is excited to form free radicals under the action of plasma, and ammonia is generated by the reaction; when the feed ratio is less than 1:4 and the space velocity is greater than 6000 h⁻¹ -1 When the hydrogen content in the reaction zone is higher than that of nitrogen, and the nitrogen content is lower, it is not conducive to ammonia synthesis. When the feed ratio is greater than 2:1, the amount of hydrogen introduced is too small, which is not enough to meet the amount required for ammonia generation, so the reaction cannot be fully completed, nor can nitrogen be activated by excessive activation hydrogen.

[0013] As a fourth limitation of the present invention, the preparation method of the supported metal catalyst is carried out in the following order: S1. Weigh out copper salt and nickel salt according to the stoichiometric ratio, and disperse them together in deionized water to obtain a mixed solution; S2. Mix the carrier with the calcium salt and stir until homogeneous to obtain a mixture; place the mixture in the mixed solution and stir magnetically at 40~100 rpm for 2~4 h to obtain a suspension; S3. After allowing the suspension to stand and age for 12-18 h, dry it at 80-120℃ for 6-12 h, and then calcine the dried sample to obtain the supported metal catalyst.

[0014] As a limitation of the preparation method of the supported metal catalyst of the present invention, in step S1, the copper salt is copper nitrate trihydrate; the nickel salt is nickel nitrate hexahydrate.

[0015] As another limitation of the preparation method of the supported metal catalyst of the present invention, in step S1, the concentration of copper ions in the mixed solution is 0.25~1.0 mol / L and the concentration of nickel ions is 0.3~0.8 mol / L.

[0016] As a third limitation of the preparation method of the supported metal catalyst of the present invention, in step S2, the support is boehmite.

[0017] This invention uses boehmite as a precursor, as both boehmite and alumina provide numerous weakly acidic sites, facilitating the adsorption of the intermediate product ·NH. X After the hydrogenation reaction is completed and ammonia is generated, gaseous ammonia is desorbed. Compared with the catalyst with alumina as support, which is obtained by loading the active component and the auxiliary agent onto boehmite and then calcining it, the catalyst with alumina support has better dispersion and the active component is less likely to agglomerate.

[0018] As a fourth limitation of the preparation method of the supported metal catalyst of the present invention, in step S2, the calcium salt is calcium carbonate.

[0019] In this invention, the active additive component calcium salt is selected as calcium carbonate. Both calcium carbonate and the precursor boehmite are poorly soluble in nitrate solutions. They are precipitated in a mixed solution by physical mixing. After calcination, some of the calcium carbonate combines with the catalyst in the form of carbon ions, improving the catalyst activity and acting as an electronic additive. The other part remains on the support in the form of calcium carbonate, increasing the specific surface area of ​​the catalyst and regulating the acidic active sites, thus acting as a structural additive.

[0020] As a fifth limitation of the preparation method of the supported metal catalyst of the present invention, in step S3, the calcination temperature is 500~700℃ and the time is 3~6 h.

[0021] The calcination conditions of this invention are calcination at 500~700℃ for 3~6 h; during the calcination stage, a thermal decomposition reaction occurs, boehmite is transformed into alumina, copper nitrate and nickel nitrate are decomposed, nitrate ions are removed, and a copper-nickel alloy is formed; nickel has excellent hydrogen absorption properties, and copper readily adsorbs free radicals. The formation of the copper-nickel alloy improves the binding ability of nitrogen free radicals under high input power conditions, and at the same time, it collides and reacts with hydrogen free radicals in the plasma phase to form ammonia gas and completes desorption.

[0022] If the calcination temperature is less than 500℃, the nitrate ions will not decompose completely, and the catalyst filling the reactor will affect the plasma discharge, resulting in low reaction conversion rate or even reactor breakdown. If the calcination temperature is higher than 700℃, the active components will sinter, the activity will decrease, and the energy efficiency and stability of the catalyst-plasma coupled reaction system will be low.

[0023] In summary, this invention uses copper and nickel as active components, boehmite (containing more weakly acidic sites) as a precursor, and calcium carbonate as a promoter to adjust the surface pH of the catalyst, thereby improving the dispersion and activity of the active components Cu and Ni and promoting the production of the intermediate product ·NH₃. x It adsorbs onto acidic sites to carry out hydrogenation reactions and can promptly desorb the ammonia product, thereby improving the ammonia yield under high-energy conditions and reducing the re-decomposition of the product.

[0024] Within the discharge region of the plasma discharge reactor, a strong electric field is generated by applying a voltage to the high-voltage electrodes. Electrons move at high speed under the influence of this electric field, colliding with nitrogen molecules and weakening their originally strong bonds. This makes the nitrogen molecules easier to open, and the nitrogen or hydrogen molecules that collide with the electrons inelasticly dissociate, generating a large number of excited nitrogen- and hydrogen-containing active groups. The dissociated nitrogen and hydrogen free radicals are adsorbed onto copper and nickel active sites, and simultaneously undergo a hydrogenation reaction to form ammonia. The ammonia generated in the plasma phase can be adsorbed onto the weakly acidic sites of the support. The presence of the auxiliary calcium carbonate can facilitate dissociation by lowering the nitrogen barrier and promote ammonia desorption by adjusting the acidity of the catalyst surface. The synergistic effect of the plasma and the catalyst promotes the efficient ammonia synthesis reaction.

[0025] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they determine the morphological characteristics and performance of the product.

[0026] The above technical solution has the following advantages or beneficial effects: 1. This invention utilizes the synergistic effect of copper-nickel bimetallic catalyst and plasma to catalyze the synthesis of ammonia. The catalyst preparation process is simple, and the reaction is carried out under mild conditions of reaction temperature of 20~50℃ and reaction pressure of 0.1~0.3 MPa, which reduces the energy consumption of the ammonia synthesis reaction and produces no harmful gases, thus meeting the requirements of green synthesis. 2. The copper-nickel bimetallic catalyst prepared by this invention introduces copper-nickel metal active components and calcium carbonate as auxiliary components using boehmite as a precursor. Calcium carbonate is introduced by physical mixing with boehmite and plays a dual role as a structural auxiliary and electronic auxiliary in the catalyst. While adjusting the surface pH, it improves the catalyst activity, reduces the re-decomposition of ammonia in the plasma phase, and improves the ammonia yield and energy efficiency of the ammonia synthesis reaction.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0028] Figure 1The following is a schematic diagram of the ammonia synthesis system in Embodiments 1-3 of the present invention, wherein: 1 is an inner quartz glass tube, 2 is an outer quartz glass tube, 3 is a cooling water jacket, 4 is an air inlet, 5 is a sieve plate, 6 is an air outlet, 7 is a cooling water inlet, 8 is a cooling water outlet, 9 is a high-voltage copper wire, 10 is a power supply, and 11 is a grounding copper wire. Figure 2 The diagram shows the cross-sectional structure of the plasma discharge reactor in Embodiments 1-3 of the present invention, wherein: 1 is the inner quartz glass tube, 2 is the outer quartz glass tube, 3 is the cooling water jacket, 4 is the air inlet, 5 is the sieve plate, 6 is the air outlet, 7 is the cooling water inlet, 8 is the cooling water outlet, and 9 is the high-voltage copper wire. Figure 3 The images shown are SEM images of the supported metal catalysts prepared in Examples 1-2 and Comparative Example 6 of the present invention, wherein: (a) is an SEM image of the catalyst prepared in Comparative Example 6, (b) is an SEM image of the catalyst prepared in Example 1, and (c) is an SEM image of the catalyst prepared in Example 2. Figure 4 The following are discharge diagrams of the supported metal catalyst and plasma coupling reaction system constructed in Example 1 and Comparative Example 9 of the present invention, wherein: (a) is the discharge diagram of Comparative Example 9, and (b) is the discharge diagram of Example 1. Detailed Implementation

[0029] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified. Example 1

[0031] This embodiment constructs an ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor. The system includes a dual-medium barrier discharge reactor and a supported metal catalyst filled within the reactor. The dual-medium barrier discharge reactor has a concentric tubular structure, consisting of a cooling water jacket 3, an outer quartz glass tube 2, and an inner quartz glass tube 1, coaxially nested from the outside in. The outer quartz glass tube 2 is a quartz glass tube with an outer diameter of 25 mm and an inner diameter of 23 mm, while the inner quartz glass tube 1 is a quartz glass tube with an outer diameter of 15 mm and an inner diameter of 13 mm. A plasma discharge region with a 5 mm inter-electrode spacing is formed between the two. A porous quartz sieve plate 5 is fixedly installed at the bottom of the plasma discharge region. The sieve plate 5 is filled with quartz sand insulating medium with a height of 1.0 cm and a particle size of 1-2 mm. 1.0 g of 20 wt.% Cu-5 wt.% Ni-2 wt.% Ca-73 wt.% Al2O3 supported catalyst particles are then evenly spread on top of the insulating medium. The inner quartz glass tube 1 is filled with a saturated sodium chloride solution with a diameter of 5 mm. One end of a high-voltage copper wire 9 is inserted into the saturated sodium chloride solution, forming a high-voltage electrode together with the saturated sodium chloride solution. The other end is electrically connected to the high-voltage output terminal of the power supply 10. The grounding terminal of the power supply 10 is connected to one end of the grounding copper wire 11, and the other end of the grounding copper wire 11 is directly grounded. The cooling water jacket 3 is a stainless steel cylindrical jacket that fits tightly against the outer wall of the outer quartz glass tube 2. A cooling water inlet 7 is opened at the bottom and a cooling water outlet 8 is opened at the top. During the experiment, 25 ℃ circulating cooling water is continuously introduced to form a cooling path and maintain the reactor wall temperature. The upper side wall of the outer quartz glass tube 2 has a raw material gas inlet 4 and a gas outlet 6 connected at the bottom. Both the gas inlet 4 and the gas outlet 6 are connected to the plasma discharge area. Nitrogen and hydrogen gas were introduced into the reactor through inlet 4 as feed gas at a molar ratio of 1:4. The space velocity of the feed gas flow through the plasma discharge zone was 3000 h⁻¹. -1 After the reaction, the gas containing unreacted nitrogen, hydrogen and generated ammonia is discharged through outlet 6. During the reaction, the reaction temperature is controlled at 30 ℃, the reaction pressure at 0.1 MPa, the discharge frequency at 12 kHz and the discharge voltage at 15 kV. The preparation method and process of the above-mentioned 20wt.%Cu-5wt.%Ni-2wt.%Ca-73wt.%Al2O3 catalyst are as follows: S1. Weigh 5.16 g of copper nitrate trihydrate and 1.70 g of nickel nitrate hexahydrate, add them together to deionized water to obtain a mixed solution. The concentration of copper ions in the resulting solution is 1.0 mol / L and the concentration of nickel ions is 0.3 mol / L. S2. Weigh 5 g of pseudoboehmite precursor and physically mix it with 0.34 g of calcium carbonate to obtain a mixture. Place the mixture in a mixed solution and magnetically stir at 100 rpm for 2 h to obtain a suspension. S3. After the suspension was allowed to stand and age for 12 h, the aged sample was dried at 120℃ for 6 h, and the dried sample was calcined at 700℃ for 3 h to obtain a 20 wt.% Cu-5 wt.% Ni-2 wt.% Ca-73 wt.% Al2O3 supported metal catalyst. The reaction results showed that the energy efficiency of the system was 5.14 gNH3 / kWh, and the ammonia yield was 1.51 mmolNH3·g. cat -1 ·h -1 . Example 2

[0032] This embodiment constructs an ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor. The construction process and method are similar to those in Example 1, except that the interelectrode spacing in the plasma discharge region is 3 mm, the reaction temperature is 20°C, the reaction pressure is 0.2 MPa, the discharge voltage is 10 kV, the discharge frequency is 8 kHz, the nitrogen to hydrogen feed molar ratio is 1:1, and the space velocity of the feed gas through the plasma discharge region is 600 h⁻¹. -1 .

[0033] In this embodiment, a 10 wt.% Cu-10 wt.% Ni-5 wt.% Ca-75 wt.% Al2O3 catalyst is used in the reaction system. The preparation method and process of this catalyst are as follows: S1. Weigh 2.52 g of copper nitrate trihydrate and 3.32 g of nickel nitrate hexahydrate, add them together to deionized water to obtain a mixed solution. The concentration of copper ions in the resulting solution is 0.52 mol / L and the concentration of nickel ions is 0.57 mol / L. S2. Weigh 5 g of pseudoboehmite precursor and physically mix it with 0.84 g of calcium carbonate to obtain a mixture. Place the mixture in a mixed solution and magnetically stir at 80 rpm for 3 h to obtain a suspension. S3. After the suspension was allowed to stand and age for 15 h, the aged sample was dried at 100℃ for 10 h, and the dried sample was calcined at 600℃ for 4 h to obtain a 10wt.%Cu-10wt.%Ni-5wt.%Ca-75wt.%Al2O3 catalyst sample. The reaction results showed that the energy efficiency of the system was 4.82 g NH3 / kWh, and the ammonia yield was 1.41 mmol NH3·g. cat -1 ·h -1 . Example 3

[0034] This embodiment constructs an ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor. The construction process and method are similar to those in Example 1, except that the interelectrode spacing in the plasma discharge region is 7 mm, the reaction temperature is 50 °C, the reaction pressure is 0.3 MPa, the discharge voltage is 20 kV, the discharge frequency is 15 kHz, the nitrogen to hydrogen feed molar ratio is 2:1, and the space velocity of the feed gas through the plasma discharge region is 6000 h⁻¹. -1 .

[0035] In this embodiment, a 5wt.%Cu-15wt.%Ni-1wt.%Ca-79wt.%Al2O3 catalyst is used in the reaction system. The preparation method and process of this catalyst are as follows: S1. Weigh 1.19 g of copper nitrate trihydrate and 4.70 g of nickel nitrate hexahydrate, add them together to deionized water to obtain a mixed solution. The concentration of copper ions in the resulting solution is 0.25 mol / L and the concentration of nickel ions is 0.8 mol / L. S2. Weigh 5 g of boehmite precursor and 0.16 g of calcium carbonate and physically mix them to obtain a mixture. Place the mixture in a mixed solution and stir magnetically at 40 rpm for 4 h to obtain a suspension. S3. After the suspension was allowed to stand and age for 18 h, the aged sample was dried at 80℃ for 12 h, and the dried sample was calcined at 500℃ for 6 h to obtain a 5wt.%Cu-15wt.%Ni-1wt.%Ca-79wt.%Al2O3 catalyst sample. The reaction results showed that the energy efficiency of the system was 4.62 g NH3 / kWh, and the ammonia yield was 1.35 mmol NH3·g. cat -1 ·h -1 .

[0036] Comparative Example To investigate the influence of different raw materials on the performance of this invention during its preparation process, the following comparative experiments were conducted. Different reaction systems were constructed for the following comparative examples, as detailed below: Comparative Example 1 This comparative example constructs a supported metal catalyst coupled with plasma reaction system. The construction process is similar to that of Example 1, except that the reaction conditions are different: the reaction temperature is 15°C, the reaction pressure is 0.4 MPa, the voltage is 5 kV, the discharge frequency is 5 kHz, the nitrogen to hydrogen feed ratio is 3:1, and the gas space velocity in the reaction zone is 7000 h⁻¹. -1 The energy efficiency of this reaction system is 2.89 g NH3 / kWh, and the ammonia yield is 0.85 mmol NH3·g. cat-1 ·h -1 This is because the discharge intensity in the reaction zone is low, the discharge is uneven, the feed gas space velocity is high, and the nitrogen content is low, which is not conducive to the ammonia synthesis reaction, resulting in low reaction efficiency.

[0037] Comparative Example 2 This comparative example prepared a supported metal catalyst-plasma-coupled reaction system. The construction process was similar to that of Example 1, except that in the catalyst preparation process, 0.34 g of calcium carbonate was replaced with 0.38 g of calcium chloride. The energy efficiency of this reaction system was 3.21 g NH3 / kWh, and the ammonia yield was 0.94 mmol NH3·g. cat -1 ·h -1 This is because when calcium chloride is used as the active component, chloride ions are difficult to remove through the calcination stage. The introduction of chloride ions into the sample has an inhibitory effect on the ammonia synthesis reaction system, inhibiting the ammonia synthesis reaction and resulting in a low ammonia yield.

[0038] Comparative Example 3 This comparative example prepared a supported metal catalyst-plasma-coupled reaction system. The construction process was similar to that of Example 1, except that calcium carbonate was not added during the catalyst preparation process. The energy efficiency of this reaction system was 4.35 g NH3 / kWh, and the ammonia yield was 1.28 mmol NH3·g. cat -1 ·h -1 This is because the support surface contains some medium-to-strong acid sites, and the generated ammonia is adsorbed on the acidic sites. The desorption efficiency is lower than that of catalysts containing basic promoters, resulting in lower energy efficiency and yield of ammonia synthesis.

[0039] Comparative Example 4 This comparative example prepared a supported metal catalyst-plasma-coupled reaction system, similar in construction procedure to Example 1, except that copper nitrate trihydrate was not added during catalyst preparation. The energy efficiency of this reaction system was 4.07 gNH3 / kWh, and the ammonia yield was 1.20 mmol NH3·g. cat -1 ·h -1 This is because the only active metal component in the catalyst is nickel. The presence of nickel can improve the hydrogen absorption performance of the process, but the performance of a single-metal active component catalyst is lower than that of a bimetallic active component catalyst.

[0040] Comparative Example 5 This comparative example prepared a supported metal catalyst-plasma-coupled reaction system, similar in construction procedure to Example 1, except that nickel nitrate hexahydrate was not added during catalyst preparation. The energy efficiency of this reaction system was 4.22 g NH3 / kWh, and the ammonia yield was 1.24 mmol NH3·g. cat -1 ·h -1 This is because the only metallic active component in this catalyst is copper. The presence of copper can improve the catalytic activity of the catalyst, but the performance of a single-metal active component catalyst is lower than that of a bimetallic active component catalyst.

[0041] Comparative Example 6 This comparative example prepared a supported metal catalyst and plasma-coupled reaction system. The construction process was similar to that of Example 1, except that the precursor boehmite was replaced with alumina during catalyst preparation. The energy efficiency of this reaction system was 4.18 g NH3 / kWh, and the ammonia yield was 1.23 mmol NH3·g. cat -1 ·h -1 This is because when boehmite is used as a precursor, the active metal component and the auxiliary component are first loaded onto the precursor, resulting in a higher specific surface area and dispersion, and thus higher catalyst activity. However, when alumina is used directly as a support to load the metal component, the active metal component is prone to agglomeration, resulting in lower dispersion and relatively lower catalyst activity.

[0042] Figure 3 The images show SEM images of the supported metal catalysts prepared in Examples 1-2 and Comparative Example 6 of this invention. It can be seen from the images that... Figure 3 In (a), a small amount of agglomerates are present on the surface of the catalyst, while Figure 3 (b) and Figure 3 (c) No agglomerates are present on the catalyst surface, indicating that the catalyst prepared using boehmite as a precursor has uniformly dispersed metal components on its surface.

[0043] Comparative Example 7 This comparative example prepared a supported metal catalyst-plasma-coupled reaction system. The construction process was similar to that of Example 1, except that in the catalyst preparation process, 0.34 g of calcium carbonate was replaced with 0.61 g of calcium acetate. The energy efficiency of this reaction system was 4.50 g NH3 / kWh, and the ammonia yield was 1.32 mmol NH3·g. cat -1 ·h -1This is because calcium acetate is soluble in nitrate solutions and exists in the form of calcium ions. After calcination, it is loaded onto the support along with the active component, acting only as an electronic catalytic agent. As a result, the catalyst prepared in this way has a poorer catalytic effect on the reaction in the plasma-coupled reaction system compared to when calcium carbonate is used as the active catalytic agent.

[0044] Comparative Example 8 This comparative example constructs a supported metal catalyst coupled with plasma reaction system. The construction process is similar to that of Example 1, except that the interelectrode spacing in the plasma discharge region is 8 mm. The energy efficiency of this reaction system is 4.42 g NH3 / kWh, and the ammonia yield is 1.30 mmol NH3·g. cat -1 ·h -1 This is because the interelectrode spacing in the reaction zone is large, the plasma discharge state in the discharge zone is unstable, the discharge intensity is small, and the energy efficiency of the ammonia synthesis reaction in the reaction zone is low.

[0045] Comparative Example 9 This comparative example constructs a supported metal catalyst coupled with plasma reaction system. The construction process is similar to that of Example 1, except that no catalyst is packed into this reaction system. The energy efficiency of this reaction system is 2.35 gNH3 / kWh, and the ammonia yield is 0.69 mmol NH3·g. cat -1 ·h -1 This is because, without a catalyst, the plasma has low activation efficiency for nitrogen and hydrogen, and the excited nitrogen and hydrogen active groups have a short residence time in the reaction zone, resulting in low ammonia synthesis efficiency. Furthermore, in a high-energy environment without a catalyst, ammonia is easily decomposed under the influence of plasma.

[0046] Figure 4 The above are discharge diagrams of the supported metal catalyst and plasma-coupled reaction systems constructed in Example 1 and Comparative Example 9 of this invention. Figure 4 (b) is a discharge diagram of the reaction system constructed in Example 1. The catalyst is located in the plasma discharge region and participates in the ammonia synthesis reaction. The discharge is uniform in all parts of the discharge region. Figure 4 (a) is a discharge diagram of the reaction system constructed in Comparative Example 9. There is no catalyst filling in the reaction zone. The discharge is uniform in all parts of the zone, but the ammonia synthesis efficiency is low.

[0047] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor, characterized in that, The system includes a dual-dielectric barrier discharge reactor and a supported metal catalyst filled within the dual-dielectric barrier discharge reactor; The dual-dielectric barrier discharge reactor includes an inner quartz glass tube (1), with an outer quartz glass tube (2) coaxially nested outside the inner quartz glass tube (1). A high-voltage copper wire (9) is inserted inside the inner quartz glass tube (1), and the other end of the high-voltage copper wire (9) is electrically connected to a power source (10). The high-voltage copper wire (9) is also electrically connected to the high-voltage output terminal of the power source (10). The grounding terminal of the power source (10) is electrically connected to a grounding copper wire (11). The other end is grounded. A sieve plate (5) is provided at the bottom inside the outer quartz glass tube (2). An air inlet (4) for raw material gas is opened on the upper side wall of the outer quartz glass tube (2). An air outlet (6) is connected to the lower end of the outer quartz glass tube (2). A cooling water jacket (3) is tightly attached to the outer wall of the outer quartz glass tube (2). A cooling water inlet (7) is opened on one side of the lower part of the cooling water jacket (3). A cooling water outlet (8) is opened on the other side of the upper part of the cooling water jacket (3). The general chemical formula of the supported metal catalyst is: xCu-yNi-zCa-(1-xyz)C, where: Cu and Ni are active components, Ca is an active additive, C is a support, x and y represent the mass percentages of the active metal components Cu and Ni, respectively, z represents the mass percentage of the active additive Ca, and 5%≤x≤20%, 5%≤y≤15%, 1%≤z≤5%.

2. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 1, characterized in that, The sieve plate (5) is filled with an insulating medium and a supported metal catalyst from bottom to top; the insulating medium is quartz sand or glass beads.

3. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 1, characterized in that, A plasma discharge region is formed between the inner quartz glass tube (1) and the outer quartz glass tube (2), and the distance between the electrodes of the plasma discharge region is 3~7 mm.

4. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 1, characterized in that, The ammonia synthesis system has a reaction temperature of 20-50℃, a reaction pressure of 0.1-0.3 MPa, a discharge frequency of 8-15 kHz, and a discharge voltage of 10-20 kV. The feed gas is nitrogen and hydrogen, fed in a molar ratio of (1:4) to (2:1), and the space velocity of nitrogen and hydrogen in the plasma discharge region is 600-6000 h⁻¹. -1 .

5. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 1, characterized in that, The preparation method of the supported metal catalyst is carried out in the following order: S1. Weigh out copper salt and nickel salt according to the stoichiometric ratio, and disperse them together in deionized water to obtain a mixed solution; S2. Mix the carrier with the calcium salt and stir until homogeneous to obtain a mixture; place the mixture in the mixed solution and stir magnetically at 40~100 rpm for 2~4 h to obtain a suspension; S3. After allowing the suspension to stand and age for 12-18 h, dry it at 80-120℃ for 6-12 h, and then calcine the dried sample to obtain the supported metal catalyst.

6. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 5, characterized in that, In step S1, the copper salt is copper nitrate trihydrate; the nickel salt is nickel nitrate hexahydrate.

7. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 5, characterized in that, In step S1, the concentration of copper ions in the mixed solution is 0.25~1.0 mol / L, and the concentration of nickel ions is 0.3~0.8 mol / L.

8. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 5, characterized in that, In step S2, the carrier is pseudoboehmite.

9. The ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 5, characterized in that, In step S2, the calcium salt is calcium carbonate.

10. An ammonia synthesis system coupled with a supported metal catalyst and a plasma reactor according to claim 5, characterized in that, In step S3, the calcination temperature is 500~700℃ and the time is 3~6 h.

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