High-entropy alloy ammonia synthesis catalyst, preparation method and application thereof

Abstract

The application discloses a high-entropy alloy ammonia synthesis catalyst, which comprises a carrier and high-entropy alloy particles loaded on the surface of the carrier; the average particle size of the high-entropy alloy particles is 2-20 nm, and the loading amount is 5-70 wt%; the high-entropy alloy particles comprise active metals and auxiliary metals; the active metals comprise at least three of Fe, Co, Mo, Ru, Os, Ni, Rh, Ir, Mn, Re, Pt, Pd and Ag; and the auxiliary metals comprise at least one of Ce, Ba, Sr, Mg, Ca, Li, K, La, Sm, W, V, Cs, Tc and Cu. The preparation method of the high-entropy alloy ammonia synthesis catalyst comprises the following steps: uniformly mixing active metal salts, auxiliary metal salts and an organic ligand with a carrier, ball milling in an inert atmosphere to obtain a precursor A, and performing heat treatment and reduction in an inert atmosphere to obtain the catalyst. The catalyst has small high-entropy alloy particle size and good dispersibility, can be applied to ammonia synthesis reaction, and exhibits good catalytic performance.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology and application, specifically relating to a high-entropy alloy ammonia synthesis catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia has attracted considerable interest as a hydrogen storage and transport medium because it can be stored in the liquid phase at a higher volumetric hydrogen density than liquid H2 under mild conditions. This is because NH3 is liquid at lower pressures and higher temperatures than H2, resulting in lower energy consumption for liquefaction and allowing for smaller, lighter storage and transport containers. Furthermore, the development of modern industry and agriculture is inextricably linked to the use of ammonia. Ammonia, as an important chemical raw material and energy carrier, has become a focus of attention. Currently, the industrial synthesis of ammonia uses the Haber-Bosch process at high temperature and high pressure (400-600°C, 20-40 MPa) to hydrogenate nitrogen to produce ammonia. However, the high temperature and high pressure synthesis conditions require high energy consumption and easily cause sintering and deactivation of the ammonia synthesis catalyst. Therefore, developing highly active ammonia synthesis catalysts under mild conditions has always been a goal pursued by researchers.

[0003] The stronger the adsorption energy of nitrogen on the surface of transition metals, the stronger their ability to dissociate N≡N, and the better their catalytic activity; at the same time, the stronger the adsorption energy of NH₃ on the surface of transition metals... x The stronger the adsorption energy, the better the NH x The more difficult it is to dissociate, the more difficult it is to separate. Therefore, the relationship between the ammonia synthesis rate of metals and the adsorption energy of nitrogen on the metal exhibits a volcano-like trend. Because high-entropy alloys mix multiple metals, their surfaces are highly heterogeneous, allowing for a large number of possible atomic arrangements. Compared to single-metal catalysts and non-high-entropy catalysts, high-entropy alloy nanoparticle catalysts break down the immiscibility gaps between metals, effectively regulating the types and proportions of metals, thereby modulating the electronic structure and d-band centers of the metals. In the ammonia synthesis reaction, this enables the alloy surface to effectively absorb nitrogen and NH4+. x The adsorption energy is continuously adjustable, thus enabling effective control of the catalytic performance of ammonia synthesis. The VS2@Bi2O3 / CC prepared by Chinese patent CN113862717B achieved an ammonia yield of 24.3 × 10⁻⁶ at -0.10 V (relative to the standard hydrogen electrode) in the electrocatalytic nitrogen reduction synthesis of ammonia. -10 mol s -1 cm -2 The Faraday efficiency reached as high as 11.5%. Chinese patent CN111686758B describes the preparation of RuFeCoNiCu high-entropy alloy nanoparticles via a solvothermal method, with optimal activity observed in a 0.1M KOH electrolyte and an NH3 yield of 58.57 μgh. -1 mg -1 cat The area yield was 29.28 μg h. -1 cm -2The Faraday efficiency is 26.4%. However, the efficiency of electrocatalytic ammonia synthesis is currently too low, and it has no prospects for industrial application. There are currently no reported examples of high-entropy alloy catalysts for thermocatalytic ammonia synthesis.

[0004] Although high-entropy alloy nanoparticle catalysts have shown promising application prospects in the field of catalysis, many problems still exist in the controllable synthesis of high-entropy alloy catalysts. At present, high-entropy alloy nanoparticle catalysts are mainly obtained by transient heating, mechanical alloying, wet chemical methods and sputtering deposition, and are used in ammonia decomposition, CO oxidation, CO2 reduction and other fields. The literature (Nature Communications, 2019, 10(1): 4011) reported that HEA CoMoFeNiCu nanoparticles with a particle size of ~22nm can be prepared by carbothermal shock, which can achieve robust adjustment of Co / Mo ratio, break the miscibility limitation of traditional bimetallic Co-Mo catalysts, and show good catalytic activity and stability in ammonia decomposition reaction, but the method has high requirements for equipment. Chinese patent CN111111693A reports a process for preparing platinum-based high-entropy alloy nanoparticle catalysts. This process involves dissolving metal precursors with organic solvents such as THF and CHCl3, followed by template-based preparation of bulk high-entropy materials. These materials are then etched with strong acids and bases to obtain monodisperse platinum-based high-entropy alloy nanoparticle catalysts with controllable particle size and good dispersion. However, this process generates a large amount of waste liquid, causing serious environmental pollution. Chinese patent CN111545767A uses a spray-drying combined with calcination method to prepare high-entropy alloy nanoparticles with uniform metal element distribution, but the phase composition of the product is difficult to control. Chinese patent CN107829007A involves uniformly mixing iron powder, cobalt powder, chromium powder, nickel powder, manganese powder, and ferrochromium nitride, followed by ball milling. The resulting high-entropy alloy powder has a uniform spherical or near-spherical particle morphology, but the particle size ranges from 20-30 μm, which is relatively large and does not reach the nanoscale. This results in low atomic utilization of the catalyst and makes it unsuitable for the thermal catalytic synthesis of ammonia under mild conditions.

[0005] In conclusion, developing a highly efficient ammonia synthesis catalyst under mild conditions remains a significant challenge. Although, theoretically, high-entropy alloy catalysts can effectively control the effects of nitrogen and NH4+... x While adsorption energy is important, there are currently no reported examples of high-entropy alloy catalysts for the thermal catalytic synthesis of ammonia. Therefore, preparing high-entropy alloy ammonia synthesis catalysts with uniform particle size and small particle diameter remains challenging. Summary of the Invention

[0006] This invention provides a high-entropy alloy ammonia synthesis catalyst, its preparation method, and its application in the thermal catalytic ammonia synthesis reaction under mild conditions. The high-entropy alloy ammonia synthesis catalyst has a uniform size distribution with an average particle size of 2-20 nm. The catalyst exhibits excellent catalytic performance and thermal stability in the ammonia synthesis reaction under mild conditions.

[0007] The technical solution of the present invention is as follows:

[0008] A high-entropy alloy ammonia synthesis catalyst includes a support and high-entropy alloy particles loaded on the surface of the support; the loading of the high-entropy alloy particles is 5-70 wt%; the average particle size of the high-entropy alloy particles is 2-20 nm.

[0009] The high-entropy alloy particles include active metals and auxiliary metals; the active metals include at least three of Fe, Co, Mo, Ru, Os, Ni, Rh, Ir, Mn, Re, Pt, Pd, and Ag; the auxiliary metals include at least one of Ce, Ba, Sr, Mg, Ca, Li, K, La, Sm, W, V, Cs, Tc, and Cu.

[0010] Preferably, based on the mass of the high-entropy alloy particles, the content of each active metal is independently 5-50 wt%; the content of the auxiliary metal is 5-50 wt%.

[0011] Preferably, the carrier is at least one of carbon material, alkaline earth metal oxide, and rare earth metal oxide. The abundant oxygen-containing functional groups and defect sites in the carrier can effectively anchor the alloy nanoparticles.

[0012] This invention also provides a method for preparing the aforementioned high-entropy alloy ammonia synthesis catalyst, comprising the following steps:

[0013] (1) After the active metal salt, auxiliary metal salt, organic ligand and carrier are mixed evenly, they are ball-milled in an inert atmosphere to obtain precursor A;

[0014] (2) Heat treatment of precursor A under an inert atmosphere and cooling to obtain alloy precursor B;

[0015] (3) Reduce precursor B in a reducing atmosphere and cool it to obtain the product.

[0016] Because the complexation constants of organic ligands with different metals vary significantly, they cannot simultaneously complex multiple metals. However, in a solid-phase mechanical ball milling system, due to the extremely high concentrations of organic ligands and metal ions, organic ligands can simultaneously complex multiple metal elements. Furthermore, under an inert atmosphere, the strong collisions and stirring of the steel balls cause mechanical deformation, and the metal precursor and the carrier material undergo repeated cold welding, milling, and re-welding processes, accelerating the diffusion of metal atoms. This makes the complexation rate and complexation strength of the organic ligands for each metal tend to be consistent, resulting in a uniformly dispersed metal composite oxide. Finally, through heat treatment and reduction, a high-entropy alloy nanocatalyst with uniform metal atom distribution is formed.

[0017] Preferably, the active metal salt and the auxiliary metal salt are one or more of sulfate, nitrate, acetylacetone salt, and acetate.

[0018] Preferably, the organic ligand is an organic acid. Further, the organic acid is at least one selected from malic acid, citric acid, tartaric acid, acetic acid, succinic acid, oxalic acid, tannic acid, and humic acid.

[0019] More preferably, the mass ratio of the organic ligand to the metal precursor is 1-100:1; the metal precursor is an active metal salt and an auxiliary metal salt.

[0020] The oxygen-containing functional groups in organic ligands can effectively form complexes with metal ions, thus effectively preventing phase separation and precipitation during the formation of high-entropy alloy nanoparticles. The addition of organic ligands can also effectively disperse metal elements, enabling the preparation of small-sized high-entropy alloy nanoparticles. When the content of organic ligands is too low, metal phase precipitation is likely to occur; while when the content of organic ligands is too high, it can easily cover the active metal components.

[0021] More preferably, the mass ratio of the organic ligand to the metal precursor is 1-60:1.

[0022] In step (2), the inert atmosphere is at least one of nitrogen, argon, and CO2.

[0023] Preferably, in step (2), the heat treatment temperature is 200-1300℃ and the heat treatment time is 2-6h.

[0024] Preferably, in the ball milling process, the ball-to-material ratio is 1-60:1, the ball milling speed is 300-800 rpm, and the ball milling time is 3-6 hours.

[0025] The ball size and ball-to-material ratio affect the uniformity of the metal and carrier, as well as the particle size of the catalyst. If the ball-to-material ratio is too large, the ball milling effect cannot be fully realized; conversely, if the ball-to-material ratio is too small, the ball milling efficiency is low. Low ball milling speed results in uneven milling; high ball milling speed causes centrifugal force to exceed gravity, causing the catalyst and steel balls to rotate together, thus failing to achieve the desired milling effect.

[0026] A further preferred option is a ball-to-material ratio of 10-30:1.

[0027] The steel ball diameter during ball milling is φ4-φ12cm.

[0028] More preferably, the steel balls include large balls and small balls, with the large balls having a diameter of φ8-φ12cm and the small balls having a diameter of φ4-φ6cm; the ratio of large balls to small balls is 1:0.5-3.

[0029] Preferably, in step (3), the reducing atmosphere is a hydrogen-containing inert gas. More preferably, it is a hydrogen-argon mixture.

[0030] Preferably, in step (3), the reduction temperature is 200-1200℃ and the reduction time is 1-6h.

[0031] In the high-entropy alloy ammonia synthesis catalyst of the present invention, the average particle size of the high-entropy alloy particles is 2-20 nm, which has a good catalytic effect on the ammonia synthesis process.

[0032] Therefore, the present invention also provides the application of the high-entropy alloy ammonia synthesis catalyst in the ammonia synthesis catalytic reaction.

[0033] The application includes: loading the high-entropy alloy ammonia synthesis catalyst into a fixed-bed reactor, and introducing hydrogen and nitrogen to carry out the reaction; the ratio of hydrogen to nitrogen is 5-0.5:1; the reaction temperature is 300-500 degrees Celsius, and the reaction pressure is 0.5-10 MPa.

[0034] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0035] (1) The high-entropy alloy catalyst prepared by the method of the present invention has uniform alloy element dispersion and uniform high-entropy alloy particle size of about 2-20 nm.

[0036] (2) The present invention uses an organic ligand-assisted ball milling method, which can effectively avoid the influence of uneven material composition caused by the difference in the complexation constant of organic ligands. The preparation method of the present invention is simple.

[0037] (3) The high-entropy alloy nanoparticle catalyst prepared by the organic ligand-assisted ball milling method of the present invention has good catalytic performance in ammonia synthesis reaction under mild conditions. Attached Figure Description

[0038] Figure 1 The XRD patterns are of the catalysts prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] Example 1

[0041] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a total metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours to obtain the precursor. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours. Finally, it was naturally cooled to room temperature to obtain Fe. 10 Ni 10 Cu 10 Co 25 Mo 45 The / NC-TA-m1200-N5-Ar600-H600 high-entropy alloy catalyst has a particle size of approximately 4.8 nm for the high-entropy alloy particles on the catalyst.

[0042] Example 2

[0043] According to a metal loading of 10wt% and an atomic percentage of ruthenium:palladium:calcium:iron:platinum of 45:25:10:10:10, ferric nitrate, chloroplatinic acid, nickel nitrate, palladium nitrate, ruthenium nitrate, 5g of tannic acid, and 50g of activated carbon were weighed and mixed evenly. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a ratio of large to small balls of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. Subsequently, the precursor was heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was raised from room temperature to the reduction temperature and held at this temperature for 2 hours. Finally, it was naturally cooled to room temperature to obtain Fe. 10 Ca 10 Pt 10 Pd 25 Ru 45 The / NC-TA-m1200-N5-Ar600-H600 high-entropy alloy catalyst has a particle size of approximately 3.8 nm for the high-entropy alloy particles on the catalyst.

[0044] Example 3

[0045] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a total metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours to obtain the precursor. The precursor was then heat-treated at 800℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at a reduction temperature of 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours. Finally, the mixture was allowed to cool naturally to room temperature to obtain Fe. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-TA-m1200-N5-Ar800-H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles on the catalyst is approximately 8.3 nm.

[0046] Example 4

[0047] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g citric acid, and 50g activated carbon were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was raised from room temperature to the reduction temperature and held at this temperature for 2 hours. Finally, it was allowed to cool naturally to room temperature to obtain Fe. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-CA-m1200-N5-Ar600-H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles is approximately 7.4 nm.

[0048] Example 5

[0049] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g magnesium oxide were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was raised from room temperature to the reduction temperature and held at this temperature for 2 hours. Finally, it was allowed to cool naturally to room temperature to obtain Fe. 10 Ni 10 Cu 10 Co 25 Mo 45 / MgO-TA-m1200-N5-Ar600-H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy is approximately 14.5 nm.

[0050] Example 6

[0051] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 500g steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a ratio of large to small balls of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours, then allowed to cool naturally to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-TA-m500-N5-Ar600-H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles is approximately 12.1 nm.

[0052] Example 7

[0053] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 3 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours, then naturally cooled to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-TA-m1200-N3-Ar600-H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles is approximately 9.7 nm.

[0054] Example 8

[0055] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and CO2 was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours, then naturally cooled to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-TA-m1200-CO25-Ar600 H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles is approximately 7.8 nm.

[0056] Example 9

[0057] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at a reduction temperature of 400℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours, then naturally cooled to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-TA-m1200-N5-Ar600-H400 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles is approximately 5.9 nm.

[0058] Example 10

[0059] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, copper nitrate, 5g tannic acid, and 50g activated carbon were weighed out with a metal loading of 10wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 35:35:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200g of steel balls (large balls with a diameter of φ10, small balls with a diameter of φ6, and a large-to-small ball ratio of 1:1) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours, then allowed to cool naturally to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 35 Mo 35 / NC-TA-m1200-N5-Ar600-H600 high-entropy alloy catalyst. The particle size of the high-entropy alloy particles is approximately 6.4 nm.

[0060] Comparative Example 1

[0061] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, and copper nitrate were weighed out with a metal loading of 10 wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. These were then mixed with 50 g of activated carbon and allowed to stand for 12 hours before drying at 110 °C. The precursor was then placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600 °C. The temperature was increased at a rate of 5 °C / min, and the mixture was heated from room temperature to the reduction temperature and held at this temperature for 2 hours, followed by natural cooling to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 25 Mo 45 / NC-T600 catalyst. The high-entropy alloy particles have a particle size of 8.5 nm.

[0062] Comparative Example 2

[0063] Ammonium molybdate, cobalt nitrate, nickel nitrate, ferric nitrate, and copper nitrate were weighed out with a metal loading of 10 wt% and an atomic percentage of molybdenum:cobalt:nickel:iron:copper of 45:25:10:10:10. The mixture was then placed in a stainless steel ball mill jar, and 1200 g of steel balls (large balls with a diameter of φ8, small balls with a diameter of φ4, and a ratio of large to small balls of 1:0.5) were added. The jar was sealed, and nitrogen gas was introduced to purge the air from the jar. The mixture was ball-milled for 5 hours. The precursor was then heat-treated at 600℃ for 3 hours under an inert atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, it was placed in a reduction furnace and reduced under a hydrogen-argon mixed atmosphere at 600℃ at a heating rate of 5℃ / min. The temperature was increased from room temperature to the reduction temperature and held at this temperature for 2 hours, then allowed to cool naturally to room temperature. Fe was obtained. 10 Ni 10 Cu 10 Co 25 Mo 45 -m1200-N5-Ar600-H600 catalyst, with a particle size of approximately 25.5 nm.

[0064] To demonstrate the beneficial effects of this invention, the inventors used the catalysts obtained in Examples 1-10 and Comparative Examples 1-2 for performance testing in an ammonia synthesis reaction. A fixed-bed continuous flow reactor was used for continuous evaluation of the ammonia synthesis reaction, and the results are shown in Table 1. 2 mL of catalyst was added to the reactor, and after completing a series of preliminary steps such as checking airtightness, a temperature ramp-up program was set. The reduced catalyst was stabilized at a certain reaction temperature for 1-3 hours before activity testing. The ammonia concentration in the outlet reaction gas was determined using a chemical absorption method, the specific steps of which are as follows: First, a certain amount of water was added to the gas absorption tube, then an indicator was added, followed by a certain amount of standard dilute sulfuric acid solution. Then, the reaction outlet gas was passed into the gas absorption tube. The ammonia in the gas underwent a neutralization reaction with the dilute sulfuric acid solution, while the gas in the outlet gas that could not be absorbed by the acid entered a wet gas flow meter, and its volume was measured. When the absorbent changed from purplish-red to pale yellow, the reaction equivalence point was reached, and the absorption time and gas volume were recorded.

[0065] Table 1. Comparison of catalytic performance of catalysts in Examples 1-10 and Comparative Examples 1-2

[0066]

[0067]

[0068] Reaction conditions: 5 MPa, 5000 h -1 H2:N2 = 3.

[0069] Table 1 shows that, as demonstrated in Examples 1 and 2, changing the elemental composition of the catalyst can effectively improve its catalytic performance. Comparing Examples 1 and 3, it was found that increasing the heat treatment temperature increases the catalyst particle size and decreases the catalytic activity. Examples 1 and 4 show that changing the type of organic acid affects the catalyst particle size, thus impacting its catalytic performance. Examples 1 and 5 show that the catalytic performance of the high-entropy alloy catalyst supported on magnesium oxide is inferior to that supported on carbon materials. Examples 6 and 7 show that reducing the mass of the steel balls and shortening the ball milling time decreases the catalytic activity. Examples 8 and 9 show that changes in the ball milling atmosphere and reduction temperature also affect the catalyst's ammonia synthesis performance. Example 10 illustrates that the catalytic performance can be adjusted by controlling the atomic percentage of each element in the catalyst.

[0070] Depend on Figure 1 As shown in Table 1, Comparative Example 1, without organic acid ball milling and heat treatment, did not form a high-entropy alloy; the metal was simply dispersed on the support. Comparative Example 2, without adding a support and changing the sphere size, produced catalyst particles with larger sizes. The catalysts obtained in Comparative Examples 1 and 2 exhibited relatively low catalytic performance in ammonia synthesis.

[0071] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of a high-entropy alloy ammonia synthesis catalyst in the ammonia synthesis catalytic reaction, characterized in that, The high-entropy alloy ammonia synthesis catalyst comprises a support and high-entropy alloy particles loaded on the surface of the support; the loading amount of the high-entropy alloy particles is 5-70 wt%; the average particle size of the high-entropy alloy particles is 2-20 nm; the high-entropy alloy particles include an active metal and an auxiliary metal; the active metal includes at least three of Fe, Co, Mo, Ru, Os, Ni, Rh, Ir, Re, Pt, Pd, and Ag; the auxiliary metal includes at least one of Ce, Ba, Sr, Mg, Ca, Li, K, La, Sm, W, V, and Cs; the support is at least one of carbon material, alkaline earth metal oxide, and rare earth metal oxide. The preparation method of the high-entropy alloy ammonia synthesis catalyst includes the following steps: (1) After the active metal salt, auxiliary metal salt, organic ligand and carrier are mixed evenly, ball milling is performed in an inert atmosphere to obtain precursor A; the organic ligand is one or more of citric acid, malic acid, tartaric acid, acetic acid, succinic acid, oxalic acid, tannic acid and humic acid. (2) Heat treatment of precursor A under an inert atmosphere and cooling to obtain alloy precursor B; the heat treatment temperature is 200-800 ℃ and the heat treatment time is 2-6 h. (3) Reduce precursor B in a reducing atmosphere and cool it to obtain the product.

2. The application of the high-entropy alloy ammonia synthesis catalyst according to claim 1 in the ammonia synthesis catalytic reaction, characterized in that, Based on the mass of the high-entropy alloy particles, the content of each active metal is independently 5-50 wt%; the content of the auxiliary metal is 5-50 wt%.

3. The application of the high-entropy alloy ammonia synthesis catalyst according to claim 1 in the ammonia synthesis catalytic reaction, characterized in that, The mass ratio of organic ligand to metal precursor is 1-100:1; the metal precursor is an active metal salt and an auxiliary metal salt.

4. The application of the high-entropy alloy ammonia synthesis catalyst according to claim 1 in the ammonia synthesis catalytic reaction, characterized in that, During the ball milling process, the ball-to-material ratio is 1-60:1, the ball milling speed is 300-800 rpm, and the ball milling time is 3-6 hours.

5. The application of the high-entropy alloy ammonia synthesis catalyst according to claim 1 in the ammonia synthesis catalytic reaction, characterized in that, In step (3), the reduction temperature is 200-1200 ℃ and the reduction time is 1-6 h.

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