A nickel-modified molybdenum carbide dual-site catalyst, a preparation method thereof and application thereof in synthesis of ammonia

Abstract

The application discloses a nickel-modified molybdenum carbide dual-site catalyst, a preparation method thereof and application of the catalyst in synthesis of ammonia. The molybdenum carbide (Mo2C)-based catalyst comprises a carrier and an active component. The carrier is Mo2C, the active component comprises metal Mo and metal Ni, and the metal Ni is loaded on the carrier. The nickel-modified molybdenum carbide dual-site catalyst is synthesized by using a wet immersion method, and the catalyst is used in the synthesis of ammonia reaction, and the catalyst exhibits excellent activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of ammonia synthesis catalysts and their preparation technology, specifically relating to a nickel-modified molybdenum carbide dual-site catalyst, its preparation method, and its application in ammonia synthesis. Background Technology

[0002] Ammonia (NH3) is an important chemical raw material widely used in agriculture, industry, and energy. It is primarily used in the manufacture of nitrogen fertilizers such as urea and as a catalyst in chemical processes and an intermediate in the synthesis of other chemicals. The traditional Haber-Bosch process uses Fe-based catalysts to synthesize ammonia under high temperature and pressure conditions, which involves significant energy consumption and carbon dioxide emissions. In recent years, ammonia has also attracted considerable attention as a potential carbon-free hydrogen storage energy carrier due to its high hydrogen content (17.8%) and high energy density (4.3 kWh / kg⁻¹). -1 At -33 ℃, it easily becomes a liquid for transportation, which helps solve the problems of hydrogen storage and transportation. With the rise of the "green ammonia" process, the process route of "renewable energy → water electrolysis to produce hydrogen → ammonia synthesis → ammonia application" has attracted widespread attention from researchers (Zhou Y, Wang J, Jiang L, et al. Unraveling the size-dependent effect of Ru-based catalysts on ammoniasynthesis at mild conditions[J]. Journal of Catalyst, 2021, 404:501-511). However, pressure-type water electrolysis to produce hydrogen requires an output pressure ≤5.0 MPa, and the typical output pressure is 1.6-3.2 MPa. The temperature of the hydrogen (H2) obtained by electrolysis after deep dehydration and deoxygenation is about 400 ℃. Therefore, to achieve the complementary integration of renewable energy power and synthetic ammonia technology, it is urgent to develop ammonia synthesis technology under relatively mild conditions (reaction conditions: ~400 ℃, 1.6~3.2 MPa) that is compatible with the renewable energy power electrolysis hydrogen production system. Existing industrial synthetic ammonia catalysts for fossil energy are difficult to meet the requirements under these relatively mild conditions. Therefore, designing and developing new and efficient low-temperature and low-pressure synthetic ammonia catalysts has become the key to connecting the "renewable energy-hydrogen-ammonia" cycle route.

[0003] In recent years, the application of non-noble metals, represented by molybdenum (Mo), in ammonia synthesis has become increasingly widespread. Among them, molybdenum carbide or other transition metal carbides exhibit higher melting points and superior electrical conductivity compared to their parent metals. The valence state and d-band center of transition metals can be significantly altered through the formation of transition metal carbides, thereby significantly improving catalytic performance. In this context, transition metal carbides are widely used as inexpensive alternatives to noble metals (such as Pt and Ru). In terms of performance, Mo metal lies to the left of the "volcano-shaped" curve, possessing a strong ability to adsorb and dissociate N2. However, due to its excessively strong nitrogen adsorption capacity, Mo-based catalysts struggle to further hydrogenate nitrogen species and desorb the product ammonia, resulting in low ammonia synthesis performance for traditional Mo-based catalysts. Therefore, the development of highly efficient Mo-based catalysts is of significant research value in the field of ammonia synthesis. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a nickel-modified molybdenum carbide dual-site catalyst, its preparation method, and its application in ammonia synthesis. The catalyst possesses both Ni and Mo active sites and exhibits excellent ammonia synthesis performance.

[0005] Based on this, the technical solution of the present invention is as follows: A molybdenum carbide two-site catalyst includes a support and an active component, wherein the support is molybdenum carbide (Mo2C) and the active component includes metallic Mo and metallic Ni, wherein the metallic Ni is supported on the support.

[0006] According to an embodiment of the present invention, in the molybdenum carbide two-site catalyst, the metallic Ni exists in ionic form. Preferably, the metallic Ni exists in the form of Ni₂Mo₃N.

[0007] According to an embodiment of the present invention, in the molybdenum carbide dual-site catalyst, metallic Ni coexists in both ionic and elemental forms. Preferably, the metallic Ni exists in both Ni₂Mo₃N and elemental Ni forms.

[0008] According to an embodiment of the present invention, the Mo2C is β-Mo2C.

[0009] According to an embodiment of the present invention, the mass fraction ratio of metallic Ni to the support Mo2C is 0.1-0.3:1. For example, it is 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1.

[0010] According to an embodiment of the present invention, in the molybdenum carbide dual-site catalyst, metallic Ni is uniformly distributed on molybdenum carbide.

[0011] According to an embodiment of the present invention, in the molybdenum carbide dual-site catalyst, metallic Mo exists in the form of β-Mo2C.

[0012] This invention also provides a method for preparing a molybdenum carbide dual-site catalyst, the method comprising the following steps: (1) The molybdenum-containing precursor is oxidized to obtain molybdenum oxide; (2) The molybdenum oxide in step (1) is carbonized to obtain an intermediate product, and then the intermediate product is passivated to obtain a support, namely molybdenum carbide (Mo2C). (3) After loading the Ni-containing precursor solution onto the support in step (2), the molybdenum carbide dual-site catalyst is prepared.

[0013] According to an embodiment of the present invention, in step (1), the molybdenum-containing precursor is selected from at least one of ammonium molybdate tetrahydrate, molybdenum chloride and sodium molybdate, preferably ammonium molybdate tetrahydrate.

[0014] According to an embodiment of the present invention, in step (1), the oxidation treatment is carried out under an oxygen-containing atmosphere. Preferably, the oxygen-containing atmosphere includes at least oxygen, and optionally includes or excludes at least one of argon, hydrogen, nitrogen, etc., for example, the oxygen-containing atmosphere is air. Preferably, the oxygen content in the oxygen-containing atmosphere is 10-100 vol%, preferably 10-30 vol%, for example, 10 vol%, 20 vol%, 30 vol%, and the N2 content is 0-90 vol%, preferably 70-90 vol%, for example, 70 vol%, 80 vol%, 90 vol%.

[0015] According to an embodiment of the present invention, in step (1), the oxidation treatment temperature is 400-600 °C, for example 400 °C, 500 °C or 600 °C; the oxidation treatment time is 2-10 h, preferably 4-8 h.

[0016] According to an embodiment of the present invention, in step (2), the carbonization process is carried out in a carbon-containing atmosphere. Preferably, the carbon-containing atmosphere comprises at least methane and hydrogen, and optionally includes or excludes at least one of argon, helium, etc. Preferably, the total volume content of methane and hydrogen in the carbon-containing atmosphere is 1-100 vol%, preferably 5-50 vol%, for example, 5 vol%, 10 vol%, 20 vol%, 30 vol%, 40 vol%, or 50 vol%. Preferably, the carbon-containing atmosphere is selected from a mixture of CH4 and H2 gases with a volume ratio of 20-40:80-60.

[0017] According to an embodiment of the present invention, in step (2), the carbonization temperature is 600-900℃, for example, 600℃, 700℃, 800℃ or 900℃; the carbonization time is 1-5 h, for example, 1 h, 2 h, 3 h, 4 h or 5 h. Preferably, the heating rate during carbonization is 1-10 ℃ min. -1 .

[0018] According to an embodiment of the present invention, in step (2), the passivation treatment is carried out in a passivation gas. Preferably, the passivation gas comprises a mixture of oxygen and an inert gas. Preferably, the inert gas is selected from any one of nitrogen, argon, helium, etc., and is preferably argon. Preferably, the volume concentration of oxygen in the passivation gas is 0.1-10 vol%, preferably 1-8 vol%, for example, 1 vol%.

[0019] According to an embodiment of the present invention, in step (2), the passivation treatment temperature is 10-30°C, for example, room temperature. The passivation treatment time is 1-10 hours, preferably 2-8 hours.

[0020] According to an embodiment of the present invention, in step (3), the Ni-containing precursor is selected from at least one of nickel chloride, nickel nitrate hexahydrate, nickel hydroxide, and nickel carbonate, preferably nickel nitrate hexahydrate.

[0021] According to an embodiment of the present invention, in step (3), the mass ratio of Ni in the Ni-containing precursor to the mass ratio of the carrier Mo2C is 0.1-0.3:1. For example, it is 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1.

[0022] According to an embodiment of the present invention, in step (3), the nickel-containing precursor solution is an aqueous solution obtained by dissolving the nickel-containing precursor in water. Preferably, the concentration of the nickel-containing precursor solution is 0.05-0.4 g / mL, more preferably 0.1-0.3 g / mL.

[0023] According to an embodiment of the present invention, in step (3), the loading method is wet impregnation, for example, adding a nickel-containing precursor solution dropwise onto the carrier.

[0024] According to an embodiment of the present invention, step (3) further includes a post-processing step, in which the obtained product is dried. The drying temperature is 60-70°C, and the drying time is 12-48 h.

[0025] According to an embodiment of the present invention, the preparation method of the catalyst specifically includes the following steps: (1) Ammonium molybdate tetrahydrate was calcined in a muffle furnace to form molybdenum oxide; (2) The molybdenum oxide powder in step (1) is further carbonized into an intermediate product in a tube furnace by passing a mixture of methane and hydrogen. The intermediate product is then passivated to obtain the carrier. (3) The Ni-containing precursor solution is loaded onto the support in step (2) and dried to prepare the catalyst.

[0026] The present invention also provides the molybdenum carbide two-site catalyst prepared by the above preparation method.

[0027] The present invention also provides the application of the above-mentioned molybdenum carbide two-site catalyst in the catalytic synthesis of ammonia.

[0028] Preferably, it is used as a catalyst for ammonia synthesis, and more preferably as a catalyst for ammonia synthesis under low temperature and low pressure conditions.

[0029] According to an embodiment of the present invention, the temperature for synthesizing ammonia is 300~400 ℃, exemplarily 300 ℃, 350 ℃, or 400 ℃; the pressure for synthesizing ammonia is 0.5~3 MPa, exemplarily 1 MPa.

[0030] The present invention also provides a method for synthesizing ammonia, which contains at least the above-mentioned molybdenum carbide two-site catalyst.

[0031] The beneficial effects of this invention are: 1. This invention utilizes a wet impregnation method to synthesize a Ni-modified molybdenum carbide dual-site catalyst, and uses the catalyst in the ammonia synthesis reaction. The catalyst exhibits excellent activity and stability.

[0032] 2. The ammonia synthesis rate of the catalyst of this invention is superior to that of traditional Mo-based catalysts. The catalyst is composed of non-precious metals, has industrialization potential, and can greatly reduce production costs.

[0033] 3. The Mo2C and Ni used in this invention have a strong interaction, and the Ni2Mo3N and Mo2C produced under in-situ conditions jointly promote the synthesis of ammonia. Attached Figure Description

[0034] Figure 1 These are the XRD patterns of the catalysts prepared in Examples 1-5 and Comparative Examples 1, 2, and 3.

[0035] Figure 2 The graph shows the ammonia synthesis reaction rate of the catalysts prepared in Examples 1-5 and Comparative Example 1 at 400 °C and 1 MPa.

[0036] Figure 3 This is a TEM image of the catalyst in Example 3.

[0037] Figure 4The stability diagram of the catalyst in Example 3 for ammonia synthesis at 400 °C and 1 MPa is shown. Detailed Implementation

[0038] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0039] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0040] Comparative Example 1 The preparation method of Mo-based catalyst is as follows: (1) Place ammonium molybdate tetrahydrate (1 g) in a muffle furnace and incubate in air at 5 °C for 1 min. -1 The temperature was raised to 500℃ and calcined for 4 hours to obtain oxides; (2) After grinding through an 80-mesh sieve, the mixture is transferred to a tube furnace and heated at 5°C for 1 minute in a mixture of CH4 and H2 with a volume ratio of 20:80. -1 Heat to 300℃, then change the rate to 1℃ min. -1 The temperature was raised to 700 °C and carburized for 2 h to obtain molybdenum carbide; after cooling to room temperature, it was passedivated by switching to an O2 / Ar mixed gas for 6 h to obtain a black powder, which is the Mo-based catalyst, labeled as β-Mo2C.

[0041] Example 1 The preparation method of Mo2C-based catalyst is as follows: (1) Place ammonium molybdate tetrahydrate (1 g) in a muffle furnace and incubate in air at 5 °C for 1 min. -1 The temperature was raised to 500℃ and calcined for 4 hours to obtain oxides; (2) After grinding through an 80-mesh sieve, the material is transferred to a tube furnace and heated at 5°C for 1 minute in a mixture of CH4 and H2 with a volume ratio of 20:80. -1 Heat to 300℃, then change the rate to 1℃ min. -1 The temperature was raised to 700 °C and carburized for 2 h to obtain molybdenum carbide. After cooling to room temperature, the mixture was passed through with a mixture of O2 and Ar for 6 h to obtain β-Mo2C.

[0042] (3) Dissolve 0.229 g of nickel nitrate hexahydrate in 1.5 mL of deionized water and sonicate for 10 min. At the same time, grind β-Mo2C and pass it through an 80-mesh sieve (0.4 g). Add nickel nitrate aqueous solution dropwise onto β-Mo2C. Finally, dry in an oven at 60 °C for 12 h to obtain a black powder catalyst, labeled as 10Ni-Mo2C, that is, the mass fraction ratio of metal Ni to support Mo2C is 0.1.

[0043] Example 2 The preparation method of Mo2C-based catalyst is as follows: (1) Place ammonium molybdate tetrahydrate (1 g) in a muffle furnace and incubate in air at 5 °C for 1 min. -1 The temperature was raised to 500℃ and calcined for 4 hours to obtain oxides; (2) After grinding through an 80-mesh sieve, the material is transferred to a tube furnace and heated at 5°C for 1 minute in a mixture of CH4 and H2 with a volume ratio of 20:80. -1 Heat to 300℃, then change the rate to 1℃ min. -1 The temperature was raised to 700 °C and carburized for 2 h to obtain molybdenum carbide. After cooling to room temperature, the mixture was passed through with an O2 / Ar mixed gas for 6 h to obtain β-Mo2C.

[0044] (3) Dissolve 0.3568 g of nickel nitrate hexahydrate in 1.5 mL of deionized water and sonicate for 10 min. At the same time, grind β-Mo2C and pass it through an 80-mesh sieve (0.4 g). Add nickel nitrate aqueous solution dropwise onto β-Mo2C. Finally, dry in an oven at 60 °C for 12 h to obtain a black powder catalyst, labeled as 15Ni-Mo2C, that is, the mass fraction ratio of metal Ni to support Mo2C is 0.15.

[0045] Example 3 The preparation method of Mo2C-based catalyst is as follows: (1) Place ammonium molybdate tetrahydrate (1 g) in a muffle furnace and incubate in air at 5 °C for 1 min. -1 The temperature was raised to 500℃ and calcined for 4 hours to obtain oxides; (2) After grinding through an 80-mesh sieve, the mixture is transferred to a tube furnace and heated at 5°C for 1 minute in a mixture of CH4 and H2 with a volume ratio of 20:80. -1 Heat to 300℃, then change the rate to 1℃ min. -1 The temperature was raised to 700 °C and carburized for 2 h to obtain molybdenum carbide. After cooling to room temperature, the mixture was passed through with an O2 / Ar mixed gas for 6 h to obtain β-Mo2C.

[0046] (3) Dissolve 0.5050 g of nickel nitrate hexahydrate in 1.5 mL of deionized water and sonicate for 10 min. At the same time, grind β-Mo2C and pass it through an 80-mesh sieve (0.4 g). Add the nickel nitrate aqueous solution dropwise onto the β-Mo2C. Finally, dry in an oven at 60 ℃ for 12 h. A black powder catalyst is obtained, labeled as 20Ni-Mo2C, which means that the mass fraction ratio of metallic Ni to the support Mo2C is 0.2.

[0047] Example 4 The preparation method of Mo2C-based catalyst is as follows: (1) Place ammonium molybdate tetrahydrate (1 g) in a muffle furnace and incubate in air at 5 °C for 1 min. -1 The temperature was raised to 500℃ and calcined for 4 hours to obtain oxides; (2) After grinding through an 80-mesh sieve, the mixture is transferred to a tube furnace and heated at 5°C for 1 minute in a mixture of CH4 and H2 with a volume ratio of 20:80. -1 Heat to 300℃, then change the rate to 1℃ min. -1 The temperature was raised to 700 °C and carburized for 2 h to obtain molybdenum carbide. After cooling to room temperature, the mixture was passed through with an O2 / Ar mixed gas for 6 h to obtain β-Mo2C.

[0048] (3) Dissolve 0.6741 g of nickel nitrate hexahydrate in 1.5 mL of deionized water and sonicate for 10 min. At the same time, grind β-Mo2C and pass it through an 80-mesh sieve (0.4 g). Add nickel nitrate aqueous solution dropwise onto β-Mo2C. Finally, dry in an oven at 60 °C for 12 h to obtain a black powder catalyst, labeled as 25Ni-Mo2C, that is, the mass fraction ratio of metal Ni to support Mo2C is 0.25.

[0049] Example 5 The preparation method of Mo2C-based catalyst is as follows: (1) Place ammonium molybdate tetrahydrate (1 g) in a muffle furnace and incubate in air at 5 °C for 1 min. -1 The temperature was raised to 500℃ and calcined for 4 hours to obtain oxides; (2) After grinding through an 80-mesh sieve, the mixture is transferred to a tube furnace and heated at 5°C for 1 minute in a mixture of CH4 and H2 with a volume ratio of 20:80. -1 Heat to 300℃, then change the rate to 1℃ min. -1 The temperature was raised to 700 °C and carburized for 2 h to obtain molybdenum carbide. After cooling to room temperature, the mixture was passed through with an O2 / Ar mixed gas for 6 h to obtain β-Mo2C.

[0050] (3) Dissolve 0.8667 g of nickel nitrate hexahydrate in 1.5 mL of deionized water and sonicate for 10 min. At the same time, grind β-Mo2C and pass it through an 80-mesh sieve (0.4 g). Add nickel nitrate aqueous solution dropwise onto β-Mo2C. Finally, dry in an oven at 60 ℃ for 12 h to obtain a black powder catalyst, labeled as 30Ni-Mo2C, that is, the mass fraction ratio of metal Ni to support Mo2C is 0.3.

[0051] Comparative Example 2 The preparation method of Mo-based catalyst is as follows: Ammonium molybdate tetrahydrate (1 g) was placed in a muffle furnace and incubated in air at 5 °C for 1 min. -1 The temperature was raised to 500 °C and calcined for 4 h to obtain oxides; After grinding through an 80-mesh sieve, the material was transferred to a tube furnace and the flow rate was set to 100 mL / min under a 99.999% NH3 atmosphere. -1 The temperature was increased to 700 ℃ at a rate of 5 ℃ / min. -1 Nitrogen permeation was performed for 2 hours, followed by cooling to room temperature; a mixture of CH4 and H2 with a volume ratio of 20:80 was then subjected to nitrogen permeation at 5 °C for 1 minute. -1 The temperature was raised to 700 °C and carburized for 2 h. After cooling to room temperature, the mixture was passed through with an O2 / Ar mixed gas for 6 h to obtain α-MoC.

[0052] Comparative Example 3 The preparation method of Mo-based catalyst is as follows: Ammonium molybdate tetrahydrate (2 g), nickel nitrate hexahydrate (2.19 g), and citric acid (7.935 g) were dissolved in 60 mL of 10% dilute nitric acid solution and heated and stirred at 60 °C for 12 h until a green gel was formed. The gel was then calcined in air at 500 °C for 2 h to obtain NiMoO. x Precursor; NiMoO x The precursor was at 10 °C min -1 The temperature was raised to 700 °C and maintained for 2 h, then cooled to room temperature, and passivated with an O2 / Ar mixed gas for 6 h to obtain Ni2Mo3N.

[0053] Application examples 0.20 g of each catalyst prepared in Examples 1-5 and Comparative Examples 1-3 were used, with a mass hourly space velocity (WHSV) of 60,000 mLg. -1 h -1The ammonia synthesis rate was determined in a continuous flow micro fixed-bed reactor. Changes in the NH3 concentration in the tail gas were measured using ion chromatography (Thermo Scientific, DIONEX, ICS-600). The reaction gas composition was a mixture of 75% H2 and 25% N2 (volume ratio). The ammonia synthesis reaction rates for different catalysts were measured at 400 °C and 1 MPa. The test results are shown in Table 1 below.

[0054] Table 1 Different catalysts at 400 o Ammonia synthesis performance at C and 1 MPa

[0055] As shown in Table 1, in Comparative Example 1 and Examples 1-5, the ammonia synthesis activity first increased and then decreased with increasing Ni content. The addition of Ni metal can promote ammonia synthesis. Comparative Example 1 and Comparative Example 2 prepared molybdenum carbide with different crystal phases. β-Mo2C has a hexagonal crystal facet, and its ammonia synthesis rate (6.8 mmol g) is relatively high. -1 h -1 ) is superior to α-MoC (2.7 mmol g) with tetragonal crystal faces. -1 h -1 Comparative Example 3 was synthesized in one step using a stable ratio of nickel-molybdenum oxide. Table 1 shows the promoting effect of Ni on Mo-based catalysts, but its catalytic performance of 9.1 mmol is still lower than that of the optimal ratio of 20Ni-Mo2C.

[0056] Catalyst performance evaluation Figure 1 The images show the XRD patterns of the catalysts prepared in Examples 1-5 and Comparative Examples 1, 2, and 3. Figure 1 It can be observed that β-Mo₂C, α-MoC, and Ni₂Mo₃N are all pure phases with good crystal forms. Furthermore, after loading nickel nitrate, the catalyst yields both β-Mo₂C with hexagonal crystal faces and a small amount of Ni₂Mo₃N, indicating a strong interaction between nickel and molybdenum carbide, resulting in a mixed phase doped with Ni₂Mo₃N under in-situ conditions. The 20Ni-Mo₂C sample, after reaction, consists of Ni₂Mo₃N and Mo₂C, while the 25Ni-Mo₂C and 30Ni-Mo₂C samples consist of Ni₂Mo₃N, Mo₂C, and Ni. A small amount of Ni reacts with Mo₂C, while excessive Ni doping causes some metallic Ni to precipitate, thus inhibiting ammonia synthesis activity.

[0057] Figure 2 The graph shows the ammonia synthesis reaction rates of the catalysts prepared in Examples 1-5 and Comparative Example 1 at 400 °C and 1 MPa. Figure 2As can be seen, the ammonia synthesis performance of β-Mo2C is approximately three times that of α-MoC. With increasing Ni loading, the catalytic performance of xNi-Mo2C first increases and then decreases, reaching a maximum value of 16.1 mmol g for 20Ni-Mo2C. -1 h -1 .

[0058] Figure 3 This is a TEM image of the catalyst prepared in Example 3. The image shows that 20Ni-Mo2C simultaneously exhibits lattice fringes of Mo2C (d=0.24 nm) and Ni2Mo3N (d=0.21 nm), confirming the existence of the two phases.

[0059] Figure 4 The figure shows the stability of the catalyst prepared in Example 3 at 400 °C and 1 MPa. It can be seen from the figure that the activity of the 20Ni-Mo2C catalyst prepared in Example 1 did not decrease significantly during the 300 h stability test, indicating that the Ni-supported molybdenum carbide dual-site catalyst prepared in this invention has good stability.

[0060] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A molybdenum carbide dual-site catalyst, characterized in that, It includes a support and an active component, wherein the support is Mo2C and the active component includes metallic Mo and metallic Ni, wherein metallic Ni is loaded on the support.

2. The catalyst according to claim 1, characterized in that, In the molybdenum carbide two-site catalyst, the metallic Ni exists in ionic form; Preferably, the metallic Ni exists in the form of Ni2Mo3N.

3. The catalyst according to claim 1, characterized in that, In the molybdenum carbide dual-site catalyst, metallic Ni exists in both ionic and elemental forms. Preferably, the metallic Ni exists in both Ni₂Mo₃N and elemental Ni forms.

4. The catalyst according to claim 1, characterized in that, The Mo2C is β-Mo2C; Preferably, the mass fraction ratio of metallic Ni to the support Mo2C is 0.1-0.3:1; Preferably, in the molybdenum carbide dual-site catalyst, metallic Ni is uniformly distributed on the molybdenum carbide.

5. The method for preparing the catalyst according to any one of claims 1-4, characterized in that, The method includes the following steps: (1) The molybdenum-containing precursor is oxidized to obtain molybdenum oxide; (2) The molybdenum oxide in step (1) is carbonized to obtain an intermediate product, and then the intermediate product is passivated to obtain a support, namely molybdenum carbide (Mo2C). (3) After loading the Ni-containing precursor solution onto the support in step (2), the molybdenum carbide dual-site catalyst is prepared.

6. The method according to claim 5, characterized in that, In step (1), the molybdenum-containing precursor is selected from at least one of ammonium molybdate tetrahydrate, molybdenum chloride, and sodium molybdate; Preferably, in step (1), the oxidation treatment is performed by calcination in an oxygen-containing atmosphere; Preferably, the oxidation treatment temperature is 400-600 °C; the oxidation treatment time is 2-10 h.

7. The method according to claim 5, characterized in that, In step (2), the carbonization process is carried out in a carbon-containing atmosphere, which includes at least methane and hydrogen. Preferably, in step (2), the carbonization temperature is 600-900℃, the carbonization time is 1-5 h, and the heating rate during carbonization is 1-10 ℃ min. -1 .

8. The method according to claim 5, characterized in that, In step (2), the passivation process is carried out in a passivation gas, which includes a mixture of oxygen and inert gas; Preferably, in step (2), the passivation treatment temperature is 10-30℃ and the passivation treatment time is 1-10h; Preferably, in step (3), the Ni-containing precursor is selected from at least one of nickel chloride, nickel nitrate hexahydrate, nickel hydroxide, and nickel carbonate; Preferably, in step (3), the mass ratio of Ni in the Ni-containing precursor to the mass ratio of the carrier Mo2C is 0.1-0.3:1; Preferably, in step (3), the nickel-containing precursor solution is obtained by dissolving the nickel-containing precursor in water, and the concentration of the nickel-containing precursor solution is 0.05-0.4 g / mL.

9. The application of the catalyst according to any one of claims 1-4 in the catalytic synthesis of ammonia, preferably as a catalyst for the synthesis of ammonia, more preferably as a catalyst for the synthesis of ammonia under low temperature and low pressure conditions; Preferably, the temperature for synthesizing ammonia is 300~400 ℃, and the pressure for synthesizing ammonia is 0.5~3 MPa.

10. A method for synthesizing ammonia, comprising at least the catalyst according to any one of claims 1-4.

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