Ni-based three-phase structure synthetic ammonia catalyst, preparation method and application thereof

Abstract

This invention discloses a Ni-based three-phase ammonia synthesis catalyst, its preparation method, and its applications. The Ni-based three-phase catalyst uses molybdenum nitride as a support and metallic Ni as the active component, with a Ni-Mo-N structure forming a third phase at the interface. Molybdenum oxide is solvated and then calcined under an ammonia atmosphere to obtain the molybdenum nitride support. The molybdenum nitride is then impregnated in a nickel nitrate solution, dried by rotary evaporation to remove moisture, and reduced under a mixed hydrogen and nitrogen atmosphere to obtain the Ni-based three-phase catalyst. The catalyst of this invention exhibits excellent reactivity and stability in both thermocatalytic and electro-activated ammonia synthesis.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a Ni-based three-phase structure ammonia synthesis catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia is one of the most fundamental chemical raw materials in modern industrial and agricultural production, mainly used in the production of nitrogen fertilizers and other nitrogen-containing chemicals, playing a vital role in human production and daily life. Furthermore, its high hydrogen content (17.7 wt%) and high energy density (3 kWh kg⁻¹) give ammonia advantages such as high energy density and ease of storage and transportation, making it considered an important carbon-free energy carrier. However, the ammonia synthesis industry is currently a high-energy-consuming and high-carbon-emission industry, with carbon emissions reaching as high as 4.2 tons per ton of ammonia, and annual carbon emissions from my country's ammonia synthesis industry estimated at approximately 200 million tons. Therefore, developing low-temperature, low-pressure ammonia synthesis catalysts and innovating ammonia synthesis reaction processes to achieve energy conservation and emission reduction is of great significance.

[0003] Traditional low-temperature, low-pressure ammonia synthesis catalysts use metallic Ru as the active center, but the high cost of Ru makes industrialization difficult. The Mars van Krevelen (MvK) mechanism, using metal nitrides with nitrogen vacancies as the core, enables efficient low-temperature, low-pressure ammonia synthesis from N2 and H2, representing an effective strategy to improve the activation capacity of nitrogen at low temperatures and achieve efficient low-temperature, low-pressure ammonia synthesis. Currently, Hosono et al. have developed a stable and highly efficient bifunctional catalyst by supporting non-precious metal Ni on rare-earth nitrides LaN and CeN (Nature, 2020, 583, 391-395; Journal of the American Chemical Society, 2020, 142, 14374-14383). This catalyst achieves a concentration of 10.9 mmol g / L at 400 °C and 1 MPa. -1 h -1 High ammonia production rates are achievable. However, the high sensitivity of rare earth nitride supports to oxygen and humidity in the air severely limits their application in catalyst preparation, loading, and use. Chinese patent CN 118925767A discloses a molybdenum-based catalyst and its preparation method. By treating molybdenum nitride under different atmospheres and temperatures, a preferred γ-Mo₂N catalyst was obtained, achieving a yield of 5.3 mmol g / L at 400℃ and 1 MPa. -1 h -1 ammonia production rate.

[0004] Improving catalyst reactivity by applying an external electric field current to the catalyst bed has been proven to be an effective strategy for enhancing the activity of catalysts in low-temperature and low-pressure ammonia synthesis. Sekine et al. reported on this strategy using Ru-Cs / SrZrO3 and Fe / Ce... 0.4 Al0.1 Zr 0.5 O2 -δ Applying a 6 mA current to the catalyst can increase the ammonia synthesis rate by 200% at the same temperature (ACS Omega, 2020, 5, 6846-6851; Chemical Science, 2017, 8, 5434-5439). However, existing literature on electroactivated ammonia synthesis processes all use oxide ammonia synthesis catalysts, requiring an external voltage of 300-600 V for a bed of only a few millimeters. This translates to tens of kV for a bed of several meters in an industrial synthesis tower, resulting in low safety and making practical application difficult.

[0005] In summary, the catalytic activity of existing molybdenum nitride catalysts still needs to be improved. Although rare earth nitrides have high activity, they face the problem of poor weather resistance in water and oxygen, making them difficult to apply. On the other hand, existing electro-activated ammonia synthesis catalysts are all oxides, requiring extremely high external voltages, which poses safety issues during industrial scale-up. Summary of the Invention

[0006] One of the technical problems to be solved by this invention is to construct a non-ruthenium metal nitride catalyst with high ammonia synthesis activity, high water and oxygen weather resistance, and high intrinsic conductivity at low temperature and low pressure. A second technical problem to be solved by this invention is to provide a method for preparing the above catalyst, enabling the in-situ construction of the Ni-Mo-N third phase component. A third technical problem to be solved by this invention is to provide the application of the above catalyst in electroactivated thermocatalytic ammonia synthesis, achieving high reaction activity under low applied electric field conditions. Ultimately, this invention overcomes the shortcomings of existing technologies.

[0007] To achieve the aforementioned objectives, the present invention employs the following technical solution:

[0008] A Ni-based three-phase ammonia synthesis catalyst, characterized in that: molybdenum nitride is used as a support, metallic Ni is used as the active component, and a Ni-Mo-N structure is generated under a reducing atmosphere to form a third phase at the interface, wherein the mass fraction of Ni in the active component is 1-10 wt%.

[0009] The preparation method of the above-mentioned Ni-based three-phase ammonia synthesis catalyst includes the following steps:

[0010] Step 1, Preparation of molybdenum nitride support:

[0011] Molybdenum oxide was added to a mixed solution of dilute nitric acid and hydrogen peroxide and stirred for 2 hours. The mixture was then transferred to a high-pressure reactor and reacted at 170°C for 24 hours. The resulting white precipitate was centrifuged, washed, and dried under vacuum at 60°C. Finally, it was calcined at 800°C under an ammonia atmosphere for 4 hours to obtain γ-Mo2N powder support.

[0012] Step 2, Preparation of Ni-based three-phase ammonia synthesis catalyst:

[0013] The γ-Mo2N support obtained in step 1 was added to a nickel nitrate aqueous solution and stirred uniformly for 2 hours. The water in the mixed solution was removed by a rotary evaporator, and the solution was dried under vacuum at 60°C. Then, it was reduced in a mixture of hydrogen and nitrogen at 500–700°C for 2 hours to obtain a Ni-based three-phase catalyst.

[0014] Preferably, the concentration of dilute nitric acid in step 1) is 1-3 mol / L, and the concentration of hydrogen peroxide is 8-10 mol / L.

[0015] Preferably, the concentration of the nickel nitrate solution in step 2) is 0.056 mol / L to 0.17 mol / L. Preferably, in step 2, a mixture of hydrogen and nitrogen is used as the reducing gas, wherein the hydrogen-nitrogen ratio is 3:1; and the heating rate during the reduction process is 1 °C / min. -1 The reduction temperature is 600℃.

[0016] This invention provides the application of the above-mentioned Ni-based three-phase structure catalyst in thermocatalytic ammonia synthesis and current-activated ammonia synthesis:

[0017] The Ni-based three-phase catalyst was granulated to 40–60 mesh and packed into an electroactivated fixed-bed reactor for ammonia synthesis. A 3:1 mixture of hydrogen and nitrogen was used as the reactant gas, the reaction pressure was 1 MPa, the reaction temperature was 360–450 °C, and the reaction space velocity was 36000 mL g / L. -1 h -1 The activation current is 0-3A.

[0018] Significant advantages of this invention:

[0019] This invention provides a method for preparing a Ni-based three-phase catalyst for ammonia synthesis. Metallic nickel is introduced onto a γ-Mo₂N support via direct impregnation, followed by temperature treatment in a mixed atmosphere of hydrogen and nitrogen. The in-situ generated Ni-Mo-N structure forms a third phase at the Ni-γ-Mo₂N interface. This catalyst exhibits good response under current-activated conditions, with the ammonia synthesis rate significantly increased by 3-4 times compared to thermal catalysis. The ammonia synthesis rate remains stable for over 100 hours under current-activated conditions, demonstrating promising application prospects. Attached Figure Description

[0020] Figure 1 The XRD patterns are those of the catalysts prepared in Example 1 and Comparative Examples 1 and 2.

[0021] Figure 2 Transmission electron micrographs of the catalysts prepared in Example 1 and Comparative Examples 1 and 2.

[0022] Figure 3For application example 1 and comparative examples 3 and 4, the conditions were set at 400°C, 1 MPa, and a mass hourly space velocity (MHV) of 36000 mL g. -1 h -1 Catalytic performance of ammonia synthesis under current conditions of 0-2A and voltage conditions of 0-6V.

[0023] Figure 4 For example, in application 1, at 1 MPa and a mass hourly space velocity of 36000 mL g / g -1 h -1 Catalytic performance of ammonia synthesis under different temperature conditions with and without current applied.

[0024] Figure 5 The catalyst in Example 1 was used at 400°C, 1 MPa, and a mass hourly space velocity of 36000 mL g. -1 h -1 Catalytic stability data under current conditions of 0–2A and voltage conditions of 0–6V. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. 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.

[0026] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a” and “described” as used in this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this invention refers to and includes any or all possible combinations of one or more of the associated listed items.

[0027] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0028] Example 1

[0029] 1.8 g of MoO3 powder was added to 13.5 mL of 9.79 mol / L H2O2 and stirred. Then, 49 mL of 1.91 mol / L dilute nitric acid solution was added and stirred for 2 h. The resulting mixture was transferred to a high-pressure reactor and heat-treated at 170 °C for 48 h. The precipitate was washed several times with ethanol and deionized water, centrifuged, and then dried under vacuum at 60 °C. The white powder was then in an NH3 atmosphere at 10 °C for [time missing]. -1 The temperature is increased to 360°C at a rate of 1°C / min. -1The temperature was rapidly increased to 800℃ and held for 4 hours, then cooled to room temperature and passivated for 2 hours in a 2% O2 / Ar atmosphere to obtain γ-Mo2N. 1 g of γ-Mo2N support powder was dispersed in 20 mL of a 0.0852 mol / L nickel nitrate solution and stirred for 2 hours. Water was then removed from the mixed solution by rotary evaporation, followed by vacuum drying at 60℃. Finally, the powder was pressed into tablets, pulverized, and sieved to obtain a 40–60 mesh catalyst. This catalyst was then subjected to passivation at 1℃ for 1 minute in an H2 / N2 (v / v = 3 / 1) atmosphere. -1 The catalyst was obtained by heating the catalyst at 600℃ for 2 hours and then naturally cooling it to room temperature. It was labeled as Ni / γ-Mo2N-600.

[0030] Comparative Example 1

[0031] 1.8 g of MoO3 powder was added to 13.5 mL of 9.79 mol / L H2O2 and stirred. Then, 49 mL of 1.91 mol / L dilute nitric acid solution was added and stirred for 2 h. The resulting mixture was transferred to a high-pressure reactor and heat-treated at 170 °C for 48 h. The precipitate was washed several times with ethanol and deionized water, centrifuged, and then dried under vacuum at 60 °C. The white powder was then in an NH3 atmosphere at 10 °C for [time missing]. -1 The temperature is increased to 360°C at a rate of 1°C / min. -1 The temperature was rapidly increased to 800℃ and held for 4 hours, then cooled to room temperature and passivated for 2 hours in a 2% O2 / Ar atmosphere to obtain γ-Mo2N. 1 g of γ-Mo2N support powder was dispersed in 20 mL of a 0.0852 mol / L nickel nitrate solution and stirred for 2 hours. Water was then removed from the mixed solution by rotary evaporation, followed by vacuum drying at 60℃. Finally, the powder was pressed into tablets, pulverized, and sieved to obtain a 40–60 mesh catalyst. This catalyst was then subjected to passivation at 1℃ for 1 minute in an H2 / N2 (v / v = 3 / 1) atmosphere. -1 The catalyst was obtained by heating the catalyst at 400℃ for 2 hours and then naturally cooling it to room temperature. It was labeled as Ni / γ-Mo2N-400.

[0032] Comparative Example 2

[0033] 1.8 g of MoO3 powder was added to 13.5 mL of 9.79 mol / L H2O2 and stirred. Then, 49 mL of 1.91 mol / L dilute nitric acid solution was added and stirred for 2 h. The resulting mixture was transferred to a high-pressure reactor and heat-treated at 170 °C for 48 h. The precipitate was washed several times with ethanol and deionized water, centrifuged, and then dried under vacuum at 60 °C. The white powder was then in an NH3 atmosphere at 10 °C for [time missing]. -1 The temperature is increased to 360°C at a rate of 1°C / min. -1The temperature was rapidly increased to 800℃ and held for 4 hours, then cooled to room temperature and passivated for 2 hours in a 2% O2 / Ar atmosphere to obtain γ-Mo2N. 1 g of γ-Mo2N support powder was dispersed in 20 mL of a 0.0852 mol / L nickel nitrate solution and stirred for 2 hours. Water was then removed from the mixed solution by rotary evaporation, followed by vacuum drying at 60℃. Finally, the powder was pressed into tablets, pulverized, and sieved to obtain a 40–60 mesh catalyst. This catalyst was then subjected to passivation at 1℃ for 1 minute in an H2 / N2 (v / v = 3 / 1) atmosphere. -1 The catalyst was obtained by heating the catalyst at 800℃ for 2 hours and then naturally cooling it to room temperature. It was labeled as Ni / γ-Mo2N-800.

[0034] Figure 1 The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2 are shown. The diffraction patterns reveal that the catalyst obtained using the synthesis method of Example 1 developed a third phase, Ni3Mo3N, in addition to Ni and γ-Mo2N. In contrast, Comparative Example 1 consisted only of two phases: Ni and γ-Mo2N support, while the catalyst prepared in Comparative Example 3 consisted of two phases: Ni2Mo3N and γ-Mo2N.

[0035] Figure 2 Transmission electron microscopy (TEM) images of the catalysts prepared in Example 1 and Comparative Examples 1-2 are shown. It can be seen that the catalyst of Example 1, prepared using the method described in this invention, has a three-phase structure of metallic Ni, Ni-Mo-N, and γ-Mo2N. In contrast, Comparative Example 1 consists of only two phases: Ni and γ-Mo2N support, while the catalyst prepared in Comparative Example 3 consists of two phases: Ni2Mo3N and γ-Mo2N.

[0036] Application Example 1

[0037] 0.2 g of the Ni / γ-Mo2N-600 catalyst prepared in Example 1 was loaded into a current-activated fixed-bed apparatus and clamped together using an electrode rod assembly. An open-type tubular furnace provided the external heating source for the reactor, with the current supplied by a programmable DC switching power supply; the reaction pressure was 1 MPa, and the mass hourly space velocity (MSV) was 36000 mL g. -1 h -1 The conditions for thermocatalytic and current-activated ammonia synthesis were as follows: applied currents of 0A and 2A, respectively. The temperature of the tubular furnace was adjusted so that the bed temperature measured by the temperature sensing element inserted in the catalyst bed was within the range of 350–450℃. The ammonia synthesis rate was calculated from the outlet gas data measured by gas chromatography. The ammonia synthesis rate under thermocatalytic conditions was 2.72 mmol g / L. cat -1 h -1 The ammonia synthesis rate under applied current conditions was 10.51 mmol / g. cat -1 h-1 .

[0038] Comparative Example 3

[0039] 0.2 g of the Ni / γ-Mo2N-400 catalyst prepared in Example 1 was loaded into a current-activated fixed-bed apparatus and clamped together using an electrode rod assembly. An open-type tubular furnace provided the external heating source for the reactor, with the current supplied by a programmable DC switching power supply; the reaction pressure was 1 MPa, and the mass hourly space velocity (MSV) was 36000 mL g. -1 h -1 The conditions for thermocatalytic and current-activated ammonia synthesis were as follows: applied currents of 0A and 2A, respectively. The temperature of the tubular furnace was adjusted so that the bed temperature measured by the temperature sensing element inserted in the catalyst bed was within the range of 350–450℃. The ammonia synthesis rate was calculated from the outlet gas data measured by gas chromatography. The ammonia synthesis rate under thermocatalytic conditions was 1.94 mmol g / L. cat -1 h -1 The ammonia synthesis rate under applied current conditions was 6.60 mmol / g. cat -1 h -1 .

[0040] Comparative Example 4

[0041] 0.2 g of Ni / γ-Mo2N-800 catalyst was loaded into an electrically activated fixed-bed reactor and secured by electrode rod assemblies. An open-type tubular furnace provided the external heating source for the reactor, with the current supplied by a programmable DC switching power supply; the reaction pressure was 1 MPa, and the mass hourly space velocity was 36000 mL g / cm³. -1 h -1 The conditions for thermocatalytic and current-activated ammonia synthesis were as follows: applied currents of 0A and 2A, respectively. The temperature of the tubular furnace was adjusted so that the bed temperature measured by the temperature sensing element inserted in the catalyst bed was within the range of 350–450℃. The ammonia synthesis rate was calculated from the outlet gas data measured by gas chromatography. The ammonia synthesis rate under thermocatalytic conditions was 1.62 mmol g / L. cat -1 h -1 The ammonia synthesis rate under applied current conditions was 3.61 mmol g. cat -1 h -1 .

[0042] Figure 3 For application example 1 and comparative examples 3-4, the conditions were set at 400°C, 1 MPa, and a mass hourly space velocity (HHSV) of 36000 mL g. -1 h -1The performance of ammonia synthesis under thermocatalysis and activation current of 1A. In Application Example 1, under the same conditions, the performance of thermocatalytic ammonia synthesis is slightly better than that of Comparative Examples 3-4. However, under current activation conditions, the performance of catalytic ammonia synthesis is significantly better than that of Comparative Examples 3 and 4, approximately 1.5 times that of Comparative Example 3 and 3 times that of Comparative Example 4.

[0043] like Figure 4 As shown, Application Example 1 was performed at 1 MPa and a mass hourly space velocity (MHV) of 36000 mL / g. -1 h -1 The ammonia synthesis rate was measured under different temperature conditions with and without applied current. Under applied current conditions, the catalytic performance for ammonia synthesis at the same temperature can be increased by approximately 100%. The Ni-based three-phase catalyst described in this invention exhibits excellent current-activated response characteristics.

[0044] like Figure 5 As shown, the catalyst Ni / γ-Mo2N-600 in Application Example 1 was used at 400 °C, 1 MPa, and a mass hourly space velocity of 36000 mLg. -1 h -1 Stability data at an activation current of 1A. The Ni / γ-Mo2N-600 catalyst was continuously operated for 130 hours. No significant decrease in ammonia synthesis performance was observed under both applied and unapplied current conditions, indicating that the Ni-based three-phase catalyst described in this invention possesses good stability.

[0045] 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. For those skilled in the art, other variations or modifications can be made based on the above description. Any improvements or equivalent substitutions to the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A Ni-based three-phase ammonia synthesis catalyst, characterized in that: Using molybdenum nitride as a carrier and metallic Ni as the active component, the Ni-Mo-N structure generated in situ during the reduction process forms a third phase at the interface, wherein the mass fraction of the active component Ni is 1-10 wt%.

2. The method for preparing a Ni-based three-phase ammonia synthesis catalyst according to claim 1, characterized in that: Step 1, Preparation of molybdenum nitride support: Molybdenum oxide was added to a mixed solution of dilute nitric acid and hydrogen peroxide and stirred for 2 hours. The mixture was then transferred to a high-pressure reactor and reacted at 170°C for 24 hours. The resulting white precipitate was centrifuged, washed, and dried under vacuum at 60°C. Finally, it was calcined at 800°C under an ammonia atmosphere for 4 hours to obtain γ-Mo2N powder support. Step 2, Preparation of Ni-based three-phase ammonia synthesis catalyst: The molybdenum nitride support obtained in step 1 was added to a nickel nitrate solution and stirred uniformly for 2 hours. The water in the mixed solution was removed by a rotary evaporator, and the solution was dried under vacuum at 60°C. Then, it was reduced in a mixture of hydrogen and nitrogen at 500–700°C for 2 hours to obtain a Ni-based three-phase catalyst.

3. The preparation method according to claim 2, characterized in that: The concentration of dilute nitric acid in step 1 is 1–3 mol / L, and the concentration of hydrogen peroxide is 8–10 mol / L.

4. The preparation method according to claim 2, characterized in that: In step 2, the concentration of nickel nitrate solution is 0.056 mol / L to 0.17 mol / L; preferably, in step 2, a mixture of hydrogen and nitrogen is used as the reducing gas, wherein the hydrogen-nitrogen ratio is 3:1; the heating rate during the reduction process is 1 to 10 °C / min.

5. The application of the Ni-based three-phase structure ammonia synthesis catalyst according to claim 1 in thermocatalytic ammonia synthesis and electroactivated ammonia synthesis, characterized in that: The high current-responsive Ni-based three-phase catalyst for current-activated ammonia synthesis was granulated to 40-60 mesh and packed into a fixed-bed reactor for current-activated ammonia synthesis. A 3:1 mixture of hydrogen and nitrogen was used as the reaction feed gas, the reaction pressure was 1 MPa, the reaction temperature was 400℃, the reaction space velocity was 36000 mL g-1h-1, and the activation current was 0-3 A.

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