A silicon carbide nanowire supported nickel-based catalyst, a preparation method thereof and application thereof in ammonia decomposition reaction

Abstract

This invention relates to a nickel-based catalyst supported on silicon carbide nanowires, its preparation method, and its application in ammonia decomposition, belonging to the field of hydrogen production and catalytic materials technology. The supported nickel-based nanowire silicon carbide catalyst of this invention uses a silicon carbide nanowire support as a substrate, on which nickel active metal nanoparticles are loaded and doped with rare earth metal additives. The active metal and rare earth metal additives are loaded onto the support via a deposition-precipitation method. The core of this invention lies in constructing a metal-support synergistic low-temperature ammonia decomposition catalyst that facilitates the dispersion of metal nanoparticles and current conduction by loading active metals and rare earth metal additives onto silicon carbide nanowires with high specific surface area and one-dimensional conductivity. By applying an external electric field, the current promotes the reaction process, accelerates low-temperature ammonia decomposition, significantly enhances ammonia decomposition activity, and ultimately enables the catalyst to exhibit high activity and high stability in ammonia decomposition for hydrogen production at lower temperatures. This is an ammonia decomposition hydrogen production technology solution that combines the advantages of low temperature, high stability, economy, and industrial applicability.

Description

Technical Field

[0001] This invention belongs to the technical field of hydrogen energy preparation and catalytic materials, and particularly relates to a nickel-based catalyst. Background Technology

[0002] Ammonia, as a promising hydrogen carrier, boasts numerous advantages, including high hydrogen content, liquefaction at room temperature and low pressure, mature storage and transportation technologies, and the absence of carbon. Ammonia decomposition for hydrogen production has attracted widespread attention as a promising large-scale hydrogen production route. Currently, ruthenium-based and nickel-based catalysts are the main types used in existing ammonia decomposition hydrogen production technologies. However, the high price of ruthenium metal restricts its large-scale industrial application. While nickel-based catalysts are lower in cost, their catalytic activity is not high enough, and achieving complete ammonia conversion typically requires reaction temperatures above 600 °C, resulting in high energy consumption. Silicon carbide possesses high thermal conductivity, high oxidation resistance, a relatively high non-porous specific surface area, and one-dimensional electrical conductivity. By loading active metals and rare earth metal promoters onto silicon carbide nanowires, a metal-support synergistic low-temperature ammonia decomposition catalyst that facilitates metal nanoparticle dispersion and current conduction can be constructed. The literature Catalysis Today 437 (2024) 114774 reports a Co / SiC supported ammonia decomposition catalyst, whose optimal ammonia decomposition rate is only 54% at 500 °C; the literature J. Ind. Eng. Chem. 94 (2021), 326-335 reports a Ru / SiC supported ammonia decomposition catalyst, whose optimal ammonia decomposition rate can only reach 40% at 550 °C. In summary, the publicly reported supported silicon carbide catalysts have prominent problems such as insufficient low-temperature activity and high cost of precious metals, resulting in poor economic efficiency. There is an urgent need to develop a supported silicon carbide ammonia decomposition catalyst that can achieve a high decomposition rate at low temperatures. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a nickel-based catalyst supported on silicon carbide nanowires, its preparation method, and its application in ammonia decomposition reactions. The prepared catalyst exhibits high activity and low cost.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A method for preparing a nickel-based catalyst supported on silicon carbide nanowires includes the following steps:

[0006] (1) Prepare a precursor solution by dissolving nickel precursor, metal auxiliary precursor and precipitant in deionized water;

[0007] (2) Add nanowire silicon carbide to the precursor solution for hydrothermal reaction, and wash and dry after the reaction to obtain the catalyst precursor;

[0008] (3) The catalyst precursor is calcined, and after calcination, it is roasted and reduced to obtain a nickel-based catalyst supported on silicon carbide nanowires.

[0009] The nickel precursor is at least one of nickel nitrate or nickel acetate; the metal element in the metal additive precursor is at least one of cerium, lanthanum, samarium, barium, strontium, and calcium; the precipitant is urea, which slowly decomposes at high temperature, gradually releasing hydroxide ions, causing the solution pH to rise, and Ni 2+ It is precipitated in the form of hydroxide and loaded onto the surface of SiC support.

[0010] The mass ratio of the nickel precursor, rare earth metal auxiliary precursor and precipitant is 1:0.001-0.5:0.5-2; the ratio of the nickel precursor to water is 1g:5-30mL.

[0011] In step (1), the dissolution is carried out under heating conditions, with a heating temperature of 50~90 ℃.

[0012] The hydrothermal reaction is carried out at a temperature of 70-90 °C for 12-24 h.

[0013] Preferably, after the hydrothermal reaction in step (2), the precipitate is collected by filtration or centrifugation, and the precipitate is repeatedly washed with a large amount of deionized water until the pH of the filtrate is close to neutral and no color develops. The drying temperature is 80~110 ℃, and the drying time is 12~24 h.

[0014] The diameter of the nanowire silicon carbide support is 100~600 nm.

[0015] The ratio of the amount of silicon carbide nanowires added in step (2) to the mass ratio of the nickel precursor in step (1) is 1:0.5-2.

[0016] The calcination is carried out in an oxygen-containing atmosphere at a temperature of 400–600 °C, a heating rate of 1–10 °C / min, and a calcination time of 4–8 h. The oxygen-containing atmosphere is air, oxygen, or an oxygen-enriched atmosphere.

[0017] The calcination and reduction are carried out in a reducing atmosphere, with a reduction temperature of 400-600 °C, a heating rate of 1-10 °C / min, and a reduction time of 2-6 h. The reducing atmosphere is a hydrogen atmosphere or a mixture of hydrogen and an inert gas.

[0018] Preferably, the reducing atmosphere is hydrogen gas with a flow rate of 20-80 mL / min.

[0019] The application of silicon carbide nanowire-supported nickel-based catalyst in ammonia decomposition reaction includes the following steps: filling the silicon carbide nanowire-supported nickel-based catalyst to form a catalyst bed, applying an external electric field in the axial direction of the catalyst bed, and introducing ammonia-containing feed gas at 300~800 °C to cause ammonia to decompose and generate hydrogen and nitrogen, thereby realizing electrocatalytic ammonia decomposition to produce hydrogen.

[0020] The reaction space velocity (WHSV) of the ammonia decomposition reaction is 6000~30000 mL g. -1 h -1 .

[0021] The applied electric field is a DC electric field with a current of 50~500 mA.

[0022] The beneficial effects of this invention are:

[0023] This invention relates to a supported nickel-based nanowire silicon carbide catalyst containing rare earth metal additives. The catalyst uses a silicon carbide nanowire support as a substrate, on which nickel active metal nanoparticles are loaded and doped with rare earth metal additives. The active metal and rare earth metal additives are loaded onto the support via a deposition-precipitation method. The core of this invention lies in constructing a metal-support synergistic low-temperature ammonia decomposition catalyst by loading active metals and rare earth metal additives onto silicon carbide nanowires with high specific surface area and one-dimensional conductivity. This facilitates the dispersion of metal nanoparticles and current conduction. By applying an external electric field, the current promotes the reaction process, accelerating low-temperature ammonia decomposition and significantly enhancing ammonia decomposition activity. Ultimately, the catalyst exhibits high activity and high stability in ammonia decomposition for hydrogen production at relatively low temperatures. This is an ammonia decomposition hydrogen production technology solution that combines the advantages of low temperature, high stability, economy, and industrial applicability.

[0024] In this invention, SiC serves as a non-metallic ceramic support, possessing extremely high thermal stability, chemical inertness, and thermal conductivity. Under common conditions, its bulk band gap is relatively large, and its conductivity is far lower than that of metals, thus it does not significantly participate in electron transport or directly provide a large number of catalytic active sites like conductive nitrides. Therefore, the adsorption and stepwise dehydrogenation reactions of NH3 mainly occur on the Ni surface, and the adsorption and dissociation of ammonia molecules likely rely on Ni active sites. Due to the weak electronic coupling between the SiC support and Ni, the Ni electronic states primarily retain metallic characteristics. In terms of electric field response, the poorly conductive SiC support is unlikely to directly participate in electron transport like LaN; electrons are primarily transferred through the metal particle network. In the Ni-SiC catalytic system, the main role of SiC is to inhibit the sintering of Ni particles through its excellent thermal stability, preventing catalyst deactivation at high temperatures. Simultaneously, the chemical inertness of SiC allows it to provide stable catalytic support at higher temperatures, making it less prone to adverse interactions with Ni metal. Due to the poor conductivity of SiC, under current activation, electrons are primarily transferred through the Ni metal particle network. Under the influence of an applied electric field, electron migration at Ni metal sites is promoted, enhancing the electron density at the metal-support interface and thus improving catalytic activity. Furthermore, the SiC support provides additional heat through the Joule heating effect, helping to maintain the high efficiency of the catalytic reaction. High ammonia decomposition activity can be achieved at 300–800 °C, significantly lower than traditional nickel-based catalytic systems. Simultaneously, using the non-noble metal Ni as the active metal offers low cost and good economic efficiency, while the silicon carbide support exhibits good thermal stability, demonstrating industrial potential. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is the X-ray diffraction (XRD) pattern of the catalyst in the embodiments of the present invention.

[0027] Figure 2 The graph shows the ammonia decomposition rate of the catalysts in the examples and comparative examples when an electric current is applied.

[0028] Figure 3 The ammonia decomposition performance of the catalysts prepared in the examples and comparative examples is shown. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The catalysts prepared in the following examples were evaluated using the following method: 100-500 mg of the prepared catalyst was loaded into a continuous flow fixed-bed reactor. Conductive rods were placed at both ends of the catalyst bed, and an applied DC electric field was applied to the axial direction of the catalyst bed. NH3 was introduced as the reaction gas, and the space velocity was set to 6000-30000 mL g / L. -1 h -1 The catalyst activity was evaluated by increasing the temperature at 1–10 °C / min to 300–800 °C and taking different temperature intervals. The ammonia concentration in the tail gas was analyzed online by gas chromatography to calculate the ammonia decomposition rate.

[0031] Example 1

[0032] Weigh 10.0 g of SiC nanowire support, 8.8 g of Ni(NO3)2·6H2O, a small amount of Ce(NO3)2·6H2O, and 7.3 g of urea. Add Ni(NO3)2·6H2O, Ce(NO3)2·6H2O, and urea to approximately 100 mL of deionized water, heat, and stir until completely dissolved. Dissolution can be done at room temperature first, then heated to 60–70 °C to ensure no solid residue remains. Add 10.0 g of SiC support to the solution, stir until homogeneous, and continue heating to approximately 90 °C, maintaining this temperature for 4 hours. Seal the mixture in a container and heat to 90 °C in an oil bath or constant temperature bath, stirring for 16 hours to allow the urea to gradually decompose into NH3 / NH4⁺, slowly increasing the pH of the solution and promoting the Ni… 2+ The precursor precipitated as a hydroxide and uniformly deposited on the SiC surface. After the reaction, the mixture was allowed to cool naturally to room temperature, and the precipitate was collected by filtration. The precipitate was repeatedly washed with a large amount of deionized water until the pH of the filtrate was close to neutral and no color change was observed. The system was filtered to separate a wet solid containing Ni precipitate. The washed wet precursor was dried overnight at 100 °C to completely remove moisture. The dried precursor was placed in an air atmosphere and calcined at 5 °C / min to 500 °C for 4 h, followed by natural cooling. The calcined product was placed in a tubular reduction furnace, and hydrogen gas was introduced (flow rate 40–50 mL / min). The temperature was increased to 500 °C at 5 °C / min and held for 2 h for reduction. After cooling, the Ni-Ce / SiC catalyst was obtained.

[0033] Example 2

[0034] Weigh 10.0 g of SiC nanowire support, 8.8 g of Ni(NO3)2·6H2O, a small amount of La(NO3)3·6H2O, and 7.3 g of urea. Add Ni(NO3)2·6H2O, La(NO3)2·6H2O, and urea to approximately 100 mL of deionized water, heat, and stir until completely dissolved. Dissolution can be done at room temperature first, then heated to 60–70 °C to ensure no solid residue remains. Add 10.0 g of SiC support to the solution, stir until homogeneous, and continue heating to approximately 90 °C, maintaining this temperature for 4 hours. Seal the mixture in a container and heat to 90 °C in an oil bath or constant temperature bath, stirring for 16 hours to allow urea to gradually decompose into NH3 / NH4⁺, slowly increasing the pH of the solution to promote Ni… 2+ The precursor precipitated as a hydroxide and uniformly deposited on the SiC surface. After the reaction, the mixture was allowed to cool to room temperature naturally, and the precipitate was collected by filtration. The precipitate was repeatedly washed with a large amount of deionized water until the pH of the filtrate was close to neutral and no color change was observed. The system was filtered to separate a wet solid containing Ni precipitate. The washed wet precursor was dried overnight at 100 °C to completely remove moisture. The dried precursor was placed in an air atmosphere and calcined at 5 °C / min to 500 °C for 4 h, followed by natural cooling. The calcined product was placed in a tubular reduction furnace, and hydrogen gas was introduced (flow rate 40–50 mL / min). The temperature was increased to 500 °C at 5 °C / min and held for 2 h for reduction. After cooling, the Ni-La / SiC catalyst was obtained.

[0035] Example 3

[0036] Weigh 10.0 g of SiC nanowire support, 8.8 g of Ni(NO3)2·6H2O, a small amount of La(NO3)3·6H2O, and 7.3 g of urea. Add Ni(NO3)2·6H2O, Sm(NO3)2·6H2O, and urea to approximately 100 mL of deionized water, heat, and stir until completely dissolved. Dissolution can be done at room temperature first, then heated to 60–70 °C to ensure no solid residue remains. Add 10.0 g of SiC support to the solution, stir until homogeneous, and continue heating to approximately 90 °C, maintaining this temperature for 4 hours. Seal the mixture in a container and heat to 90 °C in an oil bath or constant temperature bath, stirring for 16 hours to allow urea to gradually decompose into NH3 / NH4⁺, slowly increasing the pH of the solution to promote Ni… 2+The precursor precipitated as a hydroxide and uniformly deposited on the SiC surface. After the reaction, the mixture was allowed to cool naturally to room temperature, and the precipitate was collected by filtration. The precipitate was repeatedly washed with a large amount of deionized water until the pH of the filtrate was close to neutral and no color change was observed. The system was filtered to separate a wet solid containing Ni precipitate. The washed wet precursor was dried overnight at 100 °C to completely remove moisture. The dried precursor was placed in an air atmosphere and calcined at 5 °C / min to 500 °C for 4 h, followed by natural cooling. The calcined product was placed in a tubular reduction furnace, and hydrogen gas was introduced (flow rate 40–50 mL / min). The temperature was increased to 500 °C at 5 °C / min and held for 2 h for reduction. After cooling, the Ni-Sm / SiC catalyst was obtained.

[0037] Comparative Example 1

[0038] Weigh 10.0 g of SiC nanowire support, 8.8 g of Ni(NO3)2·6H2O, and 7.3 g of urea. Add Ni(NO3)2·6H2O and urea to approximately 100 mL of deionized water, heat and stir until completely dissolved. Dissolve at room temperature first, then heat to 60–70 °C to ensure no solid residue remains. Add 10.0 g of SiC support to the solution, stir well, and continue heating to approximately 90 °C, maintaining this temperature for 4 hours. Seal the mixture in a container and heat to 90 °C in an oil bath or constant temperature bath, stirring for 16 hours to allow the urea to gradually decompose into NH3 / NH4⁺, slowly increasing the pH of the solution to promote Ni… 2+ The precursor precipitated as a hydroxide and uniformly deposited on the SiC surface. After the reaction, the mixture was allowed to cool naturally to room temperature, and the precipitate was collected by filtration. The precipitate was repeatedly washed with a large amount of deionized water until the pH of the filtrate was close to neutral and no color change was observed. The system was filtered to separate a wet solid containing Ni precipitate. The washed wet precursor was dried overnight at 100 °C to completely remove moisture. The dried precursor was placed in an air atmosphere and calcined at 5 °C / min to 500 °C for 4 h, followed by natural cooling. The calcined product was placed in a tubular reduction furnace, and hydrogen gas was introduced (flow rate 40–50 mL / min). The temperature was increased to 500 °C at 5 °C / min and held for 2 h for reduction. After cooling, a 15% Ni / SiC catalyst was obtained.

[0039] like Figure 1 As shown, the catalyst prepared in the example has a SiC crystal structure.

[0040] like Figure 2 The examples and comparative examples show the ammonia decomposition performance of the catalysts prepared under the applied current.

[0041] like Figure 3 The ammonia decomposition performance of the catalysts prepared in the examples and comparative examples is shown.

[0042] Application examples

[0043] 200 mg of the catalysts prepared in Examples 1-3 and the comparative examples were placed in reactors respectively. An external DC electric field of 500 mA was applied to the catalyst bed in the axial direction, and the ammonia space velocity was 30000 mL g. -1 h -1 The ammonia flow rate was 100 mL / min, the reaction was conducted at atmospheric pressure, and the reaction temperature was 450–650 °C. Activity was evaluated at different temperature intervals. Simultaneously, 200 mg of the catalysts prepared in Examples 1–3 and the comparative example were placed in separate reactors for testing without an external DC electric field. The ammonia concentration in the tail gas was analyzed online by gas chromatography to calculate the ammonia decomposition rate. The test results are as follows: Figure 2 and Figure 3 As shown.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-based catalyst supported on silicon carbide nanowires, characterized in that, Includes the following steps: (1) Prepare a precursor solution by dissolving nickel precursor, metal auxiliary precursor and precipitant in deionized water; (2) Add nanowire silicon carbide to the precursor solution for hydrothermal reaction, and wash and dry after the reaction to obtain the catalyst precursor; (3) The catalyst precursor is calcined, and after calcination, it is roasted and reduced to obtain a nickel-based catalyst supported on silicon carbide nanowires.

2. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to claim 1, characterized in that, The nickel precursor is at least one of nickel nitrate or nickel acetate; the metal element in the metal additive precursor is at least one of cerium, lanthanum, samarium, barium, strontium, and calcium; and the precipitant is urea.

3. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to claim 2, characterized in that, The mass ratio of the nickel precursor, rare earth metal auxiliary precursor and precipitant is 1:0.001-0.5:0.5-2; the ratio of the nickel precursor to water is 1g:5-30mL.

4. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to any one of claims 1-3, characterized in that, The hydrothermal reaction is carried out at a temperature of 70-90 °C for 12-24 h.

5. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to claim 4, characterized in that, The diameter of the nanowire silicon carbide support is 100~600 nm.

6. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to claim 5, characterized in that, The ratio of the amount of silicon carbide nanowires added in step (2) to the mass ratio of the nickel precursor in step (1) is 1:0.5-2.

7. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to claim 1, characterized in that, The calcination is carried out in an oxygen-containing atmosphere at a temperature of 400-600 °C, a heating rate of 1-10 °C / min, and a calcination time of 4-8 h.

8. The method for preparing the nickel-based catalyst supported on silicon carbide nanowires according to claim 1, characterized in that, The calcination and reduction are carried out in a reducing atmosphere, with a reduction temperature of 400~600 ℃, a heating rate of 1~10 ℃ / min, and a reduction time of 2~6 h.

9. A nickel-based catalyst supported on silicon carbide nanowires prepared by the method of any one of claims 1-8.

10. The application of the silicon carbide nanowire-supported nickel-based catalyst according to claim 9 in the ammonia decomposition reaction.

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