A cobalt-based catalyst, its preparation method and application

Abstract

This invention relates to the field of catalysts, and provides a cobalt-based catalyst, its preparation method, and its application. The cobalt-based catalyst is a spinel-structured oxide M. a Al b Co c O4 was obtained through in-situ activation, wherein Co was the active component and M was a promoter metal, including alkaline earth metals or rare earth metals. The catalyst was prepared using a co-precipitation-calcination-in-situ activation process to achieve uniform dispersion and structural stability of the active component Co and the promoter metal. The catalyst was subjected to a reaction at 30 L•g... cat ‑1 •h ‑1 It exhibits good low-temperature ammonia decomposition activity under space velocity conditions, with an ammonia conversion rate of over 99.3% at 600℃.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a cobalt-based catalyst, its preparation method, and its application. Background Technology

[0002] To achieve low-temperature, high-efficiency ammonia decomposition for hydrogen production, developing high-performance ammonia decomposition catalysts is crucial. Existing ammonia decomposition catalysts mainly use Ru, Rh, Fe, Co, and Ni as active components, supported on Al₂O₃ or MgO supports. Among these active components, nickel-based catalysts have been extensively studied for ammonia decomposition. However, traditional nickel-based catalysts often suffer from poor catalytic activity (requiring a complete ammonia conversion temperature above 850 °C) and easy agglomeration of active components. Literature reports that doping nickel-based catalysts with metals can improve their catalytic activity. For example, CN113198476A shows that a Co-doped Ni-based catalyst can achieve over 99% ammonia conversion at 700 °C, but the Co content can only be increased to 5%, mainly due to the disordered coordination caused by the random adsorption of nickel-based metal precursors. CN118527147A reports a modified rare-earth oxide-supported cobalt-based catalyst. While the rare-earth oxide support can improve Co dispersion, its relatively poor temperature resistance leads to a shorter catalyst life, failing to meet the needs of industrial production. Summary of the Invention

[0003] This invention provides a cobalt-based ammonia decomposition hydrogen production catalyst with uniform distribution of active components, good structural stability, and excellent low-temperature ammonia decomposition performance.

[0004] In a first aspect of the invention, a cobalt-based catalyst is provided, said catalyst being spinel oxide M a Al b Co c O4;

[0005] Where M is an additive metal, and the additive metal is an alkaline earth metal or a rare earth metal;

[0006] Where a takes values ​​of 0 ≤ a ≤ 0.3, b takes values ​​of 0.01 ≤ b ≤ 0.3, and c = 3 - ab.

[0007] In another preferred embodiment, the value range of a is 0.08≤a≤0.25, and the value range of b is 0.08≤b≤0.25.

[0008] In another preferred embodiment, the value of a is in the range of 0.15≤a≤0.3, and the value of b is in the range of 0.05≤b≤0.2.

[0009] In another preferred example, a + b ≤ 0.3.

[0010] In another preferred embodiment, the alkaline earth metal is selected from the group consisting of magnesium, barium, calcium, strontium, or combinations thereof.

[0011] In another preferred embodiment, the alkaline earth metal is calcium or strontium.

[0012] In another preferred embodiment, the rare earth metal is selected from the group consisting of yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, or combinations thereof.

[0013] In another preferred embodiment, the rare earth metal is lanthanum or cerium.

[0014] In another preferred embodiment, the catalyst contains 60-80 wt% Co.

[0015] In another preferred embodiment, the catalyst contains 0.8 to 15 wt% of the promoter metal.

[0016] In another preferred embodiment, the catalyst is selected from the group consisting of: Al 0.3 Co 2.7 O4, La 0.21 Al 0.09 Co 2.7 O4, Ce 0.21 Al 0.09 Co 2.7 O4, Pr 0.21 Al 0.09 Co 2.7 O4, Mg 0.09 Al 0.21 Co 2.7 O4, Ca 0.15 Al 0.15 Co 2.7 O4, Ba 0.09 Al 0.21 Co 2.7 O4, or combinations thereof.

[0017] In a second aspect of the present invention, a method for preparing a cobalt-based catalyst as described in the first aspect of the present invention is provided, comprising the following steps:

[0018] (1) Provide a precipitant solution with a concentration of 0.2~1 mol / L; wherein the precipitant is potassium carbonate or sodium carbonate;

[0019] (2) According to the composition of the final catalyst, weigh out the cobalt salt, aluminum salt and M salt and dissolve them in an inert solvent, and stir until fully dissolved;

[0020] (3) Add the solution from step (1) to the solution from step (2) at once to carry out the reaction and obtain the reaction product;

[0021] (4) In an air atmosphere, the reaction product obtained in step (3) is heated to 500~700℃ at 2-5℃ / min and calcined for 4~6 hours to obtain the spinel oxide M. a Al b Co c O4.

[0022] In another preferred embodiment, step (4) further includes grinding the precursor into powder before calcination.

[0023] In another preferred embodiment, step (2) has one or more features selected from the group consisting of:

[0024] (i) The cobalt salt is selected from the group consisting of cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt chloride, or combinations thereof;

[0025] (ii) The aluminum salt is selected from the group consisting of aluminum nitrate, aluminum isopropoxide, aluminum hydroxide, or combinations thereof;

[0026] (iii) The M salt is selected from the group consisting of magnesium nitrate, calcium nitrate, calcium chloride, strontium nitrate, barium nitrate, barium hydroxide, lanthanum nitrate, cerium nitrate, praseodymium nitrate, samarium nitrate, or combinations thereof.

[0027] In another preferred embodiment, the cobalt salt is cobalt nitrate.

[0028] In another preferred embodiment, the aluminum salt is aluminum nitrate.

[0029] In another preferred embodiment, the M salt is magnesium nitrate or cerium nitrate.

[0030] In another preferred embodiment, in step (1), the precipitant is potassium carbonate.

[0031] In another preferred embodiment, in step (1), the solution is selected from the group consisting of methanol, ethanol, propanol, deionized water, or combinations thereof.

[0032] In another preferred embodiment, the solution in step (1) is deionized water.

[0033] In another preferred embodiment, in step (2), the inert solvent is selected from the group consisting of methanol, ethanol, propanol, deionized water, or combinations thereof.

[0034] In another preferred embodiment, the inert solvent in step (2) is deionized water.

[0035] In another preferred embodiment, the reaction time in step (3) is 1 to 5 hours.

[0036] In another preferred embodiment, step (3) is followed by: (3a) filtering and washing the reaction product until it is neutral, and drying the filter cake at 100-150 °C for 2-15 hours to obtain the precursor.

[0037] In another preferred embodiment, the stirring time in step (3) is 2 to 4 h; and / or the calcination temperature in step (4) is 450 to 750 °C and the calcination time is 4 to 6 h.

[0038] In a third aspect of this invention, the application of the cobalt-based catalyst as described in the first aspect of the invention is provided for catalytic ammonia decomposition to produce hydrogen.

[0039] In another preferred embodiment, the catalytic ammonia decomposition to produce hydrogen includes:

[0040] Using ammonia as a raw material, the reaction was carried out at a temperature of 500–600 °C and a mass hourly space velocity of 30 L∙g⁻¹. cat -1 ∙h -1 Under the conditions of the spinel oxide M a Al b Co c O4 comes into contact with the gas, thus producing nitrogen and hydrogen.

[0041] In another preferred embodiment, the reaction is carried out in a high-temperature reactor.

[0042] In another preferred embodiment, the catalytic ammonia decomposition further includes in-situ activation of the catalyst with ammonia before hydrogen production.

[0043] In another preferred embodiment, the ammonia activation temperature is 500-700 °C, more preferably 550-650 °C.

[0044] In another preferred embodiment, the heating rate for ammonia activation is 5~15 °C / min, more preferably 8~12 °C / min.

[0045] The beneficial technical effects of this invention: Through extensive and in-depth research, the inventors have unexpectedly developed a cobalt-based ammonia decomposition hydrogen production catalyst with uniform distribution of active components, good structural stability, low-temperature high efficiency, and long service life. This catalyst possesses a unique spinel oxidation structure, ensuring uniform dispersion of active components, stable catalyst structure, and fully exposed active sites. Simultaneously, the addition of promoters effectively increases the number of active sites, improves the electronic conductivity of the support, and adjusts the Co particle size, further enhancing the dispersion of active components. The catalyst achieves a high efficiency of 30 L / (g) cat h) Under the reaction conditions of space velocity, the ammonia decomposition efficiency reaches over 99.3% at 600 °C. Furthermore, the preparation method of the catalyst is simple and controllable. Based on these findings, this invention was completed.

[0046] Specifically, the advantages of the catalyst described in this invention are as follows:

[0047] 1. Superior performance: The catalyst exhibits uniform distribution of active components, good structural stability, and excellent low-temperature ammonia decomposition performance. The catalyst can achieve ammonia decomposition at 30 L∙g⁻¹. cat -1 ∙h -1 It can operate stably under high air speed conditions and the operating temperature can be as low as 550℃.

[0048] 2. Unique Structure: The catalyst possesses a unique spinel oxide structure. This structure consists of tetrahedral and octahedral units with an ordered distribution of oxygen vacancies. The auxiliary metal elements are uniformly distributed within the spinel structure, ensuring that the active species precipitated during in-situ reduction remain uniformly dispersed. This contributes to catalyst structural stability and ensures full exposure of active sites. This structural characteristic allows ammonia gas to fully contact the active species, thereby significantly improving ammonia decomposition efficiency.

[0049] 3. Simple and easy-to-control preparation method: The catalyst is prepared by introducing an auxiliary metal and an active metal Co into a spinel oxide precursor using a co-precipitation method. After in-situ atmosphere treatment, a highly efficient Co-based catalyst is obtained. During the co-precipitation process, the metal species and the precipitant groups achieve stable bonding. After calcination, the active metal is uniformly distributed in the spinel structure, ensuring the effective precipitation of Co during the in-situ reduction process. Overall, the method is simple and features a straightforward and easily controllable preparation process.

[0050] 4. Special Features of Additives: Additives play a crucial role in this catalytic system. Through ideal structure screening and fine-tuning, additives can regulate the precipitation behavior of Co particles in the precursor and interact with oxygen vacancies in the system, effectively improving the electronic conductivity of inactive additives. This regulatory effect not only optimizes the electronic state of cobalt, thereby promoting nitrogen recombination and desorption, but also improves the dispersion of active components by adjusting the Co particle size. This series of regulatory effects collectively improves the catalyst's lifespan and ensures its stable performance in practical applications.

[0051] In summary, the excellent ammonia decomposition activity of the catalyst described in this invention is due to the successful preparation of a spinel structure catalyst modified with an auxiliary metal via a co-precipitation method. During ammonia treatment, the active metal is exposed on the catalyst surface through in-situ precipitation. Compared to traditional supported catalysts, this structure effectively inhibits the shedding of active sites, ensures uniform dispersion of metal particles, and allows more active metal to be uniformly exposed in the reaction medium, which is beneficial for the ammonia decomposition reaction. Furthermore, the introduction of rare earth metal cerium regulates the electronic properties between vacancies and Co species in the system and modulates the interaction strength between Co and ammonia molecules, while simultaneously enhancing the basicity of the catalyst surface. The synergistic effect of electronic properties and surface basicity promotes the ammonia decomposition reaction, thus exhibiting superior ammonia decomposition performance.

[0052] Furthermore, the preparation method of the ammonia decomposition catalyst described in this invention is characterized by its simplicity and reproducibility. A low-temperature, high-efficiency cobalt-based ammonia decomposition catalyst is prepared by adding rare earth metals or alkaline earth metals as promoters to the spinel structure. The addition of these promoters significantly affects the precipitation of Co particles, effectively inhibiting the growth of active metal particles and generating more active sites. Simultaneously, the synergistic effect of Co and the promoters accelerates electron transfer during the reaction process, increasing the number of basic sites on the catalyst surface, enabling the catalyst to maintain a high ammonia decomposition rate even at a high space velocity of 600 °C.

[0053] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here. Attached Figure Description

[0054] Figure 1 These are X-ray powder diffraction patterns of the catalysts used in Examples 1-7 and Comparative Examples 1-5 before their use.

[0055] Figure 2 These are X-ray powder diffraction patterns of the catalysts used in Examples 1, 3, 5 and Comparative Examples 1, 2, 5.

[0056] Figure 3 These are the ammonia decomposition activity test results of the catalysts in Examples 3 and 5 and Comparative Examples 1 and 2. Detailed Implementation

[0057] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions, such as those described in a laboratory manual (New York: Cold Spring Harbor Laboratory Press, 1989), or as recommended by the manufacturer. Unless otherwise stated, percentages and fractions are weight percentages and weight fractions.

[0058] Example 1:

[0059] (1) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0060] (2) Mix 3.274 g of cobalt nitrate and 0.469 g of aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0061] (3) Quickly pour the potassium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0062] (4) The dried product was ground into powder and heated to 550°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 0.953 g of spinel oxide Al. 0.3 Co 2.7 O4; of which Co accounts for 68.82 wt% of the catalyst weight.

[0063] Example 2:

[0064] (1) Dissolve 2.650 g of sodium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0065] (2) Mix 3.274 g cobalt nitrate, 0.379 g lanthanum nitrate and 0.141 g aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0066] (3) Quickly pour the sodium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0067] (4) The dried product was ground into powder and heated to 700℃ in air at a heating rate of 2℃ / min. The powder was then calcined at this temperature for 6 h to obtain 1.192 g of spinel oxide La. 0.21 Al 0.09 Co 2.7O4; of which Co accounts for 62.47 wt% of the catalyst weight and La accounts for 11.45 wt% of the catalyst weight.

[0068] Example 3:

[0069] (1) Dissolve 2.650 g of sodium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0070] (2) Mix 3.274 g cobalt nitrate, 0.380 g cerium nitrate and 0.141 g aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0071] (3) Quickly pour the sodium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0072] (4) The dried product was ground into powder and heated to 550°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 1.135 g of spinel oxide Ce. 0.21 Al 0.09 Co 2.7 O4; of which Co accounts for 62.42 wt% of the catalyst weight and Ce accounts for 11.54 wt% of the catalyst weight.

[0073] Example 4:

[0074] (1) Dissolve 2.650 g of sodium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0075] (2) Mix 3.274 g cobalt nitrate, 0.381 g praseodymium nitrate and 0.141 g aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0076] (3) Quickly pour the sodium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0077] (4) The dried product was ground into powder and heated to 650°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 1.184 g of spinel oxide Pr. 0.21 Al 0.09 Co 2.7 O4; of which Co accounts for 62.37 wt% of the catalyst weight and Pr accounts for 11.60 wt% of the catalyst weight.

[0078] Example 5:

[0079] (1) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0080] (2) Mix 3.274 g cobalt nitrate, 0.096 g magnesium nitrate and 0.328 g aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0081] (3) Quickly pour the potassium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0082] (4) The dried product was ground into powder and heated to 600℃ in air at a heating rate of 2℃ / min. The powder was then calcined at this temperature for 4 h to obtain 0.990 g of spinel oxide Mg. 0.09 Al 0.21 Co 2.7 O4; of which Co accounts for 68.89 wt% of the catalyst weight and Mg accounts for 0.95 wt% of the catalyst weight.

[0083] Example 6:

[0084] (1) Dissolve 2.650 g of sodium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0085] (2) Mix 3.274 g cobalt nitrate with 0.065 g calcium chloride and 0.237 g aluminum nitrate and dissolve in 50 mL of deionized water. Stir to form a homogeneous solution.

[0086] (3) Quickly pour the sodium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0087] (4) The dried product was ground into powder and heated to 750°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 1.005 g of spinel oxide Ca. 0.15 Al 0.15 Co 2.7 O4; of which Co accounts for 68.24 wt% of the catalyst weight and Ca accounts for 2.58 wt% of the catalyst weight.

[0088] Example 7:

[0089] (1) Dissolve 2.650 g of sodium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0090] (2) Mix 3.274 g cobalt nitrate, 0.109 g barium nitrate and 0.328 g aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0091] (3) Quickly pour the sodium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0092] (4) The dried product was ground into powder and heated to 500°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 1.137 g of spinel oxide Ba. 0.09 Al 0.21 Co 2.7 O4; of which Co accounts for 65.98 wt% of the catalyst weight and Ba accounts for 5.12 wt% of the catalyst weight.

[0093] Comparative Example 1: (No additives)

[0094] (1) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0095] (2) Dissolve 3.644 g of cobalt nitrate in 50 mL of deionized water and stir to form a homogeneous solution;

[0096] (3) Quickly pour the potassium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0097] (4) The dried product was ground into powder and heated to 550°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 1.068 g of spinel oxide Co3O4.

[0098] Comparative Example 2: (Aluminum-free salt)

[0099] (1) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0100] (2) Mix 3.274 g of cobalt nitrate and 0.328 g of magnesium nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0101] (3) Quickly pour the potassium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0102] (4) The dried product was ground into powder and heated to 550°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 0.949 g of spinel oxide Mg. 0.3 Co 2.7 O4.

[0103] Comparative Example 3: (Solid-phase mixing method)

[0104] (1) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0105] (2) Dissolve 3.644 g of cobalt nitrate in 50 mL of deionized water and stir to form a homogeneous solution;

[0106] (3) Quickly pour the potassium carbonate solution from step (1) into the cobalt nitrate solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0107] (4) The dried product was ground into powder and heated to 550°C in air at a heating rate of 2°C / min. The powder was then calcined at this temperature for 6 h to obtain 1.068 g of spinel oxide Co3O4.

[0108] (5) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0109] (6) Dissolve 4.693 g of aluminum nitrate in 50 mL of deionized water and stir to form a homogeneous solution;

[0110] (7) Mix the potassium carbonate solution from step (5) with the aluminum nitrate solution from step (6), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0111] (8) The dried product was ground into powder and calcined at 550 °C for 6 h in air to obtain 1.577 g of Al2O3.

[0112] (9) Weigh 1.068 g Co3O4 and 0.077 g Al2O3 into an agate mortar and mix them in solid form to obtain an Al2O3-Co3O4 sample.

[0113] Comparative Example 4: (Immersion Method)

[0114] (1) Dissolve 3.455 g of potassium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0115] (2) Dissolve 3.644 g of cobalt nitrate in 50 mL of deionized water and stir to form a homogeneous solution;

[0116] (3) Quickly pour the potassium carbonate solution from step (1) into the cobalt nitrate solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0117] (4) The dried product was ground into powder and calcined at 550 °C for 6 h in air at a heating rate of 2 °C / min to obtain 1.068 g spinel oxide Co3O4.

[0118] (5) Weigh 0.518 g of aluminum nitrate and dissolve it in 5 mL of deionized water. Add 1.068 g of Co3O4 and impregnate overnight. The resulting sample is then dried at 120 °C for 6 h and then transferred to a tube furnace at 600 °C. It is then calcined in air at this temperature for 6 h to obtain the Al2O3 / Co3O4 sample.

[0119] Comparative Example 5: (Hydrogen Reduction)

[0120] (1) Dissolve 2.650 g of sodium carbonate in 100 mL of deionized water and stir until fully dissolved;

[0121] (2) Mix 2.730 g of cobalt nitrate and 1.187 g of aluminum nitrate and dissolve them in 50 mL of deionized water. Stir to form a homogeneous solution.

[0122] (3) Quickly pour the potassium carbonate solution from step (1) into the mixed solution from step (2), stir continuously for 2 h, then filter and dry the filter cake at 120 ℃ for 8 h;

[0123] (4) Grind the dried product into powder, heat it to 550°C in air at a heating rate of 2°C / min, calcine it at this temperature for 4 hours, and then cool it down.

[0124] (5) Then, in a hydrogen atmosphere, the temperature was increased to 550 °C at a heating rate of 5 °C / min and reduced at this temperature for 4 h to obtain 0.871 g of sample Al. 0.25 Co 0.75 O.

[0125] This sample does not require activation and can be used directly for ammonia decomposition reactions.

[0126] Test Example: Catalytic Activity Test

[0127] The catalysts used in the embodiments and comparative examples of this invention are all within 30 L•g. cat -1 • h -1The tests were conducted under space velocity conditions and at a temperature range of 500-600 °C. The catalysts of each example and comparative example were pressed into particles of 0.6-1.2 mm (0.1 g) and loaded into quartz tubes in a fixed bed. Except for Comparative Example 5, the samples of the examples and comparative examples were first activated in situ in a reactor at 500-700 °C under an ammonia atmosphere before the activity test began.

[0128] Activity testing conditions: The feed gas was high-purity ammonia (purity > 99.999%), and the mass hourly space velocity (WHSV) of the feed gas was 30 L•g. cat -1 • h -1 The exhaust gas was collected and analyzed using a Fuli F70 gas chromatograph with a thermal conductivity detector. The main analyses were of the NH3 and H2 concentrations in the exhaust gas.

[0129] The activity of the catalyst is expressed by the NH3 decomposition rate, which is calculated as: (initial ammonia content - ammonia content after reaction) / initial ammonia content × 100%.

[0130] Each embodiment and comparative example was performed at a space velocity of 30 L•g. cat -1 • h -1 The ammonia decomposition rates are shown in Table 1 and Figure 3 As shown.

[0131] Table 1. Examples and comparative examples at an air velocity of 30 L•g cat -1 • h -1 Ammonia decomposition rate (%)

[0132]

[0133] The grain size of the catalyst (311) crystal facets in each embodiment and comparative example is shown in Table 2.

[0134] Table 2 Grain size (nm) of the (311) crystal plane in the examples and comparative examples

[0135]

[0136] The XRD patterns of the catalyst samples obtained in Examples 1-7 and Comparative Examples 1-5 are as follows: Figure 1As shown in the figure, Examples 1-7 and Comparative Examples 1-4 clearly exhibit the characteristic diffraction peaks of Co3O4, indicating that the spinel structure was successfully synthesized. The diffraction peak intensities of Examples 2-4, which are doped with rare earth elements, are significantly weaker. Combined with the smaller grain size calculated in Table 2, this confirms that the doping of rare earth elements effectively inhibits the grain growth of Co. In contrast, the characteristic diffraction peaks of Comparative Example 5 near 36.6, 42.3, and 61.8° belong to the (110), (-111), and (111) crystal planes of CoO, indicating that this comparative example failed to form a spinel structure.

[0137] The XRD patterns of the samples after the reaction in Examples 1, 3, 5 and Comparative Examples 1, 2, 5 are shown below. Figure 2 As shown in the figure, the characteristic diffraction peak of the sample at around 44.3° belongs to the (111) crystal plane of Co. The peak of the (111) crystal plane of the spinel structure-derived example sample is significantly broadened compared with the peak of Comparative Example 5, indicating that the formation of the spinel structure is conducive to the formation of smaller active metal grains in the reaction.

[0138] As shown in Table 1, the catalysts prepared in Examples 1-7 exhibited good performance at high space velocities (30 L•g). cat -1 • h -1 It exhibited excellent ammonia decomposition activity at 600 °C, with an ammonia decomposition rate exceeding 99.3%. The comparison of ammonia decomposition activity results for the catalyst samples obtained in Examples 3, 5, Comparative Example 1, and Comparative Example 2 is shown in the figure below. Figure 3 As shown in the figure, the activity comparison chart further verifies the effectiveness of the catalyst design. The data in the figure and table show that the most preferred embodiment is Example 3, which achieved an ammonia decomposition rate of 93.0% at 550 °C and 99.9% at 600 °C, demonstrating excellent low-temperature ammonia decomposition activity. It is evident that it maintains a high ammonia decomposition rate throughout the 500-600 °C range, exhibiting optimal ammonia decomposition activity.

[0139] Based on the data in Table 2, it can be seen that the crystallite size of the catalysts prepared in Examples 1-7 on the (311) crystal plane is smaller than that of Comparative Examples 1-4. Among them, the crystallite size of Example 3 is smaller.

[0140] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

[0141] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cobalt-based catalyst characterized in that, The catalyst is a spinel oxide M a Al b Co c O4; Wherein, the M is an auxiliary metal; and the catalyst is selected from the group consisting of La 0.21 Al 0.09 Co 2.7 O4, Ce 0.21 Al 0.09 Co 2.7 O4, Pr 0.21 Al 0.09 Co 2.7 O4, Mg 0.09 Al 0.21 Co 2.7 O4, Ca 0.15 Al 0.15 Co 2.7 O4, Ba 0.09 Al 0.21 Co 2.7 O4. And the catalyst is prepared by a preparation method comprising the following steps: (1) providing a precipitant solution with a concentration of 0.2-1 mol / L; wherein the precipitant is potassium carbonate or sodium carbonate; (2) according to the composition of the final catalyst, weighing cobalt salt, aluminum salt and M salt, dissolving in an inert solvent, and stirring until fully dissolved; (3) adding the solution of step (1) to the solution of step (2) at one time to react, obtaining a reaction product; (4) In an air atmosphere, the reaction product obtained in step (3) is heated to 500-700 °C at a rate of 2-5 °C / min, and calcined for 4-6 hours to obtain the spinel oxide M a Al b Co c O4.

2. The cobalt-based catalyst of claim 1, wherein The catalyst is La 0.21 Al 0.09 Co 2.7 O4, Ce 0.21 Al 0.09 Co 2.7 O4 or Pr 0.21 Al 0.09 Co 2.7 O4.

3. The cobalt-based catalyst of claim 1, wherein The catalyst is Mg 0.09 Al 0.21 Co 2.7 O4, Ca 0.15 Al 0.15 Co 2.7 O4 or Ba 0.09 Al 0.21 Co 2.7 O4.

4. The cobalt-based catalyst of claim 1, wherein The step (2) has one or more features selected from the following group: (i) the cobalt salt is selected from the following group: cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt chloride, or a combination thereof; (ii) the aluminum salt is selected from the following group: aluminum nitrate, aluminum isopropylate, aluminum hydroxide, or a combination thereof; (iii) the M salt is selected from the following group: magnesium nitrate, calcium nitrate, calcium chloride, barium nitrate, barium hydroxide, lanthanum nitrate, cerium nitrate, praseodymium nitrate, or a combination thereof.

5. The cobalt-based catalyst of claim 1, wherein In step (1), the precipitant is potassium carbonate.

6. The cobalt-based catalyst of claim 1, wherein In step (3), the reaction time is 1-5 h.

7. Use of a cobalt-based catalyst as claimed in claim 1, characterized in that, For catalyzing the decomposition of ammonia to produce hydrogen gas.

8. Use of a cobalt-based catalyst according to claim 7, characterized in that, The catalytic decomposition of ammonia to produce hydrogen gas also includes in-situ activation of the catalyst with ammonia before hydrogen production; Wherein, the temperature of ammonia activation is 500-700 ℃.

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