Ammonia decomposition catalyst and method for preparing the same

Abstract

The present invention relates to a cobalt-lanthanum composite alumina catalyst comprising cobalt metal particles precipitated at high temperature, a method for manufacturing the same, and a method for ammonia decomposition or hydrogen production using the same. The present invention can provide a highly active ammonia decomposition catalyst comprising an alumina (Al2O3) carrier; a metal active material; and a co-catalyst, wherein the co-catalyst comprises cobalt (Co) metal particles; and at least one compound selected from LaCoO3, La2O3, LaAlO3, and CoAl2O4. The cobalt-lanthanum composite alumina catalyst and the method for manufacturing the same according to the present invention can increase the ammonia conversion rate by increasing the catalytic active sites through the dispersion of cobalt metal particles in nano-size within the catalyst.

Description

Technology Field

[0001] The present invention relates to a cobalt-lanthanum-based composite alumina catalyst comprising cobalt metal particles precipitated at high temperature, a method for manufacturing the same, and a method for decomposing ammonia or producing hydrogen using the same. Background Technology

[0002] Hydrogen (H2) is primarily used as an industrial raw material for the synthesis of ammonia and methanol and rectification processes; however, its utilization is gradually expanding in the fields of fuel cell power generation and hydrogen mobility. Nevertheless, hydrogen presents challenges due to its low volumetric energy density in the gaseous state and the high costs involved in establishing storage and transportation infrastructure. To address this, hydrogen carrier technology—which involves chemically fixing hydrogen for storage and transportation and then converting it back into hydrogen at the point of use—is currently being actively discussed and researched. Among these, ammonia (NH3) is identified as a promising hydrogen carrier due to its high hydrogen storage density per unit volume, ease of liquefaction, and the fact that existing large-scale production, storage, and transportation infrastructure is already established.

[0003] Ammonia can be converted into nitrogen and hydrogen through a decomposition reaction (2NH3 → N2 + 3H2) in the presence of a catalyst, which has the advantage of not emitting any carbon. Since the ammonia decomposition reaction is an endothermic reaction and typically proceeds under high temperature conditions, a catalyst with high activity and excellent thermal stability is required. Conventionally, ruthenium (Ru)-based catalysts are mainly used and possess relatively high decomposition activity; however, ruthenium (Ru) is classified as a precious metal, posing issues regarding cost and supply. Therefore, research is actively underway on the development of high-activity catalysts using non-precious metal-based active materials such as nickel (Ni), iron (Fe), and cobalt (Co), as well as on carriers that support the active materials and co-catalysts that support the performance of the active materials.

[0004] Co-catalysts can increase reaction activity and reduce the amount of metal active material used by controlling the electronic and surface chemical properties of the metal active material. In particular, the ammonia decomposition reaction involves the stepwise dissociation of NH bonds and the recombination and desorption processes of nitrogen species adsorbed on the surface; therefore, co-catalysts can increase reaction activity by improving the nitrogen adsorption energy and hydrogen desorption performance of the metal active material. The co-catalysts mainly used are alkali metals such as potassium and cesium, and research is also being conducted on alkaline earth metal oxides such as MgO, rare earth oxides such as lanthanum and cerium, and transition metal species such as cobalt. As described above, precisely designing the composition, content, and interactions of not only the metal active material but also the co-catalyst is recognized as a key factor for achieving a highly active catalytic reaction while minimizing the use of non-precious metals during the ammonia decomposition reaction. Consequently, there is an increasing need for technological development to improve catalytic performance by controlling co-catalysts. Prior art literature

[0005] Republic of Korea Published Patent Application No. 10-2026-0010976 The problem to be solved

[0006] The present invention can provide a highly active ammonia decomposition catalyst comprising an alumina (Al2O3) carrier; a metal active material; and a co-catalyst, wherein the co-catalyst comprises cobalt (Co) metal particles and at least one compound selected from LaCoO3, La2O3, LaAlO3, and CoAl2O4. Additionally, the invention can provide a method for manufacturing the ammonia decomposition catalyst. Furthermore, the invention can provide a method for decomposing ammonia using the ammonia decomposition catalyst. means of solving the problem

[0007] A cobalt-lanthanum composite alumina catalyst according to one embodiment of the present invention comprises an alumina (Al2O3) carrier; a metal active material; and a co-catalyst comprising lanthanum (La) and cobalt (Co), wherein the co-catalyst may comprise cobalt (Co) metal particles; and at least one compound selected from LaCoO3, La2O3, LaAlO3, and CoAl2O4.

[0008] In one embodiment, the cobalt (Co) metal particles may be precipitated by heat-treating LaCoO3 or CoAl2O4 under a high-temperature reducing atmosphere.

[0009] In one embodiment, the combined weight of the metal active material, lanthanum (La), and cobalt (Co) with respect to the total weight of the cobalt-lanthanum composite alumina catalyst may be 5 to 35 weight%.

[0010] In one embodiment, the combined weight of the lanthanum (La) and cobalt (Co) with respect to the total weight of the cobalt-lanthanum composite alumina catalyst may be 1 to 20 weight percent.

[0011] In one embodiment, the amount of cobalt (Co) may be 0.5 to 15 weight percent with respect to the total weight of the cobalt-lanthanum composite alumina catalyst.

[0012] In one embodiment, the molar ratio of lanthanum (La) and cobalt (Co) may be 2:1 to 1:2.

[0013] In one embodiment, the metal active material may be 5 to 25 weight percent with respect to the total weight of the cobalt-lanthanum-based composite alumina catalyst.

[0014] In one embodiment, the cobalt (Co) particles may be nanoparticles with an average diameter of 5 to 500 nm.

[0015] In one embodiment, the metal active material may be selected from at least one of the group consisting of Ru, Pd, Pt, Au, Ni, Cu, Cr, and Fe.

[0016] In one embodiment, the cobalt-lanthanum-based composite alumina catalyst may be a catalyst for ammonia decomposition.

[0017] A method for manufacturing a cobalt-lanthanum composite alumina catalyst according to one embodiment of the present invention may include the following steps: S1) a step of preparing a composite alumina carrier comprising LaCoO3 or CoAl2O4 by high-temperature heat treatment of an aqueous solution mixed with alumina (Al2O3), a lanthanum precursor, and a cobalt precursor; S2) a step of preparing a composite alumina catalyst with a metal active material immobilized by impregnating, drying, and heat-treating the composite alumina carrier and a metal active material precursor solution; and S3) a step of precipitating cobalt (Co) metal particles from the LaCoO3 or CoAl2O4 by heat-treating the composite alumina catalyst under a reducing atmosphere.

[0018] In one embodiment, in step S1, the lanthanum precursor and the cobalt precursor may each be selected from the group consisting of nitrates, chlorides, iodides, and acetates of lanthanum and cobalt, respectively.

[0019] In one embodiment, in step S1, the combined weight of the lanthanum precursor and the cobalt precursor with respect to the total weight of the aqueous solution may be 5 to 55 weight%.

[0020] In one embodiment, in step S1, the alumina may be used in an amount of 1 to 7 times the combined weight of the lanthanum precursor and the cobalt precursor.

[0021] In one embodiment, in step S1, the heat treatment temperature may be 350 to 1200 ℃.

[0022] In one embodiment, in step S2, the metal active material is selected from the group consisting of Ru, Pd, Pt, Au, Ni, Cu, Cr, and Fe, and the metal active material precursor may be selected from the group consisting of the nitride, oxide, chloride, iodide, and acetylacetonate of the metal active material.

[0023] In one embodiment, in step S2, the metal active material precursor may be used in an amount of 50 to 150 parts by weight per 100 parts by weight of the composite alumina carrier.

[0024] In one embodiment, in step S3, the reducing atmosphere may be a gaseous atmosphere containing 1 to 20 volume% of hydrogen gas.

[0025] In one embodiment, in step S3, the heat treatment temperature may be 500 to 1500 ℃. Effects of the invention

[0026] The ammonia decomposition catalyst and the method for manufacturing the same according to the present invention can increase catalytic active sites and catalytic activity by dispersing cobalt metal particles in nano-size within the catalyst. In addition, the amount of precious metal catalyst can be minimized, and mass production is possible due to the relatively simple production process, thereby ensuring the economic feasibility of the ammonia decomposition process. Specifically, by appropriately combining nickel, cobalt, and lanthanum, ammonia can be converted to a level of over 90% at 500°C or higher and close to 100% at 540°C or higher, even without a precious metal catalyst.

[0027] In addition, the stable oxide forms (lanthanum, aluminum oxide) converted after precipitating cobalt under a reducing atmosphere during the catalyst manufacturing process can increase the durability of the catalyst by preventing grain coarsening among the metal particles.

[0028] In addition, even if the catalyst deteriorates or aggregates after use, its performance can be restored relatively simply by sequentially performing oxidation and reduction treatments, thereby lowering maintenance costs. Brief explanation of the drawing

[0029] Figure 1 is a schematic diagram of the manufacturing process of the ammonia decomposition catalyst of the present invention. Figure 2 shows the X-ray diffraction spectrum results of the ammonia decomposition catalyst of the present invention according to the reduction temperature. Figure 3 is a graph showing the ammonia conversion rate (NH3Conversion, %) according to the decomposition temperature and co-catalyst content (La + Co) of the ammonia decomposition catalyst of the present invention. Figure 4 is a graph showing the ammonia conversion rate (NH3Conversion, %) at a specific temperature (520 ℃) ​​according to the co-catalyst content (La + Co) of the ammonia decomposition catalyst of the present invention. Figure 5 is a graph showing the ammonia conversion rate (NH3Conversion, %) according to the decomposition temperature (650~800 ℃) of the ammonia decomposition catalyst of the present invention. Figure 6 is a graph showing the ammonia conversion rate (NH3Conversion, %) at a specific temperature (500 ℃) according to the reduction temperature (650~800 ℃) of the ammonia decomposition catalyst of the present invention. Figure 7 is a graph showing the change in catalyst particle size and metal dispersion according to the reduction temperature of the ammonia decomposition catalyst of the present invention. Figure 8 is a graph comparing the ammonia conversion rate (NH3Conversion, %) of the Co precipitation type ammonia decomposition catalyst of the present invention and the La+Co simple mixed catalyst according to the decomposition temperature. Figure 9 is a graph comparing the ammonia conversion rate (NH3Conversion, %) according to the decomposition temperature of the ammonia decomposition catalyst of the present invention and a catalyst containing cobalt alone. Figure 10 is a graph illustrating the results of particle size and metal dispersion restoration according to the ammonia decomposition catalyst of the present invention before use, after use, and after regeneration. Figure 11 is a TEM image of the Co precipitation type ammonia decomposition catalyst of Example 6 of the present invention (Left: low magnification / Right: high magnification). FIG. 12 is a TEM image of the La+Co simple mixed catalyst of Comparative Example 2 of the present invention (Left: low magnification / Right: high magnification). Specific details for implementing the invention

[0030] Unless otherwise defined in this specification, all technical and scientific terms have the same meaning as generally understood by those skilled in the art to which the present invention pertains. The terms used in the description herein are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0031] The singular form used in this specification is intended to include the plural form unless specifically indicated otherwise in the context.

[0032] Throughout this specification, the terms “comprising,” “having,” “containing,” or “having” any component mean that, unless specifically stated otherwise, other components are not excluded but may be included, and do not exclude elements, materials, or processes not additionally listed.

[0033] The numerical ranges used herein include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited, and all possible combinations of upper and lower limits of the numerical range defined in different forms. Unless otherwise specifically defined in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding are also included in the defined numerical range.

[0034] Unless otherwise specifically defined in this specification, “about” may be considered to be a value within 30%, 25%, 20%, 15%, 10%, or 5% of the specified value.

[0035] The present invention will be described in detail below. However, this is merely illustrative and the present invention is not limited to the specific embodiments described illustratively.

[0036] A cobalt-lanthanum composite alumina catalyst according to one embodiment of the present invention comprises an alumina (Al2O3) carrier; a metal active material; and a co-catalyst comprising lanthanum (La) and cobalt (Co). The co-catalyst may comprise cobalt (Co) metal particles; and at least one compound selected from LaCoO3, La2O3, LaAlO3, and CoAl2O4. The cobalt-lanthanum composite alumina catalyst of the present invention may be in a form in which a reaction-active material is uniformly supported on a scaffold or carrier of the catalyst. Specifically, the scaffold may be alumina (Al2O3), lanthanum oxide (La2O3), lanthanum covalate (LaCoO3), lanthanum aluminate (LaAlO3), or cobalt aluminate (CoAl2O4), or a mixture thereof. In addition, the metal active material and nano-sized cobalt metal particles may be uniformly dispersed and supported within the above framework. For example, the cobalt-lanthanum composite alumina catalyst of the present invention may be composed of cobalt metal particles, alumina, and lanthanum oxide, or may be composed of cobalt metal particles, lanthanum cobalate, and cobalt aluminate, or may include all of cobalt metal particles, LaCoO3, La2O3, LaAlO3, and CoAl2O4.

[0037] The above lanthanum covalate (LaCoO3) may be a compound having a stable perovskite (ABO3) structure. However, the actual material is LaCoO due to oxygen vacancy or non-stoichiometry. 3-δ It may exist in the form (0 < δ ≤ 0.2), and this is not excluded from the present invention. Furthermore, the cobalt aluminate (CoAl2O4) may have a stable spinel (A'B'2O4) structure, and likewise, the actual material may contain partial non-stoichiometricity or crystal defects depending on synthesis conditions, heat treatment temperature, oxygen partial pressure, etc. Therefore, the compositional ratio of atoms may not fall precisely into integer ratios and may be analyzed as a non-integer composition. This is not excluded from the present invention, and it should be understood that substantially implemented or modified compositional ratios are also included within the scope of the present invention.

[0038] In one embodiment, the alumina (Al2O3) may be at least one selected from the group consisting of γ-alumina, θ-alumina, δ-alumina, or α-alumina, and, for example, may be γ-alumina having a high specific surface area. Additionally, the alumina has a specific surface area of ​​50 to 400 m² 2 / g, for example, 100 to 300 m 2 It can have a specific surface area of ​​1 / g, and a pore volume of 0.2 to 1.5 cm 3 / g, and the average pore diameter may be 2 to 50 nm. Additionally, the alumina may be in the form of a powder, granules, pellets, or extrusions, and may react with a lanthanum precursor and a cobalt precursor during the heat treatment process to form phases such as lanthanum cobalate and cobalt aluminate on the surface or inside the pores. The alumina may function as a support that promotes the dispersion of lanthanum and cobalt components and improves the thermal stability and mechanical strength of the catalyst through interaction with the metal oxide phase.

[0039] In one embodiment, the cobalt (Co) metal particles may be precipitated by heat-treating LaCoO3 or CoAl2O4 under a high-temperature reducing atmosphere. The reducing atmosphere may be an inert gas atmosphere containing 1 to 20 volume% of hydrogen gas. For example, it may be 1 to 15 volume%, 3 to 10 volume%, or 3 to 7 volume%. The reducing gas is not necessarily limited to hydrogen gas and may include, for example, carbon monoxide, ammonia, hydrocarbon gases (such as CH4), or a mixture thereof, which can precipitate cobalt at high temperatures. The inert gas may be nitrogen (N2) or argon (Ar) gas, and since hydrogen gas is hazardous, it may be diluted with the inert gas for use. The heat treatment temperature may be 500 to 1500 ℃. For example, it may be 500 ℃ or higher, 550 ℃ or higher, 580 ℃ or higher, 630 ℃ or higher, 680 ℃ or higher, 730 ℃ or higher, 780 ℃ or higher, 1500 ℃ or lower, 1200 ℃ or lower, 1000 ℃ or lower, 900 ℃ or lower, 850 ℃ or lower, and may be a value between these. Preferably, the heat treatment temperature may be 700 to 900 ℃.

[0040] Under the above conditions, a lanthanum covalate or cobalt aluminate phase with a stable structure is decomposed, and cobalt that was dissolved (or fixed) within the crystal structure can be uniformly exsolved onto the catalyst surface as fine nanoparticle-shaped cobalt metal particles. Specifically, as shown in Equation 1 below, cobalt can be exsolved from lanthanum covalate and then converted into lanthanum oxide. Additionally, as shown in Equation 2 below, cobalt can be exsolved from cobalt aluminate and then converted into alumina. In this process, as shown in Equation 3 below, lanthanum oxide and alumina may combine to form lanthanum aluminate, which has a stable perovskite structure. Therefore, the cobalt-lanthanum composite alumina catalyst of the present invention may also be referred to as a cobalt-exsolving ammonia decomposition catalyst.

[0041] [Equation 1] 2LaCoO3+ 3H2→ La2O3+ 2Co + 3H2O

[0042] [Equation 2] CoAl2O4 + H2 → Al2O3 + Co + H2O

[0043] [Equation 3] La2O3+ Al2O3→ 2LaAlO3

[0044] The lanthanum oxide or lanthanum aluminate remaining after the precipitation of cobalt forms a robust and uniform framework even during high-temperature ammonia decomposition reactions, which can physically block the particle coarsening phenomenon in which the metal active material and precipitated cobalt nanoparticles aggregate with each other. If the reaction active materials aggregate, the number of reaction active sites decreases, which can consequently lower the ammonia reaction rate and catalytic performance.

[0045] In one embodiment, the combined weight of the metal active material, lanthanum (La), and cobalt (Co) with respect to the total weight of the cobalt-lanthanum composite alumina catalyst may be 5 to 35 weight%. For example, the metal active material + La + Co content may be 5 weight% or more, 10 weight% or more, 15 weight% or more, 35 weight% or less, 30 weight% or less, 25 weight% or less, or a value between these.

[0046] In one embodiment, the combined weight of lanthanum (La) and cobalt (Co) with respect to the total weight of the cobalt-lanthanum composite alumina catalyst may be 1 to 20 wt%. For example, the La + Co content may be 1 wt% or more, 2 wt% or more, 3 wt% or more, 5 wt% or more, 9 wt% or more, 10 wt% or more, 11 wt% or more, 20 wt% or less, 15 wt% or less, 14 wt% or less, 12 wt% or less, or a value between these. When the combined weight of lanthanum and cobalt is within the above range, the amount and dispersion of cobalt metal particles precipitated on the catalyst surface through a high-temperature reduction process can be optimized, thereby optimizing the effective active sites participating in the ammonia decomposition reaction. If the combined weight of lanthanum and cobalt is less than 1 wt%, the improvement in catalytic activity due to cobalt precipitation may be insufficient, and conversely, if it exceeds 20 wt%, the pores of the support may be clogged or the specific surface area may decrease due to excessive metal oxide and cobalt precipitation.

[0047] In one embodiment, the cobalt (Co) content may be 0.5 to 15 weight percent relative to the total weight of the cobalt-lanthanum composite alumina catalyst. For example, the cobalt metal particle content may be 0.5 weight percent or more, 1 weight percent or more, 1.5 weight percent or more, 2 weight percent or more, 2.5 weight percent or more, 3 weight percent or more, 15 weight percent or less, 14 weight percent or less, 12 weight percent or less, 10 weight percent or less, 8 weight percent or less, 6 weight percent or less, 5 weight percent or less, 4.5 weight percent or less, 4 weight percent or less, 3.5 weight percent or more, and may be a value between these. When the cobalt metal content is within the above range, the effective active sites that directly participate in the ammonia decomposition reaction together with the metal active material are optimized, and the catalytic activity can be improved.

[0048] In one embodiment, the average diameter of the cobalt (Co) metal particles may be 5 to 500 nm. In one embodiment, the cobalt (Co) metal particles may consist of nanoparticles having a size of 1 to 50 nm, which may constitute 50% or more of the total number of cobalt particles. For example, 50% or more of the total number of cobalt particles may have a size (diameter) of 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, or 30 nm or less, and the lower limit may be 1 nm or more, although not specifically limited, and may be a value between these. The diameter may be a value calculated by Transmission Electron Microscopy (TEM), and "50% or more of the total number of cobalt particles" may be defined based on the number of particles counted in the TEM image. As described above, the cobalt metal particles may be of a fine nano size and may be very uniformly dispersed on the catalyst surface.

[0049] In one embodiment, the molar ratio of lanthanum (La) to cobalt (Co) may be 2:1 to 1:2. Cobalt may be included in an amount of 0.5 to 2 moles per mole of lanthanum, for example, 0.5 to 1.5 moles, 0.7 to 1.3 moles, or 0.9 to 1.1 moles per mole of lanthanum. When the molar ratio of lanthanum to cobalt is within the above range, a lanthanum cobalate crystal structure can be stably formed, and uniform precipitation of cobalt metal particles can be induced during high-temperature reduction. In addition, the lanthanum oxide or lanthanum aluminate compound remaining in the framework after precipitation effectively prevents grain coarsening even during high-temperature decomposition reactions, thereby simultaneously improving the high activity and durability of the catalyst.

[0050] In one embodiment, the metal active material may be 5 to 25 weight percent with respect to the total weight of the cobalt-lanthanum composite alumina catalyst. For example, it may be 5 weight percent or more, 10 weight percent or more, 12 weight percent or more, 14 weight percent or more, 25 weight percent or less, 20 weight percent or less, 15 weight percent or less, or a value between these. In one embodiment, the metal active material may be selected from at least one of the group consisting of ruthenium (Ru), palladium (Pd), platinum (Pt), gold (Au), nickel (Ni), copper (Cu), chromium (Cr), and iron (Fe). Among the above metal active materials, ruthenium (Ru), palladium (Pd), platinum (Pt), and gold (Au) can be classified as precious metals, while nickel (Ni), copper (Cu), chromium (Cr), and iron (Fe) can be classified as non-precious metals when comparing relative reserves and prices. The ammonia decomposition catalyst of the present invention can achieve similar ammonia decomposition performance while minimizing the content of precious metals, which have high manufacturing costs, because cobalt metal particles finely precipitated on the catalyst surface through high-temperature reduction treatment increase the activity of the catalyst. For example, 0.1 to 5 weight% of a precious metal catalyst and 5 to 15 weight% of a non-precious metal catalyst may be mixed and used, or 5 to 25 weight% of a non-precious metal catalyst alone may be included.

[0051] In one embodiment, the cobalt-lanthanum composite alumina catalyst may be a catalyst for ammonia decomposition. The ammonia decomposition reaction (2NH3 → N2 + 3H2) is an endothermic reaction and can typically be carried out in the presence of a catalyst at a temperature range of 400 to 900 °C. The reaction may be carried out under atmospheric pressure or pressurized conditions, for example, at a pressure of 1 to 5 bar. Additionally, the gaseous space velocity (GHSV) of ammonia or a mixture thereof is 1,000 to 100,000 h⁻¹ -1The range may be. The hydrogen gas produced from the above reaction can be utilized as a hydrogen source for fuel cells or as a hydrogen storage medium. The ammonia decomposition process using the cobalt-lanthanum composite alumina catalyst of the present invention can be performed under atmospheric pressure conditions and can exhibit a high ammonia decomposition rate and conversion rate even at a relatively low temperature of 400 to 600 ℃. The cobalt-lanthanum composite alumina catalyst of the present invention may have an ammonia conversion rate (%) of 70% or more, 80% or more, or 90% or more at a decomposition temperature of 520 ℃ or higher, and may have excellent ammonia decomposition performance with an ammonia conversion rate (%) of 80% or more, 90% or more, or 95% or more at 540 ℃ or higher.

[0052] A method for manufacturing a cobalt-lanthanum composite alumina catalyst according to one embodiment of the present invention may include the following steps: S1) a step of preparing a composite alumina carrier comprising LaCoO3 or CoAl2O4 by high-temperature heat treatment of an aqueous solution mixed with alumina (Al2O3), a lanthanum precursor, and a cobalt precursor; S2) a step of preparing a composite alumina catalyst with a metal active material immobilized by impregnating, drying, and heat-treating the composite alumina carrier and a metal active material precursor solution; and S3) a step of precipitating cobalt (Co) metal particles from the LaCoO3 or CoAl2O4 by heat-treating the composite alumina catalyst under a reducing atmosphere.

[0053] In one embodiment, in step S1, the lanthanum precursor and the cobalt precursor may each be selected from at least one of the group consisting of nitrates, chlorides, iodides, and acetates of lanthanum and cobalt. For example, the lanthanum precursor may be lanthanum nitrate (La(NO3)3ㆍxH2O), lanthanum chloride (LaCl3ㆍxH2O), lanthanum iodide (LaI3), or lanthanum acetate (La(CH3COO)3). Additionally, the cobalt precursor may be cobalt nitrate (Co(NO3)2ㆍxH2O), cobalt chloride (CoCl2ㆍxH2O), cobalt iodide (CoI2), or cobalt acetate (Co(CH3COO)2ㆍxH2O). In the above formula, x, representing the number of hydrates, may be an integer from 0 to 9.

[0054] In one embodiment, in step S1, the combined weight of the lanthanum precursor and the cobalt precursor relative to the total weight of the aqueous solution may be 5 to 55 weight%. The ratio of the combined weight of the lanthanum+cobalt precursor to the weight of water may be 1:1 to 1:15. The preparation temperature of the mixed aqueous solution may be 50 to 100 ℃. In one embodiment, in step S1, alumina may be used in an amount of 1 to 7 times the combined weight of the lanthanum precursor and the cobalt precursor. The water used in the aqueous solution may be removed by drying at a temperature of 80 to 150 ℃ for 5 to 24 hours.

[0055] In one embodiment, in step S1, the heat treatment temperature may be 350 to 1200 ℃. Additionally, the heat treatment may be carried out under an air atmosphere. Preferably, the heat treatment temperature may be in the range of 800 to 1000 ℃ and calcination and synthesis may be performed for 1 to 10 hours.

[0056] In one embodiment, in step S2, the metal active material may be selected from the group consisting of ruthenium (Ru), palladium (Pd), platinum (Pt), gold (Au), which can be classified as precious metals, and nickel (Ni), copper (Cu), chromium (Cr), and iron (Fe), and the metal active material precursor may be selected from the group consisting of nitrides, oxides, chlorides, iodides, and acetylacetonates of the metal active material. For example, when nickel (Ni) is used as the metal active material, nickel oxide (NiO), nickel chloride (NiCl2·xH2O), nickel nitride (Ni3N), nickel nitrate (Ni(NO3)2·xH2O), or nickel acetylacetonate (Ni(acac)2) may be used as the precursor material.

[0057] Specifically, the above S2 step may involve preparing a precursor solution by dissolving a metal active material precursor in a solvent such as water, alcohol, or ethylene glycol at a temperature of 50 to 100 °C. In one embodiment, in the above S2 step, the metal active material precursor may be used in an amount of 50 to 150 parts by weight per 100 parts by weight of the composite alumina carrier. The solvent may be removed by drying at 70 to 150 °C for 1 to 24 hours. The heat treatment or calcination conditions in the above S2 step may be carried out at a temperature of 250 to 500 °C for 1 to 5 hours under an air atmosphere.

[0058] In one embodiment, in step S3, the reducing atmosphere may be a gas atmosphere containing 1 to 20 volume% of hydrogen gas. For example, it may be 1 to 15 volume%, 3 to 10 volume%, or 3 to 7 volume%. The reducing gas is not necessarily limited to hydrogen gas and may include, for example, carbon monoxide, ammonia, hydrocarbon gases (such as CH4), or a mixture thereof, which can precipitate cobalt at high temperatures. The inert gas may be nitrogen (N2) or argon (Ar) gas, and since hydrogen gas is hazardous, it may be diluted with an inert gas for use.

[0059] In one embodiment, in step S3, the heat treatment temperature may be 500 to 1500 ℃. For example, it may be 500 ℃ or higher, 550 ℃ or higher, 580 ℃ or higher, 630 ℃ or higher, 680 ℃ or higher, 730 ℃ or higher, 780 ℃ or higher, 1500 ℃ or lower, 1200 ℃ or lower, 1000 ℃ or lower, 900 ℃ or lower, 850 ℃ or lower, or a value between these. Preferably, the heat treatment temperature may be 700 to 900 ℃.

[0060] The above-described embodiment will be explained in more detail below through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the claims.

[0061] ammonia decomposition catalyst production

[0062] [Example 1]

[0063] S1) 16.0 g of cobalt nitrate hydrate (Co(NO3)2·6H2O) was added to 180 mL of deionized water in a reaction vessel, heated to 60 ℃, and stirred for 10 minutes to dissolve it. Then, 23.6 g of lanthanum nitrate hydrate (La(NO3)3·6H2O) was added to the cobalt nitrate aqueous solution and dissolved at 60 ℃ for 10 minutes to prepare a mixed aqueous solution of cobalt nitrate and lanthanum nitrate. 80 g of cylindrical alumina pellets (Alfa Aesar) with a diameter of 3 mm and a height of 5 mm were impregnated into the mixed aqueous solution and distilled while rotating and stirring at 100 ℃ to obtain a composite alumina pellet uniformly impregnated with cobalt nitrate and lanthanum nitrate. The above composite alumina carrier was dried at a temperature of 110°C for 12 hours, then placed in an electric furnace and calcined at 200°C for 2 hours and at 900°C for 5 hours to obtain a composite alumina carrier containing cobalt aluminate (CoAl2O4) and lanthanum covalate (LaCoO3).

[0064] S2) Meanwhile, 60.7 g of nickel nitrate hydrate (Ni(NO3)2·6H2O) was added to 180 mL of deionized water in another reaction vessel, heated to 60 ℃, and stirred for 10 minutes to prepare an aqueous nickel nitrate solution. 68 g of the obtained composite alumina carrier was impregnated into the above nickel nitrate aqueous solution and distilled while rotating and stirring at 100 ℃ to obtain a composite alumina carrier impregnated with nickel nitrate. The above nickel nitrate impregnated composite alumina carrier was dried at 110 ℃ for 12 hours, then calcined in an electric furnace at 350 ℃ for 2 hours to obtain a composite alumina catalyst.

[0065] S3) The above composite alumina catalyst was placed in an electric furnace and treated at a temperature of 800 °C for 2 hours under a nitrogen gas atmosphere containing hydrogen at a concentration of 5 volume% to induce the precipitation of cobalt metal particles from cobalt aluminate (CoAl2O4) or lanthanum covalate (LaCoO3), thereby finally obtaining the cobalt-lanthanum composite alumina catalyst of the present invention (La + Co target content 10 wt%). The metal content of the catalyst prepared above was measured using inductively coupled plasma spectroscopy (Thermo Scientific, iCAP 7400) and is shown in Table 1 below. The specific surface area, pore size, etc. of the catalyst were calculated using the conventional BET (Brunauer-Emmett-Teller) measurement method, and the results are shown in Table 2 below.

[0066] [Example 2]

[0067] A cobalt-lanthanum composite alumina catalyst (La + Co target content 7 wt%) was obtained by preparing it in the same manner as in Example 1, except that the input amounts of cobalt nitrate hydrate were changed to 10.8 g and lanthanum nitrate hydrate were changed to 15.9 g. The content of each metal and the specific surface area were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0068] [Example 3]

[0069] A cobalt-lanthanum composite alumina catalyst (La + Co target content 4.5 wt%) was obtained by preparing it in the same manner as in Example 1, except that the input amounts of cobalt nitrate hydrate were changed to 6.7 g and lanthanum nitrate hydrate were changed to 9.9 g. The content of each metal and the specific surface area were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0070] [Example 4]

[0071] A cobalt-lanthanum composite alumina catalyst (La + Co target content 2.8 wt%) was obtained by preparing it in the same manner as in Example 1, except that the input amounts of cobalt nitrate hydrate were changed to 4.1 g and lanthanum nitrate hydrate were changed to 6.0 g. The content of each metal and the specific surface area were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0072] [Example 5]

[0073] A cobalt-lanthanum composite alumina catalyst (La + Co target content 13 wt%) was obtained by preparing it in the same manner as in Example 1, except that the input amounts of cobalt nitrate hydrate were changed to 21.7 g and lanthanum nitrate hydrate were changed to 31.9 g. The content of each metal and the specific surface area were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0074] [Example 6]

[0075] A cobalt-lanthanum composite alumina catalyst (La + Co target content 15 wt%) was obtained by preparing it in the same manner as in Example 1, except that the input amounts of cobalt nitrate hydrate were changed to 25.7 g and lanthanum nitrate hydrate were changed to 37.9 g. The content of each metal and the specific surface area were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0076] [Example 7]

[0077] The cobalt-lanthanum composite alumina catalyst prepared in Example 5 above, which had its activity degraded after being used for a long time in an ammonia decomposition reaction, was recovered from the reactor. The recovered catalyst was placed in an electric furnace and heat-treated at 600 °C under an air atmosphere to re-oxidize the cobalt metal and re-fix it within the crystal structure of cobalt aluminate or lanthanum covalate. Subsequently, the oxidized catalyst was reduced again at a temperature of 800 °C for 2 hours under a nitrogen gas atmosphere containing 5 volume% hydrogen.

[0078] [Example 8]

[0079] In step S3, a cobalt-lanthanum composite alumina catalyst (La + Co target content 13 wt%) was obtained by preparing it in the same manner as in Example 5, except that the heat treatment temperature was carried out at 750 ℃ ​​instead of 800 ℃.

[0080] [Example 9]

[0081] In step S3, a cobalt-lanthanum composite alumina catalyst (La + Co target content 13 wt%) was obtained by preparing it in the same manner as in Example 5, except that the heat treatment temperature was carried out at 700 ℃ instead of 800 ℃.

[0082] [Example 10]

[0083] In step S3, a cobalt-lanthanum composite alumina catalyst (La + Co target content 13 wt%) was obtained by preparing it in the same manner as in Example 5, except that the heat treatment temperature was carried out at 650 ℃ instead of 800 ℃.

[0084] [Comparative Example 1]

[0085] A catalyst not containing cobalt and lanthanum was prepared by performing steps S2 and S3 in the same manner as in Example 1 without performing process S1.

[0086] Specifically, nickel nitrate hydrate (Ni(NO3)) in a reaction vessel 2ㆍAn aqueous nickel nitrate solution was prepared by adding 60.7 g of 6H2O to 180 mL of deionized water, raising the temperature to 60 °C, and stirring for 10 minutes. 68 g of cylindrical alumina pellets with a diameter of 3 mm and a height of 5 mm were impregnated into the above nickel nitrate aqueous solution and distilled while rotating and stirring at 100 °C to obtain an alumina carrier impregnated with nickel nitrate. The nickel nitrate-impregnated alumina carrier was dried at 110 °C for 12 hours and then calcined in an electric furnace at 350 °C for 2 hours. Subsequently, the prepared catalyst was placed in an electric furnace and treated at 800 °C for 2 hours under a nitrogen gas atmosphere containing 5 volume% hydrogen, thereby finally obtaining the catalyst of Comparative Example 1. The metal content and specific surface area were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0087] [Comparative Example 2]

[0088] 21.7 g of cobalt nitrate hydrate and 31.9 g of lanthanum nitrate hydrate were added to 180 mL of deionized water in a reaction vessel, heated to 60 °C, and stirred for 10 minutes to prepare a mixed aqueous solution of cobalt nitrate and lanthanum nitrate. 80 g of cylindrical alumina pellets with a diameter of 3 mm and a height of 5 mm were impregnated into the mixed aqueous solution and distilled at 100 °C while stirring to obtain a composite alumina pellet uniformly impregnated with cobalt nitrate and lanthanum nitrate. The composite alumina carrier was dried at 110 °C for 12 hours, placed in an electric furnace, and calcined at a low temperature of 350 °C for 2 hours to obtain a composite alumina carrier containing cobalt oxide (Co3O4) and lanthanum oxide (La2O3). A nickel nitrate aqueous solution was prepared by adding 60.67 g of nickel nitrate hydrate to 180 mL of deionized water, raising the temperature to 60 ℃, and stirring for 10 minutes. 68 g of the obtained composite alumina carrier was impregnated into the nickel nitrate aqueous solution and distilled while rotating and stirring at 100 ℃ to obtain a nickel nitrate-impregnated composite alumina carrier. The nickel nitrate-impregnated composite alumina carrier was dried at 110 ℃ for 12 hours, then calcined in an electric furnace at 350 ℃ for 2 hours to obtain a composite alumina catalyst.

[0089] Subsequently, the above composite alumina catalyst was placed in an electric furnace and subjected to reduction treatment at a temperature of 800 °C for 2 hours under a nitrogen gas atmosphere containing hydrogen at a concentration of 5 volume% to obtain an alumina catalyst (La + Co target content 13 wt%) mixed with metallic nickel, metallic cobalt, and lanthanum oxide. Since it is difficult to form the parent compound, cobalt aluminate (CoAl2O4) or lanthanum covalate (LaCoO3), which is formed at high temperatures, using the method of Comparative Example 2, a catalyst was prepared in the form of a mixture of metallic cobalt simply reduced from cobalt oxide without the exsolution of nano-sized cobalt (Co) metal particles as in the example of the present invention. The content and specific surface area of ​​each metal were measured in the same manner as in Example 1 and are shown in Tables 1 and 2 below, respectively.

[0090] [Comparative Example 3]

[0091] A lanthanum-free catalyst was prepared by performing the same procedure as in Example 5, except that no lanthanum nitrate hydrate was used. The content of each metal was measured in the same manner as in Example 1 and is shown in Table 1 below.

[0092] Ni(wt%) La(wt%) Co(wt%) La+Co(wt%) Example 1 14.3 6.63 2.89 9.52 Example 2 13.9 4.23 1.93 6.16 Example 3 13.8 2.73 1.23 3.96 Example 4 14.2 1.68 0.69 2.37 Example 5 14.6 8.26 3.43 11.69 Example 6 14.0 9.10 4.14 13.24 Comparative Example 1 15.2 - - - Comparative Example 2 14.5 7.85 3.73 11.58 Comparative Example 3 15.2 - 13.00 13.00

[0093] Surface Area(m 2 / g) Pore Volume(cm 3 / g) Pore ​​Diameter(nm) Comparative Example 1 157.3 0.60 13.6 Comparative Example 2 72.8 0.43 20.1 Example 1 101 0.48 17.2 Example 2 110.2 0.51 16.4 Example 3 117 0.53 15.6 Example 4 157.1 0.54 12.7 Example 5 99.5 0.45 15.7 Example 6 81.2 0.39 18.6

[0094] The cobalt (Co) particle size of the catalysts prepared in Example 6 and Comparative Example 2 was measured using TEM (Thermo-Fisher, TALOS F-200X). Fig. 11 is a TEM image of the Co precipitation type ammonia decomposition catalyst of Example 6 of the present invention, and Fig. 12 is a TEM image of the La+Co simple mixed catalyst of Comparative Example 2 of the present invention (Left: Low magnification / Right: High magnification). As a result of the measurement, it was found that in the case of the Co precipitation type ammonia decomposition catalyst of the present invention (Fig. 11), at least 50% of the particles had a size of 30 nm or less, while in the case of the simple mixed catalyst (Fig. 12), a significant number of particles had a size exceeding 50 nm. Therefore, it was found that the Co precipitation type ammonia decomposition catalyst of the present invention forms nano-sized fine particles.

[0095] [Evaluation Example 1] Evaluation of Ammonia Decomposition Performance

[0096] To evaluate the ammonia decomposition performance of the catalysts prepared in the above examples and comparative examples, each catalyst was installed in a reactor, and the ammonia conversion rate (NH3 Conversion, %) was measured according to changes in decomposition temperature. The Gas Hourly Space Velocity (GHSV) of the mixed gas (ammonia 10% + argon 90%) injected into the reactor was 3,000 h -1 The temperature was maintained constant, and the decomposition temperature was gradually increased in the range of 460–600°C, and the gas passing through the catalyst bed was measured at a specific temperature. The concentration of unreacted ammonia discharged from the downstream end of the reactor was measured using a Fourier transform infrared spectrometer (FT-IR), and the ammonia conversion rate, which is the ratio of decomposed ammonia to the input ammonia, was calculated.

[0097] Figure 3 is a graph showing the ammonia conversion rate (NH3Conversion, %) according to the co-catalyst content (La + Co) and decomposition temperature of the ammonia decomposition catalyst of the present invention. In Figure 3, it was observed that the ammonia conversion rate was significantly lower compared to Comparative Example 1, which contained only nickel metal active material without a co-catalyst, and the cobalt-lanthanum composite alumina catalyst of the present invention. It was observed that at the same ammonia decomposition temperature, the ammonia conversion rate increased as the co-catalyst content (La+Co) increased. Specifically, it was observed that the ammonia decomposition catalyst of Example 5 (La 8.26 wt%, Co 3.43 wt%, La+Co 11.69 wt%) showed an ammonia conversion rate of 80% or more at a decomposition temperature of 500 ℃ or higher, 90% or more at 520 ℃, and approaching 100% at 540 ℃ or higher. As such, it was found that the Co precipitation type ammonia decomposition catalyst of the present invention exhibits a high ammonia conversion rate without including a precious metal catalyst. Figure 4 is a graph showing the ammonia conversion rate (NH3Conversion, %) at a specific temperature (520 ℃) ​​according to the co-catalyst content (La + Co) of the ammonia decomposition catalyst of the present invention. Since the ammonia conversion rates of Example 5 (La+Co 11.69 wt%) and Example 6 (La+Co 13.24 wt%) were similar, the optimal range of the co-catalyst content could be determined.

[0098] Figure 8 is a graph comparing the ammonia conversion rate (NH3Conversion, %) according to decomposition temperature for the Co precipitation type ammonia decomposition catalyst of the present invention and the La+Co simple mixed catalyst. When comparing the catalysts of Example 5 and Comparative Example 2, the ammonia decomposition rate of Example 5 was higher across the entire decomposition temperature range.

[0099] Figure 9 is a graph comparing the ammonia conversion rate (NH3Conversion, %) according to decomposition temperature for the ammonia decomposition catalyst of the present invention and a catalyst containing cobalt alone. The catalyst of Example 5 consists of nano-sized cobalt metal particles uniformly dispersed from a perovskite-structured lanthanum covalate or a spinel-structured cobalt aluminate under a high-temperature reducing atmosphere. On the other hand, the catalyst of Comparative Example 3 contains only cobalt without lanthanum, and it is not possible to precipitate cobalt from a stable perovskite-structured lanthanum covalate; it can be expected that the number of reaction active sites will decrease due to the aggregation of cobalt. When comparing the catalysts of Example 5 and Comparative Example 3, it was found that the ammonia decomposition rate of Example 5 was higher across the entire decomposition temperature range. As shown in the above results, it was found that the ammonia decomposition activity of the cobalt-lanthanum composite alumina catalyst of the present invention was significantly increased.

[0100] Figures 5 and 6 are graphs showing the ammonia conversion rate (NH3Conversion, %) of the ammonia decomposition catalyst of the present invention according to reduction temperature (650–800 ℃). As the reduction temperature increased, the ammonia decomposition rate showed a tendency to increase, and gradually became similar from 500 to 520 ℃, showing a high ammonia conversion rate at the same level at a decomposition temperature of 520 ℃.

[0101] [Evaluation Example 2] Evaluation of Catalyst Characteristics by Reduction Temperature

[0102] Figure 2 shows the X-ray diffraction spectrum results of the ammonia decomposition catalyst of the present invention according to the reduction temperature. Specifically, the changes in the crystal structure of the catalyst surface were observed by measuring the results of Example 5 (800 ℃), Example 8 (750 ℃), Example 9 (700 ℃), and Example 10 (650 ℃), in which a cobalt-lanthanum composite alumina catalyst (La+Co target content 13 wt%) was treated at different reduction temperatures, using an X-ray diffraction instrument (Rigaku, Dmax2500 / PC). As shown in Figure 2, it was confirmed that on the cobalt-lanthanum composite alumina catalyst of the present invention, crystal peaks of nickel (Ni), cobalt (Co), and gamma-alumina (γ-Al2O3) were distinctly mixed with crystal peaks of spinel-structured cobalt aluminate (CoAl2O4) and perovskite-structured lanthanum covalate / aluminate (LaCoO3 / LaAlO3) compounds. Regarding the changes according to reduction temperature, it was observed that significant phase transitions occurred in the crystal structure of the catalyst as the reduction temperature increased. Specifically, as the reduction temperature increased, it was confirmed that the spinel-structured cobalt aluminate and perovskite-structured lanthanum covalate phases constituting the framework of the catalyst gradually decomposed, resulting in a decrease in their crystallinity, while the crystallinity of the reduced precipitated cobalt metal particles increased significantly.

[0103] Figure 7 is a graph showing the changes in catalyst particle size and metal dispersion according to the reduction temperature of the ammonia decomposition catalyst of the present invention, measured by hydrogen chemisorption (H2 chemisorption). Hydrogen chemisorption analysis was performed using an automated chemisorption analyzer. First, the catalyst sample was mounted on the analyzer and pre-treated under an argon atmosphere to remove moisture and impurities adsorbed on the surface. Subsequently, the metal components within the catalyst were reduced by heat treatment at 400 °C for 2 hours under an argon gas atmosphere containing 5 vol% hydrogen. After reduction, residual hydrogen was removed under an argon gas atmosphere, and the catalyst was cooled to 50 °C. Then, 0.5 mL hydrogen pulses were repeatedly injected at 5-minute intervals using an argon mixed gas containing 10 vol% hydrogen. At each pulse injection, the amount of hydrogen passing through the catalyst surface without being chemically adsorbed was measured using a thermal conductivity detector (TCD), and the amount of adsorbed hydrogen was calculated by integrating the reduced area relative to the reference signal. It was determined that the monolayer adsorption saturation state was reached when the change in adsorption amount decreased to 1% or less in two consecutive pulses.

[0104] The catalyst particle size analyzed by the hydrogen chemisorption method refers to the size of the active metal (Ni, Co, etc.) formed on the surface; as particle size decreases, the surface area increases, exhibiting an inverse relationship where metal dispersion increases. Metal dispersion (%) represents the proportion of metal atoms actually exposed on the surface and capable of participating in the reaction out of the total metal atoms within the catalyst. A higher metal dispersion indicates that the reacting metals exist uniformly and widely without aggregation.

[0105] In Figure 7, it was found that before high-temperature reduction treatment, the metal dispersion was about 0.3% and the metal particle size was about 400 nm, but after high-temperature reduction treatment at 800 ℃, the metal dispersion on the surface that could participate in the reaction of the catalyst increased to about 1.3% and the metal particle size decreased to 100 nm or less.

[0106] [Evaluation Example 3] Evaluation of characteristics after catalyst regeneration

[0107] Figure 10 is a graph illustrating the results of restoring particle size and metal dispersion of the ammonia decomposition catalyst of Example 5 of the present invention before, after use, and after regeneration. As shown in Figure 10, the particle size and metal dispersion of the surface metal particles capable of participating in the reaction via the hydrogen chemisorption method were analyzed. Before use, they were 50 nm and 1.7%, respectively, while after use, the deteriorated catalyst showed a particle size of 200 nm and 0.5%, indicating a deterioration in characteristics. However, after regeneration, the catalyst of Example 7 showed a level similar to that of Example 5. Thus, the cobalt-lanthanum-based decomposition catalyst of the present invention was able to regenerate the performance of the catalyst using a relatively simple method.

[0108] As described above, the present invention has been explained by specific details and limited embodiments; however, this is provided merely to aid in a more comprehensive understanding of the invention, and the invention is not limited to the above embodiments. Those skilled in the art can make various modifications and variations from this description.

[0109] Accordingly, the present invention is not limited to the embodiments described above, and all things equivalent to or having equivalent variations to the claims set forth below, as well as the claims set forth below, shall be considered to be within the scope of the present invention.

Claims

Claim 1 A cobalt-lanthanum composite alumina catalyst for ammonia decomposition comprising an alumina (Al2O3) carrier; a metal active material; and a co-catalyst comprising lanthanum (La) and cobalt (Co), wherein the co-catalyst comprises cobalt (Co) metal particles; and at least one compound selected from LaCoO3, La2O3, LaAlO3, and CoAl2O4, and wherein the cobalt (Co) metal particles are precipitated by heat-treating LaCoO3 or CoAl2O4 under a high-temperature reducing atmosphere. Claim 2 delete Claim 3 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the combined weight of the metal active material, lanthanum (La), and cobalt (Co) is 5 to 35 weight% with respect to the total weight of the cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition. Claim 4 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the combined weight of lanthanum (La) and cobalt (Co) is 1 to 20 weight% with respect to the total weight of the cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition. Claim 5 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the cobalt (Co) is 0.5 to 15 weight% with respect to the total weight of the cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition. Claim 6 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the molar ratio of lanthanum (La) to cobalt (Co) is 2:1 to 1:

2. Claim 7 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the metal active material is 5 to 25 weight% with respect to the total weight of the cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition. Claim 8 A cobalt-lanthanum composite alumina catalyst for ammonia decomposition, wherein the cobalt (Co) metal particles have an average diameter of 5 to 500 nm. Claim 9 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the cobalt (Co) metal particles are nanoparticles having a size of 1 to 50 nm, which make up 50% or more of the total number of cobalt particles. Claim 10 A cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 1, wherein the metal active material is selected from at least one of the group consisting of Ru, Pd, Pt, Au, Ni, Cu, Cr, and Fe. Claim 11 delete Claim 12 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition, comprising: S1) a step of preparing a composite alumina carrier containing LaCoO3 or CoAl2O4 by high-temperature heat treatment of an aqueous solution mixed with alumina (Al2O3), a lanthanum precursor, and a cobalt precursor; S2) a step of preparing a composite alumina catalyst with a metal active material immobilized by impregnating, drying, and heat-treating the composite alumina carrier with a metal active material precursor solution; and S3) a step of precipitating cobalt (Co) metal particles from the LaCoO3 or CoAl2O4 by heat-treating the composite alumina catalyst under a reducing atmosphere. Claim 13 A method for preparing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 12, wherein in step S1, the lanthanum precursor and the cobalt precursor are each selected from the group consisting of nitrates, chlorides, iodides, and acetates of lanthanum and cobalt, respectively. Claim 14 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 12, wherein, in step S1, the combined weight of the lanthanum precursor and the cobalt precursor is 5 to 55 weight% relative to the total weight of the aqueous solution. Claim 15 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 12, wherein in step S1 above, alumina is used in an amount of 1 to 7 times the combined weight of the lanthanum precursor and the cobalt precursor. Claim 16 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 12, wherein in step S1 above, the heat treatment temperature is 350 to 1200 ℃. Claim 17 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 12, wherein in step S2 above, the metal active material is selected from at least one of the group consisting of ruthenium (Ru), palladium (Pd), platinum (Pt), gold (Au), nickel (Ni), copper (Cu), chromium (Cr), and iron (Fe), and the metal active material precursor is selected from at least one of the group consisting of nitrides, oxides, chlorides, iodides, and acetylacetonates of the metal active material. Claim 18 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition according to claim 12, wherein in step S2, the metal active material precursor is used in an amount of 50 to 150 parts by weight per 100 parts by weight of the composite alumina carrier. Claim 19 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition, wherein, in the above S3 step, the reducing atmosphere is a gas atmosphere containing 1 to 20 volume% of hydrogen gas. Claim 20 A method for manufacturing a cobalt-lanthanum-based composite alumina catalyst for ammonia decomposition, wherein, in the above S3 step, the heat treatment temperature is 500 to 1500 ℃.

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