Ammonia decomposition catalyst and method for producing ammonia decomposition catalyst

Abstract

The method for producing an ammonia decomposition catalyst according to an embodiment of the present disclosure can produce an ammonia decomposition catalyst by preparing a mixture of a metal oxide containing lanthanum and a dissimilar metal and an aluminum oxide, subjecting the mixture to steam treatment to form a support, and supporting an active metal on the support. An ammonia decomposition catalyst according to an embodiment of the present disclosure is manufactured by the manufacturing method described above.

Description

Technical Field

[0001] The present disclosure relates to an ammonia decomposition catalyst and a method for manufacturing the same. Background Art

[0002] Recently, due to environmental pollution problems, technologies for reducing greenhouse gases or harmful gases in the atmosphere have been developed. For this purpose, in order to replace the use of fossil fuels such as oil and coal, the demand for renewable alternative energy is increasing. As one of the renewable alternative energies, hydrogen can be mainly used.

[0003] Ammonia (NH3) can effectively store and transport hydrogen as a carbon-free fuel. For example, ammonia can be decomposed to produce hydrogen (H2) and nitrogen (N2), and the hydrogen generated from ammonia can be supplied to a fuel cell or the like. However, the reaction of decomposing ammonia into hydrogen and nitrogen is an endothermic reaction, so a large amount of heat and energy may be consumed during the decomposition process.

[0004] Therefore, in order to effectively decompose ammonia while reducing the consumption of heat and energy, an ammonia decomposition catalyst can be used. The ammonia decomposition catalyst can use active metals such as transition metals such as nickel and iron, or platinum group elements such as palladium and ruthenium to promote the decomposition reaction of ammonia.

[0005] During the ammonia decomposition reaction process, due to other components included in ammonia gas, such as moisture, etc., the performance of the ammonia decomposition catalyst may be reduced. As a result, the decomposition rate of ammonia or the production efficiency of hydrogen may be reduced. Therefore, there is a need to develop an ammonia decomposition catalyst with high activity and improved stability and lifetime characteristics. Summary of the Invention

[0006] One problem of the present disclosure is to provide an ammonia decomposition catalyst having improved moisture stability and activity.

[0007] One problem of the present disclosure is to provide a method for manufacturing an ammonia decomposition catalyst having improved moisture stability and activity.

[0008] According to an embodiment of the present disclosure, a method for manufacturing an ammonia decomposition catalyst may prepare a mixture of a metal oxide including lanthanum and a different metal and an aluminum oxide, subject the mixture to steam treatment to form a support, and load an active metal on the support, thereby manufacturing the ammonia decomposition catalyst.

[0009] In some embodiments, the steam treatment may be performed at a temperature of 300 °C to 700 °C.

[0010] In some embodiments, the steam treatment may be performed in a water vapor atmosphere having a moisture content of 500 ppm to 40000 ppm.

[0011] In some embodiments, the steam treatment may be carried out for 1 hour to 100 hours.

[0012] In some embodiments, the support may include a composite oxide containing lanthanum and aluminum and a hetero-metal oxide.

[0013] In some embodiments, the aluminum oxide may react with lanthanum through the steam treatment, thereby converting into the composite oxide containing lanthanum and aluminum.

[0014] In some embodiments, the hetero-metal oxide may have a porous structure or structural defects.

[0015] In some embodiments, lanthanum may be removed from the metal oxide containing lanthanum and the hetero-metal, thereby forming the hetero-metal oxide having a porous structure or structural defects.

[0016] In some embodiments, the composite oxide containing lanthanum and aluminum may have a perovskite crystal structure.

[0017] In some embodiments, the support and the active metal may be heat-treated in a reducing atmosphere, thereby loading the active metal on the surface of the support.

[0018] In some embodiments, the content of the active metal loaded in the hetero-metal oxide may be greater than the content of the active metal loaded in the composite oxide containing lanthanum and aluminum.

[0019] In some embodiments, the active metal may include ruthenium (Ru).

[0020] In some embodiments, the hetero-metal may include cerium (Ce) or zirconium (Zr).

[0021] The ammonia decomposition catalyst according to the embodiments of the present disclosure can be prepared by the method.

[0022] In some embodiments, the ammonia decomposition catalyst may include: a support including a composite oxide containing lanthanum and aluminum and a hetero-metal oxide having a porous structure or structural defects; and an active metal loaded in the support, wherein the content of the active metal loaded in the hetero-metal oxide is greater than the content of the active metal loaded in the composite oxide containing lanthanum and aluminum.

[0023] In some embodiments, the specific surface area of the support may be 80 m 2 / g to 200 m 2 / g.

[0024] In some embodiments, it may be that the lanthanum- and aluminum-containing composite oxide has a perovskite crystal structure.

[0025] According to an embodiment of the present disclosure, a metal oxide containing lanthanum and a different metal and an aluminum oxide can be subjected to steam treatment to form a metal oxide support, and an active metal can be loaded onto the support, thereby manufacturing an ammonia decomposition catalyst. Thereby, the dispersion degree of the active metal can be increased in the ammonia decomposition catalyst, and the ammonia decomposition catalyst can have high moisture stability.

[0026] The support may include an oxide containing a different metal having a porous structure or a structural defect. Thereby, the dispersion degree of the active metal can be increased, and it has high catalytic activity, and the catalyst can maintain high activity for a long time.

[0027] The support may include a composite oxide having a perovskite structure. Therefore, the electron-donating property as an active metal can be further improved, and the conversion performance of the ammonia decomposition catalyst can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic process flow chart of a method for manufacturing an ammonia decomposition catalyst according to an exemplary embodiment.

[0029] Figure 2 is an Ru K-edge EXAFS chart of the ammonia decomposition catalyst of Comparative Example 1.

[0030] Figure 3a is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 in the initial state.

[0031] Figure 3b is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 after heat treatment for 1 hour under the condition of a moisture content of 30000 ppm.

[0032] Figure 3c is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 after heat treatment for 100 hours under the condition of a moisture content of 30000 ppm.

[0033] Figure 4a is an XRD chart of the ammonia decomposition catalyst of Comparative Example 1 measured in the initial state.

[0034] Figure 4b is an XRD chart of the ammonia decomposition catalyst of Comparative Example 1 measured after heat treatment for 100 hours at a temperature of 500 °C and a moisture content of 30000 ppm.

[0035] Figure 5 is a chart showing the ammonia conversion rate at 400 °C as the steam treatment time increases.

[0036] Figure 6 It is a graph showing the ammonia conversion rate at 450 °C as a function of the steam treatment time.

[0037] Figure 7 It is a graph showing the ammonia conversion rate at 500 °C as a function of the steam treatment time. Detailed Description

[0038] According to an embodiment of the present disclosure, there is provided an ammonia decomposition catalyst including a lanthanum-containing carrier and an active metal.

[0039] According to an embodiment of the present disclosure, there is provided a method for manufacturing an ammonia decomposition catalyst using steam treatment.

[0040] Hereinafter, embodiments of the present disclosure will be described in further detail.

[0041] Figure 1 It is a schematic process flow diagram of a method for manufacturing an ammonia decomposition catalyst according to an exemplary embodiment.

[0042] Reference Figure 1 , a metal oxide including lanthanum and a foreign metal can be prepared (for example, step S10).

[0043] The term "foreign metal" used in this specification may refer to a metal other than lanthanum, aluminum, and the active metal. The foreign metal may include transition metals, rare earth metals, and the like.

[0044] According to an exemplary embodiment, the metal oxide may have a complex oxide form. For example, the metal oxide may include a solid solution of lanthanum and a foreign metal. The metal oxide may include oxygen anions, lanthanum cations, and cations of the foreign metal.

[0045] In some embodiments, the metal oxide may be represented by Chemical Formula 1: [[Chemical Formula 1]] La x1 M x2 O y In Chemical Formula 1, 0 < x1 < 1, 0 < x2 < 1, and 1 ≤ y < 3. M may be a foreign metal. In one embodiment, M may be Ce or Zr.

[0046] A mixture of the metal oxide and an aluminum oxide can be prepared (for example, step S20).

[0047] In some embodiments, the mixture may have a form in which the metal oxide powder and the aluminum oxide powder are mixed.

[0048] In some embodiments, the mixture may be a mixed oxide. For example, the mixture may have a form in which a metal oxide and an aluminum oxide are solid-soluted. The term "mixed oxide" used in this specification may refer to an oxide including two or more metal oxides each having different components or crystal structures.

[0049] The mixed oxide can be manufactured by uniformly mixing a metal oxide and an aluminum oxide and then performing a heat treatment.

[0050] In some embodiments, in the total weight of the mixed oxide, the content of the metal oxide containing lanthanum and a foreign metal may be 5 wt% to 40 wt%.

[0051] In some embodiments, in the total weight of the mixed oxide, the content of the aluminum oxide may be 60 wt% to 95 wt%.

[0052] The mixture can be subjected to steam treatment to form a support (e.g., step S30).

[0053] Steam treatment refers to performing a heat treatment on the mixture in a water vapor atmosphere. The water vapor atmosphere may refer to a gas atmosphere containing moisture (H2O) at a concentration or content higher than that in the atmospheric atmosphere.

[0054] The support may include a metal oxide containing lanthanum and aluminum and a foreign metal oxide. As the mixture is heat-treated in a water vapor atmosphere, the aluminum oxide reacts with lanthanum, enabling conversion into a composite oxide containing lanthanum and aluminum.

[0055] For example, through steam treatment, lanthanum elements can be extracted from the solid solution of lanthanum and a foreign metal. The extracted lanthanum elements are solid-soluted into the aluminum oxide in a water vapor atmosphere, thereby enabling the formation of a composite oxide containing lanthanum and aluminum.

[0056] According to an exemplary embodiment, the steam treatment can be performed in a water vapor atmosphere having a moisture (H2O) content of 500 ppm to 40000 ppm. The moisture content can be calculated based on the content (volume basis) of moisture in the total volume of the gas included in the water vapor atmosphere.

[0057] Within this range, lanthanum (La) can be dissolved out from the solid solution of lanthanum and a foreign metal, making it easy to dope into the aluminum oxide or recrystallize. Additionally, as the heat treatment is performed in this atmosphere, the foreign metal oxide can have a high affinity and interaction characteristics with the active metal. Thus, for example, even when driving an ammonia decomposition catalyst under moisture conditions, aggregation between active metals and a decrease in activity can be inhibited.

[0058] In some embodiments, the moisture content of the water vapor atmosphere can be from 500 ppm to 30,000 ppm or from 1,000 ppm to 30,000 ppm. Within this range, the moisture stability, thermal stability, and initial performance of the ammonia decomposition catalyst can be further improved.

[0059] In some embodiments, a water vapor atmosphere can be formed by a water bath or a water vapor generating device. For example, it can be that the gas for heat-treating the mixed oxide passes through the water bath and is thus supplied into the reactor. For example, it can be that water vapor is generated by bubbling in the water vapor generating device, and this water vapor is supplied into the reactor together with the gas. The moisture content can be adjusted by adjusting the flow rate, flow velocity, residence time of the gas passing through the water bath or the water vapor generating device, or the temperature of the water bath, etc.

[0060] Steam treatment can be carried out at a temperature of from 300 °C to 700 °C or from 450 °C to 550 °C. Within this range, it is possible to easily form a metal oxide having a perovskite crystal structure and increase the specific surface area of the heterogeneous metal oxide.

[0061] The steam treatment can be carried out for 1 hour to 100 hours. Within this range, it is possible to more easily form a support having a desired crystal structure and further improve the thermal stability and moisture stability of the ammonia decomposition catalyst.

[0062] In one embodiment, the steam treatment can also be carried out for 5 hours to 50 hours or 10 hours to 30 hours.

[0063] In some embodiments, the gas containing water vapor can include hydrogen (H2). Thereby, the crystal structure of the support can be further stabilized, and the stability and activity of the ammonia decomposition catalyst can be further improved.

[0064] In one embodiment, the gas containing water vapor can further include nitrogen (N2). The content of hydrogen in the gas containing water vapor can be 80 vol% or more, 90 vol% or more, or 95 vol% or more.

[0065] According to an exemplary embodiment, the heterogeneous metal oxide can have a porous structure or structural defects.

[0066] For example, the porous structure can refer to a form in which the heterogeneous metal oxide has a normal crystal structure but includes a plurality of pores inside and on the surface.

[0067] For example, a structural defect can refer to a form in which there are no atoms or other atoms have invaded within the crystal structure, a form of lattice distortion or dislocation, or a form in which the atoms of the lattice are combined with other atoms or are not in their normal positions. For example, structural defects can include point defects, line defects, plane defects, volume defects, etc., and can have forms such as oxygen vacancies, cracks, folds, wrinkles, tears, overlays, voids, etc.

[0068] For example, lanthanum can be removed from a metal oxide containing lanthanum and a foreign metal, thereby forming a porous structure or defect. For example, by heat-treating the mixed oxide in a water vapor atmosphere, lanthanum can be leached out from the solid solution of lanthanum and the foreign metal, and voids or structural defects can be formed in the region where lanthanum is leached out.

[0069] The foreign metal oxide has a porous structure or defect, so it can selectively load active metals on the surface and inside of the foreign metal oxide. Therefore, the content and dispersion of the active metal loaded on the carrier can be increased, and more active sites can be formed in the ammonia decomposition catalyst.

[0070] In some embodiments, the specific surface area of the carrier can be 80 m 2 / g to 200 m 2 / g. The specific surface area can be measured by the BET (Brunauer, Emmett, Teller) method adsorbed by N2. Within this range, while the stability of the carrier can be improved, the dispersion of the active metal and the activity of the ammonia decomposition catalyst can be further improved.

[0071] The foreign metal oxide can be represented by Chemical Formula 2:

Chemical Formula 2

[0072] In some embodiments, the foreign metal oxide can include cerium oxide (CeO2) or zirconium oxide (ZrO2).

[0073] The composite oxide containing lanthanum and aluminum can have a perovskite crystal structure. For example, as the mixture is heat-treated in a water vapor atmosphere, the lanthanum element can be dissolved in the aluminum oxide to form a perovskite crystal structure.

[0074] Perovskite has a three-dimensional crystal structure composed of two cations and one anion, and can refer to a crystal structure substantially similar in form to that of calcium titanate (CaTiO3). For example, perovskite can have a general formula such as ABX3 or ABCX3, in which the X atoms are located at the centers of each crystal plane.

[0075] The composite oxide containing lanthanum and aluminum has a perovskite crystal structure, so it can improve the thermal stability of the carrier and further improve the activity of the ammonia decomposition catalyst.

[0076] For example, when the active metal is electron rich, it can promote the formation of triple bonds (N≡N) between nitrogen radicals (Nradical), and can further increase the rate of nitrogen removal from ammonia. The reaction between nitrogen radicals is the step that determines the rate of the ammonia decomposition reaction. Thus, the richer the electrons of the active metal, the faster the ammonia decomposition rate.

[0077] The perovskite crystal structure has a high electron-donating property for the active metal. Therefore, as the carrier has a perovskite crystal structure, the electrons of the active metal can be made richer. Thus, the catalytic activity of the ammonia decomposition catalyst can be further improved.

[0078] The composite oxide containing lanthanum and aluminum can be represented by Chemical Formula 3:

Chemical Formula 3

[0079] In some embodiments, the oxide containing lanthanum and aluminum may include lanthanum aluminate (LaAlO3).

[0080] In some embodiments, in the total weight of the carrier, the content of the foreign metal oxide may be 5 wt% to 30 wt%.

[0081] In some embodiments, in the total weight of the carrier, the content of the composite oxide containing lanthanum and aluminum may be 70 wt% to 95 wt%.

[0082] When the contents of the foreign metal oxide and the composite oxide are within the above ranges, the dispersion degree of the active metal and the catalytic activity can be further improved, and at the same time, the conversion performance and life performance of the ammonia decomposition catalyst can be further improved.

[0083] The active metal can be loaded on the carrier (for example, in step S40).

[0084] The active metal can be loaded on the carrier to manufacture the ammonia decomposition catalyst. For example, the ammonia decomposition catalyst can be a supported catalyst.

[0085] An ammonia decomposition catalyst can selectively promote the decomposition reaction of ammonia (NH3), and hydrogen (H2) can be formed from ammonia through the ammonia decomposition catalyst. The ammonia decomposition reaction refers to the reaction in which the bonds between atoms in ammonia (NH3) are broken and ammonia is converted into hydrogen (H2) and nitrogen (N2).

[0086] As the active component of the ammonia decomposition reaction, the active metal can promote the dehydrogenation reaction of ammonia.

[0087] In some embodiments, the active metal may include transition metals and / or platinum metals. Transition metals and platinum metals are prone to attracting electrons and can convert electrons into an electron-rich state, thereby further promoting the reaction of nitrogen free radicals. Thus, the catalytic activity of the ammonia decomposition catalyst can be further enhanced, and the rate of the ammonia decomposition reaction can be increased.

[0088] In some embodiments, the active metal may include at least one of the metals belonging to Groups 8 to 10 of the periodic table.

[0089] In one embodiment, examples of the active metal may include osmium (Os), nickel (Ni), iron (Fe), cobalt (Co), platinum (Pt), palladium (Pd), ruthenium (Ru), vanadium (V), copper (Cu), chromium (Cr), tungsten (W), molybdenum (Mo), iridium (Ir), rhodium (Rh), etc.

[0090] In some embodiments, the active metal may include ruthenium (Ru). Ruthenium (Ru) has strong catalytic activity, can further promote the dehydrogenation decomposition reaction, and can further increase the ammonia decomposition rate and conversion rate.

[0091] In one embodiment, the ammonia decomposition catalyst may further include a promoter. The promoter may include metals belonging to Groups 1 to 2 of the periodic table. For example, it may include alkali metals and / or alkaline earth metals. The promoter can be loaded on the carrier together with the active metal.

[0092] In one embodiment, the promoter may include at least one of cesium (Cs), sodium (Na), potassium (K), lithium (Li), rubidium (Rb), francium (Fr), barium (Ba), calcium (Ca), strontium (Sr), beryllium (Be), and magnesium (Mg). They can be contained alone or in combination of two or more.

[0093] In one embodiment, the promoter may include alkali metals. Alkali metals can include one electron in the outermost electron layer, thus acting as an electron donor. Therefore, the electrons of active metals such as ruthenium can become richer through the promoter, and the reaction of nitrogen free radicals can be further promoted through the active metal, thereby increasing the ammonia decomposition rate.

[0094] For example, cesium (Cs) can be included as a promoter in the ammonia decomposition catalyst. Cesium has high electron-donating properties, which can further improve the activity of the ammonia decomposition catalyst. In addition, by further increasing the active sites on the surface of the active metal through cesium, the aggregation of the active metal can be inhibited, and the dispersion degree can be further improved.

[0095] In some embodiments, the carrier and the active metal compound can be heat-treated. For example, the active metal compound can be added to or mixed with the carrier for heat treatment. Through heat treatment, the active metal from the active metal compound can be loaded or doped in the carrier.

[0096] In one embodiment, the active metal compound can be at least one of nitrates, oxides, chlorides, bromides, fluorides, hydroxides, carbonates, acetates, sulfates, naphthenates, propofol, and organometallic complexes of the active metal. They can be used alone or in combination of two or more.

[0097] In one embodiment, the heat treatment can be carried out in a reducing atmosphere. For example, the carrier and the active metal compound can be reductively treated to further improve the dispersion of the active metal in the carrier.

[0098] In one embodiment, the carrier and the active metal compound can be reductively treated with reducing gases such as hydrogen, carbon monoxide, hydrocarbons, or a reducing agent such as hydrogen peroxide, hydrogen sulfide, lithium aluminum hydride, or lithium borohydride can also be added for the reductive treatment of the carrier and the active metal compound.

[0099] In one embodiment, the composite oxide and the active metal compound can be heat-treated in a reducing gas atmosphere. For example, the reducing gas atmosphere can include hydrogen (H2).

[0100] In one embodiment, as a diluent gas, the reducing gas can further include nitrogen (N2) and / or carbon dioxide (CO2).

[0101] In one embodiment, the reducing gas can include 10 vol% to 100 vol% of hydrogen in the total 100 vol% of the reducing gas. Thereby, the dispersion of the active metal in the carrier can be further improved.

[0102] In some embodiments, the heat treatment temperature of the carrier and the active metal compound can be 1000 °C or below, or 900 °C or below, and can be 200 °C or above, or 400 °C or above. Within this range, the active metal can be loaded or doped in the carrier, the aggregation of the active metal can be inhibited, and the dispersion degree can be further improved. Therefore, the activity and stability of the ammonia decomposition catalyst can be further improved.

[0103] According to an exemplary embodiment, an active metal can be selectively loaded or doped on a heterogeneous metal oxide.

[0104] As the heterogeneous metal oxide is formed by steam treatment, the affinity and interaction between the heterogeneous metal oxide and the active metal can be increased. In addition, the heterogeneous metal oxide has a porous structure and a high specific surface area, so the loading sites of the active metal can be relatively increased.

[0105] For example, the content of the active metal loaded on the heterogeneous metal oxide can be greater than the content of the active metal loaded on the composite oxide containing lanthanum and aluminum. Thereby, the water stability of the ammonia decomposition catalyst can be further increased.

[0106] In one example, in an environment where an ammonia decomposition catalyst is used, ammonia gas may contain moisture. For example, when it is common ammonia, it may contain about 0.5 vol% of moisture. However, when ammonia contains moisture, the activity and stability of the ammonia decomposition catalyst may be reduced due to the moisture. For example, when the ammonia decomposition catalyst is steam-treated, inter-bonding and agglomeration of the active metals may occur, which can reduce the dispersion of the active metals and increase the particle size. In this case, the dehydrogenation reaction rate and efficiency of the active metals can be reduced.

[0107] According to an exemplary embodiment, a carrier can be formed by steam treatment, so that the heterogeneous metal oxide has a high affinity and interaction characteristics for the active metal. As the active metal is doped on the heterogeneous metal oxide having a strong interaction with the active metal, even if ammonia contains moisture, the agglomeration between ruthenium particles can be inhibited.

[0108] According to an exemplary embodiment, the heterogeneous metal oxide has a porous structure, so the dispersion of the active metal can be further improved. Thereby, the water stability of the ammonia decomposition catalyst can be improved, and the performance and activity of the ammonia decomposition catalyst can be maintained for a long time even when the ammonia decomposition reaction is carried out under water vapor conditions.

[0109] In some embodiments, the active metal and the promoter can have a particulate form. For example, the particle size of the active metal and the promoter can be 0.1 nm to 30 nm, 1 nm to 20 nm, or 1 nm to 5 nm. Within this range, the dispersion of the active metal and the promoter and the active sites of the ammonia decomposition catalyst can be further increased, and the ammonia decomposition rate and conversion rate can be further improved.

[0110] In some embodiments, the content of the active metal may be 0.1 wt% or more, 0.5 wt% or more, and 1.0 wt% or more in the total weight of the ammonia decomposition catalyst. Within the above range, the active sites of the active metal can be increased, and the ammonia decomposition catalyst has high catalytic activity. Therefore, the initial performance of the ammonia decomposition catalyst can be further improved, and the ammonia decomposition rate and conversion rate can be increased.

[0111] In some embodiments, the content of the active metal may be 3.0 wt% or less, 2.5 wt% or less, and 2.0 wt% or less in the total weight of the ammonia decomposition catalyst. Within the above range, the dispersion of the active metal can be further improved, and the thermal stability and moisture stability of the ammonia decomposition catalyst can be increased.

[0112] In some embodiments, the content of the promoter may be 0.1 wt% to 10 wt% or 0.2 wt% to 5 wt% in the total weight of the ammonia decomposition catalyst. Within the above range, the activity of the ammonia decomposition catalyst can be further increased.

[0113] Hereinafter, embodiments of the present disclosure will be further described with reference to specific manufacturing examples. The examples and comparative examples included in the manufacturing examples are only for exemplifying the present disclosure and are not used to limit the scope of the appended patent claims. Those skilled in the art should clearly understand that various deformations and modifications can be made to the embodiments within the scope and technical concept of the present disclosure, and such deformations and modifications should also fall within the scope of the appended patent claims.

[0114] Manufacturing Example: Manufacture of Ammonia Decomposition Catalyst (1) Example A mixed oxide of lanthanum-cerium composite oxide (LaCeO2) and alumina (Al2O3) was prepared. The mixed oxide was heat-treated at 500 °C for 24 hours in a 100% volume hydrogen (H2) gas atmosphere containing 30,000 ppm of moisture (H2O) by volume to form a support.

[0115] Through X-ray diffraction analysis (XRD), it was confirmed that CeO2 and LaAlO3 with a perovskite crystal structure were formed. Specifically, in the XRD chart of the support, peaks were observed at approximately 28.3° and approximately 32.8°, which are the inherent diffraction peaks of CeO2, and peaks were observed at approximately 23.4° and approximately 33.2°, which are the inherent diffraction peaks of LaAlO3.

[0116] XRD analysis was carried out using an XRD X’pert Pro (Malvern Panalytical) at a current of 300 mA, a voltage of 50 kV, a wavelength of Cu Kα (1.5428 Å), a scanning speed of 5 degree min-1, and 2θ = 10 o ~80 o under the following conditions.

[0117] Ammonia catalyst precursor was prepared by impregnating 1 g of the support with ruthenium nitrosyl nitrate. The ruthenium compound was added until the content of ruthenium (Ru) became 1.4 wt% of the total weight of the support and ruthenium.

[0118] The ammonia catalyst precursor was dried and then reduced at a temperature of 600 °C for 4 hours in a 100% hydrogen atmosphere to prepare an ammonia decomposition catalyst (Ru / HT-CeLaAl).

[0119] (2) Comparative Example 1 An ammonia decomposition catalyst (Ru / CeLaAl) was prepared in the same manner as in Example 1, except that a mixed oxide of lanthanum-cerium composite oxide (LaCeO2) and alumina (Al2O3) was heat-treated at a temperature of 500 °C for 2 hours in a hydrogen (H2) gas atmosphere without moisture.

[0120] (3) Comparative Example 2 An ammonia catalyst precursor was prepared by impregnating 1 g of an alumina support with ruthenium nitrosyl nitrate. The ruthenium nitrosyl nitrate was added until the content of ruthenium (Ru) became 1.4 wt% of the total weight of the alumina support and ruthenium.

[0121] The ammonia catalyst precursor was dried and then reduced at a temperature of 600 °C for 4 hours in a 100 vol% hydrogen atmosphere to prepare an ammonia decomposition catalyst (Ru / Al).

[0122] (4) Comparative Example 3 An ammonia catalyst precursor was prepared by impregnating 1 g of an alumina support with ruthenium nitrosyl nitrate and potassium nitrate. The ruthenium nitrosyl nitrate was added until the content of ruthenium (Ru) became 1.4 wt% of the total weight of the alumina support and ruthenium.

[0123] The ammonia catalyst precursor was dried and then reduced at a temperature of 600 °C for 4 hours in a 100 vol% hydrogen atmosphere to prepare an ammonia decomposition catalyst (Ru / K-Al).

[0124] (5) Comparative Example 4 Impregnate 1 g of an alumina support with ruthenium nitrosyl nitrate and cesium nitrate to produce a precursor of an ammonia catalyst. Add ruthenium nitrosyl nitrate until the content of ruthenium (Ru) becomes 1.4% by weight of the total weight of the alumina support and ruthenium.

[0125] Dry the precursor of the ammonia catalyst and reduce it at a temperature of 600 °C for 4 hours in an atmosphere of 100 vol% hydrogen to produce an ammonia decomposition catalyst (Ru / Cs-Al).

[0126] Experimental Example 1 (1) Evaluation of moisture stability After heat-treating the ammonia decomposition catalysts of the examples and Comparative Example 1 under the conditions shown in Table 1 below, the ammonia decomposition performance was evaluated. Specifically, under the condition of a moisture content of 30,000 ppm, 100 vol% hydrogen (H2) gas containing 30,000 ppm of moisture was used. Under the condition of a moisture content of 6,000 ppm, nitrogen (N2) and hydrogen (H2) containing 30,000 ppm of moisture were mixed and used at a volume ratio of 20:80.

[0127] Heat-treat the ammonia decomposition catalyst at a temperature of 500 °C for the time shown in Table 1 below under each moisture content condition. Supply ammonia to the heat-treated ammonia decomposition catalyst to measure the ammonia decomposition rate.

[0128] Measure the residual ammonia content at the rear end of the reactor using a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD). Calculate the ammonia decomposition rate using the following formula.

[0129] Ammonia decomposition rate (%) = {(ammonia content supplied - residual ammonia content) / ammonia content supplied} × 100 [Table 1]

[0130] Referring to Table 1, in the examples, the ammonia decomposition catalyst maintained a high ammonia decomposition rate even when exposed to a water vapor atmosphere.

[0131] For example, in the examples, the ammonia decomposition rate of the ammonia decomposition catalyst heat-treated for 24 hours in a water vapor atmosphere of 30,000 ppm decreased by 1.5% compared to before heat treatment, and the ammonia decomposition rate of the ammonia decomposition catalyst heat-treated for 100 hours in a water vapor atmosphere of 6,000 ppm decreased by 2.1% compared to before heat treatment.

[0132] However, in Comparative Example 1, when heat-treated for 1 hour or more in a water vapor atmosphere of 30,000 ppm, the ammonia decomposition catalyst substantially did not decompose ammonia. Further, when the ammonia decomposition catalyst was heat-treated for 100 hours in a water vapor atmosphere of 6,000 ppm, the ammonia decomposition rate decreased by more than 4%.

[0133] (2)Analysis of EXAFS crystal structure The sintering phenomenon of the active metal was analyzed by EXAFS (Extended X-ray Absorption Fine Structure) in the ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1. Specifically, Ru K-edge XAFS was measured at room temperature using the 8C beam (nano-XAFS, 4 keV to 20 keV, 1012 photons / sec) of the Pohang Accelerator Laboratory (PAL PLS-II).

[0134] The following Figure 2 are Ru K-edge EXAFS charts in the initial state (fresh), the state after heat treatment for 1 hour at a water content of 30,000 ppm and a temperature of 500 °C (1 h), and the state after heat treatment for 100 hours at a water content of 30,000 ppm and a temperature of 500 °C (100 h).

[0135] Reference Figure 2 , Ru-Ru metal bonds (about 2.3 Å) were confirmed in the ammonia decomposition catalyst. As the exposure time of the ammonia decomposition catalyst to the moisture environment increased, the Ru-Ru metal bonds increased.

[0136] In Comparative Example 1, as the heat treatment of the ammonia decomposition catalyst in the water vapor atmosphere increased, the coordination number of ruthenium particles increased, and thus it was confirmed that the ruthenium particles sintered with each other.

[0137] (3)STEM image analysis The ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1 was photographed by STEM (high-angle annular dark-field scanning transmission electron microscopy). The STEM image was measured using a high-performance TEM (HR-TEM, Titan cubed G2 60-300).

[0138] Specifically, STEM images were taken using a scanning electron microscope of the initial state, the state after heat treatment at a water content of 30,000 ppm and a temperature of 500 °C for 1 hour, and the state after heat treatment at a water content of 30,000 ppm and a temperature of 500 °C for 100 hours.

[0139] Figure 3a is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 in the initial state.

[0140] Figure 3b is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 in the state after heat treatment for 1 hour under the condition of a water content of 30,000 ppm.

[0141] Figure 3c is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 in the state after heat treatment for 100 hours under the condition of a water content of 30,000 ppm.

[0142] In Figures 3a to 3c , the area indicated by the arrow is the area representing ruthenium particles supported on the carrier. Refer to Figures 3a to 3c , as the exposure time to moisture increases, the size of the ruthenium particles increases. It can be confirmed that sintering and agglomeration between ruthenium particles increase by heat treatment in a water vapor atmosphere.

[0143] (4) Analysis of XRD crystal structure The crystal structure of the ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1 was measured by XRD analysis. Under the conditions of a current of 300 mA, a voltage of 50 kV, a wavelength of Cu Kα (1.5428 Å), a scanning speed of 5 degree min -1 and 2θ = 10 o ~80 o , XRD analysis was carried out.

[0144] The following Figure 4a is an XRD chart of the ammonia decomposition catalyst measured in the initial state. Figure 4b is an XRD chart of the ammonia decomposition catalyst measured in the state after heat treatment at a water content of 30,000 ppm and a temperature of 500 °C for 100 hours.

[0145] Refer to Figure 4a and Figure 4b , as heat treatment is carried out in a water vapor atmosphere, the crystal structure of the ammonia decomposition catalyst changes. Refer to Figure 4b , compared with the initial state, the intensity of the peak belonging to perovskite increases. In a high-temperature environment, as it is exposed to moisture, together with the agglomeration of the active metal, the crystal structure of the carrier also changes.

[0146] (5)Measurement of Dispersion and Specific Surface Area Measure the dispersion and specific surface area of the ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1. Specifically, measure the dispersion and specific surface area in the initial state and after heat treatment at a temperature of 500 °C for 100 hours with a moisture content of 30,000 ppm.

[0147] Use a carbon monoxide adsorption capacity evaluation device (Micromeritics, ASAP2020) to measure the dispersion of the active metal in the ammonia decomposition catalyst. After filling 0.1 g of the catalyst into the adsorption tube, perform reduction at 300 °C, lower the temperature, and measure the saturated adsorption amount of carbon monoxide at room temperature. The adsorbed carbon monoxide molecules are considered to be chemisorbed with the ruthenium catalyst, and the dispersion is calculated therefrom.

[0148] Calculate the dispersion (%) by the following formula.

[0149] Dispersion (%) = (Surface content of the active metal measured by carbon monoxide / Content of the active metal used in the catalyst) × 100 Use a specific surface area measuring device (TriStar II Plus, MICROMERITICS) to measure the specific surface area of the ammonia decomposition catalyst by the BET method of nitrogen adsorption amount.

[0150] The measurement results are shown in Table 2 below.

[0151]

Table 2

[0152] Referring to Table 2, by heat treatment in a water vapor atmosphere, the dispersion of ruthenium particles decreases due to the agglomeration of ruthenium particles.

[0153] Experimental Example 2 Measure the ammonia decomposition rate with the steam treatment time of the ammonia decomposition catalysts of the examples and comparative examples.

[0154] Specifically, heat-treat the ammonia decomposition catalysts of the examples and comparative examples at a temperature of 500 °C in a 100 vol% hydrogen (H2) gas atmosphere containing 30,000 ppm of moisture. Measure the ammonia decomposition rate with the heat treatment time.

[0155] In the following Figures 5 to 7 show the measurement results. Figure 5 is a graph showing the ammonia decomposition rate with the heat treatment time at a reaction temperature of 400 °C, Figure 6 is a graph showing the ammonia decomposition rate with the heat treatment time at a reaction temperature of 450 °C. Figure 7It is a graph showing the ammonia decomposition rate as a function of the heat treatment time at a reaction temperature of 500°C.

[0156] Reference Figures 5 to 7 For the ammonia decomposition catalyst of the example, even when the exposure time to moisture increases, a high ammonia decomposition rate through the ammonia decomposition catalyst is maintained.

[0157] However, in the comparative examples, as the exposure time of the ammonia decomposition catalyst to moisture increases, the ammonia decomposition rate decreases.

[0158] In Comparative Example 2, when the ammonia decomposition catalyst is exposed to moisture for more than 10 hours, the ammonia decomposition rate decreases by more than 5% compared to the initial state. Additionally, as the reaction temperature of the catalyst increases, the ammonia decomposition rate decreases significantly.

[0159] In Comparative Example 4, when the exposure time of the ammonia decomposition catalyst to moisture is 15 hours or less at all temperatures, the ammonia decomposition rate also decreases sharply.

[0160] In Comparative Examples 1 and 3, even when the ammonia decomposition catalyst is exposed to a water vapor atmosphere for 2.5 hours or less, the ammonia decomposition catalyst does not have catalytic activity and the dehydrogenation reaction does not occur.

Claims

1. A method for producing an ammonia decomposition catalyst, comprising: a step of preparing a mixture of metal oxides containing lanthanum and a dissimilar metal and aluminum oxide; The step of steam-treating the mixture to form a carrier; and The step of loading active metals on the carrier.

2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein: The steam treatment is performed at a temperature of 300°C to 700°C.

3. The method for producing an ammonia decomposition catalyst according to claim 1, wherein: The steam treatment is performed under a water vapor atmosphere having a moisture content of 500 ppm to 40000 ppm.

4. The method for producing an ammonia decomposition catalyst according to claim 1, wherein: The steam treatment is performed for 1 hour to 100 hours.

5. The method for producing an ammonia decomposition catalyst according to claim 1, wherein: The carrier includes a composite oxide containing lanthanum and aluminum and a heterogeneous metal oxide.

6. The method for producing an ammonia decomposition catalyst according to claim 5, wherein: The aluminum oxide reacts with lanthanum through the steam treatment, thereby being converted into the composite oxide containing lanthanum and aluminum.

7. The method for producing an ammonia decomposition catalyst according to claim 5, wherein: The heterogeneous metal oxide has a porous structure or structural defects.

8. The method for producing an ammonia decomposition catalyst according to claim 7, wherein: Lanthanum is removed from the metal oxide containing lanthanum and a foreign metal, thereby forming the foreign metal oxide having a porous structure or structural defects.

9. The method for producing an ammonia decomposition catalyst according to claim 5, wherein: The composite oxide containing lanthanum and aluminum has a perovskite crystal structure.

10. The method for producing an ammonia decomposition catalyst according to claim 5, wherein: The step of loading the active metal on the carrier includes: heat treating the carrier and the active metal in a reducing atmosphere.

11. The method for producing an ammonia decomposition catalyst according to claim 10, wherein: The content of the active metal supported in the heterogeneous metal oxide is greater than the content of the active metal supported in the composite oxide containing lanthanum and aluminum.

12. The method for producing an ammonia decomposition catalyst according to claim 1, wherein: The active metal includes ruthenium.

13. The method for producing an ammonia decomposition catalyst according to claim 1, wherein: The dissimilar metal includes cerium or zirconium.

14. An ammonia decomposition catalyst prepared by the method according to claim 1.

15. The ammonia decomposition catalyst according to claim 14, wherein The ammonia decomposition catalyst comprises: A carrier comprising a composite oxide containing lanthanum and aluminum and a heterogeneous metal oxide having a porous structure or structural defects; and an active metal, which is supported in the carrier, The content of the active metal supported in the heterogeneous metal oxide is greater than the content of the active metal supported in the composite oxide containing lanthanum and aluminum.

16. The ammonia decomposition catalyst according to claim 15, wherein The specific surface area of ​​the carrier is 80 m 2 / g to 200m 2 / g.

17. The ammonia decomposition catalyst according to claim 15, wherein The composite oxide containing lanthanum and aluminum has a perovskite crystal structure.

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