Ammonia decomposition catalyst and method of preparing ammonia decomposition catalyst

Abstract

To provide an ammonia decomposition catalyst having improved moisture stability and activity, and a method for producing the same.SOLUTION: In a method for producing an ammonia decomposition catalyst according to embodiments of the present disclosure, a mixture of a metal oxide including lanthanum and a heterogeneous metal and an aluminum oxide is prepared, the mixture is subjected to steam treatment to form a carrier, and an active metal is supported on the carrier to produce an ammonia decomposition catalyst. The ammonia decomposition catalyst according to embodiments of the present disclosure is produced by the above-described production method.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, due to environmental problems, technologies for reducing greenhouse gases or harmful gases in the atmosphere have been developed. As a result, the demand for new renewable energy is increasing in order to replace the use of fossil fuels such as oil and coal. Hydrogen is mainly used as one of the new renewable energies.

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

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

[0005] During the process of the ammonia decomposition reaction, the performance of the ammonia decomposition catalyst may be deteriorated by other components contained in the ammonia gas, such as moisture. Therefore, the decomposition rate of ammonia or the production efficiency of hydrogen may decrease. Therefore, there is a demand for the development of an ammonia decomposition catalyst having high activity and improved stability and life characteristics.

Summary of the Invention

Problems to be Solved by 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.

Means for Solving the Problems

[0008] In the method for manufacturing an ammonia decomposition catalyst according to an embodiment of the present disclosure, a mixture of a metal oxide containing lanthanum and a different metal and an aluminum oxide is prepared, the mixture is steam-treated to form a carrier, and an active metal is supported on the carrier, whereby an ammonia decomposition catalyst can be manufactured.

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

[0010] In some embodiments, the steam treatment can be performed in a steam atmosphere having a moisture content of 500 ppm to 40,000 ppm.

[0011] In some embodiments, the steam treatment can be performed for 1 hour to 100 hours.

[0012] In some embodiments, the carrier can include a lanthanum- and aluminum-containing composite oxide and a different metal oxide.

[0013] In some embodiments, by the steam treatment, the aluminum oxide can react with lanthanum to be converted into the lanthanum- and aluminum-containing composite oxide.

[0014] In some embodiments, the different metal oxide can have a porous structure or a structural defect.

[0015] In some embodiments, lanthanum can be removed from the lanthanum and hetero-metal-containing metal oxide to form the hetero-metal oxide having a porous structure or structural defect.

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

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

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

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

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

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

[0022] In some embodiments, the ammonia decomposition catalyst includes a carrier including a lanthanum and aluminum-containing metal oxide and a hetero-metal oxide having a porous structure or structural defect; and an active metal supported on the carrier, and the content of the active metal supported on the hetero-metal oxide may be greater than the content of the active metal supported on the lanthanum and aluminum-containing composite oxide.

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

[0024] In some embodiments, the lanthanum- and aluminum-containing composite oxide can have a perovskite crystal structure.

Advantages of the Invention

[0025] According to the embodiments of the present disclosure, an ammonia decomposition catalyst can be produced by subjecting a lanthanum- and hetero-metal-containing composite oxide and an aluminum oxide to steam treatment to form a metal oxide support, and supporting an active metal on the support. Thereby, the dispersion degree of the active metal in the ammonia decomposition catalyst can be increased, and the ammonia decomposition catalyst can have high moisture stability.

[0026] The support can include a porous structure or a hetero-metal-containing oxide having a structural defect. Thereby, the dispersion degree of the active metal is improved, high catalytic activity can be achieved, and the activity of the catalyst can be maintained at a high level for a long period of time.

[0027] The support can include a composite oxide having a perovskite structure. Thereby, the electron donation property to the active metal can be further improved, and the conversion performance of the ammonia decomposition catalyst can be enhanced.

Brief Description of the Drawings

[0028]

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[0029] According to an embodiment of the present disclosure, an ammonia decomposition catalyst including a carrier containing lanthanum and an active metal is provided.

[0030] According to an embodiment of the present disclosure, a method for manufacturing an ammonia decomposition catalyst using steam treatment is provided.

[0031] Hereinafter, embodiments of the present disclosure will be described more specifically.

[0032] Figure 1 is a schematic process flowchart for explaining a method for manufacturing an ammonia decomposition catalyst according to an exemplary embodiment.

[0033] Referring to Figure 1, a metal oxide containing lanthanum and a hetero metal can be prepared (for example, step S10).

[0034] As used herein, the term "heterogeneous metal" can mean a metal other than lanthanum, aluminum, and active metals. The heterogeneous metal can include transition metals, rare earth metals, and the like.

[0035] According to an exemplary embodiment, the metal oxide can be in the form of a complex oxide. For example, the metal oxide can include a solid solution of lanthanum and a heterogeneous metal. The metal oxide can include oxygen anions, lanthanum cations, and cations of the heterogeneous metal.

[0036] In some embodiments, the metal oxide can be represented by Chemical Formula 1.

[0037] [Chemical Formula 1] La x1 M x2 O y

[0038] In Chemical Formula 1, 0 < x1 < 1, 0 < x2 < 1, and 1 ≤ y < 3 may be satisfied. M may be the heterogeneous metal. In one embodiment, M may be Ce or Zr.

[0039] A mixture of the metal oxide and an aluminum oxide can be prepared (e.g., in step S20).

[0040] In some embodiments, the mixture can have a form in which the metal oxide powder and the aluminum oxide powder are mixed.

[0041] In some embodiments, the mixture may be a mixed oxide. For example, the mixture can have a form in which the metal oxide and the aluminum oxide are solid-solved. As used herein, the term "mixed oxide" can mean an oxide containing two or more metal oxides having different compositions or crystal structures.

[0042] The mixed oxide can be produced by uniformly mixing the metal oxide and the aluminum oxide and then performing a heat treatment.

[0043] In some embodiments, the content of the lanthanum and hetero-metal-containing metal oxide may be 5 wt% to 40 wt% based on the total weight of the mixed oxide.

[0044] In some embodiments, the content of the aluminum oxide may be 60 wt% to 95 wt% based on the total weight of the mixed oxide.

[0045] The carrier can be formed by steam-treating the mixture (e.g., step S30).

[0046] The "steam treatment" means heat-treating the mixture in a water vapor atmosphere. The "water vapor atmosphere" can mean a gas atmosphere containing a higher concentration or content of moisture (H2O) than the air atmosphere.

[0047] The carrier can include a metal oxide containing lanthanum and aluminum and a hetero-metal oxide. By heat-treating the mixture in a water vapor atmosphere, the aluminum oxide can react with lanthanum and be converted into the lanthanum and aluminum-containing composite oxide.

[0048] For example, by the steam treatment, lanthanum elements can be extracted from the solid solution of lanthanum and hetero-metals. The extracted lanthanum elements can dissolve in the aluminum oxide in a water vapor atmosphere, and a lanthanum and aluminum-containing composite oxide can be formed.

[0049] 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 40,000 ppm. The moisture content can be calculated as the content of moisture in the total volume of the gas contained in the water vapor atmosphere (volume basis).

[0050] In the above range, lanthanum (La) elutes from the solid solution of the lanthanum and the different metal, and can be easily doped or recrystallized into the aluminum oxide. Further, by performing heat treatment in the above atmosphere, the different metal oxide can have high affinity and interaction characteristics with respect to the active metal. Thereby, for example, even when the ammonia decomposition catalyst is driven under moisture conditions, aggregation between the active metals and a decrease in activity can be suppressed.

[0051] In some embodiments, the moisture content of the steam atmosphere may be 500 ppm to 30,000 ppm, or 1,000 ppm to 30,000 ppm. In the above range, the moisture stability, thermal stability, and initial performance of the ammonia decomposition catalyst can be further improved.

[0052] In one embodiment, the steam atmosphere can be formed by a water bath or a steam generator. For example, the gas for heat-treating the mixed oxide can be passed through a water bath and supplied into the reactor. For example, in the steam generator, steam is generated by bubbling, and the steam can be supplied into the reactor together with the gas. By adjusting the flow rate, flow velocity, residence time of the gas passing through the water bath or steam generator, or the temperature of the water bath, the moisture content can be adjusted.

[0053] The steam treatment can be performed at a temperature of 300°C to 700°C, or 450°C to 550°C. In the above range, a metal oxide having a perovskite crystal structure can be easily formed, and the specific surface area of the different metal oxide can be increased.

[0054] The steam treatment can be performed for 1 hour to 100 hours. In the above range, a carrier having a desired crystal structure can be more easily formed, and the thermal stability and moisture stability of the ammonia decomposition catalyst can be further improved.

[0055] In one embodiment, the steam treatment can be performed for 5 hours to 50 hours, or 10 hours to 30 hours.

[0056] In some embodiments, the water vapor-containing gas can contain hydrogen (H2). Thereby, the crystal structure of the carrier can be further stabilized, and the stability and activity of the ammonia decomposition catalyst can be further improved.

[0057] In one embodiment, the water vapor-containing gas can further contain nitrogen (N2). The hydrogen content in the water vapor-containing gas may be 80% by volume or more, 90% by volume or more, or 95% by volume or more.

[0058] According to an exemplary embodiment, the heterogeneous metal oxide can have a porous structure or a structural defect.

[0059] For example, the "porous structure" can mean a form in which the heterogeneous metal oxide has a normal crystal structure but contains a large number of pores inside and on the surface.

[0060] For example, the "structural defect" can mean a form in which atoms do not exist or other atoms penetrate into the crystal structure, a form in which the crystal lattice is distorted or displaced, or a form in which the atoms of the crystal lattice are bonded to other atoms or do not exist at normal positions. For example, the 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.

[0061] For example, lanthanum can be removed from the lanthanum and hetero-metal-containing metal oxide, and the porous structure or defect can be formed. For example, by heat-treating the mixed oxide in a water vapor atmosphere, lanthanum elutes from the solid solution of lanthanum and hetero-metal, and pores or structural defects can be formed in the region where lanthanum has eluted.

[0062] Since the hetero-metal oxide has a porous structure or defect, the active metal can be selectively supported on the surface and inside of the hetero-metal oxide. Thereby, the content and dispersibility of the active metal supported on the carrier can be increased, and many active sites can be formed by the ammonia decomposition catalyst.

[0063] In some embodiments, the specific surface area of the carrier may be 80 m 2 / g to 200 m 2 / g. The specific surface area can be measured by the BET (Brunauer, Emmett, Teller) method by adsorption of N2. In the above range, the stability of the carrier can be improved, and the dispersibility of the active metal and the activity of the ammonia decomposition catalyst can be further enhanced.

[0064] The hetero-metal oxide can be represented by Chemical Formula 2.

[0065] [Chemical Formula 2] MO z

[0066] In Chemical Formula 2, 0 < z < 3 may be satisfied. M may be the hetero-metal, for example, Ce or Zr.

[0067] In some embodiments, the hetero-metal oxide can include cerium oxide (CeO2) or zirconium oxide (ZrO2).

[0068] The above-mentioned lanthanum- and aluminum-containing composite oxide can have a perovskite crystal structure. For example, by heat-treating the mixture in a steam atmosphere, the lanthanum element can be dissolved so as to form a perovskite crystal structure within the aluminum oxide.

[0069] Perovskite means a three-dimensional crystal structure formed by the bonding of two types of cations and one type of anion, and can mean a crystal structure substantially similar in form to the crystal structure of calcium titanate (CaTiO3). For example, perovskite can have a general formula such as ABX3 or ABCX3, and the X atoms in the general formula are located at the centers of each crystal plane.

[0070] Since the above-mentioned lanthanum- and aluminum-containing composite oxide has a perovskite crystal structure, the thermal stability of the carrier can be improved, and the activity of the ammonia decomposition catalyst can be further enhanced.

[0071] For example, when the electrons of the active metal become electron rich, the formation of the triple bond (N≡N) between nitrogen radicals can be promoted, and the desorption rate of nitrogen from ammonia can be further increased. The reaction between the nitrogen radicals is the rate-determining step of the ammonia decomposition reaction, and thus, the richer the electrons of the active metal, the higher the ammonia decomposition rate can be.

[0072] The perovskite crystal structure has high electron-donating properties with respect to the active metal. Therefore, when the carrier has a perovskite crystal structure, the electrons of the active metal can become richer. Thereby, the catalytic activity of the ammonia decomposition catalyst can be further enhanced.

[0073] The above-mentioned lanthanum- and aluminum-containing composite oxide can be represented by Chemical Formula 3.

[0074] [Chemical Formula 3] La y Al 2-y O3

[0075] In Chemical Formula 3, 0 < y < 2 may also be applicable.

[0076] In some embodiments, the lanthanum- and aluminum-containing oxide may include lanthanum aluminate (LaAlO3).

[0077] In some embodiments, the content of the hetero-metal oxide may be 5 wt% to 30 wt% based on the total weight of the carrier.

[0078] In some embodiments, the content of the lanthanum- and aluminum-containing composite oxide may be 70 wt% to 95 wt% based on the total weight of the carrier.

[0079] When the contents of the hetero-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 the conversion performance and the life performance of the ammonia decomposition catalyst can be further improved.

[0080] An active metal can be supported on the carrier (for example, in step S40).

[0081] By supporting the active metal on the carrier, an ammonia decomposition catalyst can be produced. For example, the ammonia decomposition catalyst may be a supported catalyst.

[0082] The ammonia decomposition catalyst can selectively promote the decomposition reaction of ammonia (NH3), and hydrogen (H2) can be formed from ammonia by the ammonia decomposition catalyst. The "ammonia decomposition reaction" means a reaction in which the bonds between atoms in ammonia (NH3) are broken and ammonia is converted into hydrogen (H2) and nitrogen (N2).

[0083] The active metal is an active component of the ammonia decomposition reaction and can promote the ammonia dehydrogenation reaction.

[0084] In some embodiments, the active metal can include a transition metal and / or a platinum metal. Since transition metals and platinum group elements can easily accept electron donation and be converted into a state rich in electrons, they can further promote the reaction of nitrogen radicals. Thereby, the catalytic activity of the ammonia decomposition catalyst can be enhanced, and the rate of the ammonia decomposition reaction can be increased.

[0085] In some embodiments, the active metal can include at least one metal belonging to Groups 8 to 10 of the periodic table.

[0086] In one embodiment, examples of the active metal 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), and the like.

[0087] In some embodiments, the active metal can include ruthenium (Ru). Since ruthenium (Ru) has strong catalytic activity, it can further promote the dehydrogenation decomposition reaction and increase the ammonia decomposition rate and conversion rate.

[0088] In one embodiment, the ammonia decomposition catalyst can further include a promoter. The promoter can include metals belonging to Groups 1 to 2 of the periodic table, and for example, can include an alkali metal and / or an alkaline earth metal. The promoter can be supported on the carrier together with the active metal.

[0089] In one embodiment, the promoter can 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). These can be included alone or in combination of two or more.

[0090] In one embodiment, the promoter can include an alkali metal. The alkali metal element contains one electron in the outermost electron shell and can function as an electron donor. Thereby, the electrons of the active metal such as ruthenium become richer due to the promoter, the reaction of nitrogen radicals by the active metal is further promoted, and the ammonia decomposition rate can be increased.

[0091] For example, the ammonia decomposition catalyst can include cesium (Cs) as a promoter. Since cesium has high electron-donating properties, the activity of the ammonia decomposition catalyst can be further increased. In addition, the active sites on the surface of the active metal are further increased by cesium, so that the aggregation of the active metal can be suppressed and the dispersion degree can be further improved.

[0092] In some embodiments, the carrier and the active metal compound can be heat-treated. For example, the active metal compound can be added or mixed to the carrier and heat-treated. By the heat treatment, the active metal derived from the active metal compound can be supported or doped in the carrier.

[0093] In one embodiment, at least one of the nitrate, oxide, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate, naphthenate, isopropoxide, and organometallic complex of the active metal can be used as the active metal compound. These can be used alone or in combination of two or more.

[0094] In one embodiment, the heat treatment can be performed in a reducing atmosphere. For example, the carrier and the active metal compound can be subjected to a reduction treatment to further improve the dispersibility of the active metal in the carrier.

[0095] In one embodiment, the reduction treatment of the carrier and the active metal compound may be performed using a reducing gas such as hydrogen, carbon monoxide, or hydrocarbon, or may be performed by adding a reducing agent such as hydrogen peroxide, hydrogen sulfide, lithium aluminum hydride, or lithium borohydride.

[0096] 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 contain hydrogen (H2).

[0097] In one embodiment, the reducing gas can further contain nitrogen (N2) and / or carbon dioxide (CO2) as a diluent gas.

[0098] In one embodiment, the reducing gas can contain 10% to 100% by volume of hydrogen based on 100% by volume of the total reducing gas. Thereby, the dispersibility of the active metal in the carrier can be further improved.

[0099] In some embodiments, the heat treatment temperature of the carrier and the active metal compound may be 1,000 °C or lower or 900 °C or lower, and may also be 200 °C or higher or 400 °C or higher. Within this range, the active metal can be supported or doped in the carrier, aggregation of the active metal can be suppressed, and the degree of dispersion can be further improved. Thereby, the activity and stability of the ammonia decomposition catalyst can be further improved.

[0100] According to an exemplary embodiment, the active metal can be selectively supported or doped on the heterogeneous metal oxide.

[0101] By forming the heterogeneous metal oxide through steam treatment, the affinity and interaction between the heterogeneous metal oxide and the active metal can be enhanced. Further, since the heterogeneous metal oxide has a porous structure and a high specific surface area, the loading sites of the active metal can be relatively increased.

[0102] For example, the content of the active metal supported on the heterogeneous metal oxide may be greater than the content of the active metal supported on the lanthanum- and aluminum-containing composite oxide. Thereby, the moisture stability of the ammonia decomposition catalyst can be further enhanced.

[0103] In one example, in an environment where the ammonia decomposition catalyst is used, ammonia gas may contain moisture. For example, in the case of common ammonia gas, it can contain about 0.5% by volume of moisture. However, when ammonia gas contains moisture, the activity and stability of the ammonia decomposition catalyst may be reduced by the moisture. For example, when the ammonia decomposition catalyst is steam-treated, bonding and aggregation may occur among the active metals, the dispersibility of the active metals may be reduced, and the particle size may increase. In this case, the rate and efficiency of the dehydrogenation reaction by the active metals may be reduced.

[0104] According to an exemplary embodiment, by forming the carrier through steam treatment, the heterogeneous metal oxide can have high affinity and interaction characteristics with respect to the active metal. By doping the active metal onto the heterogeneous metal oxide having a strong interaction with the active metal, aggregation between ruthenium particles can be suppressed even when the ammonia gas contains moisture.

[0105] According to an exemplary embodiment, due to the porous structure of the heterogeneous metal oxide, the dispersibility of the active metal can be further enhanced. Thereby, the moisture 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 steam conditions.

[0106] In some embodiments, the active metal and the cocatalyst can have a particulate form. For example, the particle size of the active metal and the cocatalyst may be 0.1 nm to 30 nm, 1 nm to 20 nm, or 1 nm to 5 nm. Within this range, the dispersibility of the active metal and the cocatalyst 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.

[0107] In some embodiments, the content of the active metal may be 0.1 wt% or more, 0.5 wt% or more, or 1.0 wt% or more based on the total weight of the ammonia decomposition catalyst. Within this range, the active sites of the active metal increase, and the ammonia decomposition catalyst can have high catalytic activity. Thereby, the initial performance of the ammonia decomposition catalyst can be further improved, and the decomposition rate and conversion rate of ammonia can be increased.

[0108] In some embodiments, the content of the active metal may be 3.0 wt% or less, 2.5 wt% or less, or 2.0 wt% or less based on the total weight of the ammonia decomposition catalyst. Within this range, the dispersibility of the active metal can be further improved, and the thermal stability and moisture stability of the ammonia decomposition catalyst can be enhanced.

[0109] In some embodiments, the content of the cocatalyst may be 0.1 wt% to 10 wt%, or 0.2 wt% to 5 wt% based on the total weight of the ammonia decomposition catalyst. Within this range, the activity of the ammonia decomposition catalyst can be further enhanced.

[0110] Hereinafter, the embodiments of the present disclosure will be described more specifically with reference to production examples. However, the examples and comparative examples included in the production examples are merely illustrative of the present disclosure and do not limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the examples are possible within the scope of the present disclosure and the scope of the technical idea, and it is natural that such deformations and modifications belong to the appended claims.

[0111] Production Example: Production 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 a temperature of 500 °C for 24 hours in a 100% hydrogen (H2) gas atmosphere containing 30,000 ppm of moisture (H2O) by volume to form a support.

[0112] By X-ray diffraction analysis (X-ray Diffraction, XRD), it was confirmed that CeO2 and LaAlO3 having a perovskite crystal structure were formed. Specifically, in the XRD graph of the support, peaks were observed at about 28.3° and about 32.8°, which are the characteristic diffraction peaks (peaks) of CeO2, and peaks were observed at about 23.4° and about 33.2°, which are the characteristic diffraction peaks of LaAlO3.

[0113] XRD analysis was performed using XRD X’pert Pro (manufactured by Marvern Panalytical) 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° to 80°.

[0114] 1 g of the support was impregnated with ruthenium nitrosyl nitrate to produce a precursor of an ammonia catalyst. The ruthenium compound was added so that the content of ruthenium (Ru) was 1.4% by weight based on the total weight of the support and ruthenium.

[0115] The ammonia catalyst precursor was dried and reduced at a temperature of 600 °C for 4 hours in a 100% hydrogen atmosphere to produce an ammonia decomposition catalyst (Ru / HT-CeLaAl).

[0116] (2) Comparative Example 1 An ammonia decomposition catalyst (Ru / CeLaAl) was produced in the same manner as in Example 1, except that a mixed oxide of the above-mentioned 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 containing no moisture.

[0117] (3) Comparative Example 2 1 g of an alumina support was impregnated with ruthenium nitrosyl nitrate to produce an ammonia catalyst precursor. Ruthenium nitrosyl nitrate was added such that the content of ruthenium (Ru) was 1.4% by weight based on the total weight of the alumina support and ruthenium. The ammonia catalyst precursor was dried and reduced at a temperature of 600 °C for 4 hours in a 100 vol% hydrogen atmosphere to produce an ammonia decomposition catalyst (Ru / Al).

[0118] (4) Comparative Example 3 1 g of an alumina support was impregnated with ruthenium nitrosyl nitrate and potassium nitrate to produce an ammonia catalyst precursor. Ruthenium nitrosyl nitrate was added such that the content of ruthenium (Ru) was 1.4% by weight based on the total weight of the alumina support and ruthenium. The ammonia catalyst precursor was dried and reduced at a temperature of 600 °C for 4 hours in a 100 vol% hydrogen atmosphere to produce an ammonia decomposition catalyst (Ru / K-Al).

[0119] (5) Comparative Example 4 1 g of an alumina support was impregnated with ruthenium nitrosyl nitrate and cesium nitrate to produce an ammonia catalyst precursor. Ruthenium nitrosyl nitrate was added such that the content of ruthenium (Ru) was 1.4% by weight based on the total weight of the alumina support and ruthenium. The ammonia catalyst precursor was dried and reduced at a temperature of 600 °C for 4 hours in a 100 vol% hydrogen atmosphere to produce an ammonia decomposition catalyst (Ru / Cs-Al).

[0120] 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.

[0121] The ammonia decomposition catalyst was heat-treated at a temperature of 500 °C for the time shown in Table 1 below under each moisture content condition. Ammonia gas was supplied to the heat-treated ammonia decomposition catalyst, and the ammonia decomposition rate was measured.

[0122] Using a gas chromatography (GC) equipped with a thermal conductivity detector (TCD), the residual ammonia content at the rear end of the reactor was measured. The ammonia decomposition rate was calculated using the following formula.

[0123] Ammonia decomposition rate (%) = {(ammonia content in supply - ammonia content in residue) / ammonia content in supply} × 100

[0124]

Table 1

[0125] Referring to Table 1, in the case of the examples, even when the ammonia decomposition catalyst was exposed to a steam atmosphere, the ammonia decomposition rate by the ammonia decomposition catalyst was maintained high.

[0126] For example, in the case of the examples, the ammonia decomposition rate of the ammonia decomposition catalyst heat-treated for 24 hours in a steam atmosphere of 30,000 ppm decreased by 1.5% compared to before the heat treatment, and the ammonia decomposition rate of the ammonia decomposition catalyst heat-treated for 100 hours in a steam atmosphere of 6,000 ppm decreased by 2.1% compared to before the heat treatment.

[0127] However, in the case of Comparative Example 1, when heat-treated for 1 hour or more in a steam atmosphere of 30,000 ppm, the ammonia decomposition catalyst could not substantially decompose ammonia. Also, when the ammonia decomposition catalyst was heat-treated for 100 hours in a steam atmosphere of 6,000 ppm, the ammonia decomposition rate decreased by 4% or more.

[0128] (2) Analysis of EXAFS crystal structure The sintering phenomenon of the active metal in the ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1 was analyzed by EXAFS (Extended X-ray Absorption Fine Structure). Specifically, Ru K-edge XAFS was measured at room temperature using the 8C beamline (nano-XAFS, 4 keV to 20 keV, 10 12 photons / sec) of the Pohang Light Source Accelerator (PAL PLS-II).

[0129] Figure 2 below is the Ru K-edge EXAFS graph in the initial state (fresh), the state after heat treatment at a moisture content of 30,000 ppm and a temperature of 500 °C for 1 hour (1h), and the state after heat treatment at a moisture content of 30,000 ppm and a temperature of 500 °C for 100 hours (100h).

[0130] Referring to Figure 2, in the ammonia decomposition catalyst, an Ru-Ru metal bond (about 2.3 Å) was confirmed. The Ru-Ru metal bond increased as the time the ammonia decomposition catalyst was exposed to the moisture environment increased.

[0131] In the case of Comparative Example 1, as the ammonia decomposition catalyst was heat-treated in a steam atmosphere, the coordination number of ruthenium particles increased. From this, it can be seen that the ruthenium particles sintered together.

[0132] (3) Analysis of STEM images 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 images were measured using a high-performance TEM (HR-TEM, Titan cubed G2 60-300).

[0133] Specifically, STEM images were taken in the initial state, the state after heat treatment at a moisture content of 30,000 ppm and a temperature of 500 °C for 1 hour, and the state after heat treatment at a moisture content of 30,000 ppm and a temperature of 500 °C for 100 hours using a scanning electron microscope.

[0134] Figure 3a is a STEM image of the ammonia decomposition catalyst of Comparative Example 1 in the initial state.

[0135] 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 moisture content of 30,000 ppm.

[0136] 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 moisture content of 30,000 ppm.

[0137] In Figures 3a to 3c, the regions indicated by the arrows are the regions showing ruthenium particles supported on the carrier. Referring to Figures 3a to 3c, as the time of exposure to moisture increased, the size of the ruthenium particles increased. It can be confirmed that sintering and aggregation between ruthenium particles increase by heat treatment in a steam atmosphere.

[0138] (4)XRD Crystal Structure Analysis The crystal structure of the ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1 was measured by XRD analysis. The XRD analysis was performed 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 a 2θ range of 10° to 80°.

[0139] Figure 4a is an XRD graph of the ammonia decomposition catalyst of Comparative Example 1 in the initial state. Figure 4b is an XRD graph of the ammonia decomposition catalyst of Comparative Example 1 in the state heat-treated at a moisture content of 30,000 ppm and a temperature of 500 °C for 100 hours.

[0140] Referring to Figures 4a and 4b, the crystal structure of the ammonia decomposition catalyst changed by heat treatment in a water vapor atmosphere. Referring to Figure 4b, the intensity of the peak corresponding to perovskite increased compared to the initial state. Exposure to moisture in a high-temperature environment changed the crystal structure of the support along with the aggregation of the active metal.

[0141] (5) Measurement of Dispersion and Specific Surface Area The dispersion and specific surface area of the ammonia decomposition catalyst (Ru / CeLaAl) of Comparative Example 1 were measured. Specifically, the dispersion and specific surface area in the initial state and in the state heat-treated at a moisture content of 30,000 ppm and a temperature of 500 °C for 100 hours were measured respectively.

[0142] The dispersion of the active metal in the ammonia decomposition catalyst was measured using a carbon monoxide adsorption capacity evaluation apparatus (ASAP 2020, manufactured by Micromeritics). After filling 0.1 g of the catalyst into the adsorption tube, it was reduced at 300 °C, and then the temperature was lowered to measure the saturated adsorption amount of carbon monoxide at room temperature. The adsorbed carbon monoxide molecules were regarded as those due to chemisorption with the ruthenium catalyst, and the dispersion was calculated. The dispersion (%) was calculated by the following formula.

[0143] Dispersion (%) = (Surface content of active metal measured by carbon monoxide / Content of active metal used in the catalyst) × 100

[0144] The specific surface area of the ammonia decomposition catalyst was measured by the BET method based on the nitrogen gas adsorption amount using a specific surface area measuring device (TriStar II Plus, manufactured by MICROMERITICS). The measurement results are shown in Table 2 below.

[0145]

Table 2

[0146] Referring to Table 2 above, by heat-treating in a water vapor atmosphere, the degree of dispersion of ruthenium particles decreased due to the aggregation of ruthenium particles.

[0147] Experimental Example 2 The ammonia decomposition rate of the ammonia decomposition catalysts of the examples and comparative examples was measured according to the steam treatment time.

[0148] Specifically, the ammonia decomposition catalysts of the examples and comparative examples were heat-treated at a temperature of 500°C in a 100 vol% hydrogen (H2) gas atmosphere containing 30,000 ppm of moisture. The ammonia decomposition rate according to the heat treatment time was measured.

[0149] The measurement results are shown in FIGS. 5 to 7. FIG. 5 is a graph showing the ammonia decomposition rate according to the heat treatment time at a reaction temperature of 400°C. FIG. 6 is a graph showing the ammonia decomposition rate according to the heat treatment time at a reaction temperature of 450°C. FIG. 7 is a graph showing the ammonia decomposition rate according to the heat treatment time at a reaction temperature of 500°C.

[0150] Referring to FIGS. 5 to 7, for the ammonia decomposition catalysts of the examples, the ammonia decomposition rate by the ammonia decomposition catalyst was maintained high even when the time of exposure to moisture increased.

[0151] On the other hand, in the case of the comparative examples, the ammonia decomposition rate decreased as the time of exposure of the ammonia decomposition catalyst to moisture increased.

[0152] When the ammonia decomposition catalyst was exposed to moisture for 10 hours or more as in Comparative Example 2, the ammonia decomposition rate decreased by 5% or more compared to the initial value. Further, as the reaction temperature of the catalyst increased, the ammonia decomposition rate decreased significantly.

[0153] As in Comparative Example 4, when the exposure time of the ammonia decomposition catalyst to moisture was 15 hours or less at all temperatures, the ammonia decomposition rate also decreased rapidly.

[0154] In the cases of Comparative Examples 1 and 3, even when the ammonia decomposition catalyst was exposed to a steam atmosphere for 2.5 hours or less, the ammonia decomposition catalyst could not have catalytic activity, and the dehydrogenation reaction did not proceed.

Claims

1. providing a mixture of a lanthanum- and foreign-metal-containing metal oxide and an aluminum oxide; steaming the mixture to form a support; and supporting an active metal on the support.

2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the steam treatment is carried out 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 carried out in a water vapor atmosphere having a moisture content of 500 ppm to 40,000 ppm.

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

5. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the support comprises a composite oxide containing lanthanum and aluminum, and a different metal oxide.

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

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

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

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

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

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

12. The method for producing an ammonia decomposition catalyst according to claim 1 , wherein the active metal comprises ruthenium (Ru).

13. The method for producing an ammonia decomposition catalyst according to claim 1 , wherein the different metals include cerium (Ce) or zirconium (Zr).

14. 13. An ammonia decomposition catalyst produced by the method of claim 1.

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

16. The specific surface area of ​​the carrier is 80 m ２ / g to 200m ２ / g.

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

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