Method of preparing catalyst for ammonia decomposition

Abstract

To provide a method of preparing a catalyst for ammonia decomposition with enhanced dispersibility.SOLUTION: According to the embodiments of the present disclosure, an ammonia decomposition catalyst may be prepared by performing heat treatment on alumina, a lanthanum compound and a cerium compound in a reducing gas atmosphere to form a composite oxide on an alumina support, and supporting an active metal including ruthenium on the composite oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing an ammonia decomposition catalyst. [Background technology]

[0002] Due to environmental issues, there is a growing demand for new and renewable energy sources to replace the use of fossil fuels such as oil and coal. Hydrogen is one of the most widely used new and renewable energies.

[0003] Ammonia (NH3) can be used as a substance that efficiently stores and transports hydrogen. For example, hydrogen can be extracted by using a reaction in which ammonia (NH3) is decomposed into hydrogen (H2) and nitrogen (N2).

[0004] However, the decomposition of ammonia into hydrogen and nitrogen is an endothermic process, which can consume a large amount of heat and energy. Therefore, obtaining hydrogen gas through the ammonia decomposition reaction can increase the heat and energy consumption. To obtain high-purity hydrogen with high efficiency, an ammonia decomposition catalyst can be used.

[0005] Ammonia decomposition catalysts can decompose ammonia at low temperatures using active metals such as transition metals such as nickel and iron, or platinum group elements such as palladium and ruthenium. Among active metals, platinum group elements have high activity in the ammonia decomposition reaction, but are rare and expensive compared to transition metals such as nickel and iron, which can reduce processability and economic efficiency.

[0006] Furthermore, when the support of the ammonia decomposition catalyst contains metal particles, research and development is underway to develop an ammonia decomposition catalyst that can prevent the metal particles from agglomerating and decompose ammonia efficiently at low cost. Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the present disclosure is to provide a method for producing an ammonia decomposition catalyst with improved dispersibility. [Means for solving the problem]

[0008] In a method for producing an ammonia decomposition catalyst according to an embodiment of the present disclosure, a composite oxide can be formed on an alumina support by heat treating alumina, a lanthanum compound, and a cerium compound in a reducing gas atmosphere, and an active metal including ruthenium can be supported on the composite oxide.

[0009] In some embodiments, the active metal may further comprise a promoter comprising 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).

[0010] In some embodiments, the composite oxide can be formed by heat treating the alumina, the lanthanum compound, and the cerium compound at a temperature above 600°C and up to 1,000°C.

[0011] In some embodiments, the reducing gas atmosphere may be a hydrogen atmosphere.

[0012] In some embodiments, the complex oxide can contain lanthanum, cerium, and aluminum.

[0013] In some embodiments, the composite oxide can be formed by doping the surface of the alumina with lanthanum from the lanthanum compound and cerium from the cerium compound.

[0014] In some embodiments, the alumina support may be Al2O3.

[0015] In some embodiments, the complex oxide can have a perovskite structure.

[0016] In some embodiments, the composite oxide and the active metal can be mixed and heat-treated to support the active metal containing ruthenium on the composite oxide.

[0017] In some embodiments, the heat treatment temperature of the composite oxide and the active metal may be lower than the heat treatment temperature of the alumina, the lanthanum compound, and the cerium compound.

[0018] In some embodiments, the heat treatment temperature of the composite oxide and the active metal may be 200°C to 1,000°C.

[0019] In some embodiments, the heat treatment of the composite oxide and the ruthenium compound can be carried out in a reducing gas atmosphere.

[0020] In some embodiments, the content of ruthenium supported on the composite oxide may be less than 1.5 wt % based on the total weight of the composite oxide and the active metal.

[0021] In some embodiments, the content of ruthenium supported on the composite oxide may be 0.1 wt % to 1.3 wt % based on the total weight of the composite oxide and the active metal. [Effects of the Invention]

[0022] According to an embodiment of the present disclosure, a composite oxide can be formed from alumina, a lanthanum compound, and a cerium compound in a reducing gas atmosphere. The composite oxide can have a perovskite crystal structure. The dispersion of the active metal in the composite oxide can be improved, allowing the amount of active metal used and the heat treatment temperature to be reduced.

[0023] This suppresses exposure of the active metal at high temperatures and improves the dispersion of the active metal in the composite oxide, thereby enabling high-purity hydrogen to be obtained by decomposing ammonia at a relatively low content. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic process flow diagram of a method for producing an ammonia decomposition catalyst according to an exemplary embodiment. [Figure 2] FIG. 2 is an X-ray diffraction graph of a complex oxide according to an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] According to an embodiment of the present disclosure, a method for producing an ammonia decomposition catalyst is provided.

[0026] Hereinafter, embodiments of the present disclosure will be described in more detail with reference to the drawings. However, the drawings attached to this specification are intended to illustrate preferred embodiments of the present disclosure and, together with the detailed description of the invention, serve to aid in further understanding of the technical concepts of the present disclosure, and therefore the present disclosure should not be interpreted as being limited to only the matters shown in the drawings.

[0027] FIG. 1 is a schematic process flow diagram illustrating a method for producing an ammonia decomposition catalyst according to an exemplary embodiment.

[0028] Referring to FIG. 1, alumina, a lanthanum compound, and a cerium compound can be heat-treated in a reducing gas atmosphere (eg, step S10).

[0029] In some embodiments, the lanthanum compound may be at least one of lanthanum metal or lanthanum nitrate, oxide, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate, carbonate, naphthenate, isopropoxide, and organometallic complexes, which may be used alone or in combination of two or more.

[0030] In one embodiment, the lanthanum compound may include lanthanum nitrate. Lanthanum nitrate can be completely decomposed during the heat treatment process, leaving no residue on the catalyst. This eliminates the need for a subsequent process to remove the nitrate, improving process efficiency and economic efficiency. Furthermore, since the nitrate can be supplied in large quantities, it reduces catalyst production costs and improves process economic efficiency.

[0031] In some embodiments, the cerium compound may be at least one of cerium metal and cerium nitrate, oxide, chloride, bromide, fluoride, hydroxide, carbonate, acetate, sulfate, carbonate, naphthenate, isopropoxide, and organometallic complexes, which may be used alone or in combination of two or more.

[0032] In one embodiment, the cerium compound may include cerium nitrate. The cerium nitrate can be completely decomposed during the heat treatment process, leaving no residue on the catalyst. Therefore, a subsequent process for removing the nitrate is not required, improving process economy. Furthermore, since the nitrate can be supplied in large quantities, the cost of catalyst production can be reduced.

[0033] In some embodiments, the alumina support can include Al2O3, which can have improved stability at the operating temperatures of the ammonia decomposition catalyst and thus can improve the dispersion of the ammonia catalyst.

[0034] In one embodiment, the alumina support can include alpha-alumina (α-AlO), beta-alumina (β-AlO), delta-alumina (δ-AlO), eta-alumina (η-AlO), and / or theta-alumina (θ-AlO).

[0035] According to an exemplary embodiment, alumina, a lanthanum compound, and a cerium compound may be heat treated to form an alumina support and a composite oxide (eg, step S20).

[0036] For example, the heat treatment step can form an alumina support from a portion of the alumina, and the surface of the alumina can be doped with lanthanum and cerium to form a composite oxide containing aluminum, lanthanum, and cerium on the alumina support.

[0037] According to an exemplary embodiment, the composite oxide may have a perovskite structure. For example, alumina, a lanthanum compound, and a cerium compound may be heat-treated in a reducing gas atmosphere to dissolve lanthanum and cerium in alumina to form a perovskite crystal structure.

[0038] Perovskite has a three-dimensional crystal structure formed by combining two types of cations and one type of anion, and can refer to the same type of crystal structure as calcium titanium oxide (CaTiO3). For example, perovskite can have a general formula such as ABX3 or ABCX3, where the X atom in the general formula is located at the center of each crystal face.

[0039] The perovskite structure of the composite oxide can improve the high-temperature stability of the composite oxide, and also makes it easier to support or dope active metals such as transition metals in the composite oxide even at relatively low temperatures.

[0040] When the metal compound contains cerium, a perovskite-structured composite oxide may not be smoothly formed under heat treatment conditions such as in an air atmosphere, an inert atmosphere, or an oxygen atmosphere. For example, when the metal compound is heat-treated in an inert atmosphere or an air atmosphere, the composite oxide formed therefrom may have a high proportion of a mixed oxide structure of lanthanum-cerium composite oxide and alumina in its crystal structure. For example, a mixed oxide may refer to a solid solution of different metal oxides.

[0041] When a composite oxide has a mixed oxide structure and the active metal (e.g., ruthenium) and the composite oxide are heat-treated together, the doping or support of the active metal in the composite oxide may be inhibited, which may result in a decrease in the dispersion of the active metal in the composite oxide.

[0042] According to an exemplary embodiment, the composite oxide can have a perovskite structure, and therefore the dispersibility of the active metal in the composite oxide can be improved.

[0043] In one embodiment, the proportion of the perovskite structure in the crystalline structure of the composite oxide may be 5% to 99%. This range can provide a high proportion of active sites for the active metal. Furthermore, by providing high selectivity for the ammonia decomposition catalyst, by-products can be reduced and high-purity hydrogen can be obtained.

[0044] For example, the content of the metal oxide crystal mixture can be quantified by XRD analysis calibration using an internal standard or XRD peak analysis (e.g., Rietveld refinement method). Furthermore, data processing tools provided by the XRD measurement device can be used.

[0045] In one embodiment, the reduction treatment of alumina, lanthanum compounds, and cerium compounds may be carried out using a reducing gas such as hydrogen, carbon monoxide, or hydrocarbon.

[0046] In some embodiments, hydrogen can be used as the reducing gas, and in one embodiment, the reducing gas can be diluted with nitrogen or carbon dioxide.

[0047] In some embodiments, the reducing gas may contain 10% by volume to 100% by volume of hydrogen relative to the total volume of the reducing gas. Within this range, the proportion of the perovskite crystal structure in the composite oxide can be increased. This can further improve the dispersibility of the active metal in the composite oxide.

[0048] In one embodiment, the reducing gas may contain 90% to 100% or 99% to 100% by volume of hydrogen based on the total volume of the reducing gas. For example, the reducing gas may be composed of 99.9% or 100% hydrogen gas.

[0049] In some embodiments, the heat treatment temperature for the alumina, lanthanum compound, and cerium compound may be greater than 600° C. For example, the heat treatment temperature may be greater than 600° C. and not greater than 1,200° C., greater than 600° C. and not greater than 1,000° C., 800° C. to 1,000° C., or 850° C. to 1,000° C.

[0050] The higher the heat treatment temperature of the alumina, lanthanum compound, and cerium compound in the hydrogen-containing reducing gas atmosphere is within the above-mentioned range, the higher the proportion of the perovskite structure in the crystal structure of the composite oxide can be.

[0051] For example, by subjecting a lanthanum compound and a cerium compound to heat treatment at a temperature of 900°C or higher in a reducing gas atmosphere containing 99.9% or 100% by volume of hydrogen gas, the proportion of the perovskite structure in the crystal structure of the composite oxide can be formed to be 80% to 99%, or 90% to 99%.

[0052] In some embodiments, the heat treatment time may be 1 hour to 10 hours, 3 hours to 8 hours, or 4 hours to 6 hours.

[0053] In some embodiments, the alumina support can function as a support or base layer for an ammonia catalyst, for example, the alumina support can be a support for an ammonia catalyst and improve the mechanical strength of the ammonia catalyst.

[0054] In one embodiment, the composite oxide may further contain other rare earth metals in addition to lanthanum and cerium. For example, the rare earth metal-containing compound may be heat-treated with alumina, a lanthanum compound, and a cerium compound.

[0055] In one embodiment, the rare earth metal can include at least one of scandium (Sc), yttrium (Y), neodymium (Nd), samarium (Sm), gadolinium (Gd), and ytterbium (Yb), which can be included alone or in combination of two or more.

[0056] In one embodiment, the rare earth metal-containing compound may be at least one of oxides, chlorides, bromides, fluorides, hydroxides, carbonates, acetates, sulfates, nitrates, carbonates, naphthenates, isopropoxides, and organometallic complexes of the rare earth metals, which may be used alone or in combination of two or more.

[0057] In some embodiments, the molar ratio of cerium to lanthanum in the composite oxide may be 0.1 to 10, 0.2 to 5, or 0.3 to 3. Within these ranges, the ammonia decomposition rate can be increased, and the ammonia conversion rate at low temperatures can be further improved.

[0058] According to an exemplary embodiment, an active metal can be supported on the composite oxide (for example, step S30). An ammonia decomposition catalyst can be produced by supporting an active metal on the composite oxide.

[0059] For example, the active metal is an active component of an ammonia decomposition catalyst and can promote ammonia decomposition.

[0060] According to an exemplary embodiment, the active metal may comprise an active catalyst.

[0061] According to an exemplary embodiment, the active catalyst may include a transition metal and / or a platinum group metal, for example, at least one metal belonging to groups 8 to 10 of the periodic table.

[0062] In one embodiment, the active catalyst includes osmium (Os), nickel (Ni), iron (Fe), nickel (Ni), cobalt (Co), platinum (Pt), palladium (Pd), ruthenium (Ru), vanadium (V), copper (Cu), chromium (Cr), tungsten (W), molybdenum (Mo), iridium (Ir), rhodium (Rh), zirconium (Zr), and the like.

[0063] In one embodiment, the ammonia decomposition catalyst may contain a platinum group element as an active metal. Platinum group elements have a high ionization tendency and high activity in oxidation / reduction reactions, which can further improve the ammonia decomposition rate and conversion rate.

[0064] For example, the ammonia decomposition catalyst may contain ruthenium as an active metal. Ruthenium has strong catalytic activity and can further improve the ammonia dehydrogenation decomposition reaction and catalytic activity.

[0065] According to an exemplary embodiment, the active metal of the ammonia decomposition catalyst may further include a promoter, which may include an alkali metal and / or an alkaline earth metal, for example, at least one metal belonging to Groups 1 and 2 of the periodic table.

[0066] In one embodiment, the promoter may include cesium (Cs), sodium (Na), potassium (K), lithium (Li), rubidium (Rb), francium (Fr), barium (Ba), calcium (Ca), strontium (Sr), beryllium (Be), and magnesium (Mg), which may be used alone or in combination of two or more.

[0067] In one embodiment, the co-catalyst can include an alkali metal. The alkali metal element contains one electron in its outermost electron shell and can function as an electron donor. The alkali metal element can also increase the number of active sites on the surface of the active catalyst, suppressing the aggregation of the active catalyst and further improving the dispersion of the active catalyst. As a result, the alkali metal can act as a co-catalyst to further enhance the promotion of the active catalyst in chemical reactions.

[0068] In some embodiments, the composite oxide and the active metal compound can be heat-treated. For example, the composite oxide can be added to or mixed with an active metal compound and then heat-treated. The heat treatment can support or dope the active metal derived from the active metal compound on the composite oxide.

[0069] In one embodiment, the active metal compound may be at least one of nitrates, oxides, chlorides, bromides, fluorides, hydroxides, carbonates, acetates, sulfates, carbonates, naphthenates, isopropoxides, and organometallic complexes of the active metals, which may be used alone or in combination of two or more.

[0070] In some embodiments, the heat treatment temperature of the composite oxide and the active metal compound may be 1,000° C. or less or 900° C. or less, or 200° C. or more or 400° C. or more. Within this range, the activity and stability of the catalyst can be further improved.

[0071] In one embodiment, the heat treatment temperature of the composite oxide and the active metal compound may be 600°C or less. For example, the heat treatment temperature may be 200°C to 600°C, or 400°C to 600°C. When the heat treatment temperature is 600°C or less, aggregation of the active metal due to high temperatures can be suppressed, and the activity of the catalyst can be further improved. When the heat treatment temperature is 200°C or more, the metal is sufficiently activated, and the performance of the ammonia decomposition catalyst can be improved.

[0072] In one embodiment, the heat treatment temperature of the composite oxide and the active metal compound (e.g., the heat treatment temperature in step S30) may be lower than the heat treatment temperature of the alumina, lanthanum compound, and cerium compound (e.g., the heat treatment temperature in step S10). For example, an active metal can be supported on a composite oxide having a perovskite structure, and an ammonia decomposition catalyst having a perovskite structure can be produced without an additional crystallization step after the active metal is supported. This allows the active metal to be supported at a relatively low temperature, preventing sintering of the active metal due to high temperatures and improving the dispersion and utilization of the active metal.

[0073] In one embodiment, the step of supporting the active metal on the composite oxide can be carried out in a reducing gas atmosphere, for example, the composite oxide and the active metal compound can be heat-treated in a reducing gas atmosphere.

[0074] In one embodiment, the reduction treatment of the composite oxide and active metal compound may be carried out using a reducing gas such as hydrogen, carbon monoxide, or hydrocarbon, or by adding a reducing agent such as hydrogen peroxide, hydrogen sulfide, lithium aluminum hydride, or lithium borohydride.

[0075] In one embodiment, the composite oxide and the active metal compound may be heat treated in a reducing gas atmosphere, for example, a hydrogen atmosphere.

[0076] In one embodiment, the reducing gas may be diluted with nitrogen or carbon dioxide.

[0077] In one embodiment, the reducing gas may contain 10% by volume to 100% by volume of hydrogen relative to the total volume of the reducing gas, which can further improve the dispersibility of the active metal in the composite oxide.

[0078] In one embodiment, the reducing gas may contain 90% to 100% or 99% to 100% by volume of hydrogen based on the total volume of the reducing gas. For example, the reducing gas may be composed of 99.9% or 100% hydrogen gas.

[0079] In some embodiments, the content of the active catalyst supported on the composite oxide may be 1.6 wt % or less, 1.5 wt % or less, or less than 1.5 wt %, based on the total weight of the composite oxide and the active catalyst.

[0080] In some embodiments, the content of the active catalyst supported on the composite oxide may be 0.1 wt % to 1.3 wt %, 0.15 wt % to 1.25 wt %, 0.2 wt % to 1.0 wt %, or 0.5 wt % to 0.8 wt %, based on the total weight of the composite oxide and the active catalyst.

[0081] In some embodiments, the content of the promoter may be 0.5 wt % to 6 wt % based on the total weight of the composite oxide and the active metal, which can further increase the activity of the ammonia decomposition catalyst.

[0082] According to an exemplary embodiment, the active metal is supported in a composite oxide having a perovskite crystal structure, thereby improving the dispersibility even when the content of the active metal is low, thereby reducing the amount of the active metal used and enabling the production of a highly efficient ammonia decomposition catalyst at low cost.

[0083] In one embodiment, when the content of the active catalyst is 0.1 wt% or more, the active sites of the ammonia decomposition catalyst can be further increased, thereby improving the activity of the ammonia decomposition catalyst and improving the ammonia decomposition rate and conversion rate.

[0084] In some embodiments, the complex oxide may include a compound represented by the following Chemical Formula 1:

[0085] [Chemical formula 1] La x Ce 1-x AlO3

[0086] In the above chemical formula 1, 0.05 <x≦0.95であってもよい。

[0087] In one embodiment, in Chemical Formula 1, 0.2 < x ≤ 0.85 may be satisfied, for example, 0.4 < x ≤ 0.8, or 0.45 < x ≤ 0.75 may be satisfied. When the contents of La and Ce are within the above range, the ammonia decomposition activity can be further improved, and the catalyst can have a high ammonia conversion rate even at low temperatures.

[0088] In some embodiments, the composite oxide can be formed by doping the alumina surface with lanthanum derived from the lanthanum compound and cerium derived from the cerium compound.

[0089] In one embodiment, the composite oxide can be formed by doping the alumina surface with the lanthanum and the cerium. For example, the lanthanum and the cerium can be uniformly dispersed and doped in the alumina.

[0090] In one embodiment, the lanthanum and cerium doped in the alumina can have the form of nanoparticles. For example, the diameters of the nanoparticles of the lanthanum and cerium may be 1 nm to 500 nm. The diameter of the particles can be measured, for example, by a high resolution transmission electron microscope.

[0091] In one embodiment, the oxide formed of the composite oxide on the alumina support can further contain other rare earth metals in addition to lanthanum and cerium. For example, it can contain at least one of scandium (Sc), yttrium (Y), neodymium (Nd), samarium (Sm), gadolinium (Gd), and ytterbium (Yb). These can be included alone or in combination of two or more.

[0092] The ammonia decomposition catalyst according to an embodiment of the present disclosure can include an alumina support, a composite oxide formed on the alumina support, and an active metal containing ruthenium supported on the composite oxide.

[0093] The composite oxide may contain lanthanum, cerium, and aluminum. For example, the composite oxide may be a metal oxide formed by dissolving lanthanum, cerium, and aluminum together.

[0094] According to an exemplary embodiment, the ruthenium content may be less than 1.5 wt. % relative to the total weight of the composite oxide and the active metal.

[0095] In some embodiments, the content of ruthenium supported on the composite oxide may be 0.1 wt % to 1.3 wt %, 0.15 wt % to 1.25 wt %, 0.2 wt % to 1.0 wt %, or 0.5 wt % to 0.8 wt %, based on the total weight of the composite oxide and the active metal.

[0096] According to an exemplary embodiment, the active metal may further include a promoter, which may include an alkali metal and / or an alkaline earth metal.

[0097] In some embodiments, the complex oxide may include a perovskite structure, which can further improve the high-temperature stability and catalytic activity of the ammonia catalyst and can improve the dispersibility of the active metal in the complex oxide.

[0098] In one embodiment, the proportion of the perovskite structure in the crystal structure of the composite oxide may be 5% to 99%. In this range, a high ammonia conversion rate can be obtained even at low temperatures due to the electron contribution effect to the active metal.

[0099] Hereinafter, examples of the present disclosure will be described in more detail with reference to Preparation Examples. However, the Examples and Comparative Examples included in the Preparation Examples are merely illustrative of the present disclosure and do not limit the scope of 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 and technical spirit of the present disclosure, and it is natural that such changes and modifications also fall within the scope of the appended claims.

[0100] Preparation example: composite oxide on alumina support (1) Example 1) Formation of complex oxides An aqueous solution was prepared by adding 10 g of alumina, 2.85 g of lanthanum nitrate hydrate (99%, Sigma), and 2.70 g of cerium nitrate hydrate (99%, Sigma) to deionized water and mixing at room temperature. The aqueous solution was dried at room temperature and subjected to a first heat treatment at 900°C for 4 hours in a 100% hydrogen atmosphere to produce an alumina support and a lanthanum-cerium-alumina-containing composite oxide formed on the alumina support.

[0101] 2) Ammonia catalyst production An ammonia catalyst precursor was prepared by impregnating 1 g of the composite oxide with ruthenium nitrosyl nitrate as a ruthenium compound. The ruthenium compound was added so that the content of ruthenium (Ru) was 0.8 wt % based on the total weight of the composite oxide and ruthenium.

[0102] The ammonia catalyst precursor was dried and subjected to a second heat treatment in a 100% hydrogen atmosphere at a temperature of 600° C. for 4 hours to produce an ammonia decomposition catalyst.

[0103] (2) Comparative Examples 1 to 3 A lanthanum-cerium-alumina-containing composite oxide was formed in the same manner as in Example 1, except that in the composite oxide formation step, the heat treatment conditions were changed as shown in Table 1 below.

[0104] [Table 1]

[0105] (3) Measurement of complex oxide crystals Before producing the ammonia catalyst, the crystal structures of the composite oxides produced in Example 1 and Comparative Examples 1 to 3 were measured. Figure 2 is an XRD graph of the composite oxides of the examples and comparative examples, in which squares indicate peaks of the perovskite (LaCeAlO3) crystal structure, and triangles indicate peaks of the CeO2 crystal structure. From FIG. 2, it can be observed that in Example 1, the characteristic diffraction peaks (32.9° and 23.4°) of perovskite (LaCeAlO3) are largely formed. In Comparative Examples 1 to 3, it can be observed that the characteristic diffraction peaks (28.3° and 32.8°) of the cerium oxide (CeO2) mixed oxide are largely formed.

[0106] (4) Examples 1 to 4 and Comparative Examples 4 to 8 In the examples and comparative examples, ammonia decomposition catalysts were produced in the same manner as in Example 1, except that the first heat treatment temperature, the second heat treatment temperature, and the ruthenium content were changed as shown in Table 2 below. In Table 2 below, the ruthenium content (wt%) was calculated using the following formula 1.

[0107] [Formula 1] Ruthenium content (wt%) = [Ruthenium content (weight) in ruthenium compound / {Composite oxide content (weight) + Ruthenium content (weight) in ruthenium compound}] x 100

[0108] [Table 2]

[0109] Experimental Example (1) XRD measurement Composite oxides were obtained from the catalysts produced in the examples and comparative examples, and the X-ray diffraction distributions of the composite oxides were measured. Specifically, the current was 300 mA, the voltage was 50 kV, the wavelength of Cu Kα (1.5428 Å), and the time was 5 degrees min -1 The crystal structure of the composite oxide was measured by X-ray diffraction (XRD) under the conditions of a scanning speed of 1000 kJ / cm and 2θ=10° to 80°.

[0110] (2) Measurement of dispersion The catalysts produced in the examples and comparative examples were measured using a carbon monoxide adsorption evaluation device (Micrometirics, ASAP 2020). After 0.1 g of catalyst was loaded into an adsorption tube, it was reduced at 300°C, and the temperature was lowered to measure the saturated adsorption amount of carbon monoxide at room temperature. The adsorbed carbon monoxide molecules were considered to be due to chemical adsorption with the ruthenium catalyst, and the degree of dispersion was calculated. The degree of dispersion (%) was calculated using the following formula 2.

[0111] [Formula 2] Dispersion degree (%) = (content of active metal exposed on the catalyst surface measured by carbon monoxide / content of active metal used in the catalyst) × 100

[0112] (3) Measurement of decomposition rate based on ammonia conversion temperature The exhaust gas after the ammonia decomposition reaction was measured using a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD). The residual ammonia content was determined from a calibration curve using standard gases (ammonia: Shinheung Industrial Gas Co., Ltd., dilution gas: nitrogen), and the decomposition rate was calculated using the following equation 3. The decomposition rate (%) was calculated using the following formula 3. [Formula 3] Decomposition rate (%) = {(supplied ammonia content - residual ammonia content) / supplied ammonia content} × 100 The evaluation results are shown in Table 3 below.

[0113] [Table 3]

[0114] In Table 3, P means perovskite, and M means mixed oxide.

[0115] Referring to Table 3, the composite oxides of the ammonia decomposition catalysts in Examples 1 to 3 had a perovskite crystal structure.

[0116] In Examples 1 and 2, a high ammonia decomposition rate was maintained even though the ammonia decomposition catalyst contained a relatively small amount of ruthenium. In Example 1, in which the second heat treatment temperature was relatively low, the degree of dispersion did not decrease and the ammonia decomposition rate was further improved.

[0117] In Example 4, the first heat treatment was performed at a relatively low temperature, and the composite oxide contained a crystalline structure in the form of a mixed oxide (M). However, in Example 4, even though the ammonia decomposition catalyst production process was performed at a relatively low temperature, the first heat treatment was performed in a reducing gas atmosphere, and the degree of dispersion and ammonia decomposition rate were improved compared to the comparative example.

[0118] In the comparative example, the first heat treatment was performed in an air atmosphere, and the composite oxide contained a mixed oxide structure within its crystal structure. As a result, although the ruthenium content was higher than in Examples 1 to 4, the degree of dispersion was low, or the ammonia decomposition rate at a relatively low temperature was the same or worse.

[0119] From these findings, it was confirmed that the ammonia decomposition catalyst according to the present example can improve the ammonia decomposition rate despite containing a small amount of ruthenium, and furthermore can reduce costs and ensure high-temperature stability.

Claims

1. heat-treating alumina, a lanthanum compound, and a cerium compound in a reducing gas atmosphere to form a composite oxide on an alumina support; and supporting an active metal containing ruthenium on the composite oxide.

2. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the active metal further comprises a promoter comprising 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).

3. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the composite oxide is formed by heat treating the alumina, the lanthanum compound, and the cerium compound at a temperature higher than 600°C and lower than or equal to 1,000°C.

4. The method for producing an ammonia decomposition catalyst according to claim 1 , wherein the reducing gas atmosphere is a hydrogen atmosphere.

5. The method for producing an ammonia decomposition catalyst according to claim 1 , wherein the composite oxide contains lanthanum, cerium, and aluminum.

6. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the composite oxide is formed by doping the surface of the alumina with lanthanum derived from the lanthanum compound and cerium derived from the cerium compound.

7. The alumina support is Al ２ O ３ 2. A method for producing the ammonia decomposition catalyst according to claim 1, comprising:

8. The method for producing an ammonia decomposition catalyst according to claim 1 , wherein the composite oxide has a perovskite structure.

9. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the step of supporting the active metal containing ruthenium on the composite oxide includes mixing the composite oxide and the active metal containing ruthenium and heat-treating the mixture.

10. 10. The method for producing an ammonia decomposition catalyst according to claim 9, wherein the heat treatment temperature of the composite oxide and the active metal is lower than the heat treatment temperatures of the alumina, the lanthanum compound, and the cerium compound.

11. 10. The method for producing an ammonia decomposition catalyst according to claim 9, wherein the composite oxide and the active metal are heat-treated at a temperature of 200°C to 1,000°C.

12. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the step of supporting the active metal containing ruthenium on the composite oxide is carried out in a reducing gas atmosphere.

13. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the content of ruthenium supported on the composite oxide is less than 1.5 wt % based on the total weight of the composite oxide and the active metal.

14. 2. The method for producing an ammonia decomposition catalyst according to claim 1, wherein the content of ruthenium supported on the composite oxide is 0.1% by weight to 1.3% by weight based on the total weight of the composite oxide and the active metal.

15. 9. The method for producing an ammonia decomposition catalyst according to claim 8, wherein the proportion of the perovskite structure in the crystal structure of the composite oxide is 5% to 99%.

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