Catalyst for ammonia cracking and method for producing the same

Abstract

This invention provides an ammonia cracking catalyst that exhibits high ammonia cracking efficiency even at low temperatures, and a method for producing the same. [Solution] A catalyst for ammonia cracking comprising an alumina-metal foam composite and a functional layer located on the alumina-metal foam composite. The alumina-metal foam composite comprises a metal foam and an alumina layer located on the metal foam, and the functional layer comprises a porous carrier and an active metal supported within the porous carrier.

Description

Technical Field

[0001] The present invention relates to a catalyst for ammonia cracking.

Background Art

[0002] In recent years, due to the development of industries and the increase in population, the global demand for energy has been increasing. However, fossil fuels used as energy sources are gradually depleting, and in order to address global warming and climate change caused by greenhouse gases, countries around the world are continuing to research new growth drivers in the fields of climate technologies and energy materials that can create economic benefits while contributing to the suppression of global warming. Among them, hydrogen is the most actively studied substance as an environmentally friendly energy source. Hydrogen is considered to be able to almost completely replace the existing energy usage, and since it does not contain carbon, which is the main component of carbon dioxide, it is a clean energy source and is in the spotlight because it has the largest calorific value among combustible substances. In addition, since hydrogen is used as a raw material for fuel cells, which are classified as one of the new renewable energies, its demand is expected to increase explosively in the future.

[0003] For these reasons, in recent years, as an environmentally friendly hydrogen production technology, many studies have been conducted on the process of ammonia cracking reaction for producing hydrogen from ammonia.

[0004] Ammonia (NH3) has a higher hydrogen density per unit weight or per unit volume than high-pressure hydrogen or liquid hydrogen, and when compressed at room temperature, it can be liquefied and stored at 10 bar or less, making it an excellent candidate for storage and transportation. In addition, since ammonia is in a liquid state at a lower pressure and a higher temperature than hydrogen, the cost of liquefaction is not very high, and storage and transportation are convenient. Furthermore, since ammonia is a carbon-free raw material, carbon dioxide is not generated during the hydrogen production process. The current ammonia industry is so massive that it uses approximately 50% of the world's hydrogen production for fertilizer production. Therefore, in terms of production and supply, there is the advantage of being able to utilize existing ammonia plants and processes.

[0005] The ammonia cracking reaction is an endothermic reaction in which ammonia is decomposed into hydrogen and nitrogen. The amount of heat required for the reaction depends on the composition at thermodynamic equilibrium and the ammonia supply flow rate, as follows:

[0006] NH3⇔1.5H2+0.5N2, △H=46.2kJ / mol [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] On the other hand, while the current steam reforming process for natural gas requires temperatures of approximately 700°C or higher, ammonia decomposition can be performed at an equilibrium conversion rate of approximately 450°C to 500°C, resulting in relatively lower energy costs. However, the ammonia cracking reaction is an endothermic reaction and actually takes place at temperatures above 500°C. To improve energy efficiency, catalysts are being developed to allow the ammonia decomposition reaction to occur at lower temperatures. [Means for solving the problem]

[0008] One embodiment provides an ammonia cracking catalyst that prevents desorption between the support and the catalyst powder, and has high ammonia cracking efficiency even at low temperatures.

[0009] Another embodiment provides a method for producing a catalyst for ammonia cracking.

[0010] An ammonia cracking catalyst according to one embodiment comprises an alumina-metal foam composite and a functional layer located on the alumina-metal foam composite, wherein the alumina-metal foam composite comprises a metal foam and an alumina layer located on the metal foam, and the functional layer comprises a porous carrier and an active metal supported within the porous carrier.

[0011] The ammonia cracking catalyst is characterized by having a weight ratio of alumina-metal foam composite to functional layer of 90:10 to 60:40.

[0012] The active metal is characterized by being present in an amount of 0.5% to 3.0% by weight based on the total weight of the catalyst.

[0013] The alumina in the alumina layer includes gamma-alumina, delta-alumina, ethanol-alumina, theta-alumina, or a combination thereof.

[0014] The metal form includes an alloy in which at least two of aluminum, nickel, chromium, copper, titanium, silver, tungsten, and iron are combined.

[0015] The aforementioned metal form is characterized by having a three-dimensional asymmetric structure.

[0016] The aforementioned metal foam is characterized by having a porosity of 80% by volume or more.

[0017] The weight ratio of the metal foam to the alumina layer within the alumina-metal foam composite is characterized by being 99:1 to 95:5.

[0018] The active metal is characterized by containing ruthenium (Ru), lanthanum (La), nickel (Ni), cobalt (Co), iron (Fe), cerium (Ce), or a combination thereof.

[0019] The active metal is characterized by containing lanthanum and ruthenium at a weight ratio of 3:1 to 1:1.

[0020] The porous support is characterized by being a spinel-type support.

[0021] The spinel-type support is characterized by containing MgAl2O4 or CaAl2O4.

[0022] The weight ratio of the porous support to the active metal in the functional layer is characterized by being 96:4 to 85:15.

[0023] The catalyst is further characterized by containing potassium, sodium, rubidium, cesium, or a combination thereof.

[0024] The catalyst is characterized by containing potassium and ruthenium at a weight ratio of 3:1 to 1:1.

[0025] The catalyst is characterized by having an ammonia cracking efficiency of 95% or more at 400°C to 550°C.

[0026] A method for manufacturing a catalyst for ammonia cracking according to another embodiment includes: a) a step of manufacturing an alumina-metal foam composite including a metal foam having an alumina sol-containing solution supported thereon and an alumina layer located on the metal foam; b) a step of manufacturing a composition for a functional layer by supporting an active metal on a porous support; and c) a step of obtaining a final catalyst by coating the composition for the functional layer on the alumina-metal foam composite.

[0027] The step a) of manufacturing the alumina-metal foam composite a-1) a step of supporting an alumina sol-containing solution on a metal foam, and then a-2) a step of heat-treating the obtained product of the step a-1), and is further characterized by including the above.

[0028] The step of manufacturing the functional layer composition described in b) above is: b-1) A step of heat-treating a porous support, b-2) The steps of supporting the lanthanum precursor solution on the material obtained in step b-1), followed by drying and heat treatment, b-3) The method is characterized by comprising the step of supporting a ruthenium precursor solution on the product obtained in step b-2), followed by drying and heat treatment.

[0029] The step of obtaining the final catalyst (c) is as follows: c-1) The step of supporting a solution containing the functional layer composition onto the alumina-metal foam composite, followed by drying and heat treatment.

[0030] The method further comprises, after step c-1), supporting a solution containing an alkali metal on the product obtained in step c-1), followed by drying and heat treatment.

[0031] After step c-1) or step c-2), c-3) The method further comprises a step of treating the product obtained in step c-1) or step c-2) in a hydrogen atmosphere to reduce it. [Effects of the Invention]

[0032] One embodiment of the ammonia cracking catalyst suppresses the desorption phenomenon between the support and the catalyst powder, and exhibits excellent ammonia cracking efficiency at low temperatures. [Brief explanation of the drawing]

[0033] [Figure 1] This is a photograph of a metal foam without alumina support, observed under an imaging microscope. [Figure 2] This is a photograph of a metal foam without alumina support, observed using a scanning electron microscope. [Figure 3] This is a photograph of a metal foam support with alumina attached, observed under an imaging microscope. [Figure 4] This is a photograph of a metal foam support bearing alumina, observed using a scanning electron microscope. [Figure 5] This is a photograph of the ammonia cracking catalyst according to Example 1, observed with an image microscope. [Figure 6] This is a photograph of the ammonia cracking catalyst according to Example 1, observed with a scanning electron microscope. [Figure 7] This is a photograph of the catalyst according to Comparative Example 5, observed with a scanning electron microscope. [Figure 8] This graph shows the efficiency of the ammonia cracking reaction of catalysts in the examples and comparative examples. [Modes for carrying out the invention]

[0034] The embodiments of the present invention will be described in detail below so that a person with ordinary skill in the art to which the present invention belongs can easily implement them. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0035] The ammonia cracking reaction for catalysts consists of chemiadsorption, dehydrogenation of ammonia, and recombination and desorption processes of decomposed nitrogen and hydrogen, using ammonia as a catalyst. The reaction rate of this ammonia cracking reaction is determined by the rate of nitrogen-hydrogen bond dissociation and the rate at which the generated nitrogen is desorbed from the catalyst. This can be optimized by adjusting the physicochemical properties of the catalyst, the active metal and support, the catalyst morphology, and so on.

[0036] On the other hand, ammonia cracking reactors use burners to supply heat, and the catalyst is introduced into the reactor in pellet form. However, the ceramic material that makes up the pellets has a slow heat transfer rate, so the reactor temperature drops while the endothermic reaction proceeds, reducing the catalytic efficiency. Furthermore, because the gas flow is not smooth, there is a problem called channeling, where gases pass through locally without reacting.

[0037] While increasing the catalytic efficiency mentioned above, development is underway to solve the problems in ammonia cracking reactors and to develop catalysts that possess high reaction activity, long lifespan, high heat transfer, low pressure drop, high thermal durability, and high mechanical strength.

[0038] The inventors of this application have discovered that using a metal foam composite that is not pelletized, specifically a metal foam composite supported with alumina, as a catalyst for ammonia cracking, solves the problem of differential pressure occurring at the rear end of the reactor without reducing the efficiency of the ammonia cracking reaction.

[0039] Figures 1 and 2 are photographs of metal foam without alumina supported, observed with an image microscope and a scanning electron microscope, respectively. Figures 3 and 4 are photographs of metal foam composites with alumina supported, observed with an image microscope and a scanning electron microscope, respectively. Furthermore, Figures 5 and 6 are photographs of an ammonia cracking catalyst according to one embodiment, observed using an image microscope and a scanning electron microscope, respectively.

[0040] An ammonia cracking catalyst according to one embodiment includes an alumina-metal foam composite and a functional layer located on the alumina-metal foam composite. The alumina-metal foam composite comprises a metal foam and an alumina layer located on the metal foam, and the functional layer comprises a porous carrier and an active metal supported within the porous carrier.

[0041] Because the alumina-metal foam composite supports alumina, it is possible to increase the adhesion between the metal foam and the functional layer by preventing direct contact between the metal foam and the active components of the catalyst. This suppresses the phenomenon where the desorption of active components within the catalyst reduces the activity of the reaction and generates a differential pressure at the rear end of the reactor, thereby ensuring excellent reaction efficiency of the catalyst. Furthermore, when the metal form and the active component of the catalyst are in direct contact, the different thermal expansion coefficients of the metal form and the active component can suppress the phenomenon of the active component of the catalyst being detached at high temperatures, thereby reducing the catalytic activity.

[0042] The alumina in the alumina layer of the alumina-metal foam composite includes gamma-alumina, delta-alumina, ethanol-alumina, theta-alumina, or a combination thereof. Furthermore, the alumina layer has a specific surface area of ​​200 m². 2 A value of 1 / g or more, or a stomata volume of approximately 0.4 cm³. 3 / g is also acceptable. Since the alumina layer can secure a large specific surface area and pore volume, it can increase the adhesion strength with the metal foam and enhance the reaction activity of the catalyst.

[0043] The alumina layer may further contain an organic binder. The organic binder further enhances the bonding strength between the alumina and the metal foam within the alumina layer, allowing the alumina to be coated more uniformly onto the metal foam. The organic binder may, for example, be a polymer, and as a type of sugar, it may be, but is not limited to, starch, alginic, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, hydroxypropylethylcellulose, hydroxyethylmethylcellulose, glucose, sucrose, sorbitol, or a combination thereof.

[0044] The metal foam included in the alumina-metal foam composite includes an alloy in which at least two of aluminum, nickel, chromium, copper, titanium, silver, tungsten, and iron are combined, and may, for example, include an alloy in which at least two of aluminum, nickel, and chromium are combined, but is not limited to these.

[0045] The aforementioned metal form has a three-dimensional asymmetric structure. For example, a three-dimensional asymmetrical structure is formed not in a single direction, but in any direction; one example is a network structure in which a three-dimensional asymmetrical structure is formed in any direction. By using a metal form having a three-dimensional asymmetric structure, ammonia can rapidly diffuse within the catalyst, and after the catalytic reaction, the product can rapidly move to the outside of the catalyst, thereby increasing the efficiency of the catalyst. Furthermore, it is possible to ensure high mechanical strength of the catalyst while increasing heat transfer within the catalyst.

[0046] The metal foam has a porous structure with a porosity of 80 volume% or more. For example, the porosity may be 81 volume% or more, 82 volume% or more, 83 volume% or more, or, for example, 95 volume% or less, 94 volume% or less, 93 volume% or less, 92 volume% or less, 91 volume% or less, or 90 volume% or less. If the porosity of the metal foam is 80% by volume or higher, the amount of active metal used per volume of catalyst can be reduced, and the amount of ammonia that can be cracked when the same amount of active metal is used can be increased. This allows for increased catalyst efficiency while reducing the amount of expensive metals used.

[0047] The weight ratio of the metal foam to the alumina layer within the alumina-metal foam composite may be 99:1 to 95:5. If the weight ratio of the metal foam to the alumina layer within the alumina-metal foam composite is within the aforementioned range, the alumina layer can maximize the adhesion between the metal foam and the functional layer.

[0048] The functional layer of the ammonia cracking catalyst according to one embodiment includes a porous carrier and an active metal supported on the porous carrier, which enable the catalyst according to one embodiment to activate the ammonia cracking reaction.

[0049] The porous carrier disperses the active metal and provides stable support for it. The porous carrier may be a spinel-type carrier, for example, magnesium aluminate (MgAl2O4) or calcium aluminate (CaAl2O4). Spinel-type porous supports exhibit excellent thermal stability and mechanical strength. They do not deform under the temperature conditions of ammonia cracking reactions, allowing for even more stable support of active metals.

[0050] The porous carrier can be any type of material that can disperse and support the active metal. For example, magnesium aluminate (MgAl2O4), calcium aluminate (CaAl2O4), activated carbon, graphite, mesoporous carbon, carbon nanotubes, alumina (Al2O3), silica (SiO2), titanium dioxide (TiO2), zirconia (ZrO2), cerium oxide (CeO2), magnesium oxide (MgO), or combinations thereof can be used, for example, magnesium aluminate (MgAl2O4) or calcium aluminate (CaAl2O4) can be used, but are not limited thereto. The aforementioned MgAl2O4 or CaAl2O4 is spinel-type, exhibits excellent thermal stability and mechanical strength, does not deform under the temperature conditions of the ammonia cracking reaction, and can further stably support the active metal.

[0051] The active metals include ruthenium and lanthanum, and other metals can be used together to improve the performance of the catalyst and impart additional functions to the catalyst, without reducing the efficiency of the catalyst. Ruthenium (Ru) is the main active component of the catalyst, enabling the catalyst to accelerate the ammonia cracking reaction. Lanthanum (La) can improve the activity, stability, or selectivity of the catalyst, and can further improve the performance of the catalyst by improving the dispersibility of ruthenium.

[0052] The active metal may include, for example, ruthenium (Ru), lanthanum (La), nickel (Ni), cobalt (Co), iron (Fe), cerium (Ce), or combinations thereof, for example, ruthenium, lanthanum, or combinations thereof.

[0053] The active metal contains lanthanum and ruthenium in a weight ratio of 3:1 to 1:1, and can, but is not limited to, ratios such as 2.5:1 to 1:1, 2.3:1 to 1:1, 2:1 to 1:1, or 1.5:1 to 1:1. Furthermore, by including lanthanum and ruthenium in the aforementioned weight ratio range within this active metal, the catalyst's efficiency can be further improved while ensuring the catalyst's stability.

[0054] The lanthanum metal is supported in an amount of 0.2% to 1.5% by weight based on the total weight of the ammonia cracking catalyst finally obtained, and is not limited to, for example, 0.3% to 1.5% by weight, 0.4% to 1.5% by weight, 0.5% to 1.5% by weight, 0.3% to 1.4% by weight, 0.3% to 1.3% by weight, 0.3% to 1.2% by weight, 0.3% to 1.1% by weight, or 0.3% to 1.0% by weight. By supporting lanthanum metal only within the aforementioned content range, the catalyst performance can be achieved without wasting any lanthanum metal, maximizing the activity of ruthenium and improving catalyst efficiency while ensuring catalyst durability.

[0055] The ruthenium metal is supported in an amount of 0.2% to 1.5% by weight based on the total weight of the ammonia cracking catalyst finally obtained, for example, 0.3% to 1.5% by weight, 0.4% to 1.5% by weight, 0.5% to 1.5% by weight, 0.3% to 1.4% by weight, 0.3% to 1.3% by weight, 0.3% to 1.2% by weight, 0.3% to 1.1% by weight, and 0.3% to 1.0% by weight, but is not limited to these amounts. By supporting ruthenium metal only within the aforementioned content range, it is possible to minimize the use of ruthenium metal while reducing catalyst manufacturing costs and ensuring maximum catalyst performance.

[0056] The weight ratio of the porous carrier to the active metal in the functional layer may be 96:4 to 85:15. When the weight ratio of the porous support to the active metal within the functional layer falls within the aforementioned range, the catalyst including the functional layer can maximize the activation of the ammonia cracking reaction.

[0057] The activated metal may be present in an amount of 0.5% to 3.0% by weight based on the total weight of the catalyst, and is not limited to, for example, 1.0% to 3.0% by weight, 0.5% to 2.5% by weight, 1.0% to 2.5% by weight, 0.5% to 2.0% by weight, or 1.0% to 2.0% by weight.

[0058] The catalyst may further contain alkali metals. The alkali metals in the catalyst prevent nitrogen gas generated during the ammonia cracking reaction from adhering to the catalyst, thereby increasing the reaction rate of ruthenium and further enhancing the efficiency of the catalyst.

[0059] The alkali metal may include, for example, sodium, potassium, rubidium, cesium, or a combination thereof, and may be, for example, sodium, potassium, or cesium, or for example, potassium. Potassium (K) exhibits excellent acid-degrading properties within the active metal, preventing nitrogen gas generated during the ammonia cracking reaction from adhering to the catalyst, thereby further improving the stability and efficiency of the catalyst.

[0060] The catalyst may contain alkali metals and ruthenium in a weight ratio of 3:1 to 1:1, but is not limited to these. By including alkali metals and ruthenium in the catalyst in the aforementioned ratio, the catalyst's efficiency can be further improved while ensuring the catalyst's stability.

[0061] For example, the catalyst may contain potassium and ruthenium in a weight ratio of 3:1 to 1:1, but is not limited to these. By including potassium and ruthenium in the catalyst in the aforementioned ratio, the catalyst's efficiency can be further improved while ensuring its stability.

[0062] The catalyst may contain an alumina-metal foam composite and a functional layer in a weight ratio of 90:10 to 60:40, for example, 85:15 to 60:40, or for example, 80:20 to 60:40, but is not limited thereto. When the alumina-metal foam composite and the functional layer within the catalyst are within the aforementioned weight ratio range, the adhesion between the alumina-metal foam composite and the functional layer can be maximized, thereby ensuring excellent reaction efficiency of the catalyst.

[0063] An ammonia cracking catalyst according to one embodiment can maintain a high ammonia cracking efficiency even at relatively low temperatures, and the catalyst has an ammonia cracking efficiency of 95% or more at 400°C to 550°C. For example, the catalyst may have an ammonia cracking efficiency of 95% or more at 400°C to 540°C, 400°C to 530°C, 400°C to 520°C, 400°C to 510°C, and 400°C to 500°C. Since the catalyst has high efficiency at the thermodynamic equilibrium temperature conditions of the ammonia cracking reaction, the temperature of the ammonia cracking reaction does not need to be raised further, and the energy efficiency of the ammonia cracking reaction can be increased.

[0064] Another embodiment provides a method for producing an ammonia cracking catalyst according to the first embodiment. In the method for producing the ammonia cracking catalyst described later, the characteristics of the catalyst described above will be omitted, and the catalyst is not limited by the production method described later.

[0065] The method for producing the ammonia cracking catalyst includes the steps of: a) supporting a solution containing alumina sol on a metal foam to produce an alumina-metal foam composite including the metal foam and an alumina layer located on the metal foam; b) supporting an activated metal on a porous carrier to produce a functional layer composition; and c) coating the alumina-metal foam composite with the functional layer composition to obtain a final catalyst.

[0066] The steps of a) producing the alumina-metal foam composite include a-1) supporting a solution containing alumina sol onto a metal foam; and then a-2) heat-treating the product obtained from step a-1), thereby producing the alumina-metal foam composite.

[0067] The metal foam of the alumina-metal foam composite has a three-dimensional asymmetrical network structure, and the alloy metal forming the metal foam can be obtained from an organic or ceramic skeletal material with a urethane foam or sponge structure using a shape replication method.

[0068] In step a-1) above, in which the alumina sol-containing solution is supported on the metal form, the method of supporting the alumina sol-containing solution on the metal form may be dipping or spray coating, but is not limited to these.

[0069] The solution containing the alumina sol may contain an organic binder. Using an organic binder together further enhances the bonding strength between alumina and metal foam, resulting in a more uniform coating of alumina on the metal foam.

[0070] a-1) After supporting the alumina sol solution onto a metal foam, a-2) the product obtained in step a-1 can be heat-treated. Heat treatment of the yield obtained in a-1) above further enhances the bonding strength between the alumina layer and the metal foam within the alumina-metal foam composite, thereby further improving the thermal stability of the alumina-metal foam composite. Furthermore, if an organic binder is used together with the alumina sol solution in a-1), the organic binder in the alumina-metal foam composite can be removed by performing the heat treatment in a-2).

[0071] The step of heat-treating the product obtained in step a-2) above (a-1) can be carried out at a temperature of, for example, 600°C to 800°C. By performing the process within the aforementioned temperature range, it is possible to prevent alumina phase changes and obtain an alumina-metal foam composite with further improved stability by removing the organic binder.

[0072] The step of producing the functional layer composition described in b) above is a step of supporting an active metal on a porous carrier, and may include, for example, b-1) a step of heat-treating the porous carrier; b-2) a step of supporting a lanthanum precursor solution on the product obtained in step b-1), followed by drying and heat-treating; and b-3) a step of supporting a ruthenium precursor solution on the product obtained in step b-2), followed by drying and heat-treating.

[0073] The porous carrier within the functional layer can be used after heat treatment. The porous support can be heat-treated at temperatures of, for example, 900°C to 1,000°C, but is not limited to the above temperature range and can be heat-treated at any temperature range where the weight loss of the porous support does not exceed that limit. By heat-treating the porous carrier before use, the thermal stability or mechanical properties of the porous carrier can be further enhanced.

[0074] b-2) The step of supporting the lanthanum precursor solution on the product obtained in step b-1), followed by drying and heat treatment, is a step to ensure that the porous carrier heat-treated in b-1) supports the lanthanum. For example, when MgAl2O4 is used as the porous support, La / MgAl2O4 can be obtained as the product of step b-2), and as another example, when CaAl2O4 is used as the porous support, La / CaAl2O4 can be obtained as the product of step b-2), but the method is not limited to these.

[0075] The lanthanum precursor solution in b-2) above can be lanthanum nitrate hydrate, lanthanum chloride hydrate, lanthanum acetate hydrate, lanthanum sulfate, or a combination thereof dissolved in a solvent. For example, lanthanum nitrate hydrate can be used to maximize the dispersion of lanthanum.

[0076] The solvent used in the production of the lanthanum precursor solution can be dihydrated water, ethanol, ethylene glycol, or other dihydric alcohols, and the lanthanum metal precursor can be effectively impregnated into the porous carrier using the solvent.

[0077] As described in b-2) above, the lanthanum precursor solution can be supported on a porous carrier and then dried at 100°C to 120°C, followed by heat treatment at 500°C to 600°C, but the temperature range is not limited to these temperatures. The aforementioned drying and heat treatment can remove impurities, and if lanthanum nitrate hydrate is used, any remaining nitrate can be removed.

[0078] b-3) The step of supporting the ruthenium precursor solution on the product obtained in step b-2), followed by drying and heat treatment, is a step to ensure that the porous carrier on which lanthanum was supported in step b-2) becomes supported with ruthenium. For example, when MgAl2O4 is used as the porous support, Ru-La / MgAl2O4 can be obtained as the product of step b-3), and as another example, when CaAl2O4 is used as the porous support, Ru-La / CaAl2O4 can be obtained as the product of step b-3), but the method is not limited to these.

[0079] The ruthenium precursor solution in b-3) above can be ruthenium nitrate hydrate, ruthenium chloride hydrate, ruthenium acetate hydrate, ruthenium hydroxide hydrate, ruthenium nitrosyl nitrate hydrate, or a combination thereof dissolved in a solvent. For example, ruthenium chloride hydrate can be used to maximize the dispersion of ruthenium.

[0080] The solvent used in the production of the ruthenium precursor solution can be, for example, distilled water, ethanol, or a dihydric alcohol such as ethylene glycol, and the ruthenium metal precursor can be effectively impregnated into the carrier using the solvent.

[0081] Supporting the ruthenium precursor solution on the product obtained in step b-2) above includes supporting the ruthenium on the porous carrier on which the lanthanum is supported by a pressurized injection method of the ruthenium precursor solution.

[0082] As described in b-3) above, ruthenium can be supported on the porous carrier on which lanthanum is supported, followed by drying at 100°C to 120°C and heat treatment at 200°C to 600°C, but the temperature range is not limited to these. The aforementioned drying and heat treatment can remove impurities.

[0083] For example, if ruthenium chloride hydrate is used as the ruthenium metal precursor as described above, a step can be added to remove any remaining chloride ions using an ion exchange method after the drying and heat treatment.

[0084] The ion exchange method can be carried out, for example, by washing the functional layer composition obtained from b-3) with a basic solution, but is not limited thereto. For example, the base solution may be a solution containing ammonium hydroxide, ammonium nitrate, sodium hydroxide, sodium nitrate, or a combination thereof. For instance, ammonium hydroxide can be used to maximize the efficiency of ion exchange.

[0085] The functional layer composition obtained from (b) above can have its particle size distribution uniformly adjusted through a milling process. For example, the average particle size of the particles in the functional layer composition may be 0.5 μm to 5 μm, and may be, for example, 0.7 μm to 5 μm, 1 μm to 5 μm, 0.5 μm to 4.5 μm, 0.5 μm to 4 μm, 0.5 μm to 3.5 μm, 0.5 μm to 3 μm, 0.7 μm to 3 μm, or 1 μm to 3 μm, and is not limited to these. By setting the average particle size of the particles within the functional layer composition to the aforementioned range, the functional layer composition can be further uniformly coated onto the alumina-metal foam composite.

[0086] c) An ammonia cracking catalyst according to one embodiment can be obtained by finally coating the alumina-metal foam composite obtained from a) with the functional layer composition obtained from b). The method for coating the functional layer composition onto the alumina-metal foam composite in c) above can be, for example, a dipping method or a dispersion coating method, and is not limited to, a dipping method.

[0087] The functional layer composition may be in slurry form, and the functional layer composition obtained from b) above can be dispersed in distilled water to make a slurry.

[0088] c-1) The functional layer composition can be coated onto the alumina-metal foam composite and then dried at 100°C to 120°C, followed by heat treatment at 200°C to 600°C. However, the temperature range is not limited to these, and the heat treatment process can be omitted if necessary. The aforementioned drying and heat treatment can remove impurities generated in step c) obtaining the catalyst, thereby further enhancing the activity and durability of the catalyst.

[0089] c) The step of obtaining the final catalyst may further include supporting a solution containing an alkali metal on the product obtained in step c-1). Adding an alkali metal-containing solution can further enhance the stability and performance of the catalyst.

[0090] The alkali metal may include, for example, sodium, potassium, rubidium, cesium, or a combination thereof, and may be, for example, sodium, potassium, or cesium, or potassium. The aforementioned solution containing the alkali metal refers to a solution in which the alkali metal precursor is dissolved in a solvent such as distilled water, ethanol, or a dihydric alcohol containing ethylene glycol. The alkali metal precursor can be a nitrate salt, chloride salt, acetate salt, hydroxide salt of the alkali metal, or a combination thereof.

[0091] For example, the alkali metal solution can be potassium nitrate hydrate, potassium chloride hydrate, potassium acetate hydrate, potassium hydroxide hydrate, or a solution of these in a solvent. For instance, potassium nitrate can be used to maximize the catalytic activity.

[0092] The alkali metal precursor is supported in an amount of 4% to 10% by weight based on the total weight of the ammonia cracking catalyst ultimately obtained, but is not limited to this range. By supporting alkali metal precursors only within the aforementioned content range, it is possible to improve catalyst efficiency without wasting alkali metals while ensuring catalyst durability.

[0093] c-2) The alkali metal-containing solution can be supported on the product obtained in step c-1), dried at 100°C to 120°C, and then heat-treated at 200°C to 600°C. However, the temperature range is not limited to these, and the heat treatment process can be omitted if necessary. The aforementioned drying and heat treatment can remove impurities generated during the alkali metal support process, thereby further enhancing the catalyst's activity and durability.

[0094] c-3) The product obtained in step c-1) or the product obtained in step c-2) may further include a step of reducing it by treatment in a hydrogen atmosphere. The product obtained in step c-1) or the product obtained in step c-2) can be rapidly reduced and activated by hydrogen treatment. The hydrogen treatment can be carried out using a staff method, where hydrogen gas is introduced after heating to a target temperature in a nitrogen atmosphere. However, it is not limited to this method. As described above, when hydrogen treatment is performed using the staff method, it prevents the metals in the catalyst from deforming into an alloy form at high temperatures, and each metal in the catalyst is reduced separately.

[0095] The hydrogen treatment described in c-3) above can be carried out at 400°C to 600°C, but is not limited thereto. By treating the catalyst with hydrogen within the aforementioned temperature range, the catalyst can be completely reduced while preventing aggregation of the catalyst particles or the occurrence of sintering phenomena.

[0096] The ammonia cracking catalyst obtained by the manufacturing method described above can be used in the ammonia cracking reaction of ammonia gas. The ammonia cracking reaction of the ammonia gas can be carried out using the catalyst at a temperature of 350°C to 550°C, and can, for example, be carried out at 450°C, but is not limited thereto. Furthermore, if this ammonia cracking reaction is carried out at a temperature of 350°C to 550°C, the energy cost can be minimized while maximizing the amount of hydrogen gas obtained as a result of ammonia cracking, thereby maximizing the efficiency of ammonia cracking.

[0097] In the ammonia cracking reaction of the ammonia gas, the ammonia gas is converted, for example, to approximately 3,000 h -1The reaction can be carried out by flowing at the gas space velocity, and the greater the gas space velocity, the more hydrogen gas can be produced by the decomposition of ammonia gas.

[0098] The ammonia cracking catalyst is introduced using a fixed-bed catalytic reactor during the ammonia cracking reaction. Any reactor capable of maintaining the temperature of the ammonia cracking reaction can be used without limitation, and an appropriate reactor can be selected and used depending on the purpose and application of the ammonia cracking.

[0099] The present invention will be described in more detail below through the examples of ammonia cracking catalysts and their production described above. However, the present invention is not technically limited by the following embodiments.

[0100]

[0101] Examples and Comparative Examples

[0102] Manufacturing of ammonia cracking catalysts

[0103] Example 1

[0104] As the metal form, we used a three-dimensional asymmetric metal foam (AMF) consisting of an aluminum (Al)-chromium (Cr)-nickel (Ni) alloy in the form of a cube with sides of 3 mm. A solution was prepared by mixing alumina sol with methylcellulose and starch as an organic binder in a ratio of 7:2:1. The aforementioned mixed solution was supported onto a metal foam using a dipping method. After loading, an air knife was used to open up any voids trapped within the metal foam, and then the alumina-metal foam composite was dried at 120°C for 12 hours to completely remove any moisture. Finally, the alumina was fixed to the metal foam by heat treatment at 700°C for 6 hours. (Al-AMF)

[0105] On the other hand, a solution of lanthanum nitrate (La(NO3)3·xH2O) dissolved in distilled water was prepared as a lanthanum precursor, and then supported on MgAl2O4 that had been heat-treated at 600°C using the impregnation method. After loading, the lanthanum nitrate solution was allowed to fully distribute throughout the support after a 1-hour aging process. Then, it was dried at 120°C for 12 hours to completely remove moisture from the catalyst, and finally, the lanthanum metal within the support was immobilized through a heat treatment process at 600°C for 6 hours.

[0106] As a ruthenium precursor, a solution of ruthenium chloride (RuCl3·xH2O) dissolved in distilled water was prepared, and then the ruthenium metal was supported on the La / MgAl2O4 obtained above using the impregnation method. After loading, the resulting Ru-La / MgAl2O4 was dried at 120°C for 12 hours to completely remove moisture from the catalyst, and then heat-treated at 200°C for 6 hours to immobilize the ruthenium metal within the support. Subsequently, the heat-treated Ru-La / MgAl2O4 was washed and removed using ion exchange with ammonium chloride (NH4Cl) in addition to aqueous ammonia, and then dried at 120°C for 12 hours. Here, ruthenium metal and lanthanum metal are each present in an amount of 2% by weight based on the total amount of the functional layer (Ru-La / MgAl2O4) obtained above.

[0107] After dispersing the Ru-La / MgAl2O4 obtained above in distilled water to prepare a slurry solution, the average particle size was adjusted to 2 μm using a ball mill, and then the slurry was supported onto the alumina-metal foam composite (Al-AMF) obtained above using the dipping method. Subsequently, an air knife was used to open up the voids trapped within the metal foam, followed by drying at 120°C for 12 hours to remove moisture, and then heat treatment at 200°C for 6 hours to immobilize Ru-La / MgAl2O4 onto the alumina-metal foam composite.

[0108] The Ru-La / MgAl2O4 / Al-AMF obtained above was heated to 500°C in a helium atmosphere, and then rapidly reduced while flowing hydrogen gas to finally obtain a catalyst for ammonia cracking. The results of observing the catalyst obtained in Example 1 using an image microscope are shown in Figure 5. The catalyst according to Example 1 was found to contain 0.5% by weight of lanthanum and 0.5% by weight of ruthenium, based on the total weight, and was found to contain 3 ppm of chloride ions and 0 ppm of nitrate ions.

[0109]

[0110] Example 2

[0111] After obtaining the Ru-La / MgAl2O4 / Al-AMF catalyst in Example 1, the catalyst for Example 2 was produced in the same manner as in Example 1, except that it contained approximately 6% by weight of lanthanum metal based on the total weight of the functional layer (Ru-La / MgAl2O4). This process involved supporting an aqueous potassium nitrate (KNO3) solution on the catalyst, drying it at 120°C for 12 hours to completely remove moisture, and then heat-treating it at 200°C for 6 hours. The potassium metal content in the final manufactured catalyst was confirmed to be approximately 6% by weight based on the total weight of the functional layer.

[0112]

[0113] Example 3

[0114] The catalyst according to Example 3 was manufactured in the same manner as in Example 2, except that CaAl2O4 was used instead of MgAl2O4 during the production of the functional layer, and approximately 2% by weight of lanthanum metal was included based on the total weight of the functional layer (Ru-La / CaAl2O4). The potassium metal content in the final manufactured catalyst was confirmed to be approximately 6% by weight based on the total weight of the functional layer.

[0115]

[0116] Comparative Example 1

[0117] A catalyst according to Comparative Example 1 was produced in the same manner as in Example 1, except that alumina (Al2O3) pellets were used instead of alumina-metal foam composite, by sequentially impregnating Al2O3 pellets with lanthanum metal and ruthenium metal. The catalyst obtained as described above was confirmed to contain approximately 2% by weight of ruthenium metal based on its total weight.

[0118]

[0119] Comparative Example 2

[0120] The catalyst according to Comparative Example 2 was produced in the same manner as in Comparative Example 1, except that MgAl2O4 pellets were used instead of Al2O3 pellets. The catalyst obtained as described above was confirmed to contain approximately 2% by weight of ruthenium metal based on its total weight.

[0121]

[0122] Comparative Example 3

[0123] The catalyst according to Comparative Example 3 was produced in the same manner as in Example 2, except that MgAl2O4 pellets were used instead of alumina-metal foam composite. The final catalyst produced contained approximately 2% by weight of ruthenium metal, approximately 2% by weight of lanthanum metal, and approximately 6% by weight of potassium metal, based on the total weight of the catalyst.

[0124]

[0125] Comparative Example 4

[0126] The catalyst according to Comparative Example 4 was manufactured in the same manner as in Comparative Example 3, except that the final manufactured catalyst contained approximately 3% by weight of ruthenium metal and approximately 3% by weight of lanthanum metal, based on the total weight of the catalyst.

[0127]

[0128] Comparative Example 5

[0129] A catalyst according to Comparative Example 5 was produced in the same manner as in Example 1, except that a metal foam that was not coated with alumina was used. The ruthenium metal in the catalyst obtained in Comparative Example 5 was confirmed to be present in an amount of 0.5% by weight based on the total weight of the catalyst (Ru-La / MgAl2O4 / metal foam). The results of observing the catalyst obtained in Comparative Example 5 using a scanning electron microscope are shown in Figure 7.

[0130]

[0131] The specific catalyst components and their content in Examples 1 to 3 and Comparative Examples 1 to 5 are summarized in Table 1 below. In Table 1 below, the active metal and alkali metal content in Examples 1 to 3 is based on the total weight of the functional layer, the active metal and alkali metal content in Comparative Examples 1 to 4 is based on the total weight of the catalyst, and the active metal content in Comparative Example 5 is based on the total weight of the carrier and the active metal.

[0132] [Table 1]

[0133]

[0134] Evaluation: Evaluation of ammonia cracking reaction efficiency

[0135] The ammonia cracking reaction was carried out using a fixed-bed reaction system. 3 ml of catalyst was packed into a tubular reactor, and the reactor temperature was maintained at a constant 450°C. Ammonia gas was then continuously supplied to the reactor at a constant rate of 100 cc / min, and the gas space velocity was 3,000 h. -1 It was fixed to a constant value. The reaction pressure was evaluated under atmospheric pressure conditions. The product generated after the ammonia cracking reaction was transferred to gas chromatography (GC) via an injection line and quantitatively analyzed using a thermal conductivity detector (TCD).

[0136] The ammonia conversion rate was calculated using the following formula (1), and the activity of the catalyst was evaluated based on the ammonia conversion rate.

[0137] [Formula (1)]

[0138] Ammonia conversion rate (%) = {(moles of ammonia before reaction - moles of ammonia after reaction) / (moles of ammonia before reaction)} × 100

[0139] The results of the activity evaluation of the ammonia cracking catalyst are shown in the graph in Figure 8. Referring to Figure 8, the catalyst in the example showed an ammonia conversion rate of 95% or more, which was generally higher than that of the catalyst in the comparative example. Therefore, it can be seen that the catalyst according to the example exhibits excellent efficiency in the ammonia cracking reaction at a relatively low temperature of 450°C. Furthermore, it can be confirmed that the catalyst in the example exhibits a very high ammonia conversion rate despite having a low ruthenium content per unit volume of catalyst.

[0140] Furthermore, in Comparative Example 5, which uses a metal foam that is not coated with alumina, the catalyst is observed to have the functional layer unstablely adhering to the metal foam, as shown in Figure 7, with some of the functional layer detaching from the metal foam. In contrast, in Example 1, shown in Figure 6, the catalyst is an alumina-metal foam composite with the functional layer coated on it, and it can be observed that the functional layer adheres uniformly to the alumina-metal foam composite. Referring to Figure 8, it can be confirmed that the ammonia conversion rate of the catalyst in Example 1 is much higher than that of the catalyst in Comparative Example 5, indicating that when using an alumina-metal foam composite, the efficiency of the ammonia cracking reaction of the catalyst is far superior compared to when using a metal foam that is not coated with aluminum.

[0141] Although specific embodiments of the present invention have been described and illustrated above, it will be obvious to those with ordinary skill in the art that the present invention is not limited to the described embodiments and can be modified and transformed in various ways without departing from the spirit and scope of the invention. Therefore, such modifications or variations should not be understood individually from the technical idea or viewpoint of the present invention, and the modified embodiments should be considered to fall within the scope of the claims of the present invention.

Claims

1. It comprises an alumina-metal foam composite and a functional layer located on the alumina-metal foam composite, The alumina-metal foam composite comprises a metal foam and an alumina layer located on the metal foam. The functional layer comprises a porous carrier and an active metal supported within the porous carrier, and is a catalyst for ammonia cracking.

2. The ammonia cracking catalyst according to claim 1, characterized in that the active metal is present in an amount of 0.5% to 3.0% by weight based on the total weight of the catalyst.

3. The ammonia cracking catalyst according to claim 1, characterized in that the alumina in the alumina layer includes gamma-alumina, delta-alumina, ethanol-alumina, theta-alumina, or a combination thereof.

4. The ammonia cracking catalyst according to claim 1, wherein the metal form comprises an alloy in which at least two of aluminum, nickel, chromium, copper, titanium, silver, tungsten, and iron are combined.

5. The ammonia cracking catalyst according to claim 1, characterized in that the metal form has a three-dimensional asymmetric structure.

6. The ammonia cracking catalyst according to claim 1, characterized in that the metal foam has a porosity of 80 volume percent or more.

7. The ammonia cracking catalyst according to claim 1, characterized in that the weight ratio of the metal foam to the alumina layer in the alumina-metal foam composite is 99:1 to 95:

5.

8. The ammonia cracking catalyst according to claim 1, characterized in that the active metal includes ruthenium (Ru), lanthanum (La), nickel (Ni), cobalt (Co), iron (Fe), cerium (Ce), or a combination thereof.

9. The ammonia cracking catalyst according to claim 8, characterized in that the active metal contains lanthanum and ruthenium in a weight ratio of 3:1 to 1:

1.

10. The ammonia cracking catalyst according to claim 1, characterized in that the porous carrier is a spinel-type carrier.

11. The spinel-type carrier is MgAl ２ O ４ or CaAl ２ O ４ The ammonia cracking catalyst according to claim 10, characterized by containing the following:

12. The ammonia cracking catalyst according to claim 1, characterized in that the weight ratio of the porous carrier to the active metal within the functional layer is 96:4 to 85:

15.

13. The ammonia cracking catalyst according to claim 1 or 8, characterized in that the catalyst further comprises potassium, sodium, rubidium, cesium, or a combination thereof.

14. The ammonia cracking catalyst according to claim 13, characterized in that the catalyst contains potassium and ruthenium in a weight ratio of 3:1 to 1:

1.

15. The catalyst for ammonia cracking according to claim 1, characterized in that the catalyst contains an alumina-metal foam composite and a functional layer in a weight ratio of 90:10 to 60:

40.

16. The catalyst for ammonia cracking according to claim 1, characterized in that the catalyst has an ammonia cracking efficiency of 95% or more at 400°C to 550°C.

17. a) A step of supporting a solution containing alumina sol onto a metal foam to produce an alumina-metal foam composite including the metal foam and an alumina layer located on the metal foam, b) A step of supporting an active metal on a porous carrier to produce a composition for a functional layer, c) A method for producing a catalyst for ammonia cracking, comprising the step of coating the alumina-metal foam composite with the functional layer composition to obtain a final catalyst.

18. The method for producing an ammonia cracking catalyst according to claim 17, characterized in that the solution containing the alumina sol in step a) of producing the alumina-metal foam composite further contains an organic binder.

19. The step of manufacturing the alumina-metal foam composite described above (a) is: a-1) The step of supporting a solution containing alumina sol onto a metal foam, and thereafter, a-2) A method for producing an ammonia cracking catalyst according to claim 17, characterized by comprising the step of heat-treating the product obtained in step a-1).

20. The step of manufacturing the functional layer composition described in b) above is: b-1) A step of heat-treating the porous support, b-2) The steps of supporting a lanthanum precursor solution on the product obtained in step b-1), followed by drying and heat treatment, b-3) A method for producing an ammonia cracking catalyst according to claim 17, characterized by comprising the step of supporting a ruthenium precursor solution on the product obtained in step b-2), followed by drying and heat treatment.

21. The step of obtaining the final catalyst (c) is as follows: c-1) A method for producing an ammonia cracking catalyst according to claim 17, characterized by comprising the step of supporting a solution containing the functional layer composition onto the alumina-metal foam composite, followed by drying and heat treatment.

22. After step c-1) above, c-2) A method for producing an ammonia cracking catalyst according to claim 21, characterized by comprising supporting an alkali metal-containing solution on the product obtained in step c-1), followed by drying and heat treatment.

23. After step c-1) or step c-2), c-3) A method for producing an ammonia cracking catalyst according to claim 21 or claim 22, characterized by comprising the step of treating the yield from step c-1) or step c-2) in a hydrogen atmosphere to reduce it.

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