Catalyst, method for producing catalyst, and method for producing hydrogen

Abstract

In a catalyst according to the present invention, at least one of an alkali metal element and an alkaline earth metal element, a ruthenium element and a carbon element are supported on a carrier containing cerium oxide.

Description

Catalyst, method for producing a catalyst, and method for producing hydrogen Cross-reference of related applications

[0001] This application claims priority under Japanese Patent Application No. 2024-179731, which is incorporated into the description of this application by reference.

[0002] This invention relates to a catalyst, a method for producing a catalyst, and a method for producing hydrogen.

[0003] From the perspective of reducing greenhouse gas emissions, expectations for hydrogen energy obtained by burning hydrogen are rising. However, hydrogen is extremely difficult to handle, including transportation and storage. Therefore, in recent years, a method has been proposed to produce hydrogen by using ammonia as a hydrogen energy carrier, such as by importing ammonia produced overseas, and decomposing the ammonia by contacting it with a catalyst.

[0004] For example, Patent Document 1 shows that by using a catalyst in which a transition metal such as ruthenium with a small particle size is supported on a carrier, ammonia can be decomposed with high efficiency, and hydrogen can be suitably produced.

[0005] Japanese Patent Application Publication No. 2010-194519

[0006] Incidentally, the decomposition reaction of ammonia is a highly endothermic reaction, requiring a large supply of heat to increase reaction efficiency. Therefore, the decomposition reaction of ammonia is usually carried out at high temperatures, but this results in enormous energy costs and a significant environmental burden. Furthermore, because ruthenium is expensive, there was a demand to increase the reactivity per unit of ruthenium element.

[0007] This invention has been made in view of the above problems, and aims to provide a catalyst that has relatively high activity per unit of ruthenium element and can efficiently decompose ammonia to produce hydrogen at relatively low temperatures, a method for producing the catalyst, and a method for producing hydrogen using the catalyst.

[0008] The catalyst according to the present invention has at least one of an alkali metal element and an alkaline earth metal element, a ruthenium element, and a carbon element supported on a carrier containing cerium oxide.

[0009] The present invention relates to a method for producing a catalyst having a carrier containing cerium oxide, and comprises the following steps (i) to (iii): Step (i): Impregnating the carrier with an aqueous solution of a compound containing ruthenium; Step (ii): Impregnating the carrier with an aqueous solution of a compound containing at least one of an alkali metal element and an alkaline earth metal element; Step (iii): Contacting the carrier with a gaseous or solution-like organic compound.

[0010] The hydrogen production method according to the present invention includes a step of contacting a catalyst with a gas containing ammonia to decompose the ammonia, wherein the catalyst is supported on a carrier containing cerium oxide, with at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon supported on it.

[0011] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0012] [Catalyst] The catalyst according to this embodiment has at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon supported on a carrier containing cerium oxide.

[0013] From the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures, the specific surface area of ​​the catalyst is preferably 1 m². ２ / g or more 150m ２ It is less than or equal to / g, and more preferably 20m ２ / g or more 120m ２ The value is less than or equal to / g. The specific surface area of ​​the catalyst can be determined by vacuum degassing the catalyst at 120°C for 2 hours, then performing nitrogen adsorption / desorption isotherm measurements at 77K using a BELSORP MINI X manufactured by Microtrac-Bel, and determining it using the BET multipoint method.

[0014] As a supporting mode, for example, a mode in which at least one element of an alkali metal element and an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the surface of a carrier on the same plane; a carbon-supported layer in which a carbon element is supported on the surface of a carrier, and further on the surface of the carbon-supported layer, at least one element of an alkali metal element and an alkaline earth metal element, and a ruthenium element are supported, etc. can be cited. Among these, from the viewpoint of increasing the activity per ruthenium element and efficiently decomposing ammonia at low temperatures, the supporting mode is preferably a mode in which at least one element of an alkali metal element and an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the surface of a carrier on the same plane.

[0015] The form of the carbon element supported on the carrier may be, for example, a layered form such as graphene.

[0016] Examples of the alkali metal element supported on the carrier include a lithium element, a sodium element, a potassium element, a rubidium element, a cesium element, etc. Among these, from the viewpoint of increasing the activity per ruthenium element and efficiently decomposing ammonia at low temperatures, the alkali metal element is preferably a potassium element or a cesium element, and more preferably a potassium element.

[0017] Examples of the alkaline earth metal element supported on the carrier include a magnesium element, a calcium element, a strontium element, a barium element, etc. Among these, from the viewpoint of increasing the activity per ruthenium element and efficiently decomposing ammonia at low temperatures, the alkaline earth metal element is preferably a magnesium element, a calcium element or a barium element, and more preferably a barium element.

[0018] As one aspect, the catalyst according to the present embodiment has an alkaline earth metal element, a ruthenium element, and a carbon element supported on a carrier containing cerium oxide, and the alkaline earth metal element is a barium element.

[0019] Further, as another aspect, the catalyst according to the present embodiment has an alkaline earth metal element, a ruthenium element, and a carbon element supported on a carrier containing cerium oxide, the alkaline earth metal element is a barium element, and the specific surface area of the catalyst is 1 m ２ / g or more and 150 m ２ / g or less.

[0020] At least one of the alkali metal element and the alkaline earth metal element may be derived from at least one compound selected from the group consisting of nitrates, sulfates, chloride salts, and carbonate salts. At least one of the alkali metal element and the alkaline earth metal element is preferably derived from a nitrate.

[0021] The supported amount of at least one of the alkali metal element and the alkaline earth metal element is preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.5 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the carrier, from the viewpoint of increasing the activity per ruthenium element and efficiently decomposing ammonia at low temperatures.

[0022] The ruthenium element may be derived from at least one ruthenium compound selected from the group consisting of nitrosyl ruthenium nitrate, ruthenium chloride, sodium ruthenate, potassium ruthenate, ruthenium carbonyl, and ammonium ruthenium chloride. Among these, the ruthenium element is preferably derived from nitrosyl ruthenium nitrate.

[0023] The supported amount of the ruthenium element is preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.5 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the carrier, from the viewpoint of increasing the activity per ruthenium element and efficiently decomposing ammonia at low temperatures.

[0024] The carbon element may be derived from at least one organic compound selected from the group consisting of saturated hydrocarbons such as methane, ethane, and propane; unsaturated hydrocarbons such as ethylene, acetylene, propane, and propylene; aromatic hydrocarbons such as toluene, ethylbenzene, styrene, xylene, and mesitylene; alcohols such as methanol and ethanol; and nitrogen-containing compounds such as acetonitrile and acrylonitrile. The carbon element is preferably derived from ethylene, acetylene, or toluene.

[0025] From the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures, the amount of carbon element supported is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 1 part by mass or more and 20 parts by mass or less, per 100 parts by mass of the carrier.

[0026] The cerium oxide content in the carrier is preferably 50% by mass or more, and more preferably 80% by mass or more, relative to the entire carrier, from the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures.

[0027] In addition to cerium oxide, the carrier may also contain, for example, zirconium oxide, aluminum oxide, titanium oxide, zinc oxide, lanthanum oxide, praseodymium oxide, samarium oxide, etc.

[0028] The catalyst may take the form of, for example, powder; granules; or molded bodies such as spherical, cylindrical, ring-shaped, trilobe-shaped, tetralobe-shaped, or honeycomb-shaped. If the catalyst is in the form of a molded body, the average particle size of the molded body may be 0.5 mm or more and 20 mm or less. Here, the average particle size refers to the average diameter if the molded body is spherical, and to the average diameter and average length if the molded body is cylindrical.

[0029] The catalyst according to this embodiment is preferably used in an ammonia decomposition reaction. Examples of ammonia decomposition reactions include the reactions shown in the following formulas (I) to (III).

[0030] NH ３ → 0.5N ２ +1.5H２ ... (I)

[0031] NH ３ + 0.095O ２ → 0.5N ２ + 0.19H ２ O + 1.31H ２ ... (II)

[0032] 3.6NH ３ + CO ２ → 1.8N ２ + 2H ２ O + 1.4H ２ + CH4 ... (III)

[0033] The catalyst according to this embodiment is preferably used in at least one reaction selected from the group consisting of the above formulas (I) to (III), and more preferably used in the reaction shown in the above formula (I).

[0034] [Method for producing catalyst] The method for producing the catalyst according to this embodiment is a method for producing a catalyst having a carrier containing cerium oxide, and includes the following steps (i) to (iii). Step (i): A step of impregnating a carrier with an aqueous solution of a compound containing a ruthenium element. Step (ii): A step of impregnating a carrier with an aqueous solution of a compound containing at least one element selected from an alkali metal element and an alkaline earth metal element. Step (iii): A step of bringing a gaseous or solution organic compound into contact with a carrier

[0035] <Step (i)> In step (i), a carrier is impregnated with an aqueous solution of a compound containing a ruthenium element.

[0036] The impregnation method is not particularly limited, and examples thereof include the incipient wetness method, the dry-up method, and the like.

[0037] The compound containing a ruthenium element is the same as the catalyst according to the above embodiment.

[0038] <Step (ii)> In step (ii), a carrier is impregnated with an aqueous solution of a compound containing at least one element selected from an alkali metal element and an alkaline earth metal element.

[0039] A compound containing at least one of an alkali metal element and an alkaline earth metal element is the same as the catalyst according to the present embodiment.

[0040] The impregnation method may be the same as that of step (i) above.

[0041] In the catalyst manufacturing method according to this embodiment, step (ii) is preferably performed after step (i).

[0042] Furthermore, steps (i) and (ii) may be performed simultaneously. In that case, the catalyst production method according to this embodiment may involve impregnating a carrier with an aqueous solution obtained by mixing a compound containing at least one of an alkali metal element and an alkaline earth metal element with a compound containing ruthenium.

[0043] <Step (iii)> In step (iii), a gaseous or solution-type organic compound is brought into contact with a support.

[0044] The method for bringing the organic compound into contact with the support is not particularly limited and includes, for example, chemical vapor deposition (CVD), impregnation, and spray coating.

[0045] The organic compound is the same as the catalyst according to the present embodiment described above.

[0046] In one embodiment, the method for producing the catalyst according to this embodiment involves step (iii) being performed after steps (i) and (ii). Specifically, one embodiment of the method for producing the catalyst according to this embodiment can be carried out, for example, by the following method.

[0047] First, in steps (i) and (ii), a mixed aqueous solution of a compound containing at least one of the alkali metal elements and alkaline earth metal elements, as well as a compound containing ruthenium, is impregnated into a carrier by the induce wetness method and then dried. The resulting solid is then heated in an electric tubular furnace under nitrogen flow to obtain a catalyst precursor on which at least one of the alkali metal elements and alkaline earth metal elements, as well as ruthenium, are supported.

[0048] Next, in step (iii), the catalyst precursor obtained in steps (i) and (ii) is heated under the flow of argon gas, and then a mixed gas of gaseous organic compound and argon gas is brought into contact with the catalyst precursor to support the organic compound on the catalyst precursor by CVD. Then, the catalyst is cooled to room temperature under the flow of argon gas, and a mixed gas of oxygen gas and argon gas is further circulated to obtain a catalyst on which at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon are supported on a cerium oxide-containing carrier. Specifically, a catalyst can be obtained in which at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon are supported on the surface of the carrier in the same plane.

[0049] In another embodiment of the catalyst manufacturing method according to this embodiment, step (iii) is performed before steps (i) and (ii). Specifically, another embodiment of the catalyst manufacturing method according to this embodiment can be carried out, for example, by the following method.

[0050] First, in step (iii), the support is heated under argon gas flow, and then a mixed gas of gaseous organic compound and argon gas is brought into contact with the support to deposit the organic compound onto the support by CVD. Then, the support is cooled to room temperature under argon gas flow, and a mixed gas of oxygen and argon gas is further flowed through it to obtain a support on which carbon elements are deposited.

[0051] Next, in step (i), an aqueous solution of a compound containing ruthenium, which is a catalyst raw material, is impregnated into a support bearing carbon, obtained in step (iii), by the inducer wetness method, and then dried. The resulting solid is then heated in an electric tubular furnace under nitrogen flow to obtain a catalyst precursor bearing ruthenium.

[0052] Then, as step (ii), the catalyst precursor obtained in step (i) is impregnated with a solution containing a compound containing at least one of an alkali metal element and an alkaline earth metal element, and then dried. The obtained solid is then heated in an electric tubular furnace under nitrogen flow to obtain a catalyst in which at least one of an alkali metal element and an alkaline earth metal element, a ruthenium element, and a carbon element are supported on a carrier containing cerium oxide. Specifically, a catalyst can be obtained having a carbon-supported layer on the surface of the carrier in which a carbon element is supported, and further having at least one of an alkali metal element and an alkaline earth metal element, and a ruthenium element supported on the surface of the carbon-supported layer.

[0053] In this embodiment, the method for producing the catalyst preferably involves step (iii) being performed after steps (i) and (ii), from the viewpoint of obtaining a catalyst that has high activity per unit of ruthenium element and can efficiently decompose ammonia at low temperatures.

[0054] The catalyst production method according to this embodiment preferably further includes, from the viewpoint of increasing the proportion of carbon elements having a graphene structure and improving the stability of carbon elements under ammonia decomposition reaction, step (iv): a step of heat-treating the support.

[0055] From the viewpoint of further increasing the proportion of carbon elements having a graphene structure, the temperature of the heat treatment is preferably 500°C to 1,200°C, and more preferably 600°C to 1,000°C.

[0056] Step (iv) is preferably carried out following step (iii) from the viewpoint of reducing the loss of carbon elements. That is, in another embodiment, the method for producing the catalyst according to this embodiment further comprises steps (i) to (iii) above, and further comprises step (iv), wherein step (iv) is carried out following step (iii).

[0057] [Method for producing hydrogen] The method for producing hydrogen according to this embodiment includes a step of contacting a catalyst with a gas containing ammonia to decompose the ammonia.

[0058] In the above step, an ammonia decomposition reaction similar to the reactions shown in formulas (I) to (III) described above for the catalyst according to this embodiment occurs, thereby producing hydrogen.

[0059] The catalyst consists of a carrier containing cerium oxide on which at least one of an alkali metal element and an alkaline earth metal element, ruthenium, and carbon are supported. This catalyst is the same as the catalyst according to the present embodiment.

[0060] The gas linear velocity relative to the empty cylinder when contacting the catalyst with the gas is preferably 0.1 cm / s or more, and more preferably 1 cm / s or more, at 0°C and atmospheric pressure, from the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures. Furthermore, from the viewpoint of keeping the pressure loss in the catalyst layer low, the gas linear velocity is preferably 5,000 cm / s or less, and more preferably 1,000 cm / s or less, at 0°C and atmospheric pressure.In this specification, "atmospheric pressure" means 0.1013 MPa (absolute).

[0061] The reaction temperature in the above step is preferably 200°C to 600°C, and more preferably 300°C to 500°C, from the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures.

[0062] The reaction pressure in the above step is preferably 0 MPa-G to 10 MPa-G, and more preferably 0 MPa-G to 1 MPa-G, from the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures.

[0063] The above process can be carried out using a reactor. Preferably, the reactor is at least one selected from the group consisting of an external heat exchange type fixed bed reactor, an adiabatic fixed bed reactor, a fluidized bed reactor, a pseudo-moving bed reactor, a riser type fluidized bed reactor, and a radial flow type fixed bed reactor, and more preferably, an external heat exchange type fixed bed reactor or an adiabatic fixed bed reactor. The reactor may be a single type or a combination of two or more types.

[0064] The ammonia-containing gas may further include, for example, oxygen; nitrogen; carbon monoxide; carbon dioxide; saturated hydrocarbons such as methane; hydrogen; helium; argon; water vapor, etc.

[0065] The ammonia content in the gas is preferably 80% to 100% by volume, and more preferably 90% to 100% by volume, from the viewpoint of increasing the activity per unit of ruthenium element and efficiently decomposing ammonia at low temperatures.

[0066] The hydrogen production method according to this embodiment may include a step of separating hydrogen from other components after the step of decomposing the ammonia. This makes it possible to produce hydrogen of higher purity.

[0067] Furthermore, in the hydrogen production method according to this embodiment, oxygen or air may be added to the gas containing ammonia in the step of decomposing the ammonia. This will cause the reaction shown in formula (II) to occur in addition to the reaction shown in formula (I), thereby accelerating the decomposition of ammonia.

[0068] Furthermore, in the hydrogen production method according to this embodiment, carbon dioxide may be added to the gas containing ammonia in the step of decomposing the ammonia. This causes the reaction shown in formula (III) to occur in addition to the reaction shown in formula (I), thereby accelerating the decomposition of ammonia.

[0069] It should be noted that the catalyst, catalyst manufacturing method, and hydrogen manufacturing method according to this embodiment are not limited to the embodiments described above, and various modifications are possible without departing from the gist of the disclosure in this application.

[0070] The present invention includes the following embodiments: [1] A catalyst comprising a carrier containing cerium oxide on which at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon are supported. [2] The specific surface area of ​​the catalyst is 1 m² ２ / g or more 150m ２[1] A catalyst according to [1], wherein the amount is less than or equal to / g. [3] A catalyst according to [1] or [2], wherein an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the carrier, and the alkaline earth metal element is a barium element. [4] A catalyst according to any one of [1] to [3] used in an ammonia decomposition reaction. [5] A method for producing a catalyst having a carrier containing cerium oxide, comprising the following steps (i) to (iii): Step (i): Impregnating the carrier with an aqueous solution of a compound containing a ruthenium element. Step (ii): Impregnating the carrier with an aqueous solution of a compound containing at least one of an alkali metal element and an alkaline earth metal element. Step (iii): Contacting the carrier with a gaseous or solution of an organic compound. [6] A method for producing a catalyst according to [5], wherein step (iii) is performed after steps (i) and (ii). [7] A method for producing a catalyst according to [5], wherein step (iii) is performed before steps (i) and (ii). [8] A method for producing a catalyst according to any one of [5] to [7], further comprising step (iv): a step of heat-treating the carrier, wherein the temperature of the heat treatment is 500°C or more and 1,000°C or less. [9] A method for producing a catalyst according to any one of [5] to [8], wherein step (iv) is carried out following step (iii).

[10] A method for producing hydrogen, comprising the step of contacting a catalyst with a gas containing ammonia to decompose ammonia, wherein the catalyst is supported on a carrier containing cerium oxide, with at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon being supported.

[11] The specific surface area of ​​the catalyst is 1 m ２ / g or more 150m ２ A method for producing hydrogen according to

[10] , wherein the amount is less than or equal to / g.

[12] A method for producing hydrogen according to

[10] or

[11] , wherein an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the carrier, and the alkaline earth metal element is a barium element.

[0071] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0072] (Example 1) The catalyst of Example 1 was prepared by following the steps (i) and (ii) → (iii) → (iv) below.

[0073] <Steps (i) and (ii)> Nitrosilruthenium nitrate aqueous solution (manufactured by Furuya Metal Co., Ltd., Ru(NO)(NO) ３ ), Ru content 19% by mass 10.0 g, and barium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ba (NO ３ ) ２ 3.6 g of ) was mixed thoroughly with 90.0 g of deionized water. 2.7 g of the resulting solution was then mixed with cerium oxide (manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd., HS, CeO) ２ , Specific surface area: 148m ２ 5.0 g of the material was impregnated using the inducer wetness method, and then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere. The resulting solid was then filled into a 24 mm inner diameter quartz glass tube equipped with a sheath tube for measuring the internal temperature, and then heated in an electric tubular furnace for 50 cm. ３ Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 500°C in 5 hours, and then held at the same temperature for 1 hour, thereby producing a catalyst A precursor on which barium and ruthenium elements are supported (1 part by mass of ruthenium and 1 part by mass of barium are supported per 100 parts by mass of cerium oxide; specific surface area: 89 m²). ２ 5.1 g of ( / g) was obtained.

[0074] <Step (iii)> 1.0 g of catalyst A precursor was placed in a reaction tube (inner diameter 30 mm), and while 225 mL / min of argon gas was flowed through it, the catalyst A precursor was heated from room temperature to 300°C at a heating rate of 10°C / min and held at 300°C for 30 minutes. Next, a mixed gas of acetylene gas and argon gas (acetylene gas content was 20 volume% of the mixed gas; the flow rate of acetylene gas was adjusted to 45 mL / min and the flow rate of argon gas to 180 mL / min) was introduced into the reaction tube and held at 300°C for 30 minutes to perform chemical vapor deposition (CVD) using acetylene gas as a carbon source (hereinafter referred to as acetylene CVD). Subsequently, the introduction of acetylene gas was stopped, and the mixture was cooled to room temperature (approximately 25°C) while circulating argon gas at a rate of 225 mL / min. A mixed gas of oxygen and argon (with the oxygen flow rate adjusted to 20 mL / min and the argon flow rate to 480 mL / min) was then circulated for 6 hours to obtain 0.9 g of catalyst A, in which at least one of an alkali metal element and an alkaline earth metal element, ruthenium, and carbon were supported on a carrier containing cerium oxide.

[0075] <Step (iv)> 0.9 g of catalyst A was placed in a reaction tube (inner diameter 30 mm), and under conditions where the argon gas flow rate was adjusted to 400 mL / min, catalyst B was heated from room temperature to 900 °C at a heating rate of 10 °C / min and held at 900 °C for 1 hour to perform heat treatment. After that, 0.8 g of catalyst A' was obtained by cooling to room temperature under conditions where the argon gas flow rate was adjusted to 400 mL / min.

[0076] (Example 2) Except that the holding temperature of the acetylene CVD in step (iii) was set to 350°C, 0.9 g of catalyst B of Example 2 was obtained in the same manner as in Example 1. Then, using 0.9 g of catalyst B, step (iv) was carried out in the same manner as in Example 1 to obtain 0.8 g of catalyst B'.

[0077] (Example 3) The catalyst of Example 3 was prepared by following the steps (iii) → (i) → (iii) below.

[0078] <Process (iii)> Cerium oxide (manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd., HS, CeO) ２ , Specific surface area: 148m ２1.0 g of cerium oxide (30 mm inner diameter) was placed in a reaction tube, and while 225 mL / min of argon gas was flowed through it, the cerium oxide was heated from room temperature to 600°C at a heating rate of 10°C / min and held at 600°C for 30 minutes. Next, a mixed gas of acetylene gas and argon gas (acetylene gas content was 20 vol% of the mixed gas; the flow rate of acetylene gas was adjusted to 45 mL / min and the flow rate of argon gas to 180 mL / min) was introduced into the reaction tube, and acetylene CVD was performed by holding it at 600°C for 30 minutes. Subsequently, the introduction of acetylene gas was stopped, and while 225 mL / min of argon gas was flowed through, the system was held at 600°C for 30 minutes. After cooling to room temperature (approximately 25°C), a mixed gas of oxygen and argon (with the oxygen gas flow rate adjusted to 20 mL / min and the argon gas flow rate to 480 mL / min) was flowed through for 6 hours to obtain 0.9 g of supporter F with carbon element (15 parts by mass of carbon element supported per 100 parts by mass of cerium oxide).

[0079] <Process (i)> Nitrosilruthenium nitrate aqueous solution (manufactured by Furuya Metal Co., Ltd., Ru(NO)(NO) ３ 0.6 g of 0.6 g of 19% by mass Ru-containing material was mixed thoroughly with 0.7 g of deionized water. 0.3 g of the resulting solution was impregnated onto 0.5 g of carrier F by the induce wetness method, and then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere. The resulting solid was then packed into an 8 mm inner diameter quartz glass tube equipped with a sheath tube for measuring the internal temperature, and then heated in an electric tubular furnace for 50 cm. ３ Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 400°C in 2 hours, and then maintained at the same temperature for 3 hours to obtain 0.5 g of catalyst C precursor supported with ruthenium element (5 parts by mass of ruthenium element supported per 100 parts by mass of cerium oxide).

[0080] <Process (ii)> Barium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ba(NO) ３ ) ２0.1 g of ) was added to 1.2 g of deionized water and thoroughly mixed while heating to 40°C. The resulting solution was impregnated into 0.5 g of the catalyst precursor obtained in step (i) by the induce wetness method while maintaining the temperature at 40°C, and air-dried overnight at room temperature (approximately 25°C) in an air atmosphere. The resulting solid was then packed into an 8 mm inner diameter quartz glass tube equipped with a sheath tube for measuring the internal temperature, and heated in an electric tubular furnace for 50 cm. ３ Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 400°C in 2 hours, and then held at the same temperature for 3 hours to obtain 0.5 g of catalyst C (supported with 5 parts by mass of ruthenium and 2.5 parts by mass of barium per 100 parts by mass of cerium oxide).

[0081] (Example 4) Except that step (iv) was performed following step (iii), 0.8 g of support F' (13 parts by mass of carbon element supported on 100 parts by mass of cerium oxide) was obtained in the same manner as in Example 3. Then, using support F', 0.9 g of catalyst C' was obtained by performing steps (i) → (ii) in the same procedure as in Example 3. Specifically, catalyst C' was prepared by following the procedure (iii) → (iv) → (i) → (ii). Step (iv) was performed in the same manner as in Example 1.

[0082] (Comparative Example 1) Only steps (i) and (ii) were performed, and catalyst D was prepared by following the procedure of steps (i) → (ii) below.

[0083] <Process (i)> Nitrosilruthenium nitrate aqueous solution (manufactured by Furuya Metal Co., Ltd., Ru(NO)(NO) ３ 1.4 g of cerium oxide (19% by mass, Ru content), 1.2 g of deionized water was added and mixed well to obtain a solution. The entire amount of the obtained solution was mixed with cerium oxide (manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd., HS, CeO) ２ , Specific surface area: 148m ２ 5.0 g of the material was impregnated using the inducer wetness method, and then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere. The resulting solid was then filled into a 24 mm inner diameter quartz glass tube equipped with a sheath tube for measuring the internal temperature, and heated in an electric tubular furnace for 100 cm². ３Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 400°C in 1 hour, and then maintained at the same temperature for 3 hours to obtain 5.3 g of catalyst D precursor (5 parts by mass of ruthenium element supported per 100 parts by mass of cerium oxide).

[0084] <Process (ii)> Barium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ba(NO) ３ ) ２ 0.2 g of ion-exchanged water was added to 2.2 g of 0 ３ Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 500°C in 1 hour, and then held at the same temperature for 1 hour to obtain 5.4 g of catalyst D (supported with 5 parts by mass of ruthenium and 2.5 parts by mass of barium per 100 parts by mass of cerium oxide).

[0085] (Comparative Example 2) Only steps (i) and (ii) were performed, and catalyst E was prepared by following the procedure of steps (i) → (ii) below.

[0086] <Process (i)> Nitrosilruthenium nitrate aqueous solution (manufactured by Furuya Metal Co., Ltd., Ru(NO)(NO) ３ 5.3 g of 5.3 g of 19% by mass Ru content was mixed thoroughly with 7.7 g of deionized water. The resulting solution was impregnated into 20.0 g of a carbon (C) carrier (Osaka Gas Chemical Co., Ltd.'s Granular Shirasagi (registered trademark) LH2C, 0.25 mm to 0.50 mm granular pellets, sieved to use the portion between 0.43 mm and 0.50 mm) by the induce wetness method, and then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere. The resulting solid was then packed into a 24 mm inner diameter quartz glass tube equipped with a sheath tube for measuring the internal temperature, and then heated in an electric tubular furnace for 100 cm². ３Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 400°C in 1 hour, and then maintained at the same temperature for 3 hours to obtain 21.0 g of catalyst E precursor (5 parts by mass of ruthenium element supported per 100 parts by mass of carbon).

[0087] <Process (ii)> Barium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ba(NO) ３ ) ２ 0.48 g of ) was added to 9.1 g of deionized water and dissolved. The resulting solution was impregnated into 21.0 g of catalyst E precursor obtained in step (i) by the induce wetness method, then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere, and further dried under reduced pressure at 80°C for 1 hour at 9-20 mmHg. A solution of 0.48 g of barium nitrate dissolved in 10.0 g of deionized water was further impregnated into the resulting solid by the induce wetness method, then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere, and further dried under reduced pressure at 80°C for 1 hour at 9-20 mmHg. The solid obtained from the two impregnation operations was filled into a 24 mm inner diameter quartz glass tube equipped with a sheath tube for measuring the internal temperature, and then heated in an electric tubular furnace at 100 cm ３ Under a nitrogen flow of (0°C, atmospheric pressure) / min, the internal temperature was raised to 500°C in 1 hour, and then held at the same temperature for 1 hour to obtain 21.0 g of catalyst E (supported with 5 parts by mass of ruthenium and 2.5 parts by mass of barium per 100 parts by mass of carbon).

[0088] [Measurement of Specific Surface Area] The specific surface areas of cerium oxide, catalyst A precursor, catalysts C to E, and catalysts A' to C' were measured according to the following method. Specifically, cerium oxide, catalyst A precursor, and the catalysts were degassed under vacuum at 120°C for 2 hours. Then, nitrogen adsorption / desorption isotherm measurements were performed at 77K using a BELSORP MINI X manufactured by Microtrac-Bel, and the specific surface areas of the cerium oxide, carbon-supported carrier, or catalyst were determined by the BET multipoint method. The results of the specific surface area measurements of the catalysts are shown in Table 1.

[0089] [Measurement of Carbon Loading Amount] The carbon loading amount on carrier F, carrier F', catalysts D-E, and catalysts A'-B' was measured using a thermogravimetric analyzer (TGA-50, Shimadzu Corporation) according to the following method. Specifically, the carrier or catalyst was heated from room temperature to 100°C at a rate of 10°C / min while circulating 50 mL / min of air, held at 100°C for 30 minutes, and then heated to 900°C at a rate of 10°C / min. The mass lost during this heating process was divided by the remaining mass and multiplied by 100 to calculate the carbon loading amount. The results for the carbon loading amounts obtained for the above catalysts are shown in Table 1. For catalysts C and C', the results for carriers F and F' were used directly.

[0090] [Ammonia Decomposition] <Pretreatment of Catalysts> The pretreatment of catalysts C to E and A' to C' was carried out according to the following method. Specifically, 0.05 g of the catalyst was mixed with 0.1 g of quartz sand and packed into an 8 mm inner diameter quartz glass tube equipped with a 4 mm outer diameter sheath tube for measuring the internal temperature. Then, using an electric tubular furnace, the mixture was heated for 15 cm. ３ (0°C, atmospheric pressure) hydrogen and 285 cm³ / min ３ The catalyst was pretreated by circulating nitrogen at (0°C, atmospheric pressure) / minute while raising the internal temperature to 400°C, and then maintaining that temperature for 1 hour.

[0091] <Ammonia Decomposition Reaction> The ammonia decomposition reaction of catalysts C to E and catalysts A' to C' was carried out according to the following method. Specifically, the pre-treated catalysts were heated in an electric tubular furnace at an internal temperature of 400°C with ammonia gas at 25 cm³. ３ The ammonia decomposition reaction was carried out by flowing the gas at (0°C, atmospheric pressure) / min. The gas linear velocity, calculated from the flow rate of ammonia gas and the cross-sectional area of ​​the catalyst-packed bed relative to an empty cylinder, was 1.1 cm / s at 0°C and atmospheric pressure. One hour after the start of the reaction, the reaction gas was bubbling in 190 g of 1N sulfuric acid aqueous solution for 5 minutes to absorb any remaining ammonia in the reaction gas.

[0092] <Calculation of Ammonia Concentration Reduction Rate and Ammonia Decomposition Rate per gram of Ruthenium> The ammonia concentration reduction rate and ammonia decomposition rate per gram of ruthenium for catalysts C to E and catalysts A' to C' were calculated according to the following method. Specifically, the ammonia gas supply amount CB (cm³) when ammonia gas was supplied for 5 minutes was calculated. ３ The amount of sulfuric acid lost (mL) is obtained by subtracting the amount of 1N sodium hydroxide solution required for neutralization titration with 1N sodium hydroxide solution from the amount of sulfuric acid solution (mL) obtained by partially dividing the sulfuric acid solution (mL) obtained by the sulfuric acid solution after the reaction gas has been absorbed for 5 minutes, and multiplying this by 22.4 (L / mol), which is the volume of gas at 0°C and atmospheric pressure, to obtain the remaining ammonia amount CA (cm³). ３ Using the formula below (1), the rate of decrease in ammonia concentration was calculated. The results for the remaining ammonia amount are shown in Table 1. Rate of decrease in ammonia concentration (%) = [(CB - CA) / CB] × 100 ... (1)

[0093] Furthermore, the decomposition rate of ammonia per gram of ruthenium (cm²) can be calculated from the following formula (2). ３ The ammonia decomposition rate (cm³) per gram of ruthenium was calculated. ３ ( / g - ruthenium min) = ammonia gas flow rate (cm³) ３ ( / min) × {Percentage decrease in ammonia concentration (%) / 100} / Amount of ruthenium packed (g) ... (2)

[0094] Here, the amount of ruthenium packed (g) was calculated from the following formula (3): Amount of ruthenium packed (g) = Amount of catalyst used in the ammonia decomposition reaction (g) × [Amount of ruthenium element / (Amount of ruthenium element + Amount of barium element + Amount of carbon element + Cerium oxide content)] ... (3)

[0095]

[0096] Table 1 shows that a catalyst that satisfies all the constituent requirements of the present invention can efficiently decompose ammonia and produce hydrogen at a relatively low temperature of 400°C.

[0097] Furthermore, the catalyst satisfying all the constituent elements of the present invention showed a higher ammonia decomposition rate per gram of ruthenium than the catalyst of the comparative example, indicating that the ammonia decomposition reaction activity per gram of ruthenium, a precious metal, is high. In other words, the catalyst satisfying all the constituent elements of the present invention has relatively high activity per gram of ruthenium, and therefore it was found that hydrogen can be produced efficiently using ruthenium.

[0098] In contrast, the results from Comparative Example 1 show that when carbon is not supported on the carrier, the ammonia decomposition rate per ruthenium element is low. Therefore, the catalyst of Comparative Example 1 cannot be said to be able to efficiently decompose ammonia and produce hydrogen at low temperatures.

[0099] Furthermore, the results from Comparative Example 2 show that when the support is a carbon support, the decomposition rate of ammonia per ruthenium element is low. Therefore, the catalyst in Comparative Example 2 cannot be said to be able to efficiently decompose ammonia and produce hydrogen at low temperatures.

Claims

1. A catalyst comprising a carrier containing cerium oxide, on which at least one of an alkali metal element and an alkaline earth metal element, ruthenium, and carbon are supported.

2. The specific surface area of ​​the catalyst is 1 m². ２ / g or more 150m ２ The catalyst according to claim 1, wherein the amount is less than or equal to / g.

3. The catalyst according to claim 1, wherein an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the carrier, and the alkaline earth metal element is barium.

4. The catalyst according to claim 2, wherein an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the carrier, and the alkaline earth metal element is barium.

5. A catalyst according to any one of claims 1 to 4, used in an ammonia decomposition reaction.

6. A method for producing a catalyst having a carrier containing cerium oxide, comprising the following steps (i) to (iii): Step (i): Impregnating the carrier with an aqueous solution of a compound containing ruthenium; Step (ii): Impregnating the carrier with an aqueous solution of a compound containing at least one of an alkali metal element and an alkaline earth metal element; Step (iii): Contacting the carrier with a gaseous or solution-like organic compound.

7. The method for producing a catalyst according to claim 6, wherein step (iii) is performed after steps (i) and (ii).

8. The method for producing a catalyst according to claim 6, wherein step (iii) is performed before steps (i) and (ii).

9. The method for producing a catalyst according to claim 6, further comprising step (iv): a step of heat-treating a carrier, wherein the temperature of the heat treatment is 500°C or more and 1,000°C or less.

10. The method for producing a catalyst according to claim 9, wherein step (iv) is carried out following step (iii).

11. A method for producing hydrogen, comprising the step of contacting a catalyst with a gas containing ammonia to decompose ammonia, wherein the catalyst is a carrier containing cerium oxide on which at least one of alkali metal elements and alkaline earth metal elements, ruthenium, and carbon are supported.

12. The specific surface area of ​​the catalyst is 1 m². ２ / g or more 150m ２ A method for producing hydrogen according to claim 11, wherein the amount is less than or equal to / g.

13. The method for producing hydrogen according to claim 11 or 12, wherein an alkaline earth metal element, a ruthenium element, and a carbon element are supported on the carrier, and the alkaline earth metal element is a barium element.

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