Barium nitride, metal carrier, and ammonia decomposition catalyst

Abstract

Provided is an ammonia decomposition catalyst having high ammonia decomposition activity even at a low reaction temperature and a low reaction pressure, and having stability of catalyst characteristics even when repeatedly used in a reaction after exposure to atmosphere or water. This barium nitride is represented by general formula (1). BaAN2-x (1) (In general formula (1), A represents at least one element selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x represents a value represented by 0 < = x < 2.0).

Description

TECHNICAL FIELD

[0001] The present application relates to barium nitride, metal supports, and ammonia decomposition catalysts.

[0002] This application claims priority based on Japanese Patent Application No. 2023-124281 filed in Japan on July 31, 2023, and the contents thereof are incorporated herein. BACKGROUND

[0003] Ammonia decomposition is an endothermic reaction, and the higher the temperature, the more thermodynamically favorable it is on the product side. According to the Le Chatelier principle, low pressure is more favorable on the product side. This is quite different from ammonia synthesis, which is an exothermic reaction, in which the lower the temperature, the more thermodynamically favorable it is on the ammonia generation side, and the higher the pressure, the more favorable it is on the product side. In addition, in ammonia synthesis, the N2 molecule dissociation process is generally the rate-determining stage. On the other hand, in ammonia decomposition, the N-H bond cleavage is relatively easy to proceed, and the process in which the atomic nitrogen species on the metal associates and dissociates as N2 molecules is considered to be the rate-determining stage.

[0004] In ammonia decomposition reactions, in the case of catalysts in which Ni is fixed on oxides, carbon, etc., for example, the ammonia conversion rate exceeds 90% only when the temperature is raised to a high temperature of 600°C or higher. Compared to Ru-based catalysts, the reaction temperature region used for such Ni-based catalysts is about 100°C to 200°C higher (for example, Patent Literature 1).

[0005] On the other hand, it has been reported that even when a CaNH catalyst in which Ni is supported as a supported metal instead of Ru is used, ammonia decomposition is possible (for example, Non-Patent Literature 1). It is believed that this is because the Ni surface is not an active site, and the ammonia molecule is directly activated by electrons generated in the NH defect on the CaNH as a support.

[0006] PRIOR ART DOCUMENTS PATENT LITERATURE Patent Literature 1: Japanese Patent Application Publication No. 2019-167265 NON-PATENT LITERATURE Non-Patent Literature 1: Ogasawara, Kiya et al., “Ammonia Decomposition over CaNH-Supported Ni Catalysts via an NH2- Vacancy-Mediated Mars-van Krevelen Mechanism” ACS Catal., 11, 17, p. 11005-11015 (2021) SUMMARY

[0007] Problem to be solved by the Invention The supported metal catalyst described in Patent Literature 1 generally uses a carbonaceous carrier such as activated carbon, an inorganic oxide carrier. However, these supported metal catalysts, particularly in the case where the supported metal species is other than Ru, have low reactivity and only have performance insufficient for practical use. On the other hand, the Ni supported metal catalyst described in Non-Patent Literature 1 has high reactivity, but the Ni supported CaNH catalyst is unstable in the atmosphere, and reacts with oxygen, moisture in the atmosphere, and CaNH is deteriorated by oxidation.

[0008] That is, there is a demand for an ammonia decomposition catalyst having high ammonia decomposition activity even at low reaction temperature and low reaction pressure, and having stability of catalyst characteristics even when repeatedly used for reaction after exposure to the atmosphere, water.

[0009] Means for solving the problem The present inventors have found that an ammonia decomposition catalyst capable of having both improvement of reactivity and stabilization of catalyst characteristics by supporting a transition metal on a barium nitride, and have completed the present invention.

[0010] That is, the gist of the present invention is as follows.

[0011] [1] A barium nitride represented by the following general formula (1), BaAN 2-x (1) (In the aforementioned general formula (1), A is at least one selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x represents a number satisfying 0 ≤ x < 2.0.) [2] The barium nitride according to [1], wherein, in the aforementioned general formula (1), A is Si.

[0012] [3] A metal support which is a metal support in which a transition metal is supported on a carrier, The aforementioned carrier contains the barium nitride according to [1] or [2].

[0013] [4] The metal support according to [3], characterized in that the aforementioned transition metal is at least one selected from the group consisting of Group 8, Group 9, and Group 10 metal elements of the periodic table.

[0014] [5] The metal support according to [3], characterized in that the aforementioned transition metal is at least one selected from the group consisting of Ru, Ni, Fe, and Co.

[0015] [6] The metal support according to [3], characterized in that the aforementioned transition metal is at least one selected from the group consisting of Ru and Ni.

[0016] [7] An ammonia decomposition catalyst containing the barium nitride described in [1] or [2].

[0017] [8] An ammonia decomposition catalyst containing the metal support described in any one of [3] to [6].

[0018] [9] A method for producing hydrogen, comprising: a step of bringing the ammonia decomposition catalyst described in [7] into contact with ammonia; and a step of recovering hydrogen produced by the foregoing step.

[0019]

[10] A method for producing hydrogen, comprising: a step of bringing the ammonia decomposition catalyst described in [8] into contact with ammonia; and a step of recovering hydrogen produced by the foregoing step.

[0020]

[11] Use of the barium nitride described in [1] or [2] as an ammonia decomposition catalyst.

[0021]

[12] Use of the metal support described in any one of [3] to [6] as an ammonia decomposition catalyst.

[0022] Effects of the Invention The ammonia decomposition catalyst of the present invention is suitable as an ammonia decomposition catalyst that has high ammonia decomposition activity even at a low reaction temperature and a low reaction pressure, and has stability of catalyst characteristics even when repeatedly used for a reaction after exposure to the atmosphere or water. BRIEF DESCRIPTION OF DRAWINGS

[0023] [ Figure 1 ] is a reaction formula showing a method for producing BaSiN 2-x of Example 1.

[0024] [ Figure 2 ] is a graph showing XRD results of BaSiN 2-x synthesized in Example 1.

[0025] [ Figure 3 ] is a graph showing reaction temperature dependency of ammonia decomposition efficiency in Example 1, Comparative Examples 1 and 2.

[0026] [ Figure 4 ] is a graph showing reaction temperature dependency of ammonia decomposition efficiency in Example 1 to Example 4. DETAILED DESCRIPTION

[0027] [Barium nitride] The barium nitride of one embodiment of the present invention (this embodiment) is a barium nitride represented by the following general formula (1).

[0028] BaAN 2-x (1) In the aforementioned general formula (1), A is at least one selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x represents a number indicated by 0≤x<2.0. x preferably represents a number indicated by 0≤x<1.0, and x more preferably represents a number indicated by 0≤x<0.3.

[0029] In the aforementioned general formula (1), A is preferably Si. That is, the barium nitride of the present embodiment is preferably a barium nitride indicated by general formula (2).

[0030] BaSiN 2-x (2) In the aforementioned general formula (2), x represents a number indicated by 0≤x<2.0. x preferably represents a number indicated by 0≤x<1.0, and x more preferably represents a number indicated by 0≤x<0.3.

[0031] The amount of nitrogen contained in the barium nitride of the present application is not particularly limited.

[0032] With respect to x, for example, the valence number of Ba + the valence number of A + [the valence number of N x (2-x)] = 0 is preferably satisfied so that the barium nitride is electrically neutral.

[0033] As a specific example of the barium nitride of the present application, for example, BaSiN 1.78 , BaFe 0.33 N, BaNiN, BaMo 0.33 N 1.33 , BaZrN2, and the like can be given.

[0034] <Method for manufacturing barium nitride> The method for manufacturing the barium nitride indicated by the aforementioned general formula (1) of the present application includes a step of heating Ba2N and a nitride or a metal indicated by the aforementioned general formula (3) under an argon or nitrogen atmosphere.

[0035] A s N t (3) (In the aforementioned general formula (3), s represents a number indicated by 1-3. t represents a number indicated by 0-4.) In the aforementioned general formula (3), A is at least one selected from the group consisting of Si, Fe, Ni, Mo, and Zr.

[0036] As a specific example of the nitride indicated by the aforementioned general formula (3), for example, Si3N4, Fe3N4, Ni, Mo2N, ZrN, and the like can be given.

[0037] In the aforementioned general formula (3), A is preferably Si. That is, the barium nitride of the present embodiment preferably includes a step of heating Ba2N and Si3N4 under an argon or nitrogen atmosphere.

[0038] In the above heating step, the heating temperature is preferably in the range of 600°C to 1000°C, more preferably in the range of 700°C to 1000°C, and further preferably in the range of 800°C to 900°C. For example, in the example described later, the heating temperature is 800°C. The gas pressure of the argon or nitrogen atmosphere is preferably in the range of 0.01 MPa to 3.0 MPa, and more preferably in the range of 0.1 MPa to 1.0 MPa. The argon or nitrogen can be filled into the reaction vessel, or the argon or nitrogen can be flown into the reaction vessel. The reaction time is not particularly limited, and is preferably in the range of 1 to 100 hours, more preferably in the range of 2 to 50 hours, and further preferably in the range of 5 to 20 hours. For example, in the example described later, the heating temperature is 800°C, and the reaction time is 20 hours.

[0039] The Ba2N and the nitride or metal represented by the above general formula (3) used as the raw material of the production method of the present application can be commercially available products, or can be produced by a known method. As the commercially available products, for example, high-purity chemical Si3N4 (>99.9%), high-purity chemical Fe3N4 (99.9%), high-purity chemical Ni (99.9%), high-purity chemical ZrN (98%), and the like can be mentioned.

[0040] On the other hand, as the raw material produced by a known method, for example, in the case of Ba2N, it can be synthesized by using metal Ba (99.99%) of Aldrich as a raw material and heating it at 600°C for 16 hours under a N2 atmosphere. Also, in the case of Mo2N, it can be synthesized by using high-purity chemical MoO3 (99.8%) as a raw material and heating it at 700°C for 15 hours under an ammonia stream.

[0041] The detailed production method is described in each of the embodiments described later. For example, it can include a step of heating Ba2N and a nitride corresponding to the desired barium nitride in an argon or nitrogen atmosphere.

[0042] As the treatment conditions in the above heating step, for example, a method of argon filling and heating treatment at 600°C or higher and 1000°C or lower for 1 to 50 hours, preferably at 700°C or higher and 1000°C or lower for 2 to 30 hours, and more preferably at 800°C or higher and 900°C or lower for 5 to 20 hours can be mentioned. Also, a condition of heating treatment at 600°C or higher and 1000°C or lower for 1 to 50 hours in a nitrogen stream, preferably at 700°C or higher and 1000°C or lower for 2 to 30 hours, and more preferably at 800°C or higher and 900°C or lower for 5 to 20 hours can be mentioned.

[0043] Quantification of Nitrogen Contained in Barium Nitride The BaAN thus produced as a barium nitride 2-x The amount of nitrogen in the test substance can be determined, for example, by elemental analysis using a CHN elemental analyzer.

[0044] (Metallic support) The metallic support of one embodiment (this embodiment) of the present application is one in which a transition metal is supported on a carrier. The aforementioned carrier is a barium nitride represented by the following general formula (1).

[0045] BaAN 2-x (1) In the aforementioned general formula (1), A is at least one selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x represents a number satisfying 0 ≤ x < 2.0.

[0046] [Barium nitride] The aforementioned barium nitride contained in the metallic support of this embodiment is preferably the barium nitride of this embodiment described above.

[0047] [Transition metal] The transition metal used in this embodiment is not particularly limited and is preferably at least one selected from the group consisting of metal elements of Group 8, Group 9, and Group 10 of the periodic table.

[0048] In addition, the specific metal element is not particularly limited and can be, for example, Cr, Mo, Mn, Re, Fe, Ru, Os, Co, Rh, Ni, Pd, or Pt. From the viewpoint of high bond energy with nitrogen, Mo, Re, Fe, Ru, Os, Co, or Ni can be preferably given, and Ru, Co, Fe, or Ni can be more preferably given. From the viewpoint of high reactivity, Ru is preferable. In addition, in the case where economy and the like are also taken into consideration, Ni, Co, or Fe is preferable.

[0049] Each of the aforementioned elements can be used alone or in combination with two or more. In addition, intermetallic compounds of these elements, such as Co3Mo3N, Fe3Mo3N, Ni2Mo3N, Mo2N, or the like, can be used. Each of the elements is preferably used alone or in combination with two or more, and is more preferably used alone, which is advantageous in terms of workability and cost in production.

[0050] The supported amount of the aforementioned transition metal is not particularly limited, and is usually 0.01 parts by mass (0.01 mass%) or more, preferably 0.5 parts by mass (0.5 mass%) or more, more preferably 1 part by mass (1 mass%) or more, and further preferably 2 parts by mass (2 mass%) or more, relative to 100 parts by mass of the aforementioned support. In addition, it is usually 50 parts by mass (50 mass%) or less, preferably 40 parts by mass (40 mass%) or less, more preferably 30 parts by mass (30 mass%) or less, and further preferably 20 parts by mass (20 mass%) or less. If it is the aforementioned lower limit value or more, the effect of the present application can be preferably obtained. On the other hand, if it is the aforementioned upper limit value or less, the effect of the present application in which the supported amount matches the cost can be expected.

[0051] Method for supporting transition metal to barium nitride The method for supporting transition metal to barium nitride is not particularly limited, and for example, by the following procedures (I) and (II), a metal support (hereinafter, referred to as M / BaAN 2-x having a metal fixed thereon (hereinafter, referred to as M / BaAN 2-x ) can be obtained.

[0052] Procedure (I), the barium nitride (BaAN 2-x ) represented by the aforementioned general formula (1) in powder form obtained by the aforementioned method is mixed with a compound of a metal to be supported.

[0053] Procedure (II), the mixture obtained in the aforementioned procedure is heated at 250°C for 0.5 to 4 hours in a gas atmosphere containing hydrogen, and the metal compound is thermally decomposed.

[0054] For example, BaAN 2-x and a compound of Ru, Co, Fe, Ni, or the like (as the aforementioned support) such as Ru3(CO) 12 , Co2(CO)8, Fe2(CO)9, Ni(C5H5)2 can be used to synthesize a metal support, Ru supported BaAN 2-x (referred to as Ru / BaAN 2-x ), Co supported BaAN 2-x (referred to as Co / BaAN 2-x ), Fe supported BaAN 2-x (referred to as Fe / BaAN 2-x ), and Ni supported BaAN 2-x (referred to as Ni / BaAN 2-x ).

[0055] The transition metal of the present embodiment is preferably a transition metal particle. More preferably, it is a transition metal nanoparticle having a particle diameter of 100 nm or less.

[0056] (Ammonia decomposition catalyst) The ammonia decomposition catalyst of one embodiment of the present application (this embodiment) is a catalyst in which a transition metal is supported on a support. The aforementioned support contains a barium nitride represented by the following general formula (1). The aforementioned support is preferably a barium nitride represented by the following general formula (1).

[0057] BaAN 2-x (1) In the aforementioned general formula (1), A is at least one selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x represents a number satisfying 0 ≤ x < 2.0.

[0058] [Barium nitride] The aforementioned barium nitride contained in the ammonia decomposition catalyst of this embodiment is preferably the barium nitride of this embodiment described above.

[0059] [Transition metal] The transition metal used in this embodiment is the same as the transition metal used in the metal support of this embodiment described above.

[0060] In the ammonia decomposition catalyst of this embodiment, the aforementioned support can contain the metal support of this embodiment described above. The aforementioned support can be the metal support of this embodiment described above.

[0061] <Shape of ammonia decomposition catalyst> The shape of the ammonia decomposition catalyst of this embodiment is not particularly limited, and specifically, can be any of a block shape, a powder shape, a film shape, and the like. The particle diameter of the metal support in a powder shape is not particularly limited, and is typically greater than or equal to 1 nm and less than or equal to 10 μm.

[0062] The particle diameter of the transition metal in the ammonia decomposition catalyst of this embodiment is not particularly limited, and is typically greater than or equal to 1 nm and less than or equal to 100 nm. From the viewpoint of increasing the number of step sites serving as active sites for nitrogen dissociation when used as an ammonia decomposition catalyst, it is preferably less than or equal to 20 nm. It is more preferably less than or equal to 10 nm.

[0063] <Manufacturing method of ammonia decomposition catalyst> The ammonia decomposition catalyst of the present application is a catalyst in which a transition metal is supported on a support. The aforementioned support contains a barium nitride of this embodiment (BaAN 2-x ). Alternatively, the aforementioned support contains a metal support of this embodiment. The ammonia decomposition catalyst of this embodiment is manufactured by supporting the aforementioned transition metal on the aforementioned support. The manufacturing method is not particularly limited, and is typically a method in which a transition metal or a compound that becomes a transition metal precursor (hereinafter referred to as a transition metal compound) is supported on the aforementioned support.

[0064] As the raw material for the aforementioned support used for the raw material of the ammonia decomposition catalyst of the present embodiment, commercially available reagents, industrial raw materials can be used, or a raw material for a support obtained by a known method from a corresponding metal can be used.

[0065] The method for supporting a transition metal on the aforementioned support used in the present embodiment is not particularly limited, and a known method can be used. In general, the following method can be used: a transition metal compound of a compound of a transition metal to be supported, which can be converted into a transition metal by reduction, thermal decomposition, or the like, is supported on the aforementioned support, and then converted into a transition metal.

[0066] The aforementioned transition metal compound is not particularly limited, and an inorganic compound or an organometallic complex of a transition metal that is easily thermally decomposed, or the like can be used. Specifically, a complex of a transition metal, an oxide of a transition metal, a transition metal salt such as a nitrate, a hydrochloride, or the like can be used.

[0067] For example, as the Ru compound, dodecacarbonyltriruthenium [Ru3(CO) 12 ], tetra(triphenylphosphine)ruthenium(II) dichloride [RuCl2(PPh3)4], tri(triphenylphosphine)ruthenium(II) dichloride [RuCl2(PPh3)3], tris(acetylacetone)ruthenium(III) [Ru(acac)3], ruthenocene [Ru(C5H5)2], ruthenium nitrosyl nitrate [Ru(NO)(NO3)3], potassium ruthenate, ruthenium oxide, ruthenium nitrate, ruthenium chloride, or the like can be mentioned. Tris(acetylacetone)ruthenium(III) [Ru(acac)3] is preferred.

[0068] For example, as the Fe compound, pentacarbonyliron [Fe(CO)5], dodecacarbonyltriferro [Fe3(CO) 12 ], nonacarbonyliron [Fe2(CO)9], tetracarbonyliron iodide [Fe(CO)4I2], tris(acetylacetone)iron(III) [Fe(acac)3], ferrocene [Fe(C5H5)2], iron oxide, iron nitrate, iron chloride (FeCl3), or the like can be mentioned.

[0069] As the Co compound, octacarbonylcobalt [Co2(CO)8], tris(acetylacetone)cobalt(III) [Co(acac)3], acetylacetone cobalt(II) [Co(acac)2], cobaltocene [Co(C5H5)2], cobalt oxide, cobalt nitrate, cobalt chloride, or the like can be mentioned.

[0070] As the Ni compound, nickel acetate [Ni(OCOCH3)2], acetylacetone nickel [Ni(acac)2], nickel chloride [NiCl2], nickelocene [Ni(C5H5)2], nickel nitrate, or the like can be mentioned.

[0071] Among these transition metal compounds, in the case of using a carbonyl complex of a transition metal such as [Ru3(CO) 12 ], [Fe(CO)5], [Fe3(CO) 12 ], [Fe2(CO)9], [Co2(CO)8], [Ni(C5H5)2], and the like, the transition metal is supported after the aforementioned support is heated. Thus, in the production of the ammonia decomposition catalyst of the present embodiment, from the viewpoint that the reduction treatment described later can be omitted, the aforementioned carbonyl complex of a transition metal is preferred.

[0072] In addition, in the case of using a nitrate salt of a transition metal such as ferric nitrate, cobalt nitrate, nickel nitrate, and the like, the transition metal is supported after being impregnated and supported in an aqueous solution, and then heated. Thus, as the production method of the ammonia decomposition catalyst of the present embodiment, from the viewpoints of being simple and also advantageous in terms of cost reduction, the aforementioned nitrate salt of a transition metal is preferred.

[0073] The amount of use of the aforementioned transition metal compound is not particularly limited, and an amount for achieving a desired supported amount can be appropriately used. In terms of the lower limit of the amount of use of the aforementioned transition metal compound, for example, it is 0.01 parts by mass (0.01 mass%) or more, preferably 2 parts by mass (2 mass%) or more, more preferably 10 parts by mass (10 mass%) or more, and particularly preferably 20 parts by mass (20 mass%) or more, with respect to 100 parts by mass of the aforementioned support used. On the other hand, in terms of the upper limit of the amount of use of the aforementioned transition metal compound, for example, it is 50 parts by mass (50 mass%) or less, preferably 40 parts by mass (40 mass%) or less, and more preferably 30 parts by mass (30 mass%) or less.

[0074] As the method of supporting the aforementioned transition metal compound on the support, specifically, for example, an impregnation method, a physical mixing method, a CVD method (chemical vapor deposition method), a sputtering method, or the like can be used.

[0075] The physical mixing method is a method in which the aforementioned support and the aforementioned transition metal compound are solid-mixed, and then heated under a hydrogen-containing gas atmosphere (may be gas filling or gas flow) or under vacuum. The heating temperature at this time is not particularly limited, and is typically 200°C or higher and 600°C or lower. The heating time is not particularly limited, and is typically preferably 2 hours or more.

[0076] Among these, if the transition metal compound is converted into a transition metal by thermal decomposition, the transition metal is typically supported on the aforementioned support at this stage, and becomes the ammonia decomposition catalyst of the present embodiment.

[0077] In the case where a substance other than the transition metal compound which is converted into a transition metal by thermal decomposition is used, generally, the transition metal compound is reduced to produce the ammonia decomposition catalyst of the present embodiment.

[0078] The method of reducing the aforementioned transition metal compound (hereinafter, referred to as reduction treatment) is not particularly limited as long as it does not hinder the object of the present application, and, for example, the following two methods can be given. (I) A method performed in an atmosphere containing a reducing gas. (II) A method in which a reducing agent such as NaBH4, NH2NH2, or formalin is added to a solution containing the aforementioned transition metal compound to cause deposition on the surface of the aforementioned metal hydride. The method performed in an atmosphere containing a reducing gas is preferable. As the aforementioned reducing gas, for example, hydrogen, ammonia, methanol (vapor), ethanol (vapor), methane, and ethane can be given.

[0079] In addition, in the aforementioned reduction treatment, other components other than the reducing gas can coexist in the reaction system without hindering the object of the present application, particularly, without hindering the ammonia decomposition reaction. Specifically, in the reduction treatment, in addition to the reducing gas such as hydrogen, a gas such as argon or nitrogen which does not hinder the reaction can coexist. It is preferable that nitrogen coexist.

[0080] In the case where the aforementioned reduction treatment is performed in a gas containing hydrogen, by causing nitrogen to coexist with hydrogen, it is possible to perform in parallel with the decomposition of ammonia described later. That is, in the case where the ammonia decomposition catalyst of the present embodiment is used as the ammonia decomposition catalyst described later, by placing the substance in which the aforementioned transition metal compound is supported on the aforementioned metal hydride in the reaction conditions of the ammonia decomposition reaction, it is possible to reduce the aforementioned transition metal compound and convert it into a transition metal.

[0081] The temperature at the time of the aforementioned reduction treatment is not particularly limited, and generally, it can be 200°C or higher, preferably 300°C or higher, and it is preferably performed at lower than 700°C. It is more preferable to perform at 400°C or higher and lower than 700°C. By performing within the aforementioned reduction treatment temperature range, it is possible to grow the aforementioned transition metal sufficiently and within a preferable range.

[0082] The pressure at the time of the aforementioned reduction treatment is not particularly limited, and generally, it is 0.01 MPa or higher and 10 MPa or lower. In terms of the pressure at the time of the reduction treatment, if it is set to the same conditions as the ammonia decomposition conditions described later, it is not necessary to perform complicated operations, and it is advantageous in terms of manufacturing efficiency.

[0083] The time of the aforementioned reduction treatment is not particularly limited, and in the case where it is performed at normal pressure, it is generally 1 hour or more, and preferably 2 hours or more.

[0084] In addition, in the case where it is performed under conditions in which the reaction pressure is high (for example, 1 MPa or more), it is preferable to be 1 hour or more.

[0085] In the case where other than the transition metal compound which is converted into a transition metal by thermal decomposition is used, as with the aforementioned reduction treatment method, the transition metal compound contained in the solid mixture is reduced by a usual method to become the ammonia decomposition catalyst of the present embodiment.

[0086] As the aforementioned barium nitride and the aforementioned other component other than the aforementioned transition metal, a carbonaceous substance such as activated carbon, an inorganic oxide, or the like can be contained as a carrier of the aforementioned barium nitride.

[0087] The ammonia decomposition catalyst of the present embodiment can be used as a molded body using a usual molding technique. Specifically, shapes such as granular, spherical, flaky, ring-shaped, macaroni-shaped, tetra-lobed, dice-shaped, honeycomb-shaped, and the like can be cited. In addition, it can also be used after being coated on a suitable support.

[0088] When the ammonia decomposition catalyst of the present embodiment is used, its reaction activity is not particularly limited. For example, in the case where the hydrogen generation rate at a reaction temperature of 500°C and a reaction pressure of 0.1 MPa is taken as an example, it is preferably 400 mmol g -1 h -1 As the weight hourly space velocity (WHSV) of the supplied ammonia gas, in the case where the hydrogen generation rate at a reaction temperature of 500°C and a reaction pressure of 0.1 MPa is taken as an example, it is more preferably 500 mmol g -1 h -1 The hydrogen generation rate is 500 mmol g - 1 h -1 The hydrogen generation rate is 700 mmol g -1 h -1 The hydrogen generation rate is 750 mmol g -1 h -1 The hydrogen generation rate is 750 mmol g -1 h -1 The hydrogen generation rate is 700 mmol g -1 h -1 The hydrogen generation rate is 750 mmol g -1 h -1 The hydrogen generation rate is 750 mmol g

[0089] Next, an ammonia production method using the ammonia decomposition catalyst of the present embodiment will be described.

[0090] (Hydrogen production method) Next, a method for producing hydrogen by decomposing ammonia using the ammonia decomposition catalyst of the present embodiment will be described.

[0091] The method for producing hydrogen of one embodiment of the present application (hereinafter, sometimes referred to as the method for producing hydrogen of the present embodiment) includes the following steps: continuously supplying ammonia gas with a volume fraction of 0.1 % to 100 % to a catalyst layer containing the ammonia decomposition catalyst of the present embodiment described above, and allowing the ammonia to react and decompose over the catalyst at a reaction pressure of 0.01 MPa to 1.0 MPa and a reaction temperature of 300 °C to 800 °C at a weight hourly space velocity (WHSV) of 500 mL g -1 h -1 The contact decomposition reaction is performed as described above.

[0092] In the method for producing hydrogen of the present embodiment, the ammonia decomposition catalyst of the present embodiment is used as a catalyst, and the ammonia is allowed to react and decompose over the catalyst, whereby hydrogen and nitrogen are generated.

[0093] The reaction is represented by the following formula (A).

[0094] 2NH3→ 3H2 + N2 ··· (A) As a specific production method, any method in which ammonia is allowed to contact and decompose over the catalyst to generate hydrogen can be used, and there is no particular limitation, and the production can be performed as appropriate in accordance with a known production method.

[0095] In the method for producing hydrogen of the present application, hydrogen and nitrogen are usually generated by heating the catalyst when the ammonia is allowed to contact the catalyst.

[0096] The reaction temperature in the production method of the present application is not particularly limited, and is usually higher than or equal to 300 °C, preferably higher than or equal to 350 °C, more preferably higher than or equal to 400 °C, and is usually lower than or equal to 800 °C, preferably lower than or equal to 600 °C, more preferably lower than or equal to 500 °C. The ammonia decomposition reaction is an equilibrium reaction and an endothermic reaction, and thus a high-temperature region is more advantageous, but in order to obtain a sufficient ammonia decomposition reaction rate, it is preferable to perform the reaction in the above temperature range.

[0097] This is because the decomposition reaction sufficiently proceeds in the above temperature range, and it is also advantageous in terms of equipment.

[0098] Note that when Ru is used as the transition metal of the present embodiment, the reaction temperature is further preferably higher than or equal to 400 °C and lower than or equal to 600 °C, and similarly, when Ni or Co is used, the reaction temperature is further preferably higher than or equal to 500 °C and lower than or equal to 750 °C.

[0099] The reaction pressure in the hydrogen production method of the present application is not particularly limited, and is usually 0.01 MPa or higher, preferably 0.05 MPa or higher, and is usually 1.0 MPa or lower, preferably 0.5 MPa or lower, and more preferably 0.1 MPa or lower.

[0100] The ammonia decomposition reaction is an equilibrium reaction and a volume-increasing reaction, and thus a low pressure condition is more favorable, but in order to obtain a sufficient ammonia decomposition reaction rate, it is preferable to carry out the reaction within the above-mentioned pressure range. In addition, from the viewpoint of equipment, it is favorable to carry out the reaction at 0.1 MPa.

[0101] The ammonia used in the hydrogen production method of the present application is not particularly limited, and can be either pure ammonia or ammonia diluted with an equilibrium gas, and both are acceptable. That is, ammonia gas having a volume fraction of 1 ppm to 100% can be used.

[0102] In the hydrogen production method of the present application, when recovering hydrogen produced by contacting the aforementioned catalyst with ammonia, the hydrogen can be recovered in the presence of nitrogen, or the hydrogen can be recovered in a state where the hydrogen is super-rich or substantially only hydrogen using a known method.

[0103] In the hydrogen production method of the present application, in order to separate and recover the produced hydrogen from nitrogen, the ammonia volume fraction is preferably high, and is 5% or higher, more preferably 20% or higher, and further preferably 70% or higher, in terms of volume fraction.

[0104] The weight hourly space velocity (WHSV) of ammonia is not particularly limited, and is usually 0.1 to 1000 g NH3 / g cat. hr, preferably 1 to 500 g NH3 / g cat. hr, and more preferably 5 to 200 g NH3 / g cat. hr. -1 h -1 The above makes it possible to obtain a high NH3 conversion rate.

[0105] In the hydrogen production method of the present application, from the viewpoint of improving the conversion rate, it is preferable to activate the transition metal as a catalytic active component by exposing the aforementioned catalyst to an atmosphere of a reducing gas such as hydrogen before contacting the ammonia with the aforementioned catalyst. The temperature at the time of the aforementioned exposure is not particularly limited, and is usually 300°C or higher and 700°C or lower. In addition, the time of the aforementioned exposure is not particularly limited, and is usually 30 minutes or longer and 2 hours or shorter.

[0106] In the hydrogen production method of the present application, the form of the reaction vessel is not particularly limited, and a reaction vessel that is usually used for an ammonia decomposition reaction can be used. As a specific reaction form, for example, a batch reaction form, a closed circulation system reaction form, a flow-through system reaction form, and the like can be used, and from the viewpoint of practicality, a flow-through system reaction form is preferable.

[0107] Since the decomposition reaction of ammonia is an endothermic reaction, it is advantageous to supply reaction heat while performing the reaction, and in order to improve the yield in industry, a known method for supplying reaction heat can be used. For example, a method in which the ammonia decomposition reaction is performed while a part of the ammonia raw material is oxidized using air to obtain combustion heat, and the like can be cited.

[0108] In addition, the material of the reaction vessel is not particularly limited, and a known material for ammonia decomposition reaction can be used, and for example, a general gas phase-solid phase contact reaction device using a corrosion-resistant material such as stainless steel can be used.

[0109] In the present application, the ammonia decomposition reaction can be performed using one reactor or a plurality of reactors filled with a catalyst, as in the method performed in the past. In addition, any of a method in which a plurality of reactors are connected, and a reactor having a plurality of reaction layers in the same reactor can be used.

[0110] Example Hereinafter, the present application will be described in more detail based on examples. The conversion amount of NH3 was quantified by gas chromatography, and the ammonia decomposition efficiency (NH3 conversion rate (%)) was evaluated.

[0111] (Gas chromatography (GC) analysis) The hydrogen generation amount of the following examples and comparative examples was determined by gas chromatography (GC) analysis, and was calculated using an absolute standard curve method. The measurement conditions are shown below.

[0112] [Measurement conditions] Measurement device: GC14A (Shimadzu) Column: PoraPak QS Column temperature: 80°C Carrier gas: He Gas detector: TCD (XRD measurement) X-ray diffraction of the material was measured using a D2 PHASER manufactured by Bruker with Cu Kα as the X-ray source.

[0113] Voltage: 40 kV Current: 40 mA (Example 1) [Manufacture of BaSiN2] As a raw material, Ba metal (99.99% manufactured by Aldrich) was heated at 600°C for 16 hours under N2atmosphere, and the Ba2N powder thus synthesized was mixed with Si3N4powder (high purity chemical, ≥ 99.9%) in a molar ratio of 1 : [2 / 3] in a glove box. Next, the resulting mixture was filled into a quartz glass tube, argon was filled into the quartz glass tube, and the quartz glass tube was sealed. The quartz glass tube was subjected to firing at 800°C for 20 hours using an electric furnace. Thus, BaSiN2powder was obtained.

[0114] The XRD evaluation results of the BaSiN2powder are shown in Figure 2 Compared with the calculated XRD peaks of BaSiN2, the XRD peaks of BaSiN2shifted to a larger diffraction angle, which is presumably due to defects in the crystal lattice N 3- .

[0115] [Ni supported on BaSiN2] The powder-like BaSiN20.3 g synthesized in this example and Ni (C5H5)2(98% manufactured by Tokyo Chemical Industry Co., Ltd.) 0.051 g (5 mass% with respect to BaTiO 3-x N y were put into a quartz glass reaction tube. Next, hydrogen 2.5 mL / min was circulated in the resulting quartz glass reaction tube, and the temperature was raised to 250°C over 0.5 hours, and further maintained for 1.5 hours, thus obtaining a supported material in which Ni was fixed to BaSiN2(hereinafter referred to as Ni / BaSiN2).

[0116] Using the aforementioned ammonia decomposition catalyst thus obtained, the following ammonia decomposition was performed.

[0117] [Ammonia decomposition using Ni supported BaSiN2] <Ammonia decomposition reaction> Using 5 mass% Ni / BaSiN2prepared in Example 1 as an ammonia decomposition catalyst, a reaction for generating nitrogen and hydrogen by decomposing ammonia was performed. The reaction was performed using a fixed bed circulation type reaction apparatus equipped with a glass tube in which 0.1 g of the aforementioned Ni supported material was filled as an ammonia decomposition catalyst. Before the reaction, nitrogen 5 mL / min and hydrogen 15 mL / min were circulated, the temperature was raised to 500°C over 1 hour, and further maintained for 1 hour, thus performing pretreatment of the aforementioned catalyst. In the ammonia decomposition reaction, the flow rate of ammonia gas was set to NH3: 25 mL / min (weight hourly space velocity (WHSV) 15000 mL g -1 h -1), under the condition that the reaction pressure was 0.1 MPa. The gas discharged from the aforementioned fixed bed flow-through reaction device was recovered, and the components of the recovered gas were quantified by gas chromatography. The decomposition efficiency of ammonia (conversion rate of NH3) at 360°C to 660°C was measured. The results are shown in Table 1, Figure 3

[0118] Note that, in order to evaluate the air stability of the Ni-supported BaSiN2, 5 mass% Ni / BaSiN2 prepared in Example 1 was used as a test sample. After the test sample was exposed to air for 1 hour, the catalyst characteristics of the aforementioned test sample were confirmed by performing XRD evaluation and basic performance evaluation as a catalyst, and as a result, it was confirmed that the aforementioned test sample before exposure to air was equivalent, indicating that it was a catalyst having stability in catalyst characteristics.

[0119] (Example 2) [Ru support to BaSiN2] Except that Ru3(CO) 12 (C5H5)2 was replaced with Ru3(CO)12(Aldrich, 99%), a support in which Ru was fixed to BaSiN2 (hereinafter, referred to as Ru / BaSiN2) was obtained by the same method as in Example 1.

[0120] Using the aforementioned ammonia decomposition catalyst thus obtained, the following ammonia decomposition was performed.

[0121] [Ammonia decomposition using Ru-supported BaSiN2] <Ammonia decomposition reaction> Except that 5 mass% Ru / BaSiN2 prepared in Example 2 was used, the reaction of generating nitrogen and hydrogen by decomposing ammonia was performed by the same method as in Example 1. The results are shown in Table 1, Figure 4

[0122] (Example 3) [Co support to BaSiN2] Except that Co2(CO)8 (Tokyo Chemical Industry Co., Ltd., >95%) was used instead of Ni(C5H5)2, a support in which Co was fixed to BaSiN2 (hereinafter, referred to as 5 mass% Co / BaSiN2) was obtained by the same method as in Example 1.

[0123] Using the aforementioned ammonia decomposition catalyst thus obtained, the following ammonia decomposition was performed.

[0124] [Ammonia decomposition using Co-supported BaSiN2] <Ammonia decomposition reaction> ​​Except for using the 5% by mass Co / BaSiN2 prepared in Example 2, the reaction to generate nitrogen and hydrogen by decomposing ammonia was carried out using the same method as in Example 1. The results are shown in Table 1. Figure 4 As shown.

[0125] (Example 4) [Fe loading onto BaSiN2] Except for using Fe2(CO)9 (Aldrich preparation, 98%) instead of Ni(C5H5)2, the same method as in Example 1 was used to obtain a support material with Fe fixed on BaSiN2 (hereinafter referred to as 5% Fe / BaSiN2 by mass).

[0126] Using the aforementioned ammonia decomposition catalyst obtained in this way, the following ammonia decomposition was carried out.

[0127] [Ammonia decomposition using Fe-supported BaSiN2] <Ammonia decomposition reaction> Except for using the 5% by mass Fe / BaSiN2 prepared in Example 2, the reaction to generate nitrogen and hydrogen by decomposing ammonia was carried out using the same method as in Example 1. The results are shown in Table 1. Figure 4 As shown.

[0128] (Comparative Example 1) BaTiO 3-x H z [Manufacturing] Commercially available TiO2 powder (Aldrich, 99.5%) and BaH2 powder were mixed in a glove box at a molar ratio of 1:1. The resulting mixture was then filled into a quartz glass tube, and hydrogen gas was introduced at a rate of 10 mL / min. -1 The mixture was circulated in a quartz glass tube while being sintered in an electric furnace at 800°C for 20 hours. This yielded BaTiO₂, in which some oxide ions were replaced by hydride ions. 2.01 H 0.96 powder.

[0129] BaTiO 3-x N y Powder manufacturing] The BaTiO obtained in Comparative Example 1 3-x H z The powder was heated to 600℃ in a nitrogen flow of 10 mL / min (pressure: 0.1 MPa) over 1 hour, and then subjected to heat treatment at 600℃ for 12 hours to obtain BaTiO. 3-x N y powder.

[0130] [Ni to BaTiO]3-x N y supported] The BaTiO 3-x N y powder 0.50 g and Ni(C5H5)2(Tokyo Chemical Industry Co., Ltd., 98%) 0.08 g (5 mass% relative to BaTiO 3-x N y supported) was obtained. Next, 2.5 mL / min of hydrogen was circulated in the obtained quartz glass reaction tube, and after temperature elevation to 250°C over 0.5 hours, further maintained for 1.5 hours, thereby obtaining a support on which Ni was fixed (hereinafter, referred to as 5 mass% Ni / BaTiO 3-x N y ). 3-x N y ).

[0131] Using the aforementioned ammonia decomposition catalyst thus obtained, the following ammonia decomposition was performed.

[0132] [Ammonia decomposition using Ni supported BaTiO 3-x N y <Ammonia decomposition reaction> Using the 5 mass% Ni / BaTiO 3-x N y prepared in Comparative Example 1 as an ammonia decomposition catalyst, a reaction for purifying nitrogen and hydrogen by decomposing ammonia was performed. The reaction was performed using a fixed bed circulation type reaction apparatus equipped with a glass tube in which the aforementioned Ni support 0.1 g was packed as an ammonia decomposition catalyst. Before the reaction, nitrogen 5 mL / min and hydrogen 15 mL / min were circulated, and temperature elevation to 500°C was performed over 1 hour, and maintained for 1 hour, thereby performing pretreatment of the catalyst. In the ammonia decomposition reaction, the flow rate of ammonia gas was set to NH3: 25 mL / min (weight hourly space velocity (WHSV) 15000 mL g -1 h -1 ), and the reaction was performed at a reaction pressure of 0.1 MPa. The gas discharged from the aforementioned fixed bed circulation type reaction apparatus was recovered, and the components of the recovered gas were quantified by a gas chromatograph. The decomposition efficiency of ammonia (conversion rate of NH3) at 360°C to 660°C was measured. The results are shown in Table 1, Figure 3 .

[0133] (Comparative Example 2) [Ni supported CeO2] ​As the support, CeO2(Aldrich) was used instead of BaSiN2, and otherwise, using the same method as in Example 1, a support having Ni fixed on CeO2(hereinafter, referred to as 5 mass% Ni / CeO2) was obtained.

[0134] Using the aforementioned ammonia decomposition catalyst thus obtained, the following ammonia decomposition was performed.

[0135] [Ammonia decomposition using Ni-supported CeO2] <Ammonia decomposition reaction> Using the same method as in Example 1, except for using the 5 mass% Ni / CeO2 prepared in Example 2, a reaction for purifying nitrogen and hydrogen by decomposing ammonia was performed. The results are shown in Table 1, Figure 3

[0136] [Table 1] Reaction conditions: temperature: 500°C, gas pressure: 0.1 MPa, WHSV: 15000 mL g -1 h -1 (Investigation) From Table 1, Figure 3 and Figure 4 it was found that when a ternary nitride such as BaSiN2is used as a support, it can function as an excellent ammonia synthesis and decomposition catalyst. It also showed higher ammonia decomposition reaction activity compared to the titanium oxynitride BaTiO 3-x N y N2catalyst, and the oxide CeO2catalyst. Furthermore, in terms of ammonia decomposition catalysts that have the stability of catalyst characteristics even after repeated use in reactions after exposure to the atmosphere, it has an advantage compared to conventional oxohydrides and oxynitridohydrides.​

Claims

1. The barium nitride represented by the following general formula (1), Track 2-x (1) In the general formula (1), A is selected from at least one of the group consisting of Si, Fe, Ni, Mo and Zr, and x represents the numerical value of 0 ≤ x < 2.

0.

2. The barium nitride as described in claim 1, wherein, In the general formula (1), A is Si.

3. Metal support, which is a metal support on a carrier carrying a transition metal. The carrier contains the barium nitride as described in claim 1 or 2.

4. The metal support as described in claim 3, characterized in that, The transition metal is selected from at least one element from Groups 8, 9 and 10 of the periodic table.

5. The metal support as described in claim 3, characterized in that, The transition metal is selected from at least one of the group consisting of Ru, Ni, Fe and Co.

6. The metal support as described in claim 3, characterized in that, The transition metal is selected from at least one of the groups consisting of Ru and Ni.

7. An ammonia decomposition catalyst, comprising the barium nitride as described in claim 1 or 2.

8. An ammonia decomposition catalyst comprising the metal support as described in claim 3.

9. A method for producing hydrogen, comprising: The process of contacting the ammonia decomposition catalyst according to claim 7 with ammonia; and A process for recovering hydrogen produced by the process described above.

10. A method for producing hydrogen, comprising: The process of contacting the ammonia decomposition catalyst according to claim 8 with ammonia; and A process for recovering hydrogen produced by the process described above.

11. Use of the barium nitride according to claim 1 or 2 as a catalyst for ammonia decomposition.

12. Use of the metal support according to claim 3 as an ammonia decomposition catalyst.

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