Barium nitride, metal carrier, and ammonia decomposition catalyst

Abstract

Provided is an ammonia decomposition catalyst that has a high ammonia decomposition activity even at a low reaction temperature and a low reaction pressure, and has stable catalyst characteristics even when repeatedly used in reactions after being exposed to water or the atmosphere. A barium nitride according to the present invention is represented by general formula (1).　(1): BaAN2–x (In general formula (1), A is at least one type of element selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x represents a numerical value represented by 0≤x<2.0.)

Description

Barium nitride, metal support and ammonia decomposition catalyst

[0001] The present invention relates to barium nitride, a metal support, and an ammonia decomposition catalyst. This application claims priority to Japanese Patent Application No. 2023-124281, filed on July 31, 2023, the contents of which are incorporated herein by reference.

[0002] Ammonia decomposition is an endothermic reaction, and the higher the temperature, the more thermodynamically advantageous the product side becomes. According to Le Chatelier's principle, low pressure is advantageous to the product side. This is significantly different from ammonia synthesis, which is an exothermic reaction, in which lower temperatures are thermodynamically advantageous to the ammonia production side, and higher pressures are advantageous to the product side. In ammonia synthesis, generally, N ２ On the other hand, in ammonia decomposition, the N-H bond cleavage proceeds relatively easily, and atomic nitrogen species on the metal react with N ２ The process of molecular association and desorption is said to be the rate-determining step.

[0003] In the ammonia decomposition reaction, many catalysts in which Ni is fixed to oxides or carbon do not achieve an ammonia conversion rate of more than 90% until they are heated to a high temperature of, for example, 600° C. or higher. Such Ni-based catalysts have a reaction temperature range that is about 100° C. to 200° C. higher than that of Ru-based catalysts (see, for example, Patent Document 1).

[0004] On the other hand, it has been reported that ammonia can be decomposed even when a Ni-supported CaNH catalyst is used instead of Ru as the supported metal (see, for example, Non-Patent Document 1). This is thought to be because the Ni surface is not the active site, but rather the ammonia molecules are directly activated by electrons generated at NH defects on the support CaNH.

[0005] Japanese Patent Application Laid-Open No. 2019-167265

[0006] Ogasawara, Kiya et al. , “Ammonia Decomposition over CaNH-Supported Ni Catalysts via an NH2--Vacancy-Mediated Mars-van Krevlen Mechanism” ACS Catal. , 11, 17, p. 11005-11015 (2021)

[0007] The supported metal catalysts described in Patent Document 1 typically use a carbonaceous support such as activated carbon or an inorganic oxide support. However, these supported metal catalysts have low reaction activity, especially when the supported metal species is not Ru, and have performance that is insufficient for practical use. On the other hand, the Ni-supported metal catalyst described in Non-Patent Document 1 has high reaction activity, but the Ni-supported CaNH catalyst is unstable in the atmosphere and reacts with oxygen and moisture in the atmosphere, oxidizing and altering the CaNH. In other words, there is a need for an ammonia decomposition catalyst that has high ammonia decomposition activity even at low reaction temperatures and low reaction pressures and that maintains stable catalytic properties even when repeatedly used in reactions after exposure to the atmosphere or water.

[0008] The present inventors have discovered an ammonia decomposition catalyst that can achieve both improved reaction activity and stabilized catalytic properties by supporting a transition metal on barium nitride, and have arrived at the present invention.

[0009] That is, the gist of the present invention is as follows: [1] Barium nitride represented by the following general formula (1): BaAN ２－ｘ(1) (In the general formula (1), A is at least one selected from the group consisting of Si, Fe, Ni, Mo and Zr, and x is a number expressed as 0≦x<2.0.) [2] The barium nitride according to [1], in which A is Si in the general formula (1). [3] A metal-supported product in which a transition metal is supported on a carrier, wherein the carrier contains the barium nitride according to [1] or [2]. [4] The metal-supported product according to [3], characterized in that the transition metal is at least one selected from metal elements of groups 8, 9 and 10 of the periodic table. [5] The metal-supported product according to [3], characterized in that the transition metal is at least one selected from the group consisting of Ru, Ni, Fe and Co. [6] The metal-supported product according to [3], characterized in that the transition metal is at least one selected from the group consisting of Ru and Ni. [7] An ammonia decomposition catalyst containing the barium nitride according to [1] or [2]. [8] An ammonia decomposition catalyst containing the metal-supported material according to any one of [3] to [6]. [9] A method for producing hydrogen, comprising the steps of contacting the ammonia decomposition catalyst according to [7] with ammonia and recovering the hydrogen produced by the step.

[10] A method for producing hydrogen, comprising the steps of contacting the ammonia decomposition catalyst according to [8] with ammonia and recovering the hydrogen produced by the step.

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

[12] Use of the metal-supported material according to any one of [3] to [6] as an ammonia decomposition catalyst.

[0010] The ammonia decomposition catalyst of the present invention is suitable as an ammonia decomposition catalyst that has high ammonia decomposition activity even at low reaction temperatures and low reaction pressures, and that maintains stable catalytic properties even when repeatedly used in reactions after exposure to air or water.

[0011] BaSiN of Example 1 ２－ｘ 1 is a reaction formula showing the method for producing BaSiN synthesized in Example 1. ２－ｘFig. 1 is a diagram showing XRD results of the above. Fig. 2 is a graph showing the reaction temperature dependence of ammonia decomposition efficiency in Example 1 and Comparative Examples 1 and 2. Fig. 3 is a graph showing the reaction temperature dependence of ammonia decomposition efficiency in Examples 1 to 4.

[0012] [Barium Nitride] The barium nitride according to one embodiment of the present invention (this embodiment) is a barium nitride represented by the following general formula (1).

[0013] BaAN ２－ｘ (1)

[0014] In the general formula (1), A is at least one element selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x is a numerical value expressed as 0≦x<2.0, preferably 0≦x<1.0, and more preferably 0≦x<0.3.

[0015] In the general formula (1), A is preferably Si. That is, the barium nitride of the present embodiment is preferably a barium nitride represented by the general formula (2).

[0016] BaSiN ２－ｘ (2) In the general formula (2), x represents a numerical value expressed as 0≦x<2.0. It is preferable that x represents a numerical value expressed as 0≦x<1.0, and it is more preferable that x represents a numerical value expressed as 0≦x<0.3.

[0017] The amount of nitrogen contained in the barium nitride of the present invention is not particularly limited. Preferably, x is, for example, the valence of Ba + the valence of A + [the valence of N x(2-x)] = 0 so that the barium nitride is charge neutral.

[0018] Specific examples of the barium nitride of the present invention include BaSiN １．７８ , BaFe ０．３３ N, BaNiN, BaMo ０．３３ N １．３３ , BaZrN ２ etc.

[0019] <Method for producing barium nitride> The method for producing the barium nitride of the present invention represented by the following general formula (1) is a method for producing a barium nitride by annealing Ba in an argon or nitrogen atmosphere. ２ The method includes a step of heating N and a nitride or metal represented by the following general formula (3):

[0020] A ｓ N ｔ (3) (In the general formula (3), s represents a number from 1 to 3, and t represents a number from 0 to 4.)

[0021] In the general formula (3), A is at least one selected from the group consisting of Si, Fe, Ni, Mo, and Zr. Specific examples of the nitride represented by the general formula (3) include, for example, Si ３ N ４ , Fe ３ N ４ , Ni, Mo ２ Examples of such materials include N and ZrN.

[0022] In the general formula (3), A is preferably Si. That is, the barium nitride of this embodiment can be prepared by annealing Ba in an argon or nitrogen atmosphere. ２ N and Si ３ N ４ Preferably, the method includes a step of heating the above.

[0023] In the 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 even more preferably in the range of 800°C to 900°C. For example, in the examples described later, the heating temperature was 800°C. The 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 reaction vessel may be filled with argon or nitrogen, or argon or nitrogen may be flowed through the reaction vessel. The reaction time is not particularly limited, and is preferably 1 to 100 hours, more preferably 2 to 50 hours, and even more preferably 5 to 20 hours. For example, in the examples described later, the heating temperature was 800°C, and the reaction time was 20 hours.

[0024] Ba, which is a raw material for the manufacturing method of the present invention ２The nitride or metal represented by the general formula (3) may be commercially available products or may be produced by known methods. Examples of commercially available raw materials include Si, manufactured by Kojundo Chemical Co., Ltd. ３ N ４ (>99.9%), high-purity chemically produced Fe ３ N ４ (99.9%), Ni (99.9%) manufactured by Kojundo Chemical Co., Ltd., ZrN (98%) manufactured by Kojundo Chemical Co., Ltd., etc. On the other hand, raw materials produced by known methods include, for example, Ba ２ In the case of N, metallic Ba (99.99%) manufactured by Aldrich was used as the raw material. ２ Alternatively, the compound may be synthesized by heating at 600°C for 16 hours under an atmosphere. ２ In the case of N, MoO ３ (99.8%) as the raw material, and heating it at 700° C. for 15 hours in an ammonia stream.

[0025] The detailed manufacturing method will be described in each embodiment below. ２ and heating N and a nitride corresponding to the desired barium nitride in an argon or nitrogen atmosphere.

[0026] Examples of treatment conditions for the heating step include a method in which the material is heated under argon atmosphere at 600° C. to 1000° C. for 1 to 50 hours, preferably at 700° C. to 1000° C. for 2 to 30 hours, and more preferably at 800° C. to 900° C. for 5 to 20 hours. Alternatively, the material is heated in a nitrogen stream at 600° C. to 1000° C. for 1 to 50 hours, preferably at 700° C. to 1000° C. for 2 to 30 hours, and more preferably at 800° C. to 900° C. for 5 to 20 hours.

[0027] <Quantitative Determination of Nitrogen Contained in Barium Nitride> The barium nitride BaAN produced in this manner was ２－ｘ The amount of nitrogen in the sample can be determined by analyzing the above with, for example, a CHN elemental analyzer.

[0028] (Metal Supported Material) The metal supported material of one embodiment of the present invention (present embodiment) is a support having a transition metal supported thereon. The support is barium nitride represented by the following general formula (1).

[0029] BaAN ２－ｘ (1)

[0030] In the general formula (1), A is at least one element selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x is a number satisfying the formula 0≦x<2.0.

[0031] [Barium Nitride] The barium nitride contained in the metal support of this embodiment is preferably the barium nitride of this embodiment described above.

[0032] [Transition Metal] The transition metal used in this embodiment is not particularly limited, but is preferably at least one selected from metal elements of Groups 8, 9, and 10 of the periodic table. Specific metal elements are also not particularly limited, but examples include Cr, Mo, Mn, Re, Fe, Ru, Os, Co, Rh, Ni, Pd, and Pt. Mo, Re, Fe, Ru, Os, Co, and Ni are preferred because of their high bond energy with nitrogen, and Ru, Co, Fe, or Ni is more preferred. Ru is preferred because of its high reactivity. Furthermore, when economic efficiency is also important, for example, Ni, Co, and Fe are preferred. Each of the above elements may be used alone or in combination of two or more. Furthermore, intermetallic compounds of these elements, such as Co, ３ Mo ３ N, Fe ３ Mo ３ N, Ni ２ Mo ３ N, Mo ２ It is also possible to use N, etc. Preferably, each element is used alone or in combination of two or more kinds, and more preferably, each element is used alone, which is advantageous in terms of operability and cost in the production.

[0033] The amount of the transition metal supported is not particularly limited, but is usually 0.01 parts by mass (0.01% by mass) or more, preferably 0.5 parts by mass (0.5% by mass) or more, more preferably 1 part by mass (1% by mass) or more, and even more preferably 2 parts by mass (2% by mass) or more, relative to 100 parts by mass of the support. Also, it is usually 50 parts by mass (50% by mass) or less, preferably 40 parts by mass (40% by mass) or less, more preferably 30 parts by mass (30% by mass) or less, and even more preferably 20 parts by mass (20% by mass) or less. If it is equal to or greater than the lower limit, the effects of the present invention can be preferably obtained. On the other hand, if it is equal to or less than the upper limit, the effects of the present invention can be expected, with the amount supported being commensurate with the cost.

[0034] <Method for Supporting Transition Metal on Barium Nitride> The method for supporting a transition metal on barium nitride is not particularly limited. For example, the following steps (I) and (II) can be used to support BaAN. ２－ｘ A support in which a metal is fixed to the support (hereinafter referred to as M / BaAN) ２－ｘ (I) The powdered barium nitride (BaAN) represented by the general formula (1) obtained by the above method can be obtained. ２－ｘ (II) a step of heating the mixture obtained in the above step at 250°C for 0.5 to 4 hours in a gas atmosphere containing hydrogen to thermally decompose the metal compound.

[0035] For example, BaAN ２－ｘ and Ru, a compound of a transition metal such as Ru, Co, Fe, or Ni, is added to the support. ３ (CO) １２ , Co ２ (CO) ８、 Fe ２ (CO) ９ , Ni(C ５ H ５ ) ２ Using the metal support Ru-supported BaAN ２－ｘ (Ru / BaAN ２－ｘ ), Co-supported BaAN ２－ｘ (Co / BaAN ２－ｘ (abbreviated as 、 Fe-loaded BaAN ２－ｘ (Fe / BaAN ２－ｘ ), Ni-supported BaAN ２－ｘ(Ni / BaAN ２－ｘ The transition metal according to this embodiment is preferably a transition metal particle, and more preferably a transition metal nanoparticle having a particle size of 100 nm or less.

[0036] (Ammonia decomposition catalyst) An ammonia decomposition catalyst according to one embodiment of the present invention (this embodiment) comprises a support on which a transition metal is supported. The support contains barium nitride represented by the following general formula (1). It is also preferable that the support is barium nitride represented by the following general formula (1).

[0037] BaAN ２－ｘ (1)

[0038] In the general formula (1), A is at least one element selected from the group consisting of Si, Fe, Ni, Mo, and Zr, and x is a number satisfying the formula 0≦x<2.0.

[0039] [Barium Nitride] The barium nitride contained in the ammonia decomposition catalyst of this embodiment is preferably the barium nitride of this embodiment described above.

[0040] [Transition Metal] The transition metal used in this embodiment is the same as the transition metal used in the metal-supported material of this embodiment described above.

[0041] In the ammonia decomposition catalyst of this embodiment, the support may include the metal support of this embodiment described above. Alternatively, the support may be the metal support of this embodiment described above.

[0042] <Shape of ammonia decomposition catalyst> The shape of the ammonia decomposition catalyst of this embodiment is not particularly limited, and specifically may be any of a block, powder, film, etc. The particle size of the powdered metal support is not particularly limited, but is usually 1 nm or more and 10 μm or less. The particle size of the transition metal in the ammonia decomposition catalyst of this embodiment is not particularly limited, but is usually 1 nm or more and 100 nm or less. Preferably, it is 20 nm or less, since this increases the number of step sites, which are active sites for nitrogen dissociation, when used as an ammonia decomposition catalyst. More preferably, it is 10 nm or less.

[0043] <Method for producing an ammonia decomposition catalyst> The ammonia decomposition catalyst of the present invention is a catalyst in which a transition metal is supported on a carrier. ２－ｘ ) or the support includes the metal-supported material of this embodiment. The ammonia decomposition catalyst of this embodiment is produced by supporting the transition metal on the support. There are no particular limitations on the production method, but the ammonia decomposition catalyst is usually produced by supporting the transition metal or a compound that serves as a precursor of the transition metal (hereinafter referred to as a transition metal compound) on the support.

[0044] The raw material for the carrier, which is the raw material for the ammonia decomposition catalyst of this embodiment, may be a commercially available reagent or industrial raw material, or may be obtained from the corresponding metal by a known method.

[0045] The method for supporting a transition metal on the support used in this embodiment is not particularly limited, and any known method can be used. Usually, a method is used in which a transition metal compound that is a compound of the transition metal to be supported and that can be converted into the transition metal by reduction, thermal decomposition, or the like is supported on the support, and then the compound is converted into the transition metal.

[0046] The transition metal compound is not particularly limited, and inorganic compounds or organometallic complexes of transition metals that are easily thermally decomposed can be used. Specifically, transition metal complexes, transition metal oxides, and transition metal salts such as nitrates and hydrochlorides can be used.

[0047] For example, the Ru compound is triruthenium dodecacarbonyl [Ru ３ (CO)１２ ], dichlorotetrakis(triphenylphosphine)ruthenium(II) [RuCl ２ (PPh ３ ) ４ ], dichlorotris(triphenylphosphine)ruthenium(II) [RuCl ２ (PPh ３ ) ３ ], tris(acetylacetonato)ruthenium(III) [Ru(acac) ３ ], ruthenocene [Ru(C ５ H ５ ) )], ruthenium nitrosyl nitrate [Ru(NO)(NO ３ ) ３ ], potassium ruthenate, ruthenium oxide, ruthenium nitrate, ruthenium chloride, etc. Tris(acetylacetonato)ruthenium(III) [Ru(acac)] ３ ] is preferred.

[0048] For example, iron compounds include iron pentacarbonyl [Fe(CO) ５ ], triiron dodecacarbonyl [Fe ３ (CO) １２ ], iron nonacarbonyl [Fe ２ (CO) ９ ], tetracarbonyl iron iodide [Fe(CO) ４ I ２ ], tris(acetylacetonato)iron(III) [Fe(acac) ３ ], ferrocene [Fe(C ５ H ５ ) ２ ], iron oxide, iron nitrate, iron chloride (FeCl ３ ) etc.

[0049] Examples of Co compounds include cobalt octacarbonyl [Co ２ (CO) ８ ], tris(acetylacetonato)cobalt(III) [Co(acac) ３ ], cobalt(II) acetylacetonate [Co(acac) ２ ], cobaltocene [Co(C ５ H ５ ) ２], cobalt oxide, cobalt nitrate, cobalt chloride, etc.

[0050] The Ni compound is nickel acetate [Ni(OCOCH3) ２ ], nickel acetylacetonate [Ni(acac) ２ ], nickel chloride [NiCl ２ ], nickelocene [Ni(C ５ H ５ ) ２ ], nickel nitrate, etc. Among these transition metal compounds, [Ru ３ (CO) １２ ], [Fe(CO) ５ ], [Fe ３ (CO) １２ ], [Fe ２ (CO) ９ ], [Co ２ (CO) ８ ], [Ni(C ５ H ５ ) ２ When a carbonyl complex of a transition metal such as iron nitrate, cobalt nitrate, or nickel nitrate is used, the transition metal is supported by supporting it on the support and then heating. For this reason, the above carbonyl complexes of transition metals are preferred in that the reduction treatment described below can be omitted in producing the ammonia decomposition catalyst of this embodiment. Furthermore, when a nitrate of a transition metal such as iron nitrate, cobalt nitrate, or nickel nitrate is used, the transition metal is supported by impregnation in an aqueous solution and then heating. For this reason, the above nitrates of transition metals are preferred in that the method for producing the ammonia decomposition catalyst of this embodiment is simple and leads to cost reduction.

[0051] The amount of the transition metal compound used is not particularly limited, and can be appropriately used in an amount that achieves the desired loading amount.The lower limit of the amount of the transition metal compound used is, for example, 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, particularly preferably 20 parts by mass (20 mass%) or more, relative to 100 parts by mass of the carrier used.On the other hand, the upper limit of the amount of the transition metal compound used is, for example, 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.

[0052] Specific examples of the method for supporting the transition metal compound on the carrier include impregnation, physical mixing, CVD (chemical vapor deposition), and sputtering.

[0053] The physical mixing method is a method in which the support and the transition metal compound are mixed in a solid state, and then heated in a hydrogen-containing gas atmosphere (either gas filling or gas flow) or in a vacuum. The heating temperature is not particularly limited, but is usually 200° C. or higher and 600° C. or lower. The heating time is not particularly limited, but is usually 2 hours or longer.

[0054] If the transition metal compound is one that can be converted into a transition metal by thermal decomposition, the transition metal is usually supported on the support at this stage, resulting in the ammonia decomposition catalyst of this embodiment. When a transition metal compound other than one that can be converted into a transition metal by thermal decomposition is used, the transition metal compound is usually reduced to form the ammonia decomposition catalyst of this embodiment. The method for reducing the transition metal compound (hereinafter referred to as reduction treatment) is not particularly limited as long as it does not impede the object of the present invention, and examples thereof include the following two methods. (I) A method carried out in an atmosphere containing a reducing gas. (II) A method carried out in an atmosphere containing a reducing gas. (III) A method carried out in an atmosphere containing a reducing gas. (IV ... ４ , N.H. ２ NH ２or a reducing agent such as formalin, thereby depositing the compound on the surface of the metal hydride. A preferred example is a method in which the reduction is carried out in an atmosphere containing a reducing gas. Examples of the reducing gas include hydrogen, ammonia, methanol (vapor), ethanol (vapor), methane, and ethane. Furthermore, during the reduction treatment, components other than the reducing gas may coexist in the reaction system as long as they do not inhibit the object of the present invention, particularly the ammonia decomposition reaction. Specifically, during the reduction treatment, in addition to a reducing gas such as hydrogen, a gas such as argon or nitrogen that does not inhibit the reaction may coexist. Preferably, nitrogen is coexistent. When the reduction treatment is carried out in a gas containing hydrogen, the coexistence of nitrogen with hydrogen allows the reduction treatment to be carried out in parallel with the ammonia decomposition described below. That is, when the ammonia decomposition catalyst of this embodiment is used as the ammonia decomposition catalyst described below, the transition metal compound supported on the metal hydride may be subjected to reaction conditions for the ammonia decomposition reaction, thereby reducing the transition metal compound and converting it to a transition metal.

[0055] The temperature during the reduction treatment is not particularly limited, but is usually 200°C or higher, preferably 300°C or higher, and preferably less than 700°C. It is more preferably 400°C or higher and lower than 700°C. By performing the reduction treatment within the above temperature range, the transition metal can be grown sufficiently and within a preferred range. The pressure during the reduction treatment is not particularly limited, but is usually 0.01 MPa or higher and 10 MPa or lower. Setting the pressure during the reduction treatment to the same conditions as the ammonia decomposition conditions described below eliminates the need for complicated operations, which is advantageous in terms of production efficiency. The time period for the reduction treatment is not particularly limited, but when performed at atmospheric pressure, it is usually 1 hour or longer, preferably 2 hours or longer. Furthermore, when performed under high reaction pressure conditions (e.g., 1 MPa or higher), 1 hour or longer is preferred.

[0056] When a transition metal compound other than one that is converted into a transition metal by thermal decomposition is used, the transition metal compound contained in the solid mixture is reduced by a conventional method, as in the above-described reduction treatment method, to obtain the ammonia decomposition catalyst of this embodiment.

[0057] As a component other than the barium nitride and the transition metal, carbonaceous materials such as activated carbon and inorganic oxides may be further contained as a support for the barium nitride.

[0058] The ammonia decomposition catalyst of this embodiment can be used as a molded body using a conventional molding technique. Specific examples include granular, spherical, tablet, ring, macaroni, four-leaf, cube, honeycomb, and other shapes. It can also be used after being coated on a suitable support.

[0059] When using the ammonia decomposition catalyst of this embodiment, its reaction activity is not particularly limited. For example, when the weight hourly space velocity (WHSV) of the supplied ammonia gas is 15,000 mL g －１ h －１ When using the above, the hydrogen production rate at a reaction temperature of 500 ° C. and a reaction pressure of 0.1 MPa is taken as an example. －１ h －１ It is preferable that the amount is 500 mmol g or more. －１ h －１ More preferably, it is 700 mmol g or more. －１ h －１ More preferably, it is 750 mmol g or more. －１ h －１ It is most preferable that the hydrogen production rate is 500 mmol g or more. －１ h －１ The hydrogen production rate is 700 mmol g or more, which is suitable for practical production conditions. －１ h －１ A hydrogen production rate of 750 mmol g or more is suitable for more efficient production conditions. －１ h －１ The above conditions are suitable for more efficient production conditions. Of course, if the weight hourly space velocity (WHSV) is increased, the hydrogen production rate suitable for practical production conditions can also be increased accordingly.

[0060] The method for producing ammonia using the ammonia decomposition catalyst of this embodiment will be described below.

[0061] (Method for Producing Hydrogen) Hereinafter, a method for producing hydrogen by decomposing ammonia using the ammonia decomposition catalyst of this embodiment will be described.

[0062] A method for producing hydrogen according to one embodiment of the present invention (hereinafter, sometimes referred to as a method for producing hydrogen according to this embodiment) involves continuously supplying ammonia gas at a volume fraction of 0.1% to 100% to a catalyst layer made of the ammonia decomposition catalyst according to this embodiment, and carrying out the reaction at a weight hourly space velocity (WHSV) of 500 mL / g at a reaction pressure of 0.01 MPa to 1.0 MPa and a reaction temperature of 300°C to 800°C. －１ h －１ In the hydrogen production method of this embodiment, the ammonia decomposition catalyst of this embodiment is used as a catalyst, and ammonia is decomposed by reacting on the catalyst to produce hydrogen and nitrogen. This reaction is represented by the following formula (A): 2NH ３ →3H ２ +N ２ ... (A) The specific production method is not particularly limited as long as it involves contacting ammonia on the catalyst to decompose it and generate hydrogen, and production can be carried out in accordance with any known production method.

[0063] In the hydrogen production method of the present invention, hydrogen and nitrogen are typically produced by heating the catalyst when ammonia is brought into contact with the catalyst. The reaction temperature in the production method of the present invention is not particularly limited, but is typically 300°C or higher, preferably 350°C or higher, more preferably 400°C or higher, and typically 800°C or lower, preferably 600°C or lower, more preferably 500°C or lower. Because the ammonia decomposition reaction is an equilibrium and endothermic reaction, a higher temperature range is advantageous. However, to obtain a sufficient ammonia decomposition reaction rate, it is preferable to carry out the reaction within the above-mentioned temperature range. This is because the decomposition reaction proceeds sufficiently within the above-mentioned temperature range, and is also advantageous in terms of equipment. When Ru is used as the transition metal according to this embodiment, the reaction temperature is more preferably 400°C or higher and 600°C or lower. Similarly, when Ni or Co is used, the reaction temperature is more preferably 500°C or higher and 750°C or lower.

[0064] The reaction pressure in the hydrogen production method of the present invention is not particularly limited, but is usually 0.01 MPa or more, preferably 0.05 MPa or more, and usually 1.0 MPa or less, preferably 0.5 MPa or less, and more preferably 0.1 MPa or less. Since the ammonia decomposition reaction is an equilibrium reaction and a reaction in which the volume increases, low-pressure conditions are advantageous, but in order to obtain a sufficient ammonia decomposition reaction rate, it is preferable to carry out the reaction within the above pressure range. Furthermore, in terms of equipment, it is advantageous to carry out the reaction at 0.1 MPa.

[0065] The ammonia used in the hydrogen production method of the present invention is not particularly limited, and may be either ammonia alone or ammonia diluted with a balance gas. That is, ammonia gas with a volume fraction of 1 ppm to 100% can be used. In the hydrogen production method of the present invention, when recovering hydrogen produced by contacting the catalyst with ammonia, the hydrogen may be recovered in the presence of nitrogen, or hydrogen may be recovered in an ultra-rich state or substantially in the form of hydrogen only, using a known method. In the hydrogen production method of the present invention, in order to recover hydrogen by separating the produced hydrogen and nitrogen, the ammonia volume fraction is preferably high, and is preferably 5% or more, more preferably 20% or more, and even more preferably 70% or more. The weight hourly space velocity (WHSV) of ammonia is not particularly limited, but is usually 500 mL g －１ h －１ By carrying out the above, high NH ３ The conversion is obtained.

[0066] In the hydrogen production method of the present invention, it is preferable to activate the transition metal, which is a catalytically active component, by exposing the catalyst to an atmosphere of a reducing gas such as hydrogen before contacting ammonia with the catalyst, in order to improve conversion. The temperature during the exposure is not particularly limited, but is usually 300°C or higher and 700°C or lower. The exposure time is not particularly limited, but is usually 30 minutes or higher and 2 hours or lower.

[0067] In the hydrogen production method of the present invention, the type of reaction vessel is not particularly limited, and a reaction vessel typically used for ammonia decomposition reactions can be used. Specific reaction types include batch reaction types, closed circulation reaction types, and flow-through reaction types, among which flow-through reaction types are preferred from a practical standpoint. Because the ammonia decomposition reaction is an endothermic reaction, it is advantageous to carry out the reaction while supplying reaction heat. Industrially, known methods for supplying reaction heat can be used to increase yield. For example, a method can be used in which the ammonia decomposition reaction is carried out while oxidizing a portion of the ammonia raw material with air to obtain combustion heat. Furthermore, the material of the reaction vessel is not particularly limited, and known materials for ammonia decomposition reactions can be used. For example, a typical gas-solid phase contact reaction apparatus made of a corrosion-resistant material such as stainless steel can be used.

[0068] In the present invention, the ammonia decomposition reaction can be carried out using a single reactor or multiple reactors filled with a catalyst, as in conventional methods. Also, a method in which multiple reactors are connected together or a reactor having multiple reaction layers within the same reactor can be used.

[0069] The present invention will be described in more detail below based on examples. ３ The conversion rate of ammonia was determined by gas chromatography to determine the ammonia decomposition efficiency (NH ３ Conversion rate (NH ３ Conversion (%) was evaluated.

[0070] (Gas Chromatography (GC) Analysis) The amount of hydrogen produced in the following Examples and Comparative Examples was determined by gas chromatography (GC) analysis using an absolute calibration curve method. The measurement conditions were as follows.

[0071] [Measurement conditions] Measurement device: GC14A (Shimadzu) Column: PoraPakQS Column temperature: 80°C Carrier gas: He Gas detector: TCD

[0072] (XRD Measurement) X-ray diffraction of the material was measured using a Bruker D2 Phaser with a Cu Kα X-ray source. Voltage: 40 kV Current: 40 mA

[0073] Example 1 [BaSiN ２ Manufacture of] Aldrich's metallic Ba (99.99%) was used as a raw material. ２ Ba synthesized by heating at 600°C for 16 hours under atmospheric pressure ２ N powder and Si ３ N ４ The mixture was mixed with BaSiN powder (manufactured by Kojundo Chemical, >99.9%) in a glove box at a molar ratio of 1:[2 / 3]. The resulting mixture was then filled into a quartz glass tube, which was then filled with argon gas and sealed. The quartz glass tube was then fired in an electric furnace at 800°C for 20 hours. This resulted in BaSiN ２ Powder was obtained. ２ The XRD evaluation results of the powder are shown in Figure 2. ２ The XRD peaks of BaSiN ２ The XRD peak shifts to a larger diffraction angle compared to that of the lattice N ３― We speculate that this is due to a defect in the

[0074] [BaSiN ２ Supporting Ni on BaSiN powder synthesized in this example ２ 0.3g and Ni(C ５ H ５ ) ２ (Tokyo Chemical Industry Co., Ltd., 98%) 0.051 g (BaTiO ３－ｘ N ｙ The resulting mixture (corresponding to 5% by mass of supported Ni metal relative to the total mass of the reaction mixture) was placed in a quartz glass reaction tube. Then, hydrogen was passed through the resulting quartz glass reaction tube at 2.5 mL / min, and the temperature was raised to 250°C for 0.5 hours, and then maintained at that temperature for a further 1.5 hours to obtain BaSiN ２ Ni-immobilized support (hereinafter referred to as Ni / BaSiN ２ Using the ammonia decomposition catalyst thus obtained, the following ammonia decomposition was carried out.

[0075] [Ni-supported BaSiN ２ Ammonia decomposition reaction: Ammonia decomposition reaction using 5 mass % Ni / BaSiN prepared in Example 1 ２ As an ammonia decomposition catalyst, a reaction was carried out to generate nitrogen and hydrogen by decomposing ammonia. The reaction was carried out in a fixed-bed flow reactor equipped with a glass tube packed with 0.1 g of the Ni-supported material as an ammonia decomposition catalyst. Prior to the reaction, nitrogen was passed through at 5 mL / min and hydrogen at 15 mL / min, and the temperature was raised to 500°C for 1 hour, and then maintained at that temperature for another 1 hour, thereby pretreating the catalyst. In the ammonia decomposition reaction, the flow rate of ammonia gas was NH ３ : Set to 25 mL / min (weight hourly space velocity (WHSV) 15000 mL g －１ h －１ The reaction was carried out under the conditions of a reaction pressure of 0.1 MPa. The gas coming out of the fixed-bed flow reactor was recovered, and the components of the recovered gas were quantified by gas chromatography. The ammonia decomposition efficiency (NH ３ The results are shown in Table 1 and Figure 3.

[0076] In addition, Ni-supported BaSiN ２ In order to evaluate the atmospheric stability of the 5 mass % Ni / BaSiN prepared in Example 1, ２ After exposing the sample to the atmosphere for 1 hour, the catalytic properties of the sample were confirmed by XRD evaluation and evaluation of basic performance as a catalyst, and it was confirmed that the catalytic properties were equivalent to those of the sample before exposure to the atmosphere, making it clear that the catalyst has stable catalytic properties.

[0077] Example 2

[0078] [BaSiN ２ Supporting Ru on Ni(C ５ H ５ ) ２ Instead of Ru ３ (CO) １２ BaSiN (manufactured by Aldrich, 99%) was used in the same manner as in Example 1. ２ Ru is fixed to the support (hereinafter referred to as Ru / BaSiN ２Using the ammonia decomposition catalyst thus obtained, the following ammonia decomposition was carried out.

[0079] [Ru-supported BaSiN ２ Ammonia decomposition reaction: Ammonia decomposition reaction using 5 mass % Ru / BaSiN prepared in Example 2 ２ A reaction to generate nitrogen and hydrogen by decomposing ammonia was carried out in the same manner as in Example 1, except that the following was used: The results are shown in Table 1 and FIG.

[0080] Example 3

[0081] [BaSiN ２ Co loading on Ni(C ５ H ５ ) ２ Instead of Co ２ (CO) ８ The same method as in Example 1 was used except that BaSiN (manufactured by Tokyo Chemical Industry Co., Ltd., >95%) was used. ２ Co-immobilized support (hereinafter referred to as 5 mass% Co / BaSiN ２ Using the ammonia decomposition catalyst thus obtained, the following ammonia decomposition was carried out.

[0082] [Co-supported BaSiN ２ Ammonia decomposition reaction: Ammonia decomposition reaction was carried out using the 5 mass % Co / BaSiN prepared in Example 2. ２ A reaction to produce nitrogen and hydrogen by decomposing ammonia was carried out in the same manner as in Example 1, except that the following was used: The results are shown in Table 1 and FIG.

[0083] Example 4

[0084] [BaSiN ２ Supporting Fe on Ni(C ５ H ５ ) ２ Instead of Fe ２ (CO) ９ BaSiN (manufactured by Aldrich, 98%) was used in the same manner as in Example 1. ２ A support in which Fe is fixed to the support (hereinafter referred to as 5 mass% Fe / BaSiN ２Using the ammonia decomposition catalyst thus obtained, the following ammonia decomposition was carried out.

[0085] [Fe-supported BaSiN ２ Ammonia decomposition reaction: Ammonia decomposition reaction using 5 mass % Fe / BaSiN prepared in Example 2 ２ A reaction to produce nitrogen and hydrogen by decomposing ammonia was carried out in the same manner as in Example 1, except that the following was used: The results are shown in Table 1 and FIG.

[0086] (Comparative Example 1) [BaTiO ３－ｘ H ｚ Commercially available TiO ２ powder (Aldrich, 99.5%) and BaH ２ The powder was mixed in a glove box so that the molar ratio was 1:1. The resulting mixture was then filled into a quartz glass tube, and hydrogen gas was injected into the quartz glass tube at a rate of 10 mL min －１ The mixture was fired in an electric furnace at 800°C for 20 hours while circulating air. As a result, BaTiO ２．０１ H ０．９６ A powder was obtained.

[0087] [BaTiO ３－ｘ N ｙ Preparation of Powder] BaTiO obtained in Comparative Example 1 ３－ｘ H ｚ The powder was heated to 600°C in 1 hour in a nitrogen gas flow (pressure: 0.1 MPa) at a flow rate of 10 mL / min, and then heat-treated at 600°C for 12 hours to obtain BaTiO ３－ｘ N ｙ A powder was obtained.

[0088] [BaTiO ３－ｘ N ｙ Supporting Ni on BaTiO ３－ｘ N ｙ Powder 0.50 g and Ni(C ５ H ５ ) ２ (Tokyo Chemical Industry Co., Ltd., 98%) 0.08 g (BaTiO ３－ｘ N ｙThe resulting mixture (corresponding to 5% by mass of supported Ni metal relative to the total mass of the reaction mixture) was placed in a quartz glass reaction tube. Then, hydrogen was passed through the resulting quartz glass reaction tube at a rate of 2.5 mL / min, and the temperature was raised to 250°C for 0.5 hours, and then maintained at this temperature for a further 1.5 hours to obtain BaTiO ３－ｘ N ｙ Ni-immobilized support (hereinafter referred to as 5 mass% Ni / BaTiO ３－ｘ N ｙ Using the ammonia decomposition catalyst thus obtained, the following ammonia decomposition was carried out.

[0089] [Ni-supported BaTiO ３－ｘ N ｙ Ammonia decomposition reaction: 5 mass % Ni / BaTiO prepared in Comparative Example 1 ３－ｘ N ｙ As an ammonia decomposition catalyst, a reaction was carried out to purify nitrogen and hydrogen by decomposing ammonia. The reaction was carried out in a fixed-bed flow reactor equipped with a glass tube packed with 0.1 g of the Ni-supported material as an ammonia decomposition catalyst. Prior to the reaction, nitrogen was passed through at 5 mL / min and hydrogen at 15 mL / min, and the temperature was raised to 500°C for 1 hour and maintained at that temperature for 1 hour, thereby pretreating the catalyst. In the ammonia decomposition reaction, the flow rate of ammonia gas was NH ３ : Set to 25 mL / min (weight hourly space velocity (WHSV) 15000 mL g －１ h －１ The reaction was carried out at a reaction pressure of 0.1 MPa. The gas coming out of the fixed-bed flow reactor was recovered, and the components of the recovered gas were quantified by gas chromatography. The ammonia decomposition efficiency (NH ３ The results are shown in Table 1 and Figure 3.

[0090] (Comparative Example 2) [CeO ２ Supporting Ni on BaSiN ２ Instead of CeO ２ CeO was prepared in the same manner as in Example 1, except that CeO (manufactured by Aldrich) was used. ２ Ni-immobilized support (hereinafter referred to as 5 mass% Ni / CeO ２Using the ammonia decomposition catalyst thus obtained, the following ammonia decomposition was carried out.

[0091] [Ni-supported CeO ２ Ammonia decomposition reaction: Ammonia decomposition reaction using 5 mass % Ni / CeO prepared in Example 2 ２ A reaction for purifying nitrogen and hydrogen by decomposing ammonia was carried out in the same manner as in Example 1, except that the following was used: The results are shown in Table 1 and FIG.

[0092] *Reaction conditions: Temperature: 500°C, Pressure: 0.1 MPa, WHSV: 15,000 mL g －１ h －１

[0093] (Discussion) From Table 1, Figs. 3 and 4, BaSiN ２ We have found that the use of this ternary nitride as a support functions as an excellent catalyst for ammonia synthesis and decomposition. ３－ｘ N ｙ catalysts and oxides CeO ２ The catalyst exhibits high ammonia decomposition activity compared to conventional catalysts. Furthermore, the catalyst exhibits stability in catalytic properties even when repeatedly used in reactions after exposure to the atmosphere, making it superior to conventional acid hydrides and acid nitrogen hydrides.

Claims

1. Barium nitride represented by the following general formula (1): BaAN ２－ｘ (1) (In the general formula (1), A is at least one selected from the group consisting of Si, Fe, Ni, Mo and Zr, and x is a numerical value expressed as 0≦x<2.0.) 2. The barium nitride according to claim 1, wherein in said general formula (1), A is Si.

3. A metal-supported material comprising a support and a transition metal supported thereon, the support containing the barium nitride according to claim 1 or 2.

4. The metal support according to claim 3, wherein the transition metal is at least one selected from the group consisting of metal elements of groups 8, 9 and 10 of the periodic table.

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

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

7. An ammonia decomposition catalyst comprising the barium nitride according to claim 1 or 2.

8. An ammonia decomposition catalyst comprising the metal support according to claim 3.

9. A method for producing hydrogen, comprising the steps of contacting the ammonia decomposition catalyst according to claim 7 with ammonia, and recovering the hydrogen produced by said step.

10. A method for producing hydrogen, comprising the steps of contacting the ammonia decomposition catalyst according to claim 8 with ammonia, and recovering the hydrogen produced by said step.

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

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

Images