Catalyst for ammonia synthesis

Abstract

The present invention relates to: a catalyst precursor for ammonia synthesis, the catalyst precursor including a nitrogen activation catalyst precursor loaded body (A1) in which a precursor of a catalyst component for activating nitrogen is supported by a carrier that is composed of a porous body that has a specific surface area of 1,000 m2 / g or more, and a hydrogen activation catalyst precursor loaded body (B1) in which a precursor of a catalyst component for activating hydrogen is supported by a carrier that is different from the above-described carrier; and a catalyst for ammonia synthesis obtained by activating the catalyst precursor.

Description

Ammonia synthesis catalyst

[0001] The present invention relates to a catalyst precursor for ammonia synthesis, a catalyst for ammonia synthesis, methods for producing them, and a method for producing ammonia using the catalyst for ammonia synthesis.

[0002] Technologies for fixing and utilizing nitrogen atoms are extremely important in industrial fields, including agriculture. Nitrogen atom fixation is known in nature, for example, through nitrogen fixation by rhizobia. Industrially, however, it is primarily carried out by the Haber-Bosch process and utilized for ammonia synthesis. However, because the Haber-Bosch process uses a stable iron catalyst, it can only be carried out efficiently under extremely high-temperature and high-pressure conditions. Therefore, there is a strong demand for an alternative to the Haber-Bosch process, which can synthesize ammonia under milder conditions. As such technologies, ammonia synthesis catalysts using transition metals other than iron and ammonia synthesis methods using such catalysts have been proposed in recent years. For example, Reference 1 discloses an ammonia synthesis catalyst in which a halide cluster using a transition metal atom belonging to Group V, Group VI, or Group VII is supported on a carrier.

[0003] International Publication No. 2018 / 164182

[0004] However, the catalyst described in Patent Document 1 is a complex catalytic system, and its activity as a catalyst for ammonia synthesis is not necessarily sufficient, so further improvement is required for industrial application.

[0005] An object of the present invention is to provide an ammonia synthesis catalyst and a precursor thereof that can synthesize ammonia in a relatively mild environment and have high catalytic activity suitable for industrial application.

[0006] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention encompasses the following preferred embodiments: [1] A specific surface area of ​​1000 m ２A catalyst precursor for ammonia synthesis comprising: a supported body (A1) of a nitrogen-activating catalyst precursor in which a precursor of a catalytic component that activates nitrogen is supported on a support made of a porous material having a molecular weight of 1000 or more; and a supported body (B1) of a hydrogen-activating catalyst precursor in which a precursor of a catalytic component that activates hydrogen is supported on a support different from the support. [2] The catalyst precursor for ammonia synthesis according to [1] above, wherein the support made of a porous material has a ratio of iodine adsorption to methylene blue adsorption (iodine adsorption / methylene blue adsorption) of 10 or less. [3] The catalyst precursor for ammonia synthesis according to [1] above or [2] above, wherein the precursor of the catalytic component that activates nitrogen is a metal complex containing at least one metal atom belonging to Group V, Group VI, or Group VII. [4] The catalyst precursor for ammonia synthesis according to any one of [1] to [3], wherein the precursor of the catalytic component that activates nitrogen contains at least one metal atom selected from the group consisting of molybdenum (Mo), niobium (Nb), tungsten (W), tantalum (Ta), and rhenium (Re). [5] The catalyst precursor for ammonia synthesis according to [3], wherein the metal complex is a binuclear metal complex containing at least three metal atoms selected from the group consisting of molybdenum (Mo), niobium (Nb), tungsten (W), tantalum (Ta), and rhenium (Re). [6] The catalyst precursor for ammonia synthesis according to any one of [1] to [5], wherein the porous support is a carbonaceous material. [7] The catalyst precursor for ammonia synthesis according to any one of [1] to [6], wherein the precursor of the catalytic component that activates hydrogen contains at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt). [8] The catalyst precursor for ammonia synthesis according to any one of [1] to [7], wherein the support that supports the precursor of the catalytic component that activates hydrogen is a porous inorganic material or a layered compound.[9] The catalyst precursor for ammonia synthesis according to [8] above, wherein the inorganic material comprises at least one selected from the group consisting of carbon, boron nitride, carbon nitride, silica, alumina, aluminosilicate, sodium aluminosilicate, aluminum magnesium hydroxide carbonate, titania, titanosilicate, zirconia, zirconosilicate, zinc oxide, and ceria.

[10] A method for producing the catalyst precursor for ammonia synthesis according to any of [1] to [9] above, comprising: forming a supported body (A1) of a nitrogen-activating catalyst precursor in which the precursor of the catalytic component for activating nitrogen is supported on a support made of a porous material by supporting a precursor of the catalytic component for activating nitrogen on the support; and mixing the supported body (A1) with a supported body (B1) of a hydrogen-activating catalyst precursor in which a precursor of the catalytic component for activating hydrogen is supported on a support different from the support made of a porous material.

[11] The method according to the above

[10] , wherein the precursor of the catalytic component that activates nitrogen is a polynuclear metal complex having at least three metal atoms, and the precursor of the catalytic component that activates hydrogen is a metal compound containing a metal.

[12] A specific surface area of ​​1000 m is 1000 m. ２

[13] A catalyst for ammonia synthesis comprising: a nitrogen-activating catalyst supporter (A2) in which a catalytic component for activating nitrogen is supported on a carrier made of a porous material having a molecular weight of 1000 or more; and a hydrogen-activating catalyst supporter (B2) in which a catalytic component for activating hydrogen is supported on a carrier different from the carrier.

[13] A method for producing the catalyst for ammonia synthesis according to

[12] above, comprising contacting the catalyst precursor for ammonia synthesis according to any one of [1] to [9] above with hydrogen molecules.

[14] A method for producing ammonia, comprising contacting the catalyst for ammonia synthesis according to

[12] above with a mixed gas containing nitrogen and hydrogen.

[0007] According to the present invention, it is possible to provide an ammonia synthesis catalyst and its precursor which can synthesize ammonia in a relatively mild environment and have high catalytic activity suitable for industrial application.

[0008] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0009] <Catalyst Precursor for Ammonia Synthesis> (Support of Nitrogen-Activated Catalyst Precursor) The catalyst precursor for ammonia synthesis of the present invention includes a support (A1) of the nitrogen-activated catalyst precursor (hereinafter also referred to as "support (A1)") in which a precursor of a catalytic component that activates nitrogen (hereinafter also referred to as "nitrogen-activated catalyst precursor") is supported on a support. In this specification, the nitrogen-activated catalyst precursor means a substance that exhibits catalytic activity as a nitrogen-activating catalyst by undergoing an appropriate activation treatment, for example, activation with hydrogen molecules, as described below. The support (A1) refers to a substance that includes a nitrogen-activated catalyst precursor and a support, and in which the catalyst precursor is supported on the support. A chemical bond may or may not be formed between the nitrogen-activated catalyst precursor and the support.

[0010] In the present invention, the nitrogen-activating catalyst precursor contained in the support (A1) may include various metal atoms that can function as a nitrogen-activating catalyst after activation treatment. Among these, the nitrogen-activating catalyst precursor preferably contains at least one metal atom belonging to Group V, Group VI, or Group VII of the periodic table, since this allows for the formation of a metal complex or metal cluster suitable for the present invention, as described below. Examples of transition metal atoms belonging to Group V include V (vanadium), Nb (niobium), and Ta (tantalum). Examples of transition metal atoms belonging to Group VI include Cr (chromium), Mo (molybdenum), and W (tungsten). Examples of transition metal atoms belonging to Group VII include Re (rhenium). Among these, it is more preferable for the nitrogen-activating catalyst precursor to contain at least one metal atom selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium. By including these metal atoms in the nitrogen-activating catalyst precursor, it is possible to obtain an ammonia synthesis catalyst with excellent thermal stability and catalytic activity. These metal atoms may be used alone or in combination of two or more.

[0011] In the present invention, when the nitrogen-activating catalyst precursor contains the above-mentioned metal atoms, the nitrogen-activating catalyst precursor is typically a metal complex containing such metal atoms. Here, as described above, the ammonia synthesis catalyst precursor is in a state prior to the activation treatment for developing catalytic activity. When the nitrogen-activating catalyst precursor contains metal atoms, the terms "metal complex" and "multinuclear metal complex" as the nitrogen-activating catalyst precursor refer to a composite state in which metal atoms and ligands are bonded (e.g., halide clusters). Furthermore, in this specification, "metal complex" refers to a compound that forms a metal complex molecule, and is distinguished from compounds such as metal oxides that do not form metal complex molecules. For example, as described below, metal clusters can be formed by removing ligands from a metal complex on a support. Metal clusters function as the nitrogen-activating catalyst component in the ammonia synthesis catalyst. The term "metal cluster" refers to a metal material having a nanocluster structure formed by direct bonding of core metal atoms to each other.

[0012] In one embodiment of the present invention, the nitrogen-activated catalyst precursor is preferably a metal complex containing at least one metal atom belonging to Group V, Group VI, or Group VII of the periodic table, more preferably a metal complex containing at least one metal atom selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium. From the viewpoint of forming a catalyst that can maintain high catalytic activity and can be stably stored in air, the metal atom is more preferably selected from the group consisting of molybdenum, niobium, tungsten, and tantalum, with molybdenum or tungsten being particularly preferred, and molybdenum being especially preferred.

[0013] The metal complex may be a mononuclear metal complex containing one metal atom per molecule, or a polynuclear metal complex containing multiple metal atom nuclei per molecule. In one embodiment of the present invention, the nitrogen-activating catalyst component is preferably a polynuclear metal complex because it has many nitrogen-activating sites and can maintain high catalytic activity. When the nitrogen-activating catalyst precursor is a polynuclear metal complex formed from a polynuclear metal complex, the number of nuclei constituting the polynuclear metal complex, i.e., the number of metal atoms contained in one molecule, can be determined appropriately depending on the type of metal atoms constituting the metal complex and the type of support supporting the metal complex, but is preferably at least three. When the metal complex has at least three metal atoms, a nanocluster structure consisting only of metal atoms can be suitably formed. If the number of metal atoms is too small, the metal cluster formed will be small, which tends to result in fewer nitrogen-activating sites or reduced stability. Furthermore, if the number of metal atoms is large and the metal cluster formed is too large, it will be more susceptible to metallization by thermal reduction, which tends to result in fewer nitrogen-activating sites. From the viewpoint of ensuring a sufficient number of sites for activating nitrogen, the number of metal atoms (number of nuclei) in the metal complex is preferably 3 to 200, more preferably 3 to 20. Furthermore, since higher catalytic activity can be expected, the polynuclear metal complex preferably contains at least three metal atoms belonging to Group V, Group VI, or Group VII of the periodic table, more preferably at least three metal atoms selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium.

[0014] In the present invention, the nitrogen-activated catalyst precursor has a specific surface area of ​​1000 m ２ The specific surface area of ​​the carrier is 1000 m / g or more. ２ / g or more, the nitrogen-activated catalyst precursor can be supported on the support in an appropriate size, and the catalytic activity of the resulting catalyst in ammonia synthesis is improved. In particular, when the nitrogen-activated catalyst precursor is a metal complex (particularly a polynuclear metal complex), the support having a relatively large specific surface area is excellent in preventing the catalyst precursor, such as a polynuclear metal complex, from agglomerating and adhering to the support. From the viewpoint of further enhancing the above-mentioned effect, the specific surface area of ​​the support (porous body) supporting the nitrogen-activated catalyst precursor in the present invention is preferably 1100 m ２ / g or more, more preferably 1200m ２ / g or more, more preferably 1200m ２ / g, particularly preferably 1250m ２ From the viewpoint of the mechanical strength and stability of the support (A1), the specific surface area of ​​the carrier (porous body) is preferably 5000 m ２ / g or less, more preferably 4000m ２ / g or less, more preferably 3000m ２ In one embodiment of the present invention, the specific surface area of ​​the support (porous body) supporting the nitrogen-activated catalyst precursor is preferably 1000 to 5000 m ２ / g, more preferably 1200 to 4000m ２ / g, more preferably 1250 to 3000m ２ / g. In this specification, the specific surface area means "BET specific surface area." The BET specific surface area can be calculated by a nitrogen adsorption method. In detail, it can be calculated, for example, by the method described in the examples below.

[0015] Examples of carriers for supporting the nitrogen-activated catalyst precursor include porous inorganic materials. Specific examples include carbonaceous materials such as activated carbon, boron nitride, carbon nitride, silica (silicon oxide), alumina (aluminum oxide), zeolite (aluminosilicate or sodium aluminosilicate), aluminum hydroxide magnesium carbonate, titania (titanium oxide), titanosilicate, zirconia (zirconium oxide), zirconosilicate, zinc oxide, and ceria (cerium oxide). Materials that exist as natural or synthetic materials, such as zeolites, may be used. These carriers may be used alone or in combination of two or more. Among these, porous inorganic materials are preferred. Furthermore, from the viewpoint of the stability of the carrier and the nitrogen-activated catalyst precursor at high temperatures, the carrier is preferably selected from the group consisting of carbonaceous materials, silica, alumina, zeolite, zirconia, titania, and ceria, more preferably selected from the group consisting of carbonaceous materials, silica, titania, and ceria, and even more preferably a carbonaceous material.

[0016] The support supporting the nitrogen-activated catalyst precursor preferably has a ratio of iodine adsorption to methylene blue adsorption (iodine adsorption / methylene blue adsorption, hereinafter also referred to as "iodine value / MB value") of 10 or less. The iodine value / MB value reflects the ratio of micropores to mesopores in the support. When the iodine value / MB value is 10 or less, it is easy to support the nitrogen-activated catalyst precursor on the support at an appropriate size, and the catalytic activity of the resulting catalyst in ammonia synthesis can be improved. In particular, when the porous body has more micropores than mesopores, it is effective in preventing catalyst precursors such as dinuclear metal complexes from agglomerating and adhering to the support. Note that micropores refer to pores less than about 2 nm, and mesopores refer to pores with a size of about 2 to 50 nm.

[0017] In one embodiment of the present invention, the iodine value / MB value is preferably 1.1 to 10, more preferably 1.5 to 9, and even more preferably 2 to 8. When the iodine value / MB value is within the above range, the catalyst precursor, such as a polynuclear metal complex, can be maintained independently attached to the support. This allows for maintaining the contact efficiency between the reaction medium and the catalyst precursor or the activated catalyst component. Therefore, an ammonia synthesis catalyst that is less likely to sinter and can maintain a high catalytic effect can be obtained. In the present invention, when the support supporting the nitrogen-activated catalyst precursor has the specific surface area described above and the iodine value / MB value is within the above-mentioned specific range, the above-mentioned effect can be further improved. From the viewpoint of easily controlling the specific surface area and the iodine value / MB value within the above-mentioned specific range, in one embodiment of the present invention, the support supporting the nitrogen-activated catalyst precursor is preferably a carbonaceous material, particularly activated carbon. The iodine value / MB value is calculated using the following method. Iodine value: According to JIS K 1474, activated carbon is added in varying amounts to a 0.05 mol / L iodine solution (potassium iodide is also dissolved: 0.15 mol / L) and shaken for 15 minutes. The activated carbon-containing solution is then centrifuged. The supernatant is titrated with a 0.1 mol / L sodium thiosulfate solution to determine the residual iodine concentration, and an adsorption isotherm is created. Based on the created adsorption isotherm, the adsorption amount at a residual iodine concentration of 2.5 g / L is taken as the iodine value. MB value: According to JIS K 1474, the iodine value is measured using a method based on the iodine value, and the MB value is calculated. The iodine value / MB value can be calculated from the value obtained above. In detail, it can be calculated, for example, by the method described in the Examples below.

[0018] In one embodiment of the present invention, the volumetric average particle diameter (D ５０ ) is preferably 0.1 to 800 μm, more preferably 0.5 to 600 μm, and even more preferably 1 to 500 μm. When the average particle size is within the above range, the contact efficiency between the reaction medium and the catalyst precursor or the activated catalyst component can be increased, which can lead to an improvement in catalytic activity. In particular, the D of the support of the support (B1) of the catalyst precursor that activates hydrogen (hereinafter also simply referred to as "support (B1)") ５０In relation to the D of the support (A1), ５０ By adjusting the volumetric average particle diameter (D ５０ ) means the average particle size converted into volume when the cumulative volume from the fine particle side is 50% in the particle size distribution measured by a laser scattering method. The same applies to the support (B1) that supports the hydrogen activation catalyst precursor described below. ５０ can be determined, for example, by the method described in the Examples below.

[0019] In the present invention, the amount of nitrogen-activated catalyst precursor supported on a support can be appropriately determined depending on the type of catalyst precursor and support. For example, when the nitrogen-activated catalyst precursor is a metal complex, the amount supported on the support is typically 0.01 to 100 mass%, preferably 0.05 to 50 mass%, more preferably 0.1 to 30 mass%, and even more preferably 0.5 to 20 mass%, in terms of the amount of metal per mass of support. A support amount within the above range is preferable from the viewpoint of the stability and catalytic activity of the ammonia synthesis catalyst precursor and catalyst. It can also be advantageous in terms of economy. Note that the support (A1) may contain other components, such as catalyst precursors and additives other than the nitrogen-activated catalyst precursor (hereinafter collectively referred to as "other components (A)"). To ensure the sufficient action of the nitrogen-activated catalyst precursor in the support (A1), the amount of the nitrogen-activated catalyst precursor in the support (A1) is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, or even 100% by mass, based on the total amount of components other than the carrier in the support (A1). The content of the other component (A) in the support (A1) is preferably 0 to 10% by mass, more preferably 0 to 5% by mass, and even more preferably 0 to 3% by mass, based on the total amount of components other than the carrier in the support (A1).

[0020] In the present invention, the support (A1) can be obtained by impregnating a nitrogen-activating catalyst precursor onto a support. Specifically, for example, the support (A1) having a metal complex supported on a support can be obtained by supporting a metal complex containing a metal atom that serves as the nitrogen-activating catalyst precursor, preferably a binuclear metal complex having at least three metal atoms, on the support.

[0021] As a polynuclear metal complex for forming a metal cluster that serves as a nitrogen-activating catalyst component in an ammonia synthesis catalyst, a halide cluster in which the ligand is a halogen atom is preferred. The halide cluster can eliminate the halogen atom that is the ligand by heating in an environment in which hydrogen is supplied, and can effectively form a metal cluster in a state in which it is adsorbed on the support surface. The halogen atom is preferably Cl, Br, or I. Furthermore, the halide cluster preferably has only halogen atoms as ligands, or has halogen atoms and water.

[0022] In the present invention, examples of the halide cluster include M ６ X １２ , M ６ X １２ ・nR, A ２ M ６ X １４ , A ２ M ６ X １４ ・nR, EM ６ X １４ , E.M. ６ X １４ ・nR,M ６ X ８ L ６ , A ２ M ６ X ８ L ６ , M ６ X １４ , M ６ X １４ ・nR, A ４ M ６ X １８ , or A ４ M ６ X １８nR, where M represents a metal, X represents a halogen, A and E represent +1 and +2 valent cations, respectively, R represents a first ligand, L is a second ligand, and n is a value between 0 and the sum of M+X. M is Mo, W, Cr, Mn, Tc, Re, Cu, Ti, V, Ta, Nb, Sn, Zn, Zr, or Ga, X is F, Cl, Br, I, or a mixture thereof, and A is H. ＋ , H ３ O ＋ , K. ＋ , Na ＋ , Li ＋ , ammonium (including quaternary ammonium); L is F, Cl, Br, I or a mixture thereof; E is Be ２＋ , Mg ２＋ , Ca ２＋ , Sr ２＋ , Cu ２＋ , Ni ２＋ , Ti ２＋ , Ba ２＋ or a mixture thereof; R is H ２ O, CH ３ CN, or any other solvate, e.g., MoCl ２ Molybdenum (II) chloride usually has a cluster structure. In general, six molybdenum metal atoms form a regular octahedron, and a total of eight chlorine ligands are tightly coordinated to each face of the octahedron, forming a single atomic block as a whole. In addition, there are two terminal chlorine atoms and four bridging ligands between the vertices at the six vertices of this regular octahedron, forming a solid cluster [(Mo ６ Cl ｉ８ ) Cl ａ２ Cl ａ－ａ４／２ ] (where i = inner, a = outer). Furthermore, this chlorine can be replaced by water to form various halide clusters. Specific examples include the following: MoCl ２ ・[Mo ６ Cl ８ ]Cl ２ Cl ４／２ ・[(Mo ６ Cl ８ ) Cl ４ (H ２O) ２ ] ・(H ３ O) ２ [(Mo ６ Cl ８ ) C1 ６ ]・6H ２ O ・ [(Mo ６ Cl ８ ) C1 ４ (H ２ O) ２ ]・6H ２ O ・ [(Mo ６ Cl ８ ) C1 ４ (H ２ O) ２ ] Among them, from the viewpoint of chemical stability, [(Mo ６ Cl ８ ) Cl ４ (H ２ O) ２ ], (H ３ O) ２ [(Mo ６ Cl ８ ) C1 ６ ]・6H ２ O, [(Mo ６ Cl ８ ) C1 ４ (H ２ O) ２ ]・6H ２ O, [(Mo ６ Cl ８ ) C1 ４ (H ２ O) ２ ] is preferred.

[0023] Examples of methods for preparing a support (A1) in which a polynuclear metal complex is supported on a support include: a method in which a mononuclear metal complex is bound to a support to prepare a support in which a polynuclear metal complex is supported; a method in which a pre-prepared polynuclear metal complex is impregnated onto a support; and a method in which a precursor is dissolved in a solvent, impregnated onto a support, and then thermally changed. Polynuclear metal complexes can be prepared using methods conventionally known in synthetic chemistry depending on the desired metal complex structure, etc.

[0024] Examples of methods that can be used to impregnate a polynuclear metal complex onto a support include a method in which the support is dispersed in a solution in which the polynuclear metal complex is dissolved in a suitable solvent, and the polynuclear metal complex is brought into contact with the support to impregnate the support; and a method in which, without dissolving the polynuclear metal complex in a solvent, the polynuclear metal complex and the support are each dispersed in a suitable solvent using physical means such as ultrasound or strong shear, and the two are brought into contact to impregnate the support.

[0025] The solvent for dissolving or dispersing the polynuclear metal complex or the support can be appropriately selected depending on the type of the polynuclear metal complex or the support, the impregnation method to be used, etc. Examples of soluble solvents that can be used include water, methanol, and ethanol. Examples of non-soluble solvents that can be used include saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclopentane, cyclohexane, and cyclooctane, and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0026] The conditions for impregnating the polynuclear metal complex onto the support are not particularly limited and can be appropriately determined depending on the types of polynuclear metal complex, support, and solvent, the impregnation method used, etc. For example, the concentration of the polynuclear metal complex in the solvent may be 0.01 to 20% by mass, and preferably 0.05 to 10% by mass. The temperature during impregnation may be, for example, in the range of −10 to 200° C., preferably 0 to 100° C., and more preferably 10 to 60° C.

[0027] The contact between the polynuclear metal complex and the support can be carried out by adding the support to a solution in which the polynuclear metal complex is dissolved or dispersed, and stirring or shaking the solution using a known stirring device, etc. The contact time can be appropriately determined depending on the types of the polynuclear metal complex, the support, and the solvent, the impregnation method to be used, etc.

[0028] The contact of the polynuclear metal complex with the support can be carried out under an atmosphere such as air or an inert gas atmosphere such as nitrogen. From the viewpoint of safety, it is preferable to carry out the contact under an inert gas atmosphere such as nitrogen. After impregnation onto the support, the solvent used is removed by an operation such as filtration, and the product is dried as necessary to obtain a support (A1) on which the polynuclear metal complex is supported. Drying may be carried out under heating or reduced pressure.

[0029] (Support for hydrogen-activating catalyst precursor) The catalyst precursor for ammonia synthesis of the present invention comprises a support for hydrogen-activating catalyst precursor (B1) (hereinafter also simply referred to as "support (B1)") in which a precursor of a catalytic component that activates hydrogen (hereinafter also referred to as "hydrogen-activating catalyst precursor") is supported on a support. In this specification, the hydrogen-activating catalyst precursor means a substance that exhibits catalytic activity as a hydrogen-activating catalyst by undergoing an appropriate activation treatment. The support (B1) refers to a substance that comprises a hydrogen-activating catalyst precursor and a support, and in which the catalyst precursor is supported on the support. A chemical bond may or may not be formed between the hydrogen-activating catalyst precursor and the support.

[0030] In the present invention, the hydrogen activation catalyst precursor contained in the support (B1) may be various metal atoms that can function as a hydrogen activation catalyst after activation treatment. Among these, from the viewpoint of catalytic activity, the hydrogen activation catalyst precursor preferably contains at least one transition metal selected from transition metals other than those of Groups V, VI, and VII, and more preferably contains at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt). These may be used alone or in combination of two or more.

[0031] In the ammonia synthesis catalyst precursor of the present invention, the hydrogen-activating catalyst precursor is supported on a carrier different from the carrier constituting the support (A1) of the nitrogen-activating catalyst precursor. Here, "supported on a different carrier" means that the hydrogen-activating catalyst precursor is supported on a carrier different from the carrier supporting the nitrogen-activating catalyst precursor in the support (A1) constituting the ammonia synthesis catalyst precursor. Therefore, if appropriate, the type of the carrier in the support (A1) of the nitrogen-activating catalyst and the type of the carrier in the support (B1) of the hydrogen-activating catalyst may be the same.

[0032] Conventionally, when two catalyst components are supported on separate supports, it is generally believed that catalytic activity decreases due to the physical distance between the catalyst components. However, in the present invention, it has been discovered that supporting a hydrogen-activated catalyst precursor on a support separate from that supporting a nitrogen-activated catalyst precursor can increase the catalytic activity of the resulting ammonia synthesis catalyst. Although the reason for this is unclear, in the present invention, by supporting the catalyst precursor on a porous support having a relatively large specific surface area, the catalyst precursor can be attached to the support at an appropriate size, which is thought to increase the contact efficiency between the reaction medium and the catalyst precursor or the activated catalyst components, thereby improving catalytic activity. Furthermore, for example, carbonaceous materials such as activated carbon tend to have a relatively large specific surface area and, as described above, are suitable as supports for supporting nitrogen-activated catalysts and their precursors. However, many hydrogen-activated catalysts and their precursors can damage carbonaceous materials. In the present invention, by supporting the nitrogen-activating catalyst precursor and the hydrogen-activating catalyst precursor on separate supports, the above-mentioned advantages of using a support (A1) made of a carbonaceous material such as activated carbon can be ensured, and by selecting a support suitable for supporting the hydrogen-activating catalyst precursor, a stable ammonia synthesis catalyst having high catalytic activity and excellent sustainability of catalytic activity can be obtained.

[0033] The carrier for supporting the hydrogen activation catalyst precursor has a specific surface area of ​​10 m ２ / g or more. ２When the specific surface area is 10 to 1000 m / g or more, the hydrogen-activating catalyst precursor can be supported on the support in an appropriate size, and the catalytic activity in ammonia synthesis is improved. In addition to the catalytic activity, from the viewpoint of the mechanical strength and stability of the support (B1), the specific surface area of ​​the support in the support (B1) is preferably 10 to 1000 m / g. ２ / g (1000m ２ / g or less or 1000m ２ / g), more preferably 10 to 800m ２ / g, more preferably 10 to 500 m ２ / g. The specific surface area means the "BET specific surface area." The BET specific surface area can be calculated by a nitrogen adsorption method. In detail, it can be calculated, for example, by the method described in the examples below.

[0034] Examples of carriers for supporting the hydrogen-activating catalyst precursor include porous inorganic materials or layered compounds. Specific examples of porous inorganic materials include those listed above as carriers capable of supporting the nitrogen-activating catalyst precursor. Examples of layered compounds include clays such as montmorillonite and kaolinite. These carriers may be used alone or in combination of two or more. Among these, porous inorganic materials are preferred, and more preferably contain at least one selected from the group consisting of carbon, boron nitride, carbon nitride, silica, alumina, aluminosilicate, sodium aluminosilicate, aluminum magnesium hydroxide carbonate, titania, titanosilicate, zirconia, zirconosilicate, zinc oxide, and ceria. Furthermore, from the viewpoint of the stability of the carrier and the hydrogen-activating catalyst precursor at high temperatures, the carrier is preferably selected from the group consisting of silica, alumina, zeolite, zirconia, titania, and ceria, and more preferably selected from the group consisting of silica, titania, and ceria.

[0035] In one embodiment of the present invention, the volumetric average particle diameter (D ５０) is preferably 0.1 to 500 μm, more preferably 0.5 to 400 μm, and even more preferably 1 to 300 μm. When the average particle size is within the above range, the contact efficiency between the reaction medium and the catalyst precursor or the activated catalyst component can be increased, which can lead to an improvement in catalytic activity. In particular, the D of the catalyst supporter that activates nitrogen ５０ In relation to the D of the support (B1), ５０ By adjusting the above, the catalytic activity of the resulting ammonia synthesis catalyst can be further improved.

[0036] In the present invention, the amount of hydrogen-activating catalyst precursor supported on the support can be appropriately determined depending on the type of catalyst precursor and support, etc. For example, when the hydrogen-activating catalyst precursor is a transition metal as described above, the amount supported on the support is typically 0.01 to 100 mass%, preferably 0.05 to 50 mass%, more preferably 0.1 to 30 mass%, and even more preferably 0.5 to 20 mass%, in terms of the amount of metal per mass of support. A support amount within the above range is preferable from the viewpoint of the stability and catalytic activity of the ammonia synthesis catalyst precursor and catalyst. It can also be advantageous in terms of economy. Note that the support (B1) may contain other components, such as catalyst precursors and additives other than the hydrogen-activating catalyst precursor (hereinafter collectively referred to as "other components (B)"). To ensure the sufficient action of the hydrogen activation catalyst precursor in the support (B1), the amount of the hydrogen activation catalyst precursor in the support (B1) is preferably 80 mass% or more, more preferably 85 mass% or more, even more preferably 90 mass% or more, particularly preferably 95 mass% or more, or even 100 mass%, based on the total amount of components other than the carrier in the support (B1). The content of the other component (B) in the support (B1) is preferably 0 to 10 mass%, more preferably 0 to 5 mass%, and even more preferably 0 to 3 mass%, based on the total amount of components other than the carrier in the support (B1).

[0037] In the present invention, the support (B1) can be obtained by impregnating a hydrogen activation catalyst precursor onto a support. The method for impregnating a hydrogen activation catalyst precursor onto a support is not particularly limited, and examples thereof include a method in which the support is dispersed in a solution in which a metal compound containing the transition metal is dissolved in a suitable solvent, and the metal compound is brought into contact with the support to impregnate the support, and a method in which the metal compound is not dissolved in a solvent, but the metal compound and the support are each dispersed in a suitable solvent using physical means such as ultrasound or strong shear, and the two are brought into contact to impregnate the support.

[0038] Examples of the metal compound used here include halides of transition metals other than those of Groups V, VI, and VII, such as iron, cobalt, rhodium, iridium, nickel, copper, palladium, and platinum; mineral acid salts such as nitrates and sulfates; organic acid salts such as acetic acid and propionic acid; and salts having an organic ligand, such as acetylacetonate.

[0039] The solvent for dissolving or dispersing the metal compound can be appropriately selected depending on the type of metal compound and carrier, the impregnation method used, and the like. Examples of usable soluble solvents include water; alcohols such as methanol and ethanol; esters such as ethyl acetate and methyl acetate; amides such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, and N-ethylpyrrolidone; sulfoxides such as dimethyl sulfoxide; and ethers such as diethyl ether, tetrahydrofuran, and tetrahydropyran. Examples of usable non-soluble solvents include saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclopentane, cyclohexane, and cyclooctane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0040] The conditions for impregnating the metal compound onto the support are not particularly limited and can be appropriately determined depending on the types of metal compound, support, and solvent, the impregnation method used, etc. For example, the concentration of the metal compound in the solvent may be 0.01 to 20% by mass, and preferably 0.05 to 10% by mass. The temperature during impregnation may be, for example, in the range of -10 to 200°C, preferably 0 to 100°C, and more preferably 10 to 60°C.

[0041] The contact between the metal compound and the support can be carried out by adding the support to a solution in which the metal compound is dissolved or dispersed, and stirring or shaking the solution using a known stirring device, etc. The contact time can be appropriately determined depending on the types of the metal compound, support, and solvent, the impregnation method to be used, etc.

[0042] The contact of the metal compound with the carrier can be carried out under an atmosphere such as air or an inert gas atmosphere such as nitrogen. From the viewpoint of safety, it is preferable to carry out the contact under an inert gas atmosphere such as nitrogen. After impregnation onto the carrier, the solvent used is removed by an operation such as filtration, and the product is dried as necessary to obtain a carrier (B1) in which the metal compound is supported on the carrier. Drying may be carried out under heating or reduced pressure.

[0043] In the present invention, in order to further stabilize the metal compound support (B1), the support (B1) can be heat-treated, for example, under an inert gas or oxygen. The heat treatment temperature may be equal to or higher than the decomposition temperature of the inorganic salt or organic acid salt contained in the metal compound. The heat treatment temperature is usually 150 to 800°C, and taking into consideration the stability, the decomposition efficiency of the inorganic salt or organic acid salt, and / or the stabilization after decomposition, the heat treatment can be carried out at a temperature of preferably 200 to 700°C, more preferably 250 to 600°C.

[0044] The catalyst precursor for ammonia synthesis of the present invention comprises the support (A1) and the support (B1). In the catalyst precursor for ammonia synthesis of the present invention, the content of the support (A1) to the support (B1) is not particularly limited, and may be, for example, 1:200 to 200:1, preferably 1:150 to 150:1, more preferably 1:100 to 100:1, in terms of the mass ratio of the support (A1):support (B1).

[0045] In one embodiment of the present invention, D of the carrier constituting the support (A1) ５０ and D of the carrier constituting the support (B1) ５０ The larger of these is D ５０ -1, and the smaller one is D ５０ When the ratio D is -2, ５０ -1 / D ５０ -2 is preferably 1 or more, and more preferably 1.5 or more. ５０ -1 / D ５０ When −2 is equal to or greater than the lower limit, the support (A1) and the support (B1) can be mixed uniformly, thereby enhancing the activity of the resulting ammonia synthesis catalyst. ５０ -1 / D ５０ Although -2 is not necessarily limited, it is preferably 1 to 50, more preferably 1 to 30, and even more preferably 1 to 20, and may be, for example, 1.5 to 50, 1.5 to 30, or 1.5 to 20. Either the particle size of the support (A1) or the particle size of the support (B1) may be larger.

[0046] In one embodiment of the present invention, the catalyst precursor for ammonia synthesis of the present invention can contain any combination of a support (A1) and a support (B1) as long as it can exhibit the intended catalytic effect. Examples of such combinations include the following: a combination of a support (A1) comprising a nitrogen-activating catalyst precursor containing at least one metal atom selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium, and a support that is a porous inorganic material, and a combination of a support (B1) comprising a hydrogen-activating catalyst precursor containing at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt), and a support that is a porous inorganic material; a support (A1) comprising a nitrogen-activating catalyst precursor containing at least one metal atom selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium, and a support selected from the group consisting of carbonaceous materials, silica, silica-alumina, alumina, zeolites, zirconia, titania, and ceria; and a support (B1) comprising a hydrogen-activating catalyst precursor containing at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt), and a support selected from the group consisting of silica, silica-alumina, alumina, zeolites, zirconia, titania, ceria, magnesium oxide, calcium oxide, and barium oxide; a support (A1) comprising a nitrogen-activating catalyst precursor containing at least one metal atom selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium, and a support selected from the group consisting of carbonaceous materials, silica, titania, and ceria; and a support (B1) comprising a hydrogen-activating catalyst precursor containing at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt), and a support selected from the group consisting of silica, titania, zirconia, and ceria.A combination of a support (A1) comprising a nitrogen-activating catalyst precursor containing at least one metal atom selected from the group consisting of molybdenum, niobium, tungsten, tantalum, and rhenium, and a support that is a carbonaceous material, and a support (B1) comprising a hydrogen-activating catalyst precursor containing at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt), and a support selected from the group consisting of silica, titania, zirconia, and ceria.

[0047] The ammonia synthesis catalyst precursor of the present invention may contain components other than the support (A1) and the support (B1) as long as the desired catalytic effect can be exerted. To ensure sufficient catalytic effect as an ammonia synthesis catalyst, the total amount of the support (A1) and the support (B1) in the ammonia synthesis catalyst precursor is preferably 90 mass% or more, more preferably 95 mass% or more, even more preferably 98 mass% or more, particularly preferably 99 mass% or more, based on the total amount of the ammonia synthesis catalyst precursor, and may even be 100 mass%. In other words, the total amount of other components other than the support (A1) and the support (B1) in the ammonia synthesis catalyst precursor is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 2 mass% or less, particularly preferably 1 mass% or less, based on the total amount of the ammonia synthesis catalyst precursor.

[0048] (Method for producing ammonia synthesis catalyst precursor) The ammonia synthesis catalyst precursor of the present invention can be obtained, for example, by a method comprising: supporting a precursor of a nitrogen-activating catalyst component on a carrier made of a porous material to form a supported material (A1) of the nitrogen-activating catalyst precursor on the carrier; and mixing the supported material (A1) with a supported material (B1) of the hydrogen-activating catalyst precursor, in which a hydrogen-activating catalyst precursor is supported on a carrier different from the support made of the porous material.

[0049] In the method for producing the ammonia synthesis catalyst precursor of the present invention, the support (A1) and the support (B1) can be prepared by the preparation methods described above in the sections on the support for the nitrogen-activating catalyst precursor and the support for the hydrogen-activating catalyst precursor, respectively. The support (A1) is preferably a support (A1) of a binuclear metal complex having at least three metal atoms capable of serving as a nitrogen-activating catalyst precursor. Furthermore, the support (B1) is preferably a support (B1) of a metal compound containing a metal capable of serving as a hydrogen-activating catalyst precursor.

[0050] The method for mixing the support (A1) and the support (B1) is not particularly limited, and they can be mixed using, for example, a general powder mixer such as a stirrer, a V-type mixer, a conical mixer, a ribbon mixer, a rocking mixer, a vibration mixer, a vibration sieve, or a screw kneader.

[0051] The mixture obtained by mixing the support (A1) and the support (B1) may be used in the subsequent step as a powder as a catalyst precursor for ammonia synthesis. Alternatively, the mixture may be molded into a block, tablet, or the like. The molding method is not particularly limited, and may be pressure molding, or a method of fixing the mixture using an adhesive, a binder, or the like. Taking into consideration the temperature and pressure during use in ammonia synthesis, it is preferable to use a binder to mold the mixture under pressure.

[0052] Examples of the binder include carbon materials such as graphite and carbon black, and metal oxides such as silica, alumina, titania, zirconia, etc. When a binder is used, the amount used is usually preferably 0.1 to 100 parts by mass, more preferably 0.2 to 50 parts by mass, and even more preferably 0.5 to 20 parts by mass, based on the total mass of the support (A1) and the support (B1).

[0053] When molding is performed under pressure, the pressure applied during molding may be such that the catalyst does not collapse when packed into a reactor, and is usually 1 to 5,000 kg / cm. ２ Preferably, it is in the range of 10 to 3000 kg / cm ２ , more preferably 20 to 2000 kg / cm ２ The range is.

[0054] The ammonia synthesis catalyst precursor of the present invention supports the nitrogen-activating catalyst precursor and the hydrogen-activating catalyst precursor on separate supports, allowing the nitrogen-activating catalyst precursor and the hydrogen-activating catalyst precursor to be supported on supports appropriate for their respective characteristics. This allows for the production of a stable ammonia synthesis catalyst that has high catalytic activity and excellent sustainability of catalytic activity. Furthermore, particularly when the nitrogen-activating catalyst component precursor is a dinuclear metal complex, preferably a halide cluster, the metal atom and the halogen atom form a strong bond, making it less susceptible to the effects of oxygen and moisture, and therefore can be stably stored in a support-supported state.

[0055] <Catalyst for ammonia synthesis> By subjecting the catalyst precursor for ammonia synthesis of the present invention, which is a mixture of the support (A1) and the support (B1), to an appropriate activation treatment, a catalyst having a specific surface area of ​​1000 m ２ The present invention provides a catalyst for ammonia synthesis comprising a nitrogen-activating catalyst support (A2) in which a catalytic component for activating nitrogen is supported on a porous carrier having a specific surface area of ​​1000 m / g or more, and a hydrogen-activating catalyst support (B2) in which a catalytic component for activating hydrogen is supported on a carrier different from the nitrogen-activating catalyst support (A2). ２ The present invention also covers a catalyst for ammonia synthesis comprising a nitrogen-activating catalyst support (A2) in which a catalyst component for activating nitrogen is supported on a carrier made of a porous material having a surface roughness of 1 / g or more, and a hydrogen-activating catalyst support (B2) in which a catalyst component for activating hydrogen is supported on a carrier different from the above-mentioned carrier.

[0056] In the present invention, an example of a method for activating the nitrogen-activating catalyst precursor and the hydrogen-activating catalyst precursor is a method of contacting the ammonia synthesis catalyst precursor of the present invention with hydrogen molecules. For example, the step of activating the ammonia synthesis catalyst precursor of the present invention with hydrogen molecules (hereinafter also referred to as the "activation step") is a step that can activate both the support (A1) and the support (B1) by a flow reaction in which hydrogen is continuously supplied. For example, in the ammonia synthesis catalyst precursor of the present invention, when the support (A1) is a support of a polynuclear metal complex that is a halide cluster and the support (B1) is a support of a metal compound, the catalyst precursor can be activated as follows: by supplying hydrogen to the catalyst precursor, halogen atoms are released from the halide cluster in the support (A1) and reduced to metal atoms. This forms a nitrogen-activating catalyst support (A2) in which a metal cluster is supported on a carrier. Furthermore, in the support (B1), for example, oxygen is released from the oxidation-stabilized metal component by hydrogen reduction and reduced to metal atoms. This results in the formation of a hydrogen activation catalyst support (B2) in which metal atoms are supported on a carrier. For example, the halogen atoms released from the halide clusters during the activation step can be discharged from the reaction system together with hydrogen gas as an acid, such as hydrochloric acid or oxalic acid. The generated water can also be discharged from the reaction system together with hydrogen.

[0057] The activation step can be carried out using a known apparatus. For example, it can be carried out by filling an upright reaction tube with the catalyst precursor for ammonia synthesis of the present invention. From the viewpoint of high resistance to acid, it is preferable to use a reaction tube for the activation step that is highly corrosion-resistant, preferably made of stainless steel 316, Inconel, or the like, more preferably made of Inconel, or the like.

[0058] Hydrogen can be supplied, for example, by flowing hydrogen through a reaction tube filled with the catalyst precursor for ammonia synthesis of the present invention. A flow reaction can be carried out by flowing hydrogen (hydrogen gas) through the reaction tube while heating the inside of the reaction tube at a temperature of 400 to 700°C.

[0059] In the present invention, the concentration of hydrogen flowing through the reactor is preferably substantially 100% in order to stably achieve the reduction effect. However, to prevent hydrogen adsorption, excessive heat generation due to rapid reduction, and aggregation of metal components that may occur during the activation process, a method can be used in which the concentration is gradually increased from a low concentration of, for example, about 1%. In this case, an inert gas such as nitrogen, helium, or argon can be used as the diluting gas. The hydrogen flow time is not particularly limited and can be determined appropriately depending on the treatment temperature and hydrogen concentration. For example, the hydrogen flow time can be within a range of approximately 0.1 to 24 hours, preferably 0.5 to 20 hours. The flow reaction can be suitably carried out at an absolute gas pressure within a range of 0.1 to 0.2 MPa. The gas flow can be continuous or intermittently supplied.

[0060] The catalyst for ammonia synthesis of the present invention can be obtained by forming a support (A2) for a nitrogen-activating catalyst and a support (B2) for a hydrogen-activating catalyst from the catalyst precursor for ammonia synthesis of the present invention, which is a mixture of the support (A1) and the support (B1), through an activation step.

[0061] <Method for producing ammonia> The catalyst for ammonia synthesis of the present invention can synthesize ammonia in a relatively mild environment and has high catalytic activity suitable for industrial application. Therefore, the present invention is directed to a method for producing ammonia, which comprises contacting the catalyst for ammonia synthesis of the present invention with a mixed gas containing nitrogen and hydrogen.

[0062] Ammonia synthesis using the ammonia synthesis catalyst of the present invention can be carried out using a known ammonia synthesis apparatus. For example, ammonia synthesis can be carried out in the reaction tube in which the activation step in the method for producing an ammonia synthesis catalyst has been carried out, either subsequently to or simultaneously with the activation step. Specifically, ammonia can be synthesized by heating the ammonia synthesis catalyst under temperature conditions suitable for ammonia synthesis and passing a mixed gas containing nitrogen and hydrogen through the reaction tube.

[0063] The temperature in the flow reaction during ammonia synthesis is started from a heated state within a temperature range of, for example, 50 to 700°C, and can be carried out preferably within a range of 250 to 500°C, more preferably 270 to 480°C, and even more preferably 280 to 450°C. When the temperature in the flow reaction is within the above range, the catalytic activity can be sufficiently increased and a decrease in activity due to sintering of the catalyst components can be suppressed. Therefore, ammonia can be efficiently synthesized under high catalytic activity.

[0064] In the flow reaction, ammonia can be continuously synthesized by contacting a mixed gas containing nitrogen and hydrogen with an ammonia synthesis catalyst. The mixture ratio (nitrogen:hydrogen) of nitrogen molecules (nitrogen gas) and hydrogen molecules (hydrogen gas) in the mixed gas used in the flow reaction is typically within a range of 1:10 to 10:1 by mass, preferably 1:5 to 5:1. The total flow rate of the nitrogen molecules (nitrogen gas) and hydrogen molecules (hydrogen gas) is preferably, for example, 30 to 500 ml / min (calculated at 25°C and 1 atmospheric pressure), and the space velocity (volume of gas contacting the catalyst per unit catalyst weight, per unit time (calculated at 25°C and 1 atmospheric pressure)) is preferably 9 to 150 l / h g-cat. The contact time (reaction time) is not particularly limited and can be, for example, within a range of 1 to 24 hours.

[0065] The present invention also relates to an ammonia synthesis apparatus that uses the catalyst for ammonia synthesis of the present invention. One example of the synthesis apparatus includes a reaction tube that contains a layer of the catalyst for ammonia synthesis of the present invention in at least a portion thereof. The reaction tube may have a plurality of layers containing the catalyst for ammonia synthesis of the present invention. The reaction tube is configured to ２ , N ２ The ammonia synthesis apparatus may be connected to a gas supply pipe for circulating the ammonia gas, etc., and / or a recovery pipe for recovering the synthesized ammonia. The ammonia synthesis apparatus may also be equipped with a heater for heating the gas supplied from the gas supply pipe and / or a compressor for pressurizing the gas.

[0066] The present invention will be described in more detail below based on examples, but the following examples are not intended to limit the present invention.

[0067] 1. Methods for Measuring Each Physical Property Value The physical property values ​​in the examples and comparative examples were measured by the following methods.

[0068] <BET specific surface area> The BET specific surface area of ​​the carrier in the nitrogen-activated catalyst support and hydrogen-activated catalyst support used in the examples and comparative examples was measured by adsorbing nitrogen gas onto the surface of the object at liquid nitrogen temperature and measuring the amount of nitrogen adsorbed in a monolayer. The measurement conditions were as follows. The results are shown in Table 1. [Measurement conditions] Apparatus: BELSORP-mini II manufactured by MicrotrackBell Adsorbed gas: 99.99995% by volume of nitrogen Adsorption temperature: liquid nitrogen temperature -196°C

[0069] <Measurement of Iodine Adsorption Amount / Methylene Blue Adsorption Amount (Iodine Value / MB Value)> The iodine value / MB value of the carrier in the nitrogen-activated catalyst support used in the Examples and Comparative Examples was measured and calculated according to the following method. The results are shown in Table 1. Iodine Adsorption Amount: According to JIS K 1474, activated carbon was added in varying amounts to a 0.05 mol / L iodine solution (potassium iodide also dissolved: 0.15 mol / L) and shaken for 15 minutes. The activated carbon-containing solution was then centrifuged. The supernatant was titrated with a 0.1 mol / L sodium thiosulfate solution to determine the residual iodine concentration, and an adsorption isotherm was created. The adsorption amount at a residual iodine concentration of 2.5 g / L was taken as the iodine value. Methylene Blue Adsorption Amount: According to JIS K 1474, 1.2 g of methylene blue (dry mass equivalent) was dissolved in a phosphate buffer solution at pH 7.0 to make 1 L. Varying amounts of activated carbon were added to the solution, and the mixture was shaken for 30 minutes. The activated carbon was then filtered off, and the absorbance of the resulting filtrate was measured at 665 nm to determine the residual concentration, and an adsorption isotherm was created. The adsorption amount Q (mg / g) at a residual concentration of 0.24 mg / L was calculated and converted into the adsorption amount of methylene blue solution using the following formula, which was used to determine the methylene blue adsorption capacity M (mL / g): M = Q / 1.2, where M is rounded to the nearest 10 mL.

[0070] <Volume-equivalent average particle diameter D ５０ > (average particle diameter D by laser scattering method ５０) The average particle size (particle size distribution) of the support of the nitrogen-activated catalyst precursor and the support of the hydrogen-activated catalyst precursor was measured by the following method. The support to be measured was placed in an aqueous solution containing 5 mass% of a surfactant ("Toriton X100" manufactured by Wako Pure Chemical Industries, Ltd.) and treated with an ultrasonic cleaner for 10 minutes or more to disperse it in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size / particle size distribution measuring device ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.). D ５０ is the particle size at which the cumulative volume becomes 50%, and this value was used as the average particle size. The results are shown in Table 1.

[0071] <Ammonia Production Rate> The ammonia production rate of the ammonia synthesis catalysts prepared in the Examples and Comparative Examples was evaluated according to the following method. (Ion Chromatography Analysis) The amount of ammonia produced was determined by dissolving the produced ammonia gas in an ultrapure aqueous solution of 2.5 mM oxalic acid, and then subjecting the solution to ion chromatography analysis using the absolute calibration curve method. The measurement conditions were as follows. [Measurement Conditions] Apparatus: HIC-20A sp manufactured by Shimadzu Corporation Column: Shim-pack IC-C4 manufactured by Shimadzu Corporation Length: 150 mm, inner diameter: 4.6 mm Eluent: aqueous solution of oxalic acid (2.5 mM) Column temperature: 40°C Flow rate: 1.0 mL / min

[0072] 2. Preparation of catalyst precursor for ammonia synthesis (1) Preparation of nitrogen-activated catalyst precursor (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ O was synthesized according to the method described in Inorganic Synthesis, 1970, 12, p. 170. This was supported on a suitable carrier and used as a support for the nitrogen-activated catalyst precursor.

[0073] (2) Preparation of hydrogen-activating catalyst precursor Co(acac) ２ ・2H ２A commercially available product (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the catalyst for hydrogen activation. The catalyst was supported on a carrier by the following method. Co(NO ３ ) ２ ・6H ２ Co(NO) was obtained by weighing 3000 mg of 2H2O, adding 12 g of water, and shaking the mixture. ３ ) ２ ・6H ２ O was dissolved in water. This produced Co(NO ３ ) ２ ・6H ２ An aqueous solution of CeO was obtained. ２ was weighed to have the predetermined content shown in Table 1, and Co(NO ３ ) ２ ・6H ２ An aqueous solution of Co(NO) was added and the mixture was shaken by hand. Then, water was distilled off from the suspension at around 60°C under reduced pressure, and the suspension was dried to obtain Co(NO). ３ ) ２ ・6H ２ O-CeO ２ The obtained powder sample was ground uniformly in a mortar and then stored in the air.

[0074] Co(NO ３ ) ２ ・6H ２ O-CeO ２ The support was packed and attached to a flow-type reactor, and the reaction was carried out at normal pressure under the following reaction conditions: [Reaction conditions] Air flow rate: 100 mL / min (calculated at 25°C and 1 atmosphere) First temperature rise condition / temperature rise time: 20°C to 110°C / 90 min (i.e., the temperature rise rate was 1 K / min) First holding temperature / holding time: 110°C / 12 hours Second temperature rise condition / temperature rise time: 110°C to 450°C / 5 hours 40 minutes (i.e., the temperature rise rate was 1 K / min) Second holding temperature / holding time: 450°C / 4 hours This produced Co (cobalt) oxide-CeO ２ After the support was obtained, it was stored in the air.

[0075] (3) Preparation of ammonia synthesis catalyst precursor (i) Examples 1 and 3, Comparative Example 1 Halide cluster (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ Approximately 10 mg of O was weighed, and methanol was added in an amount 800 times the weight of the halide cluster. The mixture was then shaken by hand to obtain (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ O was dissolved in methanol. ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ Subsequently, according to the description in Table 1, activated carbon 1, activated carbon 3, or zeolite was weighed as a carrier so as to have a predetermined content, and (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ A methanol solution of 0 was added. By stirring at room temperature, (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ O was supported on the support, thereby obtaining a suspension of cluster-supported particles.

[0076] The resulting suspension was evaporated under reduced pressure to remove methanol, and the cluster support was dried to obtain a powder sample of a halide cluster support of a nitrogen-activated catalyst precursor. The resulting powder sample was ground uniformly in a mortar and then stored in the atmosphere. The resulting halide cluster support and Co(acac) ２ ・2H ２ O and CeO ２were weighed out to a total of approximately 400 mg at the predetermined content rates shown in Table 1, and these were placed in an agate container for a ball mill together with several agate balls. The agate container was rotated at a rotation speed of 250 rpm for 180 seconds using a Fritsch planetary ball mill P-6, thereby mixing the powders in the container uniformly, and a powder sample of a catalyst precursor for ammonia synthesis was obtained. The obtained powder sample of catalyst precursor was stored in the atmosphere.

[0077] (ii) Example 4 Halide cluster (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ Approximately 10 mg of O was weighed out, and activated carbon 4 was weighed out according to Table 1 to give a predetermined content and added to the mixture. 15 mL of hexane was then added. The mixture was stirred by hand at room temperature and irradiated with ultrasonic waves using an ultrasonic cleaner to obtain a solution of (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ O was supported on the support. This resulted in a suspension of cluster-supported material. Hexane was distilled off from the resulting suspension under reduced pressure, and the halide cluster-supported material was dried to obtain a powder sample of the halide cluster-supported nitrogen-activated catalyst precursor. The resulting powder sample was stored in the atmosphere. Subsequently, approximately 50 mg of the resulting halide cluster-supported material was weighed, and Co oxide-CeO was added to this. ２ The support was weighed and added to give the specified content shown in Table 1, and then both were placed in an agate container for ball mill mixing together with several agate balls. The agate container was rotated at a rotation speed of 100 rpm for 25 seconds using a Fritsch planetary ball mill P-6, thereby mixing the powder inside the container uniformly, and a powder sample of a catalyst precursor for ammonia synthesis was obtained. The sample was stored in the atmosphere.

[0078] (iii) Example 2 and Comparative Example 2 Halide cluster (H ３ O) ２ [(Mo６ Cl ８ ) Cl ６ ]・6H ２ Approximately 13 mg of O was weighed out, and activated carbon 2 or zeolite carrier was weighed out according to the description in Table 1 so as to have the predetermined content, and both were placed in an agate container for ball mill mixing together with several agate balls. The powder in the container was mixed uniformly by rotating the agate container at a rotation speed of 100 rpm for 180 seconds using a Fritsch planetary ball mill P-6. The halide cluster support thus obtained was stored in the atmosphere. Next, Co(acac) ２ ・2H ２ Approximately 125 mg of CeO was weighed. ２ were weighed to give the prescribed content shown in Table 1, and both were placed in an agate container for ball mill mixing together with several agate balls. The powders in the container were mixed uniformly by rotating the agate container at a rotation speed of 250 rpm for 180 seconds using a Fritsch planetary ball mill P-6. ２ ・2H ２ The halide cluster support was weighed and added to the O support to achieve the specified content shown in Table 1, and both were placed in an agate container for ball mill mixing together with several agate balls. The agate container was rotated at a rotation speed of 100 rpm for 25 seconds using a Fritsch planetary ball mill P-6, thereby mixing the powder inside the container uniformly, and a powder sample of a catalyst precursor for ammonia synthesis was obtained. The obtained powder sample of catalyst precursor was stored in the atmosphere.

[0079] (iv) Comparative Example 3 Halide cluster (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ Approximately 10 mg of 0 was weighed, and methanol was added in an amount 800 times the weight of the halide cluster. The mixture was then shaken by hand to obtain (H ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H２ O was dissolved in methanol. ３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ A methanol solution of Co(NO) was obtained. ３ ) ２ ・6H ２ Co(NO) was obtained by weighing 3000 mg of 2H2O, adding 12 g of water, and shaking the mixture. ３ ) ２ ・6H ２ O was dissolved in water. This produced Co(NO ３ ) ２ ・6H ２ Subsequently, zeolite was weighed as a carrier to have a predetermined content as shown in Table 1, and Co(NO ３ ) ２ ・6H ２ An aqueous solution of Co(NO) was added and the mixture was shaken by hand. Then, water was distilled off from the suspension at about 60°C under reduced pressure, and the suspension was dried to obtain Co(NO). ３ ) ２ ・6H ２ The obtained powder sample was ground uniformly in a mortar and then stored in the air. Then, Co(NO ３ ) ２ ・6H ２ The O-zeolite support was packed and attached to a flow-through reactor, and the reaction was carried out at atmospheric pressure under the following reaction conditions. [Reaction conditions] Air flow rate: 100 mL / min (calculated at 25°C and 1 atmosphere) First temperature rise conditions / temperature rise time: 20°C to 110°C / 90 minutes (i.e., the temperature rise rate was 1 K / min) First holding temperature / holding time: 110°C / 12 hours Second temperature rise conditions / temperature rise time: 110°C to 450°C / 5 hours 40 minutes (i.e., the temperature rise rate was 1 K / min) Second holding temperature / holding time: 450°C / 4 hours In this way, a Co (cobalt) oxide-zeolite support was obtained, and then stored in the atmosphere. Subsequently, the Co oxide-zeolite support was weighed to have the predetermined content shown in Table 1, and (H３ O) ２ [(Mo ６ Cl ８ ) Cl ６ ]・6H ２ A methanol solution of O was added and stirred at room temperature to obtain a suspension of cluster-Co oxide support. Methanol was distilled off from the obtained suspension under reduced pressure, and the support was dried to obtain a powder sample of a catalyst precursor for ammonia synthesis. The obtained powder sample was ground to a uniform consistency in a mortar. The obtained powder sample of catalyst precursor was stored in the air.

[0080] 3. Synthesis of ammonia (1) Catalyst activation Clusters (containing H, O, and Cl) and Co (Co(acac) ２ ・2H ２ The catalyst precursors prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were packed in predetermined weights so that the total weight of the carrier (excluding the acac moiety of O, water of hydration, and oxygen moiety of Co oxide) was 200.0 mg, and the catalyst precursors were attached to a flow-type reactor. Hydrogen (purity: 99.99999% or more) was passed through the reaction tube, and activation was performed under the following conditions.

[0081] [Activation conditions] Hydrogen flow rate: 300 mL / min (calculated at 25°C and 1 atmosphere) Heating conditions / heating time: - 20°C to 550°C / 1 hour in Examples 1 and 2, and Comparative Example 2 - 20°C to 575°C / 1 hour in Example 4 - 20°C to 600°C / 1 hour in Example 3, Comparative Examples 1 and 3 Holding temperature / holding time: - 550°C / 3 hours in Examples 1 and 2, and Comparative Example 2 - 575°C / 3 hours in Example 4 - 600°C / 3 hours in Example 3, Comparative Examples 1 and 3

[0082] (2) Ammonia synthesis reaction The indicated temperature of the catalyst layer was lowered to 300°C (except for Comparative Example 3, where the temperature was lowered to 400°C), and a nitrogen / hydrogen mixed gas (volume ratio 1 / 3, oxygen 0.00001 vol% or less, water 0.00005 vol% or less) was used. The pressure inside the reaction tube was set to 1 MPa (absolute pressure), and the nitrogen / hydrogen mixed gas was flowed at a flow rate of 60 mL / min (calculated at 25°C and 1 atmosphere). The ammonia-containing gas emerging from the outlet was bubbled into a trapping solution, thereby capturing ammonia. The activity of the ammonia synthesis catalyst in each Example and Comparative Example was evaluated by the method described above in the measurement method for <Ammonia production rate>. The results are shown in Table 1.

[0083]

Claims

1. A support (A1) of a nitrogen activation catalyst precursor, on which a precursor of a catalyst component for activating nitrogen is supported, comprising a porous body having a specific surface area of 1000 m ２ / g or more, and a support (B1) of a hydrogen activation catalyst precursor, on which a precursor of a catalyst component for activating hydrogen is supported, comprising a support different from the above support, the catalyst precursor for ammonia synthesis comprising the same.

2. The carrier made of the porous body is a carrier with a ratio of iodine adsorption amount to methylene blue adsorption amount (iodine adsorption amount / methylene blue adsorption amount) of 10 or less, and is the catalyst precursor for ammonia synthesis according to claim 1.

3. The precursor of the catalyst component for activating nitrogen is a metal complex containing at least one metal atom belonging to Group V, Group VI, or Group VII, and is the catalyst precursor for ammonia synthesis according to claim 1 or 2.

4. The precursor of the catalyst component for activating nitrogen contains at least one metal atom selected from the group consisting of molybdenum (Mo), niobium (Nb), tungsten (W), tantalum (Ta), and rhenium (Re), and is the catalyst precursor for ammonia synthesis according to claim 1 or 2.

5. The metal complex is a polynuclear metal complex containing at least three metal atoms selected from the group consisting of molybdenum (Mo), niobium (Nb), tungsten (W), tantalum (Ta), and rhenium (Re), and is the catalyst precursor for ammonia synthesis according to claim 3.

6. The carrier made of the porous body is a carbonaceous material, and is the catalyst precursor for ammonia synthesis according to claim 1 or 2.

7. The precursor of the catalyst component for activating hydrogen contains at least one transition metal selected from the group consisting of iron (Fe), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), copper (Cu), palladium (Pd), and platinum (Pt), and is the catalyst precursor for ammonia synthesis according to claim 1 or 2.

8. The carrier for supporting the precursor of the catalyst component for activating hydrogen is a porous body of an inorganic material or a layered compound, and is the catalyst precursor for ammonia synthesis according to claim 1 or 2.

9. The inorganic material contains at least one selected from the group consisting of carbon, boron nitride, carbon nitride, silica, alumina, aluminosilicate, sodium aluminosilicate, magnesium aluminum hydroxide carbonate, titania, titanosilicate, zirconia, zirconosilicate, zinc oxide, and ceria, and is the catalyst precursor for ammonia synthesis according to claim 8.

10. A method for producing a catalyst precursor for ammonia synthesis according to claim 1, comprising: forming a support (A1) of a nitrogen activation catalyst precursor on which a precursor of a catalyst component for activating nitrogen is supported by supporting the precursor of the catalyst component for activating nitrogen on a support made of a porous body; and mixing a support (B1) of a hydrogen activation catalyst precursor in which a precursor of a catalyst component for activating hydrogen is supported on a support different from the support made of the porous body with the support (A1).

11. The method according to claim 10, wherein the precursor of the catalyst component for activating nitrogen is a polynuclear metal complex having at least three metal atoms, and the precursor of the catalyst component for activating hydrogen is a metal compound containing a metal.

12. A catalyst for ammonia synthesis comprising a nitrogen activation catalyst support (A2) in which a catalyst component for activating nitrogen is supported on a carrier made of a porous body having a specific surface area of 1000 m ２ / g or more, and a hydrogen activation catalyst support (B2) in which a catalyst component for activating hydrogen is supported on a carrier different from the said carrier.

13. A method for producing a catalyst for ammonia synthesis according to claim 12, comprising contacting the catalyst precursor for ammonia synthesis according to claim 1 with hydrogen molecules.

14. A method for producing ammonia, comprising contacting the catalyst for ammonia synthesis according to claim 12 with a mixed gas containing nitrogen and hydrogen.

Images