Composite, method for producing composite, catalyst, and method for producing ammonia

Abstract

The composite of the present invention comprises a mayenite type compound and an active metal and an alkaline earth metal supported on the mayenite type compound. The catalyst of the present invention contains the composite of the present invention. A method for producing the composite of the present invention comprises a first step of preparing a mayenite type compound and a second step of supporting the active metal and the alkaline earth metal on the mayenite type compound. A method for producing ammonia of the present invention comprises a step of producing ammonia by bringing a gas containing nitrogen and hydrogen into contact with the catalyst of the present invention. According to the present invention, it is possible to provide a composite that can yield a catalyst having high catalytic activity and suppressed hydrogen poisoning, a method for producing the composite, a catalyst containing the composite, and a method for producing ammonia using the catalyst.

Description

Technical Field

[0001] The present invention relates to a composite, a method for producing the composite, a catalyst containing the composite, and a method for producing ammonia using the catalyst.

Background Art

[0002] Nitrogen fertilizers such as ammonium sulfate and urea widely used in agricultural production are produced mainly from ammonia. Therefore, ammonia is a very important chemical raw material, and its production method has been studied. The most widely used ammonia production technology is the Haber-Bosch process. The Haber-Bosch process is a method for producing ammonia by bringing nitrogen and hydrogen into contact with a catalyst mainly composed of iron under high temperature and high pressure. As a synthesis method other than the Haber-Bosch process, a synthesis method using a supported metal catalyst in which ruthenium is supported on various carriers has been studied.

[0003] On the other hand, among calcium aluminosilicates having CaO, Al 2 O 3 , SiO 2 as constituent components, there is a substance called melilite in terms of mineral name, and a compound having the same crystal structure as that substance is called a "melilite-type compound". The melilite-type compound has a representative composition of 12CaO·7Al 2 O 3 (hereinafter sometimes abbreviated as "C12A7"), and C12A7 crystals have a unique crystal structure in which 2 out of 66 oxygen ions in a unit cell composed of 2 molecules are included as "free oxygen ions" in the space in the cage formed by the crystal skeleton ([Ca 24 Al 28 O 64 4+ (O 2- ) 2 ) (Non-Patent Document 1).

[0004] ​In addition, free oxygen ions in the mayenite-type compound can be replaced with various anions. Particularly, by holding the mayenite-type compound at a high temperature in a strong reducing atmosphere, all free oxygen ions can be replaced with electrons. And it has been reported that the mayenite-type compound substituted with these electrons is a conductive mayenite-type compound having good electron conduction characteristics (Non-Patent Document 2). Thus, the mayenite-type compound in which free oxygen ions are replaced with electrons is sometimes referred to as "Cl2A7 electride".

[0005] And it has been reported that a catalyst using C12A7 electride can be used as a catalyst for ammonia synthesis (Patent Document 1). Specifically, the catalyst for ammonia synthesis can be produced by heating a mayenite-type compound in a reducing atmosphere to prepare Cl2A7 electride, and supporting ruthenium using this C12A7 electride as a carrier. This catalyst has higher ammonia synthesis activity compared with conventional catalysts for ammonia synthesis, and becomes a high-performance catalyst for ammonia synthesis.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Although a catalyst using C12A7 electride as a carrier and ruthenium as a supported metal has high performance, it is desired to further increase the catalytic activity and further enhance the high performance of the catalyst. In addition, although ruthenium supported on C12A7 electride is suppressed from being poisoned by hydrogen, it is necessary to further suppress hydrogen poisoning in order to increase the hydrogen pressure and further enhance the efficiency of hydrogenation.

[0009] Therefore, an object of the present invention is to provide a composite capable of obtaining a catalyst having high catalytic activity and suppressed hydrogen poisoning, a method for producing the composite, a catalyst containing the composite, and a method for producing ammonia using the catalyst.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the present inventors have found that a catalyst having high catalytic activity and suppressed hydrogen poisoning can be obtained by using a composite in which an active metal and an alkaline earth metal are supported on a mayenite-type compound.

[0011] [1] A composite comprising a mayenite-type compound and an active metal and an alkaline earth metal supported on the mayenite-type compound. [2] The composite according to [1] above, wherein the mayenite-type compound is 12CaO·7Al 2 O 3 and. [3] The composite according to [1] or [2] above, wherein the alkaline earth metal is barium. [4] A catalyst containing the composite according to any one of [1] to [3] above. [5] A method for producing a composite, comprising a first step of preparing a mayenite-type compound and a second step of supporting an active metal and an alkaline earth metal on the mayenite-type compound. [6] The method for producing the composite according to [5] above, further comprising a third step of reducing the melilite-type compound obtained in the second step. [7] The method for producing the composite according to [5] or [6] above, wherein in the first step, the melilite-type compound is prepared by a hydrothermal synthesis method. [8] The method for producing the composite according to any one of [5] to [7] above, wherein in the second step, the loading of the active metal and the alkaline earth metal is carried out by an impregnation method. [9] The melilite-type compound is 12CaO·7Al 2 O 3 The method for producing the composite according to any one of [5] to [8] above.

[10] The method for producing the composite according to any one of [5] to [9] above, wherein the alkaline earth metal is barium.

[11] The method for producing ammonia, comprising a step of bringing a gas containing nitrogen and hydrogen into contact with the catalyst according to [4] above to produce ammonia.

[12] In the step of producing ammonia, the gas containing nitrogen and hydrogen is brought into contact with the catalyst according to [4] above under the conditions of a reaction temperature of 200 to 600 °C and a reaction pressure of 0.01 to 20 MPa in absolute pressure. The method for producing ammonia according to

[11] above.

[13] In the step of producing ammonia, the gas containing nitrogen and hydrogen is brought into contact with the catalyst according to claim 4 under the conditions of a reaction temperature of 250 to 700 °C and a reaction pressure of 0.1 to 30 MPa in absolute pressure. The method for producing ammonia according to

[11] above.

[14] In the step of producing ammonia, the gas containing nitrogen and hydrogen is brought into contact with the catalyst under the condition that the molar ratio of hydrogen to nitrogen (H 2 / N 2 ) is 0.25 to 15. The method for producing ammonia according to any one of

[11] to

[13] above.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a composite capable of obtaining a catalyst with high catalytic activity and suppressed hydrogen poisoning, a method for producing the composite, a catalyst containing the composite, and a method for producing ammonia using the catalyst.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0014] [Composite] The composite of the present invention includes a mayenite-type compound, and an active metal and an alkaline earth metal supported on the mayenite-type compound. Note that being supported on the mayenite-type compound means that the active metal and the alkaline earth metal may be directly supported on the surface of the mayenite-type compound, the active metal may be supported on the surface of the mayenite-type compound and the alkaline earth metal may be supported on the surface of the active metal, the alkaline earth metal may be supported on the surface of the mayenite-type compound and the active metal may be supported on the surface of the alkaline earth metal, or a composite of the active metal and the alkaline earth metal may be supported on the surface of the mayenite-type compound.

[0015] <Mayenite-Type Compound> The mayenite-type compound refers to a compound having a crystal structure isomorphic to mayenite. The mayenite-type compound is preferably calcium aluminosilicate having CaO, Al 2 O 3 , SiO 2 as constituent components, and more preferably 12CaO·7Al 2 O 3It is also preferable that the melilite-type compound contains calcium or aluminum, and more preferably contains both calcium and aluminum, from the viewpoint of further enhancing the catalytic activity of the composite. The crystal of the melilite-type compound is composed of cage-like structures (cages) sharing their walls and being three-dimensionally connected. Usually, anions such as O 2- are contained inside the cages of the melilite-type compound, but they can be replaced by conductive electrons by reduction treatment. 12CaO·7Al used as the melilite-type compound in the present invention 2 O 3 may be simply abbreviated as "C12A7".

[0016] The specific surface area of the melilite-type compound used in the composite of the present invention is preferably 5 m 2 / g or more. By setting the specific surface area of the melilite-type compound to 5 m 2 / g or more, sufficient catalytic activity can be obtained. The specific surface area of the melilite-type compound is more preferably 10 m 2 / g or more, and even more preferably 15 m 2 / g or more. The upper limit is not particularly limited, but is preferably 200 m 2 / g or less, and more preferably 100 m 2 / g or less. Within the above range, it is advantageous in terms of handling the composite when the composite is in powder form and the moldability of the composite.

[0017] The shape of the mayenite-type compound used in the composite of the present invention is not particularly limited, and usually includes fine particle form, granular form, bulk form, molded body form, etc. The shape of the mayenite-type compound is preferably fine particle form, bulk form or molded body form, more preferably fine particle form or molded body form, and still more preferably molded body form. Note that the molded body form may be a molded body of the mayenite-type compound alone, or a molded body of the mayenite-type compound and a binder component other than the mayenite-type compound. The binder component other than the mayenite-type compound is not particularly limited, and examples thereof include silica binder, alumina binder, titania binder, magnesia binder, and zirconia binder. These binders may be used alone or in combination of two or more, and an alumina binder is preferred. When the shape of the mayenite-type compound is fine particle form, its particle size is not particularly limited, but the primary particle size of the mayenite-type compound is usually 5 nm or more, preferably 10 nm or more, and usually 500 nm or less, preferably 100 nm or less. By making the mayenite-type compound into fine particles, the surface area per unit mass increases. The pores of the fine particles of the mayenite-type compound are not particularly limited, but since the pores of the particles of the mayenite-type compound are in the mesopore region, they are preferably 2 to 100 nm. In addition, when the mayenite-type compound is in bulk form, the mayenite-type compound is preferably a porous body having a pore structure. This is because a mayenite-type compound with a larger specific surface area can be obtained when the mayenite-type compound has a pore structure.

[0018] <Active metal and alkaline earth metal> In the composite of the present invention, the active metal and the alkaline earth metal are supported on the melilite-type compound. Thereby, compared with the case where only the active metal is supported on the melilite-type compound, the catalytic activity of the composite can be further increased and hydrogen poisoning can be further suppressed. From such a viewpoint, the preferable alkaline earth metal is at least one selected from the group consisting of magnesium, calcium, strontium and barium, the more preferable alkaline earth metal is at least one selected from the group consisting of strontium and barium, and the further preferable alkaline earth metal is barium. The active metal is not particularly limited, and examples thereof include ruthenium, cobalt and iron. Since the catalytic activity of the composite can be further enhanced, ruthenium is preferably used.

[0019] The content of the active metal is not particularly limited, but in terms of the active metal element, it is usually 0.01 part by mass or more, preferably 0.02 part by mass or more, more preferably 0.05 part by mass or more, still more preferably 0.1 part by mass or more, particularly preferably 1 part by mass or more, and usually 30 parts by mass or less, preferably 20 parts by mass or less, more preferably 15 parts by mass or less, still more preferably 10 parts by mass or less, with respect to 100 parts by mass of the melilite-type compound. When the content of the active metal is within the above range, the obtained composite can have sufficient active sites, a highly active catalyst can be obtained, and a catalyst preferable in terms of cost can be obtained.

[0020] From the viewpoint of enhancing the catalytic activity and suppressing hydrogen poisoning, in the active metal and alkaline earth metal supported on the melilite-type compound, the molar ratio of the alkaline earth metal to the active metal (number of moles of alkaline earth metal / number of moles of active metal) is preferably 0.05 or more, more preferably 0.1 or more, still more preferably 0.25 or more, preferably 10 or less, more preferably 5 or less, still more preferably 4 or less, still more preferably 3 or less, and still more preferably 2 or less. For example, the molar ratio of the alkaline earth metal to the active metal (number of moles of alkaline earth metal / number of moles of active metal) is preferably from 0.05 to 10, more preferably from 0.1 to 5, still more preferably from 0.25 to 4, still more preferably from 0.25 to 3, and still more preferably from 0.25 to 2.

[0021] Only the active metal and the alkaline earth metal may be supported on the melilite-type compound. However, in addition to the active metal and the alkaline earth metal, a metal element other than the active metal and the alkaline earth metal may be supported on the melilite-type compound. The supported metal other than the active metal and the alkaline earth metal is not particularly limited as long as it does not inhibit the activity of the composite obtained in the present invention. For example, as the supported metal other than the active metal and the alkaline earth metal, usually, at least one metal selected from the transition metals of Groups 3, 8, 9, and 10 of the periodic table, alkali metals, and rare earth metals can be used as the supported metal. The transition metals of Groups 3, 8, 9, and 10 of the periodic table are not particularly limited, and examples include yttrium, iron, and cobalt. The type of alkali metal is not particularly limited, and examples include lithium, sodium, potassium, cesium, rubidium, and the like. The type of rare earth metal is not particularly limited, and examples include lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, and the like. Among these, only the active metal and the alkaline earth metal may be supported on the mayenite-type compound. Supporting the active metal and the alkaline earth metal on the mayenite-type compound suppresses changes in the catalyst surface composition due to fluctuations in reduction conditions and the like, compared to the case where three or more metals are supported on the mayenite-type compound, and it is easier to obtain the desired catalytic activity.

[0022] [Method for producing composite material] The method for producing the composite material of the present invention includes a first step of preparing a mayenite-type compound and a second step of supporting an active metal and an alkaline earth metal on the mayenite-type compound.

[0023] (First step) In the first step, a mayenite-type compound is prepared. Hereinafter, the first step will be described by taking C12A7 as an example of the mayenite-type compound. The raw materials for producing C12A7 are not particularly limited, and various calcium-containing raw materials (hereinafter referred to as calcium sources) and aluminum-containing raw materials (hereinafter referred to as aluminum sources) can be appropriately used according to the production method.

[0024] The calcium source is not particularly limited, but specifically, calcium salts such as calcium hydroxide, calcium oxide, calcium nitrate, calcium chloride, calcium acetate; calcium alkoxides such as calcium ethoxide, calcium propoxide, calcium isopropoxide, calcium butoxide, calcium isobutoxide, etc. are used.

[0025] The aluminum source is not particularly limited, but specifically, aluminum salts such as aluminum hydroxide, aluminum oxide, aluminum nitrate, aluminum chloride, aluminum acetate; aluminum alkoxides such as aluminum ethoxide, aluminum propoxide, aluminum isopropoxide, aluminum butoxide, aluminum isobutoxide; aluminum acetylacetonate, etc. are used.

[0026] C12A7 may contain elements other than Ca, Al, and oxygen, as long as it does not inhibit the object of the present invention.

[0027] The method for preparing C12A7 is not particularly limited, but usually, a hydrothermal synthesis method, a sol-gel method, a combustion synthesis method, or a coprecipitation method can be used. Among these, the hydrothermal synthesis method is preferable in that C12A7 that is simple and has a high specific surface area can be obtained with good reproducibility.

[0028] <Hydrothermal synthesis method> Specifically, in the hydrothermal synthesis method, first, a solvent such as water or alcohol and a raw material of an inorganic oxide are placed in a pressure-resistant container, and heated at a temperature above the boiling point of the solvent for several hours to several days to obtain a precursor of the inorganic oxide. Subsequently, the obtained precursor is further heated to obtain an inorganic oxide.

[0029] The calcium source used in the hydrothermal synthesis method is not particularly limited, but usually, calcium hydroxide, calcium oxide, or a calcium salt is used, and preferably calcium hydroxide is used. The aluminum source is not particularly limited, but usually, aluminum hydroxide, aluminum oxide, or an aluminum salt is used, and preferably aluminum hydroxide is used. The mixing ratio of the calcium source and the aluminum source is not particularly limited and can be appropriately adjusted according to the desired composition. Usually, it is mixed in the stoichiometric composition of the target C12A7.

[0030] After charging the aluminum source and the calcium source into a pressure-resistant container, by heating them at a temperature above the boiling point of water, Ca 3 Al 2 (OH) 12 which is a hydroxide serving as a precursor of C12A7, can be synthesized. The heating temperature in the heat-resistant container in the hydrothermal synthesis is not particularly limited, and with a sufficient yield of Ca 3 Al 2 (OH) 12The heating temperature obtained can be appropriately selected, usually 100 °C or higher, preferably 150 °C or higher, and usually 200 °C or lower. The heating time is not particularly limited, and sufficient yield of Ca 3 Al 2 (OH) 12 The heating time obtained can be appropriately selected, usually 2 hours or longer, preferably 6 hours or longer, and usually 100 hours or shorter.

[0031] The obtained precursor of C12A7, Ca 3 Al 2 (OH) 12 can be heated (calcined) to obtain the target C12A7. The conditions for heating (calcination) are not particularly limited and can be appropriately selected within the range where C12A7 with a large specific surface area can be obtained. Usually, heating is carried out in the air. The heating temperature is not particularly limited, but usually it can be heated at 400 °C or higher, preferably 450 °C or higher, and usually 1000 °C or lower.

[0032] <Sol-gel method> C12A7 can also be produced by the sol-gel method. The sol-gel method is a method of hydrolyzing an organic or inorganic compound of a metal that is a raw material for a desired metal oxide in a solution to form a sol, and then proceeding with polycondensation to convert the sol into a gel, and creating a metal oxide by subjecting this gel to high-temperature treatment. The production method can be carried out in accordance with known methods described in, for example, J. Phys. D: Appl. Phys., 41, 035404 (2008), etc. Specifically, an aluminum source as a raw material is dissolved in a solvent, and after heating and stirring, an acid is added to prepare a hydrolyzed sol. Subsequently, a calcium source is dissolved in the solvent, the pH is adjusted as necessary, and it is gelled by heating and mixing with the sol containing the aluminum source under stirring. After filtering the obtained gel, dehydration and calcination are performed to obtain C12A7. The calcium source used in the sol-gel method is not particularly limited, but usually calcium hydroxide, calcium oxide, calcium salts, etc. are used, calcium salts are preferred, and calcium nitrate is preferred as the calcium salt. The aluminum source is not particularly limited, but usually aluminum hydroxide, aluminum oxide, aluminum alkoxide, etc. are used, and aluminum alkoxide is preferred.

[0033] <Combustion synthesis method> As a method for synthesizing C12A7, production by the combustion synthesis method is also possible. As a specific production method, it can be produced in accordance with the method described in J.Am.Ceram.Soc., 81, 2853-2863 (1998). For example, a calcium source and an aluminum source are dissolved in water, and an amorphous precursor of a melilite-type compound is obtained by heating and burning the mixed solution. By further heating and dehydrating this amorphous precursor, a melilite-type compound is obtained. The calcium source and aluminum source used in the combustion synthesis method are not particularly limited, but usually calcium salts and aluminum salts are preferred, and calcium nitrate and aluminum nitrate are more preferred. Specifically, for example, Ca(NO 3 ) 2 ·4H 2 O and Al(NO 3 ) 3 ·9H 2 O can be used as raw materials. These raw materials are dissolved in water in a stoichiometric composition, although not particularly limited. Urea is further added to the solution in which the above raw materials are dissolved, and this mixed solution is heated and burned to obtain an amorphous precursor of a melilite-type compound. The heating temperature is not particularly limited, but is usually 500 °C or higher. Then, the obtained amorphous precursor is heated and dehydrated, although not particularly limited, usually at 700 to 1000 °C, to obtain melilite-type compound powder C12A7.

[0034] <Coprecipitation method> The coprecipitation method is a method that uses a solution containing two or more types of metal ions to simultaneously precipitate sparingly soluble salts of multiple types of metals, and is a method for preparing highly uniform powders. The raw materials used in the coprecipitation method are not particularly limited, but as the calcium source and aluminum source, calcium salts and aluminum salts are usually used, and preferably nitrates of each. Specifically, an alkali such as ammonia or sodium hydroxide is added to an aqueous solution containing calcium nitrate and aluminum nitrate to simultaneously precipitate a sparingly soluble salt containing calcium hydroxide and aluminum hydroxide, and then this is filtered, dried, and calcined to obtain C12A7.

[0035] (Second step) In the second step, an active metal and an alkaline earth metal are supported. The order of supporting the active metal and the alkaline earth metal on the mayenite-type compound is not particularly limited. For example, the active metal and the alkaline earth metal may be supported on the mayenite-type compound simultaneously. In this case, the particle size of the active metal particles supported on the mayenite-type compound can be reduced, and the active metal can be highly dispersed. Also, after adding or mixing an alkaline earth metal to the precursor obtained by the hydrothermal synthesis method and then calcining, the alkaline earth metal can be supported. The average particle size of the active metal particles supported on the mayenite-type compound is preferably 1 nm or more, more preferably 1.5 nm or more, still more preferably 2 nm or more, preferably 15 nm or less, more preferably 10 nm or less, still more preferably 5 nm or less. Also, after supporting the active metal on the mayenite-type compound, the alkaline earth metal may be supported on the mayenite-type compound. In this case, the alkaline earth metal can be supported in the vicinity of the active metal, the catalytic activity of the composite can be enhanced, and when the active metal and the alkaline earth metal are in contact, the catalytic activity of the composite can be further enhanced. Also, as described above, the active metal is not particularly limited, and examples include ruthenium, cobalt, and iron, and ruthenium is preferred.

[0036] The ruthenium compound used for supporting ruthenium on the mayenite-type compound is not particularly limited as long as it can be converted into metallic ruthenium by reduction treatment. Examples of the ruthenium compound used for supporting ruthenium on the mayenite-type compound include ruthenium salts and ruthenium complexes.

[0037] Examples of ruthenium salts include ruthenium chloride (RuCl 3 ), ruthenium chloride hydrate (RuCl 3 ·nH 2 O), ruthenium acetate (Ru(CH 3 CO 2 ) X ), ruthenium nitrate, ruthenium iodide hydrate (RuI 3 ·nH 2 O), ruthenium nitrosyl nitrate (Ru(NO)(NO 3 ) 3 ), ruthenium nitrosyl chloride hydrate (Ru(NO)Cl 3 ·nH 2 O), ruthenium trinitrate (Ru(NO 3 ) 3 ), hexammine ruthenium chloride (Ru(NH 3 ) 6 Cl 3 ), etc. As ruthenium salts, ruthenium acetate, ruthenium nitrate, ruthenium nitrosyl nitrate, and ruthenium chloride are preferred in terms of obtaining high catalytic activity without breaking the structure of the mayenite-type compound in the second step.

[0038] Examples of ruthenium complexes include triruthenium dodecacarbonyl (Ru 3 (CO) 12 ), dichlorotetrakis(triphenylphosphine)ruthenium(II) (RuC 12 (PPh 3 ) 4 ), dichlorotris(triphenylphosphine)ruthenium(II) (RuC 12 (PPh 3 ) 3 ), tris(acetylacetonato)ruthenium(III) (Ru(acac) 3) Ruthenocene (Ru(C 5 H 5 ) 2 ) Dichloro(benzene)ruthenium(II) dimer ([RuC 12 (C 5 H 5 )] 2 ) Dichloro(mesitylene)ruthenium(II) dimer ([RuC 12 (mesitylene)] 2 ) Dichloro(p-cymene)ruthenium(II) dimer ([RuC 12 (p-Cymene)] 2 ) Carbonylchlorohydridotris(triphenylphosphine)ruthenium(II) ([RuHCl(CO)(PPh 3 ) 3 ) Tris(dipivaloylmethanato)ruthenium(III) ([Ru(dpm) 3 ) etc. can be used. As the ruthenium complex, triruthenium dodecacarbonyl (Ru 3 (CO) 12 ) tris(acetylacetonato)ruthenium(III) (Ru(acac) 3 ) ruthenocene (Ru(C 5 H 5 ) 2 ) etc. are preferable in terms of obtaining high catalytic activity.

[0039] Among the above ruthenium compounds, considering both the safety and production cost in the production of the composite, the ruthenium compound may be at least one ruthenium compound selected from the group consisting of ruthenium chloride, tris(acetylacetonato)ruthenium(III), and ruthenium nitrosyl nitrate.

[0040] The above compounds readily undergo thermal decomposition. Therefore, after supporting these compounds on the meyenite-type compound and then performing heat treatment for reduction, active metals can be deposited in the metallic state on the carrier. As a result, the active metals can be supported on the meyenite-type compound. Also, since the above ruthenium compound is readily reduced by hydrogen gas under heating, active metals such as ruthenium can be generated on the carrier from this aspect as well.

[0041] The method for supporting active metals on the meyenite-type compound is not particularly limited, and it can be supported by methods such as the impregnation method, thermal decomposition method, liquid phase method, sputtering method, vapor deposition method, etc. In the method of supporting active metals on the meyenite-type compound powder, a method of performing molding after supporting active metals by any of the above-mentioned supporting methods is practically used. On the other hand, in the method of supporting active metals on the molded meyenite-type compound carrier, the impregnation method or vapor deposition method is preferable in that the active metals can be uniformly dispersed on the carrier, and the impregnation method is more preferable in that uniform active metal particles are easily formed. Specifically, in the impregnation method, the meyenite-type compound is dispersed in a solution containing an active metal compound, and subsequently, the solvent of the solution containing the meyenite-type compound and the active metal compound is evaporated and dried to obtain a meyenite-type compound supporting the active metal (hereinafter sometimes referred to as an active metal-supported meyenite-type compound). The solvent used in the impregnation method preferably contains at least one selected from the group consisting of water, methanol, ethanol, 1-propanol, 2-propanol, butanol, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, acetone, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, cyclopentanone, tetrahydrofuran, methylene chloride, ethyl acetate, chloroform, diethyl ether, toluene, and hexane, and two or more kinds can also be used. Also specifically, in the vapor deposition method, the meyenite-type compound is physically mixed with the active metal compound and heated in a vacuum atmosphere, and the active metal is vapor-deposited on the meyenite-type compound as the active metal compound thermally decomposes to obtain an active metal-supported meyenite-type compound.

[0042] As the alkaline earth metal compound used for supporting an alkaline earth metal on a mayenite-type compound, a compound of at least one alkaline earth metal selected from magnesium, calcium, strontium, and barium is preferable, a compound of at least one alkaline earth metal selected from strontium and barium is more preferable, and a barium compound is still more preferable in terms of being a more abundant element.

[0043] The alkaline earth metal compound for supporting an alkaline earth metal on a mayenite-type compound is not particularly limited as long as it can support the alkaline earth metal on the mayenite-type compound. Usually, hydroxides of alkaline earth metals; inorganic acid salts such as carbonates, oxides, nitrates; carboxylates such as acetates and formates; alkoxides such as ethoxides; other organic compounds containing alkaline earth metals; metal complexes such as metal acetylacetonate complexes, etc. can be mentioned. Among them, alkoxides, metal acetylacetonate complexes, and carboxylates are preferable, and alkoxides, which are easier to react, are more preferable. For example, alkoxides used for supporting an alkaline earth metal on a mayenite-type compound include magnesium methoxide, magnesium ethoxide, magnesium phenoxide, strontium methoxide, strontium ethoxide, strontium phenoxide, barium methoxide, barium ethoxide, and barium phenoxide, etc. A preferable alkoxide is barium ethoxide.

[0044] The method for supporting an alkaline earth metal on a mayenite-type compound is the same as the method for supporting the above-described active metal.

[0045] The form of the alkaline earth metal supported on the mayenite-type compound may be in the form of the metal itself, or in the form of other compounds such as its salts, its oxides, its hydroxides, etc. The preferred form of the alkaline earth metal supported on the mayenite-type compound is the oxide. Incidentally, after the oxide of the alkaline earth metal is supported on C12A7, even after undergoing a reduction treatment, it is usually supported as an oxide as it is, and exists on the surface of the mayenite-type compound together with the reduced active metal.

[0046] In the second step, a metal other than the active metal and the alkaline earth metal can be supported on the mayenite-type compound by using a metal compound other than the active metal compound and the alkaline earth metal compound. The metal compound for supporting a metal other than the active metal and the alkaline earth metal on the mayenite-type compound is not particularly limited as long as it does not inhibit the support of the active metal and the alkaline earth metal. Usually, compounds of transition metals in Groups 3, 8, 9, and 10 of the periodic table, compounds of alkali metals, and compounds of rare earth metals are preferred. Examples of the compounds of transition metals in Groups 3, 8, 9, and 10 of the periodic table include compounds of yttrium, iron, cobalt, etc. Examples of the compounds of alkali metals include compounds of lithium, sodium, potassium, cesium, rubidium, etc. Examples of the compounds of rare earth metals include compounds of lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, etc.

[0047] (Third step) The method for producing the composite of the present invention may further include a third step of subjecting the mayenite-type compound obtained in the second step to a reduction treatment.

[0048] The conditions of the reduction treatment are not particularly limited as long as they do not inhibit the object of the present invention. For example, a method of performing the treatment in an atmosphere containing a reducing gas, or adding NaBH to a solution containing an active metal source 4 , NH 2 NH 2Alternatively, there is a method of adding a reducing agent such as formalin to deposit an active metal on the surface of the melilite-type compound. The reduction treatment is preferably carried out in an atmosphere containing a reducing gas. Examples of the reducing gas include hydrogen, ammonia, methanol (vapor), ethanol (vapor), methane, ethane, and the like. Also, during the reduction treatment, components other than the reducing gas that do not inhibit the ammonia synthesis reaction may coexist in the reaction system. Specifically, during the reduction treatment, in addition to a reducing gas such as hydrogen, gases such as argon and nitrogen that do not inhibit the reaction may coexist, or nitrogen may coexist.

[0049] The temperature of the reduction treatment is not particularly limited, but is usually 200 °C or higher, preferably 300 °C or higher, usually 1000 °C or lower, and preferably 600 °C or lower. By performing the reduction treatment within the above temperature range, the active metal particles can be grown to be within the above-mentioned preferred average particle size range. The pressure of the reduction treatment is not particularly limited, but is usually 0.1 MPa or higher and 10 MPa. The time of the reduction treatment is not particularly limited, but when carried out at normal pressure, it is usually 20 hours or longer, and preferably 25 hours or longer. Also, when carried out under conditions of high reaction pressure, for example, 1 MPa or higher, it is preferably 5 hours or longer.

[0050] The reduction treatment in the third step is preferably carried out until the average particle size of the active metal after the reduction treatment increases by 15% or more with respect to the average particle size before the reduction treatment. The upper limit of the average particle size of the active metal after the reduction treatment is not particularly limited, but is usually 200% or less. By performing the reduction treatment, the activity of the catalyst can be further enhanced. In this case, the average particle size of the active metal after the reduction treatment is preferably 1 nm or more, more preferably 1.5 nm or more, still more preferably 2 nm or more, preferably 15 nm or less, more preferably 10 nm or less, and still more preferably 5 nm or less. Here, the average particle diameter of the active metal refers to the average particle diameter measured by a direct observation method such as TEM (transmission electron microscope). In the direct observation method, the longest diameter of each of the actually observed active metals can be measured and the arithmetic mean can be calculated. The number of samples of the active metal for observing the average particle diameter may be, for example, 300 or more and 350 or less, or may be 300.

[0051] The average particle diameter of the active metal before and after the reduction treatment is determined on the assumption that all the active metals present on the surface to be measured are metals. However, as long as it does not significantly affect the calculation of the average particle diameter of the active metal, the active metals present on the surface to be measured may include the active metal compound which is the active metal source. In addition, when the active metal compound which is the active metal source accounts for the majority, since the particle diameter of the active metal cannot be measured, the active metal particle diameter is determined by the reduction treatment. The temperature of the reduction treatment is preferably 300 °C or higher, more preferably 430 °C or higher, preferably 600 °C or lower, and more preferably 450 °C or lower.

[0052] [Catalyst] The catalyst of the present invention contains the composite of the present invention, and particularly consists of the composite of the present invention. Thereby, a catalyst with high catalytic activity and suppressed hydrogen poisoning can be obtained.

[0053] The catalyst of the present invention may contain components other than the composite of the present invention as long as it does not inhibit the object of the present invention. For example, the catalyst of the present invention can contain a component that serves as a binder component for facilitating the shaping of the catalyst. Examples of the binder include metal oxides such as SiO 2 , Al 2 O 3 , ZrO 2 , TiO 2 , La 2 O 3 , CeO 2 , Nb 2 O 5 etc., and carbon materials such as activated carbon, graphite, and SiC.

[0054] The catalyst of the present invention may be subjected to a reduction treatment before use. The reduction treatment of the catalyst of the present invention can be carried out in the same manner as the reduction treatment in the third step in the method for producing the composite of the present invention described above. In addition, even under the conditions of ammonia synthesis, the catalyst of the present invention can be subjected to a reduction treatment.

[0055] The specific surface area of the catalyst of the present invention is not particularly limited, but the specific surface area based on the BET method is usually 5 m 2 / g or more, preferably 10 m 2 / g or more, usually 200 m 2 / g or less, preferably 100 m 2 / g or less. In addition, the specific surface area of the mayenite-type compound supporting the active metal and alkaline earth metal obtained after the reduction treatment is usually of the same degree as the specific surface area of the mayenite-type compound before supporting the active metal and alkaline earth metal used in its production.

[0056] The catalyst of the present invention can be appropriately used as a molded body by using ordinary molding techniques. Specifically, examples include shapes such as granular, spherical, tablet-shaped, ring-shaped, macaroni-shaped, four-leaf-shaped, dice-shaped, and honeycomb-shaped. It can also be used after coating the catalyst on a support.

[0057] The catalyst can be molded during the production of the above-mentioned composite. In this case, there is no limitation on which stage in the method for producing the composite is used, and it may be carried out following any step. Specifically, it may include a step of molding the mayenite-type compound obtained in the first step following the first step in the method for producing the composite. In addition, it may include a step of molding the mayenite-type compound supporting the active metal and alkaline earth metal obtained in the second step following the second step in the method for producing the composite. In addition, it may include a step of molding the reduced catalyst after the third step in the method for producing the composite or after the catalyst is subjected to a reduction treatment. Among these, a method including a forming step following the first step in the method for producing the composite, or a method including a forming step following the second step in the method for producing the composite, is preferable in that the active metal is uniformly dispersed on the mayenite-type compound and high catalytic activity can be obtained. Also, an alkaline earth metal can be supported on the mayenite-type compound after forming the mayenite-type compound supporting the active metal.

[0058] The catalyst of the present invention can be used as a catalyst for ammonia synthesis. However, the use of the catalyst of the present invention is not limited to ammonia synthesis. For example, the catalyst of the present invention can be used for hydrogenation of aliphatic carbonyl compounds, hydrogenation of aromatic rings, hydrogenation of carboxylic acids, synthesis of unsaturated alcohols by hydrogenation of unsaturated aldehydes, steam reforming of methane, hydrogenation of alkenes, etc., methanation by reaction of CO or CO 2 with hydrogen, Fischer-Tropsch synthesis reaction, nuclear hydrogenation of substituted aromatics, oxidation of alcohols to carbonyl compounds, gasification of lignin, etc.

[0059] [Method for producing ammonia] The method for producing ammonia of the present invention includes a step of producing ammonia by bringing a gas containing nitrogen and hydrogen into contact with the catalyst of the present invention. Thereby, ammonia can be efficiently produced. When bringing a gas containing nitrogen and hydrogen into contact with the catalyst of the present invention, first, only hydrogen may be brought into contact with the catalyst of the present invention to reduce the catalyst, and then a gas containing nitrogen and hydrogen may be brought into contact with the catalyst of the present invention. Also, a mixed gas containing hydrogen and nitrogen may be brought into contact with the catalyst of the present invention from the beginning. Furthermore, the unreacted gas recovered from the reactor at this time can also be recycled and used in the reactor.

[0060] The method for producing ammonia of the present invention is not particularly limited, but when bringing a gas containing nitrogen and hydrogen into contact with the above catalyst, ammonia synthesis is usually carried out by heating the catalyst. According to the method for producing ammonia of the present invention, ammonia can be produced under low-temperature and low-pressure conditions. The reaction temperature is preferably 200 to 600 °C, more preferably 250 to 500 °C, and still more preferably 300 to 450 °C. Since ammonia synthesis is an exothermic reaction, the low temperature region is more favorable for ammonia production in terms of chemical equilibrium theory. However, the above temperature range is preferred to obtain a sufficient ammonia production rate.

[0061] From the viewpoint of production cost, when producing ammonia under low temperature and low pressure conditions, in the ammonia production method of the present invention, the reaction pressure during the ammonia synthesis reaction is, in absolute pressure, preferably 0.01 to 20 MPa, more preferably 0.5 to 10 MPa, and still more preferably 1 to 7 MPa. In the case of a catalyst in which the active metal is supported on the mayenite-type compound but the alkaline earth metal is not supported on the mayenite-type compound, even if the reaction pressure is increased, the efficiency of the ammonia synthesis reaction is unlikely to increase.

[0062] In this case, the molar ratio of hydrogen to nitrogen (H 2 / N 2 ) to be brought into contact with the catalyst is preferably 0.25 to 15, more preferably 0.5 to 12, and still more preferably 1.0 to 10. Since the catalyst of the present invention is less likely to be poisoned by hydrogen, the molar ratio of hydrogen to nitrogen can be increased compared to the normal molar ratio of hydrogen to nitrogen when using an active metal. Thereby, the efficiency of ammonia synthesis is increased.

[0063] From the viewpoint of obtaining a better ammonia yield, the total water content in the mixed gas of nitrogen and hydrogen is usually 100 ppm or less, preferably 50 ppm or less.

[0064] The form of the reaction vessel is not particularly limited, and a reaction vessel that can be usually used for the ammonia synthesis reaction can be used. As specific reaction forms, for example, a batch reaction form, a closed circulation system reaction form, a flow system reaction form, etc. can be used. Among these, from a practical point of view, the flow system reaction form is preferred. Also, any method of filling a single type of reactor with a catalyst, or connecting a plurality of reactors, or a reactor having a plurality of reaction layers in the same reactor can be used. Since the ammonia synthesis reaction from a hydrogen-nitrogen mixed gas is an exothermic reaction with volume contraction, an industrial reaction device usually used for removing reaction heat may be used to increase the ammonia yield. For example, specifically, a plurality of reactors filled with a catalyst may be connected in series, and an intercooler may be installed at the outlet of each reactor to remove heat.

[0065] Also, as described above, the method for producing ammonia of the present invention is characterized in that ammonia can be produced under low-temperature and low-pressure conditions. However, in order to further improve the reaction rate, ammonia may be produced under medium-temperature and medium-pressure conditions. In this case, the reaction temperature is, for example, preferably 250 to 700 °C, more preferably 300 to 600 °C, and still more preferably 350 to 550 °C. Also, in this case, the reaction pressure is, in absolute pressure, preferably 0.1 to 30 MPa, more preferably 1 to 20 MPa, and still more preferably 2 to 10 MPa.

Examples

[0066] Hereinafter, the present invention will be described in more detail based on examples.

[0067] (Analysis of ammonia production amount) The ammonia production amounts in the following examples and comparative examples were determined by the absolute calibration curve method through gas chromatograph and ion chromatograph analysis of the generated ammonia gas. The analysis conditions are as follows. [Gas chromatograph analysis conditions] Device: Agilent 490 Micro GC Column: Agilent MO5A 10m B.F., CP-Sill 5CB 8m Column temperature: 80 °C [Ion chromatograph analysis conditions] Apparatus: Shimadzu HPLC Prominence Column: Shimadzu Shim-pack IC-C4 Length: 150 mm, inner diameter 4.6 mm Eluent: Mixed aqueous solution of oxalic acid (3 mM) and 18-crown-6-ether (2.0 mM) Column temperature: 40 °C Flow rate: 1.0 mL / min

[0068] (Example 1) (Synthesis of melilite-type compound) Calcium hydroxide (Ca(OH) 2 and: manufactured by High Purity Chemical Research Institute, purity 99.9%, 7.18 g) and aluminum hydroxide Al(OH) 3 : High Purity Chemical Research Institute, purity 99.9%, 8.82 g), weighed and mixed so that the molar ratio of Ca to Al was Ca:Al = 12:14 to obtain a mixed powder. Distilled water was added to the above mixed powder so that the above mixed powder became 10% by mass, and after making it into a mixed solution with a total mass of 160 g, this mixed solution was stirred and mixed at room temperature for 4 hours using a planetary ball mill. The obtained mixed solution was put into a pressure-resistant sealed container and heated (hydrothermal treatment) at 150 °C for 6 hours while stirring. The precipitate obtained by the above hydrothermal treatment was filtered off, dried and pulverized to obtain a precursor powder of a melilite-type compound: Ca 3 Al 2 (OH) 12 and about 16 g of AlOOH were obtained. This precursor powder was heated and dehydrated at 600 °C for 5 hours in the air to obtain a powder of a melilite-type compound (hereinafter, HT-C12A7 (12CaO·7Al 2 O 3 ).). The specific surface area of this melilite-type compound measured by the BET method was 63.5 m 2 / g, and it was a melilite-type compound with a large specific surface area.

[0069] <Supporting Ruthenium Compound and Alkaline Earth Metal Compound on Mordenite-Type Compound> Ruthenium nitrosyl nitrate (Ru(NO)(NO 3 ) 3 : manufactured by Alfa Aeser, model number: 12175) 0.157 g and barium diethoxide (Ba(OC 2 H 5 ) 2 : manufactured by Wako Pure Chemical Industries, Ltd., purity 99.5%) 0.227 g were dissolved in 50 mL of ethanol, stirred for about 15 minutes to obtain a mixed solution. 0.814 g of HT-C12A7 was added to the obtained mixed solution and stirred for about 3 minutes. Then, the solvent was removed from the above mixed solution using a rotary evaporator, dried, and further vacuum dried to obtain a powder of HT-C12A7 supporting ruthenium and barium (hereinafter, Ba-Ru / HT-C12A7) (Ru:Ba = 1:2 (molar ratio)). Note that the reduction treatment will be performed during the ammonia synthesis reaction.

[0070] (Comparative Example 1) The Ru raw material was triruthenium dodecacarbonyl (Ru 3 (CO) 12 : manufactured by Sigma-Aldrich, purity 99%, 0.101 g) was used, mixed with HT-C12A7 (0.95 g) obtained by the method of Example 1, sealed in a Pyrex (registered trademark) glass tube, and heated according to the following temperature program to support 5% by mass of Ru on HT-C12A7. A powder of (hereinafter, Ru / HT-C12A7) was obtained. [Temperature Program] (1) Heat from room temperature to 40 °C in 20 minutes, then maintain at 40 °C for 60 minutes (2) After (1), heat from 40 °C to 70 °C in 120 minutes, then maintain at 70 °C for 60 minutes (3) After (2), heat from 70 °C to 120 °C in 120 minutes, then maintain at 120 °C for 60 minutes (4) After (3), heat from 120 °C to 250 °C in 150 minutes, then maintain at 250 °C for 120 minutes

[0071] <Pressure Dependence of Ammonia Synthesis Reaction> Using the catalysts prepared in Example 1 and Comparative Example 1, while keeping the reaction temperature (400 °C) constant, the reaction pressure was changed, and nitrogen gas (N 2 ) and hydrogen gas (H 2 ) were reacted to carry out a reaction to produce ammonia gas (NH 3 ). 0.3 g of the catalyst obtained above was diluted with 1.2 g of quartz sand, packed into a SUS reaction tube, and the upper and lower parts of the catalyst layer were sandwiched with quartz wool. Further, 55 g of alumina balls with a diameter of 1 to 2 mm were packed on the upper part of the SUS reaction tube filled with the catalyst. The SUS tube filled with this catalyst layer was attached to a fixed-bed flow-type reactor to carry out the reaction. N 2 For H 2 The molar ratio of the gas (H 2 / N 2 ) of 3 was supplied to the reactor under the condition that the total space velocity (WHSV) of the gas of N 2 and H 2 was 36000 mLg -1 h -1 to carry out the reaction. The gas coming out of the above reactor was quantified for NH 3 by an on-line gas chromatograph. At the same time, the gas coming out of the reactor was bubbled in a 0.01 M sulfuric acid aqueous solution to dissolve the generated ammonia in the solution, and the generated ammonium ions were quantified by an ion chromatograph to measure the concentration of ammonia in the gas discharged from the reactor. The results are shown in Figure 1.

[0072] As shown in Figure 1, the amount of ammonia produced when using the catalyst of Example 1 in which metallic ruthenium and alkaline earth metals are supported on a melilite-type compound was larger than that when using the catalyst of Comparative Example 1 in which only metallic ruthenium is supported on a melilite-type compound. Further, as shown in Fig. 1, in the catalyst of Comparative Example 1 in which only metallic ruthenium is supported on the melilite-type compound, even when the reaction pressure was increased, the amount of ammonia produced could not be increased. However, in the catalyst of Example 1 in which metallic ruthenium and alkaline earth metal are supported on the melilite-type compound, by increasing the reaction pressure, the amount of ammonia produced could be increased. From this, it was found that when metallic ruthenium is supported on the melilite-type compound and further alkaline earth metal is supported on the melilite-type compound, the catalytic activity can be increased, and by increasing the reaction pressure, the catalytic reaction can be further improved.

[0073] <Dependence of ammonia synthesis reaction on ratio of hydrogen to nitrogen> Using the catalysts prepared in Example 1 and Comparative Example 1, while keeping the reaction temperature (400 °C) and reaction pressure (3.0 MPa) constant, nitrogen gas (N 2 ) to hydrogen gas (H 2 ) molar ratio (H 2 / N 2 ) was varied, and a reaction was carried out in which nitrogen gas (N 2 ) and hydrogen gas (H 2 ) were reacted to produce ammonia gas (NH 3 ). 0.3 g of the catalyst obtained above was diluted with 1.2 g of quartz sand, packed into a SUS reaction tube, and the top and bottom of the catalyst layer were sandwiched with quartz wool. Further, 55 g of alumina balls with a diameter of 1 - 2 mm were packed on the upper part of the SUS reaction tube filled with the catalyst. The SUS tube filled with the catalyst layer was attached to a fixed-bed flow-type reaction apparatus and the reaction was carried out. N 2 to H 2 mixed gas with a changed molar ratio was used, and the total gas space velocity (WHSV) of N 2 and H 2 was 18000 mLg -1 h -1Under the conditions that resulted in [the relevant situation], it was supplied to the reactor and the reaction was carried out. The gas coming out of the above reactor was quantified by an online gas chromatograph. Further, the reaction gas on the outlet side was bubbled into a 0.01 M sulfuric acid aqueous solution, the generated ammonia was dissolved in the solution, and the resulting ammonium ions were quantified by an ion chromatograph to measure the concentration of ammonia in the gas discharged from the reactor. The results are shown in Figure 2.

[0074] As shown in Figure 2, the amount of ammonia produced when using the catalyst of Example 1 in which metallic ruthenium and an alkaline earth metal are supported on a melilite-type compound was larger than when using the catalyst of Comparative Example 1 in which only metallic ruthenium is supported on a melilite-type compound. Also, as shown in Figure 2, when metallic ruthenium is supported on a melilite-type compound and further an alkaline earth metal is supported on the melilite-type compound, the molar ratio of hydrogen to nitrogen (H 2 / N 2 ) optimal for ammonia production can be shifted to the high-hydrogen side. From this, it was found that when metallic ruthenium is supported on a melilite-type compound and further an alkaline earth metal is supported on the melilite-type compound, the catalytic activity can be increased and furthermore hydrogen poisoning of the catalyst can be suppressed.

Claims

1. A mayenite type compound, An active metal supported on the mayenite type compound; The catalyst for ammonia synthesis contains a composite including an alkaline earth metal supported on the mayenite type compound using a metal alkoxide by an impregnation method using at least one solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, and butanol without using water.

2. 2. The catalyst for ammonia synthesis according to claim 1, wherein the mayenite type compound is [Ca 24 Al 28 O 64 ] 4+ (O 2− ) 2.

3. 3. The catalyst for ammonia synthesis according to claim 1, wherein the alkaline earth metal is barium.

4. A first step of preparing a mayenite type compound; and a second step of supporting an active metal and an alkaline earth metal on the mayenite type compound, The second step is a method for producing an ammonia synthesis catalyst, in which at least one solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, and butanol is used, and the alkaline earth metal is supported on the mayenite type compound by an impregnation method using a metal alkoxide without using water.

5. 5. The method for producing a catalyst for ammonia synthesis according to claim 4, further comprising a third step of reducing the mayenite type compound obtained in the second step.

6. 6. The method for producing a catalyst for ammonia synthesis according to claim 4 or 5, wherein in the first step, the mayenite type compound is prepared by a hydrothermal synthesis method.

7. 7. The method for producing a catalyst for ammonia synthesis according to claim 4, wherein in the second step, the active metal and the alkaline earth metal are supported by an impregnation method.

8. The method for producing a catalyst for ammonia synthesis according to any one of claims 4 to 7, wherein the mayenite type compound is [Ca 24 Al 28 O 64 ] 4+ (O 2− ) 2.

9. The method for producing a catalyst for ammonia synthesis according to any one of claims 4 to 8, wherein the alkaline earth metal is barium.

10. 4. A method for producing ammonia, comprising the step of producing ammonia by contacting a gas containing nitrogen and hydrogen with the catalyst for ammonia synthesis according to claim 1.

11. The method for producing ammonia according to claim 10, wherein the step of producing ammonia comprises contacting a gas containing nitrogen and hydrogen with the catalyst under conditions of a reaction temperature of 200 to 600° C. and an absolute reaction pressure of 0.01 to 20 MPa.

12. The method for producing ammonia according to claim 10, wherein the step of producing ammonia comprises contacting a gas containing nitrogen and hydrogen with the catalyst under conditions of a reaction temperature of 250 to 700° C. and an absolute reaction pressure of 0.1 to 30 MPa.

13. The step of producing ammonia is carried out by adjusting the molar ratio of hydrogen to nitrogen (H ２ / N ２ The method for producing ammonia according to any one of claims 10 to 12, wherein a gas containing nitrogen and hydrogen is contacted with the catalyst under conditions of a ratio of 0.25 to 15.

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