Process for producing a catalyst for ammonia synthesis and process for producing ammonia

Abstract

The present application provides a catalyst manufacturing method which makes the manufacturing of a supported metal catalyst for ammonia synthesis more convenient in terms of manufacturing method or manufacturing equipment, especially in terms of manufacturing on an industrial scale, and which results in a catalyst with high activity. The catalyst manufacturing method for ammonia synthesis of the present application is characterized by comprising a first step of preparing 12CaO 7Al2O3 with a specific surface area of 5 m 2 / g or more, a second step of supporting a ruthenium compound on the 12CaO 7Al2O3, and a third step of performing reduction treatment on the 12CaO 7Al2O3 on which the ruthenium compound is supported, obtained through the second step. Furthermore, the reduction treatment is performed until the average particle diameter of ruthenium after the reduction treatment is increased by 15% or more relative to the average particle diameter of ruthenium before the reduction treatment.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a catalyst for ammonia synthesis and a method for manufacturing ammonia.

[0002] This application claims priority based on Japanese Patent Application No. 2016-155951, filed in Japan on August 8, 2016, the contents of which are incorporated herein by reference. Background Technology

[0003] Nitrogen fertilizers such as ammonium sulfate and urea, which are widely used in agricultural production, are manufactured using ammonia as their main raw material. Therefore, ammonia is a very important chemical raw material, and its manufacturing methods have been continuously studied.

[0004] The Haber-Bosch process is one of the most widely used technologies for ammonia production. It is a method that uses nitrogen and oxygen as raw materials, contacting them with a catalyst primarily composed of iron under high temperature and pressure to produce ammonia.

[0005] As a synthetic method other than the Haber process, synthetic methods using supported metal catalysts that support metals such as Ru, Co, and Fe on various supports are also being studied.

[0006] On the other hand, there is a compound called "mayenite-type compound," which is calcium aluminosilicate composed of CaO, Al2O3, and SiO2, and has the same crystal structure as mayenite. The representative composition of the aforementioned mayenite-type compound can be represented by 12CaO·7Al2O3. This mayenite-type compound has the following structure: two of the 66 oxygen ions in a unit cell containing two molecules are contained as "free oxygen" within the space of a cage formed by the crystal framework (Non-Patent Document 1).

[0007] The inventors have discovered that the free oxygen ions in the aforementioned calcium aluminate compounds can be replaced by various anions, especially under a strong reducing atmosphere. By maintaining the calcium aluminate compound at high temperatures, all of the aforementioned free oxygen ions can be replaced by electrons. Furthermore, the inventors have discovered that the calcium aluminate compound after electron replacement is a conductive calcium aluminate compound with good electronic conductivity (Non-Patent Document 2). Moreover, calcium aluminate compounds in this manner, where the aforementioned free oxygen ions have been replaced by electrons, are referred to as "C12A7 electron compounds (electride)".

[0008] Furthermore, the inventors have discovered that catalysts using the aforementioned C12A7 electron compound can be used as catalysts for ammonia synthesis (Patent Document 1). Specifically, by using the aforementioned C12A7 electron compound as a support, ammonia can be synthesized by contacting a supported metal catalyst loaded with transition metals such as Ru, Fe, and Co with nitrogen and oxygen. Compared with conventional supported metal catalysts for ammonia synthesis, the aforementioned supported metal catalyst exhibits higher ammonia synthesis activity and is a high-performance ammonia synthesis catalyst.

[0009] The aforementioned C12A7 electron compound can be obtained by heating a calcium aluminate type compound under a reducing atmosphere. Furthermore, a catalyst using the aforementioned C12A7 electron compound can be obtained by loading a transition metal compound as a catalytically active component onto the C12A7 electron compound and then subjecting it to reduction treatment.

[0010] Methods for manufacturing conductive calcium aluminum oxide compounds are still under investigation, and methods to increase their specific surface area are being studied. A calcium aluminum oxide compound with micropores has been proposed (Patent Document 2).

[0011] Patent documents

[0012] Patent Document 1: International Publication No. WO2012 / 077658

[0013] Patent Document 2: International Publication No. WO 2014 / 034473

[0014] Non-patent literature

[0015] Non-patent literature 1: HB Bartl, T. Scheller and N. Jarhrb, Mineral Monatch. 1970, 547.

[0016] Non-patent literature 2: S. Matuishi, Y. Toda, M. Miyakawa, K. Hayashi, T. Kamiya, M. Hirano, I. Tanaka and H. Hosono, Science 301, 626-629 (2003). Summary of the Invention

[0017] The aforementioned C12A7 electron compounds are typically manufactured by electron-injecting calcium aluminate compounds. The electron-injection process usually requires high-temperature heating in a reducing atmosphere, or processing in a closed system or under an inert gas atmosphere (such as Ar), making the reaction operation very complex. Especially with large-scale manufacturing, specialized manufacturing equipment is required, raising concerns about the increased equipment load and manufacturing costs.

[0018] On the other hand, when injecting electrons into calcium aluminate compounds, heating at high temperatures is necessary. Therefore, even when using calcium aluminate compounds with micropores and large specific surface areas, the micropores are destroyed due to exposure to high temperatures. Consequently, when manufacturing catalysts, there is a problem that the specific surface area of ​​the aforementioned C12A7 electron compounds decreases, making it impossible to further improve performance.

[0019] In other words, in the manufacture of supported metal catalysts using the aforementioned C12A7 electron compound as a support, problems exist regarding manufacturing methods and equipment in order to improve catalyst performance, especially considering industrial-scale manufacturing. Therefore, there is a search for manufacturing methods that offer higher activity and can be produced more easily.

[0020] In order to solve the above-mentioned problems, the inventors conducted careful research and found that when using un-electron-injected calcium aluminum oxide compounds as a support, a highly efficient and reactive catalyst for ammonia synthesis can be obtained through a simpler manufacturing method by subjecting the compounds to certain processing conditions.

[0021] That is, the main idea of ​​this invention is as follows.

[0022] [1] A method for manufacturing a catalyst for ammonia synthesis, characterized in that it comprises a first step, a second step, and a third step, wherein the first step is to prepare a catalyst with a specific surface area of ​​5m². 2 The second step involves loading a ruthenium compound onto the 12CaO·7Al2O3. The third step involves reducing the ruthenium-loaded 12CaO·7Al2O3 (hereinafter referred to as ruthenium-loaded C12A7) obtained through the second step, and performing the reduction treatment until the average particle size of the ruthenium after the reduction treatment increases by more than 15% compared with the average particle size of the ruthenium before the reduction treatment.

[0023] [2] The manufacturing method described in [1] above, wherein the specific surface area of ​​the ruthenium-loaded C12A7 after the reduction treatment step is 5 m². 2 / g or more.

[0024] [3] The manufacturing method as described in [1] or [2] above, wherein, in the first step above, the above-mentioned 12CaO·7Al2O3 is prepared by hydrothermal synthesis, sol-gel method, combustion synthesis or coprecipitation method.

[0025] [4] The manufacturing method as described in any one of [1] to [3] above, wherein, in the second step above, the ruthenium compound is loaded by an impregnation method or a vapor deposition method.

[0026] [5] The manufacturing method as described in any one of [1] to [4] above, wherein the reduction process is performed by a gas containing hydrogen.

[0027] [6] The manufacturing method as described in any one of [1] to [5] above includes a step of molding the 12CaO·7Al2O3 obtained by the first step.

[0028] [7] The manufacturing method as described in any one of [1] to [5] above includes a step of forming the ruthenium load C12A7 obtained by the second step.

[0029] [8] The manufacturing method as described in any one of [1] to [7] above, wherein the catalyst for ammonia synthesis contains at least one or more alkali metal atoms or alkaline earth metal atoms.

[0030] [9] A method for producing ammonia, characterized in that it comprises a first step, a second step, a third step and a step for producing ammonia, wherein the first step is to prepare 12CaO·7Al2O3 with a surface area of ​​5 m2 / g or more; the second step is to load a ruthenium compound onto the 12CaO·7Al2O3; the third step is to reduce the 12CaO·7Al2O3 (hereinafter referred to as ruthenium-loaded C12A7) obtained by the second step until the average particle size of the ruthenium after the reduction treatment increases by 15% or more relative to the average particle size of the ruthenium before the reduction treatment; and the step for producing ammonia is to contact a gas containing nitrogen and hydrogen with an ammonia synthesis catalyst that has been reduced by the third step to produce ammonia.

[0031]

[10] The manufacturing method as described in [9] above, wherein the reduction process is performed by a gas containing hydrogen.

[0032]

[11] The manufacturing method as described in [9] above, wherein the reduction process is carried out by a gas containing hydrogen and nitrogen.

[0033]

[12] The manufacturing method as described in any one of [9] to

[11] above, wherein the catalyst for ammonia synthesis contains at least one alkali metal atom or alkaline earth metal atom.

[0034]

[13] A metal-supported material, characterized in that it has 12CaO·7Al2O3 and various metal ions supported on the 12CaO·7Al2O3, wherein the specific surface area of ​​the 12CaO·7Al2O3 is 5 m². 2 / g or more, the above-mentioned multiple metal atoms include ruthenium, and alkali metal atoms or alkaline earth metal atoms.

[0035]

[14] The metal support as described in

[13] above, wherein,

[0036] The aforementioned alkali metal atoms or alkaline earth metal atoms are oxides of alkali metals or oxides of alkaline earth metals.

[0037]

[15] The metal support as described in

[13] or

[14] above, wherein the alkali metal atom or alkaline earth metal atom is barium.

[0038]

[16] A catalyst comprising the metal supported material described in any one of

[13] to

[15] above.

[0039]

[17] The catalyst as described in

[16] above, wherein the catalyst is for ammonia synthesis.

[0040]

[18] A method for producing ammonia, characterized in that a gas containing nitrogen and hydrogen is contacted with the catalyst described in

[16] or

[17] above, thereby producing ammonia.

[0041] Compared to conventional catalysts that use C12A7 electron-carrying compounds as supports, the method for manufacturing the catalyst of the present invention enables the simpler production of a high-performance catalyst for ammonia synthesis. In particular, an ammonia synthesis catalyst can be provided through a manufacturing method suitable for industrial production.

[0042] The method for manufacturing the catalyst of the present invention enables the production of a catalyst that, when used as a catalyst for ammonia synthesis, can stably generate ammonia even during long-term continuous reactions, and exhibits minimal decrease in reactivity. In other words, the long lifespan of the resulting catalyst is advantageous in terms of enabling the production of ammonia with high efficiency. Attached Figure Description

[0043] Figure 1 A graph showing the results of ammonia synthesis reactions using the ammonia synthesis catalysts described in Examples 1-3.

[0044] Figure 2 A graph showing the results of the study on the pressure change of the ammonia synthesis reaction when using the catalyst for ammonia synthesis described in Example 3 (Example 3A).

[0045] Figure 3 A graph showing the results of the ammonia synthesis reaction using the ammonia synthesis catalyst described in Example 4 and Comparative Example 4.

[0046] Figure 4 A graph showing the results of the ammonia synthesis reaction using the ammonia synthesis catalysts described in Examples 2 and 5.

[0047] Figure 5 A graph showing the time variation of the ammonia synthesis reaction when the metal support described in Example 6 is used as a catalyst for ammonia synthesis.

[0048] Figure 6 A graph showing the results of a study on the pressure change of the ammonia synthesis reaction when the metal support described in Example 6 was used as a catalyst for ammonia synthesis (Example 11).

[0049] Figure 7 A graph showing the results of the study on the temperature change of the ammonia synthesis reaction when the metal supports described in Example 6 and Example 2 were used as catalysts for ammonia synthesis (Example 12). Detailed Implementation

[0050] The first aspect of the present invention is a method for manufacturing a catalyst for ammonia synthesis, which is a method for manufacturing a catalyst for ammonia synthesis using 12CaO·7Al2O3 with a large specific surface area and through the manufacturing process specified later.

[0051] The second aspect of the present invention is a metal support and an ammonia synthesis catalyst using the metal support, wherein the metal support has a specific surface area of ​​5 m². 2 Metal-supported materials containing 12CaO·7Al2O3 with a content of more than / g and various metal atoms, wherein the metal atoms are ruthenium, alkali metal atoms, or alkaline earth metal atoms.

[0052] The present invention will now be described in detail.

[0053] <Calcium aluminum type compounds>

[0054] Calcite-type compounds are calcium aluminosilicates composed of CaO, Al₂O₃, and SiO₂. They are compounds with the same crystal structure as calcium aluminosilicate. A representative composition of calcite-type compounds can be represented by 12CaO·7Al₂O₃.

[0055] The crystallization of calcium aluminate compounds occurs by the sharing of cage-like structures (cages) and their three-dimensional interconnection. Typically, the interior of the cages in calcium aluminate compounds contains O₂. 2- They are anions, but can be replaced with conduction electrons through chemical treatment.

[0056] The calcium aluminum oxide compounds used in this invention are referred to as 12CaO·7Al2O3, or simply as "C12A7".

[0057] The specific surface area of ​​12CaO·7Al2O3 used in this invention is 5 m². 2 / g or more. By using 12CaO·7Al2O3 with a specific surface area greater than or equal to the above range, high catalytic activity can be obtained when used as a catalyst for ammonia synthesis. When the surface area is less than the above range, sufficient catalytic activity cannot be obtained. A specific surface area of ​​10 m² is preferably preferred. 2 / g or more, preferably 15m 2 / g or more, with no specific upper limit, but preferably 200m 2 / g or less, more preferably 100m 2 / g or less. If it is below the above range, it is advantageous in terms of catalyst powder processing and formability.

[0058] The shape of 12CaO·7Al2O3 used in this invention is not particularly limited, and can generally be listed as microparticle, granular, blocky, etc., preferably microparticle or blocky, and more preferably microparticle. By forming the calcium aluminum oxide type compound into microparticles, the surface area per unit mass increases. Although the interparticle spacing is not particularly limited, it is generally formed into a mesoporous region of 2 nm or more and 100 nm or less, and is therefore preferred.

[0059] Furthermore, in the case of a bulk form, there are no particular limitations, but a porous material with a microporous structure is preferred. This is because a higher specific surface area can be obtained by having a microporous structure.

[0060] When 12CaO·7Al2O3 is in the form of microparticles, its particle size is not particularly limited. Generally, the primary particle size is 5 nm or more, preferably 10 nm or more, usually less than 500 nm, and preferably less than 100 nm.

[0061] The ammonia synthesis catalyst obtained according to the present invention is obtained by supporting a catalytically active metal on a calcium aluminate compound.

[0062] The ammonia synthesis catalyst in this invention uses ruthenium (Ru) as the catalytically active metal. Ruthenium can be used alone or in combination with other metal elements.

[0063] As for metals other than ruthenium, there are no particular limitations as long as they do not hinder the activity of the ammonia synthesis catalyst obtained in this invention. Generally, it is preferred to use one or more transition metals selected from Group 3, Group 8, Group 9 or Group 10 of the periodic table, and more preferably yttrium, iron or cobalt.

[0064] Among these, Ru alone provides stable catalytic activity and is therefore preferred. This is because, compared to using two or more catalytically active metals, Ru alone is less prone to changes in the catalyst surface composition due to variations in reduction conditions, making it easier to obtain the desired ammonia synthesis activity.

[0065] The amount of Ru used is not particularly limited relative to the mass of C12A7 used as a support, and is typically 0.01% by mass or more, preferably 0.02% by mass or more, more preferably 0.05% by mass or more, typically 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less. By being within the above range, the obtained catalyst can have sufficient active sites, thereby obtaining a highly efficient catalyst and a catalyst that is cost-effective.

[0066] Regarding the ammonia synthesis catalyst obtained according to the present invention, it may also contain components other than calcium aluminate compounds and catalytically active metals, as long as it does not hinder the purpose of the present invention.

[0067] For example, it can be added as a binder component to facilitate the shaping of the catalyst.

[0068] Specifically, examples include metal oxides such as SiO2, Al2O3, ZrO2, TiO2, La2O3, CeO2, and Nb2O5, activated carbon, graphite, and carbon materials such as SiC.

[0069] Furthermore, the ammonia synthesis catalyst obtained according to the present invention may also contain, as a component, any one of alkali metal atoms and alkaline earth metal atoms. These components function as reaction promoters in ammonia synthesis by being present within the catalyst; therefore, it is preferable to include these components.

[0070] There are no particular limitations on the types of alkali metal atoms; examples include lithium, sodium, potassium, cesium, and rubidium.

[0071] There are no particular limitations on the types of alkaline earth metal atoms; examples include magnesium, strontium, and barium.

[0072] Among the aforementioned metal atoms, barium atoms are preferred.

[0073] There are no particular limitations on the form in which alkali metal atoms and alkaline earth metal atoms are added. Examples include hydroxides of each atom; inorganic acid salts such as carbonates and nitrates; carboxylate salts such as acetates and formates; ethanol salts and other organic compounds containing each atom.

[0074] There is no particular limitation on the amount of the above reaction promoter added. Preferably, the molar ratio of the catalyst to the ruthenium atoms contained in the catalyst, based on the atomic conversion of each metal, is usually more than 0.01 times and less than 50 times, and more preferably less than 20 times.

[0075] Regarding the alkali metal atoms and alkaline earth metal atoms that can be included as reaction promoters, they can simply be present in the reaction field during the ammonia synthesis reaction, and there are no particular restrictions on their form. Examples include methods such as mixing them during the preparation of the calcium aluminate type compound as the first step (described later) to produce a calcium aluminate type compound containing them, methods of co-loading them during the loading of the Ru metal source as the second step (described later), or adding them during catalyst shaping to perform shaping, etc.

[0076] <Method for manufacturing catalysts for ammonia synthesis>

[0077] The method for manufacturing a catalyst for ammonia synthesis, which is a first aspect of the present invention (hereinafter referred to as the manufacturing method of the present invention), includes steps one through three as described below. These steps will be described sequentially below.

[0078] <First Step: Preparation of Calcium Aluminate Compound (12CaO·7Al2O3)>

[0079] The manufacturing method of the present invention includes preparing a specific surface area of ​​5m². 2 The process of producing 12CaO·7Al2O3 with a yield of 1 g or more is considered the first process.

[0080] Regarding the use in manufacturing a specific surface area of ​​5m² 2 There are no particular limitations on the raw materials for 12CaO·7Al2O3 with a weight of 1g or more. Various raw materials containing calcium (hereinafter referred to as calcium atom sources) and raw materials containing aluminum (hereinafter referred to as aluminum atom sources) may be used appropriately depending on the manufacturing method.

[0081] There are no particular limitations on the calcium atom source mentioned above. Specifically, calcium hydroxide, calcium oxide, calcium nitrate, calcium chloride, calcium acetate, and other calcium salts can be used; calcium alcohols such as calcium ethanol, calcium propoxide, calcium isopropoxide, calcium butoxide, and calcium isobutoxide can also be used.

[0082] There are no particular limitations on the aluminum atom sources mentioned above. Specifically, aluminum hydroxide, aluminum oxide, aluminum nitrate, aluminum chloride, aluminum acetate, and other aluminum salts can be used; aluminum ethoxide, aluminum propoxide, aluminum isopropoxide, aluminum butoxide, aluminum isobutoxide, and other aluminum alkoxides; aluminum acetylacetonate, etc.

[0083] As long as it does not hinder the purpose of the present invention, the calcium aluminum oxide type compound (12CaO·7Al2O3) may also contain atoms other than Ca, Al and oxygen.

[0084] Specifically, the alkali metal atoms or alkaline earth metal atoms used as reaction promoters can be used together with the calcium atom source and the aluminum atom source to carry out the first step of the present invention.

[0085] It should be clarified that "containing atoms other than Ca, Al, and oxygen" refers to substances in calcium aluminate compounds (12CaO·7Al2O3) that contain atoms other than Ca, Al, and oxygen as constituent elements. Specifically, for example, "containing alkaline earth metal atoms" refers to alkaline earth metal compounds such as monomers, salts, oxides, or hydroxides of alkaline earth metals.

[0086] Regarding the preparation of a specific surface area of ​​5m² 2 There are no particular limitations on the method for producing 12CaO·7Al2O3 with a specific surface area of ​​1 / g or more. Hydrothermal synthesis, sol-gel synthesis, combustion synthesis, or coprecipitation methods can generally be used. Among these methods, hydrothermal synthesis is preferred because it is simple and can produce 12CaO·7Al2O3 with a high specific surface area with good reproducibility.

[0087] <Hydrothermal Synthesis Method>

[0088] Hydrothermal synthesis, as a method for synthesizing well-crystallized particulate inorganic oxides, has been studied for a long time. Specifically, the method involves first adding a solvent such as water or alcohol and the inorganic oxide raw material to a pressure vessel, and heating at a temperature above the solvent's boiling point for several hours to several days to obtain a precursor compound of the inorganic oxide. Then, the obtained precursor compound is further heated to obtain the inorganic oxide.

[0089] In the case of producing calcium aluminate compounds (12CaO·7Al2O3) using a hydrothermal synthesis method, the precursor Ca3Al2(OH) is usually synthesized as a hydroxide. 12 It is typically obtained by heating the hydroxide in a pressure vessel at a temperature above the boiling point of water.

[0090] There are no particular limitations on the calcium atom source used in the hydrothermal synthesis method. Generally, calcium hydroxide, calcium oxide, and calcium salts are used among the above-mentioned calcium atom sources, with calcium hydroxide being preferred.

[0091] Furthermore, there are no particular limitations on the aluminum atom source. Generally, aluminum hydroxide, aluminum oxide, and aluminum salts are used among the aluminum atom sources mentioned above, with aluminum hydroxide being the preferred choice.

[0092] There are no particular limitations on the mixing ratio of the raw materials for the above-mentioned precursors. They can be prepared appropriately according to the desired composition, and are usually mixed with the stoichiometric composition of the target calcium aluminum oxide compound (12CaO·7Al2O3).

[0093] There are no particular limitations on the heating temperature; a suitable heating temperature that yields sufficient production can be selected, typically above 100°C, preferably above 150°C, and usually below 200°C. As long as it is within the above range, it can be manufactured using commonly used reaction equipment, which is advantageous in terms of equipment.

[0094] There is no particular limitation on the heating time; a suitable heating time that yields sufficient production can be selected, typically 2 hours or more, preferably 6 hours or more, and usually less than 100 hours. As long as it is within the above range, the target calcium aluminum type compound can be sufficiently obtained.

[0095] The above-obtained calcium aluminum oxide type compound precursor Ca3Al2(OH) was analyzed. 12 Heating and dehydration can yield a product with a specific surface area of ​​5m². 2 / g or more of 12CaO·7Al2O3.

[0096] There are no particular restrictions on the heating conditions; an appropriate selection can be made within the range that yields a large specific surface area of ​​C12A7, and heating is usually carried out in air.

[0097] There are no particular limitations on the heating temperature, but it can usually be above 400°C, preferably above 450°C, and usually below 1000°C.

[0098] Sol-gel method

[0099] Calcareous aluminum oxide compounds (12CaO·7Al2O3) can be manufactured using the sol-gel method. The sol-gel method involves hydrolyzing an organic or inorganic compound of the metal used as a raw material for the desired metal oxide in solution to form a sol, followed by condensation polymerization to transform the sol into a gel. The gel is then subjected to high-temperature treatment to produce the metal oxide. The manufacturing method can be based on known methods such as those described in J. Phys. D: Appl. Phys., 41, 035404 (2008).

[0100] In the method for manufacturing the catalyst of the present invention, specifically, the aluminum atom source described above as a raw material is dissolved in a solvent, heated and stirred, and then an acid is added to prepare a hydrolyzed sol. Next, the calcium atom source described above is dissolved in a solvent, the pH is adjusted as needed, and it is stirred together with the sol containing the aluminum atom source. Under these conditions, it is heated and mixed to gel, and then the resulting gel is filtered, dehydrated, and sintered to obtain a calcium aluminum oxide type compound.

[0101] There are no particular limitations on the calcium atom source used in the sol-gel method. Calcium hydroxide, calcium oxide, calcium salts, etc., are commonly used, with calcium salts being preferred. Calcium nitrate is the preferred calcium salt.

[0102] There are no particular limitations on the aluminum atom source mentioned above; aluminum hydroxide, aluminum oxide, or aluminum alkoxide are commonly used, with aluminum alkoxide being preferred.

[0103] Combustion Synthesis Method

[0104] Combustion synthesis can also be used to synthesize calcium aluminate compounds. Specifically, the method described in J. Am. Ceram. Soc., 81, 2853-2863 (1998) can be followed. For example, calcium and aluminum atom sources are dissolved in water, the mixed solution is heated and combusted to obtain an amorphous precursor of the calcium aluminate compound. This amorphous precursor is further heated and dehydrated to obtain the calcium aluminate compound.

[0105] There are no particular limitations on the calcium and aluminum atom sources used in the combustion synthesis method, but calcium salts and aluminum salts are generally preferred, and calcium nitrate and aluminum nitrate are more preferred.

[0106] Specifically, for example, Ca(NO3)2·4H2O and Al(NO3)3·9H2O can be used as raw materials. These raw materials are not particularly limited and can be dissolved in water in stoichiometric proportions. Urea is further added to the solution containing the above raw materials, the mixture is heated, and then combusted to obtain an amorphous precursor of a calcium aluminum oxide type compound.

[0107] There are no specific limitations on the heating temperature, but it is usually above 500℃.

[0108] Moreover, there are no particular limitations on the amorphous precursors obtained. They are usually heated to a temperature above 700°C and below 1000°C to dehydrate them, thereby obtaining calcium aluminum oxide compound powder C12A7.

[0109] <Coprecipitation Method>

[0110] Coprecipitation is a method that uses a solution containing two or more metal ions to simultaneously precipitate sparingly soluble salts of multiple metals. It is a method for preparing powders with high uniformity.

[0111] There are no particular restrictions on the raw materials used in the coprecipitation method. Calcium salts and aluminum salts are commonly used as the calcium atom source and the aluminum atom source, with nitrates being preferred.

[0112] Specifically, an alkali such as ammonia or sodium hydroxide can be added to an aqueous solution containing calcium nitrate and aluminum nitrate. After the sparingly soluble salts containing calcium hydroxide and aluminum hydroxide are precipitated simultaneously, the solution is filtered, dried, and sintered to obtain 12CaO·7Al2O3.

[0113] <Second Process: Process of Loading Ruthenium Compounds>

[0114] The manufacturing method of the present invention includes a second step of loading a ruthenium compound onto 12CaO·7Al2O3 obtained in the first step.

[0115] There are no particular limitations on the ruthenium compounds mentioned above, as long as they can be converted into metallic ruthenium, which is an active component for ammonia synthesis catalysts, through continuous reduction processes. Ruthenium salts or ruthenium complexes can be used.

[0116] Examples of ruthenium salts include ruthenium chloride (RuCl3), ruthenium chloride hydrate (RuCl3·nH2O), and ruthenium acetate (Ru(CH3CO2)). x Ruthenium chloride is preferred as a ruthenium salt because it does not damage the structure of 12CaO·7Al2O3 during the Ru loading process and achieves high ammonia synthesis activity.

[0117] As a ruthenium complex, dodecacarbonyltriruthenium (Ru3(CO)) can be used. 12 ), ruthenium(II) dichlorotetra(triphenylphosphine) (RuCl2(PPh3)4), ruthenium(II) dichlorotri(triphenylphosphine) (RuCl2(PPh3)3), ruthenium(III) tri(acetylacetone) (Ru(acac)3), ruthenium(II) dicerocene (Ru(C5H5)2), ruthenium(II) dichlorophenyl ([RuCl2(C6H6)]2), ruthenium(II) dichloro(mesitylene) ([RuCl2(mesitylene)]2), ruthenium(II) dichlorobis(4-methylisopropylphenyl) ([RuCl2(p-cymene)]2), ruthenium(II) carbonyl chloride ([RuHCl(CO)(PPh3)3]), ruthenium(III) tri(2,2,6,6-tetramethyl-3,5-heptanedione) ([Ru(dpm)3]), etc.

[0118] As a ruthenium complex, dodecacarbonyltriruthenium (Ru3(CO)) is preferred due to its high activity in ammonia synthesis. 12Ruthenium triacetylacetonate (Ru(acac)3), ruthenium dicerocene (Ru(C5H5)2), etc.

[0119] Among the aforementioned ruthenium compounds, considering both safety and cost in catalyst manufacturing, ruthenium chloride and tris(acetylacetone)ruthenium(III) are preferred.

[0120] When loading ruthenium onto C12A7, Ru3(CO) can be used for the purpose of uniform loading. 12 However, such metal carbonyl compounds decompose at 150°C, sometimes producing toxic CO. Therefore, from the perspective of ease of preparation and no need to worry about safety and hygiene, it is more advantageous to use tri(acetylacetone)ruthenium(III) (Ru(acac)3, ruthenium dicene (Ru(C5H5)2) or ruthenium salts.

[0121] These substances are prone to thermal decomposition. Therefore, after being loaded onto the C12A7 support, heat treatment is performed to precipitate the aforementioned ruthenium compound on the support in a metallic state, thereby enabling the loading of Ru. Furthermore, the aforementioned ruthenium compound is readily reduced by hydrogen upon heating, generating Ru metal on the support.

[0122] In the second step, a metal compound other than a ruthenium compound, used in conjunction with the ruthenium used in the catalyst for ammonia synthesis, can be co-loaded. As for the metal compound other than a ruthenium compound, there are no particular limitations as long as it does not hinder the loading of the ruthenium compound; generally, one or more transition metal compounds selected from Groups 3, 8, 9, or 10 of the periodic table are preferred, and yttrium, iron, or cobalt compounds are more preferred. As the metal compound other than a ruthenium compound, a metal salt or metal complex of the corresponding metal type can be used. For example, for iron and cobalt, examples of metal salts include ferric chloride (FeCl2, FeCl3), cobalt chloride (CoCl3), ferric acetate (Fe(CH3CO2)2), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), ferric oxalate hydrate (Fe(C2O4)·nH2O), ferric sulfate hydrate (FeSO4·nH2O), and cobalt acetate (Co(CH3CO2)2). Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), cobalt oxalate dihydrate (Co(C2O4)·2H2O), and cobalt sulfate hydrate (CoSO4·nH2O), etc., as metal complexes, include iron pentacarbonyl (Fe(CO)5), iron nonacarbonyl diferrate (Fe2(CO)9), iron diiodide tetracarbonyl iron (Fe(CO)4I2), ferrocene (Fe(C5H5)2), iron(III) acetylacetone (Fe(acac)3), and iron dodecacarbonyl triferrate (Fe3(CO)2). 12Examples of co-loaded ruthenium compounds include cobalt(III) acetylacetonate (Co(acac)3), cobalt(II) acetylacetonate (Co(acac)2), cobalt octacarbonyl (Co2(CO)8), and cobalt dicene (Co(C5H5)2). These co-loaded metal compounds other than ruthenium are prone to thermal decomposition. Therefore, after being loaded onto a support, heat treatment is performed to precipitate the monomeric transition metal on the substrate, thereby enabling the co-loading of metals other than ruthenium with ruthenium.

[0123] In addition, alkali metal atoms or alkaline earth metal atoms used as reaction promoters can also be co-loaded.

[0124] It should be noted that co-loading alkali metal atoms or alkaline earth metal atoms refers to loading ruthenium compounds together with metal monomers of alkali metal atoms or alkaline earth metal atoms, their respective metal salts, their respective metal oxides, metal hydroxides, and other metal compounds, which are composed of individual atoms.

[0125] There are no particular limitations on the co-supported material, but metal monomers or metal oxides are preferred. From the perspective of higher stability when used in catalytic reactions, metal oxides are preferred.

[0126] Alkaline earth metal atoms are preferred as the types of atoms to be co-loaded, and more particularly Sr and Ba are preferred. Ba is even more preferred from the perspective of being an element that exists in greater quantities.

[0127] As a specific co-supporting material, alkaline earth metal oxides are preferred, and oxides of Ba are more preferred, considering that they are not components of C12A7 and are present in greater quantities.

[0128] After loading, alkaline earth metal oxides, even after reduction treatment described later, usually remain in their original state as oxides and exist on the surface together with the reduced ruthenium metal.

[0129] Regarding the raw materials used when loading the above-mentioned co-loaded material, there are no particular limitations as long as they can load the co-loaded metal atoms. Examples of commonly used raw materials include hydroxides of each atom; inorganic acid salts such as carbonates and nitrates; carboxylate salts such as acetates and formates; ethanol salts such as ethanol salts; organic compounds containing other atoms; metal complexes such as acetylacetone metal complexes, etc. Alkoxides, acetylacetone metal complexes, and carboxylate salts are preferred, and easily reactive alkoxides are more preferred.

[0130] There are no particular limitations on the method for co-loading the above-mentioned co-loaded materials, nor on the order of loading. Specifically, they can be loaded simultaneously with the ruthenium compound or loaded separately. From the perspective of preferably loading the co-loaded material near the ruthenium, it is preferable to load the co-loaded material after loading the ruthenium compound.

[0131] There are no particular limitations on the method for loading ruthenium compounds; loading can be performed by impregnation, thermal decomposition, liquid phase method, sputtering, vapor deposition, etc. In the method of loading Ru onto 12CaO·7Al2O3 powder, the method of loading the ruthenium compound using any of the above-mentioned loading methods followed by molding is more practically used. On the other hand, in the method of loading Ru onto a pre-formed 12CaO·7Al2O3 support, impregnation or vapor deposition is preferred from the viewpoint that Ru can be uniformly dispersed on the monomer, and impregnation is more preferred from the viewpoint that it is easier to form uniform ruthenium particles. Specifically, the impregnation method involves dispersing 12CaO·7Al2O3 in a solution containing a ruthenium compound, then evaporating the solvent containing the solution of 12CaO·7Al2O3 and the ruthenium compound, and allowing it to dry, thereby obtaining 12CaO·7Al2O3 loaded with the ruthenium compound (hereinafter, sometimes also referred to as ruthenium-loaded C12A7).

[0132] In addition, specifically, the vapor deposition method involves physically mixing 12CaO·7Al2O3 with a ruthenium compound and heating it in a vacuum environment. As the ruthenium compound undergoes thermal decomposition, ruthenium is vapor-deposited onto 12CaO·7Al2O3, thereby obtaining the aforementioned ruthenium-loaded C12A7.

[0133] <Third Process: Reduction Process>

[0134] The manufacturing method of the present invention includes a step of reducing the ruthenium-supported C12A7 obtained by the second step. Specifically, the third step is to reduce the ruthenium compound supported on the ruthenium-supported C12A7 to metallic ruthenium to form a ruthenium-supported catalyst.

[0135] The reduction treatment in the third step of this invention involves performing a reduction treatment until the average particle size of the ruthenium after the reduction treatment increases by more than 15% compared to the average particle size of the ruthenium before the reduction treatment. There is no particular upper limit, but it is typically less than 200%. By performing the reduction treatment up to the above range, the ruthenium-supported C12A7 can be made into a highly active catalyst for ammonia synthesis.

[0136] Here, the average particle size of ruthenium generally refers to the average particle size obtained by the chemisorption method described later. In cases where it is difficult to measure by the chemisorption method, it refers to the average particle size obtained by direct observation methods such as TEM described later.

[0137] The average particle size of ruthenium before and after reduction treatment is determined by taking all ruthenium atoms present on the measured surface as metallic ruthenium. As long as it does not have an effect, ruthenium compounds that serve as the source of ruthenium atoms may also be included.

[0138] It should be noted that when ruthenium compounds, which serve as the source of ruthenium atoms, constitute the majority of the ruthenium, it is impossible to determine the particle size of ruthenium. Therefore, the particle size of ruthenium can also be determined through low-temperature reduction treatment.

[0139] There is no particular limitation on the average particle size of ruthenium in the reduced ruthenium-supported catalyst, which is usually above 2 nm and below 15 nm.

[0140] Regarding the conditions for the reduction treatment in the third step of the present invention, there are no particular limitations as long as they do not hinder the purpose of the present invention. For example, methods performed in an atmosphere containing a reducing gas, or methods that add reducing agents such as NaBH4, NH2NH2, or formalin to a solution containing a Ru atom source to cause precipitation on the C12A7 surface, are examples. However, it is preferred to perform the treatment in an atmosphere containing a reducing gas. Examples of reducing gases include hydrogen, ammonia, methanol (vapor), ethanol (vapor), methane, and ethane.

[0141] Furthermore, during the reduction process, components other than reducing gases that do not hinder the ammonia synthesis reaction can also coexist in the reaction system. Specifically, during the reduction process, in addition to reducing gases such as hydrogen, gases such as argon or nitrogen that do not hinder the reaction can also coexist, preferably coexisting with nitrogen.

[0142] When the reduction process is carried out in a hydrogen-containing gas, by allowing nitrogen and hydrogen to coexist, the third step described above can be performed simultaneously with the ammonia synthesis described later.

[0143] There is no particular limitation on the temperature of the reduction treatment in the third step of the present invention, but it is generally carried out at 200°C or above, preferably 300°C or above, and generally at 1000°C or below, preferably 600°C or below. This is because, by carrying out the reduction treatment within the above-mentioned temperature range, ruthenium particles will grow sufficiently and within the preferred range. Furthermore, by carrying out the above-mentioned reduction treatment, the activation energy in the ammonia synthesis reaction and the partial pressure dependence of hydrogen and nitrogen on the relative reaction rate exhibit characteristics almost identical to those of the highly reactive Ru / C12A7 electron compound.

[0144] In this invention, the pressure of the reduction treatment is not particularly limited, but is typically 0.01 MPa or higher, and usually 10 MPa. If the pressure during the reduction treatment is set to the same conditions as the ammonia synthesis conditions described later, complex operations are not required, which is advantageous in terms of manufacturing efficiency.

[0145] In this invention, the reduction treatment time is not particularly limited. When carried out under normal pressure, it is usually 20 hours or more, preferably 25 hours or more.

[0146] Furthermore, when the reaction is carried out under high pressure conditions, such as 1 MPa or higher, it is preferable to carry out the reaction for 5 hours or more.

[0147] The ruthenium-loaded material obtained after the above reduction treatment can be used as a catalyst with ammonia synthesis activity (hereinafter, sometimes simply referred to as "catalyst").

[0148] The BET specific surface area of ​​the catalyst obtained by the manufacturing method of the present invention is not particularly limited, but is typically 5 m². 2 / g, preferably 10m 2 / g or above, typically 200m 2 / g or less, preferably 100m 2 / g or less.

[0149] It should be noted that the specific surface area of ​​the ruthenium-loaded C12A7 obtained after the reduction treatment is generally the same as that of the C12A7 before the ruthenium loading was used in its manufacture.

[0150] The catalyst obtained by the manufacturing method of the present invention can be used as a molded body using conventional molding techniques. Specifically, shapes such as granules, spheres, flakes, rings, macaroni, tetralobes, dice, and honeycomb are available. The metal-supported catalyst can be coated onto a support and then used.

[0151] There is no limitation on which stage of the manufacturing method of the present invention the formation of the above catalyst is carried out, and it can be carried out in any subsequent process.

[0152] Specifically, it may also include a step following the first step above, in which the 12CaO·7Al2O3 obtained through the first step is shaped.

[0153] In addition, it may also include a step following the second step described above, in which the ruthenium-loaded C12A7 obtained through the second step is molded.

[0154] In addition, it may also include a step following the third step above, in which the catalyst obtained through the third step is shaped.

[0155] From the perspective of uniformly dispersing Ru on the support and obtaining high ammonia synthesis activity, a method that includes a molding step following the first step or a method that includes a molding step following the second step is preferred.

[0156] In addition, alkali metal atoms or alkaline earth metal atoms, which are used as reaction promoters, can be added during molding, and molding can be carried out on this basis, or they can be added to the surface of the catalyst after molding.

[0157] By employing the manufacturing method described above as the first aspect of the present invention, a metal-supported material containing multiple metal atoms loaded in 12CaO·7Al2O3 can be obtained, wherein the specific surface area of ​​12CaO·7Al2O3 is 5 m². 2 / g or more, the above-mentioned metal atoms are ruthenium, alkali metal atoms or alkaline earth metal atoms.

[0158] The inventors discovered that the aforementioned metal-supported materials, especially when used as catalysts in ammonia synthesis reactions, exhibit very high activity and are therefore highly useful as catalysts for ammonia synthesis. In other words, catalysts with activity equal to or greater than that of C12A7 electron compounds can be obtained without injecting electrons into C12A7.

[0159] The metal support material described above (hereinafter referred to as the metal support material of the present invention) and the catalyst for ammonia synthesis using it, which is a second aspect of the present invention, will now be described.

[0160] Specifically, the metal support of the present invention has a specific surface area of ​​5m². 2 Using 12CaO·7Al2O3 of 1 / g or more as a support, a metal loading material is loaded on the support along with ruthenium metal, which contains alkali metal atoms or alkaline earth metal atoms. It is preferred to load alkaline earth metal atoms, more preferably to load Sr or Ba atoms, and even more preferably to load Ba atoms.

[0161] Furthermore, there are no particular limitations on the state in which alkali metal atoms or alkaline earth metal atoms are supported. From the perspective of high stability when used as a catalyst in a reaction, oxides supported with each atom are preferred.

[0162] Specifically, it is preferred to have a specific surface area of ​​5m². 2 C12A7 with a weight of / g or more is co-loaded with metallic ruthenium and alkaline earth metal oxides. Considering that it is not a component of C12A7 and is an oxide of an element that is more abundant on Earth, oxides co-loaded with metallic ruthenium and Ba are more preferred.

[0163] The method for manufacturing the metal support of the present invention is not limited to the range in which its effects can be obtained. It is preferred to manufacture it by the manufacturing method that is the first aspect of the present invention. When using the manufacturing method of the present invention, the specific manufacturing method, conditions, etc. are as described above.

[0164] The metal-supported material of the present invention can be used as a catalyst, especially as a catalyst for ammonia synthesis. Catalysts or ammonia synthesis catalysts containing the metal-supported material of the present invention are preferred in that they have high reactivity, and more specifically, in that they can produce ammonia more efficiently at lower temperatures compared to cases without supported alkali metal or alkaline earth metal atoms.

[0165] <Methods for manufacturing ammonia>

[0166] Ammonia can be produced by using the catalyst obtained by the manufacturing method of the present invention and the catalyst containing the metal support of the present invention in an ammonia synthesis reaction.

[0167] Specifically, following the first to third steps of the above-mentioned method for manufacturing ammonia synthesis catalyst, a fourth step is performed in which a gas containing hydrogen and nitrogen is brought into contact with the obtained catalyst, thereby producing ammonia.

[0168] As a method for producing ammonia, in the third step of the above-mentioned method for producing ammonia synthesis catalyst, only hydrogen can be supplied. After obtaining a highly active catalyst, nitrogen and hydrogen can be supplied together to synthesize ammonia. Alternatively, a mixed gas containing hydrogen and nitrogen can be supplied from the beginning to continuously carry out the catalyst reduction reaction and ammonia synthesis. Furthermore, the unreacted gas recovered from the reactor at this time can also be recycled back to the reactor for use.

[0169] There are no particular limitations on the method for producing ammonia according to the present invention. When a gas containing hydrogen and nitrogen is brought into contact with the above-mentioned catalyst, ammonia synthesis is usually carried out by heating the catalyst.

[0170] There are no particular limitations on the reaction temperature, but it is generally above 200°C, preferably above 250°C, and generally below 600°C, preferably below 500°C. Since ammonia synthesis is an exothermic reaction, from the perspective of chemical equilibrium theory, the low-temperature region is favorable for ammonia formation. In order to obtain a sufficient ammonia formation rate, the above-mentioned temperature range is preferred.

[0171] There are no particular limitations on the molar ratio of nitrogen and hydrogen in contact with the catalyst described above. Generally, the ratio of hydrogen to nitrogen (H2 / N2 (volume / volume)) is usually 1 or more and 10 or less, preferably 5 or less.

[0172] There is no particular limitation on the reaction pressure during the ammonia synthesis reaction of the present invention. The pressure is typically 0.01 MPa or more, preferably 0.1 MPa or more, and typically 20 MPa or less, using a pressure gauge containing a mixture of nitrogen and hydrogen.

[0173] Preferably, before supplying the mixed gas containing nitrogen and hydrogen, the moisture and oxides adhering to the catalyst are removed using hydrogen or the like. Reduction treatment is an example of such removal method. Although the catalyst is relatively stable relative to moisture, for better ammonia yield, while not particularly limited, the total moisture content in the nitrogen and hydrogen mixed gas is generally 100 ppm or less, preferably 50 ppm or less.

[0174] There are no particular limitations on the form of the reaction vessel; any reaction vessel commonly used for ammonia synthesis can be used. Specific reaction methods include, for example, batch reaction, closed-loop reaction, and flow-through reaction. From a practical point of view, flow-through reaction is preferred. Furthermore, methods such as connecting one or more reactors packed with catalyst, or reactors with multiple reaction layers within the same reactor, can also be used.

[0175] Since the ammonia synthesis reaction based on a mixture of hydrogen and nitrogen gases is a volume-contracting exothermic reaction, reaction apparatus commonly used in industry to remove the heat of reaction can be used to improve the ammonia yield. Specifically, a method can be used where multiple reactors packed with catalyst are connected in a straight line, and an intercooler is installed at the outlet of each reactor for heat removal.

[0176] In the ammonia production method of the present invention, the ammonia synthesis catalyst obtained by the production method of the present invention can be used alone, or it can be used in combination with other known catalysts that are generally capable of being used for ammonia synthesis.

[0177] (Example)

[0178] The present invention will now be described in more detail based on embodiments.

[0179] (BET specific surface area analysis)

[0180] The BET surface area of ​​the following examples and comparative examples was determined by adsorbing nitrogen onto the surface of the object at liquid nitrogen temperature and measuring the amount of nitrogen adsorbed as a monolayer. The analytical conditions are as follows.

[0181] [Measurement Conditions]

[0182] Device: BELSORP-mini II manufactured by Malikro Corporation

[0183] Adsorbed gas: Nitrogen 99.99995% by volume

[0184] Adsorption temperature: Liquid nitrogen temperature -196℃

[0185] (Determination of average Ru particle size)

[0186] The average particle size of Ru can be determined by chemisorption of CO and by direct observation using electron microscopy. In this invention, the average particle size of Ru is typically determined by chemisorption, but in cases where chemisorption is difficult to perform, it is determined by direct observation.

[0187] <Chemical Adsorption Method>

[0188] CO molecules are adsorbed onto the surface of the object. Based on the amount of CO adsorbed, the number of metal atoms exposed on the surface is estimated, and the metal surface area (Am) per unit mass of loaded metal is calculated. The metal surface area is obtained based on the following general formula (1).

[0189] A relationship is formed between the metal surface area (Am) and the average particle size (d) of the loaded metal nanoparticles as shown in the following general formula (1). Therefore, the average particle size of the loaded Ru can be determined from the metal surface area (Am) based on general formula (2).

[0190] Am=(V chem ×(SF / 22414)×6.02×10 23 ×σ m ×10 -18) / c(1)

[0191] V chem CO adsorption capacity (cm³) 3 )

[0192] SF (stoichiometry factor): CO / Ru = 1

[0193] σ m Metal cross-sectional area of ​​1 atom (nm) 2 )

[0194] c: Mass of the metal loaded on the sample (g)

[0195] Am = 4π(d / 2) 2 ×(α / c)(2)

[0196] d: Average particle size (m) of the metal nanoparticles

[0197] α: Number of metal particles

[0198] c: Mass of the metal loaded on the sample (g)

[0199] [Measurement Conditions]

[0200] Device: BELCAT-A manufactured by Malikro Corporation

[0201] Adsorbed gas: CO / He mixed gas, CO concentration 9.5% by volume

[0202] Adsorption temperature: 50℃

[0203] It should be noted that when using the chemisorption method for determination, the test sample is pretreated as follows before the determination.

[0204] <<Sample Pretreatment Conditions>>

[0205] The sample was heated from room temperature to 400°C over 20 minutes in a He gas stream, and then held at 400°C for 30 minutes in a hydrogen gas stream. Next, it was placed at 400°C for 15 minutes in a He gas stream, and then cooled to 50°C.

[0206] Direct Observation Method

[0207] Metal nanoparticles were observed using electron microscopes such as TEM, and the size of more than 100 metal nanoparticles was measured to obtain the average value.

[0208] [Measurement Conditions]

[0209] Device: JEOL-ARM200F manufactured by Japan Spectroscopy Corporation

[0210] Accelerating voltage: 200kV

[0211] (Activation energy determination)

[0212] Activation energy is the energy required for the initial substances in a reaction to be excited from the ground state to the transition state. The lower this energy, the easier the reaction proceeds. It is calculated by determining the temperature dependence of the reaction rate and then plotting the natural logarithm of the reaction rate against the reciprocal of temperature.

[0213] The evaluation of the ammonia synthesis catalyst of the present invention involves determining the ammonia generation rate by dissolving the generated NH3 in an aqueous sulfuric acid solution and quantifying the solution using an ion chromatograph, based on the ammonia generation rate. The ammonia synthesis activity is then evaluated according to this generation rate.

[0214] (Ion chromatography analysis)

[0215] The generated ammonia gas was dissolved in a 0.05M sulfuric acid aqueous solution, and the solution was analyzed by ion chromatography. The ammonia production in the following examples and comparative examples was determined using the absolute standard curve method. The analytical conditions are as follows.

[0216] [Measurement Conditions]

[0217] Apparatus: HPLC Prominence manufactured by Shimadzu Corporation

[0218] Column: Shim-pack IC-C4, manufactured by Shimadzu Corporation

[0219] Length: 150mm, Inner Diameter: 4.6mm

[0220] Eluent: A mixed aqueous solution of oxalic acid (3 mM) and 18-crown-6-ether (2.0 mM).

[0221] Column temperature: 40℃

[0222] Flow rate: 1.0 mL / min

[0223] (Example 1)

[0224] <Synthesis of calcium aluminate compounds>

[0225] Weigh Ca(OH)₂ and Al(OH)₃ to achieve a Ca:Al molar ratio of 12:14, and mix them to obtain a mixed powder. Add distilled water to the mixed powder to achieve a powder content of 10% by mass, thus preparing a mixed solution with a total mass of 160g. Stir / mix the solution in a planetary ball mill at room temperature for 4 hours. Place the resulting mixed solution into a pressure-resistant sealed container and heat it at 150°C (hydrothermal treatment) for 6 hours while stirring.

[0226] The precipitate obtained through the above hydrothermal treatment was filtered, dried, and pulverized to obtain approximately 20g of precursor powder of a calcium aluminum oxide type compound: Ca3Al2(OH). 12 The precursor powder was dehydrated by heating at 600°C for 5 hours in air to obtain a calcium aluminate compound powder (hereinafter referred to as HT-C12A7). The specific surface area of ​​this calcium aluminate compound is 50–60 m². 2 / g is a calcium aluminum oxide type compound with a large specific surface area.

[0227] <Ruthenium compounds loaded onto calcium aluminate compounds>

[0228] 1g of the HT-C12A7 powder synthesized by the above method and 0.042g of Ru3(CO) were mixed. 12 The contents are added to a Pyrex (registered trademark) glass tube and vacuum sealed. The vacuum-sealed glass tube is then heated in an electric furnace according to the following temperature program to obtain HT-C12A7 powder loaded with 2% Ru by mass (hereinafter referred to as Ru / HT-C12A7).

[0229] [Temperature Program]

[0230] (1) The temperature is raised from room temperature to 40°C within 20 minutes, and then maintained at 40°C for 60 minutes;

[0231] (2) After (1), the temperature is increased from 40°C to 70°C within 120 minutes and then maintained at 70°C for 60 minutes;

[0232] (3) After (2), the temperature is increased from 70°C to 120°C within 120 minutes and then maintained at 120°C for 60 minutes;

[0233] (4) After (3), the temperature is increased from 120°C to 250°C within 150 minutes, and then maintained at 250°C for 120 minutes.

[0234] <Reduction treatment and subsequent ammonia synthesis reaction>

[0235] A reaction was carried out to produce ammonia (NH3) by reacting nitrogen (N2) and hydrogen (H2). 0.1 g of Ru / HT-C12A7 obtained as described above was loaded into a quartz glass tube and placed in a fixed-bed flow-through reactor. The gas flow rates were set as follows: N2: 15 mL / min, H2: 45 mL / min, totaling 60 mL / min. The reaction was conducted under the following conditions: pressure: atmospheric pressure, reaction temperature: 400 °C. The gas exiting the reactor was bubbled into a 0.005 M sulfuric acid aqueous solution to dissolve the generated ammonia. The generated ammonium ions were quantified using ion chromatography. The results are shown in Table 1 and... Figure 1 .

[0236] like Figure 1 As shown, the catalytic activity increases significantly with reaction time.

[0237] Furthermore, as shown in Table 1, the initial ammonia formation rate at 400℃ is 1.2 mmol / g·h, and the ammonia formation rate changes to 2.9 mmol / g·h after about 24 hours of reaction.

[0238] The average particle size of Ru, determined by the above chemisorption method, was 7.2 nm before the reaction and 9.0 nm after the reaction. The average particle size of Ru increased significantly after reduction treatment.

[0239] Furthermore, although the reaction time was extended thereafter, no decrease in catalytic activity was observed.

[0240] (Example 2)

[0241] Except that the Ru loading was 5% by mass, 5% by mass Ru / HT-C12A7 was prepared using the same method as in Example 1, and used as a catalyst for ammonia synthesis under the same conditions as in Example 1. Ammonia was synthesized under the same conditions as in Example 1. The results are shown in Table 1 and... Figure 1 .

[0242] like Figure 1 As shown, the catalytic activity increases significantly with reaction time.

[0243] Furthermore, as shown in Table 1, the initial ammonia formation rate at 400℃ is 2.1 mmol / g·h, and the ammonia formation rate changes to 3.6 mmol / g·h after about 24 hours of reaction.

[0244] The average particle size of Ru, determined by the above chemisorption method, was 8.9 nm before the reaction and 12.6 nm after the reaction. The average particle size of Ru increased significantly after reduction treatment.

[0245] Furthermore, although the reaction time was extended thereafter, no decrease in catalytic activity was observed.

[0246] (Example 3)

[0247] Except that the Ru loading was 10% by mass, a 10% by mass Ru / HT-C12A7 catalyst was prepared using the same method as in Example 1, and the ammonia synthesis reaction was carried out under the same conditions as in Example 1. The results are shown in Table 1 and... Figure 1 .

[0248] like Figure 1 As shown, the catalytic activity increases significantly with reaction time.

[0249] Furthermore, as shown in Table 1, the initial ammonia formation rate at 400℃ is 2.1 mmol / g·h, and the ammonia formation rate changes to 3.9 mmol / g·h after about 24 hours of reaction.

[0250] The average particle size of Ru, determined by the above chemisorption method, was 10.7 nm before the reaction and 14.0 nm after the reaction. The average particle size of Ru increased significantly after reduction treatment.

[0251] Furthermore, although the reaction time was extended thereafter, no decrease in catalytic activity was observed.

[0252] (Example 3A)

[0253] <Stress dependence of ammonia synthesis reaction>

[0254] Using the catalyst used in Example 3, the change in catalytic activity with increasing reaction pressure was observed while keeping the reaction temperature (400°C) constant, to study the pressure dependence of the ammonia synthesis reaction. Conditions other than reaction temperature and pressure were handled using the same method as in Example 3. The results are presented below. Figure 2 It should be noted that regarding the ammonia synthesis reaction rate at each reaction pressure, the reaction was continued within the measured pressure until the measured value of the activity stabilized, and the measured value at the stable point was used. The time to reach stabilization was between 1 and 2 hours.

[0255] like Figure 2As shown, the catalytic activity of the 10% by mass Ru / HT-C12A7 catalyst increases significantly with increasing reaction pressure. The ammonia formation rate becomes 10 mmol / g·h under pressure of 0.9 MPa. This result indicates that, similar to the Ru-supported C12A7 electron-bearing compounds, this catalyst does not undergo hydrogen poisoning.

[0256] (Comparative Example 1)

[0257] Powders of CaCO3 and Al2O3 were mixed to achieve a Ca:Al ratio of 12:7. The mixture was heated at 1300°C for 6 hours in an alumina crucible to obtain C12A7 via a solid-state method. The obtained C12A7 powder was then loaded with Ru using the same method as in Example 1 to synthesize a 2% (w / w) Ru-supported C12A7 catalyst. The specific surface area of ​​the 2% (w / w) Ru / C12A7 catalyst was 1 m². 2 / g.

[0258] The ammonia synthesis activity of the catalyst at 400℃ is 7.2 × 10⁻⁶. -1 mmol / g·h. No significant increase in catalytic activity was observed over time.

[0259] (Comparative Example 2)

[0260] Except for replacing Ru with 5% Fe by mass, a 5% Fe / HT-C12A7 catalyst was prepared using the same method as in Example 2, and the ammonia synthesis reaction was carried out under the same conditions as in Example 1.

[0261] As shown in Table 2, the initial ammonia formation rate at 400℃ is 1.6 × 10⁻⁶. -1 mmol / g·h. Furthermore, the ammonia formation rate after 24 hours of reaction was 1.5 × 10⁻⁶ mmol / g·h. -1 mmol / g·h. Unlike Ru, no increase in catalytic activity was observed when Fe was supported as a catalyst.

[0262] (Comparative Example 3)

[0263] Except for replacing Ru with 5% Co by mass, a 5% Co / HT-C12A7 catalyst was prepared using the same method as in Example 2, and the ammonia synthesis reaction was carried out under the same conditions as in Example 1.

[0264] As shown in Table 1, the initial ammonia formation rate at 400℃ is 0 mmol / g·h.

[0265] As shown in Table 2, the ammonia formation rate after 24 hours of reaction was 0 mmol / g·h. Unlike Ru, no increase in catalytic activity was observed when Co was supported as a catalyst.

[0266] (Example 4)

[0267] <Loading Ru onto calcium aluminate compounds>

[0268] Weigh 1.0 g of the above-mentioned HT-C12A7 synthesized using the same method as in Example 1, and 0.05 g of RuCl3·xH2O (manufactured by Aldrich Co., Ltd., 99.9%) with a Ru loading of 2% by mass. Add the solution to 100 ml of ethanol (manufactured by Kanto Chemical Co., Ltd., 99.5%), stir, and remove the solvent under reduced pressure at 40 °C using a rotary evaporator, thereby impregnating the HT-C12A7 surface with RuCl3.

[0269] The Ru loaded with RuCl3 exists in the form of RuCl3, and its particle size cannot be determined. Therefore, in order to determine the Ru particle size, a hydrogen reduction pretreatment was performed at 250 °C. That is, a reduction treatment was performed at 250 °C for 6 hours using 20% ​​by volume hydrogen / nitrogen to obtain 2% by mass Ru-loaded HT-C12A7.

[0270] The average particle size of Ru at this time was measured by TEM and found to be 1.8 nm.

[0271] The ammonia synthesis reaction was carried out using HT-C12A7 supported with 2% Ru by mass under the same conditions as in Example 1.

[0272] like Figure 3 As shown, the catalytic activity increases significantly with reaction time.

[0273] As shown in Table 1, the ammonia formation rate in the second hour at 400℃ was 1.4 × 10⁻⁶. -1 The ammonia production rate was 2.8 mmol / g·h after 50 hours of reaction. Subsequently, the temperature was lowered to 320 °C, and the ammonia synthesis activity was studied, showing a value of 4.0 × 10⁻⁶ mmol / g·h. -1 mmol / g·h. The activation energy Ea is 57 kJ / mol. Based on the activation energy, the ammonia formation rate at 300℃ is calculated to be 3.0 × 10⁻⁶. -1 mmol / g·h.

[0274] At this point, the average particle size of Ru was 2.2 nm after the reaction, showing a significant increase in average particle size.

[0275] Furthermore, although the reaction time was extended afterward, no decrease in catalytic activity was observed.

[0276] (Comparative Example 4)

[0277] Using the same catalyst as in Example 4, except that the reaction temperature for the ammonia formation reaction was set to 300°C, the ammonia synthesis reaction was carried out in the same manner as in Example 4. Figure 3 As shown, the ammonia formation rate in the second hour at 300℃ was 1.3 × 10⁻⁶. -2 mmol / g·h. After 50 hours of reaction, the ammonia formation rate was 3.5 × 10⁻⁶ mmol / g·h. -2 At mmol / g·h, almost no increase in activity was observed.

[0278] At this point, the average particle size of Ru is 1.9 nm after the reaction.

[0279] (Comparative Example 5)

[0280] Except for the catalyst pretreatment by heating at 400°C for 6 hours in an oxygen atmosphere, a 2% Ru-supported HT-C12A7 catalyst was prepared using the same method as in Example 4, and the ammonia synthesis reaction was carried out under the same conditions as in Example 1.

[0281] The initial ammonia formation rate at 400℃ is 5.2 × 10⁻⁶. -1 mmol / g·h.

[0282] With increasing reaction time, the catalytic activity increased, reaching an ammonia formation rate of 2.0 mmol / g·h approximately 24 hours after the reaction. Subsequently, although the reaction time was extended, no further increase in catalytic activity was observed.

[0283] [Table 1]

[0284]

[0285] [Table 2]

[0286]

[0287] (Example 5)

[0288] Except for weighing and mixing Ca(OH)₂, Al(OH)₃, and Ba(OH)₂ to achieve a Ca:Al:Ba ratio of 11.75:14:0.25, the calcium aluminum oxide compound was synthesized using the same method as in Example 1. Furthermore, Ru was loaded and ammonia was synthesized using the same method as in Example 1.

[0289] like Figure 4 As shown, the catalytic activity increased significantly with reaction time, and the ammonia generation rate was 5.1 mmol / g·h after about 20 hours of reaction. The average particle size of Ru, determined by the CO adsorption method, was 9.6 nm before the reaction and 13.7 nm after the reaction, indicating a significant increase in the average particle size of Ru.

[0290] Furthermore, although the reaction time was extended afterward, no decrease in catalytic activity was observed.

[0291] As shown in Examples 1-5, it can be seen that the Ru-loaded HT-C12A7 exhibits significantly enhanced catalytic activity in the ammonia synthesis reaction, demonstrating an ammonia generation rate comparable to that of the Ru / C12A7 electron compound. Figure 1 Examples 1-3 and Comparative Example 1 are shown, along with a comparison of a C12A7 electron compound loaded with 2% by mass of Ru (the compound obtained according to Comparative Example 3 as described in Publication No. WO2014 / 034473). Furthermore, the growth of Ru particles on the catalyst used was observed before and after the ammonia synthesis reaction. Therefore, it can be anticipated that the Ru particles grow and are strongly immobilized on the C12A7 support during the reaction. It is believed that at this time, the O near the interface between the Ru nanoparticles and the C12A7 cages... 2- Ions are released due to the catalytic effect of Ru, thereby forming electrons within the cage and significantly enhancing catalytic activity. In fact, the Ru / HT-C12A7 catalyst with enhanced activity exhibits a reaction order of approximately 0.5 relative to N2 and 0.9 relative to H2. The electron-free Ru / C12A7 catalyst synthesized via the solid-state method of Comparative Example 1 exhibits a reaction order of approximately 1.0 relative to N2 and 0 relative to H2. When using the Ru / C12A7 electron compound, a reaction order of approximately 0.5 relative to N2 and 1.0 relative to H2 is observed. It is evident that the Ru / HT-C12A7 catalyst exhibits ammonia synthesis activity through a mechanism almost identical to that of the Ru / C12A7 electron compound.

[0292] Furthermore, the inventors speculate that the catalyst supported on HT-C12A7 using RuCl3·xH2O as the Ru source will react with Ru3(CO). 12 The same phenomenon occurs when Ru is used as the source, resulting in a significant increase in catalytic activity during the reaction.

[0293] (Example 6)

[0294] <Synthesis of Ru / HT-C12A7 with added Ba>

[0295] 35.5 mg of barium ethoxide (Ba(OC2H5)2: manufactured by Wako Pure Chemical Industries, Ltd., purity 99.5%) was dissolved in 45 mL of ethanol and stirred for about 20 minutes. Next, 11.3 mg of water and 5 mL of ethanol were added to the solution, and the mixture was stirred for about 15 minutes to prepare a mixed solution. 0.3 g of Ru / HT-C12A7 as described in Example 2 was added to the obtained mixed solution, and the mixture was stirred for about 20 minutes. Then, the solvent was removed from the mixed solution using a rotary evaporator, and the solution was dried to obtain a powder of Ba-added Ru / HT-C12A7 (hereinafter, Ba-Ru / HT-C12A7) (Ru:Ba = 1:1 (molar ratio)).

[0296] Using the aforementioned metal-supported material Ba-Ru / HT-C12A7 as a catalyst, an ammonia synthesis reaction was carried out by contacting the catalyst with a mixture of nitrogen and hydrogen gases. The ammonia synthesis reaction was conducted using the same method as in Example 1, except that the reaction temperature was 340°C. The results are shown in Table 3.

[0297] As shown in Table 3, the ammonia formation rate after 30 hours of reaction at 340℃ was 4.7 mmol / g·h. Furthermore, the initial ammonia formation rate at 400℃ was 4.4 mmol / g·h, and the ammonia formation rate after 30 hours of reaction was 6.9 mmol / g·h.

[0298] The average particle size of Ru, determined by direct observation using TEM, was 1.6 nm before the reaction and 2.2 nm after the reaction. The reduction treatment resulted in a significant increase in the average particle size of Ru.

[0299] Furthermore, although the reaction time was extended afterward, no decrease in catalytic activity was observed.

[0300] (Example 7)

[0301] 47.6 mg of Ba(C5H7O2)2·xH2O (manufactured by Artrich Corporation: 98% purity) was dissolved in 100 mL of ethanol and stirred for about 20 minutes. Except for the addition of 0.3 g of the above Ru / HT-C12A7 to the solution, the powder of Ru / HT-C12A7-2 with added Ba was prepared by the same method as in Example 6 to obtain Ru:Ba = 1:1 (molar ratio) powder.

[0302] The ammonia synthesis reaction was carried out under the same conditions as in Example 6, except that the metal support was used as a catalyst. The results are shown in Table 3.

[0303] As shown in Table 3, the ammonia formation rate after 30 hours of reaction at 340℃ was 3.1 mmol / g·h. Furthermore, the initial ammonia formation rate at 400℃ was 4.3 mmol / g·h, and the ammonia formation rate after 30 hours of reaction was 6.9 mmol / g·h.

[0304] The average particle size of Ru is the same as in Example 6. However, through reduction treatment, the average particle size of Ru increases significantly.

[0305] Furthermore, although the reaction time was extended afterward, no decrease in catalytic activity was observed.

[0306] (Example 8)

[0307] In Example 7, the materials were prepared using the same method as in Example 7, except that tetrahydrofuran (THF) was used instead of ethanol, to obtain Ba-Ru / HT-C12A7 powder.

[0308] Ammonia synthesis was carried out under the same conditions as in Example 6, except that the Ba-Ru / HT-C12A7 was used as a catalyst. The results are shown in Table 3.

[0309] As shown in Table 3, the ammonia formation rate after 30 hours of reaction at 340℃ was 2.7 mmol / g·h. Furthermore, the initial ammonia formation rate at 400℃ was 4.0 mmol / g·h, and the ammonia formation rate after 30 hours of reaction was 5.9 mmol / g·h.

[0310] The average particle size of Ru is the same as in Example 6. However, through reduction treatment, the average particle size of Ru increases significantly.

[0311] Furthermore, although the reaction time was extended afterward, no decrease in catalytic activity was observed.

[0312] (Example 9)

[0313] Except for using 71.1 mg Ba(OC2H5)2 and 22.5 mg water, the same method as in Example 6 was used to obtain Ba-Ru / HT-C12A7 powder (Ru:Ba = 1:2 (molar ratio)).

[0314] Ammonia synthesis was carried out under the same conditions as in Example 6, except that the Ba-Ru / HT-C12A7 was used as a catalyst. The results are shown in Table 3.

[0315] As shown in Table 3, the ammonia formation rate after 30 hours of reaction at 340℃ was 3.8 mmol / g·h. Furthermore, the initial ammonia formation rate at 400℃ was 3.7 mmol / g·h, and the ammonia formation rate after 30 hours of reaction was 6.3 mmol / g·h.

[0316] The average particle size of Ru is the same as in Example 6. However, through reduction treatment, the average particle size of Ru increases significantly.

[0317] Furthermore, although the reaction time was extended afterward, no decrease in catalytic activity was observed.

[0318] (Example 10)

[0319] The ammonia synthesis reaction was carried out under the same conditions as in Example 6, except that Ru / HT-C12A7 described in Example 2 was used as the catalyst. The results are shown in Table 3.

[0320] As shown in Table 3, the ammonia formation rate after 30 hours of reaction at 340℃ was 2.3 mmol / g·h. Furthermore, the initial ammonia formation rate at 400℃ was 3.7 mmol / g·h, and the ammonia formation rate after 30 hours of reaction was 4.3 mmol / g·h.

[0321] [Table 3]

[0322]

[0323] Figure 5 This shows the time variation in ammonia synthesis when the metal-supported material described in Example 6 is used as a catalyst for ammonia synthesis. The reaction conditions were a reaction temperature of 400°C and a reaction pressure of atmospheric pressure (0.1 MPa). Figure 5 It is evident that the catalytic activity of this catalyst increases with reaction time, continuing to rise until it almost reaches the equilibrium conversion. The same applies to the metal-supported catalysts described in other examples (Examples 7-10) with added Ba; their catalytic activity continuously increases until it reaches a value close to the equilibrium conversion. Therefore, it is impossible to compare the performance of each catalyst. Thus, the reaction temperature was lowered to 340°C for comparison.

[0324] (Example 11)

[0325] <Stress dependence of ammonia synthesis reaction>

[0326] Using the same catalyst as that used in Example 6, the change in catalytic activity with increasing reaction pressure was observed while keeping the reaction temperature (400°C) constant, to study the pressure dependence of the ammonia synthesis reaction. The results are presented below. Figure 6 .

[0327] Figure 6 This indicates the change in catalytic activity when the metal-supported material described in Example 6 is used as a catalyst for ammonia synthesis, while maintaining a constant reaction temperature (400°C) and increasing the reaction pressure. The measured values ​​were obtained using the same method as in Example 3A.

[0328] like Figure 6 As shown, the catalyst in Example 6 exhibits a significant increase in catalytic activity with increasing reaction pressure. The ammonia formation rate becomes 28 mmol / g·h under a pressure of 0.9 MPa. This result indicates that, similar to the Ru-supported C12A7 electron-bearing compound, this catalyst does not experience hydrogen poisoning.

[0329] (Example 12)

[0330] <Temperature Dependence of Ammonia Synthesis Reaction>

[0331] Using the same catalyst as used in Example 6, the temperature dependence of the ammonia synthesis reaction was studied by observing the change in catalytic activity with increasing reaction temperature while keeping the reaction pressure (0.9 MPa) constant. The results are presented below. Figure 7 .

[0332] like Figure 7 As shown, the Ba-Ru / HT-C12A7 metal-supported material obtained in Example 6 exhibits significantly increased catalytic activity as the reaction temperature rises when used as a catalyst for ammonia synthesis. Furthermore, compared to the Ru / HT-C12A7 obtained in Example 2 without Ba addition, it displays exceptionally high ammonia synthesis activity across the entire temperature range from 280°C to 400°C, particularly exhibiting approximately five times the catalytic activity of the Ba-free Ru / HT-C12A7 in the low-temperature region below 340°C.

[0333] The method for manufacturing the ammonia synthesis catalyst of the present invention enables the production of a catalyst with high ammonia synthesis activity in a simple manner. Compared with the Haber process, this catalyst allows ammonia synthesis to be carried out at low pressure, thus simplifying the synthesis process, which is advantageous.

Claims

1. A method for manufacturing a catalyst for ammonia synthesis, characterized in that, It includes: The first step is to prepare a material with a specific surface area of ​​5m². 2 / g or more of 12CaO·7Al2O3; The second step involves loading a ruthenium compound onto the 12CaO·7Al2O3; and The third step involves reducing the ruthenium-loaded 12CaO·7Al2O3 (hereinafter referred to as ruthenium-loaded C12A7) obtained through the second step. The reduction treatment is carried out at 400℃~600℃ until the average particle size of the ruthenium after reduction treatment increases by more than 15% compared with the average particle size of the ruthenium before reduction treatment. The amount of ruthenium used is more than 0.01% by mass and less than 30% by mass relative to the mass of C12A7 used as a carrier.

2. The manufacturing method as described in claim 1, wherein, The specific surface area of ​​the ruthenium-loaded C12A7 after the reduction treatment process is 5 m². 2 / g or more.

3. The manufacturing method as described in claim 1, wherein, In the first step, the 12CaO·7Al2O3 is prepared by hydrothermal synthesis, sol-gel method, combustion synthesis method or coprecipitation method.

4. The manufacturing method as described in claim 1, wherein, In the second step, ruthenium compounds are loaded by impregnation or vapor deposition.

5. The manufacturing method as described in claim 1, wherein, In the reduction process, the reduction is carried out using a gas containing hydrogen.

6. The manufacturing method as described in claim 1, wherein, The manufacturing method includes a step following the first step of molding the 12CaO·7Al2O3 obtained through the first step.

7. The manufacturing method as described in claim 1, wherein, The manufacturing method includes a step following the second step, forming the ruthenium load C12A7 obtained through the second step.

8. The manufacturing method according to any one of claims 1 to 7, wherein, The catalyst for ammonia synthesis contains at least one alkali metal atom or alkaline earth metal atom.

9. A method for producing ammonia, characterized in that, It includes: The first step is to prepare a material with a specific surface area of ​​5m². 2 / g or more of 12CaO·7Al2O3; The second step involves loading a ruthenium compound onto the 12CaO·7Al2O3; The third step involves reducing the ruthenium-loaded 12CaO·7Al2O3 (hereinafter referred to as ruthenium-loaded C12A7) obtained through the second step at 400℃~600℃ until the average particle size of the ruthenium after the reduction treatment increases by more than 15% compared with the average particle size of the ruthenium before the reduction treatment. and The process of producing ammonia involves contacting a gas containing nitrogen and hydrogen with an ammonia synthesis catalyst that has undergone reduction treatment in the third step to produce ammonia. The amount of ruthenium used is more than 0.01% by mass and less than 30% by mass relative to the mass of C12A7 used as a carrier.

10. The manufacturing method as described in claim 9, wherein, In the reduction process, the reduction is carried out using a gas containing hydrogen.

11. The manufacturing method as described in claim 9, wherein, In the reduction process, the reduction is carried out using a gas containing hydrogen and nitrogen.

12. The manufacturing method according to any one of claims 9 to 11, wherein, The catalyst for ammonia synthesis contains at least one alkali metal atom or alkaline earth metal atom.

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