Hydroxide precursor, BaAl2O4 support, ammonia production catalyst, and ammonia production method.

Abstract

This invention provides a precursor for preparing a BaAl2O4 support used in a highly reactive ammonia production catalyst, which includes a hydroxide precursor containing a Ba(AlO(OH)2)2 phase (S) that is poorly soluble in water. It also provides a BaAl2O4 support, which is a calcined product of the hydroxide precursor, and an ammonia production catalyst using the same. [Solution] The hydroxide precursor of the present invention is a hydroxide precursor containing Ba(AlO(OH)2)2 phase(S). The average particle size of the hydroxide precursor is 1 to 65 μm.

Description

[Technical Field]

[0001] The present invention relates to a hydroxide precursor, a BaAl2O4 support, an ammonia production catalyst, and a method for producing ammonia. [Background technology]

[0002] The use of catalysts to accelerate chemical reactions is frequently employed. An example of such a reaction is the ammonia synthesis reaction, a hydrogenation reaction. For instance, the Haber-Bosch process is a representative method for ammonia synthesis. The Haber-Bosch process uses a doubly promoted iron catalyst containing several mass percent of Al2O3 and K2O in Fe3O4. This catalyst is directly reacted with a mixture of nitrogen and hydrogen under high temperature and pressure conditions to produce ammonia. This technology is still used industrially today, largely unchanged from its original development.

[0003] Furthermore, methods for synthesizing ammonia at temperatures lower than the reaction temperature of the Haber-Bosch process are being investigated. Catalysts capable of synthesizing ammonia by contact with nitrogen and hydrogen are being studied, and transition metals are being considered as catalytic active components. Among these, a method of using ruthenium (Ru) supported on various supports as an ammonia production catalyst has been proposed as an efficient method (for example, Patent Document 1). In addition, ammonia production catalysts that achieve both improved catalytic performance and stabilization and can be easily synthesized using typical element oxides as catalyst supports have been disclosed (for example, Patent Documents 2 and 3). Specific examples of the aforementioned typical element oxides include BaAl2O4, and methods for its synthesis, such as the solid-phase method, the sol-gel method, and the hydrothermal method using the reverse micelle method, have been disclosed.

[0004] On the other hand, BaAl2O4 is a type of composite oxide represented as barium aluminate or xBaO·yAl2O3, and has long been well known as a fluorescent material and cement raw material. Furthermore, the crystal structures of various hydrates of BaAl2O4 have been reported (for example, Non-Patent Documents 1-4). [Preliminary Technology Documents] [License]

[0005] [License 1] Special Announcement No. 2006-231229 [License 2] International Publication No. 2021 / 172107 [License 3] Special Announcement No. 2004-261728 [Non-licensed literature]

[0006] [Non-licensed Document 1] Elmer T. Carlson et al., Barium Aluminate Hydrates, Journal of Research of the National Bureau of Standards, 41, 103-109(1948). [Non-licensed Document 2] Elmer T. Carlson et al., Study of the System Barium Oxide-Aluminum Oxide-Water at 30℃, Journal of Research of tue National Bureau of Standards, 45, 381-398 (1950). [Non-licensed Document 3] FSWen et al., Synthesis and Characterization of a New Layered Barium Aluminate Containing Six-Membered Rings: BaAl2O3(OH)2·H2O, Journal of Solid State Chemistry 161, 243-248(2001). [Non-licensed Document 4] A.H.M.Ahmed et al., Barium Aluminate Hydrates III.BaO·Al2O3·2H2O and BaO·Al2O3·0.5H2O, Journal of Applied Chemistry and Biotechnology, 21, 109―112(1971).

Summary of the Invention

Problems to be Solved by the Invention

[0007] Ammonia production catalysts as described in Patent Document 1 usually use carbonaceous carriers such as activated carbon and inorganic oxide carriers. However, these supported metal catalysts do not always have sufficient performance for practical use. In addition, the ammonia production catalysts described in Patent Documents 2 and 3 use BaAl2O4 obtained by a hydrothermal method using a solid-phase method, a sol-gel method, and an inverse micelle method as a catalyst carrier, so there is room for further improving the catalytic activity. Since BaAl2O is soluble in water, when BaAl2O is used as a carrier for an ammonia production catalyst, a process using an aqueous solvent becomes unusable, which is disadvantageous from the viewpoints of the environment and cost. For example, in the step of adding an additive for promoting catalytic activity, an additive for producing a molded body, etc., there was a problem that water or an aqueous solvent could not be used. Therefore, an object of the present invention is to provide a hydroxide precursor containing a Ba(AlO(OH)2)2 phase (S) that is poorly soluble in water and is a precursor for preparing a BaAl2O4 carrier used in an ammonia production catalyst with high reaction activity. Another object is to provide a BaAl2O4 carrier that is a fired product of the hydroxide precursor and an ammonia production catalyst using the same.

Means for Solving the Problems

[0008] The gist of the present invention is as follows. 〔1〕 A hydroxide precursor containing a Ba(AlO(OH)2)2 phase (S), The hydroxide precursor having an average particle diameter of the hydroxide precursor of 1 to 65 μm. [2] Furthermore, Ba2Al2(OH) 10 A hydroxide precursor according to [1], comprising phase (T). [3] The hydroxide precursor according to [1] or [2], further comprising BaCO3. [4] Ba2Al2(OH) 10 The hydroxide precursor according to [2] or [3], wherein the weight ratio (S / T) of the Ba(AlO(OH)2)2 phase (S) to the phase (T) is 2 to 50. [5] A BaAl2O4 support, which is a calcined product of a hydroxide precursor described in any of [1] to [4]. [6] The BaAl2O4 support described in [5], A catalyst for ammonia production comprising a catalytically active metal (M1) supported on the BaAl2O4 support. [7] The ammonia production catalyst according to [6], wherein the catalytically active metal (M1) is a transition metal. [8] The ammonia production catalyst according to [6], wherein the catalytically active metal (M1) is at least one selected from the group consisting of Ru, Fe, and Co. [9] In addition, it contains additives, The ammonia production catalyst according to any one of [6] to [8], wherein the additive is an alkaline earth metal (M2).

[10] The ammonia production catalyst according to [9], wherein the alkaline earth metal (M2) is Ba.

[11] A method for producing a hydroxide precursor as described in any of [1] to [4], A method for producing a hydroxide precursor, comprising a hydrothermal reaction step of barium nitrate and aluminum nitrate under basic conditions.

[12] The method for producing a hydroxide precursor according to

[11] , wherein the base conditions are pH 13.0 or higher.

[13] The method for producing a hydroxide precursor according to

[11] , wherein the metal-equivalent molar ratio (Ba / Al) of barium nitrate to aluminum nitrate is 1 / 2 to 1 / 1.5.

[14] A method for producing the BaAl2O4 support described in [5], A method for producing BaAl2O4, comprising the step of calcining the hydroxide precursor. A method for producing an ammonia catalyst, characterized by supporting a catalytically active metal on a BaAl2O4 support as described in

[15] and [5].

[16] A method for producing ammonia, characterized by comprising the step of reacting nitrogen and hydrogen in the presence of the ammonia production catalyst described in [6]. [Effects of the Invention]

[0009] The present invention provides a precursor for preparing a BaAl2O4 support used in a highly reactive ammonia production catalyst, which includes a hydroxide precursor containing a Ba(AlO(OH)2)2 phase (S) that is poorly soluble in water. Furthermore, the present invention provides a BaAl2O4 support obtained by calcining the hydroxide precursor, and an ammonia production catalyst using the same. [Brief explanation of the drawing]

[0010] [Figure 1] This figure illustrates a method for producing a hydroxide precursor according to one embodiment of the present invention. [Figure 2] This figure illustrates a method for producing a BaAl2O4 support according to one embodiment of the present invention. [Figure 3] This figure illustrates a method for producing an M2-BaAl2O4 support with added alkaline earth metal (M2) according to one embodiment of the present invention. [Figure 4] This figure illustrates a method for producing an ammonia production catalyst according to one embodiment of the present invention. [Figure 5] This is an SEM image of the hydroxide precursor obtained in Example A2. [Figure 6] This is an SEM image of the hydroxide precursor obtained in Example A9. [Figure 7] This is an SEM image of the hydroxide precursor obtained in Example A10. [Figure 8] This figure shows the particle size histogram (particle size distribution) for Example A2. [Figure 9] This is an XRD diagram of Ba(AlO(OH)2)2 in the hydroxide precursor obtained in Example A1. a: Example A1, b: Ba(AlO(OH)2)2 (standard). [Figure 10] This is an XRD diagram of the BaAl2O4 support obtained in Example B1. a: Example B1, b: BaAl2O4 (standard). [Figure 11] This figure shows the results of evaluating the basicity of the support surface of BaAl2O4 supports obtained in Example B2 (hydrothermal method), Comparative Example B2 (solid-phase method), and Comparative Example B3 (sol-gel method) using the temperature-controlled desorption method (CO2-TPD). a: hydrothermal method, b: solid-phase method, c: sol-gel method. [Modes for carrying out the invention]

[0011] (Explanation of terms)

[0012] In this invention, "ammonia synthesis activity" means having catalytic activity for the ammonia synthesis reaction. Furthermore, "catalyst having ammonia synthesis activity" and "ammonia production catalyst" both mean a catalyst having catalytic activity for the ammonia synthesis reaction.

[0013] In this invention, "catalytically active metal" means a metal that has catalytic activity for ammonia synthesis reactions.

[0014] In this invention, "BaAl2O4" refers to anhydrous barium aluminate. "BaAl2O4 carrier" is a carrier used in the ammonia production catalyst of this invention, and is a composition mainly containing anhydrous BaAl2O4. "Main component" means that the mass content of anhydrous BaAl2O4 in the total carrier is 70% or more. Furthermore, the mass content of anhydrous BaAl2O4 in the total carrier may be 80% or more, 90% or more, 95% or more, 98% or more, or 99% or more.

[0015] In the present invention, "hydroxide precursor" means a raw material or intermediate product for producing the above-mentioned BaAl2O4 support. If the raw material or intermediate product contains two or more compounds, the hydroxide precursor may be a composition (mixture). The BaAl2O4 support is a calcined product of the hydroxide precursor. The hydroxide precursor is a composition containing barium aluminate hydrate.

[0016] "Barium aluminate hydrates" refer to those disclosed in Non-Patent Documents 1 to 4 above, for example. Specific examples include BaAl2O4 monohydrate, BaAl2O4 dihydrate, and BaAl2O4 trihydrate, and the crystal structures of various hydrates have been reported (for example, Non-Patent Documents 3 and 4). "BaAl2O4 dihydrate" refers to the compound represented by the chemical formula BaAl2O4·2H2O. The crystal structure of "BaAl2O4 dihydrate" has a Ba(AlO(OH)2)2 phase (α phase), a BaAl2O3(OH)2·2H2O phase (β phase), etc. In particular, Non-Patent Document 4 describes that the Ba(AlO(OH)2)2 phase has OH groups in its crystal structure.

[0017] In the present invention, "catalytically active metal precursor" means a raw material or intermediate product for producing a catalytically active metal. If the raw material or intermediate product contains two compounds, the catalytically active metal precursor may be a mixture.

[0018] In this invention, "slightly soluble in water" means that the degree of solubility in water at 20°C is, for example, 1 g / 30 g or less (JIS K8001). The degree of solubility in water at 20°C may be 1 g / 100 g or less, 1 g / 1000 g or less, or 1 g / 10000 g or less.

[0019] (Hydroxide precursor) One embodiment of the hydroxide precursor contains a Ba(AlO(OH)2)2 phase(S) which is sparingly soluble in water. Furthermore, it is preferable that the average particle size of the hydroxide precursor is 3 to 65 μm. The hydroxide precursor consists of Ba(AlO(OH)2)2 phase (S) and Ba2Al2(OH) 10 Phase (T) may also be included. In that case, in the hydroxide precursor, Ba2Al2(OH) 10 The weight ratio (S / T) of the Ba(AlO(OH)2)2 phase (S) to the phase (T) is preferably 2 to 25. The hydroxide precursor may also contain Ba(AlO(OH)2)2 phase(S) and BaCO3, and Ba(AlO(OH)2)2 phase(S) and Ba2Al2(OH) 10 The hydroxide precursor may contain phase (T) and BaCO3. If the hydroxide precursor contains BaCO3, it is preferable that the BaCO3 content in the hydroxide precursor is 1 to 15% by mass. Furthermore, it is preferable that the hydroxide precursor is also poorly soluble in water, and more preferably that its degree of solubility in water at 20°C (JIS K8001) is 1 g / 15 g or less.

[0020] [Average particle size of hydroxide precursors] The average particle size of the hydroxide precursor may be 1 μm or more, 2 μm or more, or 3 μm or more. It may also be 65 μm or less, 60 μm or less, or 55 μm or less. From the viewpoint of high catalytic activity of the ammonia production catalyst obtained using the hydroxide precursor, it is preferable that the average particle size of the hydroxide precursor is 1 to 65 μm, and more preferably 3 to 65 μm. Although the correlation between the average particle size of the hydroxide precursor and the catalytic activity of the final ammonia production catalyst has not yet been elucidated, it is thought that using a hydroxide precursor having an average particle size within the above range will result in a structure of the resulting BaAl2O4 support that is advantageous for the catalytic activity of the ammonia production catalyst.

[0021] The method for measuring the average particle size described above involved taking SEM images of the hydroxide precursor using a scanning electron microscope (SEM), arbitrarily selecting 30 or more particles from each field of view, calculating the equivalent circle diameter for all selected particles, and then calculating the average value of these equivalent circle diameters. The average value of the equivalent circle diameters was defined as the particle size of the precursor. Further details will be explained in the examples.

[0022] [Ba(AlO(OH)2)2 phase (S)] The above-mentioned Ba(AlO(OH)2)2 phase(S) is one of several crystal structures of the dihydrate of BaAl2O4 (BaAl2O4·2H2O). It is also called the α phase of the dihydrate of BaAl2O4 (Non-Patent Documents 1-4). In particular, the Ba(AlO(OH)2)2 phase(S) is described as having OH groups in its crystal structure (Non-Patent Document 4). The presence of the Ba(AlO(OH)2)2 phase (S) in the hydroxide precursor of this embodiment can be confirmed using an X-ray diffractometer (XRD). Details will be explained in the examples.

[0023] The content of Ba(AlO(OH)2)2 phase(S) in the hydroxide precursor of this embodiment may be 50% by mass or more, 60% by mass or more, or 65% by mass or more. It may also be 100% by mass or less, or 90% by mass or less. From the viewpoint of high catalytic activity of the ammonia production catalyst obtained using the hydroxide precursor, the content of Ba(AlO(OH)2)2 phase(S) is preferably 50 to 100% by mass, and more preferably 60 to 100% by mass. The above-mentioned content can be confirmed using an X-ray diffraction (XRD) device. The hydroxide precursor in this embodiment is the Ba(AlO(OH)2)2 phase (S) and, if necessary, the following Ba2Al2(OH) 10 In addition to phase (T) and / or BaCO3 as described below, other materials may be included.

[0024] [Ba2Al2(OH) 10 Phase (T)] The above Ba2Al2(OH) 10Phase (T) has the crystal structure of pentahydrate of 2BaO·Al2O3 (2BaO·Al2O3·5H2O) (Non-Patent Documents 1 and 2). Ba2Al2(OH) in the hydroxide precursor of this embodiment 10 The presence of Phase (T) can be confirmed using an X-ray diffractometer (XRD). Details will be described in the examples.

[0025] Ba2Al2(OH) in the hydroxide precursor of this embodiment 10 The content of Phase (T) may be 0% by mass or more, 5% by mass or more, or 10% by mass or more. Further, it may be 50% by mass or less, or 40% by mass or less. From the viewpoint of high catalytic activity of the ammonia production catalyst obtained using the hydroxide precursor, Ba2Al2(OH) 10 The content of Phase (T) is preferably 0 to 50% by mass, and more preferably 0 to 40% by mass. Regarding the above content, it can be confirmed using an X-ray diffractometer (XRD).

[0026] [Ba2Al2(OH) 10 Weight ratio (S / T) of Ba(AlO(OH)2)2 phase (S) to Phase (T)] When the hydroxide precursor of this embodiment contains Ba(AlO(OH)2)2 phase (S) and Ba2Al2(OH) 10 Phase (T), Ba2Al2(OH) 10 The weight ratio (S / T) of Ba(AlO(OH)2)2 phase (S) to Phase (T) may be 2 or more, 2.1 or more, or 2.2 or more. Further, it may be 50 or less, 25 or less, or 9 or less. From the viewpoint of high catalytic activity of the ammonia production catalyst obtained using the hydroxide precursor, Ba2Al2(OH) 10 The weight ratio (S / T) of Ba(AlO(OH)2)2 phase (S) to Phase (T) is preferably 2 to 50, and more preferably 2 to 25.

[0027] The above Ba2Al2(OH) 10The weight ratio (S / T) of the Ba(AlO(OH)2)2 phase (S) to the phase (T) can be calculated, for example, using an X-ray diffraction (XRD) or thermogravimetric differential thermal analysis (TG-DTA).

[0028] [BaCO3] If the hydroxide precursor of this embodiment contains BaCO3, the BaCO3 content in the hydroxide precursor may be 1% by mass or more, 2% by mass or more, or 4% by mass or more. It may also be 15% by mass or less, or 10% by mass or less. When the hydroxide precursor of this embodiment contains a certain amount of BaCO3, the catalytic activity of the resulting catalyst tends to be higher. The above-mentioned BaCO3 is present in the hydroxide precursor and is thought to also be present as the element Ba in the support obtained by calcining the precursor.

[0029] (Method for producing hydroxide precursors) One embodiment of the present invention provides a method for producing a hydroxide precursor (hereinafter sometimes referred to as the method for producing the preparation precursor of this embodiment), which is a method for producing the hydroxide precursor described above. The method for producing the preparation precursor of this embodiment includes a hydrothermal reaction step of barium nitrate and aluminum nitrate under basic conditions. The basic conditions are preferably pH 13.0 or higher, and more preferably pH 13.2 or higher. The metal-equivalent molar ratio (Ba / Al) of barium nitrate to aluminum nitrate is preferably 1 / 2 to 1 / 1.5, and more preferably 1 / 2 to 1 / 1.6.

[0030] The method for producing the preparation precursor of this embodiment may include, for example, the following first to third steps, as shown in Figure 1. Step 1: A step in which barium nitrate (Ba(NO3)2), aluminum nitrate (Al(NO3)3), and pure water are mixed to prepare a solution. Step 2: A step of adding a basic aqueous solution to the aforementioned solution to obtain a mixture. Third step: A step of hydrothermally treating the mixture. Furthermore, the following fourth step may be included as needed. Step 4: The process of collecting the solid product obtained in Step 3, washing it with pure water, and drying it. In the first step, the molar ratio of barium nitrate to aluminum nitrate (Ba / Al) is preferably 1 / 2 to 1 / 1.5. The total molar concentration of the barium nitrate, aluminum nitrate, and solution is preferably 0.7 to 6.0 M (mol / L). In the second step, examples of the basic aqueous solution include LiOH aqueous solution, KOH aqueous solution, NaOH aqueous solution, and ammonia aqueous solution. It is preferable that the pH of the solution after addition is 13.0 or higher. It is preferable that the total molar concentration of barium nitrate, aluminum nitrate, and the basic aqueous solution after addition is 0.5 to 2.0 M (mol / L). In the third step, the reaction conditions for the hydrothermal treatment include, for example, using a sealed reactor, under self-pressure, a reaction temperature of 160 to 200°C, and a reaction time of 5 to 20 hours. In the fourth step, the drying conditions include, for example, using a dryer at 60-80°C for 12-60 hours.

[0031] (BaAl2O4 support) The BaAl2O4 support of one embodiment of the present invention is a calcined product of the hydroxide precursor of the above embodiment. That is, it is obtained by calcining and dehydrating the hydroxide precursor. The aforementioned BaAl2O4 support contains BaAl2O4 as its main component, with a Ba / Al molar ratio in the range of 0.4 to 0.6. x It may also contain Al2O4 (for example, x = 1.8 to 2.2). Here, "main component" means that it is present in an amount of 70% by mass or more of the total mass. The BaAl2O4 content in the total mass of the BaAl2O4 carrier may be 80% by mass or more, 90% by mass or more, or 95% by mass or more. The BaAl2O4 carrier may also be BaAl2O4. The "BaAl2O4" of the present invention is anhydrous barium aluminate and may also be represented by the composite oxide formula xBaO·yAl2O3. The "BaAl2O4" of the present invention is strictly Ba x Al y O z In addition to including the expression (x=1.0, y=2.0, z=4.0), the above x, y, and z may be increased or decreased by 10%, 5%, or 2% from their respective reference values. The BET ratio surface area of ​​the BaAl2O4 support in this embodiment is 1.5 m 2 / g or more, and 2.5m 2 / g or more, and 3.0m 2 It may be 100m or more. 2 / g or less, 50m 2 / g or less, 30m 2 It may be less than / g. The BET ratio surface is, for example, 1.5 to 100 m 2 It is preferable that the amount be / g, and 3.0 to 50m 2 It is preferable that it be so.

[0032] [Surface basicity of the carrier] The surface basicity of the BaAl2O4 support in this embodiment can be evaluated using the temperature-controlled desorption method (CO2-TPD). A comparison of the surface basicity of the BaAl2O4 supports obtained in Example B2 (hydrothermal method), Comparative Example B2 (solid-phase method), and Comparative Example B3 (sol-gel method), described below, revealed differences in the basicity of supports obtained by different synthesis methods, with the support obtained by the hydrothermal method exhibiting a high amount of CO2 desorption in the temperature range of 470 to 1000°C. This suggests that the activity increases with a larger number of base points, and with a higher proportion of strong base points relative to the total number of base points in the carrier. The BaAl2O4 support in this embodiment is a calcined product of the hydroxide precursor obtained by hydrothermal synthesis. BaAl2O4 supports obtained by other synthesis methods may have surface structures with different basicity.

[0033] (Method for producing BaAl2O4 support) A method for producing a BaAl2O4 support according to one embodiment of the present invention is a method for producing the above-mentioned BaAl2O4 support. As shown in Figure 2, it includes a step of calcining the hydroxide precursor (precursor thermal decomposition, dehydration). In the firing process described above, the firing temperature may be 600°C or higher, 650°C or higher, or 700°C or higher. It may also be 850°C or lower, or 800°C or lower. The firing temperature is preferably, for example, 600 to 850°C, and more preferably 650 to 800°C. In the firing process described above, the firing time depends on the firing temperature, but may be, for example, 2 hours or more, or 3 hours or more. It may also be 20 hours or less, 15 hours or less, or 10 hours. For example, if the firing temperature is 600 to 800°C, the firing time is preferably 2 to 15 hours, and more preferably 3 to 10 hours.

[0034] (Ammonia production catalyst) An ammonia production catalyst according to one embodiment of the present invention comprises the BaAl2O4 support described above and a catalytically active metal (M1) supported on the BaAl2O4 support. The catalytically active metal (M1) is preferably a transition metal, and examples of such transition metals include Ru, Fe, and Co. The ammonia production catalyst of this embodiment preferably comprises the BaAl2O4 support described above, a catalytically active metal supported on the BaAl2O4 support, and an additive. The additive is preferably an alkaline earth metal (M2), and the alkaline earth metal (M2) is preferably barium.

[0035] [Catalytically active metal (M1)] A transition metal is preferred as the catalytically active metal (M1). The transition metal is not particularly limited, but is usually a transition metal from Group 6, 7, 8, 9, or 10 of the periodic table, preferably a transition metal from Group 6, 8, or 9, and more preferably a Group 8 or 9 metal. Furthermore, while there are no particular limitations on the specific metal elements, they are typically Cr, Mo, Mn, Re, Fe, Ru, Os, Co, Rh, Ni, Pd, and Pt. Preferably, Mo, Re, Fe, Ru, Os, and Co are used because they have high bonding energy with nitrogen. More preferably, Ru, Co, or Fe are used because they have ammonia synthesis activity when the ammonia production catalyst is used as an ammonia production catalyst. Even more preferably, Ru is used because it has the highest catalytic activity. Each of the aforementioned elements may be used individually or in combination of two or more. Preferably, each element is used individually or in combination of two or more, and more preferably, using each element individually is advantageous in terms of cost.

[0036] In the metal-supported material using the catalyst material as a support, the amount of transition metal supported is not particularly limited, but is usually 0.01 parts by mass (0.01 mass%) or more, preferably 0.5 parts by mass (0.5 mass%) or more, more preferably 1 part by mass (1 mass%) or more, and even more preferably 2 parts by mass (2 mass%) or more, per 100 parts by mass of the support, and is usually 50 parts by mass (50 mass%) or less, preferably 30 parts by mass (30 mass%) or less, more preferably 20 parts by mass (20 mass%) or less, and even more preferably 10 parts by mass (10 mass%) or less. If the amount is above the lower limit, the effects of the present invention can be obtained, and if it is below the upper limit, the effects of the present invention can be obtained in a manner that is commensurate with the amount of support and cost.

[0037] [Additives] Examples of the alkaline earth metal used as an additive include calcium, strontium, and barium. Among these, barium is preferred from the viewpoint of enhancing the catalytic activity of the ammonia production catalyst. The range of the amount of the additive added to the ammonia production catalyst of this embodiment is not particularly limited as long as high catalytic activity can be obtained, but the molar ratio (additive / catalyst active metal) to the catalytically active metal may be 0.005 or more, 0.01 or more, or 0.03 or more. It may also be 10 or less, 5 or less, or 1 or less. From the viewpoint of obtaining sufficient catalytic activity, it is preferable that the amount be between 0.005 and 10, and more preferably between 0.01 and 5. The above-mentioned additive can be added to the ammonia production catalyst using conventionally known methods such as impregnation, heat melting, vacuum deposition, and metal hydride adsorption decomposition, using the additive or its precursor. Furthermore, the additive or its precursor can also be supported when supporting the catalytically active metal described later. For example, if the additive is barium, a barium compound such as barium nitrate may be mixed with a catalytically active metal compound such as ruthenium as a barium precursor.

[0038] The additive or precursor thereof according to this embodiment can be obtained from commercially available products. The form of the additive or precursor thereof is not particularly limited, and from the viewpoint of uniform mixing with other raw materials in the subsequent method for producing the ammonia production catalyst, powder, granules, etc., can be used. Examples of additives or precursors according to this embodiment include hydroxides, carbonates, oxides, inorganic acid salts such as nitrates, acetates, formates, and other alkaline earth metals (M2), organic compounds containing other alkaline earth metals, and metal complexes such as metal acetylacetonate complexes.

[0039] The amount of additive added according to this embodiment is the additive content relative to 100% by mass of the final catalyst composition. Preferably, it is 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. Preferably, it is 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0040] [Method for producing ammonia catalyst] The ammonia production catalyst of this embodiment is obtained by supporting the catalytically active metal (M1) on the BaAl2O4 support of this embodiment. The ammonia production catalyst of this embodiment is produced by supporting the catalytically active metal (M1) on the BaAl2O4 support. The production method is not particularly limited, but it is usually produced by supporting the catalytically active metal (M1) or a compound that is a precursor of the catalytically active metal (M1) (hereinafter referred to as a catalytically active metal compound) on the support.

[0041] The method for supporting the catalytically active metal (M1) on the carrier used in this embodiment is not particularly limited, and known methods can be used. Typically, a catalytically active metal compound, which is a catalytically active metal compound to be supported and can be converted to the catalytically active metal (M1) by reduction, thermal decomposition, or the like, is supported on the carrier, and then converted to the catalytically active metal (M1).

[0042] For example, the BaAl2O4 support used in this embodiment can be pre-treated by heating it in a hydrogen atmosphere at approximately 200-500°C for several hours, for example, at 340°C for 2 hours, and then the catalytically active metal (M1) can be supported in the catalytically active metal (M1) loading step described later. In catalysts prepared using samples of the BaAl2O4 support that have been preheated under a hydrogen atmosphere, high activity can be obtained immediately after the start of the reaction, for example, when used in an ammonia synthesis reaction.

[0043] If the catalytically active metal (M1) is a transition metal, then the catalytically active metal compound is a transition metal compound. The transition metal compound is not particularly limited, but inorganic compounds or organic transition metal complexes of transition metals that are easily thermally decomposed can be used. Specifically, transition metal complexes, transition metal oxides, transition metal salts such as nitrates and hydrochlorides can be used. For example, a Ru compound is tolthenium dodecacarbonyl [Ru3(CO) 12Examples include dichlorotetrakis(triphenylphosphine)ruthenium(II) [RuCl2(PPh3)4], dichlorotris(triphenylphosphine)ruthenium(II) [RuCl2(PPh3)3], tris(acetylacetonate)ruthenium(III) [Ru(acac)3], rutenocene [Ru(C5H5)], nitrosylruthenium nitrate [Ru(NO)(NO3)3], potassium ruthenate, ruthenium oxide, ruthenium nitrate, ruthenium chloride, etc. Trilthenium dodecacarbonyl [Ru3(CO) 12 ], nitrosylruthenium nitrate [Ru(NO)(NO3)3], and tris(acetylacetonato)ruthenium(III) [Ru(acac)3] are preferred, and trilthenium dodecacarbonyl [Ru3(CO) 12 ], or more preferably, ruthenium nitrosylnitrate [Ru(NO)(NO3)3].

[0044] Examples of Fe compounds include pentacarbonyl iron [Fe(CO)5] and dodecacarbonyl triiron [Fe3(CO) 12 Examples include iron(II,III), nonacarbonyl iron [Fe2(CO)9], tetracarbonyl iron iodide [Fe(CO)4I2], tris(acetylacetonato)ferric(III) [Fe(acac)3], ferrocene [Fe(C5H5)2], iron oxide, iron nitrate, iron chloride (FeCl3), etc.

[0045] Examples of Co compounds include cobalt octacarbonyl [Co2(CO)8], tris(acetylacetonate)cobalt(III) [Co(acac)3], cobalt(II) acetylacetonate [Co(acac)2], cobaltocene [Co(C5H5)2], cobalt oxide, cobalt nitrate, and cobalt chloride. Among these transition metal compounds, [Ru3(CO) 12 ], [Fe(CO)5], [Fe3(CO) 12Carbonyl complexes of transition metals such as [Fe2(CO)9] and [Co2(CO)8] are preferable because, after being supported, the transition metal is supported by heating, thus eliminating the need for the reduction treatment described later when producing the ammonia production catalyst of this embodiment.

[0046] The amount of the transition metal compound used is not particularly limited, and an appropriate amount can be used to achieve the desired load amount. However, it is usually 0.01 parts by mass (0.01% by mass) or more, preferably 2 parts by mass (2% by mass) or more, preferably 10 parts by mass (10% by mass) or more, more preferably 20 parts by mass (20% by mass) or more, per 100 parts by mass of the carrier used, and usually 50 parts by mass (50% by mass) or less, preferably 40 parts by mass (40% by mass) or less, more preferably 30 parts by mass (30% by mass) or less.

[0047] Specific methods for supporting the transition metal compound on a support include, for example, impregnation, physical mixing, CVD (chemical vapor deposition), and sputtering.

[0048] The CVD (Chemical Vapor Deposition) method involves solid-state mixing of the support and the transition metal compound, followed by heating in a stream of inert gas such as nitrogen, argon, or helium, or under vacuum. While the heating temperature is not particularly limited, it is typically between 200°C and 600°C. The heating time is also not particularly limited, but a duration of 2 hours or more is generally preferred.

[0049] If the transition metal compound is converted to a transition metal by thermal decomposition at this stage, the transition metal is usually supported, and it becomes the ammonia production catalyst in this embodiment. If a transition metal compound other than one that is converted to a transition metal by thermal decomposition is used, the ammonia production catalyst of this embodiment is obtained by reducing the transition metal compound as usual. The method for reducing the transition metal compound (hereinafter referred to as the reduction treatment) is not particularly limited as long as it does not hinder the objective of the present invention. Examples include a method carried out in an atmosphere containing a reducing gas, or a method of adding a reducing agent such as NaBH4, NH2NH2, or formalin to a solution containing the transition metal compound and precipitating it on the surface of the BaAl2O4 support. Preferably, the treatment is carried out in an atmosphere containing a reducing gas. Examples of the reducing gas include hydrogen, ammonia, methanol (vapor), ethanol (vapor), methane, and ethane. Furthermore, during the reduction treatment, components other than reducing gases that do not inhibit the objectives of the present invention, particularly the ammonia synthesis reaction, may be present in the reaction system. Specifically, during the reduction treatment, in addition to reducing gases such as hydrogen, gases that do not inhibit the reaction, such as argon or nitrogen, may be present, and the presence of nitrogen is preferable. When the reduction treatment is carried out in a gas containing hydrogen, it can be carried out in parallel with the production of ammonia, as described later, by coexisting nitrogen with hydrogen. That is, when the ammonia production catalyst of this embodiment is used as the ammonia production catalyst described later, the transition metal compound may be reduced and converted to a transition metal by placing the BaAl2O4 support, supported on the BaAl2O4 support, under the reaction conditions of the ammonia synthesis reaction.

[0050] The temperature during the reduction treatment is not particularly limited, but is usually 200°C or higher, preferably 250°C or higher, and preferably less than 800°C. More preferably, it is carried out at 250°C or higher and less than 800°C. This is because carrying out the reduction treatment within the above temperature range allows for sufficient and favorable growth of the transition metal. The pressure during the reduction treatment is not particularly limited, but is usually between 0.01 MPa and 10 MPa. Using the same pressure conditions during the reduction treatment as those for ammonia synthesis, as described later, eliminates the need for complicated operations and is advantageous in terms of production efficiency. The duration of the reduction treatment is not particularly limited, but when carried out at atmospheric pressure, it is usually 1 hour or more, and preferably 2 hours or more. Furthermore, when the reaction is carried out under high reaction pressure conditions, such as 1 MPa or higher, it is preferable to perform the reaction for at least one hour.

[0051] If a transition metal compound other than one that is converted to a transition metal by thermal decomposition is used, the ammonia production catalyst of this embodiment is obtained by reducing the transition metal compound contained in the solid mixture by a conventional method, similar to the reduction treatment method described above.

[0052] <Method for producing ammonia-producing catalysts containing additives> The ammonia production catalyst of this embodiment may include the BaAl2O4 support of this embodiment, the catalytically active metal supported on the BaAl2O4 support, and the alkaline earth metal (M2) as an additive. In this case, the "ammonia production catalyst containing additives" may be referred to as the "second ammonia production catalyst." Furthermore, an ammonia production catalyst that does not contain additives may be referred to as the "first ammonia production catalyst." The method for producing the second ammonia production catalyst may include the step of supporting the catalytically active metal (M1) on the BaAl2O4 support and then adding the alkaline earth metal (M2). Alternatively, the method for producing the second ammonia production catalyst may include the step of adding the alkaline earth metal (M2) as an additive while supporting the catalytically active metal (M1) on the BaAl2O4 support.

[0053] Furthermore, the method for producing the second ammonia production catalyst may take advantage of the characteristics of the hydroxide precursor of this embodiment, which contains a Ba(AlO(OH)2)2 phase (S) that is poorly soluble in water, to first prepare an alkaline earth metal (M2)-containing BaAl2O4 support (M2-BaAl2O4 support). The method for preparing the M2-BaAl2O4 support may include, for example, the following first and second steps, as shown in Figure 3. Step 1: A step of mixing the hydroxide precursor of this embodiment, the alkaline earth metal (M2) compound (for example, nitrate), and water. Step 2: A process of drying and calcining the mixture obtained in Step 1. In the second step, the drying temperature is preferably 50 to 80°C, and more preferably 60 to 80°C. The calcination temperature is preferably 600 to 850°C, and more preferably 650 to 800°C. The drying and calcination may be carried out in air. The calcination may consist of thermal decomposition and a denitrification reaction.

[0054] Then, using the M2-BaAl2O4 support obtained above, a second ammonia production catalyst ("M1 / [M2-BaAl2O4]") can be produced in which a catalytically active metal (M1) is supported on the M2-BaAl2O4 support, similar to the method for producing the first ammonia production catalyst.

[0055] The ammonia production catalyst of this embodiment may further contain components other than the M2-BaAl2O4 support and the catalytically active metal (M1), such as SiO2, Al2O3, ZrO2, MgO, activated carbon, graphite, SiC, etc.

[0056] <Characteristics of ammonia production catalysts> The ammonia production catalyst of this embodiment can be used as a molded body using conventional molding techniques. Specifically, it can be in shapes such as granules, spheres, tablets, rings, macaroni, four-leaf clovers, dice, and honeycomb. It can also be used after being coated onto a suitable support.

[0057] When using the ammonia production catalyst of this embodiment, its reaction activity is not particularly limited, but taking the ammonia production rate at a reaction temperature of 300°C and a reaction pressure of 0.9 MPa as an example, it is preferably 1 mmol / g / h or more, more preferably 2 mmol / g / h or more as it is suitable for practical production conditions, even more preferably 3 mmol / g / h or more as it is suitable for more efficient production conditions, and even more preferably 5 mmol / g / h or more as it is suitable for even more efficient production conditions.

[0058] <Post-treatment of ammonia production catalysts> The method for producing the ammonia production catalyst of this embodiment may include a post-treatment step in which a compound of the catalytically active metal (M1) (e.g., a transition metal compound) is supported on a carrier and then heated in an atmosphere of hydrogen and nitrogen. The atmosphere of hydrogen and nitrogen is, for example, one in which a mixed gas flow rate containing nitrogen and hydrogen is 10 to 10,000 mL / min and the gas composition is N2 / H2 = 1 / 6 to 1 / 1 (v / v), preferably one in which a mixed gas flow rate containing nitrogen and hydrogen is 30 to 800 mL / min and the gas composition is N2 / H2 = 1 / 5 to 1 / 2 (v / v). The heating temperature is 250 to 800°C, preferably 400 to 700°C. The treatment time is 0.5 to 200 hours, preferably 1 to 100 hours. The treatment pressure is 0.5 to 2 MPa, preferably 0.7 to 1.2 MPa. It may also contain a small amount of ammonia gas. For example, it may contain 1 to 90% (v / v) of ammonia gas relative to a mixed gas containing nitrogen and hydrogen, preferably 1 to 50% (v / v). In the ammonia production catalyst of this embodiment, which is produced by performing a post-treatment on the support bearing the catalytically active metal compound by heating in the presence of nitrogen and hydrogen, high activity can be obtained immediately after the start of the reaction, for example, when used in an ammonia synthesis reaction. Furthermore, the ammonia synthesis activity, although it also depends on the composition of the catalyst in this embodiment, can be further improved depending on the length of the reaction time.

[0059] The method for producing ammonia using the ammonia production catalyst of this embodiment is described below.

[0060] (Method of producing ammonia) The method for producing ammonia according to this embodiment (hereinafter sometimes referred to as the method for this embodiment) is a method for synthesizing ammonia by reacting hydrogen and nitrogen on the supported metal catalyst or the ammonia production catalyst of this embodiment as a catalyst. The specific manufacturing method is not particularly limited, as long as it involves contacting hydrogen and nitrogen on the catalyst to synthesize ammonia; it can be manufactured in accordance with any known manufacturing method as appropriate.

[0061] In the ammonia production method of this embodiment, ammonia is typically produced by heating the catalyst when hydrogen and nitrogen are brought into contact on the catalyst. The reaction temperature in the manufacturing method of this embodiment is not particularly limited, but is usually 200°C or higher, preferably 250°C or higher, more preferably 300°C or higher, usually 600°C or lower, preferably 500°C or lower, and more preferably 450°C or lower. Since ammonia synthesis is an exothermic reaction, a lower temperature range is more favorable for ammonia production from a chemical equilibrium perspective, but it is preferable to carry out the reaction within the above temperature range in order to obtain a sufficient ammonia production rate. In the manufacturing method of this embodiment, the molar ratio of nitrogen to hydrogen that is brought into contact with the catalyst is not particularly limited, but is usually set to a ratio of hydrogen to nitrogen (H2 / N2 (volume / volume)) of 0.4 or more, preferably 0.5 or more, more preferably 1 or more, usually 10 or less, and preferably 5 or less.

[0062] The reaction pressure in the manufacturing method of this embodiment is not particularly limited, but is the pressure of the mixed gas containing nitrogen and hydrogen, and is usually 0.01 MPa or higher, preferably 0.1 MPa or higher, usually 20 MPa or lower, preferably 15 MPa or lower, and more preferably 10 MPa or lower. Furthermore, considering practical applications, it is preferable to carry out the reaction under pressure conditions of atmospheric pressure or higher.

[0063] In the manufacturing method of this embodiment, it is preferable to remove any moisture or oxides adhering to the catalyst before bringing nitrogen and hydrogen into contact with the catalyst, using a dehydrating agent, cryogenic separation, or hydrogen gas. A reduction treatment is one such removal method. In the manufacturing method of this embodiment, in order to obtain a better ammonia yield, it is preferable that the water content of the nitrogen and hydrogen used in the manufacturing method of this embodiment be low, and although not particularly limited, the total water content of the mixed gas of nitrogen and hydrogen is usually 100 ppm or less, preferably 50 ppm or less.

[0064] In the manufacturing method of this embodiment, the type of reaction vessel is not particularly limited, and any reaction vessel that can be normally used in ammonia synthesis reactions can be used. Specific reaction formats include, for example, batch reaction formats, closed-circulation reaction formats, and flow-type reaction formats. Of these, flow-type reaction formats are preferred from a practical standpoint. Furthermore, any method can be used, such as a single reactor packed with catalyst, a method of linking multiple reactors together, or a reactor having multiple reaction layers within the same reactor. The reaction to synthesize ammonia from hydrogen and nitrogen is an exothermic reaction accompanied by volume contraction. Industrially, it is preferable to remove the reaction heat to increase the ammonia yield, and known reactors equipped with commonly used heat removal methods may be used. For example, a method may be used in which multiple catalyst-filled reactors are connected in series, and an intercooler is installed at the outlet of each reactor to remove heat.

[0065] In the ammonia production method of this embodiment, the ammonia production catalyst obtained by the production method of this embodiment can be used alone or in combination with other known catalysts that can be commonly used in ammonia synthesis.

[0066] Furthermore, the used catalyst for synthesis of this embodiment after the ammonia synthesis reaction can be recovered and reused for use in a new ammonia synthesis reaction carried out after the said ammonia synthesis reaction. In addition, the supported metal contained in the catalyst for synthesis of this invention can be recovered from the used catalyst for synthesis of this invention after the ammonia synthesis reaction, and the recovered supported metal can be used to manufacture a new catalyst for synthesis of this invention. [Examples]

[0067] The present invention will be described in more detail below based on examples. The ammonia synthesis activity was evaluated by determining the ammonia production rate by quantifying the amount of NH3 produced by gas chromatography, or by dissolving the produced NH3 in an aqueous sulfuric acid solution and quantifying the solution by ion chromatography.

[0068] (Compositional analysis by X-ray diffraction (XRD)) Measurement device: Bruker D2PHASER Measurement method: The sample was placed in a 20 mm diameter powder sample holder, and the sample surface was leveled as much as possible before measurement. Semi-quantitative analysis was performed using DIFRACT EVA software (Bruker) to calculate the mass percentage of each composition.

[0069] (Measurement of average particle size using a scanning electron microscope (SEM)) Measurement equipment: JEOL NeoScope SEM (Scanning Electron Microscope) TM JCM-7000 Measurement method: Five fields of view were captured using a scanning electron microscope (SEM). More than 30 particles were arbitrarily selected from each field of view. The equivalent circle diameter was calculated for each selected particle, and then the average value of these equivalent circle diameters was calculated. The average of the equivalent circle diameters was used as the average particle diameter of the hydroxide precursor. ImageJ (public domain) was used for image processing of the average particle diameter of the hydroxide precursor.

[0070] (Method for measuring BET specific surface area) Measurement device: High-speed specific surface / pore distribution analyzer BELSORP-mini X (manufactured by MicrotracBEL) Measurement Method: The BET specific surface area was determined by adsorbing nitrogen gas onto the surface of the object at liquid nitrogen temperature and then calculating the adsorption isotherm based on the adsorption and desorption of nitrogen gas at -196°C. The measurement conditions were as follows: Sample weight: 0.5g Adsorbed gas: Nitrogen 99.99995% by volume Adsorption temperature: Liquid nitrogen temperature -196℃

[0071] (Method for evaluating catalytic activity (ammonia production rate)) The gas coming out of the fixed-bed flow reactor, described later, is bubbling into a 0.005 M sulfuric acid aqueous solution to dissolve the ammonia in the gas, and the ammonium ions (NH4) generated in the aqueous solution are then used to dissolve the ammonia in the gas. + The amount of ) was measured using an ion chromatograph. The measurement conditions were as follows: Equipment: HPLC Prominence manufactured by Shimadzu Corporation Detector: Electrical conductivity detector CDD10A VP (manufactured by Shimadzu Corporation) Column: Ion chromatogram column Shim-pack IC-C4LC-2000 plus (manufactured by Shimadzu Corporation) Eluent: Oxalic acid (2.5 mM) aqueous solution Flow rate: 1.0mL / min Column temperature: 40℃

[0072] (Evaluation of the basicity of the support surface by the thermal desorption method (CO2-TPD)) The basicity of the support surface was evaluated using the CO2-TPD (CO2 Temperature-Programmed Desorption) method with CO2 as the probe molecule. Specifically, after adsorbing CO2 molecules onto the surface of the target object, which had been cleaned by activation, the amount of CO2 gas desorbed was measured by continuously increasing the temperature of the target object. The measurement conditions were as follows. Measurement device: Microtrac-Bel catalyst analyzer BELCAT-A Gas detector: TCD Sample weight: 0.1g Pretreatment conditions: Pretreatment was performed using the following heat treatment program under gas flow. Steps 1 and 2 are for activating the sample surface before CO2 adsorption, step 5 is for CO2 adsorption onto the sample surface, and steps 3, 4, and 6 are for gas replacement and cooling within the apparatus. Step 1: Heat to 450°C at a rate of 230 ml / min of H (heating rate 10°C / min). Step 2: Maintain at 230 ml / min H, 450°C, for 60 minutes. Step 3: Maintain heat at 30 ml / min, 450°C for 30 minutes. Step 4: Cool down to 50°C in 60 minutes, using 30 ml / min of hemoglobin. Step 5: Maintain CO2-He 30 ml / min at 50°C for 60 minutes. (CO2 concentration in CO2-He mixed gas: 5.21% by volume) Step 6: Maintain a hemoglobin flow rate of 30 ml / min at 50°C for 30 minutes. Temperature-induced desorption conditions: Carrier gas flow: He 30 ml / min, heating rate: 10°C / min, measurement temperature range: 50-1000°C

[0073] (Example A1) [Preparation of hydroxide precursors] Barium nitrate (Ba(NO3)2) (manufactured by Kanto Chemical Co., Ltd., purity >99%) was used as the barium source, and aluminum nitrate nonahydrate (Al(NO3)3·9H2O) (manufactured by Kanto Chemical Co., Ltd., purity >98%) was used as the aluminum source. Ba(NO3)2 (22.5 mmol) and Al(NO3)3·9H2O (45.0 mmol) were added to pure water (11.5 mL), and the mixture was stirred at room temperature for 10 minutes to obtain a suspension. To this solution, 8 mol / L KOH aqueous solution (28.5 mL) was added while further stirring, and the mixture was stirred at room temperature for another 10 minutes. The molar ratio of Ba / Al / OH was 1 / 2 / 10.1. The obtained mixture was sealed in a Teflon-lined stainless steel autoclave (manufactured by San-ai Kagaku Co., Ltd.), and heated at 180°C for 20 hours under self-pressure to induce a hydrothermal reaction. After the reaction was complete, the solid product was collected by suction filtration, washed with pure water, and dried overnight in a 70°C dryer (EYELA). 3.696 g of the hydroxide precursor was obtained. Using the XRD compositional analysis method described above, the mass percentages of each composition of the obtained hydroxide precursors were measured and are shown in Table 1. The particle size was evaluated using the above-described SEM method for measuring the average particle size and is shown in Table 1.

[0074] [XRD of Ba(AlO(OH)2)2 powder] Figure 9 shows the XRD patterns of the powder sample obtained in Example A1 and the standard XRD pattern of Ba(AlO(OH)2)2. The sample synthesized in Example A1 matched the standard XRD pattern of Ba(AlO(OH)2)2, indicating that Ba(AlO(OH)2)2 was obtained.

[0075] (Examples A2-A12) [Preparation of hydroxide precursors] Except for the conditions shown in Table 1, the hydroxide precursors of Examples A2 to A12 were obtained by the same method as in Example 1. Using the XRD compositional analysis method described above, the mass percentages of each composition of the obtained hydroxide precursors were measured and are shown in Table 1. The particle size was evaluated using the SEM method described above and is shown in Table 1. Furthermore, the particle size histogram (particle size distribution) for Example A2 is shown in Figure 8. Furthermore, SEM images of the hydroxide precursors obtained in Examples A2, A9, and A10 are shown in Figures 5 to 7, respectively.

[0076] (Comparative Example A1) [Preparation of hydroxide precursors] The hydroxide precursor for Comparative Example A1 was obtained using the same method as in Example 1, except for the conditions shown in Table 1. The raw materials were prepared so that the total volume of pure water and 8 mol / L KOH aqueous solution was approximately 40 mL. Using the XRD compositional analysis method described above, the mass percentages of each composition of the obtained hydroxide precursors were measured and are shown in Table 1. The particle size was evaluated using the above-described SEM method for measuring the average particle size and is shown in Table 1.

[0077] [Table 1]

[0078] (Example B1) [Synthesis of BaAl2O4 support] 1.213 g of the hydroxide precursor obtained in Example A1 was placed in an alumina crucible and heated to 700°C at a heating rate of 10°C / min, and then maintained for 4 hours to obtain 1.075 g of BaAl2O4 support.

[0079] [XRD of BaAl2O4 powder] Figure 10 shows the XRD pattern of the powder sample obtained in Example B1. For comparison, the XRD pattern of standard BaAl2O4 is also shown in Figure 10. The sample synthesized in Example B1 matched the standard XRD pattern of BaAl2O4, indicating that the BaAl2O4 phase was formed to almost 100%.

[0080] (Example B2) [Synthesis of BaAl2O4 support] The BaAl2O4 support of Example B2 was obtained in the same manner as in Example B1, except that the hydroxide precursor obtained in Example A2 was used.

[0081] The BET specific surface area of ​​the sample is 7.4 m². 2 The result was / g. The results are shown in Table 2.

[0082] The basicity of the surface of the BaAl2O4 support in Example B2 was evaluated using the above-described method for evaluating the basicity of the support surface by thermal desorption (CO2-TPD). The results are shown in Figure 11 and Table 2.

[0083] (Examples B3-B11) [Synthesis of BaAl2O4 support] The BaAl2O4 supports of Examples B3 to B11 were obtained in the same manner as in Example B1, except that the hydroxide precursors obtained in Examples A3 to A11 were used.

[0084] (Example B12) [Synthesis of 0 wt% Ba-BaAl2O4 support] The 0 wt% Ba-BaAl2O4 support of Example B12 was obtained in the same manner as in Example B1, except that the hydroxide precursor obtained in Example A12 was used. This is shown in Table 3.

[0085] (Example B13) [Synthesis of 3wt%Ba-BaAl2O4 support] 0.400 g of the hydroxide precursor obtained in Example A12, 0.0228 g of barium nitrate (manufactured by Kanto Chemical Co., Ltd., >99%) (3% by mass in terms of metallic Ba relative to the hydroxide precursor), and 0.6 mL of pure water were placed in an agate mortar and mixed by a wet mixing method. The resulting mixture was dried overnight in a drying oven at 70°C. The dried mixture was placed in an alumina crucible and heated to 700°C at a heating rate of 10°C / min, and maintained at that temperature for 4 hours to obtain a barium-added BaAl2O4 support (hereinafter referred to as 3wt%Ba-BaAl2O4 support). The results are shown in Table 3.

[0086] (Example B14) [Synthesis of 7wt%Ba-BaAl2O4 support] A barium-added BaAl2O4 support (7wt%Ba-BaAl2O4 support) was obtained in the same manner as in Example B13, except that 0.0533 g of barium nitrate was used so that it amounted to 7% by mass in terms of metallic Ba relative to the hydroxide precursor. This is shown in Table 3.

[0087] (Comparative Example B1) [Synthesis of BaAl2O4 support] The BaAl2O4 support of Comparative Example B1 was obtained in the same manner as in Example B1, except that the hydroxide precursor obtained in Comparative Example A1 was used.

[0088] (Comparative example B2) [Preparation of BaAl2O4 support] <Synthesis of BaAl2O4 support by solid-phase method> 1.4801 g of barium carbonate (BaCO3) (manufactured by Kojun Chemical Laboratory Co., Ltd., 99.9%), 1.1700 g of aluminum hydroxide (Al(OH)3) (manufactured by Kojun Chemical Laboratory Co., Ltd., 99.99%), and a small amount of ethanol were placed in an agate mortar and wet-mixed in air for 1 hour. After mixing, the mixture was dried in a dryer at 70°C for 3 hours to obtain a mixed powder, which was then uniaxially compressed at 20 MPa to obtain a compact. The compact was placed in an alumina crucible, heated to 1000°C over 3 hours, maintained at that temperature for 20 hours, allowed to cool naturally, and then ground in an agate mortar to obtain a BaAl2O4 support.

[0089] The BET specific surface area of ​​the sample is 1.3 m². 2 The result was / g. The results are shown in Table 2.

[0090] The basicity of the surface of the BaAl2O4 support of Comparative Example B2 was evaluated using the above-described method for evaluating the basicity of the support surface by thermal desorption (CO2-TPD). The results are shown in Figure 11 and Table 2.

[0091] (Comparative Example B3) [Preparation of BaAl2O4 support] <Synthesis of BaAl2O4 support by sol-gel method> 15 mmol of aluminum isopropoxide (Al[OCH(CH3)2]3) (Sigma-Aldrich, ≥98%) and 7.5 mmol of diethoxybarium (Ba(OC2H5)2) (High Purity Chemical Laboratory, >99%) were placed in 100 mL of ethanol and stirred at 60°C for 10 minutes to dissolve. A mixture of 1.323 g of water and 20 mL of ethanol was then gradually added dropwise to hydrolyze the mixture and obtain a sol. The solvent was then removed using a rotary evaporator at 60-80°C to obtain a dry gel. The obtained dry gel was calcined at 800°C for 15 hours to obtain a BaAl2O4 support.

[0092] The BET specific surface area of ​​the sample is 26.7 m². 2 The result was / g. The results are shown in Table 2.

[0093] The basicity of the surface of the BaAl2O4 support of Comparative Example B3 was evaluated using the above-described method for evaluating the basicity of the support surface by thermal desorption (CO2-TPD). The results are shown in Figure 11 and Table 2.

[0094] [Table 2]

[0095] [Table 3]

[0096] (Example C1) (Preparation of ammonia production catalyst) [Ru support on BaAl2O4 support] 0.4 g of the powdered BaAl2O4 support obtained in Example B1 and Ru3(CO) 12 44.4 mg (99% Aldrich) (corresponding to 5% by mass of supported metallic Ru relative to the theoretical total yield of the Ru / BaAl2O4 catalyst described below) was placed in an agate mortar and dry-mixed in air for 10 minutes. Subsequently, the mixture was heated in a vacuum at 250°C for 2 hours to obtain a support in which Ru was immobilized on BaAl2O4 (hereinafter referred to as Ru / BaAl2O4). In the following, ammonia synthesis was carried out using the aforementioned Ru / BaAl2O4 as a catalyst.

[0097] [Ammonia synthesis using Ru / BaAl2O4] <Ammonia synthesis reaction> The Ru / BaAl2O4 catalyst was used to carry out an ammonia synthesis reaction by contacting this catalyst with a mixed gas of nitrogen and hydrogen. 0.1 g of the Ru / BaAl2O4 was packed into a SUS reaction tube, and the reaction was carried out using a fixed-bed flow reactor equipped with this tube. The moisture concentrations of the nitrogen gas and hydrogen gas used as raw materials were both below the detection limit. The flow rates of the raw material gases during this reaction were 15 mL / min for nitrogen gas and 45 mL / min for hydrogen gas (total 60 mL / min). The reaction pressure was 0.9 MPa, and the reaction temperature was 340°C. The reaction rate was measured after 8 hours using the ammonia production rate measurement method described above. It was 4.4 mmol / g / h. The results are shown in Table 4. Furthermore, this catalyst was activated before the ammonia synthesis reaction. The activation conditions were 450°C for 8 hours.

[0098] (Examples C2-C11) (Preparation of ammonia production catalyst) [Ru support on BaAl2O4 support] Except for using the powdered BaAl2O4 carrier obtained in Examples B2 to B11, a support in which Ru was immobilized on BaAl2O4 (hereinafter referred to as Ru / BaAl2O4) was obtained in the same manner as in Example C1.

[0099] [Ammonia synthesis using Ru / BaAl2O4] The ammonia synthesis reaction was carried out in the same manner as in Example C1, except that Ru / BaAl2O4 obtained in Examples C2 to C11 was used as the catalyst. The reaction rate was measured after 8 hours. The results are shown in Table 4.

[0100] (Example C12) (Preparation of ammonia production catalyst) [Ru support on 0wt%Ba-BaAl2O4 support] A support in which Ru was immobilized on 0 wt% Ba-BaAl2O4 (hereinafter, Ru / [0 wt% Ba-BaAl2O4]) was obtained in the same manner as in Example C1, except that the powdered BaAl2O4 support obtained in Example B12 was used.

[0101] [Ammonia synthesis using Ru / [0wt%Ba-BaAl2O4]] The ammonia synthesis reaction was carried out in the same manner as in Example C1, except that Ru / [0wt%Ba-BaAl2O4] obtained in Example C12 was used as the catalyst. The reaction rate was measured after 8 hours. The results are shown in Table 5.

[0102] (Example C13) (Preparation of ammonia production catalyst) [Ru support on 3wt%Ba-BaAl2O4 support] Except for using the barium-added BaAl2O4 support (3wt%Ba-BaAl2O4 support) obtained in Example B13, a support in which Ru was immobilized on 3wt%Ba-BaAl2O4 (hereinafter, Ru / [3wt%Ba-BaAl2O4]) was obtained in the same manner as in Example C12.

[0103] [Ammonia synthesis using Ru / [3wt%Ba-BaAl2O4]] The ammonia synthesis reaction was carried out in the same manner as in Example C12, except that Ru / [3wt%Ba-BaAl2O4] obtained in Example C13 was used as the catalyst. The reaction rate was measured after 8 hours. The results are shown in Table 5.

[0104] (Example C14) (Preparation of ammonia production catalyst) [Ru support on 7wt%Ba-BaAl2O4 support] Except for using the barium-added BaAl2O4 support (7wt%Ba-BaAl2O4 support) obtained in Example B14, a support in which Ru was immobilized on 7wt%Ba-BaAl2O4 (hereinafter, Ru / [7wt%Ba-BaAl2O4]) was obtained in the same manner as in Example C12.

[0105] [Ammonia synthesis using Ru / [7wt%Ba-BaAl2O4]] The ammonia synthesis reaction was carried out in the same manner as in Example C12, except that Ru / [7wt%Ba-BaAl2O4] obtained in Example C14 was used as the catalyst. The reaction rate was measured after 8 hours. The results are shown in Table 5.

[0106] (Comparative examples C1~C3) (Preparation of ammonia production catalyst) [Ru loading onto BaAl2O4] Except for using the powdered BaAl2O4 carriers obtained in Comparative Examples B1 to B3, a support in which Ru was immobilized on BaAl2O4 (hereinafter referred to as Ru / BaAl2O4) was obtained in the same manner as in Example C1.

[0107] [Ammonia synthesis using Ru / BaAl2O4] The ammonia synthesis reaction was carried out in the same manner as in Example C1, except that Ru / BaAl2O4 obtained in Comparative Examples C1-C3 was used as the catalyst. The reaction rate was measured after 8 hours. The results are shown in Table 4.

[0108] [Table 4]

[0109] [Table 5]

[0110] The conditions for ammonia production (catalyst activity evaluation conditions) for the examples and comparative examples in Tables 4 and 5 are as follows. Catalyst amount: 0.1g, Ru: 5% by mass, Activation conditions: 450℃, 8h, 0.9MPa, Reaction temperature: 340°C, reaction gas flow rate: 60 mL / min, reaction gas composition: N2 / H2 = 1 / 3 (v / v), reaction pressure: 0.9 MPa, WHSV: 36000 mL / g / h

[0111] (Consideration) Table 4 shows that catalysts using BaAl2O4 supports obtained from hydroxide precursors with particle sizes of 4.8 to 48.9 μm synthesized by hydrothermal methods (Examples C1 to C11) showed higher activity than catalysts using BaAl2O4 supports obtained from hydroxide precursors with particle sizes of 65.1 μm (Comparative Example C1), suggesting that the particle size of the hydroxide precursor affects the catalytic activity of Ru / BaAl2O4. Furthermore, catalysts using BaAl2O4 supports obtained from hydroxide precursors with particle sizes of 4.8 to 48.9 μm synthesized by the hydrothermal method (Examples C1 to C11) showed higher activity than catalysts using BaAl2O4 supports synthesized by the solid-phase method (Comparative Example C2) or the sol-gel method (Comparative Example C3). This is thought to be because, as shown in Table 2 and Figure 11, BaAl2O4 supports obtained from hydroxide precursors synthesized by the hydrothermal method have more strong basic sites on their surface than BaAl2O4 supports synthesized by the sol-gel method or the solid-phase method. Therefore, the BaAl2O4 supports obtained from hydroxide precursors synthesized by the hydrothermal method have a superior ability to donate electrons to Ru particles on the support and promote catalytic reactions on the Ru particles compared to BaAl2O4 supports synthesized by the sol-gel method or the solid-phase method. Furthermore, as shown in Table 5, catalysts using a Ba-BaAl2O4 support (Examples C13 and C14), obtained by impregnating a hydroxide precursor with Ba as an additive to promote catalytic activity using water as a solvent and then calcining, showed up to 2.7 times higher activity compared to a catalyst using a BaAl2O4 support without added Ba (Example C12). This demonstrates that the catalytic activity of BaAl2O4 was significantly improved by using a hydroxide precursor and a process using water as a solvent.

Claims

1. Ba(AlO(OH) ２ ) ２ A hydroxide precursor containing phase (S), A hydroxide precursor having an average particle size of 1 to 65 μm.

2. Furthermore, Ba ２ Al ２ (OH) １０ A hydroxide precursor according to claim 1, comprising phase (T).

3. Furthermore, BaCO ３ A hydroxide precursor according to claim 1 or 2, comprising:

4. Ba ２ Al ２ (OH) １０ phase (T) is 2 to 50, the hydroxide precursor according to claim 2. ２ ) ２ The weight ratio (S / T) of the phase (S) to the

5. BaAl is a calcined product of the hydroxide precursor described in claim 1 or 2. ２ O ４ Carrier.

6. BaAl as described in claim 5 ２ O ４ Carrier and The aforementioned BaAl ２ O ４ A catalyst for ammonia production, comprising a catalytically active metal (M1) supported on a carrier.

7. The ammonia production catalyst according to claim 6, wherein the catalytically active metal (M1) is a transition metal.

8. The ammonia production catalyst according to claim 6, wherein the catalytically active metal (M1) is at least one selected from the group consisting of Ru, Fe, and Co.

9. Furthermore, it contains additives, The ammonia production catalyst according to claim 6, wherein the additive is an alkaline earth metal (M2).

10. The ammonia production catalyst according to claim 9, wherein the alkaline earth metal (M2) is Ba.

11. A method for producing a hydroxide precursor according to claim 1 or 2, A method for producing a hydroxide precursor, comprising a hydrothermal reaction step of barium nitrate and aluminum nitrate under basic conditions.

12. The method for producing a hydroxide precursor according to claim 11, wherein the aforementioned base condition is pH 13.0 or higher.

13. The method for producing a hydroxide precursor according to claim 11, wherein the metal-equivalent molar ratio (Ba / Al) of barium nitrate to aluminum nitrate is 1 / 2 to 1 / 1.

5.

14. BaAl as described in claim 5 ２ O ４ A method for manufacturing EVs, The process includes a step of calcining the hydroxide precursor, BaAl ２ O ４ A method for manufacturing this product.

15. BaAl as described in claim 5 ２ O ４ A method for producing an ammonia catalyst, characterized by supporting a catalytically active metal on a carrier.

16. A method for producing ammonia, characterized by comprising the step of reacting nitrogen and hydrogen in the presence of the ammonia production catalyst described in claim 6.

Images