Ammonia synthesis composite catalyst and method for producing ammonia

Abstract

The ammonia synthesis composite catalyst provided by the present invention comprises a catalyst that exhibits catalytic activity in synthesis of ammonia, and a carrier that carries the catalyst. The carrier contains a hydrogen-occluding material. The hydrogen-occluding material is, e.g., a hydrogen-occluding metal. The hydrogen-occluding metal is, e.g., a hydrogen-occluding alloy. The hydrogen-occluding alloy is, e.g., a solid solution. The hydrogen-occluding alloy is, e.g., a Ti-Mn-based alloy. The catalyst includes, e.g., a transition metal. The transition metal is, e.g., at least one selected from the group consisting of Ru, Co, Ni, Fe, Mn, V, and Ti.

Description

[Technical Field]

[0001] This invention relates to a composite catalyst for ammonia synthesis and a method for producing ammonia. [Background technology]

[0002] Ammonia (NH3) is essential as a nitrogen source for various products such as artificial fertilizers and is also attracting attention as a hydrogen carrier. However, nitrogen (N2), the raw material, is an extremely stable substance with a strong triple bond. For this reason, the Haber-Bosch process, which requires high temperature and high pressure conditions, continues to be used as a mass production technology even now, more than 100 years after the invention of the process. Because maintaining high temperature and high pressure conditions requires enormous amounts of energy, various ammonia synthesis catalysts are being developed to alleviate these conditions. Patent Document 1 discloses an ammonia synthesis composite catalyst in which ruthenium is supported on a carrier containing ceria and magnesia. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-231229 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to provide a novel ammonia synthesis catalyst. [Means for solving the problem]

[0005] The present invention A catalyst that exhibits catalytic activity in the synthesis of ammonia, The system comprises a carrier supporting the catalyst, The aforementioned carrier contains a hydrogen storage material, an ammonia synthesis composite catalyst, To provide.

[0006] From another perspective, the present invention is This includes synthesizing ammonia by contacting a gas containing hydrogen and nitrogen with an ammonia synthesis catalyst. The ammonia synthesis catalyst is the ammonia synthesis composite catalyst of the present invention, in a method for producing ammonia. To provide. [Effects of the Invention]

[0007] According to the present invention, a novel ammonia synthesis catalyst is provided. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a graph showing the hydrogen storage capacity of the composite catalysts prepared in the examples. [Figure 2] Figure 2 is a graph showing the Arrhenius plot for the ammonia synthesis reaction of the composite catalyst prepared in the example. [Figure 3] Figure 3 is a graph showing the hydrogen storage capacity of the composite catalysts prepared in the examples. [Figure 4] Figure 4 is a graph showing the Arrhenius plot in the ammonia synthesis reaction for the composite catalysts prepared in the examples. [Figure 5] Figure 5 is a graph showing the hydrogen storage capacity of the composite catalysts prepared in the examples. [Figure 6] Figure 6 is a graph showing the Arrhenius plot for the ammonia synthesis reaction of the composite catalyst prepared in the example. [Modes for carrying out the invention]

[0009] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0010] [Ammonia synthesis composite catalyst] In the selection of the catalyst carrier, reduction of the activation energy due to the electron-donating property or electron-withdrawing property to the catalyst may be emphasized. For example, in an ammonia synthesis catalyst, by using an electron-donating carrier, it can be expected that the activation energy of the ammonia synthesis reaction will be reduced. On the other hand, the inventors of the present invention conceived of reducing the activation energy by the hydrogen storage ability of the carrier and completed the present invention.

[0011] That is, the ammonia synthesis composite catalyst of the present embodiment is a catalyst showing catalytic activity for the synthesis of ammonia, and a carrier supporting the catalyst, and the carrier contains a hydrogen storage material.

[0012] It is presumed that the hydrogen storage material prevents an excess or deficiency of hydrogen in the vicinity of the catalyst and reduces the activation energy of the synthesis reaction.

[0013] (Carrier) The carrier contains a hydrogen storage material. The hydrogen storage material may be the main component of the carrier. In this specification, the main component means the component with the largest content. The content rate of the hydrogen storage material in the carrier is, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, and further 99% by mass or more. The carrier may be composed of a hydrogen storage material. Examples of the hydrogen storage material are hydrogen storage metals, oxides of hydrogen storage metals, and metal organic frameworks (MOFs). An example of the oxide of a hydrogen storage metal is zeolite. Looking from another aspect, the hydrogen storage material may be a porous material such as MOF and zeolite. However, the hydrogen storage material is not limited to the above examples as long as it can store and release gaseous hydrogen. In a preferred example of the hydrogen storage material, hydrogen can be stored at a higher density than gaseous hydrogen and the stored hydrogen can be released. The hydrogen storage material has the density of liquid hydrogen (for example, the density at 20 kelvin is 70.8 kg / m 3The material may be capable of storing hydrogen at a density of 1 / 3 or more or 1 / 2 or more of that of liquid hydrogen, and also capable of releasing the stored hydrogen.

[0014] The hydrogen storage material may also be a hydrogen storage metal. Hydrogen storage metals are particularly suitable for reducing the activation energy of synthesis reactions. In this specification, a hydrogen storage metal means a metal whose maximum hydrogen storage capacity in the temperature range of 0°C to 300°C is expressed by the hydrogen-to-metal atomic ratio H / M defined in Japanese Industrial Standards (formerly Japanese Industrial Standards; JIS) H7003 as 0.01 or higher. The ratio H / M of a hydrogen storage metal may be 0.05 or higher, 0.1 or higher, or even 0.5 or higher. The hydrogen storage capacity based on the ratio H / M can be determined from a pressure-composition isotherm (PCT line) obtained by measurement using the volumetric method (Siebertz method) defined in JIS H7201. Specifically, the value of the x-axis at the point of hydrogen pressure 5 MPa on the PCT line, where the x-axis is the ratio H / M and the y-axis is the hydrogen pressure, can be defined as the above hydrogen storage capacity. The maximum hydrogen storage capacity of a hydrogen storage metal may be 0.01 or more, 0.05 or more, 0.1 or more, or even 0.5 or more, expressed as a ratio H / M, in the temperature range of 25°C, 50°C, 100°C, 150°C, 200°C, or 250°C to 300°C.

[0015] The work function W of the hydrogen storage metal may exceed 3.5 eV, and may be 3.6 eV or higher, 3.7 eV or higher, greater than 3.7 eV, 3.8 eV or higher, and even 4.0 eV or higher. In other words, the hydrogen storage metal does not need to be electron-donating to the catalyst. If the hydrogen storage metal is not electron-donating, excessive bonding between the catalyst and hydrogen can be suppressed, resulting in a more appropriate state for preventing an excess or deficiency of hydrogen to the catalyst.

[0016] The hydrogen storage metal may not substantially contain group 2 elements, such as Mg. The hydrogen storage metal may not substantially contain group 2 elements, group 3 elements, and lanthanides. In this specification, "substantially absent" means a content of 1 atomic% or less, preferably 0.5 atomic% or less, and more preferably 0.1 atomic% or less.

[0017] The hydrogen storage metal does not need to substantially contain any Group 1 elements.

[0018] A hydrogen storage metal may contain only one metal element or two or more metal elements. A hydrogen storage metal may also be a hydrogen storage alloy. In this specification, a hydrogen storage alloy means an alloy whose maximum hydrogen storage capacity in the temperature range of 0°C to 300°C is expressed as 0.01 or more by the above ratio H / M. The ratio H / M of a hydrogen storage alloy may be 0.05 or more, 0.1 or more, or even 0.5 or more. The maximum hydrogen storage capacity of a hydrogen storage alloy may be 0.01 or more, 0.05 or more, 0.1 or more, or even 0.5 or more by the ratio H / M in the temperature range of 25°C, 50°C, 100°C, 150°C, 200°C, or 250°C to 300°C. The alloy contains two or more metal elements. A hydrogen storage metal, in particular a metal composed of one metal element, may be in the state of a hydrogen-adsorbed hydride.

[0019] Examples of hydrogen-storing metals composed of a single metallic element are titanium (Ti) and zirconium (Zr).

[0020] The support may include at least one selected from Ti, Zr, TiH2, and ZrH2.

[0021] Hydrogen storage alloys include, for example, metallic elements with relatively high and relatively low bonding affinity to hydrogen. Examples of metallic elements with relatively high bonding affinity include Group 2 elements, Group 3 elements, lanthanides, actinides, Group 4 elements, Group 5 elements, and palladium (Pd). Examples of Group 2 elements are magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Examples of Group 3 elements are scandium (Sc) and yttrium (Y). Examples of lanthanides are lanthanum (La), cerium (Ce), praseodymium (Pr), samarium (Sm), terbium (Tb), holmium (Ho), erbium (Er), thulium (Tm), and lutetium (Lu). Examples of Group 4 elements are titanium (Ti), zirconium (Zr), and hafnium (Hf). Examples of Group 5 elements are vanadium (V), niobium (Nb), and tantalum (Ta). An example of an actinide is thorium (Th). Metallic elements with a relatively high affinity for hydrogen may be at least one selected from the group consisting of Mg, Ca, lanthanides, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Th, and Pd. Examples of metallic elements with a relatively low affinity for hydrogen are elements from Groups 6 to 15, and may also be elements from Groups 6 to 14, or even from Groups 6 to 13. Metalloid elements may be excluded from metallic elements with a relatively low affinity for hydrogen. Metalloid elements that may be excluded are at least one selected from the group consisting of silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and bismuth (Bi). Examples of metallic elements with relatively low bonding affinity to hydrogen include at least one selected from the group consisting of chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), and bismuth (Bi), or at least one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, and Al. The hydrogen storage alloy may contain two or more metallic elements with relatively high bonding affinity to hydrogen, or two or more metallic elements with relatively low bonding affinity to hydrogen.

[0022] The hydrogen storage alloy may be at least one selected from the group consisting of Ti-based, V-based, Mg-based, Ca-based, and Pd-based alloys. A Ti-based hydrogen storage alloy may contain Ti and at least one selected from the group consisting of Zr, V, Cr, Mn, Fe, Co, Ni, and Cu. A V-based hydrogen storage alloy may contain V and at least one selected from the group consisting of Ti, Zr, Cr, Mn, Fe, Co, Ni, and Cu. A Mg-based hydrogen storage alloy may contain Mg and at least one selected from the group consisting of Ni, Co, and Al. A Ca-based hydrogen storage alloy may contain Ca and at least one selected from the group consisting of Ni, Co, and Al. A Pd-based hydrogen storage alloy may contain Pd and at least one selected from the group consisting of Mg, Ca, and V.

[0023] The hydrogen storage alloy may be, for example, at least one selected from the group consisting of AB type, AB2 type, AB5 type, A2B type, and A5B3 type. AB type and AB2 type hydrogen storage alloys may contain at least one selected from the group consisting of Ti, Mn, Zr, and Ni. AB5 type hydrogen storage alloys may contain at least one selected from the group consisting of Mg, Ca, Sc, Y, lanthanides, Nb, Zr, Ni, Co, and Al. A2B type hydrogen storage alloys may contain at least one selected from the group consisting of Mg and Ca, and at least one selected from the group consisting of Ni, Co, and Al. A5B3 type hydrogen storage alloys may contain at least one selected from the group consisting of Sc, Zr, Hf, V, Nb, Ta, lanthanides, and Th, and at least one selected from the group consisting of Al, Ga, Si, Ge, Sn, Pb, Sb, and Bi. Examples of A5B3 type hydrogen storage alloys are Zr5Pb3, Zr5Sn3, and Ti5Ge3.

[0024] Hydrogen storage alloys may have at least one crystal structure selected from the group consisting of body-centered cubic (BCC) structure and hexagonal close-packed structure. The hexagonal close-packed structure may be the Laves phase. The Laves phase may be at least one selected from the group consisting of C14 type, C15 type, and C36 type. An example of a hydrogen storage alloy having a hexagonal close-packed structure, such as the Laves phase, as its crystal structure is the AB2 type hydrogen storage alloy.

[0025] The hydrogen storage alloy may contain at least one selected from the group consisting of solid solutions and intermetallic compounds, and may also be a solid solution.

[0026] More specific examples of hydrogen storage alloys include Ti-Mn alloys, Ti-Fe alloys, and A5B3 type intermetallic compounds. Examples of A5B3 type intermetallic compounds include Zr5Pb3, Zr5Sn3, and Ti5Ge3.

[0027] Ti-Mn alloys may be binary, ternary, or multi-component systems of quaternary or more. Ti-Mn alloys may also be TiMnV ternary alloys. In this specification, the designation AB alloy means that the total content of metal A and metal B is 50 atomic percent or more. For example, a Ti-Mn alloy means an alloy in which the total content of Ti and Mn is 50 atomic percent or more. The total content of metal A and metal B in an AB alloy may be 60 atomic percent or more, 70 atomic percent or more, or even 80 atomic percent or more. Note that alloys, including Ti-Mn alloys, may be solid solutions. In a TiMnV ternary alloy, the total content of Ti, Mn, and V may be, for example, 55 atomic percent or more, 65 atomic percent or more, 75 atomic percent or more, or even 85 atomic percent or more.

[0028] In hydrogen-storing metals, the total content of nonmetallic elements, typically at least one element selected from the group consisting of hydrogen, nitrogen, oxygen, sulfur, and halogens, may be less than 10 atomic percent, and may be 5 atomic percent or less, 3 atomic percent or less, 1 atomic percent or less, or even 0.5 atomic percent or less. Examples of halogens are fluorine, chlorine, and bromine. However, the hydrogen content is based on the number of atoms when no hydrogen is absorbed.

[0029] The hydrogen storage metal and the catalyst may be different. Furthermore, the metallic elements contained in the hydrogen storage metal may be different from the metallic elements that may be contained in the catalyst.

[0030] The carrier is usually particulate. The average particle size of the carrier is, for example, 0.01 to 500 μm, and may be 0.1 to 100 μm. However, the shape of the carrier and the average particle size are not limited to the above examples, as long as they function as an ammonia synthesis composite catalyst by supporting the catalyst. In this specification, the average particle size refers to the 50% particle size (D50) in the cumulative particle size distribution (volume basis) obtained by particle size distribution measurement by laser diffraction.

[0031] The affinity (bonding affinity) of the hydrogen storage material (especially the hydrogen storage metal) contained in the support to hydrogen may be higher than the affinity of the catalyst (especially the transition metal that may be contained in the catalyst) to hydrogen. This embodiment is particularly suitable for reducing the activation energy of the synthesis reaction. The affinity to hydrogen can be estimated by quantum chemical calculations. For example, the affinity of Ti-Mn alloys such as TiMnV ternary alloys, as well as Ti and Zr, to hydrogen is higher than the affinity of Ru to hydrogen. In one example of quantum chemical calculations, the stabilization energy corresponding to the affinity to hydrogen (e.g., hydrogen adsorption energy for the catalyst, hydrogen storage energy for the support) is determined by Density Functional Theory (DFT) calculations using the first-principles calculation program Vienna Ab initio Simulation Package (VASP). For the functional and basis sets, for example, Generalized Gradient Approximation - Perdew-Burke-Ernzerhof (GGA-PBE) and Projector Augmented Wave method (PAW method) can be used, respectively. It is also possible to use the basis sets recommended by the Materials project.

[0032] The hydrogen storage material may be a material that does not exhibit catalytic activity in the synthesis of ammonia.

[0033] (catalyst) The catalyst supported on the carrier exhibits catalytic activity in the synthesis of ammonia. The adsorption energy of nitrogen (N2) in the catalyst may be -3.0 to 1 eV, -2.5 to 0.5 eV, or even -2.0 to 0.25 eV. Catalysts with nitrogen adsorption energies within the above ranges exhibit good catalytic activity.

[0034] The catalyst may include, for example, a transition metal. The transition metal may also be the main component of the catalyst. The catalyst may be composed of transition metals.

[0035] An example of a transition metal is at least one selected from the group consisting of Ru, Co, Ni, Fe, Mn, Cr, molybdenum (Mo), tungsten (W), V, Zr, Nb, and Ti. The transition metal may be at least one selected from the group consisting of Ru, Co, Ni, Fe, Mn, Cr, Mo, W, V, and Nb, or at least one selected from the group consisting of Ru, Co, Ni, and Fe, or it may be Ru.

[0036] The catalyst is usually in particulate form. The average particle size of the catalyst is, for example, 1 to 500 nm, and may be 10 to 100 nm. However, the shape and average particle size of the catalyst are not limited to the above examples, as long as they can be supported on a carrier.

[0037] (Ammonia synthesis complex catalyst) The amount of catalyst supported in an ammonia synthesis composite catalyst varies depending on the combination of the support and the catalyst, but can be, for example, 0.1 to 96% by mass, and may also be 1 to 70% by mass, 1 to 50% by mass, 1 to 30% by mass, 1 to 20% by mass, 1 to 10% by mass, or even 2 to 7% by mass.

[0038] The ammonia synthesis composite catalyst may contain other substances besides the support and catalyst described above. Examples of other substances include co-catalysts and additives that improve catalytic activity. Co-catalysts and additives may be electron-donating. The work function of electron-donating substances may be 3.7 eV or less, 3.5 eV or less, 3.3 eV or less, or even 3.0 eV or less. Examples of co-catalysts and additives are group 2 elements, group 3 elements, and lanthanides, such as Ba, potassium (K), cesium (Cs), and sodium (Na).

[0039] [Method for producing ammonia synthesis complex catalyst] The ammonia synthesis composite catalyst of this embodiment can be manufactured, for example, by the following method. However, the method for manufacturing the catalyst is not limited to the examples below.

[0040] (Casting material) The carrier can be prepared, for example, by selecting a material with hydrogen storage ability (such as a hydrogen storage metal). A hydrogen storage alloy carrier can be prepared, for example, by a general method of mixing and melting two or more metal elements to form a hydrogen storage alloy. After melting and solidifying, heat treatment may be performed to adjust the crystal structure of the hydrogen storage alloy, etc. Commercially available hydrogen storage materials, hydrogen storage metals, or hydrogen storage alloys can also be used as carriers. The average particle size of the carrier can be adjusted by known grinding methods. However, the method of preparing the carrier is not limited to the above examples.

[0041] (Supporting the catalyst) Catalyst support can be carried out, for example, by impregnating the support in a solution of a transition metal compound and then removing the solvent from the solution (impregnation method). When the transition metal is Ru, an example of the compound is C 12 O 12 The compounds are Ru3 and ruthenium(III) acetylacetonate. However, the compounds are not limited to the above examples. Depending on the type of transition metal, known compounds that can be used in the impregnation method can be used. The solvent can be removed, for example, by heating. Reduced pressure may be used in combination with heating. However, the method of supporting the catalyst is not limited to the above examples. Depending on the type of catalyst, known support methods (for example, a method of supporting a solid catalyst under reduced pressure and heating) can be employed. By supporting the catalyst on the support, an ammonia synthesis composite catalyst is obtained.

[0042] [Method for producing ammonia] The method for producing ammonia in this embodiment includes synthesizing ammonia by contacting a gas containing hydrogen and nitrogen with an ammonia synthesis catalyst. The ammonia synthesis catalyst is the composite catalyst of this embodiment described above.

[0043] The raw material gas may contain hydrogen and nitrogen in stoichiometric ratios. It may also contain other gas species besides hydrogen and nitrogen, as needed.

[0044] The contact between the raw material gas and the ammonia synthesis composite catalyst can be carried out using known ammonia synthesis apparatus and equipment.

[0045] The temperature for ammonia synthesis is, for example, 50 to 500 °C, and may be 250 to 500 °C, or further 250 to 400 °C. The pressure for ammonia synthesis is, for example, 0.1 to 10 MPa, and may be 1 to 5 MPa.

Examples

[0046] Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the specific embodiments shown below.

[0047] (Example 1) C 12 O 12 0.126 g of Ru3 (manufactured by Tokyo Chemical Industry Co., Ltd.) was put into 500 mL of pentane (manufactured by Nacalai Tesque, Inc.), heated and melted to obtain a pentane solution of C 12 O 12 Ru3. Next, 5.94 g of a commercially available TiMnV ternary alloy (manufactured by Sigma-Aldrich Japan, Ti 51 Mn 29 V 20 ) was crushed into powder with a mortar and then put into the above solution. By heating for about 4 hours, all pentane was evaporated to obtain a catalyst in which Ru particles were supported on a TiMnV ternary alloy carrier (supporting amount: 1% by mass). The TiMnV ternary alloy used was a solid solution. For the TiMnV ternary alloy used, the maximum hydrogen storage amount in the temperature range from 0 °C to 300 °C is represented by the above ratio H / M and is 0.1 or more. Also, the work functions of Ti, Mn, and V are 4.3 eV, 4.1 eV, and 4.3 eV, respectively.

[0048] The hydrogen storage capacity of the obtained catalyst was evaluated by thermal generated gas analysis (TPD) as follows: 0.104 g of catalyst was placed in a container capable of continuously supplying a mixed gas of hydrogen and argon (hydrogen concentration 9.73 vol%), and connected to a TPD apparatus (Shimadzu Corporation, AutoChem II 2920). 50 ccm of the mixed gas was continuously flowed into the container for 60 minutes (pretreatment). The flow rate of hydrogen gas contained in the mixed gas was 4.865 ccm. After pretreatment, the container was heated and cooled in the following cycles while flowing the above mixed gas: (1) heating from 100°C to 300°C at a heating rate of 10°C / min, (2) holding at 300°C for 1 hour, (3) heating from 300°C to 1000°C at a heating rate of 10°C / min, (4) holding at 1000°C for 0.5 hours, and (5) cooling down to 100°C at a cooling rate of 20°C / min. During this time, the flow rate of hydrogen contained in the gas discharged from the container was continuously measured. The cycle was repeated three times. The measurement results of the flow rate when heating from 100°C to 1000°C are shown in Figure 1. As shown in Figure 1, the flow rate of hydrogen discharged from the container was greater than the flow rate of hydrogen flowing into the container. This confirmed that the catalyst absorbs hydrogen when cooling and releases hydrogen when heating, in other words, it has hydrogen absorption capacity. Since Ru does not possess hydrogen storage capacity, the observed hydrogen storage capacity was thought to be due to the TiMnV ternary alloy used as the support. Furthermore, an increase in the hydrogen discharge flow rate from the container was observed in the temperature range of 350-500°C, where the ammonia synthesis reaction proceeded. This was thought to be due to repeated hydrogen absorption and release from the catalyst in this temperature range.

[0049] Next, the ammonia synthesis reaction was carried out using the obtained catalyst, and the activation energy of the ammonia synthesis reaction by the catalyst was calculated using an Arrhenius plot. The ammonia synthesis reaction and the creation of the Arrhenius plot were carried out as follows: 1.00 g of catalyst was placed in a reaction tube and heated to 340-420°C. After heating was complete, a mixed gas of hydrogen and nitrogen (hydrogen flow rate 90 ccm, nitrogen flow rate 30 ccm, hydrogen and nitrogen mixing ratio in stoichiometric ratio) was flowed into the container, and the ammonia synthesis reaction was carried out. The amount of ammonia produced at each reaction temperature T was identified, and an Arrhenius plot was created based on the identified amount and reaction temperature. The created Arrhenius plot is shown in Figure 2. In the plot in Figure 2, the x-axis is the reciprocal of the reaction temperature T expressed in absolute temperature, and the y-axis is the natural logarithm of the reaction constant k (unit: μmol / g / hour). The amount of ammonia produced was identified by bubbling the gas discharged from the container into an aqueous sulfuric acid solution (concentration 0.005 mol / L), and then evaluating the resulting aqueous sulfuric acid solution using ion chromatography. The activation energy calculated from the Arrhenius plot was 64 kJ / mol, which is approximately half the activation energy (137 kJ / mol) achieved when only Ru was used as a catalyst.

[0050] (Example 2) TiMnV ternary alloy 29 Mn 51 V 14 (Fe,Cr,Zr)6 (made by Sigma-Aldrich) is used, along with C 12 O 12Catalysts (loading amounts of 1 mass%, 3 mass%, 5 mass%, and 10 mass%) were obtained in the same manner as in Example 1, except that a pentane solution of ruthenium(III) acetylacetonate was used instead of a pentane solution of Ru3. The loading amount of Ru particles was changed by varying the amount of pentane solution. The TiMnV ternary alloy used was in solid solution form. For the TiMnV ternary alloy used, the maximum hydrogen storage capacity in the temperature range from 0°C to 300°C was 0.1 or greater, expressed by the above ratio H / M. The work functions of Fe, Cr, and Zr were 4.5 eV, 4.5 eV, and 4.1 eV, respectively.

[0051] The hydrogen storage capacity of each obtained catalyst was evaluated by TPD in the same manner as in Example 1. An increase in the flow rate of hydrogen discharged from the container was observed in the temperature range of 350-500°C, where the ammonia synthesis reaction proceeds.

[0052] Next, the activation energy of each obtained catalyst for the ammonia synthesis reaction was evaluated in the same manner as in Example 1. The activation energies were 44 kJ / mol (1% by mass of supported material), 56 kJ / mol (3% by mass of supported material), 68 kJ / mol (5% by mass of supported material), and 67 kJ / mol (10% by mass of supported material).

[0053] (Example 3) The catalyst prepared in Example 2 (10% by mass of Ru supported) was dispersed in N,N-dimethylformamide to obtain a dispersion. Next, potassium nitrate was added to the dispersion, and then the N,N-dimethylformamide was completely volatilized by heating under reduced pressure to obtain a catalyst further containing K as a co-catalyst. The ratio of K to Ru was 1:1 (molar ratio). Next, the activation energy of the obtained catalyst for the ammonia synthesis reaction was evaluated in the same manner as in Example 1, and it was found to be 52 kJ / mol.

[0054] (Example 4) A catalyst (1 mass%) in which Ru particles were supported on a ZrH2 support was obtained in the same manner as in Example 2, except that ZrH2 was used instead of the TiMnV ternary alloy. For ZrH2, the maximum hydrogen storage capacity in the temperature range from 0°C to 300°C is 0.1 or more, expressed by the above ratio H / M.

[0055] The hydrogen storage capacity of the obtained catalyst was evaluated by TPD in the same manner as in Example 1. However, the heating and cooling conditions were as follows: (1) heating from 100°C to 300°C at a heating rate of 10°C / min, (2) holding at 300°C for 1 hour, (3) heating from 300°C to 600°C at a heating rate of 10°C / min, (4) holding at 600°C for 1 hour, and (5) cooling to 100°C at a cooling rate of 20°C / min. The TPD evaluation results in this cycle are shown in Figure 3 as the flow rate of hydrogen contained in the gas discharged from the container. As shown in Figure 3, it was confirmed that the catalyst has the ability to absorb and release hydrogen in the temperature range of 350-500°C (e.g., 400°C) where the ammonia synthesis reaction proceeds. Note that the values ​​on the vertical axis of Figure 3 and Figure 5 described later are relative values ​​(unit: au).

[0056] Next, the activation energy of the obtained catalyst for the ammonia synthesis reaction was evaluated in the same manner as in Example 1 (however, heating was performed at 400-460°C), and it was found to be 55 kJ / mol. The Arrhenius plot created for the evaluation is shown in Figure 4.

[0057] (Example 5) A catalyst (1% by mass) in which Ru particles were supported on a TiH2 support was obtained in the same manner as in Example 2, except that TiH2 was used instead of ZrH2. For TiH2, the maximum hydrogen storage capacity in the temperature range from 0°C to 300°C is 0.1 or more, expressed by the above ratio H / M.

[0058] The hydrogen storage capacity of the obtained catalyst was evaluated by TPD in the same manner as in Example 1. However, the heating conditions were the same as in Example 4. The TPD evaluation results in the above cycle are shown in Figure 5 as the flow rate of hydrogen contained in the gas discharged from the container. As shown in Figure 5, it was confirmed that the catalyst has the ability to absorb and release hydrogen in the temperature range of 350-500°C (e.g., 400°C) where the ammonia synthesis reaction proceeds.

[0059] Next, the activation energy of the obtained catalyst for the ammonia synthesis reaction was evaluated in the same manner as in Example 4, and was found to be 43 kJ / mol. The Arrhenius plot created for the evaluation is shown in Figure 6.

[0060] (Comparative Example 1) Except for using MgO (from a high-purity chemical company) instead of the TiMnV ternary alloy, a catalyst (1% by mass) in which Ru particles were supported on an MgO support was obtained in the same manner as in Example 2. The activation energy of the obtained catalyst for the ammonia synthesis reaction was evaluated in the same manner as in Example 1, and the activation energy was 87 kJ / mol. It should be noted that MgO is not considered to have hydrogen storage capacity.

[0061] (Comparative Example 2) Except for using carbon (from a high-purity chemical company) instead of the TiMnV ternary alloy, a catalyst (10% by mass) in which Ru particles were supported on a carbon support was obtained in the same manner as in Example 2. The activation energy of the obtained catalyst for the ammonia synthesis reaction was evaluated in the same manner as in Example 1, and the activation energy was 104 kJ / mol. It should be noted that carbon is not considered to have hydrogen storage capacity.

[0062] (Reference example) An ammonia synthesis reaction was attempted using the TiMnV ternary alloy powder used in Example 2 as a catalyst, in the same manner as in Example 2, but the synthesis reaction did not proceed. Similarly, an ammonia synthesis reaction was attempted using Ni, Fe, and TiH2 powders as catalysts, in the same manner as in Example 2, but the synthesis reaction did not proceed. [Industrial applicability]

[0063] The ammonia synthesis composite catalyst of the present invention can be used for the synthesis of ammonia.

Claims

1. A catalyst that exhibits catalytic activity in the synthesis of ammonia, The system comprises a carrier supporting the catalyst, The catalyst includes a transition metal, The transition metal is at least one selected from the group consisting of Ru, Co, and Ni. The carrier contains a hydrogen storage metal, An ammonia synthesis composite catalyst wherein the hydrogen storage metal has a maximum hydrogen storage capacity in a temperature range of 0°C to 300°C that is 0.1 or greater, expressed by the hydrogen-to-metal atomic ratio H / M as defined in JIS H7003.

2. The ammonia synthesis composite catalyst according to claim 1, wherein the work function of the hydrogen storage metal exceeds 3.5 eV.

3. The ammonia synthesis composite catalyst according to claim 1 or 2, wherein the hydrogen storage metal contains 1 atomic percent or less of group 2 elements, group 3 elements, and lanthanides.

4. The ammonia synthesis composite catalyst according to any one of claims 1 to 3, wherein the hydrogen storage metal is a hydrogen storage alloy.

5. The ammonia synthesis composite catalyst according to claim 4, wherein the hydrogen storage alloy is a solid solution.

6. The ammonia synthesis composite catalyst according to claim 4, wherein the hydrogen storage alloy is a Ti-Mn alloy.

7. The ammonia synthesis composite catalyst according to claim 6, wherein the Ti-Mn alloy is a TiMnV ternary alloy.

8. The ammonia synthesis composite catalyst according to claim 1, wherein the hydrogen storage metal is in the state of a hydrogen-storing hydride.

9. The ammonia synthesis composite catalyst according to claim 1, wherein the hydrogen storage metal is TiH₂ or ZrH₂.

10. The ammonia synthesis composite catalyst according to any one of claims 1 to 9, wherein the transition metal is at least one selected from the group consisting of Ru and Co.

11. The ammonia synthesis composite catalyst according to any one of claims 1 to 9, wherein the transition metal is Ru.

12. This includes synthesizing ammonia by contacting a gas containing hydrogen and nitrogen with an ammonia synthesis catalyst. A method for producing ammonia, wherein the ammonia synthesis catalyst is the ammonia synthesis composite catalyst described in any one of claims 1 to 11.

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