High-entropy alloy catalyst

Abstract

To provide a method for producing a high entropy alloy that can be produced simply and at low cost, to provide a method for using the high entropy alloy, to provide a high entropy alloy catalyst, and a novel high entropy alloy.SOLUTION: A method of producing a high entropy alloy comprises: obtaining a mixed solution of salts of 5 or more metals selected from the group consisting of transition metals in groups 3 to 12 of periods 4 to 6, aluminum, silicon, and lanthanoids in the presence of a solvent; drying and heating the mixed solution to obtain an oxide precursor; and obtaining a high entropy alloy by subjecting the oxide precursor, at least one reducing agent selected from CaH2, Ca, MgH2, and Mg, and a molten salt of an alkali metal salt or an alkaline earth metal salt, to heating and reducing treatment under the presence of inert gas. The high entropy alloy may be used as a catalyst for a hydrogenation reaction in a liquid phase. Furthermore, a novel high entropy alloy can be produced by the method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to methods for making high entropy alloys, methods for using high entropy alloys, high entropy alloy catalysts, and novel high entropy alloys. [Background technology]

[0002] High-entropy alloys (HEAs) have recently attracted attention as a new alloy material. HEAs are multi-component alloys (five or more components) in which various elements are randomly arranged in the crystal lattice, i.e., the configurational entropy is high. They are essentially single-phase disordered solid solutions. HEAs possess the following properties: (a) stabilization of the mixed state due to a negatively increasing entropy of mixing in the Gibbs free energy equation; (b) diffusion retardation due to a complex microstructure; (c) high hardness and reduced temperature dependence of mechanical properties due to high lattice distortion caused by the size difference of the constituent atoms; and (d) improved corrosion resistance due to the combined effect of the coexistence of multiple elements (also known as the cocktail effect). Due to their excellent corrosion and oxidation resistance and excellent friction resistance, HEAs are being explored for a variety of applications. For example, their main applications include shape-memory alloys (SMAs) for medical devices and structural materials, as well as new applications such as 3D metal printing and catalytic materials.

[0003] Methods for producing such high-entropy alloys include physical methods in which raw materials are mixed, melted, and pulverized, and chemical methods that utilize molten metal decomposition. For example, Patent Document 1 discloses a physical method for producing high-entropy alloys through processes such as raw material mixing and melting, atomization, mixed powder preparation, additive manufacturing, and pseudo-solution heat treatment. Patent Document 2 also discloses a mechanical alloying technique for obtaining solid alloys, in which elemental powders or pre-alloyed powders are pulverized in a ball mill until a homogeneous alloy is formed.

[0004] As a chemical method utilizing molten metal decomposition, a precursor alloy of each element is prepared, melted by arc melting to mix the components, and a thin plate-shaped precursor is cut out from the solidified alloy and immersed in a metal bath consisting of a specific metal to obtain a porous metal (Patent Documents 3-4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-114948 [Patent Document 2] Special Publication No. 2022-530648 [Patent Document 3] Japanese Patent Publication No. 2020-125523 [Patent Document 4] International Publication No. 2011 / 092909 Summary of the Invention [Problem to be solved by the invention]

[0006] Physical methods typically require the mixing and melting of raw materials, which requires the melting and mixing of the constituent metals at high temperatures (around 2000°C), necessitating large-scale, high-temperature-resistant equipment such as a high-frequency melting furnace. Furthermore, these methods require the use of expensive pure metals as raw materials, and involve numerous manufacturing steps, which increases the workload and costs, and each step, such as the milling process, may pose a risk of impurities being mixed in. Chemical methods also have problems, such as the use of expensive pure metals as raw materials, the complex process of selecting the metals to be used in each step, taking into account the heat of mixing and melting point, and the large number of manufacturing steps.

[0007] Such HEAs are expected to find expanded applications as various catalytic materials, and the development of novel high-entropy alloys is also desired to explore new applications for high-entropy alloys. The present invention has been made to solve the above problems, and aims to provide a method for producing high-entropy alloys simply and at low cost, as well as a method for using such high-entropy alloys. The present invention also provides high-entropy alloy catalysts and novel high-entropy alloys. [Means for solving the problem]

[0008] The present inventors discovered that high-entropy alloys can be obtained in a single step by heating and reducing precursors of metal salts or hydrates thereof in a molten salt containing an alkali metal or alkaline earth metal using calcium hydride (CaH2), calcium (Ca), or other reducing agents. This discovery led to the development of a novel high-entropy alloy catalyst and a novel high-entropy alloy.

[0009] The present invention relates to a method for producing a high-entropy alloy as set forth in (1) to (5) below. (1) A method for producing a high-entropy alloy, comprising the steps of: obtaining a mixed solution of salts of five or more metals selected from the group consisting of transition metals of periods 4-6 and groups 3-12, aluminum, silicon, and lanthanoids in the presence of a solvent; drying and heating the mixed solution to obtain an oxide precursor; and heating and reducing the oxide precursor, at least one reducing agent selected from calcium hydride, calcium, magnesium hydride, and magnesium, and a molten salt of an alkali metal salt or an alkaline earth metal salt in the presence of an inert gas to obtain a high-entropy alloy. (2) A method for producing a high-entropy alloy according to (1), wherein the step of obtaining the mixed solution is a step of mixing the metal salt and a chelating reagent in the presence of a solvent to obtain the mixed solution. (3) A method for producing a high-entropy alloy described in (1) above, wherein the step of obtaining the mixed liquid is a step of mixing a salt of the metal and an oxide of the metal (excluding the metal of the salt of the metal) in the presence of a solvent to obtain a mixed liquid. (4) A method for producing a high-entropy alloy according to (1), wherein the metal is selected from Ni, Fe, Cr, Co, Al, Mn, Ti, V, Zr, Ir, Pd, Pt, Rh, Ru, Au, Ag, Y, Ga, Ln, Ce, Pr, Nd, and Sm. (5) A method for producing a high-entropy alloy described in (2) above, wherein at least one of the five or more selected metals is a precious metal, and the step of obtaining the mixed liquid is a step of further mixing a calcium salt to obtain the mixed liquid.

[0010] The present invention also relates to methods for using the high-entropy alloys described in (6) and (7) below, high-entropy alloy catalysts described in (8) and (9) below, and novel compounds described in (10) below. (6) A method for using a high-entropy alloy, comprising producing a high-entropy alloy powder by the method for producing a high-entropy alloy according to (2) above, and using the high-entropy alloy as a catalyst for a hydrogenation reaction in a liquid phase. (7) A method for using a high-entropy alloy according to (6) above, wherein the liquid-phase hydrogenation reaction is a synthesis reaction of an amine by hydrogenation of a nitro group or an imine. (8) Atomic composition ratio is AlCoCrFeNiV, AlCoCrFeNi, CoFeNiTiCr, CoFeNiTiV, Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 , (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 ) A high-entropy alloy catalyst for liquid-phase hydrogenation reactions, comprising a high-entropy alloy represented by any one of the following formulas: (9) The high-entropy alloy catalyst according to (8) above, wherein the liquid-phase hydrogenation reaction is a synthesis reaction of an amine by hydrogenation of a nitro group or an imine. (10) The atomic composition ratio is CeMnFeCoNiZn, or (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn, or (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )A high-entropy alloy represented by the formula Ga2Ni3. [Effects of the Invention]

[0011] The present invention provides a method for producing a high-entropy alloy simply and at low cost, a method for using the high-entropy alloy, a high-entropy alloy catalyst, and a novel high-entropy alloy. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows an X-ray diffraction pattern and a scanning electron microscope (SEM) image of the HEA powder of Example 1. [Figure 2] 1 shows an X-ray diffraction pattern and an SEM image of the HEA powder of Example 2. [Figure 3] 1 shows an X-ray diffraction pattern and an SEM image of the HEA powder of Example 3. [Figure 4] 1 shows an X-ray diffraction pattern and an SEM image of the HEA powder of Example 4. [Figure 5] 1 shows an X-ray diffraction pattern and an SEM image of the HEA powder of Example 5. [Figure 6] 1 shows an X-ray diffraction pattern and an SEM image of the HEA powder of Example 6. [Figure 7] 1 shows an X-ray diffraction pattern and an SEM image of the HEA powder of Example 7. [Figure 8] 1 is an X-ray diffraction pattern of the HEA powder of Example 8. [Figure 9] 1 is an X-ray diffraction pattern of the HEA powder of Example 9. [Figure 10] 1 is an X-ray diffraction pattern of the HEA powder of Example 10. [Figure 11] 1 is an X-ray diffraction pattern of the HEA powder of Example 11. [Figure 12] 1 is an X-ray diffraction pattern of the HEA powder of Example 12. [Figure 13] 1 is an X-ray diffraction pattern of the HEA powder of Example 13. [Figure 14] 1 is an X-ray diffraction pattern of the HEA powder of Example 14. [Figure 15] 1 is an X-ray diffraction pattern of the HEA powder of Example 15. [Figure 16] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 1 as a catalyst. [Figure 17] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 2 as a catalyst. [Figure 18] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 3 as a catalyst. [Figure 19] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 4 as a catalyst. [Figure 20] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 5 as a catalyst. [Figure 21] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 6 as a catalyst. [Figure 22] 1 is a graph showing the change in p-nitrophenol concentration over time in a hydrogenation reaction using the HEA powder of Example 7 as a catalyst support. DETAILED DESCRIPTION OF THE INVENTION

[0013] A method for producing a high-entropy alloy according to an embodiment of the present invention involves reducing raw material metal element salts or hydrated oxide precursors in a molten salt containing an alkali metal or alkaline earth metal using calcium hydride (CaH2) or calcium as a reducing agent, thereby producing a high-entropy alloy in a single reaction. This method allows for the production of novel high-entropy alloys. Note that, in this specification, numerical ranges include both upper and lower limits.

[0014] A high-entropy alloy is a multi-component alloy with five or more components, which is essentially a single-phase disordered solid solution alloy, and whose mixed state is stabilized due to a negative increase in the entropy of mixing term in the Gibbs free energy equation. The stable phase formed at equilibrium is given when the Gibbs free energy (ΔG) is minimized. Thermodynamically, ΔG is given by ΔG = ΔH - TΔS, and as entropy (ΔS) increases, ΔG decreases. The entropy of mixing term for a random ideal solution is given by the following equation:

number

[0015] The method for producing a high-entropy alloy in this embodiment includes the steps of: obtaining a mixed solution from salts of five or more metals as raw materials in the presence of a solvent; drying and heating the mixed solution to obtain an oxide precursor; and heating and reducing the oxide precursor, at least one reducing agent selected from CaH2, Ca, MgH2, and Mg, and a molten salt of an alkali metal salt or alkaline earth metal salt in the presence of an inert gas to obtain a high-entropy alloy. The constituent elements of high-entropy alloys are metals selected from the group consisting of transition metals in periods 4-6 and groups 3-12 of the periodic table, aluminum, silicon, and lanthanides. Although aluminum and silicon are not transition metals, they share the same properties as the transition metals in that they can be constituent elements that form high-entropy alloys (solid solutions or intermetallic compounds). Furthermore, although silicon is technically a non-metal, it shares the same property with the transition metals and aluminum in that it forms alloys (solid solutions or intermetallic compounds) with other metal elements, and therefore is included in the metal category in this specification. For example, the elements may be selected from nickel (Ni), iron (Fe), chromium (Cr), cobalt (Co), aluminum (Al), manganese (Mn), titanium (Ti), vanadium (V), zirconium (Zr), platinum (Pt), ruthenium (Ru), rhodium (Rh), gold (Au), iridium (Ir), yttrium (Y), gallium (Ga), lanthanum (Ln), cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm). While there is no upper limit to the number of elements selected, a larger number of elements may make the elements less suitable for dissolution during the process of obtaining the mixed solution. Therefore, approximately 5-10 elements are preferred. Furthermore, each element may be present in a maximum of 35 atomic percent (molar percent).

[0016] The present embodiment is characterized by using salts of the above metals or hydrates thereof as raw materials. Conventional high-entropy alloy production requires the use of expensive pure metals as raw materials, but the raw material metal salts and hydrates thereof are easily available and inexpensive, allowing for cost reduction.

[0017] Metal salts include inorganic salts such as nitrates, sulfates, carbonates, phosphates, and chlorides of these metals, as well as organic salts such as alkoxides, acetates, and oxalates. In the case of inorganic salts, many nitrates and chlorides are soluble and inexpensively available, making them suitable. For example, if the raw metal is aluminum, Al(NO3)3·9 H 2O For cobalt, nitrate hydrates include Co(NO3)3·6H2O, for chromium, Cr(NO3)3·9H2O, for iron, Fe(NO3)3·9H2O, and for nickel, Ni(NO3)2·6H2O. For vanadium and rhodium, inexpensive chlorides such as VCl3 and RhCl3 are preferred. Metal alkoxides are also useful for titanium and silicon, as they are readily available soluble compounds. Metal alkoxides are salts commonly used in the sol-gel process. Aluminum can also be used as a metal alkoxide. The above salts can also be hydrated. Any salt can be used as long as it is a readily available soluble compound.

[0018] The metal salt or its hydrate is mixed with the chelating agent in the presence of a solvent to obtain a mixed solution. Examples of solvents include ion-exchanged water, distilled water, glycerin, alcohol (especially ethanol), glycol (especially ethylene glycol and propylene glycol), and standard organic solvents (THF, acetone, toluene). Among these, distilled water and ethanol are preferred because they are easy to handle and inexpensive to obtain. Chelating agents are organic compounds that form chelate complexes with metal ions in solution. Standard, highly safe chelating agents include ethylenediaminetetraacetic acid, citric acid, phytic acid, and gluconic acid. Using chelating agents, it is possible to obtain uniform composite metal oxide powders using the sol-gel complex polymerization method. The number of moles of the chelating agent should be 1 to 1.5 times the total number of moles of the multiple metals.

[0019] On the other hand, when the number of constituent elements in an alloy is large (e.g., six or seven or more), it can be difficult to obtain a uniform solution containing all the metals, as some raw materials are insoluble in solvents such as water or alcohol. In such cases, it is effective to prepare a suspension of some metals (preferably one type) in which fine oxide powder is suspended instead of salt (impregnation method). In this case, a chelating agent is not necessary, but it can be used when, for example, the amount of oxide is small and preparing a uniform suspension is difficult. The use of a chelating agent has the effect of obtaining a precursor in which the metal is uniformly dispersed. In addition, oxide powders such as SiO2, TiO2, and CeO2 are effective for elements with limited soluble compounds available.

[0020] The mixed solution is then dried and heated to obtain an oxide precursor. Heating may be performed in one step or multiple steps. For example, after pre-firing at a low temperature, the fired sample is uniformly pulverized and mixed in a mortar or the like using a pestle, and then fired at a high temperature, which is preferable because it allows the oxide precursor to be obtained in which the elements are uniformly dispersed. The heating temperature should be approximately 300-800°C, but 400-600°C is preferred because impurities other than metal elements (such as chelating agents) can be removed by combustion and an oxide precursor with uniformly dispersed metal elements can be obtained. The heating time, which depends on the heating temperature, should be approximately 0.5-10 hours, preferably 3-6 hours.

[0021] The oxide precursor, reducing agent, and molten salt source are then mixed and reduced by heating in the presence of an inert gas (nitrogen, argon, helium, etc.) to obtain HEA powder. After reduction, the product can be washed to remove impurities (LiCl, CaCl, CaH, CaO, etc.). The heating temperature during reduction varies depending on the type of molten salt, but must be above the melting point, generally 300-1000°C, preferably 550-800°C. Alternatively, the molten salt source may be heated first, and the oxide precursor and reducing agent may be added in a molten state, or the molten salt source and the oxide precursor or reducing agent may be mixed and heated, and then the remaining reducing agent or oxide precursor may be added. When the molten salt is a mixture of molten salts, its melting point is lower than that of a single molten salt, so it dissolves even at temperatures below 600°C. The molten salt acts as a solvent, and the oxide precursor is reduced by a reducing agent in the molten salt. This molten salt reduction method allows HEA powder to be obtained under milder conditions at lower temperatures than the physical method described above (approximately 2000°C). The oxide precursor is alloyed immediately after reduction by the molten salt reduction method, and by passing through a metallic state, it becomes a fine-particle alloy powder with a large specific surface area. The heating time depends on the heating temperature, but is approximately 0.5-10 hours, preferably approximately 3-6 hours. A lower heating temperature (e.g., approximately 550°C) requires a longer heating time (e.g., approximately 10 hours), while a higher heating temperature (e.g., approximately 700-800°C) allows for a shorter heating time (e.g., approximately 2 hours).

[0022] The reducing agent may be calcium hydride, metallic calcium, magnesium hydride, metallic magnesium, or the like. These reducing agents exhibit a strong reducing effect in the molten salt. The reducing agent may be used alone or in combination. When using multiple reducing agents, they may be mixed in advance or added separately when mixing the oxide precursor and the molten salt. In particular, CaH2 is preferred because it is a stable powder under room temperature and atmospheric conditions and can be handled relatively safely. When using CaH2 as a reducing agent, CaH2 is used in an amount equal to or greater than the number of moles of oxygen contained in the oxide precursor, taking advantage of the fact that CaH2 reacts with oxygen contained in the oxide precursor to form CaO. Preferably, the reducing agent is used in a weight ratio of 0.1 to 4 times, and preferably 1 to 2 times, the amount of the oxide precursor.

[0023] The molten salt may be an alkali metal halide, an alkaline earth metal halide, or a mixture thereof. Examples of the alkali metal halide include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI. Examples of the alkaline earth metal halide include MgF, CaF, SrF, BaF, MgCl, CaCl, SrCl, BaCl, MgBr, CaBr, SrBr, BaBr, MgI, CaI, SrI, and BaI.

[0024] The above compounds can be used alone or in combination of two or more. The combination of these compounds, the number of compounds to be combined, the mixing ratio, etc., are not limited, and can be appropriately selected based on whether they are stable and easy to handle in the atmosphere or whether they are inexpensively available. Other compounds that can be used include halides of relatively less noble metals, such as AlCl3 and ZnCl2.

[0025] In particular, the molten salt used in this embodiment is preferably a single molten salt such as LiCl or CaCl, a mixed molten salt of LiCl and KCl, or a mixed molten salt of LiCl and CaCl. Furthermore, a mixed molten salt has a lower melting point than a single molten salt, and therefore can react at a lower temperature. Therefore, when the temperature at which the alloy is formed is low (for example, when the raw material contains an easily reduced oxide such as a transition metal oxide), it is preferable to use a mixed molten salt. For example, the melting point of a mixed molten salt of LiCl and CaCl is 470°C, and therefore the reaction can occur even at a low temperature of about 550°C.

[0026] The HEA produced by the above method is a fine-particle alloy powder with a large specific surface area. Such alloy powders are expected to be used in a variety of applications, including as shape-memory alloys for medical devices and structural materials, as well as for 3D metal printer molding materials and catalyst materials. For example, when used in shape-memory alloys or 3D metal printers, the extremely small particle size makes it possible to manufacture materials and molds with complex shapes. Furthermore, because this HEA has a large specific surface area, it can be used as a catalyst material, either as a catalyst itself or as a carrier. Examples of such materials include AlCoCrFeNiV, CrMnFeCoNi, AlCoCrFeNi, CoFeNiTiCr, CoFeNiTiV, and Al. 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 These HEA powders are primarily used as structural materials that require high strength, corrosion resistance, and heat resistance, but CrMnFeCoNi is also used as a catalyst in the reaction (C) below, and these HEA powders can be used as catalysts for liquid-phase hydrogenation reactions. Furthermore, these HEA powders themselves function as catalysts, but they can also be used as catalyst supports.

[0027] For example, an example of a liquid phase hydrogenation reaction is shown below. (A) Conversion of alkenes (double bonds) and alkynes (triple bonds) to alkanes (B) Deprotection of the benzyl group (a compound containing an alcohol and a protecting benzyl group is hydrogenated to remove the benzyl group and obtain an alcohol.) (C) Hydrogenation of nitro groups or imines to obtain amines. (D) Dehalogenation reaction by hydrogenation of aromatic halides (E) Hydrogenation of aldehydes and ketones to produce alcohols or methylenes Also, (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25)2 can be used as a catalyst for liquid-phase hydrogenation reactions by supporting metal hydrogenation catalysts such as Ni, Pd, and Pt as a catalyst support. The reason why this alloy itself does not function as a catalyst is thought to be as follows: This alloy contains Ti and Zr, but these elements are located on the left side of the periodic table, have strong interactions with oxygen, and are prone to forming oxide films. This means that the active transition metals of the constituent elements Cr, Mn, Fe, and Ni are unlikely to be exposed on the surface. In particular, hydrogenation of the nitro group (C) is a common reaction in organic synthesis, with versatile applications. For example, there is the hydrogenation reaction from p-nitrophenol to p-aminophenol, in which NaBH4, hydrogen gas, LiAlH4, etc. are used as reducing agents.

[0028] Furthermore, by the above method, CeMnFeCoNiZn, (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn, (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Novel HEAs such as Ga2Ni3 can also be fabricated. These HEAs contain rare earth elements (Ce, Ln, Pr, Nd, Sm, Y) and are compatible with the above-mentioned (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 It has more basic metal properties than (Ti)2. It also has a large specific surface area. Therefore, it can be used as a catalyst or a basic support. 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2 as well as CeMnFeCoNiZn, (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2)MnFeCoNiZn, (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 New HEAs such as Ga2Ni3 can be used as catalyst supports. Furthermore, because of their strong basic metal properties, they are suitable for use as supports containing basic metals. For example, by supporting a metal catalyst for hydrogenation such as Ni, in addition to the liquid-phase hydrogenation reactions mentioned above, they can be used to synthesize hydrocarbons or oxygenated hydrocarbons by hydrogenating carbon monoxide or carbon dioxide. For example, they can be used to synthesize methane by hydrogenating carbon monoxide.

[0029] Furthermore, the above method can also be used to prepare HEAs containing precious metals such as IrPdPtRhRu, IrRhRuCoNi, AuPdPtRhRu, IrNiPtRhCo, and RuRhPdAgIrPtAu. These HEA powders are used as electrode catalysts, for example, in the electrolysis of ammonia. Furthermore, these HEA powders themselves function as catalysts. Because precious metals (such as Ir, Pd, Pt, Rh, Ru, and Au) are stable, they may not easily become oxides even when fired at around 500°C in the molten salt reduction process. Therefore, to produce HEAs containing precious metals, adding an appropriate amount of calcium salts (e.g., Ca(NO3)2, CaCl2, or (CH3COO)2Ca) to the raw materials (e.g., Ca = 30 mol%) before firing results in a composite oxide of CaO and the precious metal (or a compound in which the precious metal is dispersed in CaO), making it easier to obtain oxide precursor powder. The added Ca is removed by washing with a cleaning solution such as an aqueous solution of NH4Cl in the final step, so it does not remain in the alloy.

[0030] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples. [Example]

[0031] Example 1 Al(NO3)3·9 in distilled water H 2O Al (Fuji Wako Pure Chemical Industries, Ltd., purity 99%), Co(NO3)3·6H2O (Fuji Wako Pure Chemical Industries, Ltd., purity 98%), Cr(NO3)3·9H2O (Nacalai Tesque, Inc., purity 98%), Fe(NO3)3·9H2O (Fuji Wako Pure Chemical Industries, Ltd., purity 99%), Ni(NO3)2·6H2O (Fuji Wako Pure Chemical Industries, Ltd., purity 99.9%), VCl3 (Merck & Co., Ltd., purity 97%), and citric acid (Fuji Wako Pure Chemical Industries, Ltd.) were dissolved in a molar ratio of Al / Co / Cr / Fe / Ni / V / citric acid = 1 / 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. The solution was then pre-baked at 250°C for 2 hours. The calcined sample was crushed and mixed in a mortar with a pestle to form a powder with a uniform particle size, and then calcined again at 500°C for 2 hours to obtain an oxide precursor (AlCoCrFeNiV(Pre)). The resulting oxide precursor was mixed with CaH (Nacalai Tesque, Inc.) and LiCl-CaCl (Fuji Wako Pure Chemical Industries, Ltd., molar ratio 1:1) in a weight ratio of 2 / 6 / 3, and heated in a SUS tubular furnace (as in other examples) under an argon atmosphere at 550°C (reduction temperature) for 10 hours to perform molten salt reduction. The mixed molten salt source of LiCl and CaCl was prepared by mixing the materials in a mortar with a pestle. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities (LiCl, CaCl2, CaH2, CaO, etc.), yielding HEA powder AlCoCrFeNiV. In the following examples, unless otherwise noted, the HEA powder was prepared using the same method and conditions as in Example 1. The same reagents were used for common compounds.

[0032] The X-ray diffraction pattern and SEM image of the HEA powder are shown in Figure 1. The X-ray diffraction pattern was measured using an X-ray diffractometer (Mini Flex 600, manufactured by Rigaku Corporation) under the following conditions. Conditions: X-ray source CuKα, output 40KV, 15mA The SEM images were measured using a scanning electron microscope (JSM-7800F, manufactured by JEOL Ltd.). Figure 1 also confirms a single BCC structure, indicating that it is a single-phase solid solution alloy. Furthermore, SEM images confirmed a microstructure consisting of fine particles of 1-10 μm or smaller. Furthermore, the BET specific surface area was determined by nitrogen adsorption experiments, and was found to be 33.4 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure. In the nitrogen adsorption experiment, the sample was dried at 200°C for 30 minutes under an inert gas flow, and then the amount of nitrogen adsorbed was measured at liquid nitrogen temperature.

[0033] Example 2 Cr(NO3)3·9H2O, Mn(NO3)2·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water in a molar ratio of 1:1:1:1:1:1:7.2 (Cr / Mn / Fe / Co / Ni / citric acid) and evaporated to dryness on a hot plate. The resulting solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (CrMnFeCoNi(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2:6:3 and heated to 700°C for 2 hours under a nitrogen atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and the HEA powder CrMnFeCoNi was obtained. Figure 2 shows the X-ray diffraction pattern and SEM image of the HEA powder. Figure 2 confirms a single FCC structure, indicating that it is a single-phase solid solution alloy. The SEM image also confirms a microstructure consisting of fine particles of 1-10 μm or less. The specific surface area is 12.1 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure. The X-ray diffraction pattern, SEM image, specific surface area, etc. were measured by the same method and under the same conditions as in Example 1. This also applies to the following examples.

[0034] Example 3 Al(NO3)3·9H2O, Co(NO3)2·6H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water in a molar ratio of Al / Co / Cr / Fe / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. The resulting solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (AlCoCrFeNi(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl-CaCl2 in a molar ratio of 2 / 6 / 3 and heated at 550°C for 10 hours under an argon atmosphere for molten salt reduction. Finally, the impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder AlCoCrFeNi. Figure 3 shows the X-ray diffraction pattern and SEM image of the HEA powder. Figure 3 confirms a single BCC structure, indicating that it is a single-phase solid solution alloy. The SEM image also confirms a microstructure consisting of fine particles of 1-10 μm or less. The specific surface area is 67.5 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0035] (Examples 4-5) Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, [(CH3)2CHO]4Ti] (Fuji Wako Pure Chemical Industries, Ltd.), Cr(NO3)3·9H2O, VCl3, and citric acid were dissolved in ethanol on a hot plate to a molar ratio of Co / Fe / Ni / Ti / Cr or V / citric acid = 1 / 1 / 1 / 1 / 1 / 6, and the solution was evaporated to dryness in a 65°C oven. The solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (CoFeNiTiCr(Pre) or CoFeNiTiV(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and heated to 800°C for 2 hours under a nitrogen atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, yielding HEA powder CoFeNiTiCr (Example 4) and HEA powder CoFeNiTiV (Example 5).

[0036] Figures 4-5 show the X-ray diffraction pattern and SEM image of the HEA powder. In Example 4, a single FCC structure was confirmed from Figure 4, indicating that it was a single-phase solid solution alloy. Furthermore, the SEM image confirmed a microstructure consisting of fine particles of 1-10 μm or less. The specific surface area was 23.1 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure. Furthermore, in Example 5, a single FCC structure was confirmed from Figure 5, and it can be said to be a single-phase solid solution alloy. In addition, from the SEM image, a fine structure consisting of fine particles of 1-10 μm or less was confirmed. The specific surface area was 22.1 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0037] Example 6 Al(NO3)3·9H2O, Co(NO3)2·6H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, TiCl4, and citric acid were dissolved in distilled water to a molar ratio of Al / Co / Cr / Fe / Ni / Ti / citric acid = 0.2 / 1.5 / 1 / 1 / 1.5 / 0.5 / 7.2, and the mixture was evaporated to dryness on a hot plate. It was then pre-fired at 250°C for 2 hours. The fired sample was crushed to a roughly uniform particle size and then fired again at 500°C for 2 hours to obtain the oxide precursor (Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 The oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3, and the mixture was heated at 600 °C for 2 hours under a nitrogen atmosphere for molten salt reduction. Finally, the product was washed with a 0.1 M aqueous solution of NH4Cl and distilled water to remove impurities, and the HEA powder Al was obtained. 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 In addition, when the reduction temperature was set to 800°C (heating time was 2 hours), the HEA powder Al was also obtained. 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 obtained. Figure 6 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 6, a single FCC structure was confirmed even at reduction temperatures of 600°C (Figure 6(A)) and 800°C (Figure 6(B)), indicating that it is a single-phase solid solution alloy. Furthermore, from the SEM image, a microstructure consisting of fine particles of 1-10 μm or less was confirmed. The specific surface area was 91.7 m 2 / g(600℃), 13.6m 2 / g (800°C). From this result, it can be said that the obtained HEA powder has a fine structure.

[0038] Example 7 TiO2 (Sakai Chemical Industry Co., Ltd.), ZrO(NO3)2·2H2O (Fuji Wako Pure Chemical Industries Co., Ltd.), Cr(NO3)3·9H2O, Mn(NO3)2·6H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water to a molar ratio of Ti / Zr / Cr / Mn / Fe / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 1 / 7.2, and the solution was evaporated to dryness on a hot plate. The sample was then pre-calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and then calcined again at 500°C for 2 hours to obtain the oxide precursor ((Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2(Pre)) was obtained. The obtained oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3, and heated at 800 °C for 2 hours under a nitrogen atmosphere for molten salt reduction. Finally, the product was washed with a 0.1 M aqueous solution of NH4Cl and distilled water to remove impurities, and the HEA powder (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2 (composition: TiZrCrMnFeNi) was obtained. Figure 7 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 7, a hexagonal close-packed structure is confirmed, and it can be said that an intermetallic compound is formed. From the XRD measurement results, it is clear that the (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2 has a hexagonal crystal structure similar to TiCr2, and forms a single-phase intermetallic compound stabilized by the contribution of the mixing entropy term. SEM images also confirmed a microstructure consisting of fine particles of 1-10 μm or less. The specific surface area was 22.5 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0039] Example 8 Ce(NO3)3·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), Mn(NO3 ) 2 ·6 H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), and citric acid were dissolved in a molar ratio of Ce / Mn / Fe / Co / Ni / Zn / citric acid = 1 / 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. The resulting solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (CeMnFeCoNiZn(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and heated at 800°C for 2 hours under a nitrogen atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, yielding a novel HEA powder, CeMnFeCoNiZn. Figure 8 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 8, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area was 51.2 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0040] Example 9 La(NO3)3·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), Ce(NO3)3·6H2O, Pr(NO3)3·nH2O (Fuji Wako Pure Chemical Industries, Ltd.), Nd(NO3)3·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), Sm(NO3)3·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), Mn(NO3 ) 2 ·6 H2O, Fe(NO3 ) 3 ·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, and citric acid were dissolved in a molar ratio of La / Ce / Pr / Nd / Sm / Mn / Fe / Co / Ni / Zn / citric acid = 0.2 / 0.2 / 0.2 / 0.2 / 0.2 / 1 / 1 / 1 / 1 / 1 / 7.2, and evaporated to dryness on a hot plate. The sample was then pre-fired at 250°C for 2 hours. The fired sample was crushed to a uniform particle size and fired again at 500°C for 2 hours to obtain the oxide precursor ((La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn(Pre)) was obtained. The obtained oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3, and then heated at 800 °C for 2 hours under a nitrogen atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and a new HEA powder (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn was obtained. Figure 9 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 9, a single FCC structure is confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area is 25.8 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0041] Example 10 Y(NO3)3·nH2O (Fuji Wako Pure Chemical Industries, Ltd.), La(NO3)3·6H2O, CeO2 (Merck), Pr(NO3)3·nH2O (Fuji Wako Pure Chemical Industries, Ltd.), Nd(NO3)3·6H2O, Ga(NO3)3·nH2O (Fuji Wako Pure Chemical Industries, Ltd.), Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water to a molar ratio of Y / La / Ce / Pr / Nd / Ga / Ni / citric acid = 0.2 / 0.2 / 0.2 / 0.2 / 0.2 / 2 / 3 / 7.2, and the solution was evaporated to dryness on a hot plate. The sample was then pre-calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor ((Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3(Pre)) was obtained. The obtained oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3, and then heated at 600 °C for 2 hours under an argon atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and a new HEA powder (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3 was obtained. Figure 10 shows the X-ray diffraction pattern and SEM image of the HEA powder. Figure 10 confirms the hexagonal close-packed structure, indicating the formation of an intermetallic compound. The specific surface area is 19.9 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure. In addition, the Hermann-Morgan symbol and space group number of LnGa2Ni3 (Ln = La, Ce, Pr, Nd) are P62m and 189, and from the XRD measurement results, it was confirmed that the prepared (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3 has a single-phase crystal structure with P62m and 189 similar to LnGa2Ni3, and a single-phase intermetallic compound stabilized by the contribution of the mixing entropy term is formed.

[0042] Example 11 IrCl3·nH2O (Tokyo Chemical Industry Co., Ltd.), (NH4)2PdCl4 (Fuji Wako Pure Chemical Industries, Ltd.), HPtCl6·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), RhCl3 (Tanaka Kikinzoku Kogyo Kogyo K.K.), RuCl3·nH2O (Fuji Wako Pure Chemical Industries, Ltd.), Ca(NO3)2·4H2O (Fuji Wako Pure Chemical Industries, Ltd., 30 mol% added), and citric acid were dissolved in distilled water to a molar ratio of Ir / Pd / Pt / Rh / Ru / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2, and the solution was evaporated to dryness on a hot plate. It was then pre-calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (IrPdPtRhRu(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3, and then heated at 600 °C for 2 hours under an argon atmosphere for molten salt reduction. Finally, the product was washed with a 0.1 M aqueous solution of NH4Cl and distilled water to remove impurities, yielding the HEA powder IrPdPtRhRu. Figure 11 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 11, a single FCC structure is confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area is 32.6 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0043] Example 12 IrCl3·nH2O, RhCl3 (Tanaka Kikinzoku Kogyo Co., Ltd.), RuCl3·nH2O (Fuji Wako Pure Chemical Industries, Ltd.), Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water in a molar ratio of Ir / Rh / Ru / Co / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. The resulting solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (IrRhRuCoNi(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and heated at 600°C for 2 hours under an argon atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and the HEA powder IrRhRuCoNi was obtained. Figure 12 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 12, a single FCC structure is confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area is 69.9 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0044] Example 13 HAuCl4·4H2O (Fuji Wako Pure Chemical Industries, Ltd.), (NH4)2PdCl4 (Fuji Wako Pure Chemical Industries, Ltd.), HPtCl6·6H2O (Fuji Wako Pure Chemical Industries, Ltd.), RhCl3, RuCl3·nH2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water to a molar ratio of Au / Pd / Pt / Rh / Ru / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2, and the solution was evaporated to dryness on a hot plate. The resulting solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (AuPdPtRhRu(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and heated at 600°C for 2 hours under an argon atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and the HEA powder AuPdPtRhRu was obtained. Figure 13 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 13, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area was 50.2 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0045] Example 14 IrCl3·nH2O, Ni(NO3)2·6H2O, HPtCl6·6H2O, RhCl3·3H2O, Co(NO3)2·6H2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water in a molar ratio of Ir / Ni / Pt / Rh / Co = 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. The resulting solution was then calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (IrNiPtRhCo(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and heated at 600°C for 2 hours under an argon atmosphere for molten salt reduction. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and the HEA powder IrNiPtRhCo was obtained. Figure 14 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 14, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area was 25.5 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0046] Example 15 RuCl3-nH2O, RhCl3·3H2O, (NH4)2PdCl4, AgNO3 (Fuji Wako Pure Chemical Industries, Ltd.), IrC l 3 nH 2O, HPtCl6·6H2O, HAuCl4·4H2O, Ca(NO3)2·4H2O, and citric acid were dissolved in a molar ratio of Ru / Rh / Pd / Ag / Ir / Pt / Au = 1 / 1 / 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. The resulting solution was then pre-calcined at 250°C for 2 hours. The calcined sample was crushed to a uniform particle size and calcined again at 500°C for 2 hours to obtain the oxide precursor (RuRhPdAgIrPtAu(Pre)). The resulting oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and heated at 600°C for 2 hours under an argon atmosphere for molten salt reduction. Finally, the product was washed with 0.1M NH4Cl aqueous solution and distilled water to remove impurities, yielding the HEA powder RuRhPdAgIrPtAu. Figure 15 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 15, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. The specific surface area was 34.2 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0047] Table 1 shows the results of the HEA powders prepared in Examples 1-15 above. [Table 1] From the above results, it is possible to obtain oxide precursors of salts or hydrates of each metal element by a simple method of heating and reducing them in a molten salt containing an alkali metal or alkaline earth metal using calcium hydride (CaH2) or calcium as a reducing agent. 2 / g and 20m 2 It was confirmed that alloy powder with fine particles of approximately 1-10 μm or less and a large specific surface area of ​​1 μm or more / g could be obtained. Thus, the HEA powder of this example can be used for structural materials that require microfabrication and for 3D metal printers. It is also suitable as a catalyst material that requires a large specific surface area and fine particles. Below, we show an example in which the HEA powder obtained in Examples 1-7 was used as a catalyst for the synthesis of amines by hydrogenation of nitro groups.

[0048] Example 16 The HEA powder obtained in Examples 1-6 was used in the hydrogenation reaction of p-nitrophenol to p-aminophenol to evaluate the catalytic activity of the HEA. p-Nitrophenol (maximum absorption wavelength: 401 nm) is converted to p-aminophenol (maximum absorption wavelength: 303 nm) by the hydrogenation reaction. A glass tube was charged with 100 mg of HEA powder, 1 mL of 14 mM p-nitrophenol solution, 1 mL of 0.42 M NaBH4 solution, and 7 mL of distilled water, and the mixture was heated to initiate the hydrogenation reaction. The reaction temperature (heating temperature) was set within the range of approximately 20-60°C depending on the HEA powder used. The experimental methods and conditions were the same for all examples. However, in Examples 1-3, reactions were carried out at multiple reaction temperatures, and in Examples 4-6, the reaction temperature was 50°C. The HEA powder should be added in a weight ratio of 1-500 times, preferably 10-100 times, the weight of p-nitrophenol. At regular intervals from the start of the reaction, 100-500 μL of the test solution was taken from the glass tube and diluted (with distilled water) in a 5 mL volumetric flask. The absorbance was measured at 300-500 nm using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1280) to measure the changes in the concentrations of p-nitrophenol and p-aminophenol. The results are shown in Figures 16-21. Figures 16-21 correspond to Examples 1-6, respectively.

[0049] These results indicate that the hydrogenation reaction of p-nitrophenol proceeded with the HEA catalyst. Furthermore, the HEA powder obtained in Examples 1-3 exhibited an activity effect at all temperatures, and the concentration significantly decreased with increasing temperature, confirming an increase in the reaction rate. Furthermore, it was found that almost all or most of the p-nitrophenol was converted to p-aminophenol in a short period of time, generally 10-30 minutes. These results confirmed that the obtained HEA catalyst exhibited excellent liquid-phase hydrogenation activity. In heterogeneous catalytic reactions, the reaction proceeds on the surface of the catalyst. Therefore, it is preferable to use a catalyst with a large specific surface area. The results showed that the high specific surface area of ​​the HEA catalyst obtained in this example works effectively in the hydrogenation reaction. In particular, the Al obtained by reduction at 600°C, which has the largest specific surface area, 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 The catalyst (Example 6) showed the fastest reaction rate (Fig. 21). 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 This is also preferable in the case of AlCoCrFeNi (Example 3, Figure 18), since almost the entire amount reacted within 3 minutes. In particular, in Example 3, good results were obtained even at a relatively low reaction temperature (38°C).

[0050] The HEA powder obtained in Example 7 was used as a Ni-supported catalyst supporting 10 wt% Ni, and the HEA catalytic activity was evaluated. The Ni-supported catalyst was prepared by the following method. The HEA powder ((Ti) obtained in Example 7) was dissolved in distilled water. 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2) was suspended, and then Ni(NO3)2·6H2O was dissolved in it to a weight ratio of HEA / Ni = 9 / 1, and evaporated to dryness on a hot plate. After that, it was heated at 500 °C for 1 hour under argon flow to obtain a Ni-supported catalyst with 10 wt% Ni supported.

[0051] The HEA catalytic activity of the Ni-supported catalyst (100 mg) and the HEA powder (100 mg) obtained in Example 7 was evaluated using the same method and conditions as those for the HEA powder obtained in Examples 1-6 (reaction temperature: 50°C). The results are shown in Figure 22. From these results, it was confirmed that the HEA powder alone showed almost no catalytic activity, but that the Ni-supported catalyst showed good catalytic activity in a short reaction time.

[0052] Example 17 The crystallite diameters of the HEA powders obtained in Examples 8 to 15 were calculated from the XRD measurement results using the Scherrer equation. The results are shown in Table 2. [Table 2]

[0053] Table 2 also indicates that the HEA powders obtained in Examples 8-15 are alloy powders of nano-sized particles. The HEA powders obtained in Examples 8-10 are also suitable as catalytic materials, which require a large specific surface area and nano-sized particles. Regarding the HEA powders obtained in Examples 11-15, the calculation limit is around 3-5 nm, and quantitative crystallite diameters cannot be clearly determined. However, the broad peaks observed in XRD clearly indicate the formation of crystallites smaller than 5 nm. The HEA powders obtained in Examples 11-15 can be used as electrode catalysts, such as catalysts for the electrolysis of ammonia. [Industrial Applicability]

[0054] This shape-memory alloy has potential for use in a variety of fields, including medical devices and structural materials, as well as in new application areas such as 3D metal printers and as a catalytic material.

Claims

1. The atomic composition ratio is AlCoCrFeNiV, AlCoCrFeNi, CoFeNiTiCr, CoFeNiTiV, Al ０．２ Co １．５ CrFeNi １．５ Ti ０．５ , (Ti ０．５ Zr ０．５ ) (Cr ０．２５ Mn ０．２５ Fe ０．２５ Ni ０．２５ ) ２ A high-entropy alloy catalyst for liquid-phase hydrogenation reactions, comprising a high-entropy alloy represented by any one of the following formulas:

2. The high-entropy alloy catalyst according to claim 1, wherein the high-entropy alloy represented by the formula (Ti0.5Zr0.5)(Cr0.25Mn0.25Fe0.25Ni0.25)2 carries one or more metals selected from the group consisting of Ni, Pd and Pt.

3. The high-entropy alloy catalyst according to claim 1 or 2, wherein the liquid-phase hydrogenation reaction is a synthesis reaction of an amine by hydrogenation of a nitro group or an imine.

4. A method for producing an amine, comprising a step of hydrogenating a compound or imine having a nitro group in the liquid phase in the presence of the high-entropy alloy catalyst described in claim 1 or 2.

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