Method for producing single metal powder, and method for producing single metal powder catalyst

Abstract

A method for producing a single metal powder and a method for producing a single metal powder catalyst, wherein: an alkaline earth metal salt is mixed with a single metal salt selected from the group consisting of transition metals in periods 4 to 6 and groups 3 to 12, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanides in the presence of a solvent; the mixed solution is dried and heated to obtain an oxide precursor; the oxide precursor, a molten salt, and a reducing agent selected from alkaline earth metals, hydrides of alkaline earth metals, and hydrides of alkali metals are heated and reduced in the presence of an inert gas to obtain a product; and the product is washed to obtain a single metal powder.

Description

Method for producing single metal powder, method for producing single metal powder catalyst

[0001] The present disclosure relates to a method for producing a single metal powder and a method for producing a single metal powder catalyst, and more particularly to a method for producing nano-sized single metal fine particles and a method for producing a single metal fine particle catalyst.

[0002] While single-metal powders are used in a variety of applications, including electronic components for electrical devices, electrode materials, magnetic materials, ink materials, and medical devices, nano-sized metal particles (metal nanoparticles) in particular have attracted attention as next-generation structural and functional materials because of their unique properties compared to larger particles. For example, in addition to the aforementioned electrode materials, magnetic materials, ink materials, and medical devices, their main applications include use in a variety of fields, such as solid catalysts for automobile exhaust gas purification, petroleum refining, fine chemistry, and fuel cells.

[0003] Because metal reserves are limited, reducing the amount of metal used is an important issue. For example, it is known that in solid catalysts, reactions proceed only on the surfaces of nanoparticles on the order of nanometers (approximately 1-100 nm). By miniaturizing the metal to increase its specific surface area and enhance its reactivity, the amount of metal used can be reduced. Methods for producing such metal nanoparticles include physical methods and chemical methods that utilize molten metal decomposition methods and liquid-phase reduction methods.

[0004] One physical method is to generate metal nanoparticles by heating and evaporating a metal using arc plasma and then rapidly cooling it (Patent Document 1). Another chemical liquid-phase reduction method involves obtaining metal nanoparticles by subjecting a solution containing a dissolved metal to an appropriate reduction treatment. For example, Patent Document 2 describes a method for generating metal nanoparticles by adding a reducing agent to a metal ion-containing solution containing a surfactant and a dissolved metal. Other methods for producing metal nanoparticles include external irradiation with ultrasound (Patent Document 3) or microwaves (Patent Documents 4 and 5). Furthermore, Patent Document 6 discloses a method for reducing a metal salt by adding a reducing agent to a metal salt solution, in which hydrogen nanobubbles (microbubbles) are added to the metal salt solution to promote the reduction reaction and produce metal nanoparticles. Patent Document 7 also discloses a method for producing metal nanoparticles by thermal decomposition of a metal carbonyl complex.

[0005] JP 2017-95751 A JP 2017-179546 A JP 2019-151891 A JP 2020-111831 A JP 2019-77923 A JP 2017-206750 A JP 2017-088909 A

[0006] The physical methods described above use expensive pure metals as raw materials and also require expensive equipment capable of withstanding high temperatures. The chemical methods described above require expensive additives or special equipment for external reduction promotion treatments. Furthermore, particularly when using ultrasound or microwave irradiation, careful adjustment of irradiation conditions is required. In reduction treatments, the higher the temperature conditions (e.g., 300°C or higher), the larger the size of the resulting single metal, such as metal nanoparticles, or the particles aggregate, resulting in a smaller specific surface area. Therefore, lower temperature conditions are desirable, but this results in a slower reduction rate.

[0007] Such single metal powders are expected to have expanded applications as next-generation structural and functional materials, and single metal powders with larger specific surface areas are desired to improve the functionality of the materials. In particular, expanded use as various catalytic materials is also desired. The present disclosure has been made to solve the above-mentioned problems, and aims to provide a method for producing a single metal powder and a method for producing a single metal powder catalyst that can produce a single metal powder with a large specific surface area simply and at low cost.

[0008] The inventors discovered that it is possible to produce single metal powders, particularly metal nanoparticles, by preparing an oxide precursor by mixing a salt of a metal element with an alkaline earth metal salt and then reducing the oxide precursor using a molten salt as a solvent. In this reduction process, high-temperature conditions that dissolve the molten salt enable a rapid reduction rate and produce metal nanoparticles with high crystallinity. Furthermore, the alkaline earth metal in the alkaline earth metal salt mixed into the raw material inhibits metal particle size increase and aggregation. Furthermore, the alkaline earth metal is easily removed by washing or other methods, acting as a template within the oxide precursor, resulting in metal nanoparticles with a large specific surface area. Furthermore, the alkali metal salt or alkaline earth metal salt used as the molten salt and the alkaline earth metal hydride or alkali metal hydride used as the reducing agent are composed only of common elements, allowing for the easy production of metal nanoparticles using relatively inexpensive reagents.

[0009] The present disclosure relates to the following methods for producing single metal powder: (1) A method for producing a single metal powder, comprising the steps of: mixing a salt of a single metal selected from the group consisting of transition metals of periods 4-6 and 3-12, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanoids with an alkaline earth metal salt in the presence of a solvent to obtain a mixed solution; drying and heating the mixed solution to obtain an oxide precursor; heating and reducing the oxide precursor, at least one reducing agent selected from alkaline earth metals, alkaline earth metal hydrides, and alkali metal hydrides, and an alkali metal salt and / or a molten salt of an alkaline earth metal salt in the presence of an inert gas to obtain a product; and washing the product to obtain a single metal powder. (2) The method for producing a single metal powder according to (1), wherein a calcium salt is used as the alkaline earth metal salt in the mixed solution obtaining step. (3) The method for producing a single metal powder according to (1) or (2), wherein the step of obtaining the product is a step of heating at 300-800°C. (4) The method for producing a single metal powder according to any one of (1) to (3), wherein the step of obtaining the single metal powder is a step of removing alkaline earth metals from the product using an acidic solution. (5) The method for producing a single metal powder according to any one of (1) to (4), wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, V, Cr, Mn, Nb, Mo, Ta, W, Re, Zn, Ga, Cd, In, Sn, Pb, and Bi. (6) The method for producing a single metal powder according to (5), wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au.

[0010] The present disclosure also relates to a method for producing a single metal powder catalyst described below: (7) A method for producing a single metal powder catalyst, comprising the steps of: mixing a salt of a single metal selected from the group consisting of transition metals of Periods 4-6 and 3-12, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanoids with an alkaline earth metal salt in the presence of a solvent to obtain a mixed solution; drying and heating the mixed solution to obtain an oxide precursor; heating and reducing the oxide precursor, at least one reducing agent selected from alkaline earth metals, alkaline earth metal hydrides, and alkali metal hydrides, and an alkali metal salt and / or a molten salt of an alkaline earth metal salt in the presence of an inert gas to obtain a product; and washing the product to obtain a single metal powder. (8) The method for producing a single metal powder catalyst described in (7) above, wherein a calcium salt is used as the alkaline earth metal salt in the mixed solution obtaining step. (9) The method for producing a single metal powder catalyst according to (7) or (8), wherein the step of obtaining the product is a step of heating at 300-800°C. (10) The method for producing a single metal powder catalyst according to any one of (7) to (9), wherein the step of obtaining the single metal powder catalyst is a step of removing alkaline earth metals from the product using an acidic solution. (11) The method for producing a single metal powder catalyst according to any one of (7) to (10), wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, V, Cr, Mn, Nb, Mo, Ta, W, Re, Zn, Ga, Cd, In, Sn, Pb, and Bi. (12) The method for producing a single metal powder catalyst according to (11), wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au.

[0011] According to the present disclosure, it is possible to provide a method for producing a single metal powder and a method for producing a single metal powder catalyst, which are capable of producing a single metal powder with a large specific surface area simply and at low cost.

[0012] 1 is an X-ray diffraction pattern of Ni powder in Example 1. FIG. 2 is an SEM image of Ni powder in Example 1. FIG. 3 is an X-ray diffraction pattern of Ru powder in Example 2. FIG. 4 is an SEM image of Ru powder in Example 2. FIG. 5 is an X-ray diffraction pattern of Rh powder in Example 3. FIG. 6 is an SEM image of Rh powder in Example 3. FIG. 7 is an X-ray diffraction pattern of Ir powder in Example 4. FIG. 8 is an SEM image of Ir powder in Example 4. FIG. 9 is an X-ray diffraction pattern of Pt powder in Example 5. FIG. 10 is an SEM image of Pt powder in Example 5.

[0013] A method for producing a single metal powder according to an embodiment of the present disclosure involves reducing an oxide precursor, which is a mixture of a raw material metal salt and an alkaline earth metal salt, in a molten salt using a reducing agent, and then removing the alkaline earth metal from the product. Note that, in this specification, numerical ranges include upper and lower limits. Furthermore, the term "single metal" does not necessarily mean a 100% purity, and may include trace amounts of impurity elements, but refers to a purity of approximately 96-98% (mass%) or more, which is considered to be substantially 100%.

[0014] Specifically, the method for producing a single metal powder of this embodiment includes the steps of: mixing a salt of a single metal selected from the group consisting of transition metals of Periods 4-6 and 3-12, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanides with an alkaline earth metal salt in the presence of a solvent to obtain a mixed solution; drying and heating the mixed solution to obtain an oxide precursor; heating and reducing the oxide precursor, at least one reducing agent selected from alkaline earth metals, alkaline earth metal hydrides, and alkali metal hydrides, and a molten salt of an alkali metal salt in the presence of an inert gas to obtain a product; and washing the product to obtain a single metal powder. The step of washing the product to obtain a single metal powder is, for example, a step of removing the alkaline earth metal of the alkaline earth metal salt used as a raw material from the product. The step of removing the alkaline earth metal from the alkaline earth metal salt used as the raw material is, for example, a step of removing the alkaline earth metal from the alkaline earth metal salt in the step of obtaining the mixed solution from the product to obtain a single metal powder, as will be described in detail later.

[0015] The single metal is a metal selected from the group consisting of transition metals of periods 4-6 and groups 3-12 of the periodic table, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanides. Although aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanides are not transition metals, they share the same properties as the transition metals in that they can exist as solid single metals at room temperature and pressure. Furthermore, while silicon, germanium, arsenic, selenium, antimony, and tellurium are strictly speaking metalloids, they share the same property as the transition metals and aluminum, etc., in that they are solid elements that can exist as solid single metals at room temperature and pressure. Therefore, they are included in the metal category in this specification. Technetium, a radioactive element, and mercury, a liquid, are excluded. The single metal is selected from, for example, iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), vanadium (V), chromium (Cr), manganese (Mn), niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), rhenium (Re), zinc (Zn), gallium (Ga), cadmium (Cd), indium (In), tin (Sn), lead (Pb), bismuth (Bi), etc. In particular, the single metal is preferably selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au because they have a weak affinity for oxygen and are easily maintained in a reduced state in the atmosphere.

[0016] As described above, according to this embodiment, the metal salts can be used as raw materials. The metal salts used as raw materials are easily available and inexpensive, which allows for cost reduction.

[0017] Metal salts (salts of a single metal) include inorganic salts such as metal nitrates, sulfates, carbonates, phosphates, and chlorides, as well as organic salts such as alkoxides, acetates, and oxalates. In the case of inorganic salts, many nitrates or chlorides are soluble and inexpensively available, making them suitable. For example, when the single metal is nickel, Ni(NO ３ ) ２ ・6H ２ O, in the case of iron, Fe(NO ３ ) ３ ・9H ２ In addition, when the single metal is ruthenium, there are hydrates of nitrates such as RuCl ３ ・nH ２ O, for rhodium, RhCl ３ ・3H ２ O, IrCl for yttrium ３ ・xH ２ O, H in the case of platinum ２ PtCl ６ (NO ３ ) ３ ・6H ２ O, for vanadium, VCl ３ , RhCl ３ Inexpensively available chlorides such as those mentioned above are preferred. Metal alkoxides are preferably used for Ti and Si because they are readily available soluble compounds. Metal alkoxides are salts that are often used in the sol-gel method. Metal alkoxides may also be used for Al. The above salts may be hydrates. Any salt may be used as long as it is a readily available soluble compound.

[0018] The metal salt and alkaline earth metal salt are then mixed in the presence of a solvent to obtain a mixed solution. A chelating agent may also be added to obtain the mixed solution. Examples of suitable solvents include ion-exchanged water, distilled water, glycerin, alcohol (especially ethanol), glycols (especially ethylene glycol and propylene glycol), and standard organic solvents (THF, acetone, and toluene). Among these, distilled water and ethanol are preferred due to their ease of handling and low cost. The chelating agent is an organic compound that forms a chelate complex with the metal ions in the solution. Standard, highly safe chelating agents include ethylenediaminetetraacetic acid, citric acid, phytic acid, and gluconic acid. Using a chelating agent, a uniform metal oxide powder can be obtained using a sol-gel complex polymerization method. The chelating agent should be used in a molar amount that is 1 to 1.5 times the molar amount of the metal.

[0019] The alkaline earth metal salts include inorganic salts such as nitrates, sulfates, carbonates, phosphates, and chlorides of calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), etc., as well as organic salts such as alkoxides, acetates, and oxalates. In the case of inorganic salts, nitrates or chlorides are preferred because they are soluble and inexpensively available. Furthermore, calcium is preferred as the alkaline earth metal of the alkaline earth metal salt because it is inexpensive and easily available. For example, when the alkaline earth metal salt is a calcium salt, Ca(NO ３ ) ２ and CaCl ２ , (CH ３ COO) ２ Examples include calcium and calcium hydroxide. These calcium salts can be added in appropriate amounts. For example, in order for the added calcium to occupy a sufficient volume within the oxide precursor to function as a template, the molar ratio of calcium to the number of moles of metal contained in the salt of a single metal can be set to Ca / metal = 0.1-4.0, preferably Ca / metal = 0.5-2.0. The same can be applied to salts of alkaline earth metals other than calcium.

[0020] The mixed solution containing the metal salt and alkaline earth metal salt is then dried and heated to obtain an oxide precursor. Heating may be performed in one step or multiple steps. For example, after pre-calcination at a low temperature, the calcined sample is uniformly pulverized and mixed in a mortar or the like using a pestle, and then calcined at a high temperature, which is preferable because it yields an oxide precursor in which the elements are uniformly dispersed. The heating temperature is preferably 300-800°C, but 400-600°C is preferred because it allows impurities other than the metal elements (e.g., chelating agents) to be removed by combustion or because it yields an oxide precursor in which the metal elements are uniformly dispersed. The heating time, which varies depending on the heating temperature, is preferably 0.5-10 hours, and preferably 3-6 hours.

[0021] In the process of obtaining this oxide precursor, a composite oxide of an alkaline earth oxide (e.g., CaO) and a metal (or a compound in which a metal is dispersed in CaO) is obtained by the action of an alkaline earth metal salt (e.g., calcium salt) during firing, making it easier to obtain an oxide precursor powder. That is, in the process of obtaining the oxide precursor by drying and heating the mixed liquid, at least one of the metal salt and the alkaline earth metal salt contained in the mixed liquid is oxidized. The oxide precursor is, for example, a metal oxide that is a precursor of an alloy. The metal oxide may be a composite oxide of an alkaline earth oxide and a metal, or a compound in which a metal is dispersed in an alkaline earth oxide.

[0022] Then, the oxide precursor, the reducing agent, and the molten salt source are mixed and reduced by heating in the presence of an inert gas (nitrogen, argon, helium, etc.). In this reduction process, the alkaline earth metal of the alkaline earth metal salt is present between the metal particles in the oxide precursor, thereby increasing the size of the metal particles and suppressing aggregation of the metal particles. After reduction, the alkaline earth metal of the alkaline earth metal salt forms a product as NH ４The alkaline earth metal can be removed by washing with a washing solution such as a Cl aqueous solution. As a result, the alkaline earth metal acts as a template, resulting in metal nanoparticles with a large specific surface area. That is, the method for producing a single metal powder includes a step of washing the product obtained in the step of obtaining a product to obtain a single metal powder. In this step of obtaining a single metal powder, the alkaline earth metal of the alkaline earth metal salt obtained in the step of obtaining the mixed solution is removed from the product obtained in the step of obtaining a product, thereby obtaining a single metal powder. The washing solution may be a general acidic solution capable of removing alkaline earth metals, such as NH ４ Weakly acidic solutions such as Cl solution, phosphoric acid solution, and acetic acid solution, and strongly acidic solutions such as perchloric acid solution, sulfuric acid solution, nitric acid solution, and hydrochloric acid solution can be used. Furthermore, solutions using organic solvents other than aqueous solutions may be used, and mixed solutions of aqueous solutions and organic solvents may also be used. The acidic solution preferably has a pH in the range of 3-6, and more preferably about pH 4 (e.g., pH 3.5 to 4.5). At this time, impurities (e.g., LiCl, CaCl ２ , CaH ２ , CaO, etc.) can also be removed.

[0023] The heating temperature during reduction varies depending on the type of molten salt. However, it is preferably a temperature above the melting point, i.e., 300-1000°C, preferably 300-800°C, and more preferably 360-600°C, from the viewpoint that the reduction rate is sufficiently fast and a high specific surface area can be easily obtained by using relatively low temperatures. Alternatively, the molten salt source may be heated first, and the oxide precursor and reducing agent may be added to the molten salt source in its molten state, i.e., in the molten salt state. Alternatively, 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 mixed molten salt, its melting point is lower than that of a single molten salt, and it melts even at temperatures below 600°C, for example. The molten salt acts as a solvent, and the oxide precursor is reduced by the reducing agent in the molten salt. By using this molten salt reduction method, a single metal can be obtained easily and at low cost. The heating time, depending on the heating temperature, is preferably 0.5-10 hours, preferably 3-6 hours. If the heating temperature is low (for example, about 550°C), the heating time may need to be extended (for example, about 10 hours), but if the heating temperature is high (for example, 700-800°C), the heating time can be shortened (for example, about 2 hours).

[0024] The reducing agent may be at least one selected from alkaline earth metals, alkaline earth metal hydrides, and alkali metal hydrides. Examples include elemental metals such as Mg, Ca, Sr, and Ba, hydrides thereof, and hydrides of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Calcium hydride, metallic calcium, magnesium hydride, metallic magnesium, and lithium hydride are preferred because they are relatively inexpensive, have good chemical stability, and are easy to handle. These reducing agents exhibit strong reducing properties in the molten salt. The reducing agents 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, CaH ２ is a stable powder under room temperature and atmospheric conditions, and is therefore relatively safe to handle. ２ When used as a reducing agent, CaH ２reacts with oxygen contained in the oxide precursor to become CaO, and CaH ２ Preferably, the reducing agent is used in an amount of about 0.1 to 4 times, more preferably about 1 to 2 times, by weight relative to the oxide precursor.

[0025] 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 compounds such as 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. ２ , CaF ２ , SrF ２ , BaF ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , MgBr ２ , CaBr ２ , SrBr ２ , BaBr ２ , MgI ２ , CaI ２ , SrI ２ , BaI ２ Compounds such as the following can be used.

[0026] 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 depending on whether they are stable in the atmosphere, easy to handle, or inexpensively available. In addition, AlCl ３ , ZnCl ２ Even halides of relatively less noble metals such as fluorine, fluorine, thiamin ...

[0027] In particular, the molten salt used in this embodiment is LiCl, CaCl ２ A single molten salt such as LiCl and KCl, a mixed molten salt of LiCl and CaCl２ It is preferable to use a mixed molten salt of the above. Furthermore, since the melting point of the mixed molten salt is lower than that of a single molten salt, the reaction can occur at a low temperature. Therefore, when the temperature at which a single metal 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, since the melting point of a mixed molten salt of LiCl and KCl is 350°C, the reaction can be carried out even at a low temperature of about 360°C (for example, 355 to 365°C).

[0028] The single metal powder produced by the above method is a metal nanoparticle with a large specific surface area. Nanoparticles are finely divided particles on the nanometer order (approximately 1-100 nm), with an average particle size of approximately several nanometers (approximately 2-3 nm) to several tens of nanometers (approximately 10-30 nm), i.e., particles of 2 nm to 30 nm, and particularly particles of 2 nm to 10 nm. Here, the average particle size is calculated from the metal density and BET specific surface area, as described below. Such metal nanoparticles are expected to be used in a variety of applications, including medical devices and structural materials, as well as electronic materials and catalyst materials. Furthermore, they contribute to improving functionality, such as catalytic properties, electrode properties, gas storage properties, and sensing properties, in fields such as electronic components for electrical devices, electrode materials, magnetic materials, ink materials, medical devices, automobile exhaust gas purification, petroleum refining, fine chemistry, and fuel cells.

[0029] For example, when used in medical devices or structural materials, the extremely small particle size allows for use as a raw material for microfabricated products. Furthermore, because of the large specific surface area of ​​this single metal, it is particularly suitable as a catalytic material. That is, single metal powders can be used as single metal powder catalysts. Therefore, the above-described method for producing single metal powders can be used as single metal powder catalysts. Furthermore, single metals such as Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au can be used as catalytic materials, primarily as hydrogenation catalysts or oxidation catalysts. These single metals can function as catalysts themselves, either supported on a carrier or alone, or used as catalyst carriers. For example, in the case of hydrogenation catalysts, the average particle size of the particles is preferably 50 nm or less, and more preferably 10 nm or less. According to this embodiment, such metal nanoparticles can also be produced.

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

[0031] Example 1: Ni(NO) was dissolved in distilled water as a single metal salt. ３ ) ２ ・6H ２ O (Fuji Wako Pure Chemical Industries, Ltd., purity 99.9%) and Ca(NO ３ ) ２ ・4H ２ NiO (manufactured by Fuji Wako Pure Chemical Industries, Ltd., purity 98.5%) and citric acid (manufactured by Fuji Wako Pure Chemical Industries, Ltd.) were dissolved in a molar ratio of Ni / Ca / citric acid = 1 / y / (1 + y) × 1.2, and the solution was evaporated to dryness on a hot plate. y was selected from 0.5 and 2.0. The sample was then pre-fired at 250°C for 2 hours. The fired sample was crushed and mixed in a mortar with a pestle to form a powder with a roughly uniform particle size, and then fired again at 500°C for 2 hours to obtain an oxide precursor.

[0032] The obtained oxide precursor was heated and reduced at (1) 360°C or (2) 600°C. (1) In the reduction at 360°C, the oxide precursor and CaH ２LiH (manufactured by Nacalai Tesque, Inc.) or LiH (manufactured by Sigma-Aldrich, purity 95%) and LiCl-KCl (manufactured by Fuji Wako Pure Chemical Industries, Ltd., molar ratio 60:40) were mixed in a weight ratio of 2 / 6 / 3, and the mixture was heated in an SUS cylindrical container (similar to other examples) at 360°C for 2 hours under an argon atmosphere to perform molten salt reduction. The mixed molten salt source of LiCl and KCl was prepared by mixing in a mortar with a pestle. Finally, 0.1 M NH ４ The impurities (LiCl, KCl, CaH) were removed by washing the product with aqueous Cl solution and distilled water. ２ , CaO, etc.) were removed to obtain Ni powder. The Ni powders obtained here are Nos. 2 to 4 in Table 1. (2) In the reduction at 600°C, the oxide precursor and CaH ２ and LiCl were mixed in a weight ratio of 2 / 6 / 3, and the mixture was heated in an SUS cylindrical container under an argon atmosphere at 600°C for 2 hours for molten salt reduction. The subsequent cleaning process was carried out in the same manner as in (1) above. The Ni powder obtained here is No. 6 in Table 1. As a comparative example, a Ni powder was prepared by setting y=0 and using Ca(NO ３ ) ２ ・4H ２ Ni powder was obtained under the same conditions as in Example 1, except that no O (alkaline earth metal salt) was added. The Ni powders obtained here are No. 1 and No. 5 in Table 1. In the following examples, unless otherwise noted, metal powders were produced using the same method and conditions as in Example 1. Furthermore, the same reagents were used for common compounds.

[0033] The prepared Ni powder was subjected to X-ray diffraction pattern measurement, SEM image measurement, elemental analysis, nitrogen adsorption experiment, etc. Figure 1 shows the Ni powder No. 2 (Ca addition molar ratio 0.5, reducing agent CaH ２, reduction temperature 360°C). The reference data in the figure was referenced from the PDF (Powder Diffraction File) database by the ICDD (International Centre for Diffraction Data). The same applies to the other examples below. Figure 2 shows an SEM image of Ni powder No. 2. The X-ray diffraction pattern was measured using an X-ray diffractometer (SmartLab (registered trademark), manufactured by Rigaku Corporation) under the following conditions: X-ray source: CuKα, output: 40 kV, 40 mA. The SEM image was measured using a scanning electron microscope (JEOL Ltd., JSM-7800F). Elemental analysis was performed by placing the sample powder in a dedicated sample holder and then measuring it under vacuum using an X-ray fluorescence analyzer (ZSX Primus II, manufactured by Rigaku Corporation) using an X-ray tube with a Rh target (3 kW). In the nitrogen adsorption experiment, the sample was dried at 150°C for 60 minutes under an inert gas flow, and then the amount of nitrogen adsorption (BET specific surface area) was measured at liquid nitrogen temperature. The average particle size was calculated using the metal density and BET specific surface area listed in the Materials Project database (URL: https: / / materialsproject.org / ), assuming that the sample powder was composed of spherical particles. Table 1 shows the results of the nitrogen adsorption experiment.

[0034] From Figure 1, the production of Ni was confirmed. Furthermore, from the results of elemental analysis, the purity of Ni was 99.5 (Mass%). Therefore, it was confirmed that high purity Ni powder was produced. Furthermore, from the results of Table 1, it can be seen that Ca(NO ３ ) ２ ・4H ２ It can be seen that the addition of O dramatically increased the specific surface area of ​​the Ni powder. In addition, the average particle size also decreased. Therefore, the calcium salt (Ca(NO ３ ) ２ ) resulted in the production of Ni powder with a large specific surface area. In other words, the effect of adding calcium salt is that calcium acts as a template during reduction, suppressing the aggregation of metals.２ When LiH was used as the reducing agent instead of Ca, the specific surface area was further improved. Li is a smaller element than Ca, and it is thought that Li therefore acts as a template, resulting in finer Ni powder. In addition, SEM images confirmed a fine structure consisting of fine particles of 30-50 nm or smaller. From these results, it can be said that the obtained Ni powder is Ni nanoparticles with a fine structure.

[0035] Examples in which the metal elements were changed are shown below. In the following examples, the X-ray diffraction patterns, SEM images, elemental analysis, specific surface area, etc. were measured using the same apparatus and under the same methods and conditions as in Example 1.

[0036] Example 2: RuCl as a single metal salt ３ ・nH ２ Ru powder was prepared using RuO (manufactured by Fuji Wako Pure Chemical Industries, Ltd.) under the same conditions and methods as in Example 1. The Ru powders obtained here are Nos. 7 to 11 in Table 2. Figure 3 shows the Ru powder No. 8 (Ca addition molar ratio 2, reducing agent CaH ２ Figure 3 shows the X-ray diffraction pattern of the Ru powder (reduction temperature: 360°C), and Figure 4 shows an SEM image of the Ru powder. Figure 3 confirms the production of Ru. Furthermore, the results of elemental analysis showed that the purity of Ru was 99.3 (mass%). Therefore, it was confirmed that a highly pure Ru powder was produced. Furthermore, the SEM image confirmed a microstructure consisting of fine particles of 30-50 nm or less.

[0037] Example 3: RhCl as a single metal salt ３ ・3H ２ Rh powder was prepared using Rh powder No. 12 to 16 in Table 2. In the (2) reduction at 600°C, LiH was also used as the reducing agent (No. 16). Figure 5 shows the results of the Rh powder No. 15 (Ca addition molar ratio 2, reducing agent CaH ２FIG. 5 shows the X-ray diffraction pattern of the Rh powder (reduction temperature: 600°C), and FIG. 6 shows an SEM image of the Rh powder. The generation of Rh was confirmed from FIG. 5. Furthermore, the result of elemental analysis showed that the purity of Rh was 98.7 (mass%). Therefore, it was confirmed that a highly pure Rh powder was produced. Furthermore, the SEM image confirmed a fine structure consisting of fine particles of 30-50 nm or less.

[0038] Example 4: IrCl as a single metal salt ３ ・xH ２ Ir powder was prepared using Ir powder No. 17 to No. 20 in Table 2. In the (2) reduction at 600°C, LiH was also used as the reducing agent (No. 20). Figure 7 shows the Ir powder No. 19 (Ca addition molar ratio 2, reducing agent CaH ２ FIG. 7 shows the X-ray diffraction pattern of the Ir powder (reduction temperature: 600°C), and FIG. 8 shows an SEM image of the Ir powder. The generation of Ir was confirmed from FIG. 7. Furthermore, the results of elemental analysis showed that the purity of Ir was 98.4 (mass%). Therefore, it was confirmed that high-purity Ir powder was produced. Furthermore, the SEM image confirmed a fine structure consisting of fine particles of 30-50 nm or less.

[0039] Example 5: H as a single metal salt ２ PtCl ６ ・6H ２ Pt powders were prepared using H2O (manufactured by Fuji Wako Pure Chemical Industries, Ltd., purity 98.5%) under the same conditions and methods as in Example 1. The Pt powders obtained here are Nos. 21 and 22 in Table 2. ２ PtCl ６ ・6H ２ Since O has high solubility at high temperatures and tends to form a porous structure, reduction at 600°C (2) was performed. ２) shows the X-ray diffraction pattern, and FIG. 10 shows an SEM image of the Pt powder. The production of Pt was confirmed from FIG. 9. Furthermore, the results of elemental analysis showed that the purity of Pt was 98.5 (mass%). Therefore, it was confirmed that a highly pure Pt powder was produced. Furthermore, the SEM image confirmed a fine structure consisting of fine particles of 30-50 nm or less.

[0040] Table 2 shows the results for the single metals prepared in Examples 2-5 above.

[0041] From Table 2, the specific surface area is large, approximately 10 m ２ It was confirmed that single metal powders with a specific surface area of ​​1 / g or more were produced. Furthermore, the SEM images in each figure confirmed a microstructure consisting of fine particles of 30-50 nm or less. These results indicate that the resulting metal powders are nanoparticles with a fine structure. It is preferable to select a reduction temperature that is sufficiently high so that single metal powders are easily formed after the oxide precursor is reduced. Selecting Ni or Ru as the constituent element is particularly preferable, since single metal powders with a large specific surface area can be obtained at relatively low reduction temperatures. Because these single metals are nanoparticles with a large specific surface area, they can be used as solid catalysts for automobile exhaust gas purification, petroleum refining, fine chemistry, fuel cells, and the like. For example, Ni powder is well known as a hydrogenation catalyst or electrode catalyst for alkenes, fats and oils, fatty acids, aromatic compounds, nitriles, etc.; Ru powder is used as a catalyst for ammonia synthesis or ammonia decomposition by hydrogen reduction of nitrogen; Rh powder is used as a hydrogenation catalyst for alkenes or a catalyst for purifying exhaust gas; Ir powder is used for hydrogenation and cyclization of cyclopentane; and Pt powder is used as a solid catalyst such as an electrode catalyst or a typical oxidation catalyst for fuel cells, etc.

[0042] The present disclosure has applicability in a variety of fields, including use as a catalyst material in addition to medical devices and structural materials.

Claims

1. A process of mixing a salt of a single metal selected from the group consisting of transition metals of periods 4-6, groups 3-12, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanides with an alkaline earth metal salt in the presence of a solvent to obtain a mixed solution, The process involves drying and heating the aforementioned mixture to obtain an oxide precursor. A step of heating and reducing the oxide precursor, at least one reducing agent selected from alkaline earth metals, alkaline earth metal hydrides, and alkali metal hydrides, and an alkali metal salt and / or a molten alkaline earth metal salt in the presence of an inert gas to obtain a product. A step of washing the aforementioned product to obtain a single metal powder. A method for producing a single metal powder comprising the following:

2. The method for producing a single metal powder according to claim 1, wherein a calcium salt is used as the alkaline earth metal salt in the step of obtaining the mixed liquid.

3. The method for producing a single metal powder according to claim 1 or claim 2, wherein the step of obtaining the product is a step of heating at 300-800°C.

4. The method for producing a single metal powder according to claim 1 or claim 2, wherein the step of obtaining the single metal powder is a step of removing alkaline earth metals from the product using an acidic solution.

5. A method for producing a single metal powder according to claim 1 or claim 2, wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, V, Cr, Mn, Nb, Mo, Ta, W, Re, Zn, Ga, Cd, In, Sn, Pb, and Bi.

6. The method for producing a single metal powder according to claim 5, wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au.

7. A method for producing a single metal powder catalyst, A process of mixing a salt of a single metal selected from the group consisting of transition metals of periods 4-6, groups 3-12, aluminum, silicon, gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, lead, bismuth, and lanthanides with an alkaline earth metal salt in the presence of a solvent to obtain a mixed solution, The process involves drying and heating the aforementioned mixture to obtain an oxide precursor. A step of heating and reducing the oxide precursor, at least one reducing agent selected from alkaline earth metals, alkaline earth metal hydrides, and alkali metal hydrides, and an alkali metal salt and / or a molten alkaline earth metal salt in the presence of an inert gas to obtain a product. A step of washing the aforementioned product to obtain a single metal powder. A method for producing a single metal powder catalyst comprising the above.

8. The method for producing a single metal powder catalyst according to claim 7, wherein a calcium salt is used as the alkaline earth metal salt in the step of obtaining the mixed liquid.

9. The method for producing a single metal powder catalyst according to claim 7 or claim 8, wherein the step of obtaining the product is a step of heating at 300-800°C.

10. The method for producing a single metal powder catalyst according to claim 7 or claim 8, wherein the step of obtaining the single metal powder is a step of removing an alkaline earth metal from the product using an acidic solution.

11. A method for producing a single-metal powder catalyst according to claim 7 or claim 8, wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, V, Cr, Mn, Nb, Mo, Ta, W, Re, Zn, Ga, Cd, In, Sn, Pb, and Bi.

12. The method for producing a single-metal powder catalyst according to claim 11, wherein the single metal is selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au.