Metallic material and catalyst containing the same

Abstract

The metal material contains a nucleus containing two or more kinds of metal elements and crystal grains containing one or more kinds of metal elements, and the metal elements contained in the crystal grains constitute at least a part of the surface of metal particles.SOLUTION: The metallic material contains nuclei containing two or more kinds of metallic elements and crystalline grains containing one or more kinds of metallic elements, wherein the metallic elements contained in the crystalline grains are metallic elements having standard electrode potentials (25 °C, 1atm) higher than 0V and equal to or lower than 50V, and the crystalline grains constitute at least a part of the surfaces of metallic particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metallic material and a catalyst containing the same. [Background technology]

[0002] Metals are used as catalysts for many chemical reactions. Catalysts are required to have a high ability to efficiently promote reactions (high catalytic activity) and to be able to prevent a decrease in catalytic activity due to heat or corrosion (durability). Generally, precious metals are used as catalysts, but because precious metals are scarce and expensive, there is a demand for reducing their use.

[0003] For example, in the case of Pt-based catalysts, as in Non-Patent Document 2, it is known that Pt-Fe, Pt-Co, and Pt-Ni alloys have catalytic activity 10 to 20 times higher than that of Pt alone, and currently, Pt-Co alloys are the mainstream of Pt-based catalysts. In recent years, there has been a demand for Pt-based catalysts that are more catalytically active and durable than Pt-Co alloys, and as in Non-Patent Document 1, the use of high-entropy alloys as catalysts has been considered. However, the high-entropy alloys in Non-Patent Document 1 have limitations on the types of metals that can be used to form the alloy, which has resulted in limited compositions. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] J.Am.Chem.Soc.2022,144,8,p3365-3369 [Non-patent document 2] Surface Science 2004,Vol.25,No.5,p279-284 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a metal material comprising a nucleus containing two or more metal elements and crystal grains containing one or more metal elements, wherein the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than 1.50 V, and the crystal grains constitute at least a portion of the surface of a metal particle. [Means for solving the problem]

[0006] As a result of extensive research to solve these problems, the present inventors have found that the above object can be achieved, and have arrived at the present invention.

[0007] The gist of the present invention is as follows. <1> A metallic material comprising a nucleus containing two or more metal elements and crystal grains containing one or more metal elements, wherein the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than 1.50 V, and wherein the crystal grains constitute at least a portion of the surface of the metallic particle. <2> The core containing the metal element contains two or more metal elements selected from the group consisting of Cr, Fe, Co, Ni, and Mn. <1> The metal material according to claim 1. <3> The crystal grains containing metallic elements contain precious metals. <1> or <2> The metal material according to claim 1. <4> The crystal grains containing metal elements contain platinum. <1> ~ <3> The metal material according to claim 1. <1> ~ <4> A catalyst comprising the metal material described in 1. [Effects of the Invention]

[0008] According to the present invention, a metal material can be provided which comprises a nucleus containing two or more metal elements and crystal grains containing one or more metal elements, wherein the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of more than 0 V and not more than 1.50 V, and the crystal grains constitute at least a portion of the surface of a metal particle. The metal material of the present invention can be suitably used as a catalyst for reactions such as hydrogen generation, hydrogenation, ammonia generation, and carbon dioxide reduction. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a TEM image of the metal material of Example 2. Crystal grains are observed in the area surrounded by a solid line on the surface of the metal particle in the image, and it can be seen that the crystal grains make up at least a part of the surface of the metal particle. [Figure 2] This is a STEM-EDX image of the metal material of Example 2. When comparing the mapping images of each element, it is clear that cobalt, chromium, iron, manganese, nickel, zinc, and zirconium are distributed evenly throughout the metal material, with each metal mixed to form a solid solution. On the other hand, copper is distributed unevenly throughout the metal material, and it can be confirmed that each is distributed as crystal grains. [Figure 3] 1 is an SEM image of a metal material of Example 3. [Figure 4] 1 is a TEM image of the metal material of Example 3. Crystal grains are observed in the area surrounded by a solid line on the surface of the metal particle in the image, and it can be confirmed that the crystal grains constitute at least a part of the surface of the metal particle. [Figure 5] This is a STEM-EDX image of the metal material of Example 3. When comparing the mapping images of each element, it is clear that cobalt, chromium, iron, manganese, nickel, zinc, and zirconium are distributed evenly throughout the metal material, forming a solid solution in which each metal is uniformly mixed. On the other hand, copper and ruthenium are distributed unevenly throughout the metal material, and it can be confirmed that they are each distributed as crystal grains. [Figure 6] FIG. 10 is an image diagram of the metal material of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] The metal material of the present invention comprises a nucleus containing two or more metal elements and crystal grains containing one or more metal elements, wherein the metal elements contained in the crystal grains have a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than 1.50 V, and the crystal grains constitute at least a portion of the surface of the metal particle.

[0011] Crystal grains are minute crystals in which atoms are arranged in a lattice pattern. In the present invention, the catalytic activity is improved by the electronic interaction (ligand effect) and geometric interaction (ensemble effect) between the crystal grains and the different metal elements contained in the nuclei, resulting in a metallic material with excellent catalytic activity.

[0012] From the viewpoint of catalytic activity, the average particle size of the crystal grains is preferably 5 nm or less, more preferably 4 nm or less, and even more preferably 3 nm or less. The smaller the average particle size of the crystal grains, the higher the probability of contact with the reaction substrate, which increases the number of active sites and improves catalytic activity.

[0013] The crystal grains must contain one or more metal elements, preferably metal elements with catalytic properties. From the viewpoint of the reduction rate during crystal grain formation, the metal elements must be metal elements with a standard electrode potential (25°C, 1 atm) greater than 0 V and less than or equal to 1.50 V (e.g., Re (0.30 V), Cu (0.34 V), Ru (0.46 V), Rh (0.76 V), Os (0.90 V), Pd (0.95 V), Ir (1.16 V), Pt (1.18 V)). Noble metal elements (Ru, Rh, Os, Pd, Ir, Pt) are particularly preferred, with platinum being most preferred. The metal elements may be one type or two or more types.

[0014] It is preferable that the crystal grains have a plurality of crystal grains. In the present invention, it is preferable that the crystal grains have a large number of fine crystal grains.

[0015] The shape of the core is not particularly limited, and includes spherical and elliptical shapes as well as irregular shapes and aggregates of scale-like particles.

[0016] The metal element contained in the core is not particularly limited, and examples thereof include lithium and beryllium from Period 2 of the periodic table, sodium, magnesium, and aluminum from Period 3, potassium to gallium from Period 4, rubidium to tin from Period 5, cesium to polonium from Period 6, and francium to hassium, copernicium, and flerovium from Period 7. The metal element may contain a semimetal and be in an amorphous state, or may contain oxygen, fluorine, etc. and be in a ceramic or semiconductor state.

[0017] The core preferably contains two or more elements selected from the group consisting of Cr, Fe, Co, Ni, and Mn, more preferably three or more elements, even more preferably four or more elements, and particularly preferably all five elements. The metal elements contained in the crystal grains may also be contained in the core, but the content is preferably low. If the core contains only one type of metal element, the metal element contained in the core and the element contained in the crystal grains may form an alloy, which may prevent the formation of crystal grains.

[0018] When the nucleus is in a more stable solid solution state where many metal elements are randomly distributed, it becomes stronger against heat and corrosion and has improved durability. The entropy of mixing, which indicates the mixed state of metal elements in a solid solution state, can be calculated from the following formula (1), where R is the metal element gas constant, χi is the mole fraction of the metal components that form the nucleus, and n is the number of components. ΔS in the following formula (1) mix The larger the value, the more stable the polymer is. It is preferably 1.0R or more, more preferably 1.3R or more, and particularly preferably 1.5R or more.

[0019] Formula (1) JPEG2026009044000002.jpg25134

[0020] From the viewpoint of catalytic activity, the specific surface area (BET method) of the metal material is 100m 2 / g or more, and 150m 2 / g or more is more preferable, and 170m 2 / g or more is more preferable, and 200m 2It is most preferable that the saturation coefficient is 1 / g or more.

[0021] By measuring the metallic material of the present invention using TEM and STEM-EDX, the location of crystal grains, the average particle size, the state of the constituent metallic elements, the distribution of metallic elements present in the core of the metallic material, etc. can be evaluated.

[0022] The method for producing the metallic material of the present invention is not particularly limited, but it is preferable to synthesize it by wet synthesis, which will be described later, because of its ease of control.

[0023] Examples of wet synthesis include a method (first method) in which solution A containing metal ions other than the metal element to be made into crystal grains, solution B containing the metal ions to be made into crystal grains, and solution C containing a reducing agent are prepared; a method (second method) in which the metal element to be made into crystal grains is protected with a chelating agent, mixed with the other metal ions, and reduced with a reducing agent; and a method (third method) that uses a standard electrode potential difference. Among these, method 1 is preferred because of its ease of control. Below, method 1 will be explained.

[0024] The raw material for the metal particles can be metal ions obtained by dissolving a metal salt in a solvent such as water. There are no particular restrictions on the metal salt, as long as it can dissolve in the reaction solvent used and provide metal ions in a reducible state. It is preferable that solutions A and B are different solvents. Furthermore, it is preferable that solutions A and C are easily mixed, and more preferably the same solvent, so that the metal element contained in solution A can become a nucleus. For example, solutions A and C can be water, and solution B can be an alcohol that is miscible with water, DMF, NMP, or the like.

[0025] As mentioned above, it is not clear why adjusting the type of solvent used causes crystal grains to form at least a portion of the surface of metal particles. However, it is presumed that by adjusting the reaction conditions (e.g., type of solvent, temperature, order of mixing, etc.) so that the rate of the reduction reaction of the metal ions that serve as the raw material for the nuclei is greater than the rate of the reduction reaction of the metal ions that become the crystal grains, crystal grains are generated near the surface of the metal particles after some of the nuclei have been generated.

[0026] The concentration of each metal ion in solutions A and B is preferably 5 to 1000 mmol / L, more preferably 30 to 300 mmol / L, and even more preferably 50 to 200 mmol / L, since this improves the yield of the obtained metal material and tends to increase the specific surface area. Furthermore, the concentration of each metal ion does not need to be constant and can be increased or decreased as needed.

[0027] The reducing agent is not particularly limited, and examples thereof include reducing agents containing boron atoms such as sodium borohydride, potassium borohydride, and dimethylamine borane, hydrazines such as hydrazine and phenylhydrazine, alcohols such as isopropyl alcohol and ethylene glycol, amines such as octylamine and triethylamine, organic acids such as ascorbic acid and formic acid, and phosphorus-based reducing agents such as sodium hypophosphite. Among these, it is preferable to use reducing agents containing boron atoms such as sodium borohydride, potassium borohydride, and dimethylamine borane, and it is more preferable to use sodium borohydride.

[0028] The concentration of the reducing agent in solution C is not particularly limited, but it is preferable to use a reducing agent in an amount 1.2 to 2.0 mol times the total amount of metal ions, and therefore the concentration is preferably 30 to 10,000 mmol / L, more preferably 180 to 3,000 mmol / L, and even more preferably 300 to 2,000 mmol / L.

[0029] In wet synthesis, solutions A and B are simultaneously mixed with solution C. The time required for mixing can be adjusted appropriately depending on the amount to be synthesized. Stirring is performed as needed during mixing. After mixing, the resulting metal material is preferably refined and fired.

[0030] The temperature at which the wet synthesis is carried out is preferably 5 to 40°C from the viewpoint of controlling the rate of the reduction reaction and controlling the average particle size of the crystal grains.

[0031] Purification after the synthesis reaction can be carried out by centrifugation, filtration, etc. The purified and recovered metal material can also be made into small particles by pulverization.

[0032] The refined metal material is preferably fired at a temperature equal to or higher than the temperature at which it will be used, so that it can be used suitably at the temperature at which it will actually be used. The firing time is preferably 3 hours or more. Moreover, it can be converted into an oxide by supplying oxygen during firing.

[0033] The metal material of the present invention can be suitably used as a catalyst for reactions such as hydrogen generation, hydrogen addition, ammonia generation, and carbon dioxide reduction, because the crystal grains constitute at least a part of the surface of the metal particles. [Example]

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The metal nanomaterials were evaluated by the following methods.

[0035] (1) Molar fraction of component elements The obtained metal material was fired, and then the mole fraction of each of the detected metal and metalloid elements was determined by ICP-AES. Let R be the gas constant, χi be the mole fraction of component i, and n be the number of components. From the above equation (1), ΔS mix was calculated. ΔS mix If the ratio is 1.5R or more, the durability is excellent.

[0036] (2) Specific surface area The obtained metal material was dried in a vacuum and then subjected to a degassing treatment at 200°C for 30 minutes in a vacuum. The amount of nitrogen gas adsorbed on the degassed metal material was measured by nitrogen gas adsorption method, and the specific surface area was calculated from the amount of adsorption by the BET equation.

[0037] (3) Characteristic values ​​of core and surface metal particles The obtained metal material was photographed by TEM and STEM-EDX, and the crystallinity of the nuclei and the presence or absence of crystal grains on the surface were evaluated from the field of view.

[0038] (4) Average grain size Ten crystal grains were randomly selected from the TEM image of the obtained metal material, and the average value of the length of their major axes was taken as the average particle size of the crystal grains.

[0039] Example 1 To prepare solution A, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were dissolved in 200 g of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 12.95 g (25 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. Solution C was prepared by dissolving 9.66 parts by mass (256 mmol) of sodium borohydride in 200 g of water. Solutions A and B were added dropwise to Solution C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was diluted by pouring it into 200 parts by mass of water. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water, and then calcined at 70°C for one hour and at 300°C for four hours in the atmosphere to obtain the metal material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0040] Example 2 Solution A: 6.65 g (25 mmol) of chromium (III) chloride hexahydrate, 4.95 g (25 mmol) of manganese (II) chloride tetrahydrate, 4.95 g (25 mmol) of iron (II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, 5.95 g (25 mmol) of nickel chloride hexahydrate, 4.26 g (25 mmol) of copper chloride dihydrate, 3.41 g (25 mmol) of zinc chloride, and zirconium chloride octahydrate. 8.06 g (25 mmol) of this solution was dissolved in 320 g of water (chromium(III) chloride hexahydrate: manganese(II) chloride tetrahydrate: iron(II) chloride tetrahydrate: cobalt chloride hexahydrate: nickel chloride hexahydrate: copper chloride dihydrate: zinc chloride: zirconium oxide chloride octahydrate = 12.5 mol%:12.5 mol%:12.5 mol%:12.5 mol%:12.5 mol%:12.5 mol%:12.5 mol%:12.5 mol%). Solution C was prepared by dissolving 15.92 parts by mass (410 mmol) of sodium borohydride in 320 g of water. Solution A was added dropwise to Solution C over 15 minutes, and then allowed to stand for an additional 10 minutes. The reaction solution was diluted by pouring it into 320 parts by mass of water. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water, and then calcined at 70°C for one hour and at 300°C for four hours in the atmosphere to obtain a metallic material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, Ni, and Zn as metal elements in the core, and contains Cu as crystal grains on the surface of the metal particles.

[0041] Example 3 Solution A: 6.65 g (25 mmol) of chromium (III) chloride hexahydrate, 4.95 g (25 mmol) of manganese (II) chloride tetrahydrate, 4.95 g (25 mmol) of iron (II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, 5.95 g (25 mmol) of nickel chloride hexahydrate, 4.26 g (25 mmol) of copper chloride dihydrate, 3.41 g (25 mmol) of zinc chloride, 8.06 g (25 mmol) of zirconium chloride octahydrate, and ruthenium chloride n-hydrate. 6.54 g (25 mmol) of the monohydrate was dissolved in 360 g of water (chromium(III) chloride hexahydrate: manganese(II) chloride tetrahydrate: iron(II) chloride tetrahydrate: cobalt chloride hexahydrate: nickel chloride hexahydrate: copper chloride dihydrate: zinc chloride: zirconium chloride oxide octahydrate: ruthenium chloride n-hydrate = 11.1 mol%: 11.1 mol%: 11.1 mol%: 11.1 mol%: 11.1 mol%: 11.1 mol%: 11.1 mol%: 11.1 mol%). As solution C, 17.44 g (461 mmol) of sodium borohydride was dissolved in 360 g of water. Solution A was added dropwise to Solution C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was diluted by pouring it into 360 parts by mass of water. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water, and then calcined at 70°C for one hour and at 300°C for four hours in the atmosphere to obtain a metallic material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, Ni, and Zn as metal elements in the core, and contains Cu and Ru as crystal grains on the surface of the metal particles.

[0042] Example 4 To prepare solution A, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were dissolved in 200 g of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 25.90 g (50 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. To prepare solution C, 15.19 g (375 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were added dropwise to Solution C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was diluted by pouring it into 200 parts by mass of water. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water, and then calcined at 70°C for one hour and at 300°C for four hours in the atmosphere to obtain the metal material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0043] Example 5 To prepare solution A, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were dissolved in 200 g of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). As solution B, 25.90 g (50 mmol) of hydrogen hexachloroiridate hexahydrate was dissolved in 100 g of ethanol. To prepare solution C, 15.19 g (375 mmol) of sodium borohydride was dissolved in 200 g of water. Solutions A and B were added dropwise to Solution C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was diluted by pouring it into 200 parts by mass of water. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water, and then calcined at 70°C for one hour and at 300°C for four hours in the atmosphere to obtain the metal material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and contains Ir as crystal grains on the surface of the metal particles.

[0044] Example 6 To prepare solution A, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were dissolved in 200 g of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). As solution B, 12.95 g (25 mmol) of hydrogen hexachloroiridate hexahydrate was dissolved in 100 g of ethanol. To prepare solution C, 12.80 g (256 mmol) of hydrazine monohydrate was mixed with 200 g of ethylene glycol. Liquid A was heated to 85°C, Liquid B to 50°C, and Liquid C to 90°C. Solutions A and B were added dropwise to Liquid C over 5 minutes, and then allowed to stand for another 10 minutes. The reaction liquid was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined in air at 70°C for one hour and at 300°C for four hours to obtain the metal material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and contains Ir as crystal grains on the surface of the metal particles.

[0045] Example 7 To prepare solution A, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were dissolved in 200 g of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). Solution B was prepared by dissolving 12.95 g (25 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. To prepare solution C, 10.00 g (200 mmol) of hydrazine monohydrate and 2.12 g (56 mmol) of sodium borohydride were mixed with 200 g of water. The mixture was heated to 85°C for liquid A, 50°C for liquid B, and 80°C for liquid C. Solutions A and B were added dropwise to solution C over 5 minutes, and then allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water for dilution. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined in air at 70°C for 1 hour and at 300°C for 4 hours to obtain the metal material of the present invention. It has been confirmed that the metal material of the present invention contains Cr, Mn, Fe, Co, and Ni as metal elements in the core, and Pt as crystal grains on the surface of the metal particles.

[0046] Comparative Example 1 As solution A, 29.75 g (125 mmol) of nickel chloride hexahydrate was dissolved in 200 g of water. Solution B was prepared by dissolving 12.82 g (25 mmol) of chloroplatinic acid hexahydrate in 100 g of ethanol. To prepare Solution C, 9.66 parts by mass (256 mmol) of hydrazine monohydrate was dissolved in 200 g of water. Solution A heated to 90°C and solution B at room temperature were added dropwise to solution C heated to 90°C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined in air at 70°C for one hour and at 300°C for four hours to obtain a metal material. In the metallic material, the core contains Ni as a metallic element, but no crystal grains were observed.

[0047] Comparative Example 2 To prepare solution A, 6.65 g (25 mmol) of chromium(III) chloride hexahydrate, 4.95 g (25 mmol) of manganese(II) chloride tetrahydrate, 4.95 g (25 mmol) of iron(II) chloride tetrahydrate, 5.95 g (25 mmol) of cobalt chloride hexahydrate, and 5.95 g (25 mmol) of nickel chloride hexahydrate were dissolved in 200 g of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt chloride hexahydrate:nickel chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%). As solution B, 10.30 g (25 mmol) of tetrachloroauric acid tetrahydrate was dissolved in 100 g of ethanol. Solution C was prepared by dissolving 9.66 parts by mass (256 mmol) of sodium borohydride in 200 g of water. Solutions A and B were added dropwise to Solution C over 15 minutes, and then allowed to stand for another 10 minutes. The reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was collected by filtration using a PTFE filter (T100A090C), washed three times with water and three times with methanol, and calcined in air at 70°C for one hour and at 300°C for four hours to obtain a metal material. In the metallic material, the core contains the metallic elements Cr, Mn, Fe, Co, and Ni, but the formation of Au crystal grains could not be confirmed.

[0048] The mole fractions of the elements in the metal materials of Examples 1 to 7 and Comparative Examples 1 and 2, as well as the evaluation results, are shown in Tables 1 and 2.

[0049] [Table 1]

[0050] [Table 2]

[0051] The metal materials of Examples 1 to 7 comprised a core containing two or more metal elements and crystal grains containing one or more metal elements, the metal elements contained in the crystal grains having a standard electrode potential (25°C, 1 atm) of greater than 0 V and less than or equal to 1.50 V, and the crystal grains constituted at least a portion of the surface of the metal particles. In particular, the metal materials of Examples 2 and 3 had a core containing a total of seven metal elements, Cr, Fe, Co, Ni, Mn, and further Zn and Zr, which were randomly distributed in a single, stabilized state as a solid solution, resulting in a large ΔS. In the metal composite material of Comparative Example 1, the core metal element was only nickel, so the nickel formed an alloy with platinum during the reduction reaction, and platinum crystal grains were not formed. In Comparative Example 2, the standard electrode potential of gold (standard electrode potential 1.52 V) was too high, so the gold that would become crystal grains was reduced too quickly and separated as coarse particles.

Claims

1. The core contains two or more metal elements and crystal grains contain one or more metal elements, the metal element contained in the crystal grains is a metal element having a standard electrode potential (25°C, 1 atm) of more than 0 V and not more than 1.50 V, A metallic material characterized in that the crystal grains constitute at least a part of the surface of a metallic particle.

2. 2. The metallic material according to claim 1, wherein the core containing a metallic element contains two or more metallic elements selected from the group consisting of Cr, Fe, Co, Ni, and Mn.

3. 3. The metallic material according to claim 1, wherein the crystal grains containing a metallic element contain a noble metal.

4. 3. The metallic material according to claim 1, wherein the crystal grains containing a metal element contain platinum.

5. A catalyst comprising the metallic material according to claim 1 or 2.

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