Metal nanomaterials with high specific surface area

Abstract

The present invention provides a metal nanomaterial having a higher specific surface area than conventional metal nanomaterials. The present invention relates to a metal nanomaterial having a specific surface area of 60 m 2 / g or more by the nitrogen gas adsorption method.

Description

Technical Field

[0001] The present invention relates to a metal nanomaterial having a high specific surface area.

Background Art

[0002] Metal nanomaterials are used as catalysts for various reactions. In order to be used as a catalyst for various reactions, it is required to have a high specific surface area.

[0003] As nanomaterials having a high specific surface area, Non-Patent Document 1 discloses a metal nanoporous material made of a high-entropy alloy of TiVNbMoTa produced by a de-composition method from a precursor alloy, having a specific surface area of 3.6 to 55.7 m 2 / g. Further, Patent Document 1 discloses metal nanowires produced by reducing metal ions in an aqueous solution of carboxymethyl cellulose salt, having a specific surface area of 16 to 57 m 2 / g. However, the specific surface area of the materials described in any of the documents was less than 60 m 2 / g.

[0004] In recent years, high-entropy alloys have attracted attention as catalysts for various reactions. For example, Non-Patent Document 2 discloses a method for improving the catalytic activity by increasing the specific surface area of a high-entropy alloy powder by an etching treatment. However, the specific surface area of the high-entropy alloy described in Non-Patent Document 2 was insufficient at 9 m 2 / g at most.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] The present invention solves the above problems and aims to provide a metal nanomaterial having a higher specific surface area than conventional metal nanomaterials. [Means for Solving the Problems]

[0008] As a result of intensive studies, the present inventors have found that by mixing four or more types of metal ions in a specific molar ratio and performing a liquid - phase reduction reaction using a reducing agent, the above object can be achieved, and thus the present invention has been reached.

[0009] The gist of the present invention is as follows. <1> A metal nanomaterial having a specific surface area of 60 m 2 / g or more by the nitrogen gas adsorption method. <2> Containing four or more types of metal elements, When the total content (molar ratio) of all metal elements constituting the metal nanomaterial is 100 mol%, the content (molar ratio) of each of the top four metal elements with a higher content is 5 - 50 mol%. The metal nanomaterial according to <1>. <3> The metal nanomaterial according to <2>, wherein the content (molar ratio) of each of the top four metal elements is 10 - 45 mol%. <4> The metal nanomaterial according to <2> or <3>, wherein the metal nanomaterial contains at least one metal element among iron, cobalt, and nickel. <5> The metal nanomaterial according to any one of <2> to <4>, wherein the metal nanomaterial contains iron, cobalt, and nickel. <6> Among the metal elements contained in the metal nanomaterial, the content (molar ratio) of each metal element other than the top four metal elements is 25 mol% or less when the total content of all metal elements constituting the metal nanomaterial is 100 mol%. The metal nanomaterial according to any one of <2> to <5>. <7> The metal nanomaterial contains four or more metal elements selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium, and platinum. The metal nanomaterial according to any one of <2> to <6>. <8> The specific surface area is 100 m 2 / g or more, The total content (molar ratio) of chromium, iron, cobalt, zirconium, and lanthanum contained in the metal nanomaterial is 80 mol% or less. The metal nanomaterial according to any one of <2> to <7>. <9> The specific surface area is 150 m 2 / g or more. The metal nanomaterial according to <8>. <10> The content of boron is 3 parts by mass or more with respect to 100 parts by mass of the metal nanomaterial. The metal nanomaterial according to any one of <2> to <9>. <11> The specific surface area is 100 m 2 / g or more. The metal nanomaterial according to any one of <1> to <10>. <12> The loss on ignition is 0.1 mass% or less. The metal nanomaterial according to any one of <1> to <11>. <13> The metal nanomaterial has a form of nanoparticles, a form of microparticles formed by binding or aggregating the nanoparticles, or a composite form thereof. The metal nanomaterial according to any one of <1> to <12>. <14> A method for producing a metal nanomaterial, which comprises mixing and dissolving four or more metal salts, and performing a liquid-phase reduction reaction using a reducing agent to produce the metal nanomaterial according to any one of <1> to <13>. <15> The method for producing a metal nanomaterial according to <14>, wherein a reducing agent containing a boron atom is used as the reducing agent.

Advantages of the Invention

[0010] According to the present invention, a metal nanomaterial having a higher specific surface area than conventional nanomaterials can be provided. The metal nanomaterial of the present invention can be suitably used as a catalyst for reactions such as hydrogen generation, hydrogenation, ammonia generation, etc., and as an electrode catalyst for fuel cells.

Brief Description of the Drawings

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Modes for Carrying Out the Invention

[0012] [Metal Nanomaterial] The metal nanomaterial of the present invention preferably is an alloy containing four or more metal elements and having no main component, and more preferably is a high-entropy alloy containing five or more metal elements and having no main component. "Having no main component" means that no metal element (or there is no metal element) having a content exceeding 50 mol% (particularly 45 mol% or more) with respect to the total content of all metal elements constituting the metal nanomaterial. Further, since the obtained metal nanomaterial is likely to have a higher specific surface area, the metal nanomaterial preferably contains four or more metal elements including at least one metal element among iron, cobalt, and nickel, more preferably contains four or more metal elements including iron and nickel, and even more preferably contains four or more metal elements including iron, cobalt, and nickel.

[0013] In the present invention, the metal elements that can be contained in the metal nanomaterial refer to lithium and beryllium in the second period of the periodic table, sodium, magnesium, and aluminum in the third period, potassium to gallium in the fourth period, rubidium to tin in the fifth period, cesium to polonium in the sixth period, francium to hassium, copernicium, and flerovium in the seventh period. The periodic table is a long-period type periodic table. For example, potassium to gallium in the fourth period includes all elements from atomic number 19 (potassium) to atomic number 31 (gallium) in the arrangement (or sequence) in the periodic table.

[0014] In the present invention, as metal elements other than iron, cobalt, and nickel that can be contained in the metal nanomaterial, from the viewpoint of further increasing the specific surface area and further improving the catalytic activity, chromium, manganese, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium, and platinum are preferable, and chromium, manganese, copper, zinc, zirconium, and yttrium are more preferable. Note that the metal nanomaterial of the present invention may contain a non-metal element or a semi-metal element (for example, boron), and the metal element contained in the metal nanomaterial may be oxidized. The metal nanomaterial of the present invention may be excluded from the metal nanomaterial supported on a carrier such as a carbon material such as graphene or carbon fiber, or an inorganic material such as alumina or zirconia.

[0015] In the metal nanomaterial of the present invention, the content (molar ratio) of each of the top four metal elements with a higher content (simply referred to as the "top four metal elements") is usually 5 to 50 mol% when the total of all metal elements is 100 mol%. From the viewpoint of further increasing the specific surface area and further improving the catalytic activity, it is preferably 5 to 45 mol%, more preferably 10 to 45 mol%, even more preferably 10 to 35 mol%, particularly preferably 10 to 30 mol%, and sufficiently preferably 10 to 25 mol%. If the molar ratio is less than 5 mol% for one type of metal element or exceeds 50 mol% for one type of metal element, the specific surface area of the obtained metal nanomaterial will not be sufficiently large, and when used as a catalyst, the performance will be inferior, which is not preferable.

[0016] In this specification, the content (molar ratio) of the metal element in the metal nanomaterial is the value when the total of all metal elements is 100 mol%, and specifically, it is the content (or ratio) with respect to the total content (100 mol%) of all metal elements constituting the metal nanomaterial. The content (molar ratio) of the metal element in the metal nanomaterial uses the value calculated from the value measured by the ICP - AES method. The content (molar ratio) of the metal element in the metal nanomaterial can be rounded to an integer value after rounding off the decimal part.

[0017] From the perspective of further increasing the specific surface area, the top four metal elements preferably include at least one metal element among iron, cobalt, and nickel, and more preferably include iron, cobalt, and nickel. When there are n or more (n is an integer of 2 or more (for example, 2)) metal elements with the fourth highest content among the top four metal elements, the top four metal elements may be "3 + n" types (for example, 5 types) of metal elements including all of the n or more metal elements.

[0018] Among the metal elements contained in the metal nanomaterial of the present invention, the content (molar ratio) of each metal element other than the top four metal elements is not particularly limited. When the total of all metal elements is 100 mol%, it is usually 25 mol% or less (especially 0.1 to 25 mol%). From the perspective of further increasing the specific surface area and further improving the catalytic activity, it is preferably 0.5 to 25 mol%, more preferably 0.5 to 20 mol%, and still more preferably 1 to 15 mol%.

[0019] The total content (molar ratio) of chromium, iron, cobalt, zirconium, and lanthanum contained in the metal nanomaterial of the present invention is usually 90 mol% or less. From the perspective of further increasing the specific surface area and further improving the catalytic activity, it is preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less, and particularly preferably 50 mol% or less. The lower limit value of the total content is not particularly limited. For example, the total content may be 10 mol% or more. From the perspective of further increasing the surface area and further improving the catalytic activity, it is preferably 20 mol% or more, more preferably 30 mol% or more, and still more preferably 40 mol% or more.

[0020] The number of types of metal elements contained in the metal nanomaterial of the present invention is usually 4 or more as described above. For example, it may be 4 to 20 types. From the viewpoint of further increasing the specific surface area and further improving the catalytic activity, it is preferably 4 to 12 types, more preferably 4 to 10 types, still more preferably 5 to 9 types, and particularly preferably 5 to 8 types. The metal elements recognized as being contained in the metal nanomaterial of the present invention are those whose content rate measured by the ICP-AES method is 0.1% by mass or more (particularly 0.5% by mass or more) based on 100% by mass of the metal nanomaterial.

[0021] The specific surface area of the metal nanomaterial of the present invention is desirably high because it affects the activity of the catalyst, and it is necessary to be 60 m 2 / g or more, preferably 85 m 2 / g or more, more preferably 90 m 2 / g or more, still more preferably 100 m 2 / g or more, particularly preferably 130 m 2 / g or more, most preferably 150 m 2 / g or more, sufficiently preferably 170 m 2 / g or more, more sufficiently preferably 200 m 2 / g or more, even more sufficiently preferably 250 m 2 / g or more. When the specific surface area is less than 60 m 2 / g, it is not preferable because the performance is inferior when used as a catalyst. The upper limit value of the specific surface area is not particularly limited. For example, the specific surface area may be 500 m 2 / g or less (particularly 400 m 2 / g or less).

[0022] The metal nanomaterial of the present invention preferably has a reaction rate of 90% or more in the first reaction as a hydrogenation reaction catalyst, more preferably 95% or more. The reaction rate in the fifth reaction is preferably 70% or more, more preferably 90% or more. Also, in the catalytic activity evaluation (evaluation over time) described in the evaluation method described later, the reaction rate after 5 minutes is preferably 70% or more, more preferably 90% or more.

[0023] In this specification, the reaction rate as a hydrogenation reaction catalyst is based on the reduction rate of the absorbance at a wavelength of 400 nm from the initial value in the hydrogenation reaction of p-nitrophenol with sodium borohydride.

[0024] In the metal nanomaterial of the present invention, boron, a semi-metal element, can be contained. Boron is contained in the metal nanomaterial depending on the production method. From the viewpoint of further increasing the specific surface area and further improving the catalytic activity, the content of boron is preferably 3 parts by mass or more, more preferably 4 parts by mass or more, and still more preferably 5 parts by mass or more with respect to 100 parts by mass of the metal nanomaterial. The upper limit value of the boron content is not particularly limited. For example, the boron content is preferably 10 parts by mass or less, more preferably 9 parts by mass or less. By containing boron, it may generally become more corrosion-resistant. In the definition of the boron content, 100 parts by mass of the metal nanomaterial means 100 parts by mass of the total mass of the metal nanomaterial. Therefore, the boron content is the ratio with respect to the entire metal nanomaterial containing boron.

[0025] The metal nanomaterial of the present invention refers to nanoparticles having a particle size of about several tens of nm (particularly 10 to 100 nm). These nanoparticles may further be aggregates of finer nanosheets. Also, since it may be difficult to handle nanoparticles, the units of the nanoparticles can be further combined or aggregated to be processed into powders or particles having a particle size of micro size or more (particularly 1 to 100 μm). By processing to a size of about several tens of μm, recovery with a filter or the like becomes easy while maintaining gas diffusion and permeability, and it becomes easy to handle as a catalyst. The metal nanomaterial may have porosity. Therefore, the microparticles formed by bonding or aggregating the nanoparticles may have porosity, or the nanoparticles themselves may have porosity.

[0026] In this specification, for independent particles, the particle size refers to the maximum length of the particle, and for particles linearly bonded, it refers to the diameter of the portion with the maximum thickness. When the particles are aggregated to form a porous body, the ligament size can be used as the particle size. The particle size uses the value measured by the following method. The obtained product was vacuum dried and photographed at 100,000 times magnification using a scanning electron microscope (SEM). The particle sizes of the nanomaterials were measured at 100 arbitrary points in 10 fields of view, and the average value was calculated.

[0027] Since the metal nanomaterial of the present invention usually has no coating (especially an organic coating) on its surface, the loss on ignition is 0.1 mass% or less (especially 0.01 mass% or less).

[0028] The loss on ignition is the ratio of the mass reduced by firing to the mass before firing, and the value measured by the following method is used. The obtained metal nanomaterial was degassed at 200 °C for 30 minutes in a vacuum state, and the mass was measured. This value was taken as the mass before firing. Further, the metal nanomaterial was fired at 800 °C for 4 hours in a vacuum state, and the mass was measured. The loss on ignition was calculated by dividing the mass reduced from before firing by the mass before firing.

[0029] [Method for Producing Metal Nanomaterial] The metal nanomaterial of the present invention can be obtained, for example, by mixing and dissolving four or more types of metal salts and performing a liquid-phase reduction reaction using a reducing agent. The compounding amount (molar ratio) of the metal salts in the method for producing the metal nanomaterial is usually directly reflected in the content (molar ratio) of the metal elements in the metal nanomaterial. Therefore, the types and compounding amounts (molar ratios) of the four or more types of metal salts used may be determined based on the types and contents (molar ratios) of the metal elements constituting the above-described metal nanomaterial. For example, the description of the four or more types of metal salts and their compounding amounts (molar ratios) can be obtained by replacing "metal element" and "content" with "metal salt" and "compounding amount" respectively (especially by replacing "total content (100 mol%) of all metal elements constituting the metal nanomaterial" with "total compounding amount (100 mol%) of all metal salts"), and applying the description of the metal elements constituting the above-described metal nanomaterial and their contents.

[0030] The metal salt can be converted into metal ions by dissolving it in a solvent such as water. The shape of the metal salt is not particularly limited as long as it can be dissolved in the reaction solvent used and supply metal ions in a reducible state.

[0031] The metal salt is not particularly limited as long as it can be dissolved in the solvent. For example, chlorides, nitrates, sulfates, acetates, etc. of the above-described metal elements may be used.

[0032] The concentration of each metal ion in the reaction solution is preferably 5 to 1000 mmol / L. Since the yield of the obtained metal nanomaterial is improved and the specific surface area tends to be large, it is more preferably 30 to 300 mmol / L, and even more preferably 50 to 200 mmol / L.

[0033] The reducing agent is not particularly limited, and 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 can be used. Among them, from the viewpoint of further increasing the specific surface area and further improving the catalytic activity in metal nanomaterials, 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. On the other hand, in the case of amines and organic acids, the excess reducing agent coordinates to the metal nanoparticles and forms a film of amine or organic acid, which may seal the active sites of the catalyst and may not be usable depending on the use of the catalyst.

[0034] The concentration of the reducing agent in the reaction solution is not particularly limited, but it is preferably 50 to 2000 mmol / L, more preferably 100 to 1500 mmol / L, and even more preferably 200 to 1200 mmol / L. When the concentration of the reducing agent is less than 50 mmol / L, the reduction reaction may not proceed sufficiently. When the concentration of the reducing agent exceeds 2000 mmol / L, rapid foaming may occur due to the progress of the reduction reaction, and the reaction may not occur uniformly.

[0035] The reaction solvent is not particularly limited as long as the metal ions and the reducing agent can be dissolved. However, water is preferable because the specific surface area of the obtained metal nanomaterial becomes sufficiently large and the performance is improved when used as a catalyst.

[0036] The temperature at which the reduction reaction is carried out is not particularly limited, but a temperature from room temperature to the boiling point of the solvent is preferable, and it is more preferable to carry out the reaction at room temperature from the viewpoint of simplicity.

[0037] The time of the reduction reaction is not particularly limited as long as the metal nanomaterial can be produced, but it is preferably 1 minute to 1 hour.

[0038] The reduction reaction may or may not be carried out in a magnetic field.

[0039] After the reduction reaction, the metal nanomaterial can be obtained by purification and recovery through centrifugation, filtration, etc.

[0040] The metal nanomaterial of the present invention can be suitably used as a catalyst for reactions such as hydrogen generation, hydrogenation, ammonia generation, etc. and as an electrode catalyst for fuel cells.

Examples

[0041] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. The evaluation of the metal nanomaterial was carried out by the following method.

[0042] (1) Molar ratio of metal elements and (2) boron content After the obtained metal nanomaterial was vacuum-dried, the content ratios of the metal elements and boron were determined by the ICP-AES method using the metal nanomaterial. Then, with the total amount of all metal elements being 100 mol%, the molar ratio of each metal element was calculated.

[0043] (3) Specific surface area After the obtained metal nanomaterial was vacuum-dried, it was further degassed at 200 °C for 30 minutes in a vacuum state. Using the degassed metal nanomaterial, the adsorption amount of nitrogen gas was measured by the nitrogen gas adsorption method, and the specific surface area was calculated from the adsorption amount by the BET equation. The specific surface area was evaluated according to the following criteria. ◎: 100 m 2 / g or more ○: 85 m 2 / g or more and less than 100 m 2 / g △: 60 m 2 / g or more and less than 85 m 2 / g ×: Less than 60 m 2 / g

[0044] (4) Catalytic activity evaluation (repeated evaluation) After vacuum drying the obtained metal nanomaterial, following the method of Non-Patent Document 2, the catalytic activity was evaluated by the following method. To 10 mg of the metal nanomaterial, 7 mL of water, 1 mL of an aqueous solution of p-nitrophenol (1.4 mmol / L), and 1 mL of sodium borohydride (0.42 mol / L) were added, and the mixture was stirred for 5 minutes. After separating the catalyst and the reaction solution by centrifugation, the supernatant was collected and filtered through a 0.45-μm syringe filter. The absorbance of the obtained solution at 400 nm was measured, and the reaction rate was calculated based on the decrease rate from the initial value.

[0045] The catalyst durability was evaluated by repeated measurement. To the catalyst separated in the above step, 7 mL of water, 1 mL of an aqueous solution of p-nitrophenol (1.4 mmol / L), and 1 mL of sodium borohydride (0.42 mol / L) were newly added, and the mixture was stirred for 5 minutes. After separating the catalyst and the reaction solution by centrifugation, the supernatant was collected and filtered through a 0.45-μm syringe filter. The absorbance of the obtained solution at 400 nm was measured, and the reaction rate was calculated based on the decrease rate from the initial value. By repeating this step, the reaction rate after 5 reactions was calculated. The catalytic activity was evaluated according to the following criteria for the reaction rate of the "fifth time". ◎: The reaction rate was 90% or more; ○: The reaction rate was 60% or more and less than 90%; △: The reaction rate was 40% or more and less than 60%; ×: The reaction rate was less than 40%.

[0046] (6) Particle size The obtained product (metal nanomaterial) was vacuum dried and photographed at 100,000 times using a scanning electron microscope (SEM). The particle sizes of the nanomaterials were measured at 100 arbitrary points in 10 fields of view, and the average value was calculated.

[0047] Example 1 6.65 parts by mass (25 mol parts) of chromium(III) chloride hexahydrate, 4.95 parts by mass (25 mol parts) of manganese(II) chloride tetrahydrate, 4.95 parts by mass (25 mol parts) of iron(II) chloride tetrahydrate, 5.95 parts by mass (25 mol parts) of cobalt(II) chloride hexahydrate, 5.95 parts by mass (25 mol parts) of nickel(II) chloride hexahydrate were dissolved in 200 parts by mass of water (chromium(III) chloride hexahydrate:manganese(II) chloride tetrahydrate:iron(II) chloride tetrahydrate:cobalt(II) chloride hexahydrate:nickel(II) chloride hexahydrate = 20 mol%:20 mol%:20 mol%:20 mol%:20 mol%), and bubbling of nitrogen gas was started. After 10 minutes from the start of bubbling, dropping of an aqueous solution in which 8.05 parts by mass (213 mol parts) of sodium borohydride was dissolved in 200 parts by mass of water was started. After dropping over 15 minutes, it was left standing for another 10 minutes. The concentrations of chromium(III) ions, manganese(II) ions, iron(II) ions, cobalt ions, and nickel ions in the reaction solution were all 63 mmol / L, and the concentration of the reducing agent was 533 mmol / L. Bubbling of nitrogen gas was stopped, and the reaction solution was poured into 200 parts by mass of water and diluted. The resulting black solid was filtered and recovered using a PTFE filter of "T100A090C", washed three times each with water and methanol, and vacuum dried at room temperature for 24 hours to obtain a metal nanomaterial (NM).

[0048] Examples 2 to 16 and Comparative Examples 4 and 5 (Examples 8-9 and 16: Reference Examples) Except that the types and amounts (mol parts) of the raw materials were changed to the values described in Table 1, the same operations as in Example 1 were carried out to obtain each metal nanomaterial (NM).

[0049]

Table 1

[0050] Comparative Example 1 0.59 parts by mass (2.48 mole parts) of nickel(II) chloride hexahydrate, 0.28 parts by mass (0.93 mole parts) of trisodium citrate dihydrate, 0.29 parts by mass (0.0050 mole parts) of chloroplatinic acid hexahydrate, and 0.75 parts by mass of Serogen BSH-6 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were dissolved in water. Further, a 5% aqueous sodium hydroxide solution was added dropwise to adjust the pH to 11.5, and water was added so that the total amount became 75 parts by mass to prepare a nickel ion solution. On the other hand, 1.25 parts by mass (25.0 mole parts) of hydrazine monohydrate was mixed with water, and further, a 5% aqueous sodium hydroxide solution was added dropwise to adjust the pH to 11.5, and water was added so that the total amount became 25 parts by mass to prepare a reducing agent solution. After heating both the nickel ion solution and the reducing agent solution to 80 - 85 °C, they were mixed while maintaining the temperature, a magnetic field of 100 mT was applied, and a reduction reaction was carried out for 20 minutes. Then, after filtration and recovery using a PTFE filter of T100A090C, they were washed three times each with water and methanol, and vacuum dried at room temperature for 24 hours to obtain a metal nanomaterial (nanowire, NW).

[0051] Comparative Example 2 8.55 parts by mass (43 mole parts) of iron(II) chloride tetrahydrate was dissolved in 300 parts by mass of water, placed in a magnetic circuit with a central magnetic field of 130 mT, and nitrogen gas bubbling was started. After 10 minutes from the start of bubbling, the dropping of an aqueous solution prepared by dissolving 7.00 parts by mass (185 mole parts) of sodium borohydride in 175 parts by mass of water was started. After dropping over 15 minutes, it was left standing for another 10 minutes. The concentration of iron ions in the reaction solution was 91 mmol / L, and the concentration of the reducing agent was 389 mmol / L. Thereafter, the application of the magnetic field and the nitrogen gas bubbling were stopped, and the reaction solution was poured into 200 parts by mass of water and diluted. The resulting black nanowires were filtered and recovered using a PTFE filter of T100A090C, washed three times each with water and methanol, and vacuum dried at room temperature for 24 hours to obtain a metal nanomaterial (nanowire, NW).

[0052] Comparative Example 3 2.85 parts by mass (14 mol parts) of iron(II) chloride tetrahydrate, 3.31 parts by mass (14 mol parts) of cobalt(II) chloride hexahydrate, and 3.31 parts by mass (14 mol parts) of nickel(II) chloride hexahydrate were dissolved in 300 parts by mass of water, placed in a magnetic circuit with a central magnetic field of 130 mT, and nitrogen gas bubbling was started. After 10 minutes from the start of bubbling, the dropping of an aqueous solution in which 7.00 parts by mass (185 mol parts) of sodium borohydride was dissolved in 175 parts by mass of water was started. After dropping over 15 minutes, it was left standing for another 10 minutes. The concentrations of iron(II) ions, cobalt ions, and nickel ions in the reaction solution were each 30 mmol / L, and the concentration of the reducing agent was 389 mmol / L. Thereafter, the same operations as in Comparative Example 2 were carried out, followed by filtration, washing, and drying to obtain a metal nanomaterial (nanowire, NW).

[0053] Comparative Example 6 The same method as in Example 1 was carried out except that 10.7 parts by mass (213 mol parts) of hydrazine monohydrate was used instead of sodium borohydride, but the reduction reaction did not proceed and no metal nanomaterial was obtained.

[0054] Comparative Example 7 The same method as in Example 1 was carried out except that 22.6 parts by mass (213 mol parts) of sodium hypophosphite monohydrate was used instead of sodium borohydride, but the reduction reaction did not proceed and no metal nanomaterial was obtained.

[0055] Reference Example 1 The data described in Non-Patent Document 2 was cited. The method for producing the catalyst in Reference Example 1 in Non-Patent Document 2 is as follows. 20 parts by mass of a high-entropy alloy powder (particle size of about 20 μm) having an equimolar composition of CrMnFeCoNi purchased from Nanjing Mingchang New Material Technology Co., Ltd and 35 parts by mass of 98% sulfuric acid were added to 600 parts by mass of water, and stirred at 25 °C for 72 hours. The obtained solid was recovered by filtration and vacuum dried at 40 °C for 1 hour to obtain the catalyst of Reference Example 1. The specific surface area of the obtained catalyst was 9 m 2 / g.

[0056] Table 2 shows the production conditions, compositions, and evaluation results of the metal nanomaterials of Examples 1 to 16 and Comparative Examples 1 to 6.

[0057] [Table 2]

[0058] The metal nanomaterials of Examples 1 to 16 were prepared by mixing four or more metal ions with the molar ratios of the top four metal elements with higher contents (molar ratios) all being 5 to 50 mol% and performing a liquid-phase reduction reaction using a reducing agent. Therefore, the specific surface area was sufficiently large at 60 m 2 / g or more, and the catalytic activity was also high.

[0059] In the metal nanomaterial of Comparative Example 5, aluminum was not reduced.

[0060] The metal nanomaterials obtained in Examples 1 to 16 had a loss on ignition of 0.01 mass% or less.

[0061] The SEM image of the metal nanomaterial of Example 2 is shown in FIG. 1. From FIG. 1, it was revealed that the metal nanomaterial of Example 2 had a form in which countless nanoparticles were bonded (or aggregated).

[0062] The enlarged image of the SEM image of the metal nanomaterial of Example 2, as well as the mapping images (EDS) of chromium element, iron element, cobalt element, nickel element, and copper element are shown in FIGS. 2 to 7, respectively, and the image obtained by overlapping the mappings of these respective elements is shown in FIG. 8. From FIGS. 2 to 8, it was revealed that the metal nanomaterial of Example 2 uniformly contained each metal element within a single particle.

Industrial Applicability

[0063] The metal nanomaterial of the present invention is useful as a catalyst for reactions such as hydrogen generation, hydrogenation, ammonia generation, etc. and an electrode catalyst for fuel cells.

Claims

1. Specific surface area by nitrogen gas adsorption method is 60 m ２ / g or more, a metal nanomaterial, comprising four or more types of metal elements, wherein when the total content of all metal elements constituting the metal nanomaterial is 100 mol%, the content (molar ratio) of each of the top four metal elements with a higher content is 5 to 50 mol%, a metal nanomaterial.

2. The metal nanomaterial according to claim 1, wherein the content (molar ratio) of each of the top four metal elements is 10 to 45 mol%.

3. The metal nanomaterial according to claim 1, wherein the metal nanomaterial contains at least one metal element among iron, cobalt, and nickel.

4. The metal nanomaterial according to claim 1, wherein the metal nanomaterial contains iron, cobalt, and nickel.

5. Among the metal elements contained in the metal nanomaterial, when the total content of all metal elements constituting the metal nanomaterial is 100 mol%, the content (molar ratio) of each metal element other than the top four metal elements is 25 mol% or less, the metal nanomaterial according to claim 1.

6. The metal nanomaterial according to claim 1, wherein the metal nanomaterial contains four or more metal elements selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium, and platinum.

7. The specific surface area is 100 m ２ / g or more, The metal nanomaterial according to claim 1, wherein the total content (molar ratio) of chromium, iron, cobalt, zirconium, and lanthanum contained in the metal nanomaterial is 80 mol% or less.

8. The specific surface area is 150 m ２ / g or more, the metal nanomaterial according to claim 7.

9. The content of boron is 3 parts by mass or more with respect to 100 parts by mass of the metal nanomaterial, the metal nanomaterial according to claim 1.

10. The specific surface area is 100 m ２ / g or more, the metal nanomaterial according to claim 1.

11. The firing loss is 0.1% by mass or less, the metal nanomaterial according to claim 1.

12. The metal nanomaterial has a form of nanoparticles, a form of microparticles formed by binding or aggregating the nanoparticles, or a composite form thereof, the metal nanomaterial according to claim 1.

13. A method for producing a metal nanomaterial, comprising mixing and dissolving four or more types of metal salts, and performing a liquid-phase reduction reaction using a reducing agent to produce the metal nanomaterial according to any one of claims 1 to 12.

14. The method for producing a metal nanomaterial according to claim 13, wherein a reducing agent containing boron atoms is used as the reducing agent.

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