Metallic nanomaterial with high specific surface area

Abstract

To provide a metallic nanomaterial with a higher specific surface area than that of conventional metallic nanomaterials.SOLUTION: The metallic nanomaterial of the present invention has a specific surface area of 60 m2 / g or more, as determined by the nitrogen gas adsorption method.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Metal nanomaterials are used as catalysts for various reactions, and in order to be used as catalysts for various reactions, they are required to have a large specific surface area.

[0003] As an example of a nanomaterial with a high specific surface area, Non-Patent Document 1 describes a high-entropy alloy of TiVNbMoTa produced by a dealloying method from a precursor alloy, with a specific surface area of ​​3.6 to 55.7 m. 2 Patent Document 1 also discloses a metal nanoporous material having a specific surface area of ​​16 to 57 m2 produced by reducing metal ions in an aqueous solution of carboxymethyl cellulose salt. 2 / g of metal nanowires are disclosed. However, the specific surface area of ​​the materials described in each document is less than 60 m 2 / g.

[0004] In recent years, high-entropy alloys have been attracting attention as catalysts for various reactions. For example, Non-Patent Document 2 discloses a method for improving catalytic activity by increasing the specific surface area of ​​high-entropy alloy powder through etching treatment. However, the specific surface area of ​​the high-entropy alloy described in Non-Patent Document 2 is only 9 m 2 / g, which was insufficient. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 062090 Brochure [Non-patent literature]

[0006] [Non-Patent Document 1] Advanced Materials 2019,1906160 [Non-Patent Document 2] Journal of Materials Chemistry A 2020,18318. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is intended to solve the above-mentioned problems, and has an object to provide a metal nanomaterial having a higher specific surface area than conventional metal nanomaterials. [Means for solving the problem]

[0008] As a result of extensive research, the inventors discovered that the above object can be achieved by mixing four or more types of metal ions in a specific molar ratio and carrying out a liquid phase reduction reaction using a reducing agent, and thus arrived at the present invention.

[0009] The gist of the present invention is as follows. <1> The specific surface area measured by nitrogen gas adsorption is 60m 2 / g or more of a metal nanomaterial. <2> Contains four or more metal elements, When the total content of all metal elements constituting the metal nanomaterial is taken as 100 mol %, the content (molar ratio) of each of the top four metal elements having the highest content (molar ratio) is 5 to 50 mol %. <1> The metal nanomaterial described in <3> The content (molar ratio) of each of the top four metal elements is 10 to 45 mol %. <2> The metal nanomaterial described in <4> The metal nanomaterial comprises at least one metal element selected from the group consisting of iron, cobalt, and nickel; <2> or <3> The metal nanomaterial described in <5> The metal nanomaterials include iron, cobalt, and nickel; <2> ~ <4> 2. The metal nanomaterial according to claim 1 . <6> Among the metal elements contained in the metal nanomaterial, the content (molar ratio) of each of the metal elements 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%. <2> ~ <5> 2. The metal nanomaterial according to claim 1 . <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; <2> ~ <6> 2. The metal nanomaterial according to claim 1 . <8> The specific surface area is 100m 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; <2> ~ <7> 2. The metal nanomaterial according to claim 1 . <9> The specific surface area is 150m 2 / g or more, <8> The metal nanomaterial described in <10> The content of boron is 3 parts by mass or more relative to 100 parts by mass of the metal nanomaterial. <2> ~ <9> 2. The metal nanomaterial according to claim 1 . <11> The specific surface area is 100m 2 / g or more, <1> ~ <10> 2. The metal nanomaterial according to claim 1 . <12> Loss on firing is 0.1% by mass or less; <1> ~ <11> 2. The metal nanomaterial according to claim 1 . <13> The metal nanomaterial has a nanoparticle form, a microparticle form formed by bonding or aggregating the nanoparticles, or a composite form thereof. <1> ~ <12> 2. The metal nanomaterial according to claim 1 . <14> Four or more kinds of metal salts are mixed and dissolved, and a liquid phase reduction reaction is carried out using a reducing agent. <1> ~ <13> 13. A method for producing a metallic nanomaterial, comprising the steps of: producing the metallic nanomaterial according to any one of the preceding claims. <15> A reducing agent containing a boron atom is used as the reducing agent. <14> A method for producing a metal nanomaterial according to claim 1. Effect of the Invention

[0010] According to the present invention, it is possible to provide a metal nanomaterial having a higher specific surface area than conventional nanomaterials. The metallic nanomaterial of the present invention can be suitably used as a catalyst for reactions such as hydrogen production, hydrogenation, and ammonia production, and as an electrode catalyst for fuel cells. [Brief description of the drawings]

[0011] [Figure 1] 1 is a SEM image of Example 2. [Diagram 2] 1 is an enlarged SEM image of Example 2. [Diagram 3] 1 is a mapping image (EDS) of chromium element in Example 2. [Figure 4] 1 is a mapping image (EDS) of iron element in Example 2. [Diagram 5] 1 is a mapping image (EDS) of cobalt element in Example 2. [Figure 6] 1 is a mapping image (EDS) of nickel element in Example 2. [Figure 7] 1 is a mapping image (EDS) of copper element in Example 2. [Figure 8] 1 is an image in which mapping of each element is superimposed on the electron beam image of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Metal nanomaterials] The metal nanomaterial of the present invention is preferably an alloy containing four or more metal elements and no main component, and more preferably a high-entropy alloy containing five or more metal elements and no main component. "No main component" means that no metal element is contained (or does not exist) with a content of more than 50 mol% (particularly 45 mol% or more) relative to the total content of all metal elements constituting the metal nanomaterial. In addition, 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 of 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, and francium to hassium, copernicium, and flerovium in the seventh period. The periodic table is a long-period periodic table. For example, potassium to gallium in the fourth period include all elements from atomic number 19 (potassium) to atomic number 31 (gallium) in the arrangement (or sequence) of the periodic table.

[0014] In the present invention, the metal elements other than iron, cobalt, and nickel that may be contained in the metal nanomaterial are preferably chromium, manganese, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium, and platinum, and more preferably chromium, manganese, copper, zinc, zirconium, and yttrium, from the viewpoint of further increasing the specific surface area and further improving the catalytic activity. The metal nanomaterial of the present invention may contain a nonmetallic element or a semimetallic element (e.g., boron), and the metal element contained in the metal nanomaterial may be oxidized. The metal nanomaterial of the present invention may exclude metal nanomaterials 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 contents (molar ratios) of the top four metal elements with the highest content (molar ratio), which may simply be referred to as the "top four metal elements", are usually 5 to 50 mol% when the total of all metal elements is 100 mol%, and 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 content of even one metal element is less than 5 mol%, or if the content of even one metal element is more than 50 mol%, the specific surface area of ​​the obtained metal nanomaterial will not be sufficiently large, and the performance will be inferior when used as a catalyst, which is not preferable.

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

[0017] From the viewpoint of further increasing the specific surface area, the top four metal elements preferably include at least one of iron, cobalt, and nickel, and more preferably iron, cobalt, and nickel. When the fourth most abundant metal element is present in n or more types (n is an integer of 2 or more (e.g., 2)), the top four metal elements may be "3+n" types (e.g., 5 types) of metal elements including all of the n or more metal elements.

[0018] Among the metal elements contained in the metallic nanomaterial of the present invention, the content (molar ratio) of each metal element other than the top four metal elements is not particularly limited, and when the total of all metal elements is 100 mol%, it is usually 25 mol% or less (particularly 0.1 to 25 mol%), and from the viewpoint 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 even 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, and from the viewpoint 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, even more preferably 60 mol% or less, and particularly preferably 50 mol% or less. The lower limit of the total content is not particularly limited, and for example, the total content may be 10 mol% or more, and from the viewpoint of further increasing the surface area and further improving the catalytic activity, it may be preferably 20 mol% or more, more preferably 30 mol% or more, and even more preferably 40 mol% or more.

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

[0021] The specific surface area of ​​the metal nanomaterial of the present invention is preferably as high as possible since it affects the activity of the catalyst. 2 / g or more, and 85m 2 / g or more, and 2 / g or more is more preferable, and 100m 2 More preferably, it is 130m / g or more. 2 / g or more is particularly preferred, and 150m 2 / g or more is highly preferable, and 170m 2 / g or more is more preferable, and 200m 2 / g or more, and more preferably 250m 2 / g or more. 2 If the specific surface area is less than 500 m / g, the performance is poor when used as a catalyst, which is not preferable. 2 / g or less (especially 400m 2 / g or less).

[0022] The metallic nanomaterial of the present invention preferably has a first reaction rate of 90% or more, preferably 95% or more, and a fifth reaction rate of 70% or more, more preferably 90% or more. In addition, in the catalytic activity evaluation (time-dependent evaluation) described in the evaluation method described below, 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 catalyst is based on the rate of decrease from the initial value of absorbance at a wavelength of 400 nm in the hydrogenation reaction of paranitrophenol with sodium borohydride.

[0024] The metalloid element boron can be contained in the metal nanomaterial of the present invention. Boron is contained in the metal nanomaterial by the manufacturing 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 more preferably 5 parts by mass or more, relative to 100 parts by mass of the metal nanomaterial. The upper limit of the content of boron is not particularly limited, and for example, the content of boron is preferably 10 parts by mass or less, more preferably 9 parts by mass or less. By containing boron, the corrosion resistance may generally be improved. In addition, in the definition of the content of boron, 100 parts by mass of the metal nanomaterial means 100 parts by mass of the entire metal nanomaterial. Therefore, the content of boron is a ratio 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 be an aggregate of even finer nanosheets. Since nanoparticles may be difficult to handle, the nanoparticle units may be further bonded or aggregated to be processed into powders or particles having a particle size of micron size or more (particularly 1 to 100 μm). By processing to a size of about several tens of μm, it becomes easy to collect the nanoparticles using a filter or the like while maintaining the gas diffusion and permeability, and the nanoparticles can be easily handled as catalysts. 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, the particle size refers to the maximum length of the particle in the case of independent particles, and refers to the diameter of the part with the maximum thickness in the case of linearly bonded particles. In the case of particles that are aggregated to form a porous body, the ligament size can be used as the particle size. The particle size is measured by the following method. The resulting product was vacuum dried and photographed at 100,000x magnification using a scanning electron microscope (SEM). The particle size of the nanomaterial was measured at 100 random points within 10 fields of view, and the average value was calculated.

[0027] The metallic nanomaterial of the present invention generally does not have a coating (particularly an organic coating) on ​​its surface, and therefore the loss on firing is 0.1% by mass or less (particularly 0.01% by mass or less).

[0028] The loss on firing is the ratio of the mass lost by firing to the mass before firing, and is measured by the following method. The obtained metal nanomaterial was degassed in a vacuum at 200°C for 30 minutes, and its mass was measured. This value is the pre-sintering mass. The metal nanomaterial was then sintered in a vacuum at 800°C for 4 hours, and its mass was measured. The sintering weight loss was calculated by dividing the mass lost from before sintering by the pre-sintering mass.

[0029] [Mechanical manufacturing method for metal nanomaterials] The metal nanomaterial of the present invention can be obtained, for example, by mixing and dissolving four or more kinds of metal salts and performing a liquid phase reduction reaction using a reducing agent. The amount (molar ratio) of the metal salts in the manufacturing method of the metal nanomaterial is usually reflected directly in the content (molar ratio) of the metal elements in the metal nanomaterial. Therefore, the type and amount (molar ratio) of the four or more kinds of metal salts used may be determined based on the type and content (molar ratio) of the metal elements constituting the metal nanomaterial described above. For example, the explanation of the four or more kinds of metal salts and their amount (molar ratio) can be applied by replacing "metal element" and "content" with "metal salt" and "amount" respectively (especially by replacing "total content (100 mol%) of all metal elements constituting the metal nanomaterial" with "total amount (100 mol%) of all metal salts constituting the metal nanomaterial").

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

[0031] The metal salt is not particularly limited as long as it dissolves in the solvent, and for example, chlorides, nitrates, sulfates, acetates, etc. of the above-mentioned metal elements may be used.

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

[0033] The reducing agent is not particularly limited, but may be a reducing agent containing a boron atom such as sodium borohydride, potassium borohydride, or dimethylamine borane, a hydrazine such as hydrazine or phenylhydrazine, an alcohol such as isopropyl alcohol or ethylene glycol, an amine such as octylamine or triethylamine, an organic acid such as ascorbic acid or formic acid, or a phosphorus-based reducing agent such as sodium hypophosphite. Among them, from the viewpoint of further increasing the specific surface area of ​​the metal nanomaterial and further improving the catalytic activity, it is preferable to use a reducing agent containing a boron atom such as sodium borohydride, potassium borohydride, or dimethylamine borane, and it is more preferable to use sodium borohydride. On the other hand, amines or organic acids may not be usable depending on the application of the catalyst, because the excess reducing agent is coordinated to the metal nanoparticles and forms a coating of the amine or organic acid, which blocks the active site of the catalyst.

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

[0035] The reaction solvent is not particularly limited as long as it is capable of dissolving the metal ions and the reducing agent, but water is preferred because it provides a sufficiently large specific surface area for the resulting metal nanomaterial, thereby improving performance when used as a catalyst.

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

[0037] The reduction reaction time 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 purifying and recovering the material through centrifugation, filtration, etc.

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

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. The metal nanomaterials were evaluated by the following methods.

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

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

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

[0045] The catalyst durability was evaluated by repeated measurements. 7 mL of water, 1 mL of aqueous solution of paranitrophenol (1.4 mmol / L), and 1 mL of sodium borohydride (0.42 mol / L) were added to the catalyst separated in the above process and stirred for 5 minutes. After separating the catalyst from the reaction solution by centrifugation, the supernatant was collected and filtered with a 0.45 μm syringe filter. The absorbance of the obtained solution at 400 nm was measured, and the reaction rate was calculated from the rate of decrease from the initial value. This process was repeated five times to calculate the reaction rate after the reaction. The catalytic activity was evaluated based on the reaction rate in the "fifth run" according to the following criteria. ◎: Response rate was 90% or higher; ○: Response rate was 60% or more but less than 90%; △: response rate was 40% or more but less than 60%; ×: Response rate is less than 40%.

[0046] (6) Particle size The resulting product (metal nanomaterial) was vacuum dried and photographed at 100,000x magnification using a scanning electron microscope (SEM). The particle size of the nanomaterial was measured at 100 random 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 chloride hexahydrate, and 5.95 parts by mass (25 mol parts) of nickel chloride hexahydrate were dissolved in 200 parts by mass 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%), and bubbling of nitrogen gas was started. After 10 minutes had elapsed from the start of bubbling, the dropwise addition 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 for 15 minutes, the solution was allowed to stand 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. The bubbling of nitrogen gas was stopped, and 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 each with water and methanol, and dried in vacuum at room temperature for 24 hours to obtain a metal nanomaterial (NM).

[0048] Examples 2 to 16 and Comparative Examples 4 and 5 Except for changing the types and amounts (parts by mole) of the raw materials to those shown in Table 1, the same procedure as in Example 1 was carried out to obtain each metal nanomaterial (NM).

[0049] [Table 1]

[0050] Comparative Example 1 0.59 parts by mass (2.48 parts by mol) of nickel chloride hexahydrate, 0.28 parts by mass (0.93 parts by mol) of trisodium citrate dihydrate, 0.29 parts by mass (0.0050 parts by mol) of chloroplatinic acid hexahydrate, and 0.75 parts by mass of Cellogen 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 mol parts) of hydrazine monohydrate was mixed with water, and then 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. The nickel ion solution and the reducing agent solution were both heated to 80-85°C, and then mixed while maintaining the temperature, and a magnetic field of 100 mT was applied to perform a reduction reaction for 20 minutes. After that, the mixture was filtered and collected using a T100A090C PTFE filter, washed three times each with water and methanol, and dried in vacuum at room temperature for 24 hours to obtain a metal nanomaterial (nanowire, NW).

[0051] Comparative Example 2 8.55 parts by mass (43 mol parts) of iron(II) chloride tetrahydrate was dissolved in 300 parts by mass of water, and the solution was placed in a magnetic circuit with a central magnetic field of 130 mT, and nitrogen gas bubbling was started. After 10 minutes had elapsed from the start of bubbling, 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 to be dropped. After dropping over 15 minutes, the solution was left to stand 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. After that, the application of the magnetic field and the bubbling of nitrogen gas were stopped, and the reaction solution was diluted by pouring it into 200 parts by mass of water. The resulting black nanowires were collected by filtration using a T100A090C PTFE filter, washed three times each with water and methanol, and dried in vacuum 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 chloride hexahydrate, and 3.31 parts by mass (14 mol parts) of nickel chloride hexahydrate were dissolved in 300 parts by mass of water, and the solution was placed in a magnetic circuit with a central magnetic field of 130 mT, and bubbling of nitrogen gas was started. After 10 minutes had elapsed from the start of bubbling, dripping 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 dripping over 15 minutes, the solution was left to stand 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 to collect by filtration, wash, and dry, thereby obtaining a metal nanomaterial (nanowire, NW).

[0053] Comparative Example 6 A method similar to that of Example 1 was carried out except that 10.7 parts by mass (213 parts by mole) 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 A method similar to that of Example 1 was carried out, except that 22.6 parts by mass (213 parts by mole) 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 cited is from Non-Patent Document 2. The method for producing the catalyst of Reference Example 1 in Non-Patent Document 2 is as follows. 20 parts by mass of a high-entropy alloy powder (particle size approximately 20 μm) of 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 resulting solid was collected 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 resulting catalyst was 9 m 2 / g.

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

[0057] [Table 2]

[0058] The metallic nanomaterials of Examples 1 to 16 were prepared by mixing four or more kinds of metal ions, with the top four metallic elements with the highest content (molar ratio) being in the molar ratio range of 5 to 50 mol %, and then carrying out a liquid-phase reduction reaction using a reducing agent. As a result, the specific surface area was 60 m 2 / g or more, and the catalytic activity was also high.

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

[0060] The metallic nanomaterials obtained in Examples 1 to 16 had a firing loss of 0.01% by mass or less.

[0061] An SEM image of the metallic nanomaterial of Example 2 is shown in Figure 1. Figure 1 makes it clear that the metallic nanomaterial of Example 2 has a morphology in which countless nanoparticles are bonded (or aggregated).

[0062] Enlarged SEM images of the metal nanomaterial of Example 2 and mapping images (EDS) of the elements chromium, iron, cobalt, nickel, and copper are shown in Figures 2 to 7, respectively, and an image in which the mapping of each element is superimposed is shown in Figure 8. Figures 2 to 8 reveal that the metal nanomaterial of Example 2 contains each metal element uniformly within a single particle. [Industrial Applicability]

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

Claims

1. The specific surface area obtained by the nitrogen gas adsorption method is 60 m². ２ A metal nanomaterial having a concentration of 1 / g or more, The aforementioned metal nanomaterial contains four or more metal elements and boron. A metal nanomaterial in which, when the total content of all metal elements constituting the aforementioned metal nanomaterial is set to 100 mol%, the content (molar ratio) of each of the top four metal elements with the highest content (molar ratio) is between 5 and 50 mol%.

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

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

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

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

6. The metal nanomaterial according to claim 1, wherein the metal nanomaterial comprises 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 aforementioned specific surface area is 100 m². 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 aforementioned specific surface area is 150 m². ２ The metal nanomaterial according to claim 7, wherein the amount is 1 / g or more.

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

10. The aforementioned specific surface area is 100 m². ２ The metal nanomaterial according to claim 1, wherein the amount is 1g or more.

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

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

13. A method for producing a metal nanomaterial, comprising mixing and dissolving four or more metal salts, and carrying out a liquid-phase reduction reaction using a reducing agent to produce a 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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