Metal nanomaterial having high specific surface area

Abstract

The present invention provides a metal nanomaterial which has a higher specific surface area than conventional metal nanomaterials. The present invention relates to a metal nanomaterial which has a specific surface area of 60 m2 / g or more as determined by a nitrogen gas adsorption method.

Description

Metal nanomaterials with high specific surface area

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

[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 a nanomaterial having 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 m / g, which is produced by reducing metal ions in an aqueous solution of carboxymethyl cellulose salt. ２ However, the specific surface area of ​​the materials described in each of these documents is 60 m ２ / g or less.

[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. However, the specific surface area of ​​the high-entropy alloys described in Non-Patent Document 2 is only 9 m at most. ２ / g, which was insufficient.

[0005] International Publication No. 2018 / 062090 Pamphlet

[0006] Advanced Materials 2019, 1906160 Journal of Materials Chemistry A 2020, 18318.

[0007] The present invention is intended to solve the above-mentioned problems, and aims to provide a metal nanomaterial having a higher specific surface area than conventional metal nanomaterials.

[0008] As a result of extensive research, the present inventors have 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 have arrived at the present invention.

[0009] The gist of the present invention is as follows: <1> A specific surface area of ​​60 m2 as measured by a nitrogen gas adsorption method. ２ / g or more. <2> The metallic nanomaterial according to <1>, which contains four or more types of metallic elements, and when the total content of all metallic elements constituting the metallic nanomaterial is taken as 100 mol%, the contents (molar ratios) of the top four metallic elements with the highest contents (molar ratios) are all 5 to 50 mol%. <3> The metallic nanomaterial according to <2>, which contains the top four metallic elements with the highest contents (molar ratios) are each 10 to 45 mol%. <4> The metallic nanomaterial according to <2> or <3>, which contains at least one metallic element selected from iron, cobalt, and nickel. <5> The metallic nanomaterial according to any one of <2> to <4>, which contains iron, cobalt, and nickel. <6> The metallic nanomaterial according to any one of <2> to <5>, wherein, among the metallic elements contained in the metallic nanomaterial, the content (molar ratio) of each of the metallic elements other than the top four metallic elements is 25 mol% or less when the total content of all metallic elements constituting the metallic nanomaterial is 100 mol%. <7> The metallic nanomaterial according to any one of <2> to <6>, wherein the metallic nanomaterial contains four or more metallic elements selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium, and platinum. <8> The metallic nanomaterial according to any one of <2> to <6>, wherein the specific surface area is 100 m ２ / g or more, and the total content (molar ratio) of chromium, iron, cobalt, zirconium, and lanthanum contained in the metal nanomaterial is 80 mol % or less. ２<10> The metallic nanomaterial according to any one of <2> to <9>, wherein the boron content is 3 parts by mass or more per 100 parts by mass of the metallic nanomaterial. <11> The metallic nanomaterial according to <8>, wherein the specific surface area is 100 m ２ / g or more. <12> The metallic nanomaterial according to any one of <1> to <11>, having a calcination loss of 0.1 mass% or less. <13> The metallic nanomaterial according to any one of <1> to <12>, having a nanoparticle form, a microparticle form formed by bonding or agglomerating the nanoparticles, or a composite form thereof. <14> A method for producing a metallic nanomaterial, comprising mixing and dissolving four or more types of metal salts, and carrying out a liquid-phase reduction reaction using a reducing agent to produce the metallic nanomaterial according to any one of <1> to <13>. <15> A method for producing a metallic nanomaterial according to <14>, wherein a reducing agent containing a boron atom is used as the reducing agent.

[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, and ammonia generation, or as an electrode catalyst for fuel cells.

[0011] 1 is an SEM image (enlarged) of Example 2, which is an SEM image of Example 2. FIG. 2 is a mapping image (EDS) of chromium element of Example 2. FIG. 3 is a mapping image (EDS) of iron element of Example 2. FIG. 4 is a mapping image (EDS) of cobalt element of Example 2. FIG. 5 is a mapping image (EDS) of nickel element of Example 2. FIG. 6 is a mapping image (EDS) of copper element of Example 2. FIG. 7 is an image in which mapping of each element is superimposed on the electron beam image of Example 2.

[0012] [Metal Nanomaterial] The metal nanomaterial of the present invention is preferably an alloy containing four or more metal elements but no major component, and more preferably a high-entropy alloy containing five or more metal elements but no major component. "No major component" means that the metal nanomaterial does not contain (or does not contain) any metal elements whose content exceeds 50 mol% (particularly 45 mol% or more) of the total content of all metal elements constituting the metal nanomaterial. Furthermore, since this makes it easier to obtain a metal nanomaterial with a higher specific surface area, the metal nanomaterial preferably contains four or more metal elements including at least one of iron, cobalt, and nickel, more preferably four or more metal elements including iron and nickel, and even more preferably four or more metal elements including iron, cobalt, and nickel.

[0013] In the present invention, the metal elements that can be contained in the metallic nanomaterial refer to lithium and beryllium in Period 2 of the periodic table, sodium, magnesium, and aluminum in Period 3, potassium to gallium in Period 4, rubidium to tin in Period 5, cesium to polonium in Period 6, and francium to hassium, copernicium, and flerovium in Period 7. The periodic table is a long-period table. For example, potassium to gallium in Period 4 includes 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, metal elements other than iron, cobalt, and nickel that can be contained in the metal nanomaterial are preferably chromium, manganese, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium, and platinum, with chromium, manganese, copper, zinc, zirconium, and yttrium being more preferred, from the viewpoint of further increasing the specific surface area and further improving the catalytic activity. The metal nanomaterial of the present invention may also contain nonmetallic elements or semimetallic elements (e.g., boron), and the metal elements contained in the metal nanomaterial may be oxidized. The metal nanomaterial of the present invention may not be metal nanomaterials supported on a support such as a carbon material (e.g., graphene, carbon fiber, etc.) or an inorganic material (e.g., alumina, zirconia, etc.).

[0015] In the metallic nanomaterial of the present invention, the contents (molar ratios) of the top four metallic elements with the highest content (molar ratio), hereafter referred to simply as the "top four metallic elements," are typically all 5-50 mol% when the total of all metallic elements is taken as 100 mol%. From the viewpoint of further increasing the specific surface area and further improving catalytic activity, it is preferably 5-45 mol%, more preferably 10-45 mol%, even more preferably 10-35 mol%, particularly preferably 10-30 mol%, and fully preferred to be 10-25 mol%. If the content of even one metallic element is less than 5 mol%, or if the content of even one metallic element is more than 50 mol%, the specific surface area of ​​the resulting metallic nanomaterial will not be sufficiently large, resulting in inferior performance when used as a catalyst, and this is not preferred.

[0016] In this specification, the content (molar ratio) of a metal element in a metal nanomaterial is a value when the total 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 treated as an integer value by rounding off decimal points.

[0017] From the viewpoint of further increasing the specific surface area, the top four metal elements preferably include at least one metal element selected from iron, cobalt, and nickel, and more preferably include iron, cobalt, and nickel. When the metal element with the fourth highest content is present in n or more types (n is an integer of 2 or greater, for example, 2), 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] Of 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, 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 metallic 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 this 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 typically 4 or more as described above, and may be, for example, 4 to 20. From the viewpoint of further increasing the specific surface area and further improving the catalytic activity, the number 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 those whose content, as measured by ICP-AES, is 0.1% by mass or more (particularly 0.5% by mass or more) relative to 100% by mass of the metallic nanomaterial.

[0021] The specific surface area of ​​the metal nanomaterial of the present invention is preferably as high as possible because it affects the catalytic activity. ２ / g or more, and ２ / g or more, and ２ / g or more is more preferable, and 100m ２ / g or more, and more preferably 130m 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 250m ２ / g or more. ２ If the specific surface area is less than 500 m / g, the performance will be poor when used as a catalyst, which is not preferable. ２ / g or less (especially 400m ２ / g or less).

[0022] As a hydrogenation reaction catalyst, 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. Furthermore, 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 metallic nanomaterial of the present invention may contain the metalloid element boron. Boron is incorporated into the metallic nanomaterial through a manufacturing process. From the viewpoint of further increasing the specific surface area and further improving catalytic activity, the boron content is preferably 3 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the metallic nanomaterial. The upper limit 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. The inclusion of boron generally may improve corrosion resistance. Note that, in the definition of the boron content, 100 parts by mass of the metallic nanomaterial refers to 100 parts by mass of the entire metallic nanomaterial. Therefore, the boron content is a ratio relative to the entire metallic nanomaterial containing boron.

[0025] The metallic nanomaterial of the present invention refers to nanoparticles with a particle size of approximately several tens of nanometers (particularly 10 to 100 nm). These nanoparticles may also be aggregates of even finer nanosheets. Because nanoparticles can be difficult to handle, the nanoparticle units can be further bonded or aggregated to form powders or particles with particle sizes of micrometers or larger (particularly 1 to 100 μm). Processing to a size of approximately several tens of μm facilitates collection using filters while maintaining gas diffusion and permeability, making them easier to handle as catalysts. The metallic nanomaterial may be porous. Therefore, microparticles formed by bonding or aggregating nanoparticles may be porous, or the nanoparticles themselves may be porous.

[0026] In this specification, particle size refers to the maximum length of the particle in the case of independent particles, and refers to the diameter of the thickest part in the case of linearly bonded particles. When particles aggregate to form a porous body, the ligament size can be used as the particle size. The particle size used is a value measured by the following method. The obtained product was vacuum dried and photographed at 100,000 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.

[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 calcination loss is the ratio of the mass lost by calcination to the mass before calcination, and is measured using the value measured by the following method. The obtained metal nanomaterial was degassed in a vacuum at 200°C for 30 minutes, and the mass was measured. This value is the mass before calcination. The metal nanomaterial was then calcined in a vacuum at 800°C for 4 hours, and the mass was measured again. The calcination loss was calculated by dividing the mass lost from before calcination by the mass before calcination.

[0029] [Method for Producing Metallic Nanomaterials] The metallic nanomaterials of the present invention can be obtained, for example, by mixing and dissolving four or more metal salts and performing a liquid-phase reduction reaction using a reducing agent. The amount (molar ratio) of the metal salts used in the metallic nanomaterial production process typically directly reflects the content (molar ratio) of the metal elements in the metallic nanomaterial. Therefore, the types and amounts (molar ratios) of the four or more metal salts used can be determined based on the types and contents (molar ratios) of the metal elements constituting the metallic nanomaterial. For example, the description of the four or more metal salts and their amounts (molar ratios) 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 metallic nanomaterial" with "total content (100 mol%) of all metal salts").

[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 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, from the viewpoint of further increasing the specific surface area and further improving the catalytic activity of the metal nanomaterial, it is preferable to use reducing agents containing boron atoms such as sodium borohydride, potassium borohydride, and dimethylamine borane, and sodium borohydride is more preferable. On the other hand, amines and organic acids may be unusable depending on the application of the catalyst, as excess reducing agent coordinates with the metal nanoparticles and forms a coating of the amine or organic acid, blocking the active sites 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 reducing agent concentration is less than 50 mmol / L, the reduction reaction may not proceed sufficiently. If the reducing agent concentration exceeds 2000 mmol / L, rapid foaming may occur as the reduction reaction proceeds, and the reaction may not occur uniformly.

[0035] The reaction solvent is not particularly limited as long as it can dissolve the metal ions and reducing agent, but water is preferred because it gives the resulting metal nanomaterial a sufficiently large specific surface area and improves 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 at room temperature from the viewpoint of simplicity.

[0037] The reduction reaction time is not particularly limited as long as it is possible to produce a metal nanomaterial, but it is preferably set to 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 by centrifugation, filtration, etc.

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

[0041] 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.

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

[0043] (3) Specific Surface Area The obtained metal nanomaterial was vacuum dried and then further degassed in a vacuum at 200°C for 30 minutes. The amount of nitrogen gas adsorbed by the degassed metal nanomaterial was measured by nitrogen gas adsorption method, and the specific surface area was calculated from the amount of adsorption using the BET formula. The specific surface area was evaluated according to the following criteria: ◎: 100 m 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 vacuum-dried, and then its catalytic activity was evaluated according to the method described in Non-Patent Document 2. To 10 mg of the metal nanomaterial, 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 and stirred for 5 minutes. The catalyst and reaction solution were separated by centrifugation, and 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 from the rate of decrease from the initial value.

[0045] The catalyst durability was evaluated by repeated measurements. To the catalyst separated in the above process, 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 and stirred for 5 minutes. The catalyst and the reaction solution were separated by centrifugation, and the supernatant was collected and filtered through a 0.45 μm syringe filter. The absorbance of the resulting solution was measured at 400 nm, 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. The catalytic activity of the "fifth" reaction rate was evaluated according to the following criteria: ◎: The reaction rate was 90% or more; ○: The reaction rate was 60% or more but less than 90%; △: The reaction rate was 40% or more but less than 60%; ×: The reaction rate was less than 40%.

[0046] (6) Particle size The resulting product (metal nanomaterial) was vacuum dried and photographed using a scanning electron microscope (SEM) at 100,000 magnification. The particle size of the nanomaterial was measured at 100 random points within 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 since the start of bubbling, dropwise addition of an aqueous solution of 8.05 parts by mass (213 mol parts) of sodium borohydride dissolved in 200 parts by mass of water was started. After the dropwise addition over 15 minutes, the mixture 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 reducing agent concentration 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 with water and three times with 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 Each metal nanomaterial (NM) was obtained by performing the same operations as in Example 1, except that the type and amount (molar parts) of raw materials were changed to the values ​​listed in Table 1.

[0049]

[0050] Comparative Example 1 0.59 parts by mass (2.48 mol parts) of nickel chloride hexahydrate, 0.28 parts by mass (0.93 mol parts) of trisodium citrate dihydrate, 0.29 parts by mass (0.0050 mol parts) of chloroplatinic acid hexahydrate, and 0.75 parts by mass of Cellogen BSH-6 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were dissolved in water. Furthermore, a 5% aqueous solution of sodium hydroxide was added dropwise, the pH was adjusted to 11.5, and water was added so that the total amount was 75 parts by mass, to prepare a nickel ion solution. Meanwhile, 1.25 parts by mass (25.0 mol parts) of hydrazine monohydrate was mixed with water, and further, a 5% aqueous solution of sodium hydroxide was added dropwise, the pH was adjusted to 11.5, and water was added so that the total amount was 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, then mixed while maintaining the temperature, and a magnetic field of 100 mT was applied to carry out the reduction reaction for 20 minutes. After that, the mixture was filtered using a T100A090C PTFE filter, washed three times with water and three times with 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) of iron(II) chloride tetrahydrate was dissolved in 300 parts by mass of water and placed in a magnetic circuit with a central magnetic field of 130 mT. Nitrogen gas bubbling was initiated. Ten minutes after the start of bubbling, an aqueous solution of 7.00 parts by mass (185 mol) of sodium borohydride dissolved in 175 parts by mass of water was added dropwise. After the dropwise addition took 15 minutes, the mixture was allowed to stand for another 10 minutes. The iron ion concentration in the reaction solution was 91 mmol / L, and the reducing agent concentration was 389 mmol / L. The application of the magnetic field and the nitrogen gas bubbling were then 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 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 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. Nitrogen gas bubbling was initiated. After 10 minutes had elapsed since the start of bubbling, the dropwise addition of an aqueous solution containing 7.00 parts by mass (185 mol parts) of sodium borohydride dissolved in 175 parts by mass of water was initiated. After the dropwise addition over 15 minutes, the solution was allowed 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 reducing agent concentration was 389 mmol / L. The same operations as in Comparative Example 2 were then performed, followed by filtration, recovery, 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 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 The same method as in 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: Data from Non-Patent Document 2 was cited. The catalyst of Reference Example 1 in Non-Patent Document 2 was produced by the following method. 20 parts by mass of a high-entropy alloy powder (particle size approximately 20 μm) with 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 resulting 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 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]

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

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

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

[0061] An SEM image of the metallic nanomaterial of Example 2 is shown in Figure 1. Figure 1 reveals 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 chromium, iron, cobalt, nickel, and copper elements 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.

[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 measured by nitrogen gas adsorption is 60m ２ / g or more.

2. A metal nanomaterial as described in claim 1, which contains four or more metal elements, and 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 the highest content (molar ratio) is 5 to 50 mol %.

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

4. The metallic nanomaterial of claim 2, wherein the metallic nanomaterial contains at least one metallic element selected from the group consisting of iron, cobalt, and nickel.

5. The metallic nanomaterial of claim 2, wherein the metallic nanomaterial comprises iron, cobalt, and nickel.

6. A metal nanomaterial as described in claim 2, wherein the content (molar ratio) of each of the metal elements contained in the metal nanomaterial 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%.

7. The metallic nanomaterial of claim 2, wherein the metallic nanomaterial contains four or more metallic elements selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, yttrium, lanthanum, ruthenium, rhodium, palladium and platinum.

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

9. The specific surface area is 150 m ２ The metal nanomaterial according to claim 8, wherein the metal nanomaterial has a molecular weight of 1.001 or more.

10. The metallic nanomaterial according to claim 2, wherein the boron content is 3 parts by mass or more per 100 parts by mass of the metallic nanomaterial.

11. The specific surface area is 100 m ２ The metal nanomaterial according to claim 1, wherein the metal nanomaterial has a molecular weight of 1000 or more.

12. The metal nanomaterial according to claim 1, having a firing loss of 0.1 mass% or less.

13. The metallic nanomaterial according to claim 1, which has the form of nanoparticles, the form of microparticles formed by bonding or agglomerating said nanoparticles, or a composite form thereof.

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

15. The method for producing a metallic nanomaterial according to claim 14, wherein a reducing agent containing a boron atom is used as the reducing agent.

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