WO2023063353A1 - Catalyseur - Google Patents

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WO2023063353A1
WO2023063353A1 PCT/JP2022/038047 JP2022038047W WO2023063353A1 WO 2023063353 A1 WO2023063353 A1 WO 2023063353A1 JP 2022038047 W JP2022038047 W JP 2022038047W WO 2023063353 A1 WO2023063353 A1 WO 2023063353A1
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metal particles
catalyst
metal
mass
compound
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PCT/JP2022/038047
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Japanese (ja)
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直也 阿部
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株式会社フルヤ金属
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties

Definitions

  • the present invention relates to catalysts. More particularly, it relates to catalysts used in chemical reactions, electrochemical reactions, and exhaust gas purification reactions.
  • Pt group metals are transition metals belonging to groups 8, 9 and 10 of the periodic table, and are a general term for metals composed of six elements of Pt, Pd, Rh, Ru, Ir and Os. Since electrons in the d-orbitals in the outermost shells of Pt group metals form covalent bonds with hydrogen and oxygen, catalysts using Pt group metals are expected to exhibit high activity in oxidation and reduction reactions. Are known. In addition, it is chemically stable, has high resistance to acids and alkalis, and has excellent heat resistance due to its high melting point. Due to such advantages, catalysts using Pt group metals have been put to practical use in various industries.
  • Pt group metals are used as catalysts for chemical reactions in fine chemical fields such as petroleum refining, petrochemicals, medicines, fragrances, and foods.
  • catalysts containing Pt group metals are used in various chemical reactions such as hydrogenation reactions, dehydrogenation reactions, oxidation reactions, coupling reactions, olefin metathesis reactions and polymerization reactions.
  • these Pt group metals are also known as electrode catalysts used in electrodes of polymer electrolyte fuel cells, polymer electrolyte water electrolysis devices, electrolytic layers for the soda industry, chemical sensors, and the like.
  • Pt group metals are used in large amounts in exhaust gas purification catalysts for automobiles.
  • Exhaust gas from gasoline-powered automobiles contains hydrocarbons, carbon monoxide, and nitrogen oxides, which are regulated substances due to their adverse effects on the environment.
  • Pt, Pd, and Rh are used as three-way catalysts that simultaneously decompose hydrocarbons, carbon monoxide, and nitrogen oxides.
  • Pt and Pd are said to be particularly excellent in the ability to decompose hydrocarbons and carbon monoxide.
  • Diesel vehicles have a high air-fuel ratio and excellent fuel efficiency, but have the problem of generating a large amount of nitrogen oxides in the exhaust gas.
  • Pt and Pd are indispensable for purifying the exhaust gas of gasoline and diesel vehicles, and due to the tightening of exhaust gas regulations in recent years, it is necessary to increase the amount of Pt and Pd used per vehicle to clear the regulations. be.
  • the Pd—Fe metal particles having a metal loading rate of 1.5% by mass and an average particle size in the range of 9 nm to 50 nm are at least one of CeO 2 , ZrO 2 and Al 2 O 3 .
  • An exhaust gas purifying catalyst supported on an oxide carrier containing as a main component has been proposed.
  • Non-Patent Document 1 discloses a Pd—Fe or Pt—Fe-supported Al 2 O 3 catalyst, and although the metal particles have a fine particle size of about 5 nm, the metal support rate is as small as 0.5% by mass. Therefore, it is considered difficult to exhibit sufficient activity.
  • Non-Patent Document 2 discloses a Pd—Fe-supported Al 2 O 3 catalyst. Although the amount of supported metal is as large as 5% by mass or more, the particle size of the metal particles is as large as 10 nm or more, so good catalytic activity is not expected.
  • the present inventors have completed the present invention as a result of diligent studies to solve the above problems. That is, the present invention has the following aspects.
  • Metal particles containing Pd and Fe or Pt and Fe having an average particle size of less than 8 nm and a support are included, and the metal particles are 1% by mass or more when the total mass of the metal particles and the support is 100% by mass.
  • catalyst [2] The catalyst according to [1] above, wherein the metal particles are metal particles containing Pd and Fe. [3] The catalyst according to [2] above, wherein part of the metal particles containing Pd and Fe is an alloy containing Pd and Fe. [4] The catalyst according to [1] above, wherein the metal particles are metal particles containing Pt and Fe. [5] The catalyst according to [4] above, wherein part of the metal particles containing Pt and Fe is an alloy containing Pt and Fe.
  • the carrier is alumina, silica, silica-alumina, calcia, magnesia, titania, ceria, zirconia, ceria-zirconia, lanthana, lanthana-alumina, tin oxide, tungsten oxide, aluminosilicate, aluminophosphate, borosilicate, phosphotungstic acid, At least one selected from the group consisting of hydroxyapatite, hydrotalcite, perovskite, cordierite, mullite, silicon carbide, activated carbon, carbon black, acetylene black, carbon nanotube and carbon nanohorn of the above [1] to [7].
  • Catalyst according to any one of the preceding claims.
  • the catalyst according to [8] above, wherein the carrier is at least one selected from the group consisting of alumina, ceria and zirconia.
  • the amount of Pt group metal used is reduced while providing a catalyst with performance equal to or better than that of conventional exhaust gas purification catalysts.
  • the catalyst of the present invention (hereinafter also referred to as “the present catalyst”) contains metal particles having an average particle diameter of less than 8 nm containing Pd and Fe or Pt and Fe and a support, and the total mass of the metal particles and support is The amount of the metal particles is 1% by mass or more based on 100% by mass.
  • the shape of the metal particles is spherical and can be confirmed with a transmission electron microscope (hereinafter also referred to as "TEM").
  • the average particle size of the metal particles is less than 8 nm, preferably 1 nm or more. Also, the average particle size is preferably 7.95 nm or less, more preferably 4.5 nm or less. When the average particle diameter is 8 nm or more, the specific surface area of the metal particles containing Pd and Fe or Pt and Fe is reduced, and it is considered that the catalytic activity is lowered.
  • the average particle size can be measured by TEM. 20 or more primary particles are selected from the metal particles shown in the TEM image, and the longest length of the particles is visually measured as the particle diameter. The average particle size was obtained by dividing the total particle size of each particle by the number of particles whose particle sizes were measured. The number of primary particles to be measured is not particularly limited as long as it is 20 or more.
  • the present catalyst has metal particles containing at least Pd and Fe or Pt and Fe, and the metal particles are metal particles in which Pd and Fe or Pt and Fe are alloyed or not alloyed. It's okay. Also, metals other than Pd, Pt and Fe may be contained in the present catalyst, and they may be alloy particles with at least one of Pd, Pt and Fe. Other metals include Ni, Co, Cu, Ru, Rh, Ag, Os, Ir, Au, and the like.
  • the present catalyst may contain a single metal such as Pd, Pt or Fe, and may contain these in the form of compounds such as chlorides and oxides.
  • the metal particles in the present catalyst may not be supported on the carrier, or may be in a state of falling off from the carrier.
  • the metal particles are preferably metal particles made of Pd and Fe.
  • the present catalyst preferably does not contain metals other than Pd and Fe other than the carrier described later.
  • the metal particles are composed of Pd and Fe, at least part of the metal particles is preferably an alloy of Pd and Fe.
  • the alloy is a substance composed of two or more metal elements.
  • STEM-EDX scanning transmission electron microscope
  • At least part of the metal particles made of Pd and Fe is an alloy of Pd and Fe, it is difficult to quantify the alloy in the metal particles, but when the metal particles are observed by the STEM-EDX or powder XRD measurement, If the observation result that can be judged as the alloy is obtained, it can be said that at least a part of the metal particles composed of Pd and Fe is an alloy of Pd and Fe. That is, at least a part of the metal particles made of Pd and Fe is an alloy of Pd and Fe means that each element is found in the image of the same field of view in the metal particles contained in the present catalyst by STEM-EDX or powder XRD measurement. A single diffraction peak pattern that exists at the same position or is different from the diffraction peaks of Pd alone and Fe alone is confirmed.
  • the alloy of Pd and Fe preferably exists as an intermetallic compound, and it is preferable that a single diffraction peak pattern different from the diffraction peaks of Pd alone and Fe alone is confirmed.
  • the metal ratio of Pd and Fe is preferably 1:1 in terms of molar ratio, and the structure thereof is more preferably fct (face-centered tetragonal) structure.
  • the ratio of Pd is preferably 50 at % to 60 at % when the total atomic weight of Pd and Fe is 100 at %. Presence of Pd at a ratio within the above range allows Pd and Fe to form an fct (face-centered tetragonal) structure alloy, which is thought to improve the durability of the catalyst.
  • the metal particles are preferably metal particles made of Pt and Fe.
  • the present catalyst preferably does not contain metals other than Pt and Fe other than the carrier described later.
  • the metal particles are composed of Pt and Fe, at least part of the metal particles is preferably an alloy of Pt and Fe.
  • At least part of the metal particles made of Pt and Fe is an alloy of Pt and Fe
  • it is difficult to quantify the alloy in the metal particles but when the metal particles are observed by the STEM-EDX or powder XRD measurement, If the observation result that can be judged as the alloy is obtained, it can be said that at least a part of the metal particles composed of Pt and Fe is an alloy of Pt and Fe. That is, when at least part of the metal particles made of Pt and Fe is an alloy of Pt and Fe, each element is found in the image of the same field of view in the metal particles contained in the present catalyst by STEM-EDX or powder XRD measurement. A single diffraction peak pattern that exists at the same position or is different from the diffraction peaks of Pt alone and Fe alone is confirmed.
  • the alloy of Pt and Fe preferably exists as an intermetallic compound, and it is preferable that a single diffraction peak pattern different from the diffraction peaks of Pt alone and Fe alone is confirmed.
  • the metal ratio of Pt and Fe is preferably 1:1 in terms of molar ratio, and the structure thereof is more preferably fct (face-centered tetragonal) structure.
  • the ratio of Pt is preferably 35 at % to 55 at % when the total atomic weight of Pt and Fe is 100 at %. Presence of Pt in the ratio described above allows Pt and Fe to form an fct (face-centered tetragonal) structure alloy, which is thought to improve the durability of the catalyst.
  • the metal content in the present catalyst is the ratio of metal particles when the total mass of all metals and supports contained in the present catalyst is 100% by mass, and the supported metal particles are preferably 1% by mass or more.
  • the metal content is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.
  • the metal content can be measured, for example, by high frequency inductively coupled plasma emission spectroscopy (ICP-OES analysis) after a catalyst solution pretreatment step.
  • the catalyst When this catalyst is used as an exhaust gas purifying catalyst for automobiles, the catalyst is used in an atmosphere of 1000° C. or more, and is used in the above environment for 20 years, which is the assumed service life of automobiles. Therefore, when the present catalyst is used as a catalyst for purifying automobile exhaust gas, the carrier contained in the present catalyst preferably has heat resistance and a large specific surface area. From this point of view, it is preferably at least one selected from the group consisting of alumina, ceria and zirconia. The larger the specific surface area of the carrier, the greater the amount of metal particles that it adsorbs, so the specific surface area is preferably 50 m 2 /g or more, more preferably 100 m 2 /g or more.
  • the present catalyst can be used as a catalyst for chemical reactions, electrode reactions, and exhaust gas purification reactions.
  • this catalyst is used in a chemical reaction
  • the structure of the reaction vessel is classified into fixed bed reactor, moving bed reactor, fluidized bed reactor, stirred tank reactor, bubble column reactor, etc.
  • a fixed-bed reactor has a structure in which a cylindrical container is filled with a catalyst, and a gaseous or liquid reaction fluid flows through the voids of the particles.
  • the shape of the catalyst is not particularly limited, it is preferable to use the catalyst in the form of pellets because of its high porosity.
  • this catalyst When this catalyst is used in an electrode reaction, it can be suitably used as an anode catalyst for fuel cells.
  • a hydrogen molecule supplied from the outside releases two electrons at the anode to become hydrogen ions (protons). Flow power is generated.
  • oxygen molecules taken from the air receive electrons returning from an external circuit and become oxygen ions. Oxygen ions combine with hydrogen ions that have migrated through the proton transport agent to form water.
  • the chemical reaction on the anode side can be expressed by the following formula (1), the chemical reaction on the cathode side by the following formula (2), and the overall reaction by the following formula (3).
  • 2H 2 ⁇ 4H + + 4e ⁇ (1) 4H + + O 2 +4e ⁇ ⁇ 2H 2 O (2)
  • Pt/C is usually used as an anode catalyst for fuel cells, but by replacing it with this catalyst, the reaction (3) can be efficiently promoted.
  • the present catalyst When the present catalyst is used as an exhaust gas purifying catalyst, it is preferable that the present catalyst is wash-coated, coated on a ceramic honeycomb, and supported on the ceramic honeycomb.
  • the catalyst-carrying ceramic honeycomb is preferable because it can efficiently bring the exhaust gas into contact with the catalyst by mounting it on the muffler system.
  • the impregnation support method which is a general catalyst production method
  • one or more kinds of metal raw materials are dissolved in a solvent, a carrier having pores is added and mixed, and then the solvent is removed by a drying process to remove the metal raw materials. It is adsorbed and supported on a carrier.
  • impurities such as inorganic substances in the metal raw material are decomposed and removed, and metal particles are formed on the support.
  • the metal raw material is densely present on the support, and when the metal particles are formed by heat treatment, the metal raw material aggregates with each other, and the metal on the support increases. Particle size increases. Therefore, it has been difficult to manufacture a catalyst in which metal particles having a small particle size are supported while increasing the amount of supported metal particles.
  • a precursor having a small particle size is produced, and the obtained precursor is carried on a support in a highly dispersed manner.
  • the precursor is reduced by heat treatment in a reducing atmosphere or the like, and can be supported on the support in the form of a single metal or an alloy.
  • the heat treatment temperature it is possible to order the crystal structure like an intermetallic compound of Pd and Fe or Pt and Fe.
  • a catalyst supporting metal particles imparted with properties such as chemical stability of the alloy structure and magnetism.
  • the precursor is not a metal raw material such as an inorganic salt used in the impregnation supporting method, but a solid state such as an elemental metal, an alloy, or an oxide.
  • the precursor contains at least Pd and Fe or Pt and Fe, and may be an alloy containing other metals than Pd, Pt and Fe.
  • Other metals include Ni, Co, Cu, Ru, Rh, Ag, Os, Ir, Au, and the like.
  • Pd, Pt and Fe may also exist as single metals.
  • the method for producing the present catalyst is, for example, (1) In a solution containing a Pd compound and an Fe compound, or a Pt compound and an Fe compound, the Pd compound and the Fe compound, or the Pt compound and the Fe compound are subjected to at least one reaction of a decomposition reaction and a reduction reaction to form Pd and Fe. or obtaining a precursor containing Pt and Fe; (2) a step of mixing the carrier into the liquid containing the precursor obtained in (1) above to obtain a carrier; and (3) a step of heat-treating the carrier obtained in (2) above. can be manufactured.
  • Step (1) When the target catalyst contains Pd and Fe, in step (1), the Pd compound and the Fe compound are subjected to at least one of decomposition reaction and reduction reaction in a solution containing the Pd compound and the Fe compound to convert Pd and Fe. to obtain a precursor containing Precursors are solid states such as elemental metals, alloys, and oxides.
  • the precursor contains at least Pd and Fe, and may be an alloy containing other metals than Pd and Fe. Pd and Fe may also be present as single metals.
  • Various salts of Pd or Fe ions, organometallic complexes, and the like may be used as the Pd compound and the Fe compound.
  • Pd compounds include Pd(II) acetylacetonate, Pd(II) acetate, Pd(II) chloride, tetraamminedichloro Pd(II) monohydrate, diamminedichloro Pd(II), diamminedinitro Pd(II), Pd(II) sulfate, Pd(II) sulfate dihydrate, Pd(II) nitrate, Potassium tetrachloroPd(II)ate, Sodium tetrachloroPd(II)ate, TetrachloroPd(II) ) acid ammonium and the like.
  • Pd(II) acetylacetonate is preferred.
  • Fe compounds include pentacarbonyl Fe, nonacarbonyl di-Fe, dodecacarbonyl tri-Fe, Fe (II) acetylacetonate, Fe (III) acetylacetonate, ferrocene [bis (cyclopentadienyl) Fe (II) ], Fe(III) chloride, Fe(III) chloride hexahydrate, Fe(II) chloride tetrahydrate, Fe(II) sulfate, Fe(II) sulfate heptahydrate, Fe(III) ammonium sulfate , Fe(II) bromide, Fe(II) iodide, Fe(III) sulfate nonahydrate, Fe(II) sulfate hydrate, Fe(II) nitrate, Fe(III) nitrate, Fe(III) nitrate ) nonahydrate, Fe(III) perchlorate, Fe(III) pyrophosphate
  • the Pt compound and the Fe compound are subjected to at least one of decomposition reaction and reduction reaction in a solution containing the Pt compound and the Fe compound to decompose Pt and Fe. to obtain a precursor containing Precursors are solid states such as elemental metals, alloys, and oxides.
  • the precursor contains at least Pt and Fe, and may be an alloy containing other metals than Pt and Fe. Pt and Fe may also be present as single metals.
  • Various salts of Pt or Fe ions, organometallic complexes, and the like may be used as the Pt compound and the Fe compound.
  • Pt compounds include Pt(II) acetylacetonate, Pt(II) chloride, Pt(IV) chloride, tetrachloro Pt(II) acid, hexachloro Pt(IV) acid, hexachloro Pt(IV) Acid hexahydrate, ammonium tetrachloro Pt(II) acid, potassium tetrachloro Pt(II) acid, sodium tetrachloro Pt(II) acid, ammonium hexachloro Pt(IV) acid, potassium hexachloro Pt(IV) acid, hexachloro Sodium Pt(IV) acid, Potassium tetracyanoPt(II) acid, Potassium trichloroamine Pt(II) acid, Dinitrosulfide Pt(II) acid, Diammine dichloro Pt(II), Tetraammine Pt(II) hydroxide, Te
  • the solution of the Pd compound and the Fe compound or the solution of the Pt compound and the Fe compound is a liquid in which the Pd compound and the Fe compound are dissolved in a solvent, or a liquid in which the Pt compound and the Fe compound are dissolved in a solvent.
  • An organic solvent or water is preferred as the solvent.
  • the organic solvent is liquid at room temperature and has a boiling point higher than the reaction temperature at which the Pd compound or Fe compound decomposes or undergoes a reductive reaction, or an organic solvent at which the Pt compound or Fe compound decomposes or undergoes a reductive reaction. Those having a boiling point higher than the reaction temperature are preferred.
  • organic solvents examples include 1-octanol, octyl ether, octadecene, triphenylmethane, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, butanol, isobutanol, ethoxyethanol, dimethylformamide, xylene, N- Methylpyrrolidinone, dichlorobenzene, toluene, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethyl lactate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, dipropylene glycol monomethyl ether , diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol butyl methyl ether, tripropy
  • the amount of the solvent is preferably an amount capable of dissolving various metal compounds, and the total molar concentration of Pd, Pt and Fe in the solution of the Pd compound, Pt compound and Fe compound is preferably 0.001 to 10 mol/L, for example.
  • the decomposition reaction or reduction reaction in step (1) is a liquid phase reaction, and at least one of these reactions may be included.
  • the decomposition reaction can be performed, for example, by a hot soap method or a hydrothermal synthesis method.
  • the reduction reaction can be performed by a liquid phase reduction method using a reducing reagent, a polyol method, or a reverse micelle method.
  • a hot soap method and a polyol method are preferred in order to efficiently carry out the loading onto the carrier in step (2).
  • the reaction temperature of the decomposition reaction or reduction reaction is not particularly limited as long as it is a temperature at which the Pd compound, Pt compound and Fe compound undergo the decomposition reaction or reduction reaction. °C to 600 °C, more preferably 200 °C to 400 °C, still more preferably 250 °C to 300 °C.
  • the reaction time of the decomposition reaction or reduction reaction is not particularly limited as long as the decomposition reaction or reduction reaction of the Pd compound, Pt compound and Fe compound is completed. For example, it is 1 minute to 24 hours, preferably 10 minutes. 5 hours, more preferably 30 minutes to 2 hours.
  • Step (1) may be carried out by either a batch system or a flow system.
  • additives may be added as necessary.
  • Additives include stabilizers, reducing agents, and the like.
  • the stabilizer is used to prevent the particles from becoming coarse when the Pd compound, Pt compound, and Fe compound are decomposed or reduced and nucleated, and then grains grow.
  • stabilizers include surfactants and polymer protective agents.
  • surfactants include oleylamine, oleic acid, TOP (trioctyl phosphate), tributyl phosphate, tetraethylene glycol, sodium dodecylbenzenesulfonate, phenylphosphonic acid, myristic acid, dodecanethiol, and dodecylamine.
  • polymer protective agents include polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, poly-N-vinylacetamide, polyethyleneimine, and polyacrylic acid-based polymers.
  • the amount of the stabilizer added to the metal is not particularly limited, and is, for example, 0.1 to 10 times the molar amount of Pd, Fe or Pt, preferably 0.5 to 2 times the molar amount. is.
  • the reducing agent in the present invention is used to reduce each metal source compound to efficiently obtain single metal particles or alloy particles.
  • reducing agent hydrazine, sodium borohydride, sodium diphosphite, lithium aluminum hydride, sodium sulfite, sodium phosphinate and the like can be used.
  • 1,2-alkanediols such as ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol, tetraethylene glycol, and 1,2-hexadecanediol can be used.
  • the amount of the reducing agent added to Pd, Pt and Fe is not particularly limited, and is, for example, 1 to 10 times the molar amount, preferably 2 to 5 times the molar amount of 1 mol of the Pd, Fe or Pt. .
  • a metal compound other than the Pd compound, Pt compound and Fe compound may be added.
  • the elements constituting the resulting precursor include at least Pd and Fe, or Pt and Fe, and other than Pd or Pt and Fe.
  • An alloy containing a metal may also be used.
  • Other metals include Ni, Co, Cu, Ru, Rh, Ag, Os, Ir, Au, and the like. Pd, Pt and Fe may also be present in the precursor as single metals.
  • the state of the precursor in step (1) is preferably a solid state such as a metal element, an alloy, or an oxide that is insoluble in the liquid in step (2).
  • a solid state such as a metal element, an alloy, or an oxide that is insoluble in the liquid in step (2).
  • the liquid containing the precursor is a state in which the precursor is dispersed and fluidized in at least one solvent selected from organic solvents and pure water. Any solvent may be used as long as it does not dissolve or react with the precursor and the carrier, and pure water is generally used. Organic solvents can be used when the precursor and carrier react with pure water.
  • the organic solvent to be used is preferably a solvent that can be distilled off by evaporation in order to support the precursor on the carrier, and is preferably an organic solvent that has a relatively low boiling point and is easily available.
  • step (1) methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, carbon tetrachloride, chloroform, dichloromethane, monochloromethane, n-pentane, n-hexane, n-heptane, cyclohexane, acetone, acetonitrile , ethyl acetate, benzene, toluene, diethyl ether, tetrahydrofuran and the like.
  • the solvent used in step (1) may be used subsequently in step (2), or the carrier may be added to the solution in which the precursor is obtained to mix the precursor and the carrier.
  • the amount of the solvent is preferably such that the precursor and the carrier can be sufficiently mixed, for example, 10 to 1000 times the volume of the carrier.
  • the carrier used in step (2) includes alumina, silica, silica-alumina, calcia, magnesia, titania, ceria, zirconia, ceria-zirconia, titania-zirconia, lanthana, lanthana-alumina, tin oxide, tungsten oxide, aluminosilicate, Aluminophosphate, borosilicate, phosphotungstic acid, hydroxyapatite, hydrotalcite, perovskite, cordierite, mullite, silicon carbide, activated carbon, carbon black, acetylene black, carbon nanotube and carbon nanohorn.
  • the larger the specific surface area of the carrier the greater the amount of metal particles that it adsorbs, so the specific surface area is preferably 50 m 2 /g or more, more preferably 100 m 2 /g or more.
  • the amount of support is 1 to 99 times or less, preferably 4 to 99 times or less, the mass of Pd, Pt and Fe.
  • a carrier is obtained by mixing the precursor and the carrier in a liquid.
  • the mixing method is to mix the precursor and the liquid, and sufficiently disperse the precursor with an ultrasonic homogenizer or the like.
  • This precursor dispersion is then mixed with the carrier and thoroughly stirred.
  • the resulting slurry dispersion of the precursor and carrier is dried using a rotary evaporator or the like to remove the solvent and sufficiently dried using a drier. This yields a support in which the precursor is supported on the support.
  • step (3) the carrier obtained in step (2) is heat-treated.
  • the heat treatment decomposes and removes impurities such as a stabilizer and a dispersion medium contained in the support, and a catalyst containing metal particles containing at least Pd and Fe or Pt and Fe and a support can be obtained.
  • a catalyst containing metal particles containing at least Pd and Fe or Pt and Fe and a support can be obtained.
  • heat-treating alloy species that form intermetallic compounds such as Pd and Fe and Pt and Fe
  • stable Orderly transition can be made to an fct (face-centered cubic) structure, which is an ordered structure.
  • the precursor contained in the support When the precursor contained in the support is a single metal such as Pd, Fe, or Pt, it may be oxidized by oxygen in the air at room temperature to form oxide particles. Therefore, the heat treatment process is performed in a vacuum atmosphere, an inert gas atmosphere, or a reducing gas atmosphere in which oxygen does not exist. Further, when the precursor contained in the support is an oxide, the supported catalyst may not have the desired catalytic activity, so it is preferable to reduce the oxide to a simple metal. If the precursor contained in the support does not contain an oxide, the heat treatment is performed in a vacuum atmosphere or an inert gas atmosphere. Whether or not the precursor contained in the carrier contains an oxide can be confirmed by analysis of the crystal structure by X-ray diffraction (hereinafter "XRD") measurement. Since the precursor may contain an extremely small amount of oxide or may generate oxide over time, the step of heat-treating the support is preferably performed in an atmosphere containing a reducing gas.
  • XRD X-ray diffraction
  • Examples of the reducing gas include hydrogen, carbon monoxide, and hydrocarbon gas.
  • a reducing gas atmosphere is an atmosphere containing the reducing gas.
  • the concentration of the reducing gas in the reducing gas atmosphere may be at least the stoichiometry required to reduce the metal element from oxide to metal, and the volume of all gas components in the reaction vessel is 100%. In this case, the reducing gas may be 0.1 to 100%.
  • Gas components other than the reducing gas are not particularly limited as long as they do not react with the reducing gas. For example, inert gases such as helium, nitrogen, and argon can be used.
  • the step of reducing using the reducing gas may be either a closed system or a fluid system, the support obtained in step (2) is put into an arbitrary reaction vessel, and the precursor is heated under the reducing gas atmosphere. is reduced.
  • the reducing gas is flowing.
  • the temperature conditions in the step (3) are not particularly limited, the temperature at which the organic impurities in the step (1) are decomposed is preferable.
  • the temperature conditions for the reduction are not particularly limited, but the temperature at which the organic impurities are decomposed in the step (1) and the oxides generated by the air oxidation in the steps (1) and (2) are reduced. temperature is preferred.
  • metal particles containing Pd and Fe or Pt and Fe can be ordered to have a crystal structure like an intermetallic compound having an ordered structure. It is desirable to have an order transition temperature that provides a centered cubic crystal structure. Therefore, the reaction temperature is preferably 100°C to 1000°C, more preferably 300°C to 800°C, and even more preferably 400°C to 600°C.
  • reaction time in the step (3) is as short as possible so that the metal particles on the support do not coarsen due to thermal aggregation.
  • the reaction time is preferably 1 to 300 minutes, more preferably 10 to 120 minutes, still more preferably 10 to 60 minutes.
  • the present catalyst is obtained through the heat treatment in step (3).
  • the resulting catalyst can be used as a catalyst for chemical reactions, electrode reactions, and exhaust gas purification reactions, as described above.
  • the amount of metal particles contained in the present catalyst can be controlled by adjusting the amount of precursor relative to the support in step (2).
  • the average particle size of the metal particles contained in the present catalyst can be controlled, for example, by the following method.
  • the finer the average particle size of the precursor the more the average particle size of the metal particles contained in the target catalyst. is easy to maintain fineness
  • the larger the average particle size of the precursor the larger the average particle size of the metal particles contained in the target catalyst.
  • the average particle size can be controlled by adjusting the concentration of the metal raw material and the reaction time. The lower the metal raw material concentration, the finer the average particle size of the precursor produced, and the higher the metal raw material concentration, the coarser the average particle size of the precursor.
  • Formation of the precursor is divided into two stages: nucleation from the metal source and grain growth to metal particles.
  • the number of nuclei formed in the solution increases in proportion to the concentration of the metal raw material, and the probability that the nuclei collide with each other and grow to form coarse particles increases.
  • the shorter the reaction time the finer the average particle size of the precursor is maintained, and the longer the reaction time, the longer the grain growth time, so that the average particle size of the precursor tends to become coarser.
  • the average particle size of the alloy particles contained in the target catalyst tends to be coarsened.
  • the longer the heat treatment is performed the larger the average particle size of the metal particles contained in the target catalyst tends to be.
  • the higher the temperature of the precursor the more vigorously the precursor moves on the surface of the support, and the more the precursor comes into contact with other precursors, the more likely it is to grow particles and form aggregates.
  • the longer the heat treatment time the higher the probability of particle growth, and the easier the formation of aggregates. Therefore, the average particle size of the metal particles contained in the target catalyst is coarsened. In order to keep the average particle size of the metal particles contained in the catalyst fine, it is necessary to lower the temperature of the heat treatment and perform the heat treatment in a short period of time.
  • the present invention is not limited to the configurations of the above embodiments.
  • the present catalyst may be added with any other configuration, or may be replaced with any configuration that exhibits the same function.
  • Example 1 Preparation of Al 2 O 3 catalyst supporting 1.2% by mass Pd—Fe alloy nanoparticles (1. Preparation process of metal particles containing Pd and Fe) In a nitrogen atmosphere, 250.5 mg (0.822 mmol) of Pd(II) acetylacetonate (Pd(C 5 H 7 O 2 ) 2 , manufactured by Fuji Film Wako Pure Chemical Industries) and 0.5 mg of an organic stabilizer were placed in a three-necked flask.
  • Pd(II) acetylacetonate Pd(C 5 H 7 O 2 ) 2 , manufactured by Fuji Film Wako Pure Chemical Industries
  • the dodecacarbonyl-3-Fe solution was subsequently added to the Pd(II) acetylacetonate solution heated to 140°C, and the solution in the flask was heated to 280°C. The mixture was stirred at a temperature of 280° C. for 60 minutes to react. As a result, metal particles containing Pd and Fe were generated in the flask. The solution in the flask was then cooled to room temperature.
  • a centrifugal separator was used to separate the metal particles containing Pd and Fe, the precipitate of the organic stabilizer, and the solvent.
  • the recovered metal particles containing Pd and Fe and the precipitate of the organic stabilizer were dried under reduced pressure at room temperature for 4 hours, and further vacuum dried at 60° C. for 4 hours. Metal particles containing Pd and Fe were thus obtained.
  • the obtained impregnated supported powder in which the metal particles containing Pd and Fe were supported on Al 2 O 3 was dried under reduced pressure at 80 ° C. for 4 hours, and the metal particles containing Pd and Fe in the supported powder were 1.2% by mass.
  • An impregnated and adsorbed Al 2 O 3 powder was obtained.
  • Example 2 Preparation of Al 2 O 3 catalyst supporting 3.2% by mass Pd—Fe alloy nanoparticles (1. Preparation step of metal particles containing Pd and Fe) Metal particles containing Pd and Fe were obtained in the same manner as in Example 1.
  • Example 1 The catalyst obtained in Example 1 was subjected to STEM-EDX analysis. From FIGS. 3A to 3D, it can be seen that Pd and Fe are alloyed because the elemental mapping images of Pd and Fe overlap.
  • Powder X-ray diffraction of the catalyst of Example 2 was performed. Powder XRD was measured using an XRD apparatus (Ultima IV manufactured by Rigaku). As a specific measurement condition, CuK ⁇ rays were used, and the diffraction angle of the RSRP-Si standard powder sample was first adjusted so that the diffraction angle of the Si (220) plane was 48.28 in terms of 2 ⁇ .
  • ⁇ indicates a peak attributed to the Pd—Fe alloy
  • ⁇ indicates a peak attributed to Al 2 O 3 .
  • 2 ⁇ 40.11°, which is the diffraction peak of the (111) plane of the Pd metal alone
  • Example 1 As an index of the exhaust gas purification performance of this catalyst, the catalyst of Example 1 was evaluated for its CO oxidation activity.
  • the CO oxidation activity evaluation method was carried out using a catalyst analyzer (BELCAT II, manufactured by Microtrac Bell), which is a fixed-bed flow reactor.
  • the catalytic activity of the catalyst of Example 1 which is the present catalyst, was the highest.
  • the present catalyst was impregnated with 1.2% by mass of Pd/Al 2 O 3 catalyst of Comparative Example 1, which is Pd alone, and 1.2% by mass of metal particles containing Pd and Fe of Test Example 1. showed higher activity compared to the Al 2 O 3 catalyst. From the comparison between Example 1 and Test Example 1, it can be seen that the present catalyst, which is an alloy of Pd and Fe, exhibits superior catalytic activity. From the comparison of Example 1 and Comparative Example 1, which have the same metal loading, it was found that at low temperatures of 250° C.
  • alloying Pd with Fe exhibits better catalytic activity than single metals.
  • low-temperature activation of catalysts is required because engines often stop and restart due to idling stop and hybridization. Since this catalyst has excellent catalytic activity at lower temperatures, even after the engine is cold-started, it can immediately function to purify exhaust gas and comply with regulations, so it is considered to be a useful catalyst. Therefore, it is considered that this catalyst is an exhaust gas catalyst that exhibits better performance than conventional catalysts while reducing the amount of Pd used.
  • Example 1 Pd(II) acetylacetonate (Pd( C5H7O2 ) 2 ) was replaced with a Pt compound such as Pt (II) acetylacetonate (Pt( C5H7O2 ) 2 ) . and in the same manner as above, a metal particle-supported Al 2 O 3 catalyst containing alloy particles of Pt and Fe can be obtained.
  • a Pt compound such as hexachloroPt(IV) acid hexahydrate (H 2 PtCl 6.6H 2 O) was used instead of palladium chloride (II) (PdCl 2 ).
  • a Pt nanoparticle-supported Al 2 O 3 catalyst is obtained.
  • an Al 2 O 3 powder impregnated and adsorbed with metal particles containing Pt and Fe can be obtained.
  • the CO oxidation activity of the metal particles containing the Pt and Fe alloy particles, the Pt nanoparticle-supported Al 2 O 3 catalyst, and the Al 2 O 3 powder impregnated and adsorbed with the metal particles containing Pt and Fe were measured in the same manner as described above.
  • the catalyst in which Pt is alloyed with Fe is considered to exhibit superior catalytic activity to Pt single metal. It is considered that this catalyst is an exhaust gas catalyst that exhibits superior performance to that of conventional catalysts while reducing the amount of Pt used, as with Pd.

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Abstract

Le problème décrit par la présente invention est de fournir un catalyseur de purification de gaz d'échappement qui nécessite moins de Pt ou de Pd et présente des performances similaires ou supérieures aux catalyseurs classiques. La solution selon l'invention porte sur un catalyseur comprenant un support et des particules métalliques qui contiennent du Pd et du Fe ou du Pt et du Fe et ont un diamètre moyen de particule inférieur à 8 nm, si la masse totale du support et des particules métalliques est de 100 % en masse, la masse des particules métalliques étant d'au moins 1 % en masse.
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