WO2023276793A1 - 排ガス浄化用酸化触媒 - Google Patents

排ガス浄化用酸化触媒 Download PDF

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Publication number
WO2023276793A1
WO2023276793A1 PCT/JP2022/024770 JP2022024770W WO2023276793A1 WO 2023276793 A1 WO2023276793 A1 WO 2023276793A1 JP 2022024770 W JP2022024770 W JP 2022024770W WO 2023276793 A1 WO2023276793 A1 WO 2023276793A1
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catalyst
particles
exhaust gas
oxidation catalyst
gas purification
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French (fr)
Japanese (ja)
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準基 長久保
靖幸 伴野
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NE Chemcat Corp
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NE Chemcat Corp
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Priority to CN202280044871.6A priority Critical patent/CN117615845A/zh
Priority to EP22832941.3A priority patent/EP4364841A4/en
Priority to JP2023531846A priority patent/JPWO2023276793A1/ja
Publication of WO2023276793A1 publication Critical patent/WO2023276793A1/ja
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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
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
    • 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
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • 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
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/44—Palladium
    • 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
    • B01J35/19—Catalysts containing parts with different compositions
    • 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0244—Coatings comprising several layers
    • 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0248—Coatings comprising impregnated particles
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • This disclosure relates to an oxidation catalyst for exhaust gas purification. More specifically, the present invention relates to an oxidation catalyst for purifying exhaust gases, which is obtained by combining a plurality of oxidation catalyst particles that do not contain ceria, and which is excellent in low-temperature purification performance.
  • the exhaust gas emitted from boilers, gas turbines, lean-burn gasoline engines, diesel engines, and other lean-burn engines contains many harmful substances derived from fuel and combustion air.
  • harmful substances include hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), PM (Particulate Matter), etc. Regulations on the emissions of these harmful substances are introduced year by year. Enhanced.
  • a combination of exhaust gas purifiers such as DOC (diesel oxidation catalyst), DPF (Diesel Particulate Filter), and SCR (Selective Catalytic Reduction) is used as a method for purifying these harmful components.
  • the DPF A DOC catalyst that oxidizes HC, CO, and NO is installed on the internal combustion engine side of the SCR and the SCR.
  • Patent Document 1 various exhaust gas purification systems capable of burning PM with NOx even at low temperatures have been studied.
  • the catalyst contains a ceria compound or a ceria-zirconia composite oxide that adsorbs and retains pollutants such as NOx when the catalyst is inactive at low temperatures and releases pollutants when the catalyst reaches its activation temperature.
  • Patent Document 3 a method for suppressing contaminants at cold start is used.
  • Patent Document 4 discloses an oxide material in which a platinum group element such as palladium and a component of a rare earth oxide such as ceria are supported on a heat-resistant metal oxide support containing lanthana, zirconia, etc., and two other materials. Ceria's fragile sulfur tolerance is improved and excellent catalytic activity is exhibited by using an oxidation catalyst composite containing a specific oxidation material.
  • Patent Document 1 JP-A-01-318715
  • Patent Document 2 JP-A-2005-248964
  • Patent Document 3 JP-A-2018-530419
  • Patent Document 4 JP-A-2018-511475
  • an object of the present disclosure is to provide a new exhaust gas purifying catalyst that does not contain a Ce compound, which has been conventionally considered essential for low-temperature catalytic activity, and that has excellent low-temperature oxidation activity.
  • the present disclosure has been made in view of the above problems, and by reducing the content of Ce, which inhibits low-temperature activity, and adding a compound that improves low-temperature activity, It was found that it is possible to provide an exhaust gas oxidation catalyst for diesel engines that has excellent catalytic activity (HC, CO, and NOx oxidation performance). That is, the gist of the present disclosure is as follows.
  • An oxidation catalyst for purifying an exhaust gas comprising a base material and a catalyst layer provided on the base material, The catalyst layer includes first catalyst particles and second catalyst particles, The first catalyst particles include first carrier particles containing a rare earth element other than cerium, and palladium (Pd) supported on the carrier particles, An oxidation catalyst for exhaust gas purification, wherein the second catalyst particles include second carrier particles, and platinum (Pt) and palladium (Pd) supported on the carrier particles.
  • the rare earth element other than cerium is at least one light rare earth element selected from the group consisting of lanthanum, praseodymium, neodymium, samarium, and europium.
  • FIG. 1 is a schematic perspective view showing one embodiment of a substrate.
  • An exhaust gas purifying oxidation catalyst includes a substrate and a catalyst layer provided on the substrate.
  • the members constituting the exhaust gas purifying oxidation catalyst will be described in detail below.
  • the substrate is not particularly limited as long as it can support the catalyst layer described below and is made of a material having a certain degree of fire resistance, and conventionally known substrates can be used.
  • substrate materials include alumina, silica, mullite (alumina-silica), cordierite, cordierite-alpha alumina, zircon mullite, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon. , ceramics such as petalite, aluminosilicates, aluminum titanate, silicon carbide, and silicon nitride, and metal materials such as refractory metals such as stainless steel and corrosion-resistant alloys such as ferritic stainless steel based on iron.
  • the above inorganic or metallic materials may be used singly or in combination of two or more.
  • alumina, silica, mullite, cordierite, stainless steel, and silicon carbide are preferred, and those containing cordierite, stainless steel, and silicon carbide are more preferred.
  • preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 99% by mass or more (including 100% by mass) of the entire substrate is made of the above material. .
  • the base material may contain other components with the above-described material as a main component.
  • Fe 2 O 3 , SiO 2 , Na 2 O, etc. which are known to improve the heat resistance of the carrier, may be added to the above materials.
  • the shape of the substrate is also not particularly limited, and various shapes such as spherical, cylindrical, bead-like, pellet-like, prismatic, tablet-like, needle-like, film-like, honeycomb monolithic, etc. can do. Among these, beads, pellets, and honeycomb monoliths are preferred. Therefore, the substrate according to a preferred embodiment of the present disclosure is made of alumina, silica, mullite, cordierite, or stainless steel, and preferably has a bead, pellet, or honeycomb monolith shape. A honeycomb monolith made by Wright is more preferred.
  • the substrate 1 is cylindrical in shape with a cylindrical outer peripheral surface 10 , an inlet end 20 and an outlet end 30 .
  • the substrate 1 comprises a plurality of fine parallel gas flow passages 40 formed in the substrate 1 .
  • a flow passageway 40 is defined by the wall and extends through the substrate 1 from the inlet end 20 to the outlet end 30 and is shaped to allow flow of the exhaust gas stream.
  • the partitioning wall may have a substantially regular polygonal shape, for example a square, with the exhaust gas flow passage 40 .
  • the base material 1 has a predetermined length along the exhaust gas flow direction.
  • the length of the base material is about 25.4 mm to 400 mm depending on the outer diameter. Further, the outer diameter of the substrate is approximately 76.5 mm to 400 mm.
  • the size of one circulation passage 40 partitioned by the wall is about 1.0 mm to 2.15 mm on each side.
  • a catalyst layer is provided on the substrate described above. More specifically, a catalyst layer is formed on the surface of the walls in the substrate 1 .
  • the catalyst layer includes first catalyst particles and second catalyst particles, the first catalyst particles include first support particles containing a rare earth element other than cerium, and and palladium (Pd). That is, the present disclosure does not include cerium-zirconium compounds (hereinafter referred to as CZ compounds), etc., which have conventionally been used as supporting components for palladium.
  • a second carrier It is used in combination with second catalyst particles in which platinum and palladium are supported on the particles.
  • Cerium compounds, especially CZ compounds have excellent oxygen storage capacity, so they especially store NOx, which is most difficult to oxidize catalytically at low temperatures, and suppress NOx in exhaust gas even in low temperature environments such as when the engine is started. Therefore, it is used in conventional oxidation catalysts for purifying exhaust gas.
  • Such an exhaust gas purifying oxidation catalyst containing a CZ compound can release NOx and the like when the catalyst portion reaches a high temperature.
  • the reaction of harmful components in the exhaust gas in the DOC catalyst is an oxidation reaction, it is necessary for oxygen molecules or oxygen radicals to contact and react with the harmful components.
  • the CZ compound which has an excellent oxygen storage capacity at low temperatures, occludes oxygen molecules and oxygen radicals used in the oxidation reaction before reacting with harmful components, and as a result, it is thought that the purification rate decreased.
  • catalyst particles in which palladium is supported on carrier particles containing a rare earth element that does not contain cerium element and promotes the reaction in a low temperature range and platinum / palladium that exhibits excellent low temperature catalytic performance.
  • oxygen molecules or oxygen radicals can sufficiently come into contact with the harmful components in the exhaust gas even in a low temperature range. be done.
  • the first catalyst particles constituting the catalyst layer are obtained by supporting palladium on the first carrier particles containing rare earth elements other than cerium.
  • Rare earth elements other than cerium include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium ( Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).
  • oxides of these can be used as carrier particles.
  • the oxides of rare earth elements are sesquioxides (Re 2 O 3 , where Re is a rare earth element) except for praseodymium (Pr) and terbium (Tb).
  • Praseodymium oxide is typically Pr 6 O 11 and terbium oxide is typically Tb 4 O 7 . These may be composite oxides of two or more kinds.
  • the first carrier particles may contain oxides such as zirconia, niobia, yttria and alumina in addition to the rare earth oxides described above.
  • the rare earth oxide and the oxide such as zirconia may be separate particles, but a composite oxide in which both are combined is preferably used.
  • a lanthana-zirconia composite oxide can be particularly preferably used.
  • the first carrier particles can also be produced by a known method. These production methods are not particularly limited, but a coprecipitation method and an alkoxide method are preferred.
  • an alkaline substance is added to an aqueous solution obtained by mixing a rare earth salt and various salts of other elements, such as a zirconium salt, which are blended as necessary, in a predetermined stoichiometric ratio, and hydrolysis is performed.
  • a method of coprecipitating the precursor and calcining the hydrolysis product or coprecipitate can be exemplified.
  • the types of various salts used here are not particularly limited. Hydrochlorides, oxyhydrochlorides, nitrates, oxynitrates, carbonates, phosphates, acetates, oxalates, citrates and the like are generally preferred.
  • the type of alkaline substance is not particularly limited. Aqueous ammonia solutions are generally preferred.
  • the alkoxide method for example, a mixture obtained by mixing the alkoxide of the rare earth element and the alkoxide of another element, such as zirconium alkoxide, which is blended as necessary, in a predetermined stoichiometric ratio, is hydrolyzed, and then calcined. is preferred.
  • the type of alkoxide used here is not particularly limited. Generally, methoxide, ethoxide, propoxide, isopropoxide, butoxide, and ethylene oxide adducts thereof are preferred.
  • the rare earth metal element may be blended as a metal alkoxide or blended as various salts described above.
  • the firing conditions for the subsequent firing treatment are not particularly limited and may be in accordance with conventional methods.
  • the firing atmosphere may be an oxidizing atmosphere, a reducing atmosphere, or an air atmosphere.
  • the calcination temperature and treatment time vary depending on the desired composition and its stoichiometric ratio. °C to 800 °C for 30 minutes to 2 hours. In addition, you may dry under reduced pressure using a vacuum dryer etc. prior to high temperature baking.
  • the average particle diameter (D50) of the first support particles can be appropriately set according to the desired performance, and is not particularly limited. from the viewpoint of increasing In addition, in this specification, the average particle diameter D50 means the median diameter measured using a laser diffraction particle size distribution analyzer.
  • the above-described particles and palladium nitrate are mixed, a liquid medium such as water is added, and kneaded by a ball mill or the like to prepare a slurry. It can be obtained by firing.
  • the firing temperature is preferably 400°C to 800°C, more preferably 500°C to 700°C.
  • the firing time is preferably 10 minutes to 6 hours, more preferably 0.5 hours to 2 hours.
  • the second catalyst particles constituting the catalyst layer are platinum (Pt) and palladium (Pd) supported on second carrier particles.
  • the second carrier particles are not particularly limited, and can be appropriately selected from those known in the art according to the required performance, and the type is not particularly limited. For example, silica, boehmite, alumina ( ⁇ -Al 2 O 3 , ⁇ -Al 2 O 3 , ⁇ -Al 2 O 3 , ⁇ -Al 2 O 3 , ⁇ -Al 2 O 3 , ⁇ -Al 2 O 3 ).
  • metal oxides or metal composite oxides such as lanthanum oxide, neodymium oxide and praseodymium oxide, perovskite-type oxides, barium compounds, anatase titania, zeolites, etc.
  • porous particles having a large BET specific surface area are preferable as the base material.
  • Specific examples include alumina, silica, boehmite, silica-alumina, and the like.
  • Examples of alumina include ⁇ -alumina, ⁇ -alumina, and ⁇ -alumina.
  • Silica includes amorphous, glassy, and colloidal silica, as well as crystalline silica having a variety of different phase modifications. Silica generally has a higher BET specific surface area than alumina and highly dispersed platinum group elements. Silica-alumina can be crystalline or amorphous. In silica-alumina, the Si/Al ratio varies and is appropriately set according to the application.
  • Examples of titania include anatase titania.
  • Examples of crystalline zeolites include ZSM-type zeolite and ⁇ -type zeolite. The base particles can be used singly or in combination of two or more.
  • the average particle diameter (D50) of the second carrier particles can be appropriately set according to the desired performance, and is not particularly limited. from the viewpoint of increasing The definition of the average particle size is the same as above.
  • the above-described particles are mixed with platinum nitrate and palladium nitrate, a liquid medium such as water is added, and the mixture is kneaded with a ball mill or the like to prepare a slurry.
  • a slurry can be obtained by drying and firing.
  • the firing temperature is preferably 400°C to 800°C, more preferably 500°C to 700°C.
  • the firing time is preferably 10 minutes to 6 hours, more preferably 0.5 hours to 2 hours.
  • the ratio of platinum and palladium supported on the second carrier particles is preferably Pt:Pd of 1:0.1 to 10, more preferably 1:0.2 to 4, in mass ratio.
  • the catalyst layer may contain other components as long as it contains the above-described first catalyst particles and second catalyst particles.
  • Other components include various additives known in the art, such as binders such as boehmite and alumina sol, dispersion stabilizers such as nonionic surfactants and anionic surfactants, pH adjusters, viscosity adjusters, Platinum group elements other than platinum and palladium, such as rhodium (Rh), and the like can be used, but are not particularly limited to these.
  • binders such as boehmite and alumina sol
  • dispersion stabilizers such as nonionic surfactants and anionic surfactants
  • pH adjusters pH adjusters
  • viscosity adjusters such as platinum group elements other than platinum and palladium, such as rhodium (Rh), and the like can be used, but are not particularly limited to these.
  • Platinum group elements other than platinum and palladium, such as rhodium (Rh), and the like can be used, but are not particularly
  • binders examples include various sols such as boehmite, alumina sol, titania sol, silica sol, and zirconia sol. Also, soluble salts such as aluminum nitrate, aluminum acetate, titanium nitrate, titanium acetate, zirconium nitrate, zirconium acetate can be used as binders. In addition, acids such as acetic acid, nitric acid, hydrochloric acid and sulfuric acid can also be used as binders.
  • the amount of the binder used is not particularly limited, it is preferably 0.01% by mass to 15% by mass, more preferably 0.05% by mass to 10% by mass, relative to the total amount of the catalyst layer.
  • the catalyst layer may contain catalysts, co-catalysts and various additives known in the art.
  • a barium-containing compound can also be used as an additive in the catalyst layer. Addition of a barium-containing compound is expected to improve heat resistance and activate catalytic performance.
  • Examples of barium-containing compounds include sulfates, carbonates, composite oxides, oxides, and the like, but are not particularly limited to these. More specifically, BaO, Ba ( CH3COO ) 2 , BaO2 , BaCO3, BaZrO3 , BaAl2O4 etc. are mentioned.
  • the amount of the barium-containing compound used is not particularly limited, but is preferably 1% by mass to 20% by mass, more preferably 2% by mass to 15% by mass, relative to the total amount of the catalyst layer.
  • the content ratio of the first catalyst particles and the second catalyst particles contained in the catalyst layer can be appropriately set according to the desired performance, and is not particularly limited, but is 50% by mass to 100% by mass with respect to the total amount of the catalyst layer. is preferred, more preferably 70% by mass to 95% by mass, and still more preferably 90% by mass to 95% by mass.
  • the content of the first catalyst particles contained in the catalyst layer is preferably 10% to 90% by mass, more preferably 30% to 70% by mass, with respect to the total amount of the first catalyst particles and the second catalyst particles. is more preferred.
  • the catalyst layer provided on the substrate surface does not need to have the same composition in all of them, and the composition of the catalyst layer may be different between the vicinity of the entrance end of the substrate and the vicinity of the exit end of the substrate.
  • a catalyst layer may be laminated.
  • a catalyst layer containing first catalyst particles and a catalyst layer containing second catalyst particles may be laminated.
  • it is preferable that the first catalyst particles and the second catalyst particles are contained in the same catalyst layer.
  • the catalyst layer is formed by kneading the above-described first catalyst particles and second catalyst particles, and other optional components such as a binder and a dispersion stabilizer, into a liquid medium such as water and kneading the mixture with a ball mill or the like. It can be formed by preparing a slurry, coating the slurry on the surface of the base material, and then drying and baking it. As the coating method, various known coating methods, wash coating methods, and zone coating methods can be applied. A catalyst layer having a desired thickness can be formed by adjusting the coating amount.
  • drying temperature is not particularly limited, it is preferably 70°C to 200°C, more preferably 80°C to 150°C.
  • the firing temperature is not particularly limited, but is preferably 300°C to 650°C, more preferably 400°C to 600°C.
  • a known heating means such as an electric furnace or a gas furnace can be used.
  • the coating amount can be appropriately set according to the desired performance and is not particularly limited, but considering the effects of pressure loss, engine output, fuel consumption, etc., per unit volume (1 L) of the substrate, 10 g to 100 g is preferable, more preferably. is 12g to 80g, more preferably 15g to 60g.
  • per unit volume (1 L) of the base material means not only the net volume of the base material but also the volume of voids formed inside the base material. means.
  • the cells are partitioned inside the substrate, it means the total bulk volume of 1 L including the volume of the cells in addition to the pure volume of the substrate and the volume of the voids.
  • the amount of palladium in the entire catalyst layer can be appropriately set according to the desired performance, and is not particularly limited. 5 g to 5 g, more preferably 0.6 g to 1.5 g.
  • the amount of platinum in the entire catalyst layer can be appropriately set according to the desired performance, and is not particularly limited. 0.5 g to 5 g, more preferably 1.2 g to 3.0 g.
  • the amount of palladium and the amount of platinum in the catalyst layer can be adjusted by adjusting the mixing ratio of the carrier particles and the noble metal element (platinum or palladium) when preparing the first catalyst particles and the second catalyst particles.
  • Exhaust gas purifying oxidation catalysts can be used as catalysts for purifying exhaust gases from diesel engines, gasoline engines, jet engines, boilers, gas turbines, etc., but are particularly useful for purifying exhaust gases that come into contact with exhaust gases from diesel engines. It can be suitably used as an oxidation catalyst.
  • the oxidation catalyst for purifying exhaust gas can be arranged in the exhaust system of various engines.
  • the number of installations and installation locations can be appropriately designed according to exhaust gas regulations. For example, if exhaust gas regulations are strict, the number of installation locations may be two or more, and the installation locations may be arranged under the floor behind the catalyst immediately below the exhaust system.
  • the oxidation catalyst for purifying exhaust gas of the present embodiment even if it does not contain a Ce compound, which has been considered essential in the past, it can be used not only when starting at low temperatures but also in various driving specifications including high-speed driving at high temperatures. , can exhibit excellent CO, HC, and NOx purification effects.
  • the catalyst inlet gas temperature was varied from 25°C to 600°C at a constant heating rate (10°C/min), and the gas composition at the catalyst inlet and outlet was analyzed by FTIR to determine the HC purification rate. . Then, the temperature (light-off temperature, HC-T50) at which the HC purification rate reached 50% was measured.
  • the purification rate of CO and NOx was measured by the same method, and the point at which it reached 50% (T50) and the point at which it reached 75% (T75) were defined. Further, the purification rate at the temperature, for example, the CO purification rate at 300° C. is defined as “CO_C300”. That is, “HC_T50” is the temperature at which 50% of the HC in the inflow gas is converted, and “HC_C300” is the reaction rate (%) of HC at 300°C.
  • the purification rate is obtained from the composition of the gas at the outlet side/the amount of gas at the inlet side, the amount of NOx that has been occluded in advance is released by heat, and if the purification reaction is insufficient, The NOx concentration of the effluent gas increases, and the purification rate may take a negative value. In either case, lower temperatures for T50 and T75 are more preferable, and higher temperatures for C300 and the like are more preferable.
  • Example 1 A cordurite honeycomb substrate was prepared, and a slurry containing 40 g/L of the Pt—Pd/SiO 2 —Al 2 O 3 catalyst particles obtained in Reference Example 2 was applied to the substrate so as to have a washcoat amount of 60 g/L. A catalyst layer was formed on the substrate surface by coating the material, drying at 150° C. for 2 hours, and firing at 550° C. for 0.5 hour. Next, the slurry containing 40 g/L of the Pd/LZ catalyst particles obtained in Reference Example 1 was coated on the substrate after calcination so that the wash coat amount was 80 g/L, and the temperature was 150°C. After drying for 2 hours at 550° C., firing was performed for 0.5 hours.
  • Example 1 A catalyst layer was formed on the substrate surface under the same conditions as in Example 1, except that the substrate was not coated with the slurry containing the Pd/LZ catalyst particles obtained in Reference Example 1. did.
  • Example 2 A catalyst layer was formed on the substrate surface under the same conditions as in Example 1, except that the substrate was not coated with the slurry containing the Pt—Pd/SiO 2 —Al 2 O 3 catalyst particles obtained in Reference Example 2. formed.
  • Comparative Example 3 using a conventional ceria-zirconia-based carrier has excellent NOx storage performance, but has poor CO and HC purification performance at low temperatures. low and inadequate.
  • Comparative Example 4 in which alumina particles supporting Pt--Pd were further coated in order to compensate for this, although the low-temperature purification performance was improved, it can be said that it is still at an insufficient level.
  • Example 1 in which catalyst particles in which Pd is supported on a lanthanum-zirconia-based carrier and catalyst particles in which Pt--Pd is supported on a silica-alumina carrier are used in combination, excellent CO, HC, It can be seen that it has NOx purification performance.
  • the result of Example 1 is an excellent effect that cannot be expected from the results of Comparative Examples 1 and 2 using each particle alone.

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