WO2020241250A1 - 排気ガス浄化触媒構造体及びその製造方法 - Google Patents
排気ガス浄化触媒構造体及びその製造方法 Download PDFInfo
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- WO2020241250A1 WO2020241250A1 PCT/JP2020/019041 JP2020019041W WO2020241250A1 WO 2020241250 A1 WO2020241250 A1 WO 2020241250A1 JP 2020019041 W JP2020019041 W JP 2020019041W WO 2020241250 A1 WO2020241250 A1 WO 2020241250A1
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- WIPO (PCT)
- Prior art keywords
- mass
- exhaust gas
- rare earth
- metal
- catalyst layer
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/10—Carbon or carbon oxides
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/12—Hydrocarbons
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/14—Nitrogen oxides
Definitions
- the present invention relates to an exhaust gas purification catalyst structure and a method for manufacturing the same, which can be suitably used for purifying exhaust gas emitted from an internal combustion engine of an automobile including a motorcycle and a motorcycle.
- Carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) are used as catalysts for treating exhaust gas emitted from internal combustion engines such as automobiles (hereinafter referred to as “exhaust gas purification catalysts”).
- exhaust gas purification catalysts Is oxidatively reduced, and a ternary catalyst (Three way catalyst: TWC) is used.
- a catalyst composition in which a noble metal such as palladium (Pd) or rhodium (Rh), which is a catalytically active component, is supported on an inorganic porous body having a high specific surface area is prepared from ceramics or metal. It is known that a catalyst layer is provided on the base material.
- the exhaust gas purification catalyst of a saddle-type vehicle such as a motorcycle may be subject to large vibration depending on the running conditions
- stainless steel having excellent impact resistance is usually used as a base material for forming the catalyst layer.
- a metal carrier made of stainless steel or the like is used. Examples of the metal carrier include a honeycomb body provided with an outer cylinder body and a metal foil material provided inside the outer cylinder body and forming a flow path for exhaust gas.
- the exhaust gas purification catalyst for riding saddle-type vehicles has a limited space for mounting the catalyst compared to the exhaust gas purification catalyst for motorcycles, and exhibits high purification performance despite its small capacity. Is required.
- Examples of the exhaust gas purification catalyst for such a saddle-type vehicle include a catalyst layer containing palladium (Pd), which is a metal having a high ability to catalyze the oxidation reaction of HC and CO, on a metal carrier, and reduction of NOx.
- Pd palladium
- Rh rhodium
- a catalyst structure in which a catalyst layer containing rhodium (Rh), which is a metal having a high ability to catalyze a reaction, is laminated is known.
- Rh rhodium
- such a catalyst structure needs to be manufactured by performing two steps, a step of forming a catalyst layer containing Pd and a step of forming a catalyst layer containing Rh, which causes a problem that the manufacturing cost rises. There is. Therefore, from the viewpoint of reducing the manufacturing cost, there is a demand for a catalyst structure in which a catalyst layer containing both Pd and Rh is formed in one step.
- Patent Document 1 describes palladium particles and rhodium particles that have been previously grown to a specific particle size in order to suppress a decrease in active points due to the growth of noble metal particles due to fluctuations in temperature and atmosphere due to automobile driving conditions. Catalysts are disclosed, including those carried on separate carrier particles.
- the present inventors have found that when the catalyst disclosed in Patent Document 1 is formed on a metal carrier, the following problems occur.
- OSC material an auxiliary catalyst (hereinafter, referred to as "OSC material") having an oxygen storage capacity (OSC: Oxygen Storage capacity) in order to improve the catalyst performance.
- OSC oxygen storage capacity
- Patent Document 1 when the catalyst disclosed in Patent Document 1 is formed on a metal carrier, if a catalyst containing a non-Ce rare earth element is used as the OSC material, the metal carrier is used. It was found that the metal foil material of No. 1 may be stretched due to the tensile force due to volume expansion. This is because the non-Ce rare earth element contained in the catalyst layer diffuses into the oxide film formed on the surface of the metal foil material and easily dissolves, and when the non-Ce rare earth element diffuses into the oxide film, it is a condition of automobile driving. It is considered that the fluctuation causes volume expansion when the oxide film is exposed to a high temperature, and the metal foil material is stretched by the tensile force due to the volume expansion.
- foil stretching In this phenomenon of the metal foil material stretching (hereinafter referred to as "foil stretching"), there is a temperature difference between the central portion and the outer peripheral portion of the honeycomb body, and the axial metal foil material expands near the center of the honeycomb body. It is thought that this is also the cause.
- an object of the present invention is to provide an exhaust gas purification catalyst structure capable of reducing manufacturing cost and suppressing foil elongation, and a method for manufacturing the same.
- the first aspect of the present invention is A metal carrier composed of an outer cylinder and a metal foil material provided inside the outer cylinder and forming a flow path for exhaust gas.
- a catalyst layer provided on a surface of the metal foil material forming the flow path is provided.
- the catalyst layer contains a noble metal, an OSC material containing cerium and a rare earth element other than cerium (non-Ce rare earth element), and alumina, and the content of the non-Ce rare earth element is an oxide with respect to 100% by mass of the catalyst layer.
- the second aspect of the present invention is Alumina is added to the solution containing the first noble metal, the first noble metal is supported on the alumina to form a slurry containing alumina carrying the first noble metal, and cerium and a rare earth element other than cerium (non-Ce rare earth element). ) And the solution containing the second noble metal are added to the slurry in this order, the second noble metal is supported on the OSC material, and the slurry further containing the OSC material carrying the second noble metal is prepared.
- the catalyst layer is an exhaust gas purification catalyst structure characterized in that the content of non-Ce rare earth elements is 2.52% by mass or more and 4.62% by mass or less in terms of oxide with respect to 100% by mass of the catalyst layer. Propose a manufacturing method.
- the exhaust gas purification catalyst structure proposed by the present invention maintains the oxygen occlusion and release ability of the OSC material contained in the catalyst layer by keeping the content of the non-Ce rare earth element contained in the catalyst layer within a specific range. It is possible to suppress the diffusion of rare earth elements into the oxide film formed on the surface of the metal foil material, suppress the foil elongation, and improve the structural durability.
- an alumina supporting a first noble metal and an OSC material containing cerium and a non-Ce rare earth element supporting a second noble metal are layered in one layer.
- the catalyst layer contained in can be formed, the number of manufacturing steps can be reduced, and the manufacturing cost can be reduced.
- two types of precious metals can be selectively supported on two types of carriers individually in one step. Even when one catalyst layer containing a noble metal is formed, the obtained exhaust gas purification catalyst structure is difficult to alloy two kinds of noble metals due to high temperature, and deterioration of catalyst performance can be suppressed. Foil elongation is suppressed and structural durability is also excellent.
- An example of the embodiment of the present invention is a metal carrier composed of an outer cylinder, a metal foil material provided inside the outer cylinder and forming a flow path for exhaust gas, and the metal foil material.
- the catalyst layer is provided with a catalyst layer provided on the surface forming the flow path, and the catalyst layer contains a noble metal, an OSC material containing cerium and a rare earth element other than cerium (non-Ce rare earth element), and alumina. It is an exhaust gas purification catalyst structure in which the content of non-Ce rare earth element with respect to 100% by mass of the catalyst layer is 2.52% by mass or more and 4.62% by mass or less in terms of oxide.
- the metal carrier includes an outer cylinder and a metal foil material provided inside the outer cylinder and forming a flow path for exhaust gas.
- the outer cylinder may be, for example, a cylindrical shape that is opened in the front-rear direction.
- Examples of the material constituting the outer cylinder of the metal carrier include refractory metals such as stainless steel (SUS) and corrosion-resistant alloys based on iron.
- the metal foil material is preferably made of stainless steel containing aluminum (Al).
- Al stainless steel containing aluminum
- an oxide film containing aluminum oxide (Al 2 O 3 ) as a main component is formed on the surface of the metal foil material, which can improve the oxidation resistance. it can.
- the metal foil material is more preferably made of Fe—Cr—Al stainless steel in order to improve the oxidation resistance at high temperatures.
- the stainless steel containing Al which is a raw material of the metal foil material, contains C and Si in order to improve the toughness of the metal foil material, in addition to Al and each element of Fe and Cr contained as necessary. Mn may be contained in order to improve the oxidation resistance.
- the stainless steel containing Al, which is a raw material of the metal foil material may contain a rare earth element such as La in order to improve the adhesion of the Al 2 O 3 oxide film.
- the content of aluminum (Al) in the metal foil material is preferably 3.0% by mass or more and 6.0% by mass or less.
- Al content in the metal foil material is 3.0% by mass or more and 6.0% by mass or less, the surface of the metal foil material serving as the flow path surface of the exhaust gas is formed without lowering the toughness of the metal foil material.
- a film of aluminum oxide (Al 2 O 3 ) can be formed, and the oxidation resistance at high temperatures can be improved.
- the metal carrier preferably includes a flat plate-shaped metal foil material and a corrugated plate-shaped metal foil material inside the outer cylinder.
- a honeycomb body also referred to as a "metal honeycomb”
- the metal carrier is formed in a roll shape by alternately stacking a flat plate-shaped metal foil material and a corrugated metal foil material and repeatedly winding them around the axial direction, and the outer cylinder of the roll-shaped outer cylinder is formed. It can be formed by joining inside the body.
- the contact portion between the flat plate-shaped metal foil material and the corrugated metal foil material may be joined by, for example, diffusion joining or brazing joining, and the outer peripheral corrugated metal foil material or flat plate-shaped metal foil material may be joined.
- the contact portion between the metal foil material and the outer cylinder may be joined by brazing or the like.
- a catalyst layer can be formed by adhering a slurry described later with a wash coat or the like to the surface of the metal carrier that forms the exhaust gas flow path, that is, the surface of the inner wall of each channel.
- the thickness of the metal foil material is preferably a thickness that can increase the number of exhaust passages (cells) of the metal honeycomb per unit area to improve the cell density and reduce the back pressure.
- the thickness of the metal foil material may be adjusted according to the cell density of the metal honeycomb, but is preferably 20 ⁇ m or more and 60 ⁇ m or less, and more preferably 30 ⁇ m or more and 50 ⁇ m or less.
- the thickness of the metal foil material is preferably 45 ⁇ m or more and 55 ⁇ m or less, and when 400 cells per square inch, the thickness of the metal foil material is It is preferably 25 ⁇ m or more and 45 ⁇ m or less, and more preferably 30 ⁇ m or more and 40 ⁇ m or less.
- honeycomb bodies may be arranged side by side on the gas side and the gas side at regular intervals in a metal outer cylinder.
- the outer cylinder body may be used as an exhaust pipe or a muffler, and the honeycomb body may be arranged inside the exhaust pipe or the muffler.
- a cylindrical punching metal When a punching metal called a punching pipe or a punching tube is used, heat resistance is improved and a through hole is formed by punching, so that a large area can be obtained, exhaust gas purification performance is improved, and exhaust resistance in the exhaust pipe is small. Therefore, it can be used, for example, in an exhaust gas purification device for a motorcycle or a motorcycle.
- the catalyst layer contains noble metal, OSC material containing rare earth elements other than cerium and cerium, and alumina, and the content of rare earth elements (non-Ce rare earth elements) other than cerium is 100% by mass of the catalyst layer.
- it is in the range of 2.52% by mass or more and 4.62% by mass or less, preferably in the range of 3.15% by mass or more and 4.62% by mass or less, and more preferably 3.15% by mass.
- the non-Ce rare earth elements contained in the catalyst layer form an oxide film formed on the surface of the metal foil material. It becomes difficult to spread. If the diffusion of non-Ce rare earth elements contained in the catalyst layer to the oxide film on the surface of the metal foil material can be suppressed, the volume of the oxide film caused by the diffusion of the rare earth elements in the oxide film on the surface of the metal foil material. Expansion can be suppressed and foil elongation can be suppressed. When the foil stretches, the flow path of the exhaust gas becomes narrow and the back pressure rises, which affects the output of the engine.
- the metal foil material and the catalyst layer may be peeled off, and when the foil elongation is further increased, the metal foil material forming the exhaust gas flow path may be separated from the outer cylinder body. Durability may be inadequate.
- the exhaust gas purification catalyst structure of the present embodiment by providing the catalyst layer described above, it is possible to suppress foil elongation, thereby suppressing a decrease in engine output and structural durability. You will be able to improve your sexuality.
- the non-Ce rare earth element contained in the catalyst layer is preferably derived from the OSC material contained in the catalyst layer.
- the heat resistance of the OSC material can be improved, the crystal strain can be increased, and the oxygen occlusion / release ability can be improved. Further, when the non-Ce rare earth element is contained in the OSC material, the affinity between the OSC material and the specific precious metal is improved, and the specific precious metal can be selectively supported on the OSC material.
- the mass of the catalyst layer may be obtained by measuring the mass of the catalyst layer of the manufactured exhaust gas purification catalyst structure, or may be obtained from the amount of material used in manufacturing the exhaust gas purification catalyst structure. Good.
- the oxide-equivalent content of the non-Ce rare earth element may be obtained by measuring the content ratio of the non-Ce rare earth element in the produced exhaust gas purification catalyst structure and obtaining the oxide-equivalent mass from the measurement result. , It may be obtained from the amount of oxides of non-Ce rare earth elements used in producing the exhaust gas purification catalyst structure.
- the content of the non-Ce rare earth element in the catalyst layer is in the range of 2.52% by mass or more and 4.62% by mass or less, preferably 3.15% by mass or more, with respect to 100% by mass of the catalyst layer.
- It is in the range of 62% by mass or less, more preferably in the range of 3.15% by mass or more and 4.20% by mass or less, and even more preferably in the range of 3.15% by mass or more and 3.36% by mass or less. It is particularly preferably in the range of 3.33% by mass or more and 3.36% by mass or less.
- Non-Ce rare earth elements are scandium (Sc), ytterbium (Y), lantern (La), placeodim (Pr) neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), Examples thereof include dysprosium (Dy), formium (Ho), erbium (Er), samarium (Tm), ytterbium (Yb) and lutetium (Lu).
- At least one rare earth element selected from the group consisting of neodymium (Nd), lanthanum (La), yttrium (Y) and praseodymium (Pr) is preferable, and neodymium (Nd) and lanthanum (La) are used. It is more preferable that it is at least one rare earth element selected from.
- These non-Ce rare earth elements can improve the heat resistance of the OSC material or increase the crystal strain to improve the oxygen occlusion and release ability of the OSC material.
- the non-Ce rare earth element can strengthen the interaction with a specific noble metal and increase the affinity when supporting the noble metal on the OSC material, and can make a specific noble metal, for example, rhodium (Rh) into the OSC material. It can be selectively supported.
- a specific noble metal for example, rhodium (Rh) into the OSC material. It can be selectively supported.
- the content of neodymium with respect to 100% by mass of the catalyst layer is preferably in the range of 1.48% by mass or more and 4.20% by mass or less in terms of oxide. It is more preferably in the range of 2.10% by mass or more and 4.20% by mass or less, and further preferably in the range of 2.10% by mass or more and 2.97% by mass or less.
- the heat resistance and oxygen occlusion / release ability of the OSC material can be improved, and a more effective affinity for a specific precious metal can be exhibited.
- neodymium does not diffuse to the oxide film on the surface of the metal foil material, and the foil elongation of the metal foil material on which the catalyst layer is supported can be suppressed.
- the content of lantern with respect to 100% by mass of the catalyst layer is preferably in the range of 0.42% by mass or more and 1.23% by mass or less in terms of oxide. It is more preferably 1.04% by mass or more and 1.13% by mass or less, still more preferably 1.05% by mass or more and 1.13% by mass or less, and even more preferably. Is in the range of 1.05% by mass or more and 1.10% by mass or less.
- the rare earth element contains lanthanum and the lanthanum content is within the above range, the heat resistance and oxygen occlusion / release ability of the OSC material can be improved, and an effective affinity for precious metals can be exhibited.
- the lanthanum does not diffuse to the oxide film on the surface of the metal foil material, and the foil elongation of the metal foil material on which the catalyst layer is supported can be suppressed.
- the ratio (non-Ce rare earth element / Al) of the content (mass%) of the non-Ce rare earth element in the catalyst layer to the content (mass%) of Al in the metal foil material is 0.2 or more and 1.1 or less. It is preferably in the range of 0.3 or more and 1.0 or less, more preferably 0.4 or more and 0.9 or less, still more preferably 0.46 or more and 0.84 or less. Yes, particularly preferably in the range of 0.57 or more and 0.76 or less.
- the ratio of the content of non-Ce rare earth elements in the catalyst layer to the content of Al in the metal foil material (mass%) is in the above range, the non-Ce rare earth elements contained in the catalyst layer are on the surface of the metal foil material. It is difficult to diffuse into the formed oxide film, and foil elongation can be suppressed.
- the OSC material preferably contains a co-catalyst having an oxygen storage capacity (OSC: Oxygen Storage capacity), and can be a carrier of a noble metal having a catalytic ability.
- OSC oxygen storage capacity
- a material containing cerium and a rare earth element other than cerium is used, for example, a porous body such as cerium oxide or a ceria-zirconia composite oxide, and further non-Ce. Examples thereof include those containing rare earth elements.
- the OSC material contains non-Ce rare earth elements in order to improve heat resistance and oxygen storage / release ability.
- the non-Ce rare earth element is preferably at least one rare earth element selected from the group consisting of neodymium (Nd), lanthanum (La), yttrium (Y) and praseodymium (Pr), and is preferably neodymium (Nd) and lanthanum (Nd). It is more preferable that it is at least one rare earth element selected from La). It is preferable that at least one non-Ce rare earth element is contained in the OSC material, and two or more kinds of non-Ce rare earth elements may be contained in the OSC material.
- the content of the non-Ce rare earth element contained in the OSC material is preferably 1.0% by mass or more and 12.0% by mass or less, more preferably 1.5% by mass or more 11 with respect to 100% by mass of the total amount of the OSC material. It is 0.0% by mass or less, more preferably 2.0% by mass or more and 10.0% by mass or less.
- the non-Ce rare earth element contained in the OSC material is 1.0% by mass or more with respect to 100% by mass of the total amount of the OSC material, the heat resistance and oxygen storage / release ability of the OSC material are improved, and it becomes a specific precious metal.
- the non-Ce rare earth element contained in the OSC material is 12.0% by mass or less, it is possible to suppress the diffusion of the non-Ce rare earth element from the catalyst layer to the oxide film on the surface of the metal foil material, and the foil. Elongation can be further suppressed.
- the content of non-Ce rare earth elements contained in the OSC material means the total amount of each rare earth element when two or more kinds of non-Ce rare earth elements are contained.
- the non-Ce rare earth element contained in the OSC material is neodymium
- the content of neodymium is preferably 1.0% by mass or more and 12.0% by mass or less, based on 100% by mass of the total amount of the OSC material.
- the non-Ce rare earth element contained in the OSC material does not have to contain lanthanum, and may contain lanthanum.
- the content of the lantern is preferably 0.1% by mass or more and 3.0% by mass or less, based on 100% by mass of the total amount of the OSC material. It is preferably 0.2% by mass or more and 2.5% by mass or less, and more preferably 0.3% by mass or more and 2.0% by mass or less.
- the average particle size (D50) of the OSC material is preferably 3 ⁇ m or more and 12 ⁇ m or less.
- the average particle size (D50) of the OSC material is more preferably 4 ⁇ m or more and 9 ⁇ m or less.
- the average particle size (D50) of the OSC material and the average particle size (D50) of alumina described later are 50% volume particles integrated from the small diameter side in the volume-based particle size distribution by the laser diffraction scattering type particle size distribution measurement method. Refers to the diameter.
- the alumina catalyst layer preferably contains alumina as an inorganic porous body that supports a noble metal.
- the alumina contained in the catalyst layer may be a simple substance of alumina or an inorganic porous body containing alumina as a main material.
- the inorganic porous body containing alumina as a main material include silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-magnesium oxide, alumina-barium oxide, and alumina-lanthanum oxide. Examples thereof include at least one inorganic porous body selected from the group consisting of.
- the catalyst layer may contain two or more types of alumina and an inorganic porous body other than alumina.
- Alumina has a high specific surface area and can disperse and support a noble metal such as palladium (Pd).
- Pd palladium
- rhodium (Rh) when rhodium (Rh) is supported on alumina, rhodium (Rh), which is a metal that is relatively easily oxidized, reacts with alumina to irreversibly produce a rhodium compound, which is a rhodium (Rh). Purification performance may deteriorate. Therefore, alumina preferably supports, for example, palladium (Pd) other than rhodium (Rh) among the noble metals.
- the average particle size (D50) of alumina is preferably 5 ⁇ m or more and 25 ⁇ m or less.
- the average particle size (D50) of alumina is 5 ⁇ m or more and 25 ⁇ m or less, the diffusivity of the exhaust gas in the layer can be improved, the exhaust gas purification performance can be improved, and the metal carrier and the catalyst can be improved.
- the adhesion of the layers can be further improved.
- the average particle size (D50) of alumina is more preferably 7 ⁇ m or more and 22 ⁇ m or less, and further preferably 10 ⁇ m or more and 20 ⁇ m or less.
- the catalog values can be adopted.
- the alumina may contain lanthanum oxide (La 2 O 3 ).
- the content ratio of lanthanum oxide in alumina is too large, the specific surface area of alumina becomes small, and the dispersibility of precious metals such as palladium (Pd) supported on alumina may decrease.
- the content of lanthanum oxide in alumina is preferably 1.2% by mass or less, and more preferably 1.0% by mass or less.
- the mixing ratio of OSC material and alumina is an OSC material with respect to alumina in order to support individual noble metals to improve the dispersibility of the noble metals and suppress the alloying of two different noble metals.
- the mass ratio (OSC material / alumina) of the mass ratio of the OSC material when alumina is 1, is preferably 0.2 or more and 4 or less, more preferably 0.3 or more and 3 or less, and further preferably. Is 0.5 or more and 2 or less.
- the noble metal preferably contains palladium (Pd) and rhodium (Rh).
- Palladium (Pd) is a metal having a high ability to catalyze the oxidation reaction of hydrocarbons (HC) and carbon monoxide (CO).
- palladium (Pd) is easily alloyed with rhodium (Rh).
- rhodium (Rh) When palladium (Pd) and rhodium (Rh) are alloyed, the catalytic performance deteriorates. Therefore, palladium (Pd) and rhodium (Rh) are preferably supported on individual carriers, and palladium (Pd) is preferably supported on alumina or an inorganic porous body containing alumina as a main material. ..
- Rhodium (Rh) is a metal having a high ability to catalyze the reduction reaction of NOx.
- rhodium (Rh) is a metal that is relatively easily oxidized. Therefore, as described above, when rhodium (Rh) is supported on alumina, rhodium (Rh), which is a metal that is relatively easily oxidized, becomes alumina.
- Rhodium (Rh) is preferably supported on the OSC material because it reacts and irreversibly produces a rhodium compound, which deteriorates the catalytic performance of rhodium.
- the precious metal may contain platinum (Pt), silver (Ag), gold (Au), ruthenium (Ru), osmium (Os), and iridium (Ir) in addition to palladium (Pd) and rhodium (Rh). Good.
- the mass ratio (Pd / Rh) of palladium (Pd) to rhodium (Rh) contained in the catalyst layer is 0.2 or more in terms of metal in order to exert the catalytic ability of the noble metal and support it on individual carriers. It is preferably 8.8 or less, more preferably 0.3 or more and 1.7 or less, and further preferably 0.4 or more and 1.6 or less.
- the total amount of palladium (Pd) and rhodium (Rh) supported on the catalyst layer is preferably 0.1 g or more and 2.0 g or less, more preferably 0.2 g, per 1 L of the volume of the metal carrier in terms of metal. It is 1.9 g or less.
- the catalyst layer may contain a stabilizer, if necessary.
- the stabilizer include at least one element selected from the group consisting of alkaline earth metals and alkali metals, boron, silicon, hafnium, thorium and the like.
- the catalyst layer can contain at least one element selected from the group consisting of magnesium, barium, boron, thorium, hafnium, silicon, calcium and strontium.
- the catalyst layer may contain a binder, if necessary.
- an inorganic binder for example, a water-soluble solution such as alumina sol, silica sol, or zirconia sol can be used.
- the catalyst layer is dried by adhering a slurry containing a noble metal, an OSC material containing cerium and a non-Ce rare earth element, and alumina to a metal carrier by a wash coat or the like, for example, by a method for manufacturing an exhaust gas purification device described later.
- a catalyst layer can be formed.
- alumina is added to a solution containing the first noble metal, the first noble metal is supported on the alumina, and the alumina on which the first noble metal is supported is supported.
- the catalyst layer includes a step of forming a catalyst layer by adhering to a metal carrier provided inside an outer cylinder and formed of a metal foil material forming a flow path for exhaust gas, and the catalyst layer is 100 mass by mass of the catalyst layer.
- This is a method for producing an exhaust gas purification catalyst structure in which the content of the non-Ce rare earth element with respect to% is 2.52% by mass or more and 4.62% by mass or less in terms of oxide.
- the first noble metal is dispersed and supported on the alumina having a high specific surface area, and the first slurry containing the alumina supporting the first noble metal is formed.
- an OSC material containing cerium and a non-Ce rare earth element and a solution containing a second noble metal are added to the first slurry in this order, the non-Ce rare earth element and the second noble metal contained in the OSC material are added.
- a second noble metal is selectively carried on the OSC material, and a second slurry further containing the OSC material carrying the second noble metal is formed.
- the first noble metal and the second noble metal are supported on different carriers of alumina and OSC material, respectively. That is, in one step, the first noble metal and the second noble metal can be supported on different carriers of the alumina and the OSC material.
- the first noble metal and the second noble metal can be supported on different carriers of the alumina and the OSC material.
- the first noble metal is preferably palladium (Pd), and the second noble metal is preferably rhodium (Rh).
- the first noble metal is palladium (Pd)
- palladium (Pd) can be dispersed and supported on alumina having a high specific surface area, and then when the second noble metal is rhodium (Rh), it is contained in the OSC material.
- Rhodium (Rh) can be selectively carried on the OSC material by the affinity between the non-Ce rare earth element and rhodium (Rh), which is a second precious metal.
- a single layer of catalyst layer can be formed without causing the problem, the number of manufacturing steps can be reduced, and the manufacturing cost can be reduced.
- the slurry produced in one step can be attached to a metal carrier by a method such as wash coating as in the conventional case, and this can be dried or fired to form a catalyst layer.
- the temperature at which the slurry is coated and then dried is preferably, for example, 50 ° C. or higher and 150 ° C. or lower, particularly 70 ° C. or higher and 120 ° C. or lower.
- the content of the non-Ce rare earth element in the catalyst layer is in the range of 2.52% by mass or more and 4.62% by mass or less in terms of oxide with respect to 100% by mass of the catalyst layer, preferably 3.15% by mass. It is in the range of 4.62% by mass or less, more preferably in the range of 3.15% by mass or more and 4.20% by mass or less, and further preferably in the range of 3.15% by mass or more and 3.36% by mass or less.
- the non-Ce rare earth element contained in the catalyst layer can be applied to the oxide film on the surface of the metal foil material. Diffusion can be suppressed.
- the content of the non-Ce rare earth element in the catalyst layer is in the range of 2.52% by mass or more and 4.62% by mass or less in terms of oxide with respect to 100% by mass of the catalyst layer, preferably 3.15% by mass. % Or more and 4.62% by mass or less, more preferably 3.15% by mass or more and 4.20% by mass or less, and even more preferably 3.15% by mass or more and 3.36% by mass. It is within the following range, and particularly preferably within the range of 3.33% by mass or more and 3.36% by mass or less.
- any known method can be adopted as the method of adhering the slurry and the method of drying or firing the slurry to form the catalyst layer for producing the exhaust gas purification catalyst structure, and the method is limited to the above example. It's not a thing.
- the exhaust gas purification catalyst structure can be suitably used for purifying the exhaust gas discharged from the internal combustion engine of a saddle-type vehicle such as a motorcycle or a motorcycle.
- a saddle-type vehicle such as a motorcycle or a motorcycle.
- the exhaust gas purification catalyst structure by arranging the exhaust gas purification catalyst structure in the exhaust passage of the internal combustion engine of the saddle-type vehicle, the effect can be further exerted.
- one or more exhaust gas purification devices provided with an exhaust gas purification catalyst structure can be arranged in an exhaust pipe or a muffler. At this time, since the exhaust gas purification device reacts with the high-temperature combustion gas to promote a chemical reaction (oxidation / reduction action), it is preferable to arrange the catalyst directly under the exhaust port having a high exhaust gas temperature.
- the air-fuel ratio of the exhaust gas flowing in the exhaust passage is combined with a carburetor and a secondary air supply mechanism.
- a saddle-mounted vehicle set to have a value of 14 or more (particularly 14.5 or more) can be mentioned.
- a secondary air supply mechanism using a reed valve that operates according to the exhaust pressure is used as the secondary supply mechanism, normally, when the negative region in the exhaust pulsation becomes a small engine speed or load state, The supply amount of the secondary air is reduced and a reduced atmosphere is likely to be formed, and if the reduced atmosphere continues, the catalyst performance will not be stabilized.
- the air-fuel ratio of the exhaust gas flowing in the exhaust passage is set to 14 or more by the combination with the carburetor and the secondary air supply mechanism, the catalytic performance can be stably exhibited.
- It has a dirty side and a clean side as an exhaust gas purification device suitable for setting the air-fuel ratio of the exhaust gas flowing in the exhaust passage to be 14 or more by combining with a carburetor and a secondary air supply mechanism.
- An air cleaner that purifies the air sucked into the dirty side from the outside and supplies it to the engine via the clean side, and a secondary air supply mechanism that supplies secondary air from the clean side of the air cleaner to the exhaust port side of the engine.
- An exhaust gas purification device provided with the above can be mentioned, and it is effective to provide the exhaust gas purification catalyst in the exhaust passage of the internal combustion engine.
- the exhaust gas purification device shown in FIG. 1 can be exemplified.
- the exhaust gas purification device 10 shown in FIG. 1 is mounted on a saddle-mounted vehicle in which fuel is mixed with air supplied from the air cleaner 11 to the engine (internal combustion engine) 12 by a carburetor 13, and secondary air (purification) is provided from the air cleaner 11.
- a secondary air supply mechanism 20 for supplying air) to the exhaust port 12B of the engine 12 and an exhaust muffler 15 connected to the engine 12 via an exhaust pipe 14 are provided, and exhaust gas purification is performed in the exhaust muffler 15.
- the catalyst structure may be installed.
- the arrow X indicates the flow of air
- the arrow Y indicates the vacuum pressure
- the arrow Z indicates the flow of blow-by gas generated in the crankcase.
- the inside of the air cleaner case 11A is divided into two chambers, a dirty side (outside air introduction chamber) 11C and a clean side (clean air chamber) 11D, by a partition wall 11B.
- the dirty side 11C is provided with an outside air introduction port 11E, and outside air is introduced into the dirty side 11C through the outside air introduction port 11E.
- a filter element 11F is arranged on the partition wall 11B so as to cover an opening communicating the dirty side 11C and the clean side 11D, and after the air in the dirty side 11C has passed through the filter element 11F and purified, the clean side 11D Introduced in.
- the clean side 11D is provided with an air discharge port 11G, which is connected to the carburetor 13 via the connecting tube 16 and communicates with the intake port 12A of the engine 12 via the carburetor 13.
- the engine 12 is a general two-cycle engine or four-cycle engine mounted on a motorcycle or the like, and has an intake valve 12D for opening and closing an intake port 12A communicating with a cylinder hole (cylinder) 12C in the engine 12 and a cylinder hole.
- An exhaust valve 12E for opening and closing an exhaust port 12B communicating with the 12C is provided, and a piston 12F slidably arranged in the cylinder hole 12C is connected to the crankshaft 12H via a conrod 12G.
- Air is sucked into the cylinder hole 12C above the piston 12F via the carburetor 13, and fuel is supplied from the carburetor 13 to supply a mixture of fuel and air to the engine 12.
- the exhaust stroke in which the piston 12F rises with the exhaust valve 12E open (the intake valve 12D is closed) is carried out, so that the combustion gas Is discharged to the exhaust port 12B and discharged to the exhaust pipe 14 as exhaust gas.
- An exhaust muffler 15 is connected to the rear end of the exhaust pipe 14, and the exhaust muffler 15 functions as a silencer that silences high-temperature and high-pressure exhaust gas that has passed through the exhaust pipe 14 and discharges the exhaust gas to the outside.
- the exhaust muffler 15 is configured as a multi-stage expansion type in which the exhaust muffler 15 is divided into a plurality of chambers by a plurality of partition walls 15A and 15B, and each chamber is communicated with a communication pipe 15C, 15D, 15E, and is the most upstream side.
- the exhaust gas purification catalyst structure 30 containing the catalyst may be arranged in the front chamber located in.
- the secondary air supply mechanism 20 is a mechanism for sending the air (secondary air) of the clean side 11D of the air cleaner 11 to the exhaust port 12B of the engine 12, and connects the clean side 11D of the air cleaner and the exhaust port 12B of the engine 12.
- a secondary air supply pipe 21 is provided.
- a valve unit 22 is provided in the middle of the secondary air supply pipe 21, and a reed valve 23 for preventing exhaust gas from flowing back from the exhaust port 12B to the secondary air supply pipe 21 is provided in the valve unit 22 and the exhaust port 12B. It is provided between and.
- FIG. 1 shows a state in which the reed valve 23 is arranged above the engine 12 at a position closer to the exhaust port 12B from the viewpoint of improving the followability of the reed valve 23.
- the valve unit 22 includes a secondary air supply control valve 24 that prevents the supply of secondary air to the exhaust port 12B when the engine is decelerated, and the secondary air supply control valve 24 is a valve with the intake port 12A of the engine 12. It is configured to operate in response to the vacuum pressure of the intake port 12A transmitted via the communication pipe 25 connecting the unit 22.
- Reference numeral 35 in the drawing is a communication pipe that communicates the clean side 11D of the air cleaner 11 and the crankcase of the engine 12. The communication pipe 35 returns the blow-by gas generated in the crankcase to the engine 12 through the air cleaner 11 and the carburetor 13 and functions as a crankcase emission control device for preventing the release of the blow-by gas.
- the air-fuel ratio is set to the rich side in order to smoothly follow the acceleration request from the driver, so that the oxygen concentration in the exhaust gas tends to be low. Therefore, the purification function is stabilized by increasing the oxygen concentration in the exhaust gas by providing the secondary air supply mechanism 20, for example, the endurance distance of the exhaust gas regulation (state below the exhaust gas regulation value) set in some countries. It is preferable to set the secondary air supply mechanism 20 and the carburetor 13 so as to satisfy at least the mileage that maintains the above.
- the catalyst inlet air-fuel ratio is set to be 15 or more in the entire region of 55 km / h or less. be able to.
- the catalyst inlet air-fuel ratio is set to be 15 or more in the entire region of 55 km / h or less. be able to.
- saddle-type vehicle refers to not only saddle-type two-wheeled vehicles, saddle-type tricycles, and saddle-type four-wheeled vehicles, which are generally referred to as saddle-type vehicles, but also scooter-type motorcycles. It includes. Further, in the present specification, when expressed as "X or more" (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably larger than X” or “less than Y”. It also includes the intention that "is preferable”.
- Example 1 Ceria-zirconia composite oxide as OSC material (composition: Nd 2 O 3 : 5.3% by mass, CeO 2 : 21% by mass, ZrO 2 : 72% by mass, La 2 O 3 : 1.7% by mass, average grain Diameter (D50) 8 ⁇ m), Alumina (composition: Al 2 O 3 : 99.0 mass%, La 2 O 3 : 1.0 mass%, average particle size (D50) 15 ⁇ m), and zirconia as an inorganic binder Each sol was prepared.
- the metal carrier is a stainless metal honeycomb carrier (300 cells / inch 2 , ⁇ 40 mm) containing aluminum (Al) having an outer cylinder made of stainless steel, a flat plate-shaped metal foil material, and a corrugated metal foil material. ⁇ L 90 mm, capacity 113 ml, Al content 5.5 mass%, metal foil material thickness 50 ⁇ m) was fired at 500 ° C. for 1 hour to remove oil and dust adhering to the metal carrier.
- Pure water is added to an aqueous solution of Pd nitric acid, 42 parts by mass of the above alumina is added, and the mixture is stirred for 2 hours to form a first slurry containing alumina carrying Pd, and then the above-mentioned ceria-zirconia composite oxidation is added to the first slurry.
- a second slurry for forming a catalyst layer was obtained by adding 42 parts by mass of a substance, then adding an aqueous solution of Rh nitrate, and further adding 12 parts by mass of the binder material.
- the total content ratio of Pd, Rh and other components contained in the second slurry for forming the catalyst layer was 4 parts by mass.
- Other components include barium added to the second slurry as a stabilizer.
- the stainless metal honeycomb metal carrier is immersed in the second slurry for forming the catalyst layer, the excess slurry in the cell of the metal carrier is removed by air blowing, dried, and then 500 in the air atmosphere.
- An exhaust gas purification catalyst structure (hereinafter, also referred to as “catalyst structure”) was obtained by firing at ° C. for 1 hour to form a catalyst layer.
- the solid content (wash coat amount (WC amount)) of the second slurry adhering to the metal carrier was 90 g per 1 L of the volume of the catalyst structure (volume of the metal carrier).
- the amount of Pd carried is 8 g per cubic foot (cft) of the volume of the catalyst structure in terms of metal
- the amount of Rh carried is 1 cubic foot (cft) of the volume of the catalyst structure in terms of metal. It was 6 g per unit, and the mass ratio of Pd / Rh was 1.33.
- Table 1 the mass of the catalyst layer, the content of oxides of non-Ce rare earth elements in the catalyst layer, the content of Nd 2 O 3 in the catalyst layer, the content of La 2 O 3 in the catalyst layer, and the metal foil. The content of non-Ce rare earth elements in the catalyst layer with respect to the content of Al in the material was calculated from the amount used.
- Example 2 instead of the zirconia composite oxide, ceria different composition - - ceria used in Example 1 zirconia composite oxide (composition Nd 2 O 3: 10 wt%, CeO 2: 30 wt%, ZrO 2: 60 wt% , Average particle size (D50) 8 ⁇ m) was used, but a catalyst structure was prepared in the same manner as in Example 1.
- Example 3 instead of the zirconia composite oxide, ceria different composition - - ceria used in Example 1 zirconia composite oxide (composition Nd 2 O 3: 5 wt%, CeO 2: 5 wt%, ZrO 2: 88.5 A catalyst structure was produced in the same manner as in Example 1 except that mass%, La 2 O 3 : 1.5 mass%, and average particle size (D50) 8 ⁇ m) were used.
- Example 4 The amount of Pd carried is 8.6 g per cubic foot (cft) of the catalyst structure in terms of metal, and the amount of Rh carried is 5.4 g per cubic foot (cft) of catalyst structure in terms of metal.
- a catalyst structure was prepared in the same manner as in Example 1 except that the addition amounts of the Pd nitrate aqueous solution and the Rh aqueous solution were adjusted.
- Example 5 Pd nitrate is 7 g per cubic foot (cft) volume of the catalyst structure in terms of metal, and 7 g per cubic foot (cft) volume of catalyst structure in terms of metal.
- a catalyst structure was prepared in the same manner as in Example 1 except that the addition amounts of the aqueous solution and the Rh aqueous solution were adjusted.
- Example 6 The amount of Pd carried is 4.7 g per cubic foot (cft) of the catalyst structure in terms of metal, and the amount of Rh carried is 9.3 g per cubic foot (cft) of catalyst structure in terms of metal.
- a catalyst structure was prepared in the same manner as in Example 1 except that the addition amounts of the Pd nitrate aqueous solution and the Rh aqueous solution were adjusted.
- Example 7 A catalyst structure was produced in the same manner as in Example 1 except that the amount of alumina used was changed to 28 parts by mass and the amount of the ceria-zirconia composite oxide used was changed to 56 parts by mass.
- Example 8 A catalyst structure was produced in the same manner as in Example 1 except that the amount of alumina used was changed to 56 parts by mass and the amount of the ceria-zirconia composite oxide used was changed to 28 parts by mass.
- Example 9 The amount of Pd supported is 24 g per cubic foot (cft) of the catalyst structure in terms of metal, and the amount of Rh supported is 18 g per cubic foot (cft) of catalyst structure in terms of metal.
- a catalyst structure was produced in the same manner as in Example 1 except that the addition amounts of the aqueous solution and the Rh aqueous solution were adjusted and the amount of alumina used was changed to 39 parts by mass.
- Comparative Example 1 instead of the zirconia composite oxide, ceria different composition - - ceria used in Example 1 zirconia composite oxide (composition Nd 2 O 3: 15 wt%, CeO 2: 15 wt%, ZrO 2: 70 wt% , Average particle size (D50) 8 ⁇ m) was used, but a catalyst structure was prepared in the same manner as in Example 1.
- Comparative Example 2 Instead of the ceria-zirconia composite oxide used in Example 1, a ceria-zirconia composite oxide having a different composition (composition: CeO 2 : 30% by mass, ZrO 2 : 70% by mass, average particle size (D50) 8 ⁇ m) A catalyst structure was prepared in the same manner as in Example 1 except that the above was used.
- Comparative Example 3 A catalyst structure was prepared in the same manner as in Example 1 except that the amount of alumina used was changed to 84 parts by mass and the ceria-zirconia composite oxide was not added.
- Comparative Example 4 The catalyst structure is the same as in Comparative Example 3, except that the solid content (WC amount) of the second slurry attached to the stainless metal honeycomb carrier is changed to 150 g per 1 L of the volume of the catalyst structure (volume of the metal carrier). The body was made.
- Comparative Example 5 First, pure water was added to the aqueous solution of nitric acid Pd, and 84.3 parts by mass of the alumina used in Example 1 and 12 parts by mass of the binder material used in Example 1 were added to obtain a slurry for forming a lower layer. .. The total content ratio of Pd and other components contained in the lower layer forming slurry was 3.7 parts by mass. On the other hand, pure water was added to the aqueous solution of Rh nitrate, and 87.7 parts by mass of the above alumina and 12 parts by mass of the above binder material were further added to obtain a slurry for forming an upper layer.
- the total content ratio of Rh and other components contained in the upper layer forming slurry was 0.3 parts by mass.
- the upper layer and the lower layer are used as one catalyst layer, and the mass of the catalyst layer, the content of oxides of non-Ce rare earth elements in the catalyst layer, the content of La 2 O 3 in the catalyst layer, and the metal foil material.
- the content of the non-Ce rare earth element in the catalyst layer with respect to the Al content of the above was calculated from the amount used.
- the content of the non-Ce rare earth element contained in the catalyst layer is in the range of 2.52% by mass or more and 4.62% by mass or less in terms of oxide, and the foil.
- the elongation was suppressed and the structure was durable.
- palladium (Pd) is supported on alumina and rhodium (Rh) is supported on the OSC material even when the catalyst layer is one layer. Therefore, the alloying of two different noble metals, palladium and rhodium, was suppressed, and excellent exhaust gas purification performance was maintained.
- the exhaust gas purification catalyst structures of Comparative Examples 3 and 4 do not contain an OSC material serving as an auxiliary catalyst, and both palladium and rhodium are supported on alumina, which is a kind of carrier. Palladium and rhodium were alloyed, resulting in reduced catalytic performance. Since the exhaust gas purification catalyst structure of Comparative Example 5 did not contain the OSC material serving as an auxiliary catalyst, the catalyst performance was deteriorated. Further, in the exhaust gas purification catalyst structure of Comparative Example 5, since the catalyst layer has a two-layer structure of a lower layer and an upper layer, the number of manufacturing steps is increased and the manufacturing cost is increased.
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Abstract
Description
外筒体と、外筒体の内部に設けられ、排気ガスの流路を形成する金属箔材とを用いて構成された金属担体と、
前記金属箔材の前記流路を形成する面に設けられた触媒層とを備え、
前記触媒層は、貴金属と、セリウム及びセリウム以外の希土類元素(非Ce希土類元素)を含むOSC材と、アルミナとを含有し、触媒層100質量%に対する、非Ce希土類元素の含有量が酸化物換算で2.52質量%以上4.62質量%以下である、排気ガス浄化触媒構造体を提案する。
第一の貴金属を含む溶液にアルミナを添加し、第一の貴金属をアルミナに担持させ、第一の貴金属を担持したアルミナを含むスラリーを形成し、セリウム及びセリウム以外の希土類元素(非Ce希土類元素)を含むOSC材と、第二の貴金属を含む溶液とをこの順序で前記スラリーに添加し、第二の貴金属をOSC材に担持させ、第二の貴金属を担持したOSC材をさらに含むスラリーを形成する工程と、
前記スラリーを、外筒体と、外筒体の内部に設けられ、排気ガスの流路を形成する金属箔材とを用いて構成された金属担体に付着させて触媒層を形成する工程とを含み、
前記触媒層は、触媒層100質量%に対する、非Ce希土類元素の含有量が酸化物換算で2.52質量%以上4.62質量%以下とすることを特徴とする排気ガス浄化触媒構造体の製造方法を提案する。
本発明が提案する排気ガス浄化触媒構造体の製造方法は、第一の貴金属を担持させたアルミナと、第二の貴金属を担持させたセリウム及び非Ce希土類元素を含むOSC材とを一つの層に含有する触媒層を形成することができ、製造工程を少なくし、製造コストを低減することができる。また、本発明が提案する排気ガス浄化触媒構造体の製造方法は、一つの工程で2種類の貴金属を、それぞれ選択的に個別に2種類の担持体に担持させることができるため、2種類の貴金属を含む一つの触媒層を形成した場合であっても、得られる排気ガス浄化触媒構造体は、2種類の貴金属が高温によって合金化しにくく、触媒性能の低下を抑制することができ、しかも、箔伸びが抑制され、構造耐久性にも優れるものである。
金属担体は、外筒体と、外筒体の内部に設けられ、排気ガスの流路を形成する金属箔材とを備える。外筒体は、例えば前後に開口された円筒状であってもよい。金属担体の外筒体を構成する材料は、耐火性金属、例えばステンレス鋼(SUS)又は鉄を基とする耐食性合金などを挙げることができる。
金属箔材は、アルミニウム(Al)を含むステンレス鋼からなるものであることが好ましい。金属箔材が、Alを含むステンレス鋼からなるものであると、金属箔材の表面に酸化アルミニウム(Al2O3)を主成分とする酸化被膜が生成され、耐酸化性を向上させることができる。金属箔材は、高温での耐酸化性を向上するために、Fe-Cr-Al系ステンレス鋼からなるものであることがより好ましい。金属箔材の原料となるAlを含むステンレス鋼は、Al、及び必要に応じて含まれるFe、Crの各元素の他に、金属箔材の靭性を向上させるためにC、Siが含まれていてもよく、耐酸化性を向上するためにMnが含まれていてもよい。また、金属箔材の原料となるAlを含むステンレス鋼は、Al2O3酸化被膜の密着性を改善するために、La等の希土類元素が含まれていてもよい。
また、円筒状のパンチングメタルを使用することも可能である。パンチングパイプ又はパンチングチューブと呼ばれるパンチングメタルを使用すると、耐熱性が向上し、パンチングにより通孔が形成されるため、広い面積が得られ、排気ガス浄化性能を向上し、排気管内における排気抵抗が小さくなるので、例えば自動二輪車、自動四輪車の排気ガス浄化装置に用いることができる。
触媒層は、貴金属と、セリウム及びセリウム以外の希土類元素を含むOSC材と、アルミナとを含有し、触媒層100質量%に対する、セリウムを除く希土類元素(非Ce希土類元素)の含有量が酸化物換算で、2.52質量%以上4.62質量%以下の範囲内であり、好ましくは3.15質量%以上4.62質量%以下の範囲内であり、より好ましくは3.15質量%以上4.20質量%以下の範囲内であり、よりさらに好ましくは3.15質量%以上3.36質量%以下の範囲内であり、特に好ましくは3.33質量%以上3.36質量%以下の範囲内である。触媒層は、触媒層100質量%に対する、非Ce希土類元素の含有量の上限が上記範囲であるため、触媒層に含まれる非Ce希土類元素が、金属箔材の表面に形成された酸化被膜に拡散し難くなる。触媒層中に含まれる非Ce希土類元素の金属箔材表面の酸化被膜への拡散を抑制することができると、金属箔材表面の酸化被膜中の希土類元素の拡散を起因とする酸化被膜の体積膨張を抑制することができ、箔伸びを抑制することができる。箔伸びが起こると、排気ガスの流路が狭くなり、背圧が上昇することで、エンジンの出力に影響を及ぼす。また、箔伸びが大きくなると、金属箔材と触媒層が剥離する場合があり、箔伸びがさらに大きくなると外筒体から排気ガスの流路を形成する金属箔材が分離する場合があり、構造耐久性が不十分である場合がある。これに対して、本実施形態の排気ガス浄化触媒構造体によれば、上述した触媒層を備えることにより、箔伸びを抑制することが可能となり、これにより、エンジンの出力低下の抑制及び構造耐久性の向上を図ることができるようになる。
なお、触媒層に含まれる非Ce希土類元素は、触媒層に含まれるOSC材に由来するものであることが好ましい。OSC材として、非Ce希土類元素を含むものを用いることにより、OSC材の耐熱性を向上させ、結晶歪みを大きくして酸素吸蔵放出能を向上させることができる。また、非Ce希土類元素がOSC材に含まれていると、OSC材と特定の貴金属との親和性が向上し、特定の貴金属を選択的にOSC材に担持することができる。触媒層の質量は、製造された排気ガス浄化触媒構造体の触媒層の質量を測定することで求めてもよいし、排気ガス浄化触媒構造体を製造する際の材料の使用量から求めてもよい。また、非Ce希土類元素の酸化物換算の含有量は、製造された排気ガス浄化触媒構造体について非Ce希土類元素の含有割合を測定し、測定結果から酸化物換算の質量を求めてもよいし、排気ガス浄化触媒構造体を製造する際の非Ce希土類元素の酸化物の使用量から求めてもよい。
触媒層中の非Ce希土類元素の含有量は、触媒層100質量%に対して、2.52質量%以上4.62質量%以下の範囲内であり、好ましくは3.15質量%以上4.62質量%以下の範囲内であり、より好ましくは3.15質量%以上4.20質量%以下の範囲内であり、よりさらに好ましくは3.15質量%以上3.36質量%以下の範囲内であり、特に好ましくは3.33質量%以上3.36質量%以下の範囲内である。
OSC材は、酸素ストレージ能(OSC:Oxygen Storage capacity)を有する助触媒を含むことが好ましく、触媒能を有する貴金属の担持体とすることができる。OSC材としては、セリウム及びセリウム以外の希土類元素(非Ce希土類元素)が含まれているものが用いられ、例えばセリウム酸化物、又はセリア-ジルコニア複合酸化物などの多孔質体に、さらに非Ce希土類元素が含まれるもの等を挙げることができる。OSC材は、耐熱性及び酸素吸蔵放出能を向上するために、非Ce希土類元素が含まれている。非Ce希土類元素は、ネオジム(Nd)、ランタン(La)、イットリウム(Y)及びプラセオジム(Pr)からなる群から選ばれる少なくとも1種の希土類元素であることが好ましく、ネオジム(Nd)及びランタン(La)から選ばれる少なくとも1種の希土類元素であることがさらに好ましい。非Ce希土類元素は、少なくとも1種がOSC材に含有されていることが好ましく、2種類以上の非Ce希土類元素がOSC材に含有されていてもよい。
触媒層は、貴金属を担持する無機多孔質体として、アルミナを含むことが好ましい。触媒層に含有させるアルミナとしては、アルミナ単体であってもよいし、アルミナを主材とする無機多孔質体であってもよい。アルミナを主材とする無機多孔質体としては、例えばシリカ-アルミナ、アルミノ-シリケート類、アルミナ-ジルコニア、アルミナ-クロミア、アルミナ-セリア、アルミナ-酸化マグネシウム、アルミナ-酸化バリウム、及びアルミナ-酸化ランタンからなる群から選ばれる少なくとも1種の無機多孔質体が挙げられる。触媒層は、アルミナと、アルミナ以外の無機多孔質体の2種類以上を含んでいてもよい。アルミナは、高比表面積を有し、パラジウム(Pd)などの貴金属を分散して担持することができる。その一方で、アルミナにロジウム(Rh)が担持されてしまうと、比較的酸化され易い金属であるロジウム(Rh)がアルミナと反応して、不可逆的にロジウム化合物が生成され、ロジウム(Rh)の浄化性能が低下してしまう場合がある。そのため、アルミナは、貴金属の中でもロジウム(Rh)以外の、例えばパラジウム(Pd)を担持することが好ましい。
かかる観点から、アルミナの平均粒径(D50)は、より好ましくは7μm以上22μm以下であり、さらに好ましくは10μm以上20μm以下である。市販品ついては、カタログ値を採用することができる。
OSC材とアルミナの配合比率は、それぞれ個別の貴金属を担持して貴金属の分散性を向上し、2種類の異なる貴金属の合金化を抑制するために、アルミナに対するOSC材の質量比(OSC材/アルミナ)として、アルミナを1とした場合のOSC材の質量比が、好ましくは0.2以上4以下であり、より好ましくは0.3以上3以下であり、さらに好ましくは0.5以上2以下である。
貴金属は、パラジウム(Pd)及びロジウム(Rh)を含むことが好ましい。パラジウム(Pd)は、炭化水素(HC)や一酸化炭素(CO)の酸化反応を触媒する能力が高い金属である。その一方でパラジウム(Pd)はロジウム(Rh)と合金化しやすい。パラジウム(Pd)とロジウム(Rh)が合金化すると、触媒性能が低下する。そのため、パラジウム(Pd)とロジウム(Rh)は、それぞれ個別の担持体に担持されることが好ましく、パラジウム(Pd)はアルミナ又はアルミナを主材とする無機多孔質体に担持されることが好ましい。ロジウム(Rh)は、NOxの還元反応を触媒する能力が高い金属である。その一方でロジウム(Rh)は、比較的酸化され易い金属であるため、前述のとおり、ロジウム(Rh)がアルミナに担持されると、比較的酸化され易い金属であるロジウム(Rh)がアルミナと反応し、不可逆的にロジウム化合物が生成されて、ロジウムの触媒性能が低下してしまうため、ロジウム(Rh)はOSC材に担持されることが好ましい。貴金属は、パラジウム(Pd)、ロジウム(Rh)の他に、白金(Pt)、銀(Ag)、金(Au)、ルテニウム(Ru)、オスミウム(Os)、イリジウム(Ir)を含んでいてもよい。
触媒層は、必要に応じて、安定化材を含んでいてもよい。安定化材としては、例えば、アルカリ土類金属及びアルカリ金属からなる群から選ばれる少なくとも一種の元素、ホウ素、ケイ素、ハフニウム、トリウム等が挙げられる。安定化材として、触媒層は、マグネシウム、バリウム、ホウ素、トリウム、ハフニウム、ケイ素、カルシウム及びストロンチウムからなる群から選択される少なくとも一種の元素を含むことができる。
触媒層は、必要に応じて、バインダを含んでいてもよい。バインダ成分としては、無機系バインダ、例えばアルミナゾル、シリカゾル、ジルコニアゾル等の水溶性溶液を使用することができる。
本発明の実施形態の一例は、第一の貴金属を含む溶液にアルミナを添加し、第一の貴金属をアルミナに担持させ、第一の貴金属を担持したアルミナを得て、前記第一の貴金属を担持したアルミナを含む第1のスラリーを形成し、セリウム及び非Ce希土類元素を含むOSC材と、第二の貴金属を含む溶液とをこの順序で前記第1のスラリーに添加し、第二の貴金属をOSC材に担持させ、第二の貴金属を担持したOSC材をさらに含む第2のスラリーを形成する工程と、前記第2のスラリーを、外筒体と、外筒体の内部に設けられ、排気ガスの流路を形成する金属箔材を用いて構成された金属担体に付着させて触媒層を形成する工程を含み、前記触媒層は、触媒層100質量%に対する、非Ce希土類元素の含有量が酸化物換算で2.52質量%以上4.62質量%以下とする排気ガス浄化触媒構造体の製造方法である。
排気ガス浄化触媒構造体は、自動四輪車や、自動二輪車などの鞍乗型車両の内燃機関から排出される排気ガスを浄化するために好適に用いることができる。
中でも、例えば鞍乗型車両の内燃機関の排気通路に排気ガス浄化触媒構造体を配置することにより、その効果をより一層効果的に発揮させることができる。例えば、排気ガス浄化触媒構造体を備えた排気ガス浄化装置は、エキゾーストパイプ又はマフラー内に1又は複数個配置することができる。この際、排気ガス浄化装置は、高温の燃焼ガスと反応することで化学反応(酸化・還元作用)が促進されるため、排出ガス温度の高い排気ポートの直下に触媒を配置するのが好ましい。
二次供給機構に、排気圧に応じて作動するリードバルブを用いた二次空気供給機構を使用した場合、通常は、排気脈動における負の領域が小さいエンジン回転数或いは負荷の状態になると、二次空気の供給量が低下して還元雰囲気になり易く、この還元雰囲気の状態が続くと触媒性能が安定化しなくなる。しかし、キャブレター及び二次空気供給機構との組合せにより、排気通路内を流れる排気ガスの空燃比が14以上になるように設定すれば、安定して触媒性能を発揮させることができる。
本明細書において「鞍乗型車両」とは、一般に鞍乗型車両といわれている鞍乗型二輪車、鞍乗型三輪車、鞍乗型四輪車だけでなく、スクーター型自動二輪車も包含するものである。
また、本明細書において、「X以上」(Xは任意の数字)或いは「Y以下」(Yは任意の数字)と表現した場合、「Xより大きいことが好ましい」或いは「Y未満であることが好ましい」旨の意図も包含する。
OSC材としてセリア-ジルコニア複合酸化物(組成はNd2O3:5.3質量%、CeO2:21質量%、ZrO2:72質量%、La2O3:1.7質量%、平均粒径(D50)8μm)、アルミナ(組成はAl2O3:99.0質量%、La2O3:1.0質量%、平均粒径(D50)15μm)、及び、無機系バインダとしてのジルコニアゾルをそれぞれ準備した。
金属担体は、ステンレス鋼からなる外筒体と、平板状の金属箔材と及び波板状の金属箔材を備えたアルミニウム(Al)を含むステンレス製メタルハニカム担体(300セル/inch2、φ40mm×L90mm、容量113ml、Al含有量5.5質量%、金属箔材の厚さ50μm)を500℃で1時間焼成して金属担体に付着した油分やゴミを取り除いておいた。
作製した触媒構造体において、Pdの担持量は金属換算で触媒構造体の体積1立方フィート(cft)当たり8gであり、Rhの担持量は金属換算で触媒構造体の体積1立方フィート(cft)当たり6gであり、Pd/Rhの質量比は1.33であった。
表1において、触媒層の質量、触媒層中の非Ce希土類元素の酸化物の含有量、触媒層中のNd2O3の含有量、触媒層中のLa2O3の含有量、金属箔材中のAlの含有量に対する触媒層中の非Ce希土類元素の含有量は、それぞれ使用量から算出した。
実施例1で使用したセリア-ジルコニア複合酸化物に代えて、組成が異なるセリア-ジルコニア複合酸化物(組成はNd2O3:10質量%、CeO2:30質量%、ZrO2:60質量%、平均粒径(D50)8μm)を用いた以外は、実施例1と同様に触媒構造体を作製した。
実施例1で使用したセリア-ジルコニア複合酸化物に代えて、組成が異なるセリア-ジルコニア複合酸化物(組成はNd2O3:5質量%、CeO2:5質量%、ZrO2:88.5質量%、La2O3:1.5質量%、平均粒径(D50)8μm)を用いた以外は、実施例1と同様に触媒構造体を作製した。
Pdの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり8.6g、Rhの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり5.4gとなるように、硝酸Pd水溶液及びRh水溶液の添加量を調整した以外は、実施例1と同様に触媒構造体を作製した。
Pdの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり7g、Rhの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり7gとなるように、硝酸Pd水溶液及びRh水溶液の添加量を調整した以外は、実施例1と同様に触媒構造体を作製した。
Pdの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり4.7g、Rhの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり9.3gとなるように、硝酸Pd水溶液及びRh水溶液の添加量を調整した以外は、実施例1と同様に触媒構造体を作製した。
アルミナの使用量を28質量部に、上記セリア-ジルコニア複合酸化物の使用量を56質量部にそれぞれ変更した以外は、実施例1と同様に触媒構造体を作製した。
アルミナの使用量を56質量部に、上記セリア-ジルコニア複合酸化物の使用量を28質量部にそれぞれ変更した以外は、実施例1と同様に触媒構造体を作製した。
Pdの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり24g、Rhの担持量が金属換算で触媒構造体の体積1立方フィート(cft)当たり18gとなるように、硝酸Pd水溶液及びRh水溶液の添加量を調整し、上記アルミナの使用量を39質量部に変更した以外は、実施例1と同様に触媒構造体を作製した。
実施例1で使用したセリア-ジルコニア複合酸化物に代えて、組成が異なるセリア-ジルコニア複合酸化物(組成はNd2O3:15質量%、CeO2:15質量%、ZrO2:70質量%、平均粒径(D50)8μm)を用いた以外は、実施例1と同様に触媒構造体を作製した。
実施例1で使用したセリア-ジルコニア複合酸化物に代えて、組成が異なるセリア-ジルコニア複合酸化物(組成はCeO2:30質量%、ZrO2:70質量%、平均粒径(D50)8μm)を用いた以外は、実施例1と同様に触媒構造体を作製した。
上記アルミナの使用量を84質量部に変更し、セリア-ジルコニア複合酸化物は添加しなかった以外は、実施例1と同様に触媒構造体を作製した。
上記ステンレス製メタルハニカム担体に付着させる第2のスラリーの固形分量(WC量)を、触媒構造体の体積(金属担体の体積)1L当たり150gに変更した以外は、比較例3と同様に触媒構造体を作製した。
まず、硝酸Pd水溶液に、純水を加え、さらに実施例1で使用したアルミナを84.3質量部及び実施例1で使用したバインダ材12質量部を加えることで、下層形成用スラリーを得た。なお、下層形成用スラリーに含まれるPd及びその他成分の合計の含有割合は、3.7質量部であった。
他方、硝酸Rh水溶液に、純水を加え、さらに上記アルミナを87.7質量部及び上記バインダ材12質量部を加えることで、上層形成用スラリーを得た。なお、上層形成用スラリーに含まれるRh及びその他成分の合計の含有割合は、0.3質量部であった。
表1において、上層及び下層を一つの触媒層として、触媒層の質量、触媒層中の非Ce希土類元素の酸化物の含有量、触媒層中のLa2O3の含有量、金属箔材中のAlの含有量に対する触媒層中の非Ce希土類元素の含有量を、それぞれ使用量から算出した。
実施例1~9及び比較例1~5の触媒構造体を、ガソリンエンジンのマフラーに組み込み、下記条件にて耐久処理を施した。そして、耐久処理後における箔材の伸び量を測定し、下記基準にて耐箔伸び性を評価した。なお、箔材の伸び量は、耐久処理前後のメタルハニカム担体の軸方向の長さの差から求めた。
<耐久処理>
ガソリンエンジン:排気量2,300cc
燃料:無鉛ガソリン
熱耐久条件:850℃×64時間(A/Fを12.5(12秒)、14.6(42秒)、20.0(6秒)で変化させるサイクルを繰り返した)
被毒耐久条件:700℃×6時間(潤滑油を含むブレンドガソリンを用いて耐久)
<基準>
A:耐久処理後の箔材の伸び量が1.0mm以下であった。
B:耐久処理後の箔材の伸び量が1.0mm超であった。
上述した耐箔伸び性の耐久処理を施した触媒構造体を、図1に示す基本構成を有し、二次エアをカットした状態の自動二輪車のマフラーに組み込み、下記条件でCO、HC及びNOxの排出量の総量をそれぞれ測定することで、触媒構造体の実車浄化性能を評価した。結果を表1に示す。なお、表1中では、COの排出量は、1/10倍の値を記載した。
使用車両:単気筒125cc自動二輪車
燃料:無鉛ガソリン
走行モード:WMTC
測定方法:ISO6460に準拠
Claims (12)
- 外筒体と、外筒体の内部に設けられ、排気ガスの流路を形成する金属箔材とを用いて構成された金属担体と、
前記金属箔材の前記流路を形成する面に設けられた触媒層とを備え、
前記触媒層は、貴金属と、セリウム及びセリウム以外の希土類元素(非Ce希土類元素)を含むOSC材と、アルミナとを含有し、触媒層100質量%に対する、非Ce希土類元素の含有量が酸化物換算で2.52質量%以上4.62質量%以下であることを特徴とする、排気ガス浄化触媒構造体。 - 前記非Ce希土類元素がネオジムを含み、前記触媒層100質量%に対するネオジムの含有量が、酸化物換算で1.48質量%以上4.20質量%以下である、請求項1に記載の排気ガス浄化触媒構造体。
- 前記非Ce希土類元素がランタンを含み、前記触媒層100質量%に対するランタンの含有量が、酸化物換算で0.42質量%以上1.23質量%以下である、請求項1又は2に記載の排気ガス浄化触媒構造体。
- 前記貴金属が、パラジウム及びロジウムを含む、請求項1~3のいずれか1項に記載の排気ガス浄化触媒構造体。
- 前記金属担体が、平板状の金属箔材と、波板状の金属箔材とを備える、請求項1~4のいずれか1項に記載の排気ガス浄化触媒構造体。
- 前記金属箔材が、アルミニウムを含むステンレス鋼からなる、請求項1~5のいずれか1項に記載の排気ガス浄化触媒構造体。
- 前記金属箔材中のアルミニウムの含有量が3.0質量%以上6.0質量%以下である、請求項6に記載の排ガス浄化触媒構造体。
- 前記金属箔材中のアルミニウム(Al)の含有量(質量%)に対する前記触媒層中の非Ce希土類元素の含有量(質量%)の比(非Ce希土類元素/Al)が0.46以上0.84以下である、請求項6又は7に記載の排ガス浄化用触媒構造体。
- 前記金属箔材の厚さが20μm以上60μm以下である、請求項1~8のいずれか1項に記載の排ガス浄化用触媒構造体。
- 乗鞍型車両用の排気ガス浄化触媒構造体である、請求項1~9のいずれか1項に記載の排気ガス浄化用触媒構造体。
- 第一の貴金属を含む溶液にアルミナを添加し、第一の貴金属をアルミナに担持させ、第一の貴金属を担持したアルミナを含む第1のスラリーを形成し、セリウム及びセリウム以外の希土類元素(非Ce希土類元素)を含むOSC材と、第二の貴金属を含む溶液とをこの順序で前記第1のスラリーに添加し、第二の貴金属をOSC材に担持させ、第二の貴金属を担持したOSC材をさらに含む第2のスラリーを形成する工程と、
前記第2のスラリーを、外筒体と、外筒体の内部に設けられ、排気ガスの流路を形成する金属箔材とを用いて構成された金属担体に付着させて触媒層を形成する工程とを含み、
前記触媒層は、触媒層100質量%に対する、非Ce希土類元素の含有量が酸化物換算で2.52質量%以上4.62質量%以下とすることを特徴とする排気ガス浄化触媒構造体の製造方法。 - 前記第一の貴金属がパラジウムであり、前記第二の貴金属がロジウムである、請求項11に記載の排気ガス浄化触媒構造体の製造方法。
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US17/611,372 US20220212173A1 (en) | 2019-05-24 | 2020-05-13 | Exhaust gas cleaning catalyst structure and production method therefor |
CN202080038312.5A CN113874111A (zh) | 2019-05-24 | 2020-05-13 | 废气净化催化剂结构体及其制造方法 |
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JP2014161809A (ja) * | 2013-02-26 | 2014-09-08 | Honda Motor Co Ltd | 排気ガス用触媒装置 |
JP2017164735A (ja) | 2016-03-10 | 2017-09-21 | 株式会社キャタラー | 排ガス浄化触媒及びその製造方法 |
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JP6213508B2 (ja) * | 2015-03-20 | 2017-10-18 | トヨタ自動車株式会社 | 触媒コンバーター |
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JPH05184926A (ja) * | 1992-01-10 | 1993-07-27 | Cataler Kogyo Kk | 排ガス浄化用触媒 |
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