WO2016092957A1 - 排気ガス浄化触媒 - Google Patents
排気ガス浄化触媒 Download PDFInfo
- Publication number
- WO2016092957A1 WO2016092957A1 PCT/JP2015/079678 JP2015079678W WO2016092957A1 WO 2016092957 A1 WO2016092957 A1 WO 2016092957A1 JP 2015079678 W JP2015079678 W JP 2015079678W WO 2016092957 A1 WO2016092957 A1 WO 2016092957A1
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- WIPO (PCT)
- Prior art keywords
- catalyst
- alumina
- catalyst layer
- exhaust gas
- osc material
- Prior art date
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- 239000003054 catalyst Substances 0.000 title claims abstract description 367
- 239000000463 material Substances 0.000 claims abstract description 132
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- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 41
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- 238000000746 purification Methods 0.000 claims description 65
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- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 52
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- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
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- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
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- B01J37/0225—Coating of metal substrates
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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
- 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
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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
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/101—Three-way catalysts
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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
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
- F01N3/28—Construction of catalytic reactors
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- B01D2255/1021—Platinum
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- B01D2255/1023—Palladium
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- B01D2255/20—Metals or compounds thereof
- B01D2255/206—Rare earth metals
- B01D2255/2065—Cerium
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D2255/9022—Two layers
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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
- F01N2370/00—Selection of materials for exhaust purification
- F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors
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- 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
- the present invention relates to an exhaust gas purification catalyst that can be suitably used to purify exhaust gas discharged from an internal combustion engine such as a four-wheel vehicle or a two-wheel vehicle.
- exhaust gas purifying catalyst As a catalyst for treating such exhaust gas (hereinafter referred to as “exhaust gas purifying catalyst”), a three-way catalyst (TWC) that can oxidize and reduce CO, THC, and NOx is used. Yes.
- a three-way catalyst a noble metal is supported on an inorganic porous body having a high specific surface area, for example, an alumina porous body having a high specific surface area, and this is used as a base material such as a refractory ceramic or a metal honeycomb structure.
- a base material such as a refractory ceramic or a metal honeycomb structure.
- a co-catalyst referred to as an “OSC material” having an oxygen storage capacity (OSC) that releases oxygen in a reducing atmosphere and absorbs oxygen in an oxidizing atmosphere is known.
- OSC material oxygen storage capacity
- OSC materials having oxygen storage ability.
- Ceria can desorb and absorb attached oxygen and lattice oxygen in cerium oxide depending on the oxygen partial pressure in the exhaust gas, and can efficiently purify CO, THC, and NOx. It has the characteristic of expanding the air-fuel ratio range (window). That is, when the exhaust gas is reducible, cerium oxide desorbs oxygen and supplies oxygen into the exhaust gas [CeO 2 ⁇ CeO 2 ⁇ x + (x / 2) O 2 ]. On the other hand, when the exhaust gas is oxidizing, cerium oxide takes oxygen into oxygen vacancies and [CeO 2-x + (x / 2) O 2 ⁇ CeO 2 ) oxygen in the exhaust gas. Reduce the concentration to cause a reduction reaction.
- cerium oxide functions as a buffer that reduces changes in the oxidizing and reducing properties of exhaust gas, and has a function of maintaining the purification performance of the catalyst.
- a ceria-zirconia composite oxide in which zirconia is dissolved in ceria is further excellent in oxygen storage capacity (OSC), and thus is added to many catalysts as an OSC material.
- OSC oxygen storage capacity
- Ceria-zirconia composite oxide and noble metal are compatible with each other.
- the anchor effect works, it is difficult to sinter (sinter) even under heat load, and maintain dispersibility. Can do. Therefore, the ceria-zirconia composite oxide is used not only as an OSC material but also as a noble metal support.
- ceria-zirconia is a rare earth (rare earth) and expensive, there is a limit to using ceria-zirconia composite oxide as a noble metal support when providing an inexpensive catalyst.
- an OSC material such as ceria or ceria-zirconia composite oxide, together with alumina, is used as a noble metal carrier, and a catalyst that can stably exhibit catalyst purification performance at low cost has been disclosed. Yes.
- Patent Document 1 Japanese Patent Application Laid-Open No. 6-226096
- a first catalyst layer formed on the surface of a catalyst carrier, containing Pd and alumina, and formed on the outer surface of the first catalyst layer
- An exhaust gas purifying catalyst comprising a second catalyst layer comprising Pd and ceria is disclosed.
- Patent Document 2 Japanese Patent Laid-Open No. 10-296085
- the upper layer of the catalyst coat layer is a fireproof mainly composed of activated alumina.
- An inorganic oxide, and at least one selected from Ce, Zr and a compound thereof, and Rh, and the lower layer of the catalyst coat layer includes a refractory inorganic oxide mainly composed of activated alumina, Ce, Zr,
- An exhaust gas-purifying catalyst comprising Pd and Ba is disclosed.
- Patent Document 3 Japanese Patent Application Laid-Open No. 2001-79404 discloses a heat-resistant support carrier, a first coating layer that is directly supported on the surface of the heat-resistant support carrier, and a surface of the first coating layer.
- a catalyst for exhaust gas purification comprising the second coating layer, wherein the first coating layer contains palladium and alumina, and palladium is supported on a part or all of the alumina, and the second coating layer
- the layer includes at least one of platinum and rhodium and a zirconium-cerium composite oxide, and at least one of platinum and rhodium is supported on a part or all of the zirconium-cerium composite oxide.
- An exhaust gas purifying catalyst characterized by this is disclosed.
- Patent Document 4 Japanese Patent Application Laid-Open No. 2002-11350 discloses an exhaust gas purifying catalyst in which a first coating layer is formed on a heat-resistant support carrier and a second coating layer is formed on the first coating layer.
- the first coating layer contains alumina on which palladium is supported
- the second coating layer includes a Ce—Zr-based composite oxide in which platinum and rhodium are supported together, and the composite oxide has a composition.
- an exhaust gas purifying catalyst characterized in that it contains a Zr—Ce composite oxide in which platinum and rhodium are coexistingly supported.
- Patent Document 5 Japanese Patent Application Laid-Open No. 2013-184125 discloses an exhaust gas purification catalyst having a Pd catalyst layer containing Pd particles and an Rh catalyst layer formed on the Pd catalyst layer and containing Rh particles.
- a Pd carrier for supporting Pd particles is a composite oxide containing Al 2 O 3 as a main component and containing ZrO 2 . .
- Patent Document 6 Japanese Patent Laid-Open No. 2013-220401
- the upper layer contains Pt and Rh as catalyst metals
- the catalyst metal The oxide carrier has a CeZr composite oxide and an alumina composite oxide containing La, and Pt in the upper layer is an alumina composite oxide containing La Rh in the upper layer is supported on each of the CeZr-based composite oxide and the alumina composite oxide containing La, and the lower layer contains Pd as a catalytic metal and does not contain Rh.
- the oxide carrier supporting the catalyst metal has a CeZr composite oxide and an alumina composite oxide containing La.
- the lower layer Pd is composed of the CeZr composite oxide and the L Exhaust gas purifying catalyst, characterized by being carried on each of the alumina composite oxide containing is disclosed.
- Patent Document 7 Japanese Patent Application Laid-Open No. 2014-117701 includes a carrier and a catalyst layer formed on the carrier, and the catalyst layer is supported on the first support including alumina and the first support.
- a gas purification system for an internal combustion engine comprising: a first catalyst containing Pd; a second support containing a ceria-zirconia composite oxide; and a second catalyst containing Rh supported on the second support.
- a catalyst is disclosed.
- Patent Document 8 Japanese Patent Application Laid-Open No. 2014-144426 discloses a first catalyst layer containing Pd, an OSC material and an inorganic porous material, and a second catalyst containing Pt, Rh, or both, and an inorganic porous material.
- a catalyst layer, and a catalyst comprising a structure in which the second catalyst layer is disposed above the first catalyst layer, wherein the first catalyst layer includes Co, Ni, Mn,
- An exhaust gas purification catalyst characterized by containing one or more transition metals selected from the group consisting of Cu and Fe is disclosed.
- Patent Document 9 discloses a catalyst structure including a base material, an upper catalyst layer, and a lower catalyst layer, and the upper catalyst layer is made of an oxide whose crystal structure belongs to an apatite type.
- the catalyst structure is a porous layer containing an inorganic porous body
- the lower catalyst layer is a porous layer containing an inorganic porous body having an oxygen storage / release function (OSC function). It is disclosed.
- OSC function oxygen storage / release function
- an exhaust gas purification catalyst for a straddle-type vehicle such as a two-wheeled vehicle has a special problem different from an exhaust gas purification catalyst for a four-wheeled vehicle.
- an exhaust gas purification catalyst for a two-wheeled vehicle has a limited space for mounting the catalyst as compared with that for a four-wheeled vehicle, so that it is required to exhibit a high degree of purification ability while having a small capacity.
- the exhaust gas purification catalyst for a two-wheeled vehicle has a special problem different from the exhaust gas purification catalyst for a four-wheeled vehicle. The proposal like this is made.
- Patent Document 10 Japanese Patent Laid-Open No. 2001-145836
- the exfoliation of the catalyst layer due to heat and vibration is minimized, thermal deterioration of the catalyst material is suppressed, and excellent purification performance is exhibited under severe conditions.
- an exhaust gas purifying catalyst a metal carrier made of a cylindrical heat-resistant stainless steel punching metal, a heat-resistant inorganic oxide undercoat layer to which an oxygen storage material on the surface of the carrier is added, and the undercoat layer
- An exhaust gas purification catalyst comprising a catalyst-carrying layer carrying a catalyst in the above, and an exhaust gas purification catalyst using cerium oxide or a composite oxide of cerium and zirconium as the oxygen storage material has been proposed. Yes.
- Patent Document 11 (WO2010 / 109734) has a first catalyst layer formed on the surface of a carrier and a second catalyst layer formed thereon, and the first catalyst layer has an amount of CeO 2 .
- a carrier made of a composite oxide having 45 to 70% by mass, ZrO 2 content of 20 to 45% by mass, Nd 2 O 3 content of 2 to 20% by mass, and La 2 O 3 content of 1 to 10% by mass.
- the second catalyst layer has an amount of ZrO 2 of 50 to 95% by mass, an amount of CeO 2 of 0 to 40% by mass, Nd 2 O
- a carrier composed of a composite oxide having an amount of 3 to 2 to 20% by mass and an amount of La 2 O 3 of 1 to 10% by mass, and a catalyst component composed of a supported metal Rh or Rh oxide, Or a catalyst component comprising a supported metal Rh or Rh oxide and a metal Pt or Pt oxide?
- Patent Document 12 Japanese Patent Application Laid-Open No. 2013-208578 discloses a base material, palladium as a catalyst active component, an inorganic porous material as a catalyst carrier, and a promoter as a straddle-type vehicle exhaust gas purification catalyst.
- a palladium single-layer catalyst for straddle-type vehicle exhaust gas comprising a catalyst layer as a single layer containing ceria (CeO 2 ) particles and barium as components is disclosed.
- JP-A-6-2226096 Japanese Patent Laid-Open No. 10-296085 JP 2001-79404 A JP 2002-11350 A JP 2013-184125 A JP 2013-220401 A JP 2014-117701 A JP 2014-144426 A WO2014 / 156676 JP 2001-145836 A WO 2010/109734 JP 2013-208578 A
- exhaust gas purification catalysts for saddle-ride type vehicles are more subject to atmospheric fluctuations and are easily exposed to high temperatures. Therefore, the pores of the material constituting the catalyst each time it is used Tends to block. As a result, there is a problem that the supported noble metal is buried in the pores and the catalytic activity may be reduced.
- the straddle-type vehicle not only has to reduce the size of the catalyst compared to a four-wheeled vehicle, but also has a higher exhaust gas flow rate. Most of them are used. For this reason, the exhaust gas is not sufficiently diffused deep into the catalyst layer, and there has been a problem that the performance of the catalyst cannot be sufficiently obtained.
- the first object of the present invention is to reduce the amount of rare earths having OSC ability, and yet to have the necessary OSC ability, and the heat resistance and reaction of noble metals. It is an object of the present invention to provide a new exhaust gas purification catalyst that can maintain or improve the performance, and in particular, can improve the NOx purification performance. Furthermore, the second object of the present invention is to prevent the pores of the catalyst structural material from being blocked even after repeated use, and further to diffuse the exhaust gas deep into the catalyst layer. It is to provide a new exhaust gas purification catalyst that can be used.
- the present invention firstly has a first catalyst layer formed on the surface of a substrate made of ceramics or metal, and a second catalyst layer formed on the upper side of the first catalyst layer, and the first catalyst
- the present invention secondly, in the exhaust gas purification catalyst proposed by the present invention first, the average particle diameter (D50) of alumina of the first catalyst layer is 10 ⁇ m to 16 ⁇ m, and the first catalyst layer
- An exhaust gas purification catalyst is proposed in which the average particle size (D50) of the OSC material is 3 ⁇ m to 12 ⁇ m.
- the exhaust gas purifying catalyst proposed by the present invention is the OSC material by adjusting the mass ratio of the OSC material and alumina in each of the first catalyst layer and the second catalyst layer according to the role of each layer.
- the necessary OSC ability can be obtained, the heat resistance and maintenance or reactivity of the noble metal can be improved, and in particular, the NOx purification performance can be enhanced.
- the exhaust gas purification catalyst proposed by the present invention secondly is further used by adjusting the particle shapes of the alumina and OSC materials, which are the main materials of the first catalyst layer and the second catalyst layer, It is possible to prevent clogging of the pores of the catalyst constituent material, and it is possible to diffuse the exhaust gas deep into the catalyst layer.
- a catalyst according to an example of this embodiment (referred to as “the present catalyst”) includes a first catalyst layer formed on the surface of a base material and a second catalyst layer formed on the upper side of the first catalyst layer. Exhaust gas purification catalyst.
- the “catalyst layer” of the first catalyst layer and the second catalyst layer means a layer having a gas adsorption action or a gas purification catalyst action. If the catalyst active component such as a noble metal is contained, the gas purification catalyst action is obtained. Applicable because it has. Further, the first catalyst layer and the second catalyst layer are collectively referred to as “the present catalyst layer”.
- the material of the base material of the catalyst include refractory materials such as ceramics and metal materials.
- Materials for the ceramic substrate include refractory ceramic materials such as cordierite, cordierite-alpha alumina, silicon nitride, zircon mullite, spojumen, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, Examples thereof include zircon, petalite, alpha alumina, and aluminosilicates.
- the material for the metal substrate include refractory metals such as stainless steel (SUS) or iron-based corrosion resistant alloys.
- the shape of the substrate examples include a honeycomb shape, a pellet shape, and a spherical shape.
- honeycomb material for example, cordierite material such as ceramics can be used.
- a honeycomb body made of a metal material such as ferritic stainless steel (also referred to as “metal honeycomb”) can be used.
- the metal honeycomb can be formed by rolling a metal foil made of stainless steel, heat resistant steel, or the like.
- a metal outer cylinder instead of the outer cylinder, the honeycomb body may be directly inserted into the exhaust pipe or the muffler.
- a cylindrical punching metal When punching metal called punching pipe or punching tube is used, heat resistance is improved and through holes are formed by punching, so that a large surface area is obtained, exhaust gas purification performance is improved, and exhaust resistance in the exhaust pipe is reduced. For example, it is suitable for a two-wheeled vehicle.
- a honeycomb-shaped base material for example, a monolith type base material having many fine gas flow passages, that is, a large number of channels parallel to the inside of the base material may be used so that the fluid flows inside the base material.
- the catalyst layer can be formed by coating the inner wall surface of each channel of the monolith substrate with the catalyst composition by wash coating or the like.
- the first catalyst layer preferably contains a noble metal containing palladium (Pd) as a main component as a catalytic active component. That is, in the first catalyst layer, it is preferable that at least the most noble metal is Pd, and among them, 50% by mass or more of the noble metal of the first catalyst layer, of which 80% by mass or more, of which 90% by mass or more. It is preferable that Pd occupies (including 100% by mass).
- the supported amount of Pd in the entire catalyst is preferably 0.5 to 2.0 g per liter of the catalyst in terms of metal, among which 1.0 g or more or 1.8 g or less. Among these, it is especially preferable that it is 1.25 g or more or 1.6 g or less.
- the first catalyst layer preferably includes a promoter (referred to as “OSC material”) having oxygen storage capacity (OSC).
- OSC material include porous bodies such as cerium oxide, zirconium oxide, and ceria-zirconia composite oxide.
- the average particle diameter (D50) of the OSC material in the first catalyst layer is preferably 3 ⁇ m to 12 ⁇ m. This is because if the average particle diameter (D50) of the OSC material of the first catalyst layer is 3 ⁇ m to 12 ⁇ m, it is easy to ensure adhesion to the substrate and purification performance. From this viewpoint, the average particle diameter (D50) of the OSC material in the first catalyst layer is preferably 3 ⁇ m to 12 ⁇ m, and particularly preferably 4 ⁇ m or more and 9 ⁇ m or less.
- the pore diameter of the OSC material in the first catalyst layer is preferably 50 nm to 90 nm. This is because if the pore diameter of the OSC material of the first catalyst layer is 50 nm or more, the gas diffusibility is improved, and if it is 90 nm or less, the production stability is excellent. From this point of view, the pore diameter of the OSC material of the first catalyst layer is preferably 50 nm to 90 nm, more preferably 55 nm or more and 85 nm or less, and particularly preferably 60 nm or more and 80 nm or less.
- the first catalyst layer is an inorganic porous body supporting a noble metal, and is a porous body mainly composed of alumina. More specifically, for example, alumina, silica-alumina, alumino-silicates, alumina-zirconia, alumina- It is preferable to contain a porous material composed of a compound selected from chromia, alumina-ceria, alumina-magnesium oxide, alumina-barium oxide, alumina-lanthanum oxide and alumina-zirconia-ceria, or a mixture of two or more thereof.
- the average particle diameter (D50) of alumina in the first catalyst layer is preferably 5 ⁇ m to 20 ⁇ m. If the average particle diameter (D50) of the alumina of the first catalyst layer is 5 ⁇ m or more, the exhaust gas diffusibility in the layer can be improved and the exhaust gas purification performance can be improved. On the other hand, when the particle size of alumina is larger than 20 ⁇ m, the adhesion to the substrate may be weakened. From this viewpoint, the average particle diameter (D50) of alumina in the first catalyst layer is preferably 5 ⁇ m to 20 ⁇ m, more preferably 7 ⁇ m or more and 18 ⁇ m or less, and particularly preferably 10 ⁇ m or more and 16 ⁇ m or less.
- the pore diameter of alumina in the first catalyst layer is preferably 15 nm to 35 nm. This is because if the pore diameter of the alumina of the first catalyst layer is 15 nm to 35 nm, the purification performance can be effectively secured. From this viewpoint, the pore diameter of alumina in the first catalyst layer is preferably 15 nm to 35 nm, particularly 17 nm or more and 33 nm or less, and particularly preferably 20 nm or more and 30 nm or less.
- composition composition Alumina has a high specific surface area and can disperse and carry a noble metal such as Pd.
- OSC materials such as ceria-zirconia composite oxide and noble metals are compatible with each other. When noble metals are supported on the OSC materials, an anchor effect works, and it is difficult to sinter (sinter) even under a thermal load. Can be maintained.
- OSC materials such as ceria-zirconia are rare earths (rare earths) and are expensive, it is required to reduce the amount of rare earths (rare earths) used while maintaining the necessary OSC capability.
- alumina becomes extremely hard when fired. Therefore, when the base material, particularly the SUS base material, is thermally expanded or cooled and contracted as the engine starts or stops, the alumina or the catalyst layer peels off from the base material. I had the problem of being easy. It has been found that when the particle size of the alumina of the first catalyst layer is increased, the problem becomes remarkable and the alumina or the present catalyst layer is more easily peeled off from the substrate. In response to this problem, it has been found for the first time that when the OSC material is mixed in a certain amount or more with alumina in the first catalyst layer, the alumina or the catalyst layer is hardly peeled off from the substrate, particularly the SUS substrate.
- the OSC material is 1/5 or more, especially 14.8 or more in mass ratio with respect to alumina.
- Employing such a blending ratio is particularly effective in a catalyst using alumina having a particle size of 10 ⁇ m or more.
- the 1st catalyst layer may contain the stabilizer as needed.
- the stabilizing material include alkaline earth metals and alkali metals. Of these, one or more metals selected from the group consisting of magnesium, barium, boron, thorium, hafnium, silicon, calcium, and strontium can be selected.
- the first catalyst layer may contain a binder as necessary.
- an inorganic binder for example, an aqueous solution such as alumina sol can be used.
- the first catalyst layer can further contain other components than the above as necessary.
- the second catalyst layer preferably contains platinum (Pt) or rhodium (Rh) or a noble metal mainly composed of these two components as a catalytically active component. That is, in the second catalyst layer, it is preferable that at least the most noble metal is platinum (Pt) or rhodium (Rh), and in particular, 50% by mass or more of the noble metal of the second catalyst layer, of which 80% by mass. Of these, platinum (Pt) or rhodium (Rh) preferably accounts for 90% by mass or more (including 100% by mass).
- the supported amount of Pt and Rh in the entire catalyst is preferably 0.1 g to 0.5 g per liter of the catalyst in terms of metal, and in particular, 0.12 g or more or 0.3 g In the following, it is particularly preferably 0.14 g or more or 0.18 g or less.
- OSC material examples of the OSC material contained in the second catalyst layer include porous bodies such as cerium oxide, zirconium oxide, and ceria-zirconia composite oxide.
- the OSC material of the first catalyst layer and the OSC material of the second catalyst layer may be the same or different.
- the average particle diameter (D50) and the pore diameter of the OSC material contained in the second catalyst layer are different even when the OSC material of the first catalyst layer and the OSC material of the second catalyst layer are the same. Also good.
- the average particle size (D50) of the main material of the first catalyst layer, that is, alumina is 10 ⁇ m to 16 ⁇ m
- the average particle size of the main material of the second catalyst layer, that is, the OSC material ( D50) is preferably 4 ⁇ m to 10 ⁇ m, and more preferably as described above for each component.
- the second catalyst layer is an inorganic porous body supporting a noble metal, and is a porous body mainly composed of alumina. More specifically, for example, alumina, silica-alumina, alumino-silicates, alumina-zirconia, alumina- It is preferable to contain a porous material composed of a compound selected from chromia, alumina-ceria, alumina-magnesium oxide, alumina-barium oxide, alumina-lanthanum oxide and alumina-zirconia-ceria, or a mixture of two or more thereof.
- the alumina of the first catalyst layer and the alumina of the second catalyst layer may be the same or different.
- the average particle diameter (D50) and the pore diameter of the alumina contained in the second catalyst layer may be the same or different between the alumina of the first catalyst layer and the alumina of the second catalyst layer, respectively.
- composition composition As described above, the OSC material such as ceria-zirconia composite oxide and the noble metal are compatible with each other, and when the noble metal is supported on the OSC material, an anchor effect works and it is difficult to sinter (sinter) even when a thermal load is applied. Thus, dispersibility can be maintained.
- OSC materials such as ceria-zirconia are rare earths (rare earths) and are expensive, it is required to reduce the amount used while maintaining the necessary OSC capability.
- alumina has a high specific surface area and can disperse and support noble metals such as Pd.
- the amount of alumina in the second catalyst layer is preferably relatively small.
- the content of the OSC material is larger than that of alumina.
- the 2nd catalyst layer may contain the stabilizer as needed.
- the stabilizing material include alkaline earth metals and alkali metals. Of these, one or more metals selected from the group consisting of magnesium, barium, boron, thorium, hafnium, silicon, calcium, and strontium can be selected.
- the second catalyst layer may contain a binder as necessary.
- a binder component an inorganic binder, for example, an aqueous solution such as alumina sol can be used.
- the second catalyst layer can further contain other components than the above as necessary.
- the second catalyst layer may be provided on the upper side of the first catalyst layer, that is, on the side opposite to the base material, in other words, on the exhaust gas flow path side.
- Other layers may or may not be present.
- a layer that is not a catalyst layer such as a layer made of porous refractory inorganic oxide powder, or a porous refractory inorganic oxide powder and a promoter component.
- Other layers such as layers may be present.
- the thickness of the present catalyst layer (the total thickness of the first catalyst layer and the second catalyst layer) is preferably 80 ⁇ m to 150 ⁇ m from the viewpoint of ensuring catalyst performance and keeping back pressure low.
- the void volume of this catalyst layer is the logarithmic differential void volume distribution obtained when the void distribution is measured by a mercury intrusion porosimeter.
- the first peak is more preferably present in the range of the void volume diameter of 18 nm to 33 nm, and particularly preferably in the range of the void volume diameter of 20 nm to 30 nm.
- the second peak is more preferably in the range of the void volume diameter of 50 nm to 150 nm, and particularly preferably in the range of the void volume diameter of 100 nm to 120 nm.
- the present catalyst is prepared so as to have the first peak in the range of the void volume diameter of 15 nm to 35 nm and the second peak in the range of the void volume diameter of 50 nm to 200 nm.
- the “first peak” refers to the peak with the highest peak height in the logarithmic differential void volume distribution measured by a mercury intrusion porosimeter
- the “second peak” refers to the second peak height. Means a high peak. Note that the line assuming that the peak does not exist, that is, the peak whose vertical height from the background is less than 0.002 ml / g is considered to be noise of a measuring device or the like, and thus is defined by the present invention. It does not fall under “peak”.
- the first peak existing in the pore volume diameter range of 15 nm to 35 nm is derived from the pore diameter of alumina
- the second peak present in the void volume diameter range of 50 nm to 200 nm is the pore diameter of the OSC material. Therefore, these peak positions can be adjusted by changing the pore volume diameter and differential pore volume of the alumina and OSC material, the amount of the alumina or OSC material, firing conditions, and the like. It should be noted that the pore diameter of alumina or OSC material as the catalyst raw material does not necessarily match the pore diameter of the catalyst layer.
- the mercury intrusion porosimeter makes use of the high surface tension of mercury and applies pressure to the measurement object to cause mercury to enter, and the pore volume diameter and logarithmic differential void volume distribution are calculated from the pressure at that time and the amount of mercury injected. It is a device to measure. Therefore, the target void is only an open pore (a void communicating with the outside), and a closed pore (an independent void) is not included in the target. Further, the “void volume diameter” means the diameter of the bottom surface when the gap is approximated to a cylinder, and is calculated by the following equation.
- dr ⁇ 4 ⁇ cos ⁇ / p ( ⁇ : surface tension, ⁇ : contact angle, p: pressure)
- the surface tension of mercury is known, and the contact angle shows a unique value for each apparatus, so the void volume diameter can be calculated from the pressure of the mercury that has been injected.
- the void volume of the catalyst layer can be measured by peeling only the catalyst layer from the catalyst and measuring the void distribution with a mercury intrusion porosimeter.
- a noble metal, alumina and OSC material, and if necessary, a stabilizer, a binder, and the like, and water are mixed and stirred to form a slurry, and the resulting slurry is, for example, a ceramic honeycomb body.
- the substrate may be wash coated and fired to form the first catalyst layer on the substrate surface, and then the second catalyst layer as the upper layer (surface layer) may be formed in the same manner as described above.
- alumina and OSC material, further stabilizing material, binder, etc., if necessary, and water are mixed and stirred to form a slurry, and the obtained slurry is washed on a substrate such as a ceramic honeycomb body.
- a substrate such as a ceramic honeycomb body.
- the second catalyst layer as the upper layer (surface layer) may be formed as described above. However, it is not limited to these manufacturing methods.
- This catalyst can be suitably used for purifying exhaust gas discharged from an internal combustion engine of a straddle-type vehicle such as a four-wheeled vehicle or a two-wheeled vehicle.
- a straddle-type vehicle such as a four-wheeled vehicle or a two-wheeled vehicle.
- the present catalyst by arranging the present catalyst in the exhaust passage of the internal combustion engine of the saddle riding type vehicle, the effect can be exhibited more effectively.
- one or a plurality of the present catalysts can be arranged in, for example, an exhaust pipe or a muffler. At this time, since this catalyst reacts with high-temperature combustion gas to promote a chemical reaction (oxidation / reduction action), it is preferable to dispose the catalyst directly under the exhaust port having a high exhaust gas temperature.
- the air-fuel ratio of exhaust gas flowing in the exhaust passage is 14 or more (particularly 14.5 or more) by the combination of a carburetor and a secondary air supply mechanism.
- a straddle-type vehicle equipped with an exhaust gas purification device set in such a manner can be given.
- 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 to easily become a reducing atmosphere, and when the state of the reducing atmosphere continues, the catalyst performance is not stabilized.
- the air-fuel ratio of the exhaust gas flowing in the exhaust passage is set to 14 or more by the combination of the carburetor and the secondary air supply mechanism, the catalyst performance can be exhibited stably.
- an exhaust gas purification device suitable for setting the air-fuel ratio of exhaust gas flowing in the exhaust passage to be 14 or more by combining with a carburetor and a secondary air supply mechanism, it has a dirty side and a clean side.
- An air cleaner that purifies 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 purifying apparatus provided with the above-mentioned and the catalyst can be effectively provided in the exhaust passage of the internal combustion engine.
- the exhaust gas purification device shown in FIG. 1 can be exemplified.
- An exhaust gas purification device 10 shown in FIG. 1 is mounted on a straddle-type vehicle that mixes fuel supplied to an engine (internal combustion engine) 12 from an air cleaner 11 with a carburetor 13, and receives secondary air (purification from the air cleaner 11. 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.
- the catalyst is placed in the exhaust muffler 15. Install it.
- arrow X indicates the air flow
- arrow Y indicates the vacuum pressure
- arrow Z indicates the flow of blow-by gas generated in the crankcase.
- the air cleaner 11 has an air cleaner case 11A that is partitioned 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 disposed on the partition wall 11B so as to cover an opening that communicates the dirty side 11C and the clean side 11D. After the air in the dirty side 11C is purified by passing through the filter element 11F, the clean side 11D is disposed. To be introduced.
- the clean side 11D is provided with an air discharge port 11G.
- the air discharge port 11G 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 includes an intake valve 12D that opens and closes an intake port 12A communicating with a cylinder hole (cylinder) 12C in the engine 12, and a cylinder hole.
- An exhaust valve 12E that opens and closes an exhaust port 12B that communicates with 12C, and a piston 12F that is slidably disposed in the cylinder hole 12C is connected to the crankshaft 12H via a connecting rod 12G.
- an exhaust stroke is performed in which the piston 12F rises with the exhaust valve 12E open (the intake valve 12D is closed), 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 the high-temperature and high-pressure exhaust gas that has passed through the exhaust pipe 14 and discharges it to the outside.
- the exhaust muffler 15 is divided into a plurality of chambers by a plurality of partition walls 15A and 15B, and each chamber is configured as a multistage expansion type that communicates with communication pipes 15C, 15D, and 15E. What is necessary is just to arrange
- the secondary air supply mechanism 20 is a mechanism for sending clean side 11D air (secondary air) 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 the exhaust gas from flowing backward from the exhaust port 12B to the secondary air supply pipe 21 is provided with the valve unit 22 and the exhaust port 12B.
- FIG. 1 shows a state in which the reed valve 23 is disposed above the engine 12 that is 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 decelerates.
- the secondary air supply control valve 24 is connected to the intake port 12A of the engine 12 and the valve. It is configured to operate according to the vacuum pressure of the intake port 12 ⁇ / b> A transmitted through the communication pipe 25 that connects 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 functions as a crankcase emission control device that returns blowby gas generated in the crankcase to the engine 12 through the air cleaner 11 and the carburetor 13 and prevents the release of blowby 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 thin. Therefore, by providing the secondary air supply mechanism 20, the purification function is stabilized by increasing the oxygen concentration in the exhaust gas.
- the endurance distance of the exhaust gas regulation provided in some countries (the state below the exhaust gas regulation value) It is preferable to set the secondary air supply mechanism 20 and the carburetor 13 so as to satisfy at least the travel distance maintaining the above.
- the catalyst inlet air-fuel ratio is set to 15 or more in the entire region of 55 km / h or less. be able to.
- the performance of the catalyst can be stabilized over a long period of time.
- the “saddle-type vehicle” includes not only a saddle-type motorcycle, a saddle-type tricycle, and a saddle-type four-wheel vehicle, which are generally referred to as a saddle-type vehicle, but also a scooter-type motorcycle. is there.
- X to Y X and Y are arbitrary numbers
- X is greater than X” and “preferably greater than X” or “preferably greater than Y”.
- small is also included.
- X or more” X is an arbitrary number
- Y or less Y is an arbitrary number
- Example 1 Ceria-zirconia composite oxide B10 (D50: 6.5 ⁇ m, pore diameter 66 nm, BET specific surface area: 38 m 2 / g), alumina A4 (D50: 13 ⁇ m, pore diameter 22 nm, BET specific surface area 105 m 2 / g), and Alumina sol as an inorganic binder was prepared.
- a stainless steel metal honeycomb carrier 300 cell, ⁇ 30 mm ⁇ L30 mm, 21 cc capacity test piece) was fired at 500 ° C. for 1 hour to remove oil and dust adhering to the carrier.
- Pure water was added to the Pd nitrate solution and 65 parts by mass of the alumina A4 was added. After stirring for 2 hours, 16 parts by mass of the ceria-zirconia composite oxide B10 and 12 parts by mass of the binder material were added. A layer Pd-containing slurry was obtained (Pd: 1.6 parts by mass).
- pure water was added to the Rh nitrate solution and 70 parts by mass of the ceria-zirconia composite oxide B10 was added. After stirring for 2 hours, 20 parts by mass of the alumina A4 and 8 parts by mass of the binder material were added. A two-catalyst layer Rh-containing slurry was obtained (Rh: 0.2 parts by mass).
- the excess slurry in the cell is removed by air blowing and dried, followed by firing at 500 ° C. for 1 hour in an air atmosphere.
- a first catalyst layer was formed.
- the metal honeycomb carrier on which the first catalyst layer has been formed is immersed in the slurry containing the second catalyst layer Rh, the excess slurry in the cell is removed by air blowing and dried, and then at 500 ° C. in an air atmosphere.
- a catalyst (sample) was produced by firing for 1 hour to form a second catalyst layer.
- the supported amount of Pd was 1.4 g per liter of the catalyst in terms of metal
- the supported amount of Rh was 0.16 g per liter of the catalyst in terms of metal.
- Example 2 In Example 1, the amount of alumina A4 in the first catalyst layer Pd-containing slurry was changed to 70 parts by mass, and the amount of ceria-zirconia B10 was changed to 11 parts by mass, as in Example 1. A catalyst (sample) was prepared.
- Example 3 In Example 1, except that the amount of ceria-zirconia B10 in the second catalyst layer Rh-containing slurry was changed to 90 parts by mass and the amount of alumina A4 was changed to 0 parts by mass, the same as in Example 1.
- a catalyst (sample) was prepared.
- Example 1 (Comparative Example 1) In Example 1, the amount of alumina A4 in the first catalyst layer Pd-containing slurry was changed to 41 parts by mass, and the amount of ceria-zirconia B10 was changed to 40 parts by mass. A catalyst (sample) was prepared.
- Example 2 (Comparative Example 2) In Example 1, the amount of ceria-zirconia B10 in the second catalyst layer Rh-containing slurry was changed to 40 parts by mass, and the amount of alumina A4 was changed to 50 parts by mass, as in Example 1. A catalyst (sample) was prepared.
- the blending amount at the time of production and the content when measured after the catalyst production are the same value (the same applies to other examples and comparative examples).
- the pore diameters of the ceria-zirconia composite oxide and alumina used as raw materials were the first peak with the highest peak height in the logarithmic differential void volume distribution obtained by measurement in the same way as the logarithmic differential void volume distribution measurement described later. This is the value of the pore volume diameter.
- Example 4 In Example 1, a catalyst (sample) was prepared in the same manner as in Example 1 except that alumina (D50: 13 ⁇ m, pore diameter 28 nm, BET specific surface area 99 m 2 / g) was used instead of the first layer of alumina A4. Produced.
- alumina D50: 13 ⁇ m, pore diameter 28 nm, BET specific surface area 99 m 2 / g
- Example 5 In Example 1, ceria-zirconia composite oxide (D50: 6.5 ⁇ m, pore diameter 50 nm, BET specific surface area: 39 m 2 / g) was used instead of ceria-zirconia composite oxide B10 of the second layer. Produced a catalyst (sample) in the same manner as in Example 1.
- Example 6 In Example 1, as shown in Table 2, the catalyst (sample) was prepared in the same manner as in Example 1 except that the slurry coating amount of the first layer was reduced by 20% and the slurry coating amount of the second layer was increased by 20%. Produced.
- Example 7 In Example 1, as shown in Table 2, the catalyst (sample) was added in the same manner as in Example 1 except that the slurry coating amount of the first layer was increased by 20% and the slurry coating amount of the second layer was decreased by 20%. Produced.
- Example 3 (Comparative Example 3)
- the amount of alumina A4 in the first catalyst layer Pd-containing slurry was changed to 81 parts by mass, and the amount of ceria-zirconia B10 was changed to 0 parts by mass, as in Example 1.
- a catalyst (sample) was prepared.
- ⁇ Adhesion test> The catalyst (sample) stored in the atmosphere at room temperature was placed in an electric path heated to 900 ° C. and allowed to stand for 60 minutes to bring the product temperature to 900 ° C. The surface of the catalyst (sample) was observed in an atmosphere. In all different product lots, samples with no peeling observed were evaluated as “good”, and samples with a partial peeling observed in part of the product lot were evaluated as “ ⁇ (usual)”. Samples in which peeling was observed in all different product lots were evaluated as “x (poor)”.
- Example 8 In Example 1, a catalyst (sample) was obtained in the same manner as in Example 1 except that alumina (D50: 13 ⁇ m, pore diameter 12 nm, BET specific surface area 120 m 2 / g) was used instead of alumina A4 in the first catalyst layer. Was made.
- alumina D50: 13 ⁇ m, pore diameter 12 nm, BET specific surface area 120 m 2 / g
- Example 9 In Example 1, ceria-zirconia composite oxide (D50: 6.5 ⁇ m, pore diameter 26 nm, BET specific surface area: 60 m 2 / g) was used instead of ceria-zirconia composite oxide B10 in the second catalyst layer. Except for the above, a catalyst (sample) was prepared in the same manner as in Example 1.
- Example 10 In Example 1, a catalyst (sample) was used in the same manner as in Example 1 except that alumina (D50: 2 ⁇ m, pore diameter 22 nm, BET specific surface area 104 m 2 / g) was used instead of alumina A4 in the first catalyst layer.
- alumina D50: 2 ⁇ m, pore diameter 22 nm, BET specific surface area 104 m 2 / g
- Example 11 In Example 1, a catalyst (sample) was used in the same manner as in Example 1 except that alumina (D50: 25 ⁇ m, pore diameter 22 nm, BET specific surface area 102 m 2 / g) was used instead of alumina A4 in the first catalyst layer.
- alumina D50: 25 ⁇ m, pore diameter 22 nm, BET specific surface area 102 m 2 / g
- Example 12 In Example 1, ceria-zirconia composite oxide (D50: 1 ⁇ m, pore diameter 66 nm, BET specific surface area: 37 m 2 / g) was used instead of ceria-zirconia composite oxide B10 in the second catalyst layer.
- a catalyst (sample) was prepared in the same manner as in Example 1.
- Example 13 In Example 1, ceria-zirconia composite oxide (D50: 16 ⁇ m, pore diameter 66 nm, BET specific surface area: 38 m 2 / g) was used instead of ceria-zirconia composite oxide B10 in the second catalyst layer.
- a catalyst (sample) was prepared in the same manner as in Example 1.
- the catalyst layer was peeled off from the catalyst (sample) produced in Examples 1, 4 to 5 and Comparative Examples 8 to 13, and the void distribution was measured as follows.
- the measurement of the logarithmic differential void volume distribution is a method of measuring the pore (void) distribution by changing the pressure applied to mercury and measuring the amount of mercury that has entered the pores at that time.
- an automatic porosimeter “Autopore IV9520” manufactured by Shimadzu Corporation was used for measurement under the following conditions and procedures.
- Measurement condition Measurement environment: 25 ° C Measurement cell: sample chamber volume 3 cm 3 , press-fit volume 0.39 cm 3 Measurement range: 0.0048 MPa to 255.106 MPa Measurement point: 131 points (dots are engraved at equal intervals when the pore diameter is taken logarithmically) Press-fit volume: adjusted to be 25% or more and 80% or less.
- Table 3 shows the positions of the first peak and the second peak in the range of the pore volume diameter of 5 nm to 200 nm of the logarithmic differential pore volume distribution obtained by measurement as described above.
- a first peak is observed in the range of 15 to 35 nm in the pore volume diameter in the range of 5 to 200 nm in the logarithmic differential pore volume distribution. It was also found that it is preferable to have the second peak in the range of the void volume diameter of 50 nm to 200 nm. Among them, the first peak is more preferably present in the range of the void volume diameter of 18 nm to 33 nm, and it can be considered that the first peak is particularly preferably present in the range of the void volume diameter of 20 nm to 30 nm.
- the second peak is more preferably present in the range of the void volume diameter of 50 nm to 150 nm, and it can be considered that the second peak is particularly preferably present in the range of the void volume diameter of more than 100 nm to 120 nm.
- Example 1 Example 1 except that a stainless steel metal honeycomb carrier was immersed in the second catalyst layer Rh-containing slurry to form a catalyst layer and then immersed in the first catalyst layer Pd-containing slurry to form a catalyst layer.
- a catalyst (sample) was prepared in the same manner as described above. That is, a catalyst (sample) was produced in the same manner as in Example 1 except that the compositions of the first catalyst layer and the second catalyst layer were reversed in Example 1.
- Ceria-zirconia composite oxide B10 (D50: 6.5 ⁇ m, pore diameter 66 nm, BET specific surface area: 38 m 2 / g), alumina A4 (D50: 13 ⁇ m, pore diameter 22 nm, BET specific surface area 105 m 2 / g), and inorganic Alumina sol as a system binder was prepared.
- a stainless steel metal honeycomb carrier was fired at 500 ° C. for 1 hour to remove oil and dust adhering to the carrier.
- a stainless steel metal honeycomb carrier 300 cell, ⁇ 30 ⁇ 30L, capacity 21 cc test piece
- a stainless steel metal honeycomb carrier 300 cell, ⁇ 30 ⁇ 30L, capacity 21 cc test piece
- Pd / Rh-containing slurry 300 cell, ⁇ 30 ⁇ 30L, capacity 21 cc test piece
- a catalyst was produced by firing at 500 ° C. for 1 hour in an atmosphere to form a first catalyst layer.
- the supported amount of Pd was 1.4 g per liter of catalyst in terms of metal
- the supported amount of Rh was 0.16 g per liter of catalyst in terms of metal.
- the first catalyst layer contains Pd as a noble metal. It was found to be contained, and it was found that the second catalyst layer (upper layer) preferably contained Rh. Since it has been known that Rh and Pt have the same action and characteristics (see, for example, JP2013-220401A, JP2014-144426A, etc.), Rh in the above embodiment is set to Pt. It can be considered that the same effect can be obtained even if it is replaced.
- the supported amount of Pd is preferably 0.5 to 2.0 g per liter of the catalyst in terms of metal.
- the amount of Rh supported is less than 0.1 g per liter of the catalyst in terms of metal, the exhaust gas purification performance tends to be insufficient, and conversely if it exceeds 0.5 g, the product cost is low.
- the supported amount of Rh is preferably 0.1 to 0.5 g per liter of the catalyst in terms of metal.
- the improvement of NOx purification performance was recognized compared with the comparative example.
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Abstract
Description
このような三元触媒としては、高い比表面積を有する無機多孔質体、例えば高い比表面積を有するアルミナ多孔質体に貴金属を担持し、これを基材、例えば耐火性セラミック又は金属製ハニカム構造で出来ているモノリス型(monolithic)基材に担持したり、或いは、耐火性粒子に担持したりしたものが知られている。
自動車等の内燃機関は、加速、減速、低速走行、高速走行等の運転状況に応じて空燃比は大きく変化するため、酸素センサー(ジルコニア)を用いてエンジンの作動条件によって変動する空燃比(A/F)を一定に制御している。しかし、このように空燃比(A/F)を制御するだけでは、触媒が十分に浄化触媒性能を発揮することができないため、触媒層自身にも空燃比(A/F)を制御する作用が求められる。そこで、空燃比の変化に起因して発生する触媒の浄化性能の低下を触媒自体の化学的作用により防止する目的で、触媒活性成分である貴金属に助触媒を加えた触媒が用いられている。
また、このようなセリアにジルコニアを固溶させたセリア-ジルコニア複合酸化物は、酸素ストレージ能(OSC)がさらに優れているため、OSC材として多くの触媒に加えられている。
しかしながら、セリア-ジルコニアは希土類(レアアース)であり高価であるため、安価な触媒を提供しようとする場合には、セリア-ジルコニア複合酸化物を貴金属の担持体として使用するには限界があった。
そのため従来から、アルミナと共に、セリアやセリア-ジルコニア複合酸化物などのOSC材を貴金属の担持体として使用して、安価で且つ、安定して触媒浄化性能を発揮することができる触媒が開示されている。
このように、2輪自動車用の排気ガス浄化触媒に関しては、4輪自動車用の排気ガス浄化触媒とは異なる特殊な課題を抱えているため、従来、2輪自動車用の排気ガス浄化触媒に関して次のような提案がなされている。
また、鞍乗型車両は、4輪自動車に比べて、触媒を小型化せざるを得ないばかりか、排気ガスの流速が速いため、触媒は、通過する排気ガスの空間速度が極めて高い環境で使用されるケースがほとんどである。そのため、触媒層の深くまで排ガスが十分に拡散せず、触媒の性能を十分に引き出せないという課題も抱えていた。
さらに本発明の第2の目的は、使用を重ねても、触媒構材料が有する細孔が閉塞してしまうことを防ぐことができ、さらには、触媒層の深くまで排気ガスを拡散させることができる、新たな排気ガス浄化触媒を提供することにある。
本発明が第2に提案する上記排気ガス浄化触媒はさらに、第一触媒層及び第二触媒層それぞれの主要材料であるアルミナ及びOSC材の粒形を調整することによって、使用を重ねても、触媒構材料が有する細孔が閉塞してしまうことを防ぐことができ、さらには、排気ガスを触媒層の深くまで拡散させることができる。その結果、これらに担持される貴金属成分の細孔内への埋没を防ぐことができ、さらには触媒層中のガス拡散を向上させることができるため、高温の排気ガスに晒され、かつ触媒を通過する高空間速度な排ガス雰囲気下で使用される内燃機関においても、触媒活性の低下が生じにくく、かつ触媒層全体を有効利用することができる。よって、特に鞍乗型車両用排気ガス浄化三元触媒として極めて好適である。
本実施形態の一例に係る触媒(「本触媒」と称する)は、基材の表面に形成された第一触媒層と、該第一触媒層の上側に形成された第二触媒層とを有する排気ガス浄化触媒である。
また、第一触媒層及び第二触媒層をまとめて「本触媒層」とも称する。
本触媒の基材の材質としては、セラミックス等の耐火性材料や金属材料を挙げることができる。
セラミック製基材の材質としては、耐火性セラミック材料、例えばコージライト、コージライト-アルファアルミナ、窒化ケイ素、ジルコンムライト、スポジュメン、アルミナ-シリカマグネシア、ケイ酸ジルコン、シリマナイト(sillimanite)、ケイ酸マグネシウム、ジルコン、ペタライト(petalite)、アルファアルミナおよびアルミノシリケート類などを挙げることができる。
金属製基材の材質としては、耐火性金属、例えばステンレス鋼(SUS)または鉄を基とする耐食性合金などを挙げることができる。
ハニカム材料としては、例えばセラミックス等のコージェライト質のものを用いることができる。また、フェライト系ステンレス等の金属材料からなるハニカム体(「メタルハニカム」とも称する)を用いることもできる。
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、耐熱性が向上するとともにパンチングにより通孔が形成されるため、広い表面積が得られて排気ガス浄化性能が向上し、しかも排気管内における排気抵抗が小さくなるので、例えば2輪自動車用として好適である。
第一触媒層は、貴金属、OSC材及びアルミナを含有し、且つ、前記OSC材及びアルミナを、OSC材:アルミナ=1:7~1:3の質量比率で含有することを特徴とする触媒層である。
第一触媒層は、触媒活性成分として、パラジウム(Pd)を主成分とする貴金属を含有するのが好ましい。すなわち、第一触媒層において、少なくとも最も量の多い貴金属がPdであるのが好ましく、中でも第一触媒層の貴金属のうちの50質量%以上、その中でも80質量%以上、その中でも90質量%以上(100質量%を含む)を、Pdが占めるのが好ましい。
また、本触媒がハニカム形状の場合、本触媒全体において、Pdの担持量は金属換算で触媒1L当たり0.5~2.0gであるのが好ましく、中でも1.0g以上或いは1.8g以下、その中でも1.25g以上或いは1.6g以下であるのが特に好ましい。
第一触媒層は、酸素ストレージ能(OSC:Oxygen Storage capacity)を有する助触媒(「OSC材」と称する)を含むのが好ましい。
OSC材としては、例えばセリウム酸化物、ジルコニ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を挙げることができる。
かかる観点から、第一触媒層におけるOSC材の平均粒径(D50)は、3μm~12μmであるのが好ましく、中でも4μm以上或いは9μm以下であるのが特に好ましい。
かかる観点から、第一触媒層のOSC材の細孔径は、50nm~90nmであるのが好ましく、中でも55nm以上或いは85nm以下、その中でも60nm以上或いは80nm以下であるのが特に好ましい。
第一触媒層は、貴金属を担持する無機多孔質体として、アルミナを主材とする多孔質体、より具体的には、例えばアルミナ、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、アルミナ-酸化ランタン及びアルミナ-ジルコニア-セリアから選択される化合物又はそれら2種類以上の混合物からなる多孔質体を含有するのが好ましい。
かかる観点から、第一触媒層におけるアルミナの平均粒径(D50)は5μm~20μmであるのが好ましく、中でも7μm以上或いは18μm以下、その中でも10μm以上或いは16μm以下であるのが特に好ましい。
かかる観点から、第一触媒層におけるアルミナの細孔径は15nm~35nmであるのが好ましく、中でも17nm以上或いは33nm以下、その中でも20nm以上或いは30nm以下であるのが特に好ましい。
アルミナは高比表面積を有しており、Pdなどの貴金属を分散担持することができる。他方、セリア-ジルコニア複合酸化物などのOSC材と貴金属は相性がよく、該OSC材に貴金属を担持するとアンカー効果が働き、熱負荷をかけても焼結(シンタリング)し難くなり、分散性を維持することができる。但し、セリア-ジルコニアなどのOSC材は希土類(レアアース)であり高価であるため、必要なOSC能を維持しつつ、希土類(レアアース)の使用量を減らすことが求められる。
かかる観点から、前記第一触媒層においては、前記OSC材及びアルミナを、OSC材:アルミナ=1:7~1:3の質量比率で含有するのが好ましく、中でも1:7~1:3.3、その中でも1:7~1:3.6、さらにその中でも1:7~1:3.8の質量比率で含有するのが特に好ましい。
そのため、基材と本触媒層との密着性を確保する観点からすると、第一触媒層においては、前記OSC材はアルミナに対して、質量比で1/5以上、中でも1/4.8以上、さらにその中でも1/4.5以上、さらにその中でも1/4.2以上の割合で含ませることが好ましい。このような配合比を採用することは、特に粒径が10μm以上のアルミナを用いた触媒において効果的となる。
第一触媒層は、必要に応じて、安定化材を含んでいてもよい。
該安定化材としては、例えばアルカリ土類金属やアルカリ金属を挙げることができる。中でも、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、カルシウムおよびストロンチウムから成る群から選択される金属のうちの一種又は二種以上を選択可能である。
第一触媒層は、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等の水溶液を使用することができる。
第一触媒層は、さらに、必要に応じて上記以外の他の成分を含有することができる。
第二触媒層は、貴金属、OSC材及びアルミナを含有し、且つ、前記OSC材及びアルミナを、OSC材:アルミナ=1:1~10:0の質量比率で含有することを特徴とする触媒層である。
第二触媒層は、触媒活性成分として、白金(Pt)又はロジウム(Rh)又はこれら両成分を主成分とする貴金属を含有するのが好ましい。すなわち、第二触媒層において、少なくとも最も量の多い貴金属が白金(Pt)又はロジウム(Rh)であるのが好ましく、中でも第二触媒層の貴金属のうちの50質量%以上、その中でも80質量%以上、その中でも90質量%以上(100質量%を含む)を、白金(Pt)又はロジウム(Rh)が占めるのが好ましい。
また、本触媒がハニカム形状の場合、本触媒全体において、Pt及びRhの担持量は金属換算で触媒1L当たり0.1g~0.5gであるのが好ましく、中でも0.12g以上或いは0.3g以下、その中でも0.14g以上或いは0.18g以下であるのが特に好ましい。
第二触媒層が含有するOSC材としては、例えばセリウム酸化物、ジルコニ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を挙げることができる。第一触媒層のOSC材と第二触媒層のOSC材とが同じであっても、異なっていてもよい。
また、第二触媒層が含有するOSC材の平均粒径(D50)及び細孔径は、それぞれ第一触媒層のOSC材と第二触媒層のOSC材とが同じであっても、異なっていてもよい。
なお、各層の主材を対比すると、第一触媒層の主材すなわちアルミナの平均粒径(D50)が10μm~16μmであり、且つ、第二触媒層の主材すなわちOSC材の平均粒径(D50)が4μm~10μmであるのが好ましく、さらに好ましくは各成分について上記のとおりである。
第二触媒層は、貴金属を担持する無機多孔質体として、アルミナを主材とする多孔質体、より具体的には、例えばアルミナ、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、アルミナ-酸化ランタン及びアルミナ-ジルコニア-セリアから選択される化合物又はそれら2種類以上の混合物からなる多孔質体を含有するのが好ましい。第一触媒層のアルミナと第二触媒層のアルミナとが同じであっても、異なっていてもよい。
また、第二触媒層が含有するアルミナの平均粒径(D50)及び細孔径は、それぞれ第一触媒層のアルミナと第二触媒層のアルミナとが同じであっても、異なっていてもよい。
上述のように、セリア-ジルコニア複合酸化物などのOSC材と貴金属とは相性がよく、該OSC材に貴金属を担持するとアンカー効果が働き、熱負荷をかけても焼結(シンタリング)し難くなり、分散性を維持することができる。但し、セリア-ジルコニアなどのOSC材は、希土類(レアアース)であり高価であるため、必要なOSC能を維持しつつ、使用量を減らすことが求められる。他方、アルミナは、高比表面積を有しており、Pdなどの貴金属を分散担持することができる反面、アルミナにRhが担持されると、両者が反応してロジウム化合物などが不可逆的に生じ、Rhの浄化性能が失活してしまうため、第二触媒層では、アルミナの量を比較的少なくするのが好ましく、例えばアルミナよりもOSC材の含有量が多い方が好ましい。
かかる観点から、第二触媒層においては、前記OSC材及びアルミナを、OSC材:アルミナ=1:1~10:0の質量比率で含有することが好ましく、中でも2.2:1~10:1、その中でも2.2:1~6.3:1、その中でも2.5:1~5:1、さらにその中でも3.0:1~3.8:1であるのが好ましい。
第二触媒層は、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やアルカリ金属を挙げることができる。中でも、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、カルシウムおよびストロンチウムから成る群から選択される金属のうちの一種又は二種以上を選択可能である。
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等の水溶性溶液を使用することができる。
第二触媒層は、さらに、必要に応じて上記以外の他の成分を含有することができる。
本触媒においては、第一触媒層の上側、すなわち基材とは反対側、言い換えれば排ガス流路側に第二触媒層を備えていればよいから、第一触媒層と第二触媒層との間に他の層が存在しても、しなくてもかまわない。例えば第一触媒層と第二触媒層の間に、触媒層ではない層、例えば多孔質耐火性無機酸化物粉体からなる層や、多孔質耐火性無機酸化物粉体及び助触媒成分からなる層などの他の層が存在していてもよい。
また、第一触媒層と第二触媒層の厚さの比は、第一触媒層:第二触媒層=1:1.23~1:1.35であるのが好ましく、その中でも1:1.26~1:1.3であるのが特に好ましい。
本触媒において、本触媒層、すなわち第一触媒層及び第二触媒層の両方を含めた触媒層の空隙容積は、水銀圧入ポロシメータにより空隙分布を測定した際、得られた対数微分空隙容積分布の空隙容積径5nm~200nmの範囲において、空隙容積径15nm~35nmの範囲に第1ピークを有し、空隙容積径50nm~200nmの範囲に第2ピークを有することが好ましい。
他方、第2ピークは、空隙容積径50nm~150nmの範囲に存在するのがさらに好ましく、その中でも空隙容積径100nm~120nmの範囲に存在するのが特に好ましい。
なお、そのピークが存在しないと仮定した場合のライン、すなわちバックグラウンドからの垂直高さが0.002ml/g未満のピークは、測定装置などのノイズであると考えられるため、本発明が規定する「ピーク」に該当するものではない。
なお、触媒原料となるアルミナやOSC材の細孔径は、触媒層の細孔径と必ずしも一致するものではない。
また、上記「空隙容積径」は、空隙を円柱近似した際の底面の直径を意味し、次の式により算出される。
dr=-4σcosθ/p(σ:表面張力、θ:接触角、p:圧力)
この式において、水銀の表面張力は既知であり、接触角は装置毎で固有の値を示すため、圧入した水銀の圧力から空隙容積径を算出することができる。
また、本触媒層の空隙容積は、触媒から触媒層のみを剥がして、水銀圧入ポロシメータで空隙分布を測定することで測定することができる。
本触媒を作製するには、例えば、貴金属、アルミナ及びOSC材、必要に応じてさらに安定化材、バインダなどと、水とを混合・撹拌してスラリーとし、得られたスラリーを例えばセラミックハニカム体などの基材にウォッシュコートし、これを焼成して、基材表面に第一触媒層を形成した後、上記同様に上層(表面層)としての第二触媒層を形成すればよい。
但し、これらの製法に限定されるものではない。
本触媒は、4輪自動車や、2輪自動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本触媒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。具体的には、例えば、本触媒は、例えば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、本触媒は、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。
なお、図1において、矢印Xは空気の流れを示し、矢印Yはバキュームプレッシャを示し、矢印Zはクランクケース内で発生したブローバイガスの流れを示している。
続いて、4サイクルエンジンの一般的な圧縮行程、燃焼工程を経た後に、排気バルブ12Eが開いた状態(吸気バルブ12Dは閉)でピストン12Fが上昇する排気行程が実施されることにより、燃焼ガスが排気ポート12Bに排出され、排気ガスとして排気管14に排出される。
排気管14の後端には排気マフラー15が接続され、この排気マフラー15は、排気管14を通った高温・高圧の排気ガスを消音して外部に排出するサイレンサとして機能する。
また、図中符号35は、エアクリーナ11のクリーンサイド11Dと、エンジン12のクランクケースとを連通する連通管である。この連通管35は、クランクケース内で発生するブローバイガスをエアクリーナ11およびキャブレター13を通してエンジン12に戻し、ブローバイガスの放出を防止するクランクケースエミッション制御装置として機能する。
本発明において「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。
本発明において「X~Y」(X,Yは任意の数字)と表現する場合、特にことわらない限り「X以上Y以下」の意と共に、「好ましくはXより大きい」或いは「好ましくはYより小さい」の意も包含する。
また、「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。
第一触媒層及び第二触媒層におけるOSC材及びアルミナの質量比率を変化させて最適な比率を検討した。
セリア-ジルコニア複合酸化物B10(D50:6.5μm、細孔径66nm、BET比表面積:38m2/g)、アルミナA4(D50:13μm、細孔径22nm、BET比表面積105m2/g)、および、無機系バインダとしてのアルミナゾルをそれぞれ準備した。
基材については、ステンレス製メタルハニカム担体(300セル、φ30mm×L30mm、容量21ccのテストピース)を500℃で1時間焼成して担体に付着した油分やゴミを取り除いておいた。
他方、硝酸Rh溶液に純水を加えると共に上記セリア-ジルコニア複合酸化物B10を70質量部添加し、2時間撹拌後、上記アルミナA4を20質量部及び上記バインダ材を8質量部を加え、第二触媒層Rh含有スラリーを得た(Rh:0.2質量部)。
次に、第一触媒層を形成したメタルハニカム担体を、上記第二触媒層Rh含有スラリーに浸漬した後、エアブローでセル中の余剰スラリーを除去し、乾燥させた後、大気雰囲気中500℃で1時間焼成して第二触媒層を形成させて、触媒(サンプル)を作製した。
作製した該触媒(サンプル)において、Pdの担持量は金属換算で触媒1L当たり1.4gであり、Rhの担持量は金属換算で触媒1L当たり0.16gであった。
実施例1において、第一触媒層Pd含有スラリーにおけるアルミナA4の配合量を70質量部に変更すると共に、セリア-ジルコニアB10の配合量を11質量部に変更した以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第二触媒層Rh含有スラリーにおけるセリア-ジルコニアB10の配合量を90質量部に変更すると共に、アルミナA4の配合量を0質量部に変更した以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第一触媒層Pd含有スラリーにおけるアルミナA4の配合量を41質量部に変更すると共に、セリア-ジルコニアB10の配合量を40質量部に変更した以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第二触媒層Rh含有スラリーにおけるセリア-ジルコニアB10の配合量を40質量部に変更すると共に、アルミナA4の配合量を50質量部に変更した以外は、実施例1と同様に触媒(サンプル)を作製した。
原料として用いたセリア-ジルコニア複合酸化物及びアルミナの細孔径は、後述する対数微分空隙容積分布測定と同様に測定して得られた対数微分空隙容積分布において、最もピーク高さの高い第1ピ一クの空隙容積径の値である。
実施例1~3および比較例1~2で作製した触媒(サンプル)を、900℃に保持した電気炉に投入し、C3H6、O2およびN2でA/F=14.5に調整された混合ガスを20L/minで流して24時間熱処理し、その後室温まで冷却した。次いで、下記組成のモデルガス中のCO、HCおよびNOxそれぞれの50%浄化率に到達する温度(℃)を測定して、各々の触媒の三元浄化性能を評価した。評価条件は下記の通りである。
CO:0.9%
C3H6:900ppm
C3H8:450ppm
NO:1000ppm
O2:0.85%
CO2:14%
H2O:10%
N2:残部
A/F:14.5
ガス流速:50L/min
昇温速度:20℃/min
他方、第二触媒層では、前記OSC材及びアルミナを、OSC材:アルミナ=1:1~10:0の質量比率で含有することが好ましく、中でも2.2:1~10:1、その中でも2.2:1~6.3:1、その中でも2.5:1~5:1、さらにその中でも3.0:1~3.8:1であるのが好ましいと考えることができる。
第一触媒層及び第二触媒層におけるOSC材及びアルミナの質量比率を変化させて、基材との密着性の観点から最適な比率を検討した。
実施例1において、第一層のアルミナA4の代わりに、アルミナ(D50:13μm、細孔径28nm、BET比表面積99m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第二層のセリア-ジルコニア複合酸化物B10の代わりに、セリア-ジルコニア複合酸化物(D50:6.5μm、細孔径50nm、BET比表面積:39m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、表2に示すように、第一層のスラリー塗布量を20%減らし、第二層のスラリー塗布量を20%増やした以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、表2に示すように、第一層のスラリー塗布量を20%増やし、第二層のスラリー塗布量を20%減らした以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第一触媒層Pd含有スラリーにおけるアルミナA4の配合量を81質量部に変更すると共に、セリア-ジルコニアB10の配合量を0質量部に変更した以外は、実施例1と同様に触媒(サンプル)を作製した。
大気下室温雰囲気で保管していた触媒(サンプル)を、900℃に加熱した電気路内に入れて60分間静置して品温を900℃にした後、該触媒(サンプル)を大気下室温雰囲気に出して、触媒(サンプル)の表面を観察した。
異なる全ての製品ロットにおいて、剥離が観察されなかったサンプルについては「○(good)」と評価し、製品ロットの一部について剥離が観察されたサンプルについては「△(usual)」と評価し、異なる全ての製品ロットにおいて剥離が観察されたサンプルについては「×(poor)」と評価した。
よって、上記実施例・比較例及びこれまで発明者が行ってきた試験結果などから、基材と第一触媒層との密着性及び浄化性能などを総合的に考慮すると、第一触媒層において、OSC材及びアルミナの質量比率は、OSC材:アルミナ=1:5~1:3であるのが好ましく、中でも1:4.8~1:3.3、その中でも1:4.5~1:3.6、さらにその中でも1:4.2~1:3.8であるのがさらに好ましいと考えることができる。
第一触媒層及び第二触媒層におけるアルミナ及びOSC材の粒径及び細孔径を変化させて、本触媒層の最適な空隙分布を検討した。
実施例1において、第一触媒層のアルミナA4の代わりに、アルミナ(D50:13μm、細孔径12nm、BET比表面積120m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第二触媒層のセリア-ジルコニア複合酸化物B10の代わりに、セリア-ジルコニア複合酸化物(D50:6.5μm、細孔径26nm、BET比表面積:60m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第一触媒層のアルミナA4の代わりに、アルミナ(D50:2μm、細孔径22nm、BET比表面積104m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第一触媒層のアルミナA4の代わりに、アルミナ(D50:25μm、細孔径22nm、BET比表面積102m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第二触媒層のセリア-ジルコニア複合酸化物B10の代わりに、セリア-ジルコニア複合酸化物(D50:1μm、細孔径66nm、BET比表面積:37m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1において、第二触媒層のセリア-ジルコニア複合酸化物B10の代わりに、セリア-ジルコニア複合酸化物(D50:16μm、細孔径66nm、BET比表面積:38m2/g)を用いた以外は、実施例1と同様に触媒(サンプル)を作製した。
実施例1、4~5・比較例8~13で作製した触媒(サンプル)から触媒層を剥がして、次のようにして空隙分布を測定した。
対数微分空隙容積分布の測定は、水銀に加える圧力を変化させ、その際の細孔中に進入した水銀の量を測定することにより、細孔(空隙)分布を測定する方法である。
細孔内に水銀が侵入し得る条件は、圧力P、細孔直径D、水銀の接触角と表面張力をそれぞれθとσとすると、力の釣り合いからPD=-4σCOSθで表すことができる。この際、接触角と表面張力を定数とすれば、圧力Pとそのとき水銀が侵入し得る細孔直径Dは反比例することになる。このため、圧力Pとそのときに侵入する液量Vを、圧力を変えて測定し、得られたP-V曲線の横軸Pを、そのままこの式から細孔直径に置き換え、空隙分布を求めることができる。
測定環境:25℃
測定セル:試料室体積 3cm3、圧入体積 0.39cm3
測定範囲:0.0048MPa から 255.106MPa まで
測定点:131点(細孔径を対数でとったときに等間隔になるように点を刻んだ)
圧入体積:25%以上80%以下になるように調節した。
排気圧力:50μmHg
排気時間:5.0min
水銀注入圧力:0.0034MPa
平衡時間:10secs
(高圧パラメーター)
平衡時間:10secs
(水銀パラメーター)
前進接触角:130.0degrees
後退接触角:130.0degrees
表面張力:485.0mN/m(485.0dynes/cm)
水銀密度:13.5335g/mL
(1)実施例・比較例で得た触媒(サンプル)の中央部から5mm×5mm×10mmをコアリングし、測定を行った。
(2)低圧部で0.0048MPaから0.2068MPa以下の範囲で46点測定。
(3)高圧部で0.2241MPaから255.1060MPa以下の範囲で85点測定。
(4)水銀圧入圧力及び水銀圧入量から、細孔径分布を算出する。
なお、上記(2)、(3)、(4)は、装置付属のソフトウエアにて、自動で行った。
上記同様に、各々の触媒(サンプル)の三元浄化性能を評価した。
中でも、第1ピークは、空隙容積径18nm~33nmの範囲に存在するのがさらに好ましく、その中でも空隙容積径20nm~30nmの範囲に存在するのが特に好ましいものと考えることができる。
他方、第2ピークは、空隙容積径50nm~150nmの範囲に存在するのがさらに好ましく、その中でも空隙容積径100nm超120nm以下の範囲に存在するのが特に好ましいものと考えることができる。
第一触媒層及び第二触媒層における貴金属の担持量、積層構成を変化させて最適な範囲を検討した。
実施例1において、ステンレス製メタルハニカム担体を第二触媒層Rh含有スラリーに浸漬して触媒層を形成した後、第一触媒層Pd含有スラリーに浸漬して触媒層を形成した以外、実施例1と同様に触媒(サンプル)を作製した。すなわち、実施例1において、第一触媒層と第二触媒層の組成を逆転させた以外、実施例1と同様に触媒(サンプル)を作製した。
セリア-ジルコニア複合酸化物B10(D50:6.5μm、細孔径66nm、BET比表面積:38m2/g)、アルミナA4(D50:13μm、細孔径22nm、BET比表面積105m2/g)、および無機系バインダとしてのアルミナゾルをそれぞれ準備した。
基材については、ステンレス製メタルハニカム担体を500℃で1時間焼成して担体に付着した油分やゴミを取り除いておいた。
Pdの担持量は金属換算で触媒1L当たり1.4gであり、Rhの担持量は金属換算で触媒1L当たり0.16gであった。
上記同様に、各々の触媒(サンプル)の三元浄化性能を評価した。
なお、従来からRhとPtは同様の作用及び特徴を有することが分かっているため(例えば特開2013-220401号公報、特開2014-144426号公報など参照)、上記実施例のRhをPtに置き換えても同様の効果が得られるものと考えることができる。
他方、Rhの担持量は、金属換算で触媒1L当たり0.1g未満である場合には、排気ガス浄化性能が不十分となる傾向があり、逆に0.5gを超える場合には製品コストが高くなり、そのコストに見合った効果の増強が得られる傾向がみられることが分かった。よって、Rhの担持量は、金属換算で触媒1L当たり0.1~0.5gとなるようにすることが好ましいことが分かった。
なお、各実施例は、比較例と比べて、特にNOx浄化性能の向上が認められた。
実施例1~3で得られた触媒(サンプル)と、比較例1~2で得られた触媒(サンプル)を、それぞれ図1に示した排気ガス浄化装置を搭載した自動二輪車に装着し、実車耐久試験を行った。その結果を図2に示した。
Claims (7)
- セラミックス又は金属からなる基材の表面に形成された第一触媒層と、該第一触媒層の上側に形成された第二触媒層とを有し、
前記第一触媒層は、貴金属、OSC材及びアルミナを含有し、且つ、前記OSC材及びアルミナを、OSC材:アルミナ=1:7~1:3の質量比率で含有することを特徴とし、
前記第二触媒層は、貴金属、OSC材及びアルミナを含有し、且つ、前記OSC材及びアルミナを、OSC材:アルミナ=1:1~10:0の質量比率で含有することを特徴とする排気ガス浄化触媒。 - 第一触媒層のアルミナの平均粒径(D50)が10μm~16μmであり、且つ、第一触媒層のOSC材の平均粒径(D50)が3μm~12μmであることを特徴とする請求項1記載の排気ガス浄化触媒。
- 第一触媒層において、OSC材及びアルミナの質量比率が、OSC材:アルミナ=1:5~1:3であることを特徴とする請求項1又は2に記載の排気ガス浄化触媒。
- 基材の材質がステンレス鋼(SUS)であることを特徴とする請求項1~3の何れかに記載の排気ガス浄化触媒。
- 水銀圧入ポロシメータにより測定される対数微分空隙容積分布における空隙容積径5nm~200nmの範囲において、空隙容積径15nm~35nmの範囲に第1ピークを有し、且つ空隙容積径50nm~200nmの範囲に第2ピークを有することを特徴とする請求項1~4の何れかに記載の排気ガス浄化触媒。
- 前記第一触媒層における、アルミナの細孔径が15nm~35nmであることを特徴とする請求項1~5の何れかに記載の排気ガス浄化触媒。
- 前記第二触媒層における、OSC材の細孔径が50nm~90nmであることを特徴とする請求項1~6の何れかに記載の排気ガス浄化触媒。
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BR112017002337-7A BR112017002337B1 (pt) | 2014-12-12 | 2015-10-21 | catalisador de purificação de gás de escape |
CN201580046648.5A CN106794449B (zh) | 2014-12-12 | 2015-10-21 | 排气净化催化剂 |
US15/504,430 US10022705B2 (en) | 2014-12-12 | 2015-10-21 | Exhaust gas purifying catalyst |
JP2016563562A JP6334731B2 (ja) | 2014-12-12 | 2015-10-21 | 排気ガス浄化触媒 |
CA2956294A CA2956294C (en) | 2014-12-12 | 2015-10-21 | Exhaust gas purifying catalyst |
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2015
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WO2018202639A1 (en) * | 2017-05-01 | 2018-11-08 | Dsm Ip Assets B.V. | Metal powderdous catalyst for hydrogenation processes |
CN110582351A (zh) * | 2017-05-01 | 2019-12-17 | 帝斯曼知识产权资产管理有限公司 | 用于氢化工艺的金属粉末催化剂 |
US11167270B2 (en) | 2017-05-01 | 2021-11-09 | Dsm Ip Assets B.V. | Metal powderdous catalyst for hydrogenation processes |
CN110582351B (zh) * | 2017-05-01 | 2023-02-28 | 帝斯曼知识产权资产管理有限公司 | 用于氢化工艺的金属粉末催化剂 |
WO2022004638A1 (ja) | 2020-06-30 | 2022-01-06 | 株式会社キャタラー | 排ガス浄化用触媒 |
Also Published As
Publication number | Publication date |
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PH12017500280A1 (en) | 2017-07-03 |
BR112017002337B1 (pt) | 2021-01-12 |
EP3231511A4 (en) | 2018-07-25 |
US20170232425A1 (en) | 2017-08-17 |
PH12017500280B1 (en) | 2017-07-03 |
TW201627056A (zh) | 2016-08-01 |
BR112017002337A2 (pt) | 2018-01-16 |
US10022705B2 (en) | 2018-07-17 |
JP6334731B2 (ja) | 2018-05-30 |
CN106794449A (zh) | 2017-05-31 |
MY180110A (en) | 2020-11-23 |
TWI655027B (zh) | 2019-04-01 |
CA2956294C (en) | 2018-11-27 |
CN106794449B (zh) | 2019-09-27 |
EP3231511A1 (en) | 2017-10-18 |
JPWO2016092957A1 (ja) | 2017-04-27 |
CA2956294A1 (en) | 2016-06-16 |
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