WO2016039302A1 - 排ガス浄化用触媒 - Google Patents
排ガス浄化用触媒 Download PDFInfo
- Publication number
- WO2016039302A1 WO2016039302A1 PCT/JP2015/075374 JP2015075374W WO2016039302A1 WO 2016039302 A1 WO2016039302 A1 WO 2016039302A1 JP 2015075374 W JP2015075374 W JP 2015075374W WO 2016039302 A1 WO2016039302 A1 WO 2016039302A1
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- WO
- WIPO (PCT)
- Prior art keywords
- exhaust gas
- catalyst
- density
- purifying catalyst
- gas flow
- Prior art date
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- 239000003054 catalyst Substances 0.000 title claims abstract description 261
- 238000000746 purification Methods 0.000 title claims abstract description 56
- 239000000463 material Substances 0.000 claims abstract description 48
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- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 16
- 239000000758 substrate Substances 0.000 claims description 34
- 229910000510 noble metal Inorganic materials 0.000 claims description 18
- 230000009467 reduction Effects 0.000 claims description 6
- 230000003647 oxidation Effects 0.000 claims description 4
- 238000007254 oxidation reaction Methods 0.000 claims description 4
- 229910052751 metal Inorganic materials 0.000 abstract description 95
- 239000002184 metal Substances 0.000 abstract description 95
- 230000003197 catalytic effect Effects 0.000 abstract description 18
- 239000010970 precious metal Substances 0.000 abstract 1
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- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 21
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 13
- 239000010948 rhodium Substances 0.000 description 12
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 11
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- 239000000203 mixture Substances 0.000 description 6
- 229910052763 palladium Inorganic materials 0.000 description 6
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
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- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 5
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- 230000015572 biosynthetic process Effects 0.000 description 5
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- 241001272720 Medialuna californiensis Species 0.000 description 3
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
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- 229910052878 cordierite Inorganic materials 0.000 description 3
- 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 3
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- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
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- 239000000654 additive Substances 0.000 description 2
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- 229910000505 Al2TiO5 Inorganic materials 0.000 description 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
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- 230000010718 Oxidation Activity Effects 0.000 description 1
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- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
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- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
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- 150000002484 inorganic compounds Chemical class 0.000 description 1
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- 229910052762 osmium Inorganic materials 0.000 description 1
- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 description 1
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- 230000008569 process Effects 0.000 description 1
- AABBHSMFGKYLKE-SNAWJCMRSA-N propan-2-yl (e)-but-2-enoate Chemical compound C\C=C\C(=O)OC(C)C AABBHSMFGKYLKE-SNAWJCMRSA-N 0.000 description 1
- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
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- 239000010935 stainless steel Substances 0.000 description 1
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- 239000002344 surface layer Substances 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
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- 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
- F01N2510/00—Surface coverings
- F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
- F01N2510/068—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings
- F01N2510/0684—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings having more than one coating layer, e.g. multi-layered coatings
-
- 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 purifying catalyst provided in an exhaust system of an internal combustion engine. Specifically, the present invention relates to an exhaust gas purifying catalyst in which a catalytic metal is supported at a high density on a specific portion of a catalyst layer. Note that this international application claims priority based on Japanese Patent Application No. 2014-184125 filed on September 10, 2014, the entire contents of which are incorporated herein by reference. Yes.
- Exhaust gas discharged from an internal combustion engine such as an automobile engine contains harmful components such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO x ).
- exhaust gas purification catalysts have been used to efficiently remove these exhaust gas components.
- the exhaust gas purifying catalyst typically has a form in which a noble metal functioning as a catalyst (hereinafter simply referred to as “catalyst metal”) is supported on a porous carrier.
- Typical examples of the catalyst metal include platinum group noble metals such as platinum (Pt), rhodium (Rh) and palladium (Pd).
- platinum platinum
- Rh rhodium
- Pd palladium
- Patent Document 1 discloses an exhaust gas purification catalyst comprising a base material having a plurality of through holes in the exhaust gas flow direction and a catalyst layer formed on the inner wall surface of the through holes and containing a noble metal. It is described that the thickness of the catalyst layer is adjusted so that the flow pressure of the exhaust gas is uniform between the holes.
- the present invention has been created to solve such problems, and an object of the present invention is to provide an exhaust gas purifying catalyst in which the performance of the catalytic metal is appropriately exhibited and the exhaust gas purifying performance is excellent during warm-up. .
- the flow rate of the exhaust gas is relatively small when the internal combustion engine is warmed up. For this reason, the exhaust gas tends to flow through a specific portion of the exhaust gas purifying catalyst.
- the exhaust gas purifying catalyst has a portion having a relatively large exhaust gas flow rate and a portion having a relatively small exhaust gas flow rate.
- the catalyst layer is formed on the substrate by the wash coat method, the catalyst metal is supported substantially uniformly (homogeneously) in each through hole of the exhaust gas purifying catalyst. As a result, the catalytic metal was not effectively utilized at the time of warming up the internal combustion engine in the part where the flow rate of the exhaust gas is small and / or the part where the catalyst temperature is relatively low.
- an exhaust gas purifying catalyst that is disposed in an exhaust passage connected to an internal combustion engine such as an automobile engine and purifies exhaust gas discharged from the internal combustion engine.
- Such an exhaust gas purifying catalyst includes a base material, and a catalyst layer formed on the base material, the noble metal functioning as an oxidation and / or reduction catalyst, and a catalyst layer including a carrier supporting the noble metal. Yes.
- a tip portion located on the upstream side in the exhaust gas flow direction has a portion with a relatively large exhaust gas flow rate when the internal combustion engine is warmed up. There is a part where the flow rate of the exhaust gas is relatively small.
- the catalyst layer at the portion where the flow rate of the exhaust gas is relatively high is provided with a high density portion where the noble metal is supported at a higher density than the catalyst layer at the portion where the flow rate of the exhaust gas is relatively low.
- the high-density portion is formed shorter than the entire length of the exhaust gas-purifying catalyst in the exhaust gas flow direction from the tip portion.
- the catalyst metal By increasing the catalyst metal density at the part where the exhaust gas flow rate is large when the internal combustion engine is warmed up, the catalyst metal can be used effectively. That is, when the catalyst metal density in the high-density portion is made equal to the conventional one, the amount of catalyst metal used should be reduced while maintaining the same warm-up performance (performance for raising the temperature of the exhaust gas purification catalyst). Can do. Alternatively, when the same amount of catalyst metal as in the prior art is intensively supported on the high density portion, the warm-up property can be improved relatively. For example, the temperature of the catalyst (typically upstream) can be quickly raised from the state in which the exhaust gas purifying catalyst is cold, centering on the high density portion.
- the “tip portion” is a portion located on the most upstream side of the exhaust passage in a state where the exhaust gas purifying catalyst is disposed at a predetermined position of the exhaust passage (exhaust pipe), and a portion where the exhaust gas contacts substantially first.
- the density of the noble metal in the high-density portion is 1.5 times or more the density of the noble metal in the portion where the flow rate of the exhaust gas is relatively small.
- the catalyst layer has a laminated structure of two or more layers having different structures from each other when viewed from the base material. And the said high-density part is formed in the uppermost layer part of this laminated structure.
- the high density portion is 10% away from the tip when the total length of the exhaust gas purification catalyst is 100% in the exhaust gas flow direction. % To a length of 50% or less.
- the effect of this invention is implement
- it can suppress that a catalyst metal moves from a high-density part, and can suppress the fall of the catalyst activity by sintering or alloying.
- the high density portion is 9% or more and 64% or less when the total area of the cross section perpendicular to the exhaust gas flow direction is 100%. It is formed in area.
- the tip portion of the exhaust gas purifying catalyst has a circular shape, and the relative relative to the inner peripheral circular portion including the center of the circular shape. There is a part with a large exhaust gas flow rate, and there is a part with a relatively small exhaust gas flow rate in the outer peripheral part adjacent to the inner peripheral circular part.
- the high density portion is preferably formed in the inner circumferential circular portion having an inner diameter of 30% to 80% of the outer diameter of the base material.
- the high density portion is formed at a position away from the outer periphery so as not to contact the outer periphery of the cross section of the exhaust gas purifying catalyst. ing. Heat tends to escape from the outer peripheral portion of the exhaust gas purifying catalyst as compared to the inner portion, and the warm-up time tends to be relatively long. Therefore, by providing the high density portion at a position away from the outer periphery, it is possible to improve the warm-up property better.
- a cross section of the exhaust gas purifying catalyst orthogonal to the exhaust gas flow direction is circular.
- the said cross section of the said high-density part is formed in the circular shape whose diameter is smaller than the circular shape of the said catalyst for exhaust gas purification.
- the circular shape of the high-density portion may be arranged concentrically with the circular shape of the exhaust gas purification catalyst.
- the circular center of the high-density portion may be eccentric with respect to the circular center of the exhaust gas purifying catalyst.
- FIG. 1 is a perspective view schematically showing an exhaust gas purifying catalyst according to an embodiment.
- FIG. 2 is an end cross-sectional view schematically showing a front end portion of the exhaust gas purifying catalyst of FIG.
- FIG. 3 is a cross-sectional view schematically showing the configuration of the rib wall portion of the exhaust gas purifying catalyst according to one embodiment.
- FIG. 4 is a graph comparing the warm-up properties of the exhaust gas purifying catalysts according to Comparative Example and Example 1.
- FIG. 5 is a graph comparing the warm-up properties of the exhaust gas purifying catalysts according to Comparative Example and Example 2.
- FIG. 6 is a diagram schematically illustrating an exhaust gas flow rate at the time of engine start according to an embodiment.
- FIG. 7 is an end cross-sectional view schematically showing a front end portion of an exhaust gas purifying catalyst according to another embodiment.
- FIG. 8 is an end cross-sectional view schematically showing a front end portion of an exhaust gas purifying catalyst according to another embodiment.
- FIG. 9 is a diagram schematically showing an exhaust gas purifying apparatus according to an embodiment.
- FIG. 9 is a diagram schematically illustrating the exhaust gas purification device 17 according to an embodiment.
- the exhaust gas purifying device 17 is provided in the exhaust system of the internal combustion engine 12.
- the internal combustion engine (engine) 12 is supplied with an air-fuel mixture containing oxygen and fuel gas.
- the internal combustion engine 12 burns this air-fuel mixture and converts the combustion energy into mechanical energy.
- the air-fuel mixture combusted at this time becomes exhaust gas and is discharged to the exhaust system.
- the internal combustion engine 12 having the configuration shown in FIG. 9 is mainly composed of an automobile gasoline engine.
- the exhaust gas purifying device 17 is preferably mounted on an internal combustion engine 12 of an eco car in which the engine is frequently stopped, for example, during traveling or temporarily stopped.
- eco-cars include passenger cars with an idling stop function (idling stop cars) and hybrid cars.
- the exhaust gas purifying device 17 can be applied to engines other than gasoline engines (for example, diesel engines).
- One end of the exhaust manifold 13 is connected to an exhaust port (not shown) of the internal combustion engine 12.
- the other end of the exhaust manifold 13 is connected to the exhaust pipe 14.
- the arrow in a figure has shown the distribution direction of waste gas.
- an exhaust gas exhaust passage is formed by the exhaust manifold 13 and the exhaust pipe 14.
- the exhaust gas purification device 17 includes an exhaust passage (exhaust manifold 13 and exhaust pipe 14), an ECU 15, and an exhaust gas purification catalyst 10.
- the ECU 15 is an engine control unit that controls the internal combustion engine 12 and the exhaust gas purification device 17.
- the ECU 15 includes a digital computer and other electronic devices as components as in a general control device.
- the ECU 15 is provided with an input port (not shown).
- the ECU 15 is electrically connected to sensors (for example, a pressure sensor 18) installed in each part of the internal combustion engine 12 and the exhaust gas purification device 17. Thereby, information detected by each sensor is transmitted to the ECU 15 as an electrical signal through the input port.
- the ECU 15 is also provided with an output port (not shown).
- the ECU 15 controls the operation of each part of the internal combustion engine 12 and the exhaust gas purification device 17 by transmitting a control signal via the output port.
- FIG. 1 is a diagram schematically illustrating an exhaust gas purifying catalyst 10 according to an embodiment.
- the exhaust gas flow direction is depicted by the arrow direction. That is, the left side in FIG. 1 is the upstream side of the exhaust passage (exhaust pipe 14), and the right side is the downstream side of the exhaust passage.
- the exhaust gas-purifying catalyst 10 includes a base material 1 and a catalyst layer containing a catalytic metal formed on the base material 1.
- the exhaust gas purifying catalyst 10 is characterized by an appropriate arrangement of the catalyst metal based on the exhaust gas flow rate when the internal combustion engine 12 is warmed up. Specifically, it is characterized by having a high-density portion 6 in which a catalyst metal is supported at a high density on the tip portion (tip surface) 1a. Therefore, other configurations are not particularly limited, and can be applied to various internal combustion engines by appropriately selecting a base material, a support, and a catalyst metal, which will be described later, and molding them into a desired shape according to the application.
- the base material 1 constitutes the skeleton of the exhaust gas-purifying catalyst 10.
- a base material what was conventionally used for this kind of use can be suitably employ
- the material of the substrate 1 is preferably heat resistant. Examples of the heat resistant material include ceramics such as cordierite, aluminum titanate, silicon carbide (SiC), and alloys such as stainless steel.
- the shape of the substrate can be, for example, a honeycomb shape, a foam shape, a pellet shape, or the like. As an example, in FIG. 1, a honeycomb base material 1 having a cylindrical outer shape is employed.
- the honeycomb substrate 1 includes a plurality of through holes (cells) 2 regularly arranged in the cylinder axis direction, and a plurality of partition walls (rib walls) 4 partitioning the cells 2.
- the cell 2 is an exhaust gas flow path, and the partition wall 4 is configured so that the exhaust gas can come into contact therewith.
- the external shape of the whole base material 1 may be an elliptic cylinder shape, a polygonal cylinder shape, etc. instead of a cylindrical shape.
- the capacity of the base material 1 (total volume of the base material 1 and overall bulk volume) is usually 0.1 L or more, preferably 0.5 L or more, for example, 5 L or less, preferably 3 L or less, more preferably 2 L or less. There should be.
- the total length of the base material 1 in the exhaust gas flow direction is usually about 10 to 500 mm, for example, about 50 to 300 mm.
- the catalyst layer is formed on the substrate 1.
- a catalyst layer having a predetermined property for example, length or thickness
- the catalyst layer includes a catalyst metal that functions as an oxidation and / or reduction catalyst, and a carrier that supports the catalyst metal.
- the exhaust gas supplied to the exhaust gas purifying catalyst is in contact with the catalyst layer while flowing in the cell 2 of the base material 1 so that harmful components are purified.
- HC and CO contained in the exhaust gas are oxidized by the catalytic function of the catalyst layer and converted (purified) into water (H 2 O), carbon dioxide (CO 2 ), and the like.
- NO x is reduced by the catalytic function of the catalyst layer and converted (purified) into nitrogen (N 2 ).
- metal species that can function as various oxidation catalysts and reduction catalysts can be employed. Typical examples include rhodium (Rh), palladium (Pd), and platinum (Pt), which are platinum group noble metals. Alternatively, ruthenium (Ru), osmium (Os), iridium (Ir), silver (Ag), gold (Au), or the like may be used. Moreover, you may use what alloyed 2 or more types of metal among these. Furthermore, other metal species such as alkali metals, alkaline earth metals, and transition metals may be used. Among these, it is preferable to use a combination of two or more metal species as the catalyst metal.
- the catalyst metal is preferably used as fine particles having a sufficiently small particle diameter.
- the average particle size of the catalyst metal particles is usually about 1 to 15 nm, preferably 10 nm or less, 7 nm or less, and further 5 nm or less.
- an inorganic compound conventionally used in this type of exhaust gas purifying catalyst can be appropriately employed.
- a porous carrier having a relatively large specific surface area here, the specific surface area measured by the BET method; hereinafter the same
- Preferable examples include alumina (Al 2 O 3 ), ceria (CeO 2 ), zirconia (ZrO 2 ), silica (SiO 2 ), titania (TiO 2 ), and solid solutions thereof (for example, ceria-zirconia composite oxide ( CZ composite oxide)), or a combination thereof.
- Carrier particles may in view of heat resistance and structural stability, a specific surface area of approximately 50 ⁇ 500m 2 / g, for example, is 200 ⁇ 400m 2 / g.
- the average particle size of the carrier particles is typically 1 to 500 nm or less, for example, 10 to 200 nm or less.
- FIG. 2 is an end cross-sectional view schematically showing a front end (front end surface) 1a of the cylindrical exhaust gas purification catalyst 10 shown in FIG.
- the tip 1a is a cross section orthogonal to the exhaust gas flow direction of the exhaust gas purifying catalyst 10.
- the front end portion 1a is a portion located on the most upstream side of the exhaust passage when the exhaust gas purifying catalyst 10 is disposed in the exhaust passage.
- tip part 1a ie, the cross section of the base material 1, has a substantially circular shape.
- a catalyst layer is formed on the surface of the partition wall 4 at the tip 1 a of the exhaust gas purifying catalyst 10.
- a high density portion 6 is formed in the catalyst layer of the tip portion 1a.
- the high density portion 6 is formed at a position not in contact with the outer periphery of the distal end portion 1a (away from the outer periphery).
- a catalyst metal is supported on the high density portion 6 at a relatively high density.
- the high density portion 6 is a portion having a relatively large exhaust gas flow rate when the internal combustion engine 12 is warmed up.
- the high-density portion 6 is formed in a circular shape that is slightly smaller than the circular shape of the distal end portion 1a.
- the shape of the high-density portion 6 is not limited to a circular shape, and may be, for example, a half-moon shape, an elliptical shape, an oval shape, or a polygonal shape. Further, for example, the shapes of the tip portion 1a and the high-density portion 6 may be the same or different.
- a low density portion 8 is formed in a portion of the catalyst layer closer to the outer periphery than the high density portion 6.
- the low density portion 8 carries the catalyst metal at a lower density than the high density portion 6.
- the low density portion 8 is a portion where the exhaust gas flow rate is relatively small when the internal combustion engine 12 is warmed up.
- the catalytic metal can be effectively utilized by reducing the catalytic metal density at the portion where the exhaust gas flow rate is small.
- the low density portion 8 is formed on the outer peripheral portion of the high density portion 6. As described above, the portion near the outer periphery of the exhaust gas purifying catalyst 10 is easily radiated, and the temperature tends to be lower than that of the central portion.
- the low density portion 8 may contain a catalyst metal at a lower density than the high density portion 6 as in the present embodiment, or may not contain a catalyst metal.
- the content (supported amount) of the catalyst metal in the high-density portion 6 is not particularly limited, but is, for example, approximately 1 g or more per unit volume (1 liter) of the honeycomb substrate 1, typically 2 g or more, for example, 5 g or more. Good. Further, the ratio of the catalyst metal density (average density) between the high density portion 6 and the low density portion 8 is preferably substantially equal to or higher than the ratio of the gas amount when the internal combustion engine 12 is warmed up. As an example, the catalyst metal density (average density) of the high density portion 6 is approximately 1.5 times or more, typically 1.7 times or more, preferably 2 times or more, for example, 3 times that of the low density portion 8. It is good that it is more than twice, especially 3.3 times or more. By setting it as the above range, the exhaust gas purification performance can be improved more particularly when the internal combustion engine 12 is warmed up.
- the content of the catalyst metal in the high-density portion 6 is not too much.
- per unit volume (1 liter) of the honeycomb substrate 1 It may be 50 g or less, typically 30 g or less, for example, 10 g or less.
- the catalyst metal density (average density) of the high density portion 6 is approximately 10 times or less, typically 8 times or less, preferably 7 times or less, for example, 6.7 times or less, with respect to the low density portion 8. There should be. By setting it as the said range, the growth (sintering) and alloying of a catalyst metal particle can be suppressed, and a desired catalyst activity can be obtained stably.
- the catalyst metal density of the high-density portion 6 may be substantially uniform at the tip portion 1a.
- it may be formed in a gradation so that the catalyst metal density gradually changes according to the exhaust gas flow rate or the like. Good.
- the catalyst metal density may be varied stepwise. For example, you may form the high density part 6 from which a catalyst metal density differs in steps so that the density of a catalyst metal may become high, so that the center of the high density part 6 is approached.
- the size and arrangement of the high-density portion 6 are determined based on the distribution of the exhaust gas flow rate when the internal combustion engine 12 is warmed up. Therefore, the size of the high-density portion 6 is not particularly limited, but is a cross section orthogonal to the exhaust gas flow direction of the exhaust gas purification catalyst 10 from the viewpoint of exhibiting the effect of the present invention (the effect of improving warm-up property) at a high level.
- the area ratio of the high-density portion 6 is approximately 9% or more, typically 25% or more, for example, 36% or more, preferably 49% or more.
- the density section 6 the inner portion of the tip portion 1a is formed, the outer diameter of the distal end portion 1a of the substrate 1 (diameter of the circumscribed circle) is taken as D O, high density section 6
- the diameter D i is 30% or more of D 2 O , typically 50% or more, for example 60% or more, preferably 70% or more.
- the area ratio of the high-density portion 6 in the distal end portion 1a is approximately 90% or less, typically 81% or less, preferably 64% or less, for example 56% or less.
- the diameter D i of the high-density portion 6 is typically 95% or less of D 2 O , typically Is 90% or less, preferably 80% or less, for example 75% or less.
- the arrangement position of the high-density portion 6 in the tip portion 1a is determined mainly by the positional relationship between the internal combustion engine 12 and the exhaust gas purification catalyst 10.
- the internal combustion engine 12 and the exhaust gas purification catalyst 10 are arranged in a substantially straight line and communicated with each other via a straight exhaust passage, as shown in FIG. It is preferable to provide the high density portion 6 concentrically with the tip portion 1a so that the circular center of the high density portion 6 and the center of the high density portion 6 overlap each other.
- the internal combustion engine 12 and the exhaust gas purification catalyst 10 are communicated with each other through an exhaust passage having a “bend” (having a bent portion) such as an L shape or an S shape, or having an inclined portion.
- the circular center of the high-density part 6 When it exists, it is good for the circular center of the high-density part 6 to be eccentric with respect to the circular center of the front-end
- the circular center of the high-density portion 6 when the outer diameter D O of the substrate 1 is 100%, the circular center of the high-density portion 6 is 5% or more linearly from the circular center of the tip portion 1a, for example, 10 to 30%. It is in a position separated by a certain distance.
- FIG. 6 shows the results of measurement of the exhaust gas flow rate at the time of starting the engine by arranging the cylindrical exhaust gas purification catalyst 10A on a vehicle having an exhaust pipe with a bent pipe.
- the darker the part the greater the exhaust gas flow rate at engine start.
- FIG. 6 shows that when the exhaust gas purifying catalyst 10A is arranged in a bent exhaust passage, the exhaust gas flow rate increases at a position deviated from the center of the tip.
- the arrangement of the high-density portions 6 as shown in FIGS. 7 and 8 can be suitably employed.
- a circular high-density portion 6B is formed at a portion on the right side of the center of the cylindrical base material 1B where the exhaust gas flow rate is large.
- the circular center of the high-density portion 6 is located at a distance of about 20% from the circular center of the tip portion 1a.
- the low density part 8B is formed in the site
- a half-moon shaped high density portion 6C is formed in the right half where the exhaust gas flow rate is large at the tip of the cylindrical substrate 1C.
- the half-moon shaped low-density part 8C is formed in the left half where the exhaust gas flow rate is relatively small.
- FIG. 3 is a cross-sectional view showing the configuration of the surface portion of the base material 30 of the exhaust gas purifying catalyst 100.
- the exhaust gas flow direction is drawn in the direction of the arrow. That is, the left side in FIG. 3 is the upstream side of the exhaust passage (exhaust pipe 14), and the right side is the downstream side of the exhaust passage.
- the two-layered catalyst layer 20 is formed on the surface of the rib wall 34 of the substrate 30.
- the catalyst layer 20 includes a lower layer 22 formed on the surface of the substrate 30 and an upper layer 21 formed on the lower layer 22.
- the lower layer 22 is formed to have the same length as the entire length Lw of the base material 30 in the exhaust gas flow direction so as to cover the surface of the base material 30.
- the upper layer 21 constitutes a surface layer portion (uppermost layer) of the catalyst layer 20.
- the upper layer 21 is divided into a front portion 24 disposed on the upstream side in the exhaust gas flow direction and a rear portion 26 disposed on the downstream side in the exhaust gas flow direction.
- the front portion 24 includes a front end portion 24a located on the upstream side in the exhaust gas flow direction.
- the front part 24 and the rear part 26 are each formed shorter than the full length of the base material 30 in the exhaust gas flow direction.
- the sum of the length Lf of the front portion 24 and the length of the rear portion 26 is formed to be substantially the same as the entire length Lw of the base material 30.
- the kind of the carrier and the catalyst metal supported on the carrier are made.
- kinds, content ratios and the like can be made different from each other.
- the arrangement of the catalyst metal can be appropriately adjusted with reference to the configuration of a conventional exhaust gas purifying catalyst.
- the lower layer 22 includes Pd and / or Pt
- the upper layer 21 (for example, the rear portion 26) includes Rh.
- a high density portion 24 b is formed in a part of the front portion 24 constituting the upper layer 21. That is, the carrier of the front part 24 is a catalyst metal carrier carried on the high density part 24b at a high density.
- the portion other than the high density portion 24b may not include the catalyst metal, but it is more preferable that it includes the catalyst metal.
- Pd is included in the high density portion 24b
- any portion of the front portion 24 other than the high density portion 24b includes one or more of Pd, Rh, and Pt. These metals may be alloyed.
- portions other than the high density portion 24b of the front portion 24 include Pd, Rh, or an alloy of these metals.
- the high-density portion 24b includes a catalyst metal other than Pd, Rh, and Pt, it is preferable that the same portion of the front portion 24 other than the high-density portion 24b or a metal alloy thereof is included.
- the average thickness of the front portion 24 (the length in the stacking direction of the catalyst layer 20) is usually about 10 to 200 ⁇ m, preferably about 30 to 100 ⁇ m.
- the average thickness of the front portion 24 may be the same as or different from that of the rear portion 26.
- the length Lf of the front portion 24 in the exhaust gas flow direction is not particularly limited, but is usually 1 to 500 mm, for example, about 5 to 150 mm.
- the length Lf of the front portion 24 when the total length Lw of the base material 30 (exhaust gas purification catalyst 100) is 100% is approximately 10% or more, typically 20% or more, for example, 24% or more from the front end portion 24a. It is good to be.
- the length Lf of the front portion 24 is usually less than 100% of the total length Lw of the substrate 30, typically 60% or less, for example, 50% or less.
- a high density portion 24 b is formed inside the front portion 24.
- the catalyst metal of the high density portion 24 b is supported on the carrier of the front portion 24.
- the part of the high density part 24b and the part in which the high density part 24b is not formed are maintained at substantially the same average thickness (for example, within a range of about ⁇ 5%). Therefore, for example, the pressure loss can be reduced compared to the case where the high density portion 24 b is formed on the surface of the front portion 24.
- the high density portion 24b is formed on the outermost surface of the front portion 24, and is disposed so as to be in better contact with the exhaust gas.
- the length Lh of the high-density portion 24b in the exhaust gas flow direction is not particularly limited because it may vary depending on the type and size of the base material 30.
- the length Lh of the high-density portion 24b is 10% or more from the tip portion 24a, typically 20% or more. For example, it may be 24% or more.
- the length Lh of the high-density portion 24b is typically shorter than the front portion 24, and is generally 90% or less, preferably 50% or less, for example 43% or less, of the total length Lw of the base material 30. Thereby, it can prevent that a catalyst metal moves from the high-density part 24b, and can suppress the fall of the catalyst activity by sintering or alloying.
- the length Lh of the high-density portion 24b is 10 to 95%, typically 50 to 90%, for example 70 to 80%, of the total length Lf of the front portion 24.
- the high density portion 24b is 10 to 95%, typically 50 to 90%, for example 70 to 80%, of the total length Lf of the front portion 24.
- a large amount of catalyst metal is contained in a region near the tip 24a in the exhaust gas flow direction.
- the range from the front end 24a to 50% of the total length Lw of the base material is defined as the upstream region, and the downstream side thereafter (that is, the range from the rear end portion (terminal portion) 26a to 50% of the total length Lw of the base material. )
- the total amount of catalyst metal contained in the upstream region is preferably sufficiently larger than that in the downstream region. For example, approximately 70% or more, preferably 80% or more, for example, 90% or more of the total amount of catalytic metal contained in the exhaust gas purifying catalyst 100 may be disposed in the upstream region.
- the downstream region may not contain the catalytic metal, but it is more preferred that it is contained. For example, approximately 5% or more, preferably 10% or more, for example, 20% or more of the total amount of catalytic metal contained in the exhaust gas purification catalyst 100 may be disposed in the downstream region.
- the catalyst metal By including the catalyst metal also in the downstream region, it is possible to better reduce the emission during high load operation with a large exhaust gas flow rate (for example, during high-speed driving of an automobile).
- the upper layer 21 including the front portion 24 and the rear portion 26 is formed on the surface of the lower layer 22, and the catalyst layer 20 has two upper and lower portions over the entire length of the base material 30 in the exhaust gas flow direction.
- the upper layer 21 and the lower layer 22 may be partially laminated.
- only the front part 24 may be laminated on the lower layer 22.
- the lower layer 22 may not be provided.
- the high density portion 24b is formed inside the front portion 24, but the present invention is not limited to this.
- the high density portion 24 b may be formed on the surface of the front portion 24.
- the high-density part 24b may be formed in the part including the front-end
- a high density portion 24 b may be formed across the front portion 24 and the rear portion 26.
- the front portion 24 is formed with a length of 30% of the total length from the front end portion 24a of the exhaust gas purification catalyst 100
- the rear portion is formed with a length of 90% of the total length from the rear end portion 26a of the exhaust gas purification catalyst 100. Assume that the portion 26 is formed.
- the manufacturing method of the catalyst for exhaust gas purification disclosed here is not specifically limited, For example, the following processes: (1) Prepare a base material for forming an exhaust gas purification catalyst; (2) disposing the base material in an exhaust passage connected to the internal combustion engine and confirming an exhaust gas flow rate distribution during fast idle operation (warming up) from start of the internal combustion engine to completion of warming up; (3) forming a catalyst layer on the substrate so as to carry a noble metal at a high density in a portion having a relatively large exhaust gas flow rate based on the obtained exhaust gas flow rate distribution; It can manufacture by the manufacturing method including this.
- the substrate and the noble metal (catalyst metal), those described above can be used as appropriate.
- confirmation of the distribution of the exhaust gas flow rate and loading of the noble metal can be performed by the same method as before.
- the step (3) includes (3-1) forming the lower layer 22 on the surface of the base material.
- a slurry for forming a lower layer containing a desired catalytic metal component and a carrier powder is prepared. This slurry is coated on the surface of the honeycomb substrate 30 using a conventionally known wash coating method or the like (step 3-1).
- a slurry for forming a front part containing a desired catalyst metal component for example, the same metal component as the catalyst metal of the lower layer 22
- a desired carrier powder is prepared. This slurry is laminated and coated on the surface of the lower layer 22 from the front end portion 24a side using a wash coat method or the like (step 3-2).
- a slurry for forming a rear part containing a desired catalyst metal component for example, a metal component different from the catalyst metal of the lower layer 22
- a desired carrier powder is prepared.
- This slurry is laminated and coated on the surface of the lower layer 22 from the side of the rear end portion 26a using a wash coat method or the like (step 3-3).
- the slurry for forming each of the above-mentioned layers may appropriately contain arbitrary additive components such as conventionally known oxygen storage / release materials, binders and additives in addition to the catalyst metal and the carrier.
- oxygen storage / release material for example, a CZ composite oxide can be used.
- binder for example, alumina sol or silica sol can be used.
- the formation range of the high density portion 26b is set based on the distribution of the exhaust gas flow rate in (2) above. Specifically, the formation range of the high density portion 24b is set in a portion where the exhaust gas flow rate is large during the first idle operation.
- the formation range of the high density portion 24b is set by, for example, the area ratio of the high density portion 24b occupying the front end portion 24a and the length Lh of the high density portion 24b in the exhaust gas flow direction (step 3-4).
- the density ratio between the high-density portion 26b and other portions is determined based on the distribution of the exhaust gas flow rate.
- a slurry containing a desired catalyst metal component (for example, the same metal component as the catalyst metal of the front portion 24) at a desired concentration is prepared.
- This slurry is applied (supplied) to the set range including the tip 24a using a conventionally known impregnation support method or the like.
- the catalyst metal is locally supported at high density on the carrier (step 3-5).
- the obtained composite is heat-treated at a predetermined temperature and time (step 3-6).
- the heat treatment conditions are not particularly limited because they can vary depending on the shape and size of the substrate or carrier.
- the catalyst layer 20 can be formed by drying at about 80 to 300 ° C. for about 1 to 10 hours, then raising the temperature and firing at about 400 to 1000 ° C. for about 2 to 4 hours.
- the exhaust gas-purifying catalyst 100 including the laminated structure type catalyst layer 20 shown in FIG. 3 can be obtained.
- the exhaust gas purifying catalyst according to this test example includes a cylindrical honeycomb base material and a catalyst layer provided on the base material.
- the catalyst layer has an upper and lower two-layer structure as viewed from the substrate. In the exhaust gas flow direction, the lower layer is formed with the same length as the entire length of the substrate.
- the upper layer constituting the uppermost layer portion of the catalyst layer is composed of a front portion formed in a portion corresponding to 30% of the total length of the base material from the front end portion in the exhaust gas flow direction, and a total length of the base material from the rear end portion in the exhaust gas flow direction.
- the rear portion is formed in a portion corresponding to 70%.
- a high density portion is formed in a substantially cylindrical shape with a predetermined length from the front end portion (upstream end surface) in the exhaust gas flow direction.
- a high density portion satisfies the following conditions.
- -It is formed in a circular shape having a diameter D i that is 70% of the outer diameter D O of the honeycomb substrate at the front end in the exhaust gas flow direction (cross section orthogonal to the exhaust gas flow direction).
- -In the exhaust gas flow direction (cylinder axis direction) it is formed in a portion (inside the front portion) of 20% (20 mm) of the total length of the base material from the tip portion.
- the Pd-supported mixed powder and the alumina binder were mixed at a mass ratio of 97: 3, and an appropriate amount of pure water was added to prepare a lower layer forming slurry.
- This slurry was wash-coated from the tip of the substrate to the entire substrate (100% of the total length of the substrate) and dried at 150 ° C. for 1 hour.
- alumina powder and an aqueous palladium nitrate solution were mixed, dried at 120 ° C., and baked at 500 ° C. for 1 hour to obtain a Pd-supported powder having a Pd support ratio of about 1% by mass.
- the Pd-supported powder and the CZ composite oxide powder as a non-supported body were mixed at a mass ratio of 2: 1, and an appropriate amount of pure water was added to prepare a front portion forming slurry. This slurry was wash-coated from the tip of the substrate to a portion corresponding to 30% of the total length of the substrate, and dried at 150 ° C. for about 1 hour.
- the CeO 2 —ZrO 2 composite oxide powder and the rhodium nitrate aqueous solution are mixed, dried at 120 ° C., and calcined at 600 ° C. for 2 hours, whereby the Rh loading rate is about 0.25% by mass.
- a powder was obtained.
- the Rh-supported powder and alumina powder as a non-supported substance were mixed at a mass ratio of 1: 1, and an appropriate amount of pure water was added to prepare a slurry for forming a rear part. This slurry was wash-coated from the rear end of the substrate to a portion corresponding to 70% of the total length of the substrate, and dried at 150 ° C. for about 1 hour.
- Example 1 The configuration of the catalyst layer of Example 1 is summarized below.
- Exhaust gas purifying catalyst of this example at the distal end of the exhaust gas flow direction, except for forming a circular high density portion at the same size as the outer diameter D O of the honeycomb base material is the same as Example 1. That is, the exhaust gas-purifying catalyst was obtained in the same manner as in Example 1 except that a 5 g / L palladium nitrate aqueous solution having a length of 20 mm from the tip was applied to a range of 100% of the outer diameter D O of the substrate. (Comparative example) was produced. The total amount of catalyst metal contained in the exhaust gas purifying catalyst of the comparative example is approximately twice that of Example 1.
- Table 1 summarizes the characteristics of exhaust gas purification catalysts. The symbols in Table 1 correspond to those in FIG. Further, the portion described as “low density portion” in Table 1 indicates a portion which is the front portion and where the high density portion 24b is not formed.
- the “high density part / low density part” means the catalyst metal density at the part where the exhaust gas flow rate is relatively low (low density part) when the internal combustion engine is warmed up and the part where the exhaust gas flow rate is relatively high (high density). Part) with the catalyst metal density.
- the warm-up property of the obtained exhaust gas-purifying catalyst (Comparative Example, Example 1) was evaluated. Specifically, the inlet gas temperature was compared when the purification rate of each harmful component reached 50% from the engine start to the first idle. The inlet gas temperature was measured at a pipe center position 100 mm from the front end surface of the exhaust gas purifying catalyst. The results are shown in FIG.
- Example 1 showed warm-up property equivalent to that of the comparative example, although the amount of catalyst metal used was approximately half that of the comparative example. That is, in the exhaust gas purifying catalyst of Example 1, the amount of catalyst metal used could be reduced (halved) while maintaining excellent warm-up properties.
- Example 2 In the exhaust gas purifying catalyst of this example, the amount of catalyst metal used in the high-density part is set to I.D. 2 times that of Example 1. That, 20 mm from the tip, 70% of the substrate center and the same circle center shaped inner diameter D i, similarly to the Example 1 except that imparted aqueous palladium nitrate solution of 10 g / L, the exhaust gas purifying catalyst Example 2 was prepared. Note that the total amount of catalytic metal contained in the exhaust gas purifying catalyst of Example 2 is substantially the same as in the comparative example. Table 2 below summarizes the characteristics of the exhaust gas purifying catalyst. The symbols and terms in Table 2 are the same as in Table 1 above.
- Example 2 For the obtained exhaust gas purification catalyst (Example 2), the warm-up property was evaluated in the same manner as described above. The results are shown in FIG. As shown in FIG. 5, in Example 2, although the amount of catalyst metal used was the same as that in the comparative example, the entering gas temperature was lower than that in the comparative example. That is, in the exhaust gas purifying catalyst of Example 2, the warming-up property can be improved while keeping the amount of the catalyst metal used as it is by carrying the catalyst metal at a high density by concentrating the catalyst metal on the portion where the exhaust gas flow rate is large.
- Example III (Examples 5 to 8)
- a cylindrical honeycomb substrate made of cordierite having a volume of about 0.6 L and a length of 60 mm was used, and the length of the high-density portion in the exhaust gas flow direction was varied. . That is, in the same manner as in Example 1 except that a 5 g / L palladium nitrate aqueous solution was applied in the range of 24.3 to 42.3% of the total length of the base material in the direction of exhaust gas flow from the front end, Examples 3 to 6) were prepared.
- Table 3 below summarizes the characteristics of the exhaust gas purifying catalyst of each example. The symbols and terms in Table 3 are the same as in Table 1 above.
- Example 3 shows the inlet gas temperature when the HC component reaches the 50% purification rate. As shown in Table 3, when the length of the high-density portion was 50% or less, 40% or less, 30% or less, and particularly 25% or less, the entering gas temperature was lowered and the warm-up property was excellent.
- Base material 1a 24a Front end (starting end) 2 cells (through holes) 4, 34 Bulkhead (rib wall) 6, 6B, 6C, 24b High-density portion 8, 8B, 8C Low-density portion 10, 10A, 10B, 10C, 100 Exhaust gas purification catalyst 20 Catalyst layer 21 Upper layer 22 Lower layer 24 Front portion 26 Rear portion 26a Rear end (termination) Part)
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Abstract
Description
なお、本国際出願は2014年9月10日に出願された日本国特許出願2014-184125号に基づく優先権を主張しており、その出願の全内容は本明細書中に参照として組み入れられている。
即ち、上記高密度部の触媒金属密度を従来と同等にする場合には、同等の暖機性(排ガス浄化用触媒を昇温する性能)を維持したまま、触媒金属の使用量を低減することができる。或いは、従来と等量の触媒金属を高密度部に集中的に担持させる場合には、相対的に暖機性を向上させることができる。例えば、排ガス浄化用触媒が冷えている状態から、上記高密度部を中心にして、触媒(典型的には上流側)の温度を速やかに上昇させることができる。そのため、触媒暖機性が向上して、内燃機関の暖機時に排ガスを一層クリーンな状態で外部へ排出することができる。
なお、ここで「先端部」とは、排ガス浄化用触媒を排気通路(排気管)の所定の位置に配置した状態で排気通路の最も上流側に位置し、略最初に排ガスが接触する部位をいう。
ここで、上記排気通路がストレート状である場合は、上記排ガス浄化用触媒の円形状と同心円状に上記高密度部の円形状が配置されているとよい。
或いは、上記排気通路が屈曲部及び/又は傾斜部を有する場合は、上記排ガス浄化用触媒の円形状の中心に対して上記高密度部の円形状の中心が偏心しているとよい。
ECU15は、内燃機関12と排ガス浄化装置17の制御を行うエンジンコントロールユニットである。ECU15は、一般的な制御装置と同様にデジタルコンピュータおよびその他の電子機器を構成要素として含んでいる。ECU15には、入力ポート(図示せず)が設けられている。ECU15は、内燃機関12や排ガス浄化装置17の各部位に設置されているセンサ(例えば圧力センサ18)と電気的に接続されている。これにより、各々のセンサで検知した情報が上記入力ポートを介して電気信号としてECU15に伝達される。ECU15にはまた、出力ポート(図示せず)が設けられている。ECU15は、出力ポートを介して制御信号を送信することによって、内燃機関12や排ガス浄化装置17の各部位の稼働を制御している。
図1は、一実施形態に係る排ガス浄化用触媒10を模式的に示す図である。この図では、排ガス流動方向を矢印方向で描いている。即ち、図1中の左側が排気通路(排気管14)の上流側であり、右側が排気通路の下流側である。
排ガス浄化用触媒に供給された排ガスは、基材1のセル2内を流動している間に触媒層と接触することで有害成分が浄化される。例えば、排ガスに含まれるHCやCOは触媒層の触媒機能によって酸化され、水(H2O)や二酸化炭素(CO2)などに変換(浄化)される。また、NOxは触媒層の触媒機能によって還元され、窒素(N2)に変換(浄化)される。
低密度部8は、高密度部6の外周部分に形成されている。上述の通り、排ガス浄化用触媒10の外周に近い部分は放熱され易く、中央部分に比べて温度が低くなりがちである。このため、相対的に暖まり易い内側部分(先端部1aの中央側)に高密度部6を設けることで、暖機性を向上する効果がより良く得られる。なお、低密度部8には、本実施形態のように高密度部6よりも低密度で触媒金属を含んでいてもよいし、触媒金属を含んでいなくてもよい。
先端部1aの内側部分に高密度部6が形成されている図2の態様では、基材1の先端部1aの外径(外接円の直径)をDOとしたときに、高密度部6の直径Diが、DOの30%以上、典型的には50%以上、例えば60%以上、好ましくは70%以上であるとよい。上記範囲とすることにより、排ガス浄化機能がより良く働き、特に内燃機関12の暖機時における有害成分のエミッションを高度に抑制することができる。
また他の一例として、内燃機関12と排ガス浄化用触媒10とが、例えばL字形状やS字形状等の「曲げ」のある(屈曲部を有する)あるいは傾斜部を有する排気通路で連通されている場合は、先端部1aの円形状の中心に対して、高密度部6の円形状の中心が偏心しているとよい。例えば、基材1の外径DOを100%としたときに、高密度部6の円形状の中心が、先端部1aの円形状の中心から直線状に5%以上、例えば10~30%程度の距離を隔てた位置にある。
また、例えば図8に示す排ガス浄化用触媒10Cでは、円筒形状の基材1Cの先端部において、排ガス流量の多い右側半分に半月形状の高密度部6Cが形成されている。そして、相対的に排ガス流量の少ない左側半分に半月形状の低密度部8Cが形成されている。
図3に示す形態では、基材30のリブ壁34の表面に、二層構造の触媒層20が形成されている。触媒層20は、基材30の表面に形成された下層22と、下層22上に形成され上層21とを備えている。下層22は、基材30の表面を覆うように、基材30の排ガス流動方向の全長Lwと同じ長さに形成されている。
排ガス流動方向におけるフロント部24の長さLfは特に限定されないが、通常1~500mm、例えば5~150mm程度であるとよい。基材30(排ガス浄化用触媒100)の全長Lwを100%としたときのフロント部24の長さLfは、先端部24aから概ね10%以上、典型的には20%以上、例えば24%以上であるとよい。フロント部24の長さLfは、基材30の全長Lwの通常100%未満、典型的には60%以下、例えば50%以下であるとよい。
また、下流領域には触媒金属を含んでいなくてもよいが、含んでいるとなお好ましい。例えば排ガス浄化用触媒100に含まれる触媒金属の総量の概ね5%以上、好ましくは10%以上、例えば20%以上が下流領域に配置されているとよい。下流領域にも触媒金属を含むことで、排ガス流量の多い高負荷運転時(例えば自動車の高速走行時)のエミッションをより良く低減することができる。
(1)排ガス浄化用触媒形成用の基材を用意すること;
(2)上記基材を内燃機関と連結された排気通路に配置して、上記内燃機関の始動から暖機完了までのファーストアイドル運転時(暖機時)における排ガス流量の分布を確認すること;
(3)上記得られた排ガス流量の分布に基づいて、相対的に排ガス流量の多い部位には貴金属を高密度担持するように、基材上に触媒層を形成すること;
を包含する製造方法によって製造することができる。
また、例えば図3に示すような触媒層20を備えた排ガス浄化用触媒100を製造する場合は、上記(3)の工程が、(3-1)上記基材の表面に、下層22形成用組成物を付与すること;(3-2)下層22の表面に、先端部24a側からフロント部24形成用組成物を付与すること;(3-3)下層22の表面に、後端部26a側からリア部26形成用組成物を付与すること;(3-4)先端部24aにおいて、高密度部26bの形成範囲を設定すること;(3-5)上記設定した範囲に、先端部24a側から高密度部26b形成用組成物を付与すること;(3-6)熱処理により触媒層20を形成すること;が包含される。
次いで、所望の触媒金属成分(例えば下層22の触媒金属と同種の金属成分)と所望の担体粉末とを含むフロント部形成用スラリーを調製する。このスラリーを、先端部24aの側からウォッシュコート法等を用いて下層22の表面に積層コートする(工程3-2)。
次いで、所望の触媒金属成分(例えば下層22の触媒金属と異なる金属成分)と所望の担体粉末とを含むリア部形成用スラリーを調製する。このスラリーを、後端部26aの側からウォッシュコート法等を用いて下層22の表面に積層コートする(工程3-3)。
次いで、所望の触媒金属成分(例えばフロント部24の触媒金属と同種の金属成分)を所望の濃度で含むスラリーを調製する。このスラリーを、従来公知の含浸担持法等を用いて、先端部24aを含む上記設定した範囲に付与(供給)する。これにより、高密度部24bでは、担体に触媒金属が局所的に高密度担持される(工程3-5)。
以上により、例えば図3に示す積層構造タイプの触媒層20を備えた排ガス浄化用触媒100を得ることができる。
(例1)
本試験例に係る排ガス浄化用触媒は、円筒形状のハニカム基材と、該基材上に設けられた触媒層とを備えている。触媒層は基材からみて上下二層構造である。排ガス流動方向において、下層は、基材の全長と同じ長さで形成されている。触媒層の最上層部分を構成する上層は、排ガス流動方向の先端部から基材の全長の30%にあたる部分に形成されているフロント部と、排ガス流動方向の後端部から基材の全長の70%にあたる部分に形成されているリア部とで構成されている。この排ガス浄化用触媒の触媒層には、排ガス流動方向の先端部(上流側の端面)から所定の長さで略円筒形状に高密度部が形成されている。かかる高密度部は、次の条件を満たしている。
・排ガス流動方向の先端部(排ガス流動方向と直交する断面)において、ハニカム基材の外径DOの70%の直径Diを有する円形状に形成されている。
・排ガス流動方向(筒軸方向)において、先端部から基材全長の20%(20mm)の部分(フロント部の内部)に形成されている。
先ず、基材として、容積(セル通路の容積も含めた全体の嵩容積をいう)が凡そ0.9L、長さが100mmの円筒形状のハニカム基材(コージェライト製)を準備した。
次に、アルミナ粉末とCeO2-ZrO2複合酸化物粉末と硝酸パラジウム水溶液とを混合し、250℃で8時間乾燥した後、500℃で4時間焼成した。これにより、Pdを担持した状態のアルミナ粉末とCZ複合酸化物粉末とがAl2O3:CZ=3:1の質量比で混合されたPd担持混合粉末を得た。かかるPd担持混合粉末とアルミナバインダーとを質量比97:3で混合し、適量の純水を加えて下層形成用スラリーを調製した。このスラリーを基材の先端部から基材全体(基材全長の100%)にウォッシュコートし、150℃で1時間乾燥した。
その後、この複合体を500℃で1時間焼成することによって、基材上に上述のような構成の触媒層が形成された排ガス浄化用触媒(例1)を得た。
上層(フロント部):アルミナ(Pd担持)、CZ複合酸化物
フロント部のうち、高密度部にはPdがその他の部位より高密度に含まれている。
(リア部) :CZ複合酸化物(Rh担持)、アルミナ
下層 :アルミナ(Pd担持)、CZ複合酸化物(Pd担持)
本例の排ガス浄化用触媒は、排ガス流動方向の先端部において、ハニカム基材の外径DOと同じ大きさで円形状の高密度部を形成したこと以外は例1と同様である。即ち、基材の外径DOの100%の範囲に、当該先端部から20mmの長さで、5g/Lの硝酸パラジウム水溶液を付与したこと以外は例1と同様にして、排ガス浄化用触媒(比較例)を作製した。なお、比較例の排ガス浄化用触媒に含まれる触媒金属の総量は、例1の凡そ2倍である。
上記得られた排ガス浄化用触媒(比較例、例1)の暖機性を評価した。具体的には、エンジン始動からファーストアイドルで、各有害成分の浄化率50%に到達したときの入りガス温度を比較した。なお、入りガス温度は、排ガス浄化用触媒の先端面から100mmの配管中心位置で測定した。結果を図4に示す。
(例2)
本例の排ガス浄化用触媒では、高密度部の触媒金属使用量をI.の例1の2倍にした。即ち、先端部から20mm、基材中心と同一円心状の内径Diの70%の範囲に、10g/Lの硝酸パラジウム水溶液を付与したこと以外は上記例1と同様に、排ガス浄化用触媒(例2)を作製した。なお、例2の排ガス浄化用触媒に含まれる触媒金属の総量は、比較例とほぼ同じである。下表2に、排ガス浄化用触媒の特徴を纏める。表2中の符号や用語は、上記表1と同様である。
(例5~8)
本例の排ガス浄化用触媒では、容積が凡そ0.6L、長さが60mmの円筒形状のハニカム基材(コージェライト製)を使用し、排ガス流動方向における高密度部の長さを異ならせた。即ち、先端部からの排ガス流動方向に基材全長の24.3~42.3%の範囲に5g/Lの硝酸パラジウム水溶液を付与したこと以外は上記例1と同様に、排ガス浄化用触媒(例3~6)を作製した。下表3に、各例の排ガス浄化用触媒の特徴を纏める。表3中の符号や用語は、上記表1と同様である。
1a、24a 先端部(始端部)
2 セル(貫通孔)
4、34 隔壁(リブ壁)
6、6B、6C、24b 高密度部
8、8B、8C 低密度部
10、10A、10B、10C、100 排ガス浄化用触媒
20 触媒層
21 上層
22 下層
24 フロント部
26 リア部
26a 後端部(終端部)
Claims (9)
- 内燃機関と連結された排気通路に配置され、該内燃機関から排出される排ガスの浄化を行う排ガス浄化用触媒であって、
基材と、該基材上に形成された触媒層とを備え、
前記触媒層は、酸化及び/又は還元触媒として機能する貴金属と、該貴金属を担持する担体とを含み、
前記排ガス浄化用触媒が前記排気通路に配置された際、排ガス流動方向の上流側に位置する先端部には、前記内燃機関の暖機時に相対的に排ガスの流量が多い部位と、相対的に排ガスの流量が少ない部位とがあり、
前記相対的に排ガスの流量が多い部位の触媒層には、前記相対的に排ガスの流量が少ない部位の触媒層と比べて前記貴金属が高密度に担持された高密度部が設けられており、
前記高密度部は、前記先端部から前記排ガス流動方向に前記排ガス浄化用触媒の全長よりも短く形成されている、排ガス浄化用触媒。 - 前記高密度部における前記貴金属の密度が、前記相対的に排ガス流量が少ない部位における前記貴金属の密度の1.5倍以上である、請求項1に記載の排ガス浄化用触媒。
- 前記触媒層は前記基材からみて相互に構成の異なる2層以上の積層構造を有しており、
該積層構造の最上層部分に前記高密度部が形成されている、請求項1又は2に記載の排ガス浄化用触媒。 - 前記排ガス流動方向において、前記排ガス浄化用触媒の全長を100%としたときに、前記高密度部は前記先端部から10%以上50%以下の長さで形成されている、請求項1~3のいずれか一項に記載の排ガス浄化用触媒。
- 前記排ガス浄化用触媒の前記排ガス流動方向と直交する断面の総面積を100%としたときに、前記高密度部は9%以上64%以下の面積に形成されている、請求項1~4のいずれか一項に記載の排ガス浄化用触媒。
- 前記高密度部は、前記排ガス浄化用触媒の前記断面の外周に接しないように、前記外周から離れた位置に形成されている、請求項5に記載の排ガス浄化用触媒。
- 前記排ガス浄化用触媒の前記排ガス流動方向と直交する断面が円形状であって、前記高密度部の前記断面が前記排ガス浄化用触媒の円形状よりも直径の小さい円形状に形成されている、請求項1~6のいずれか一項に記載の排ガス浄化用触媒。
- 前記排気通路は、前記内燃機関と連結された部位から前記排ガス浄化用触媒の配置された部位までの間がストレート状であり、
前記排ガス浄化用触媒の円形状と同心円状に前記高密度部の円形状が配置されている、請求項7に記載の排ガス浄化用触媒。 - 前記排気通路は、前記内燃機関と連結された部位から前記排ガス浄化用触媒の配置された部位までの間に屈曲部及び/又は傾斜部を有し、
前記排ガス浄化用触媒の円形状の中心に対して前記高密度部の円形状の中心が偏心している、請求項7に記載の排ガス浄化用触媒。
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