(19) Japan Patent Office (JP)
`
`(12) JAPANESE UNEXAMINED PATENT
`APPLICATION PUBLICATION (A)
`
`(11) Patent Application
`Disclosure No.
`2002-159859
`(P2002-159859A)
`(43) Publication Date June, 04 2002 (Heisei 14)
`Theme Code (Reference)
`A 3G090
`3G091
`4D048
`4G069
`
`(51) Int. Cl.7
`B 01 J 27/185
`B 01 D 53/94
`B 01 J 32/00
`35/04
`
`Ident. Code
`
`FI
`B 01 J
`
`301
`
`27/185
`32/00
`35/04
`
`301E
`301P
`331Z
`
`(22) Date of Filing
`
`November 22, 2000
`(Heisei 12)
`
`(72) Inventor
`
`Examination Request: Not Yet Total No. of Claims: 13 OL (Total 10 pages) continued on last page
`(21) Application No.
`JPA 2000-356347
`(71) Applicant
`000000158
`(P2000-356347)#
`IBIDEN CO., LTD.
`Kanda-Cho 2-1,
`Ogaki, Gifu#
`Noriyuki Taoka
`1-1 Kitagata, Ibigawa-cho,
`Ibi-gun, Gifu-Ken
`c/o IBIDEN CO., LTD.
`Yutaka Yoshida
`1-1 Kitagata, Ibigawa-cho,
`Ibi-gun, Gifu-Ken
`c/o IBIDEN CO., LTD.
`100068755
`Attorney
`Hiroshisen Onda
`
`(72) Inventor
`
`(74) Agent
`
`(Continued on Final Page)
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`(54) Title of Invention
`A Catalyst for Exhaust Gas Purification
`
`(Revised)
`(57) Abstract
`[Problem] To provide an easily manufactured
`catalyst for exhaust gas purification that removes
`hydrocarbons contained in exhaust gas, carbon
`monoxide and nitrogen oxide black sooty
`particulate.
`[Resolution Means] A catalyst for exhaust gas
`purification wherein a ceramic carrier is
`configured by ceramic particles 20 composed of
`zirconium phosphate, and the ceramic particles
`constituting a ceramic carrier is made to function
`as a catalyst for gas purification. At least a portion
`of the cations contain an alkali metal or alkaline
`earth metal catalyst 16. Also, a catalyst coating
`layer 22 is carried in the ceramic particles 20.
`This is composed of alumina particles 23 by
`ceramic oxide and zirconia particles 24. Also,
`other metal catalysts and the like are used in
`combination.
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`Scope of Claims !
`What is claimed is:
`[Claim 1] A catalyst for exhaust gas purification that removes hydrocarbons contained in exhaust gas,
`carbon monoxide and nitrogen oxide black sooty particulate, comprising a catalyst for exhaust gas
`purification, wherein at least a portion of cations of ceramic particles constituting a ceramic carrier
`composed of zirconium phosphate is substituted with an alkali metal or an alkaline earth metal.
`[Claim 2] A catalyst for exhaust gas purification that removes hydrocarbons contained in exhaust gas,
`carbon monoxide, and nitrogen oxide black sooty particulate, comprising a catalyst for exhaust gas
`purification, wherein an alkali metal or alkaline earth metal catalyst is contained in ceramic particles
`constituting a ceramic carrier composed of zirconium phosphate.
`[Claim 3] The catalyst for exhaust gas purification according to claim 1 or 2, wherein the ceramic
`carrier is composed of NZP having a three-dimensional network structure.
`[Claim 4] The catalyst for exhaust gas purification according to any one of claims 1 to 3, wherein a
`catalyst coating layer, which is composed of ceramic oxide particles that carry a precious metals
`catalyst, is carried in the ceramic particles.
`[Claim 5] The catalyst for exhaust gas purification according to any one of claims 1 to 4, wherein a
`catalyst coating layer, which is composed of particles of a ceramic oxide that carries an alkali metal or
`alkaline earth metal catalyst, is carried in the ceramic particles.
`[Claim 6] The catalyst for exhaust gas purification according to claim 5, wherein an alkali metal and
`alkaline earth metal catalyst constituting the catalyst coating layer, contains at least one element
`selected from lithium, sodium, potassium, and barium.
`[Claim 7] The catalyst for exhaust gas purification according to any one of claims 4 to 6, wherein a
`ceramic oxide constituting the catalyst coating layer, contains at least one element selected from
`alumina, zirconia, titania and silica.
`[Claim 8] The catalyst for exhaust gas purification according to any one of claims 5 to 7, wherein a
`catalyst constituting a catalyst contained in the ceramic particles and the catalyst coating layer are the
`same material.
`[Claim 9] The catalyst for exhaust gas purification according to any one of claims 4 to 8, wherein a
`rare earth metal co-catalyst is carried in ceramic oxide particles of the catalyst coating layer.
`[Claim 10] The catalyst for exhaust gas purification according to claim 9, wherein the co-catalyst
`contains at least one simple substance or compound selected from cerium or lanthanum.
`[Claim 11] The catalyst for exhaust gas purification according to any one of claims 1 to 10, wherein
`the ceramic carrier is a honeycomb structure having of a plurality of through holes divided by cell
`walls.
`[Claim 12] The catalyst for exhaust gas purification according to claim 11, wherein both ends of the
`ceramic carrier are alternately sealed in a checkered pattern by a sealing body.
`[Claim 13] A catalyst for exhaust gas purification for removing hydrocarbons contained in exhaust
`gas, carbon monoxide, and nitrogen oxide black sooty particulate comprising:
`ceramic particles that are substituted by an alkali metal or alkaline earth metal, and constitute a
`ceramic carrier of a honeycomb structure composed of zirconium, and
`a catalyst coating layer carried by the ceramic particles, and contains alumina particles that carry
`an alkali metal catalyst, an alkaline earth metal catalyst, a previous metal catalyst and a rare earth
`metal co-catalyst.
`[Detailed Description of the Invention]
`[0001]
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`[Field] The present invention relates to a catalyst for exhaust gas purification that removes
`hydrocarbons contained in an exhaust gas, carbon monoxide, and nitrogen oxide black sooty
`particulates.
`[0002]
`[Related Art] Conventionally, as a catalyst for exhaust gas purification of this type, for example, a
`catalyst carrying filter 100 for purifying exhaust gas of a diesel engine is known. As illustrated in
`Fig. 4, the catalyst carrying filter 100 is connected to the exhaust side of a diesel engine, each cell
`101 that becomes an exhaust gas passageway is formed in a honeycomb shape, and the cells 101
`are alternately sealed. Then, the catalyst carrying filter 100 collects particulates (PM: black sooty
`particulate) deposited in the interior, and purifies exhaust gas through oxidation of PM, HC and
`CO, and by reducing NOx.
`[0003] For formation materials of the catalyst carrying filter 100, there are porous silicon carbide
`sintered bodies having excellent heat resistance and thermal conductivity. Then, as shown in Fig. 5,
`an alumina coating layer (catalyst coating layer) 103 is formed on the surface of the silicon carbide
`particles constituting a ceramic carrier 102. The alumina coating layer 103 is formed by drying and
`firing after the slurry containing the alumina particles is impregnated in the ceramic carrier 102.
`Further, in the alumina coating layer, a catalyst 104 composed of precious metals of Pt, Pd, Rh, and
`the like is carried. The catalyst 104 is carried in the alumina coating layer 103 through drying and
`firing after a palladium nitrate aqueous solution and the like is impregnated in an alumina coated
`ceramic carrier 102.
`[0004]
`[Problem to be Solved by the Invention] However, in the conventional catalyst for exhaust gas
`purification, in order to function as a catalyst in the ceramic carrier 102, the precious metal catalyst
`104 must be carried in the silicon carbide particle 105. Therefore, it takes time for a catalyst to be
`carried and the manufacturing efficiency is decreasing and the cost is increasing.
`[0005] The present invention was made in view of the above-mentioned problems and the purpose
`is to occlude more NOx even without specially carrying the catalyst in a ceramic carrier, rather than
`when being carried by having a NOx occlusion component in the carrier itself. In other words, it
`offers a catalyst for exhaust gas purification that can have the function of a catalyst for exhaust gas
`purification in the ceramic particles themselves constituting the ceramic carrier.
`[0006]
`[Means for Solving the Problem] To solve the problems above, with the invention according to
`claim 1, the catalyst for exhaust gas purification that removes hydrocarbons contained in the
`exhaust gas, carbon monoxide, and nitrogen oxide black sooty particulates is characterized in that
`at least a portion of the cations of the ceramic particles constituting the ceramic carrier composed
`of zirconium phosphate is substituted with an alkali metal or alkaline earth metal.
`[0007] With the invention according to claim 2, the catalyst for exhaust gas purification that
`removes hydrocarbons contained in the exhaust gas, carbon monoxide, and nitrogen oxide black
`sooty particulates is characterized by including an alkali metal or an alkaline earth metal catalyst in
`the ceramic particles constituting the ceramic carrier composed of the zirconium phosphate.
`[0008] With the invention according to claim 3, the catalyst for exhaust gas purification according
`to claim 1 or 2 is characterized in that the ceramic carrier is composed of NZP having a
`three-dimensional network structure.
`[0009] With the invention according to claim 4, the catalyst for exhaust gas purification according
`to any one of the claims 1 to 3 is characterized in that a catalyst coating layer, which is composed
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`of particles of ceramic oxide for carrying a catalyst of precious metals and the like, is carried in the
`ceramic particles.
`[0010] With the invention according to claim 5, the catalyst for exhaust gas purification according
`to any one of the claims 1 to 4, is characterized in that a catalyst coating layer, which is composed
`of particles of ceramic oxide for carrying a catalyst alkali metals or alkaline earth metals, is carried
`in the ceramic particles.
`[0011] With the invention according to claim 6, the catalyst for exhaust gas purification according
`to claim 5, is characterized in that a catalyst of alkali metal and alkaline earth metal constituting the
`catalyst coating layer contains at least one element selected from lithium, sodium, potassium, and
`barium.
`[0012] With the invention according to claim 7, the catalyst for exhaust gas purification according
`to any one of the claims 4 to 6 is characterized in that a ceramic oxide constituting the catalyst
`coating layer contains at least one element selected from alumina, zirconia, titania and silica.
`[0013] With the invention according to claim 8, the catalyst for exhaust gas purification according
`to any one of claims 5 to 7 is characterized in that a catalyst constituting a catalyst contained in the
`ceramic particles and the catalyst containing layer are composed of the same material.
`[0014] With the invention according to claim 9, the catalyst for exhaust gas purification according
`to any one of claims 4 to 8, is characterized in that a rare earth metal co-catalyst and the like is
`carried in particles of ceramic oxide of the catalyst coating layer.
`[0015] With the invention according to claim 10, the catalyst for exhaust gas purification
`according to claim 9 is characterized in that the co-catalyst contains at least one simple substance
`of compound selected from cerium and lanthanum.
`[0016] With the invention according to claim 11, the catalyst for exhaust gas purification
`according to any one of claims 1 to 10 is characterized in that the ceramic carrier is a honeycomb
`structure having a plurality of through holes divided by cell walls.
`[0017] With the invention according to claim 12, the catalyst for exhaust gas purification
`according to claim 11 is characterized in that the ceramic carrier is alternately sealed at both ends
`in a checkered pattern by a sealing body.
`[0018] With the invention according to claim 13, the catalyst for exhaust gas purification for
`removing hydrocarbons contained in the exhaust gas, carbon monoxide, and nitrogen oxide black
`sooty particulates, is characterized by composing a ceramic carrier of a honeycomb structure
`composed of zirconium phosphate, and containing a ceramic particle substituted by an alkali metal
`or alkaline earth metal, and a catalyst coating layer carried in the ceramic particle, including an
`alumina particle for carrying an alkali metal based catalyst, an alkaline earth metal based catalyst,
`a precious metal based catalyst, and a rare earth metal based co-catalyst.
`[0019] TXU kQScY^]l ^V cXU _aUbU]c Y]eU]cY^] is described below. According to the invention of
`claim 1, at least a portion of the cations of ceramic particles constituting a ceramic carrier
`composed of zirconium phosphate is substituted with an alkali metal or an alkaline earth metal.
`Therefore, even without specially carrying the catalyst in a ceramic carrier, it is able to function as
`a catalyst for exhaust gas purification in the ceramic particles themselves constituting the ceramic
`carrier.
`[0020] According to the invention of claim 2, an alkali metal or alkaline earth metal catalyst is
`contained in ceramic particles constituting a ceramic carrier composed of zirconium phosphate.
`Therefore, even without specially carrying the catalyst in a ceramic carrier, it is able to function as
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`a catalyst for exhaust gas purification in the ceramic particles themselves constituting the ceramic
`carrier.
`[0021] According to the invention of claim 3, a ceramic carrier, since it is composed of NZP
`having a three-dimensional network structure, has excellent heat resistance and thermal shock
`resistance. Also, since the specific surface area is large, and because the area contacting the alkali
`metal or alkaline earth metal for carrying out a function as a catalyst increases, it is possible to
`facilitate the purification of exhaust gas.
`[0022] According to the invention of claim 4, the catalyst coating layer, which is composed of
`particles of ceramic oxide carrying the catalyst of precious earth metals and the like, is carried.
`Therefore, it is possible to improve the performance of the purification of exhaust gas.
`[0023] According to the invention of claim 5, the catalyst coating layer, which is composed of
`particles of ceramic oxide carrying an alkali metal or alkaline earth metal catalyst and the like, is
`carried. Therefore, it is possible to improve the performance of the purification of exhaust gas.
`[0024] According to the invention of claim 6, the alkali metal and alkaline earth metal catalyst
`constituting the catalyst coating layer, because it contains at least one element selected from
`lithium, sodium, potassium, and barium, it is possible to improve the durability of the catalyst.
`[0025] According to the invention of claim 7, the ceramic oxide constituting the catalyst coating
`layer contains at least one element selected from alumina, zirconia, titania and silica. Therefore,
`the ceramic oxide, since it contains a high specific surface area, is suitable for carrying a catalyst.
`In particular, when titania is selected, the sulfur components that obstruct activity of the catalyst
`can facilitate separation from the ceramic carrier. For example, when using a catalyst for exhaust
`gas purification to purify exhaust gas of a diesel engine, it is effective to use titania in a ceramic
`carrier for diesel engines since they often contain sulfur in the fuel.
`[0026] According to the invention of claim 8, the catalyst constituting a catalyst that is contained
`in ceramic particles and the catalyst coating layer is the same material. Therefore, the
`compatibility of the two increases compared to when using by combining different types of
`material, and the catalyst coating layer can strongly adhere to the ceramic particles. Thus, for
`example, when cleaning the catalyst for exhaust gas purification it will be difficult for the catalyst
`coating layer to separate from the ceramic particles.
`[0027] According to the invention of claim 9, the rare earth metal co-catalyst and the like is carried
`in particles of ceramic oxide of the catalyst coating layer. Therefore, compared to when using the
`catalyst alone, it is possible to actively supply oxygen to the exhaust gas by the oxygen
`concentration regulation action of the exhaust gas. For example, when using a catalyst for exhaust
`gas purification to purify exhaust gas of a diesel engine, the efficiency of combustive removal of
`diesel particulates is improved.
`[0028] According to the invention of claim 10, the co-catalyst contains at least one simple
`substance or compound selected from cerium and lanthanum. Therefore, it is possible to improve
`the durability of the catalyst.
`[0029] According to the invention of claim 11, since the ceramic carrier is a honeycomb structure
`having a plurality of through holes divided by cell walls, the area that can make the exhaust gas
`contact the catalyst increases. Thus, it is possible to improve the purification efficiency of the
`exhaust gas.
`[0030] According to the invention of claim 12, since both ends of the ceramic carrier are
`alternately sealed in a checkered pattern with a sealing body, exhaust gas that penetrated from one
`end of the ceramic carrier, between the time it exits from the other end, will certainly pass through
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`the cell wall. Therefore, it is possible to further improve the purification efficiency of the exhaust
`gas.
`[0031] According to the invention of claim 13, an alkali metal or alkaline earth metal catalyst is
`contained in ceramic particles composed of zirconium phosphate. Therefore, even without
`specially carrying the catalyst in a ceramic carrier, it is able to function as a catalyst for exhaust gas
`purification in the ceramic particles themselves constituting the ceramic carrier. In addition, since
`an alkali metal catalyst and the like, an alkaline earth metal catalyst and the like, and a precious
`metal catalyst and the like are carried in ceramic particles, it is possible to further improve the
`purification efficiency of exhaust gas. Furthermore, since the rare earth metal co-catalyst is carried
`in the ceramic particles, compared to when using the catalyst alone, it is possible to actively supply
`oxygen to the exhaust gas by the oxygen concentration regulation action of the exhaust gas. For
`example, when using a catalyst for exhaust gas purification to purify exhaust gas of a diesel engine,
`the efficiency of combustive removal of diesel particulates.
`[0032]
`[Embodiment of the Invention] An embodiment in which the present invention is embodied as a
`catalyst carrying filter that purifies exhaust gas from a diesel engine is described below in detail
`based on figures.
`[0033] As shown in Fig. 1 (a), (b), and Fig. 2, the catalyst carrying filter 10 as a catalyst for exhaust
`gas purification provides a ceramic carrier 15, and the ceramic carrier 15 is disposed in the exhaust
`gas path of the diesel engine not illustrated. The ceramic carrier 15 has a honeycomb structure.
`That is, a plurality of cells 11 is systematically formed in the ceramic carrier 15 along the axial
`direction thereof as through holes. The cells 11 are mutually separated by a cell wall 12. Of the
`plurality of cells 11, approximately half are open on the upstream side end face, and the remaining
`are open on the downstream side end face. That is, the end face of the ceramic carrier 15 exhibits
`a checkered pattern by alternately disposing an opening part and a sealed part.
`[0034] The thickness of the cell wall 12 is set to approximately 0.4mm. The density of the cells 11
`is 200 to 350 cells/square inch. The pores of the porous cell wall 12 are within an average pore
`diameter range of 5µm to 250µm, that is measured by a mercury penetration method. It is
`preferable that the cell wall 12 collects fine particulate when having a pore diameter of this degree.
`That is, diesel particulate can be reliably collected by setting the average pore diameter of the cell
`wall 12 within such range. When the average pore diameter of the cell wall 12 is less than 5 µm,
`the pressure loss that occurs when exhaust gas passes through the cell wall 12 becomes excessively
`large which may cause the engine to stop. Further, when the average pore diameter exceeds 250
`µm, fine particulate can no longer be collected efficiently.
`[0035] Further, the porosity of the porous cell wall 12 in the ceramic carrier 15 is set to 40-60%.
`Alternatively to this range, the porosity of the ceramic carrier 15 may be set within a range of
`50-60%. When porosity is less than 40%, the pressure loss that occurs when exhaust gas passes
`through the cell wall 12 becomes excessively large which may cause the engine to stop. Further,
`when porosity exceeds 60%, fine particulate can no longer be collected efficiently. Along with
`that, when porosity exceeds 60%, it becomes easy for a crack to develop in the ceramic carrier 15
`due to deteriorated mechanical strength. That is, the porosity and mechanical strength of the
`ceramic carrier 15 have an inversely proportional relationship.
`[0036] As stated above, by setting the average pore diameter of the ceramic carrier 15 between 5
`µm to 250 µm, and the porosity to 40-60%, pressure loss can be reduced and mechanical strength
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`can be improved. Along with that, the collection efficiency of the particulate contained in exhaust
`gas can be increased.
`[0037] As shown in Fig. 3, the ceramic carrier 15 is constituted from ceramic particles 20
`composed of zirconium phosphate. That is, the ceramic carrier 15 is composed of zirconium
`phosphate particles. The ceramic carrier 15 is sintered, after combining and kneading ceramic
`powder blended with zirconium phosphate with an organic binder, a lubricant, a plasticizer, and
`water, and being molded by extrusion. The ceramic carrier 15 used in the present embodiment is a
`zirconium phosphate (abbreviated as NZP) that has a three dimensional network structure.
`[0038] In the present embodiment, the gaps that occur between each ceramic particle 20 are not
`completely filled in the cell wall 12, so pressure loss is considerably small because the pores are
`maintained without change. Furthermore, the zirconium phosphate composed of a three
`dimensional network structure also has excellent heat resistance, corrosion resistance, and thermal
`shock resistance. Also, the ceramic carrier 15 constituted by zirconium phosphate, because of its
`porosity, can achieve a sufficient specific surface area. Furthermore, because the area where the
`exhaust gas contacts the catalyst becomes larger, oxidation of CO and HC in the exhaust gas can be
`accelerated.
`[0039] The ceramic particles 20 that constitute the ceramic carrier 15, substitute at least one part of
`the cation with an alkali metal or an alkaline earth metal. In other words, a catalyst 16 that is either
`an alkali metal or an alkaline earth metal is contained in the ceramic particles 20. Furthermore, the
`ceramic particles 20 themselves that constitute the ceramic carrier 15 function as a catalyst for
`exhaust gas purification.
`[0040] At least one element selected from lithium (Li), sodium (Na), or potassium (K) can be used
`as a catalyst 16 that is an alkali metal. For example, when the H atom of the ceramic particles 20
`composed of zirconium phosphate is substituted with Li, the composition formula is as follows.
`That is, the composition formula, HZr2(PO4)3, before substitution, is substituted, and becomes
`LiZr2(PO4)3 after substitution. Similarly, when the composition formula is substituted with Na, it
`becomes NaZr2(PO4)3, and when substituted with K it becomes KZr2(PO4)3.
`[0041] At least one element selected from barium (Ba), magnesium (Mg), or calcium (Ca) can be
`used as a catalyst 16 that is an alkaline earth metal. For example, when the H atom of the ceramic
`particles 20 composed of zirconium phosphate is substituted with Li, the composition formula
`becomes Ba[Zr2(PO4)3]2. Similarly, when substituted by Mg or Ca, the composition formulas
`become Mg[Zr2(PO4)3]2 and Ca[Zr2(PO4)3]2 respectively. For reference, the above information is
`put in order and shown in table 1.
`[0042]
`[Table 1]!!
`Before substitution
`
`HZr2(PO4)
`
`After substitution (alkali
`metal)
`LiZr2(PO4)
`NaZr2(PO4)
`KZr2(PO4)
`
`After substitution (alkaline
`earth metal)
`Ba[Zr2(PO4)3]2
`Mg[Zr2(PO4)3]2
`Ca[Zr2(PO4)3]2
`
`! F
`
`urther, other than zirconium phosphate (NZP) composed of a three dimensional network
`structure, it is possible to change into other zirconium phosphates such as AZP, ZSP, ZPP, and
`CZP, shown in table 2.
`[0043]
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`[Table 2]
`
`Name
`
`Abbreviati
`on
`
`Composition formula
`
`Crystal
`
`1
`
`2
`
`3
`
`4
`
`amorphous
`zirconium
`phosphate
`amorphous!
`zirconium
`silico-phospha
`te
`Amorphous
`polyphosphate
`
`Layered
`zirconium
`phosphate
`
`AZP
`
`ZSP
`
`ZPP
`
`CZP
`
`@
`
`shape
`
`shape
`shape
`shape
`shape
`
`shape
`shape
`shape
`
`amorphou
`s
`
`amorphou
`s
`
`amorphou
`s
`
`crystal
`
`Specifi
`c
`surface
`area
`
`350
`
`220
`
`As shown in Fig. 3, a catalyst coating layer 22 is carried on the ceramic particles 20 constituting
`the ceramic carrier 15. This catalyst coating layer 22 is composed of alumina particles 23 that are
`ceramic oxide particles, and zirconia particles 24. Other than the ceramic oxide particles, titania,
`silica, or a chemical including at least one chemical selected from these two chemicals may be
`used. The ceramic oxides are suitable as a carrier for catalysts because they have a high specific
`surface area.
`[0044] Further, when titania is selected, a sulfur component that hinders catalyst activation can
`accelerate separation from the ceramic carrier 15. For example, when a catalyst for exhaust gas
`purification is used for purifying exhaust gas in a diesel engine, sulfur components are often
`contained in fuel. Therefore, it can be said that it is particularly effective to use titania as a ceramic
`carrier 15 for a diesel engine.
`[0045] Other than Al2O3 and ZrO2 given above, TiO2 or SiO2 is single type of ceramic oxide for a
`specific combination of ceramic oxides. Examples of a double type ceramic oxide include the
`combinations of Al2O3/ZrB2, Al2O3/TiO2, Al2O3/SiO2, ZrO2/TiO2, or ZrO2/SiO2. Examples of a
`triple type ceramic oxide include the combinations of Al2O3/ZrO2/TiO2, Al2O3/ZrO2/SiO2,
`Al2O3/TiO2/SiO2, or ZrO2/TiO2/SiO2. Examples of a quadruple type ceramic oxide include the
`combination of Al2O3/ZrO2/TiO2/SiO2.
`[0046] On the front surface of the alumina particles 23 that constitute the catalyst coating layer 22,
`a catalyst 25 that is an alkali metal or an alkaline earth metal, a catalyst 26 that is a precious metal,
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`and a co-catalyst 27 that is a rare earth metal, are uniformly dispersed. At least one simple
`substance or a compound selected from lithium (Li), sodium (Na), potassium (K), calcium (Ca),
`and barium (Ba), can be used as the catalyst 25 that is either an alkali metal or an alkaline earth
`metal. For example, a binary alloy or a ternary alloy can be used as the compound, based on the
`element combination.
`[0047] Examples of a binary alloy include Li/Na, Na/K, Li/Na, Li/Ca, Li/Ba, Ca/Ba, Na/Ba,
`Na/Ca, K/Ba, K/Ca, and the like. Examples of a ternary alloy include Li/Na/K, Li/Na/Ba,
`Li/Na/Ca, Li/K/Ba, Li/K/Ca, Li/Ba/Ca, Na/K/Ba, Na/Ba/Ca, K/Ba/Ca.
`[0048] At least one substance or a compound selected from rhodium (Rh), platinum (Pt),
`palladium (Pd), gold (Au), silver (Ag), or copper (Cu) may be carried on the alumina particles 23,
`as the precious metal catalyst 26. Examples of a binary alloy compound include, Rh/Pt, Rh/Pd,
`Rh/Au, Rh/Ag, Rh/Cu, Pt/Pd, Pt/Au, Pt/Ag, Pt/Cu, Pd/Au, Pd/Ag, Pd/Cu, Au/Ag, Au/Cu, or
`Ag/Cu.
`[0049] Also, Rh/Pt/Pd, Rh/Pt/Au, Rh/Pt/Ag, Rh/Pt/Cu, Rh/Pd/Au, Rh/Pd/Ag, Rh/Pd/Cu,
`Rh/Au/Ag, Rh/Au/Cu, Rh/Ag/Cu, Pt/Pd/Au, Pt/Pd/Ag, Pt/Pd/Cu, Pd/Au/Ag, Pd/Au/Cu,
`Pd/Ag/Cu, Au/Ag/Cu may be used for the ternary alloy, and at least one substance selected from
`the rare earth metal-like cerium (Ce) and lanthanum (La) for a rare earth metal co-catalyst 27, or
`rare earth oxides such as ceria (CeO2) or lantana (La2O3). Incidentally, for the present
`embodiment, lithium was selected as an alkali metal catalyst 25, platinum was selected as a
`precious metal catalyst 26, and further, ceria was selected as a co-catalyst 27.
`[0050] When ceria and the like is dispersed in the alumina particles 23 (it is preferable that a
`precious metal catalyst such as Pt and the like is dispersed together), via the oxygen concentration
`regulation action held by ceria, a supply of oxygen in the exhaust gas is made active, combustion
`and removal efficiency for soot (diesel particulate) adhered to a filter are improved, and the
`regeneration rate of the catalyst carrying filter 10 becomes considerably improved. Further, the
`durability of the ceramic carrier 15 can be improved.
`[0051] That is, rare earth oxides such as ceria and the like, not only improve the heat resistance of
`alumina, but also serve to control the oxygen concentration on the front surface of the ceramic
`carrier 15. Generally, due to exhaust gas composition constantly changing between a fuel rich
`region and a fuel lean region, the operation atmosphere on the front surface of the catalyst carrying
`filter 10 also changes drastically. Incidentally, oxygen is supplied to the atmosphere when exhaust
`gas becomes a rich region, and in contrast, excessive oxygen in the atmosphere is occluded when
`exhaust gas becomes a lean region. In this way, by controlling the oxygen concentration in the
`atmosphere, the ceria bears an operation expanding the range of the air fuel ratio that can!
`efficiently remove hydrocarbon, carbon monoxide, or NOx.
`[0052] Titania particles 28 are carried by the alumina particles 23, other than the catalyst 25, 26
`and co-catalyst 27. The reason the titania particles 28 are carried by the alumina particles 23, is
`that when a sulfur dioxide is adhered to the alumina particles 23, the sulfur dioxide is oxidized by
`a metal catalyst in an oxygen enriched atmosphere, and becomes a sulfur trioxide (SO3). Further,
`because the sulfur trioxide is reacted with the steam contained in exhaust gas, and becomes
`sulfuric acid (H2SO4), and when the sulfuric acid is adhered to alumina, it forms an alkali metal
`salt (Na2 SO4). Furthermore, due to the titania particles 28 being carried by the alumina particles
`23, it becomes difficult for the sulfur dioxide (SO2) contained in the exhaust gas to adhere to the
`alumina particles 23. Along with that, even when the sulfur dioxide adheres to the alumina
`particles 23, it can be easier to separate the sulfur dioxide from there.
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`[0053] A precious metal catalyst 29 is carried by the zirconia particles 24 that constitute the
`catalyst coating layer 22. At least one element selected from rhodium (Rh), platinum (Pt), or
`palladium (pd) can be used as a precious metal catalyst 26. Incidentally, in the present
`embodiment, the precious metal catalyst 29 carried by the zirconia particles 24 becomes rhodium.
`The reason rhodium is carried by the zirconia particles 24, is because the capability to reduce the
`hydrogen in steam contained in the exhaust gas is higher than when carried by the alumina
`particles 23.
`[0054] Furthermore, the catalyst for exhaust gas purification of the present embodiment has the
`effects shown below.
`(1) One part of the ceramic particles 20 that constitute the ceramic carrier 15 composed of
`zirconium phosphate, is substituted with an alkali metal or an alkaline earth metal. In other words,
`the ceramic particles 20 of the ceramic carrier 15 have a catalyst 16 that is either an alkali metal or
`an alkaline earth metal. Furthermore, in the present embodiment, the catalyst coating layer 22 is
`carried by the ceramic particles 20, but even when this catalyst coating layer 22 is not carried, the
`ceramic carrier 15 alone can function as a catalyst. Therefore, for example, by cleaning the
`ceramic carrier 15, in the worst case, even when the catalyst coating layer 22 separates from the
`ceramic particles 20, functional deterioration as a catalyst for exhaust gas purification can be
`reliably prevented.
`[0055] (2) The ceramic carrier 15 has excellent heat resistance and thermal shock resistance due to
`being composed of NZP having a three dimensional network structure. Therefore, even when the
`ceramic carrier 15 reaches a high temperature by being exposed to exhaust gas, the collection
`efficiency of diesel particulate and functional deterioration as a catalyst can be prevented.
`Furthermor