(l9)The Patent Office Japan (12) KOKAI TOKKYO KOHO
`
`(1 1} Patent Kokai No.
`
`(Unexamined Patents Bulletin)
`
`2003-1544223
`
`(51) Int. Class.
`BOID 39:’l4
`39f20
`53/94
`35/04
`
`B01]
`
`Identifier
`ZAB
`
`301
`
`Fl
`BOID 39:44
`39f20
`35f04
`
`B015
`
`FOIN 3X02
`
`(P2003- I S4223A)
`(43) Date ofdisclosure: 27 May 2003
`Theme code (for reference)
`ZABB 3G090
`D 3G09l
`4D019
`4D048
`4G069
`
`301E
`3011,
`301C
`
`Examination requested: N0 Number of claims: 3]
`
`0L
`
`(Total 27 pages [originaI]}
`C ‘on.'fnm:.s' on t'a.s'.-' page
`
`(21) Patent Application No.2002-210300
`{P2002-2]0300)
`
`(22) Date of filing: [8 July 2002
`
`(31) Priority filing; Japan Patent
`Application No.2001-218318 (P2001-
`218318}
`
`(32) Convention date: 18 July 2001
`(33) Convention state: Japan (JP)
`
`(71) Applicant: 000000153
`1biClBl1C0.. Ud-
`l Kanda-cho 2-choine, Kanda-ku,
`Ogaki-shi, Gifu, Japan.
`(72) Inventor‘: Masaaki Kojima
`cfo Ibiden Co. Ogaki-lfiita Plant,
`1-] Kitagata, lbigawa-cho, Ibi-gun, Gl‘l'l.l_
`(72) Inventor: Noriyuki Taoka
`cfo Ibiden Co. Ogaki-Kita Plant,
`1-1 Kitagata, lbigawa-cho, Ibi-gun, Gifu.
`
`100036535
`{74)Ag€i1tI
`Yasuo Yasutomi. Patent Attorney.
`
`(‘onrinttes on 19.5-{page
`
`(54) [Title of invention] Catalytic filter, method of manufacturing same, and an exhaust gas
`
`cleaning system
`
`(5?) [Abstract]
`
`[Task] To provide a catalytic filter wherein the amount of noble metal catalyst can be reduced
`
`without change in the soot regeneration rate despite regeneration being repeated to some
`
`extent and wherein pressure loss is small.
`
`[Solution] A catalytic filter characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of through—ho|es separated by cell walls are
`
`alternately closed with plugs, and wherein catalyst is supported, a predefined amount of the
`
`aforesaid catalyst being supported at one end and relatively little of the catalyst being
`
`supported going towards the other end.
`
`[diagrams see Drawings, Figure 5]
`
`1
`
`JM 1010
`
`

`
`[Claims]
`
`[Claim 1] A catalytic filter, characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of through—holes separated by cell walls are
`
`alternately closed with plugs and wherein catalyst is supported, a predefined amount of the
`
`aforesaid catalyst being supported at one end and relatively little of the catalyst being
`
`supported going towards the other end.
`
`[Claim 2] A catalytic filter, characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of through-holes separated by cell walls are
`
`alternately closed with plugs and wherein catalyst is supported; wherein a catalyst support site
`
`is provided in a zone extending from one end face to a point displaced towards the other end
`
`face by a predefined length and a non-catalyst supporting site is provided in a zone extending
`
`from the said point to the other end face.
`
`[Claim 3] A catalytic filter, characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of through-holes separated by cell walls are
`
`alternately closed with plugs and wherein catalyst is supported; wherein a catalyst support site
`
`is provided in a zone extending from one end face to a point displaced towards the other end
`
`face by 112-4X5 of the overall length of the filter and a non-catalyst supporting site is provided
`
`in a zone extending from the said point to the other end face.
`
`[Claim 4] The catalytic filter set down in any of Claims 1-3 characterised in that the aforesaid
`
`catalyst comprises at
`
`least one element chosen from the group comprising noble metal
`
`elements, elements ofperiodic table Group VI and elements ofperiodic table Group VIII.
`
`[Claim 5] The catalytic filter set down in any ofClaims 1-3 characterised in that the aforesaid
`
`catalyst comprises at
`
`least one element chosen from the group comprising alkali metal
`
`elements, alkaline earth metal elements, rare earth elements and transition metal elements.
`
`[Claim 6] A catalytic filter, characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of througl1—ho|es separated by cell walls are
`
`alternately closed with plugs and wherein catalyst is supported; wherein a predefined amount
`
`of NOX selective reduction catalyst component andfor NOX occlusion catalyst component
`
`arefis supported towards one end and relatively little of the NOx selective reduction catalyst
`
`component andfor NOx occlusion catalyst component arefis supported going towards the
`other end.
`
`2
`
`

`
`[Claim ?] A catalytic filter, characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of through-holes separated by cell walls are
`
`alternately closed with plugs and wherein catalyst is supported; wherein a site supporting an
`
`NOx selective reduction catalyst component andfor NOx occlusion catalyst component is
`
`provided in a zone extending from one end face to a point displaced towards the other end
`
`face by a predefined length and a site not supporting NOx selective reduction catalyst
`
`component andfor NOx occlusion catalyst component is provided in a zone extending from
`
`the said point to the other end face.
`
`[Claim 8] A catalytic filter, characterised as a ceramic filter wherein the two ends of a
`
`honeycomb structure possessing a plurality of through-holes separated by cell walls are
`
`alternately closed with plugs and wherein catalyst is supported; wherein a site supporting an
`
`NOx selective reduction catalyst component andfor NOx occlusion catalyst component is
`
`provided in a zone extending from one end face to a point displaced towards the other end
`
`face by 112-4J5 of the overall
`
`length of the filter and a site not supporting NOx selective
`
`reduction catalyst component andfor NOx occlusion catalyst component is provided in a zone
`
`extending from the said point to the other end face.
`
`[Claim 9] The catalytic filter set down in any ofClaims 6-8 characterised in that the aforesaid
`
`NOx occlusion catalyst component is constituted by a component comprising at least one
`
`element chosen from the group comprising alkali metals, alkaline earth metals, rare earths and
`transition metals in addition to noble metal elements.
`
`[Claim 10} The catalytic filter set down in any of Claims 1-9 characterised in that a support
`
`material is supported on the cell wall surface of the aforesaid filter.
`
`[Claim ll] The catalytic filter set down in any of Claims 1-9 characterised in that a
`
`predefined amount of support material is supported on the cell wall surface towards one end
`
`of the aforesaid filter and relatively little of the support material is supported going towards
`the other end.
`
`[Claim 12] The catalytic filter set down in any of Claims 1-9 characterised in that a site
`
`supporting a support material is provided on the cell wall surface of the aforesaid filter in a
`
`zone extending from one end face to a point displaced towards the other end face by a
`
`predefined length and a site not supporting support material is provided in a zone extending
`
`from the said point to the other end face.
`
`3
`
`

`
`[Claim 13} The catalytic filter set down in any of Claims 1-9 characterised in that a site
`
`supporting a support material is provided on the cell wall surface of the aforesaid filter in a
`
`zone extending from one end face to a point displaced towards the other end face by U2-4E5
`
`of the overall length of the filter and a site not supporting support material is provided in a
`
`zone extending from the said point to the other end face.
`
`[Claim 14] The catalytic filter set down in any of Claims 10-l3 characterised in that the
`
`aforesaid support material comprises at least one material chosen from the group comprising
`
`alumina, zirconia, titania and silica.
`
`[Claim 15] The catalytic filter set down in any of Claims I0-14 characterised in that the
`
`aforesaid support material is constituted by acicular alumina.
`
`[Claim 16] The catalytic filter set down in any of Claims 1-15 characterised in that the
`
`aforesaid filter is constituted by a ceramic porous body containing silicon.
`
`[Claim l'i'] The catalytic filter set down in any of Claims 1-15 characterised in that the
`
`aforesaid filter is constituted by a ceramic porous body containing at least one ceramic chosen
`
`from the group comprising silicon carbide, silicon nitride, cordierite, mullite, sialon, and
`silica.
`
`[Claim 18] The catalytic filter set down in any of Claims 1-17 characterised in that a
`
`predfined amount of catalyst promoter is supported on the cell wall surface of the aforesaid
`
`filter towards one end, and relatively little of the catalyst promoter is supported going towards
`the other end.
`
`[Claim 19] The catalytic filter set down in any of Claims 1-17 characterised in that a catalyst
`
`promoter support site is provided on the cell wall surface of the aforesaid filter in a zone
`
`extending from one end face to a point displaced towards the other end face by a predefined
`
`length and a non-catalyst promoter supporting site is provided in a zone extending from the
`
`said point to the other end face.
`
`[Claim 20] The catalytic filter set down in any of Claims 1-]? characterised in that a catalyst
`
`promoter support site is provided on the cell wall surface of the aforesaid filter in a zone
`
`extending from one end face to a point displaced towards the other end face by U2-4X5 of the
`
`overall length of the filler and a non-catalyst promoter supporting site is provided in a zone
`
`extending from the said point to the other end face.
`
`4
`
`

`
`[Claim 2]] The catalytic filter set down in any of Claims 18-20 characterised in that the
`
`aforesaid catalyst promoter is constituted by one comprising rare earth oxide.
`
`[Claim 22} The catalytic filter set down in any of Claims 18-20 characterised in that the
`
`atbresaid catalyst promoter comprises at least one element chosen from the group comprising
`
`alkali metals, alkaline earth metals, rare earth elements and transition metal elements.
`
`[Claim 23} The catalytic filter set down in any of Claims 18-20 characterised in that the
`
`aforesaid catalyst comprises at
`
`least one entity or compound chosen from the group
`
`comprising cerium (Ce), lanthanum (La), barium (Ba), calcium (Ca) and potassium (K).
`
`[Claim 24] The catalytic filter set down in any ofClaims 1-23 characterised in that the zones
`
`wherein the support material, catalyst promoter and catalyst are supported on the cell wall
`
`surface of the aforesaid filter are of the same length from one end face towards the other end
`face.
`
`[Claim 25] A method of manufacturing a catalytic filter, characterised in that a zone
`
`extending from one end face of the filter to a point displaced towards the other end face by a
`
`predefined length is impregnated with a solution of metal compounds containing noble metal
`and then dried.
`
`[Claim 26] A method of manufacturing a catalytic filter, characterised in that an alumina
`
`support material is applied to a filter by a process comprising a solution impregnation step
`
`wherein a zone extending from one end face of the filter to a point displaced towards the
`
`other end face by a predefined length is impregnated in a solution of metal compounds
`
`containing aluminium, a drying step wherein the impregnated filter is dried, a precalcination
`
`step wherein an amorphous alumina film is formed by heating and calcining the dried filter at
`
`a temperature of not
`
`less than 300-500°C, a hydrothermal
`
`treatment step wherein the
`
`precalcined filter is treated by immersion in hot water and then dried, and a final calcination
`
`step wherein the hydrothermally treated filter is calcined at 500-l2(}0°C.
`
`[Claim 27] A method of manufacturing a catalytic filter, characterised in that a rare earth
`
`oxide film is applied to a filter by a process comprising a solution impregnation step wherein
`
`a zone extending from one end face of the filter to a point displaced towards the other end
`
`face by a predefined length is impregnated in a solution of metal compounds containing rare
`
`earth elements, a drying step wherein the impregnated filter is dried, and a calcination step
`
`wherein the dried filter is heated and calcined in a nitrogen atmosphere at a temperature of
`
`500-800°C, forming a rare earth oxide film.
`
`5
`
`

`
`[Claim 28] An exhaust gas cleaning system characterised in that the filter of any of Claims 1-
`
`24 is installed in a diesel engine exhaust passage such that the end where a relatively large
`
`amount of catalyst is supported faces the exhaust gas inlet side and the end where relativeiy
`
`little or no catalyst is supported faces the discharge side.
`
`[Claim 29] An exhaust gas cleaning system characterised in that the filter of any of Claims 1-
`
`24 is installed in a diesel engine exhaust passage such that the end where a relatively large
`
`amount of catalyst is supported faces the exhaust gas inlet side and the end where relativeiy
`
`little or no catalyst is supported faces the discharge side, a heater is installed on the exhaust
`
`gas inlet side of the aforesaid filter, and the filter is regenerated using the heater.
`
`[Claim 30] An exhaust gas cleaning system characterised in that the filter of any of Claims 1-
`
`24 is installed in the exhaust passage of a diesel engine with post-ignition, with the end where
`
`a relatively large amount of catalyst is supported facing the exhaust gas inlet side and the end
`
`where relatively little or no catalyst is supported facing the discharge side.
`
`[Claim 31] A catalytic filter characterised in that a specified amount of catalyst is supported
`
`at one end and relatively little of the catalyst is supported going towards the other end.
`
`[Detailed Description of Invention]
`
`[0001]
`
`[Inventive field of art] The invention relates to a catalytic filter, a method of manufacturing a
`
`catalytic filter, and an exhaust gas cleaning system.
`
`[0002]
`
`[Prior art] The number of motor vehicles has increased dramatically since the turn of the
`
`century, and this increase has been matched by a continual, steep increase in the amount of
`
`exhaust gas discharged from the internal combustion engines of vehicles. The various
`
`substances contained in the exhaust gas from diesel engines in particular cause pollution and
`
`because of this they are now seriously impacting on the global environment. Research
`
`findings have recently been reported indicating that
`
`the suspended particulate matter
`
`(hereunder abbreviated to PM) in exhaust gas, such as soot and SOF {soluble oil fraction}, are
`
`sometimes responsible for allergic disorders and reduced sperm counts. Thus, the fonnulation
`
`of measures to remove PM from exhaust gas is considered an urgent task facing mankind.
`
`[0003] Many diverse kinds of exhaust gas cleaner apparatus have been proposed in this
`
`context. Figure 18 is a schematic sketch of an ordinary exhaust gas cleaner. As shown in
`
`6
`
`

`
`Figure 18,
`
`the ordinary exhaust gas cleaner 101 has a construction whereby the exhaust
`
`channel 104 connected with the exhaust manifold 103 ofa diesel engine is provided along its
`
`path with a casing 105, within which is mounted a filter 10 containing fine pores. Besides a
`
`metal or alloy, the material wherefrom the filter 10 is fonned can be a ceramic. A honeycomb
`
`filter of cordierite is a known example typitying a filter 10 comprising ceramic. The use of
`
`silicon carbide as filter-forming material has recently been regarded ideal from the standpoint
`
`of high heat resistance, mechanical strength and trapping efficiency, chemical stability, and
`
`small pressure loss.
`
`[0004] The aforesaid honeycomb filter has numerous cells extending in its axial direction.
`
`Hence, when exhaust gas passes through the filter 10, PM is trapped by the filter walls (cell
`
`walls). As the amount of PM trapped in the filter increases, the resistance within the filter is
`
`increased, and the pressure loss increases. Regeneration, a procedure whereby the temperature
`
`in the filter is increased to a predefined temperature (ignition temperature) to ignite and burn
`
`off the PM, has therefore been adopted.
`
`[0005] Currently, an exhaust gas cleaner effects ignition either with exhaust gas heat only
`
`(self ignition mode) or with heat from a heating means such as a burner or heater in addition
`
`to the exhaust gas heat (heated ignition mode), and a method frequently used is to lower the
`
`ignition temperature by supporting a catalyst uniformly on the cell walls of the filter. Japan
`
`Patent Kokai No. 2001-207836 further discloses art whereby an N0x absorption catalyst
`
`component is for the most part supported on the exhaust gas inlet side of the honeycomb
`filter.
`
`[0006]
`
`[Problem addressed by the invention] However, it has been found that, when regeneration of
`
`the whole diesel particulate filter (DPF) whereon PM has been trapped is repeated at fixed
`
`intervals, filter performance deteriorates. Figure 19 is a graph of the relation between the
`
`number of regeneration cycles and regeneration rate. “Regeneration rate” is here the ratio of
`
`the weight of accumulated soot removed from the filter (the amount of regeneration) to the
`
`weight of soot accumulated in the filter, expressed as a percentage. It will be seen from the
`
`graph in Figure 19 that initially the PM is burned off by regeneration at a high regeneration
`
`rate, but as the process is repeated again and again, the regeneration rate decreases and the
`
`reactivity of the catalyst progressively declines.
`
`[0007]
`
`[Means of solving the problem] To solve the problem of deterioration in filter performance,
`
`the inventors conducted wide-ranging trial and error tests. Firstly, supposing that catalyst
`
`7
`
`

`
`loading was linked to deterioration in performance, increase in the amount of catalyst was
`
`considered. However, it was impossible to halt deterioration in filter performance this way
`
`since pressure loss
`
`increased when the catalyst
`
`loading was increased. Contrary to
`
`expectations, when the temperature was measured at different locations with thermocouples
`
`inserted in the filter under regeneration, the temperature was found to be higher on the exit
`
`side than the exhaust gas inlet side. This was considered to be a problem of filter and heater
`
`location, and regeneration was therefore carried out with the heater fitted on the exhaust gas
`
`inlet side that tended to fall in temperature. Figure 20 is a graph of the change in temperature
`
`in the filter during regeneration. It was found that, while the exhaust gas inlet side of the filter
`
`could be controlled to around 600°C, at which the catalyst reacts well, the discharge side rose
`
`above 800°C, as shown by the graph in Figure 20. When attention was turned to the catalyst,
`
`it was further established that the noble metal used as catalyst undergoes sintering above
`
`800°C (the metal transforming to large particles), whereupon reactivity deteriorates and the
`
`catalyst becomes unusable.
`
`[0008] On the basis of these observations, the inventors turned their attention to the catalyst
`
`loading on the exhaust gas inlet side and established that ifthe catalyst support location was
`
`changed from overall uniform support to support at varying concentration or partial support,
`
`the soot regeneration rate remained unchanged after regeneration. had to a degree been
`
`repeated. The inventors were also able to prevent wasteful consumption of the noble metals,
`
`etc, used as catalyst, which are a valuable resource, thus reducing cost, and succeeded in
`
`creating a catalytic filter that has little pressure loss.
`
`[0009] The basis ofthis is that reduction in the amount of noble metal, etc, on the exhaust gas
`
`discharge side reduces the amount of catalyst of noble metal, etc, degrading.
`
`[0010] (1) The catalytic filter of the invention is characterised as a ceramic filter wherein the
`
`two ends of a honeycomb structure possessing a plurality of through-holes separated by cell
`
`walls are alternately closed with plugs and wherein catalyst is supported, a predefined amount
`
`of the aforesaid catalyst being supported at one end and relatively little of the catalyst being
`
`supported going towards the other end.
`
`[001]] (2) The catalytic filter of the invention is characterised as a ceramic filter wherein the
`
`two ends of a honeycomb structure possessing a plurality of through~holes separated by cell
`
`walls are alternately closed with plugs and wherein catalyst is supported; wherein a catalyst
`
`support site is provided in a zone extending from one end face to a point displaced towards
`
`the other end face by a predefined length and a non-catalyst supporting site is provided in a
`
`zone extending from the said point to the other end face.
`
`8
`
`

`
`[0012] (3) The catalytic filter of the invention is characterised as a ceramic filter wherein the
`
`two ends of a honeycomb structure possessing a plurality of through-holes separated by cell
`
`walls are alternately closed with plugs and wherein catalyst is supported; wherein a catalyst
`
`support site is provided in a zone extending from one end face to a point displaced towards
`
`the other end face by IE2-4X5 of the overall length of the filter and a non-catalyst supporting
`
`Site is provided in a zone extending from the said point to the other end face.
`
`[0013] (4) The catalytic filter in any of (1)-(3) above is characterised in that the aforesaid
`
`catalyst comprises at
`
`least one element chosen from the group comprising noble metal
`
`elements, elements of periodic table Group VI and elements of periodic table Group VIII.
`
`[0014] (5) The catalytic filter in any of (1)-(3) above is characterised in that the aforesaid
`
`catalyst comprises at
`
`least one element chosen from the group comprising alkali metal
`
`elements, alkaline earth metal elements, rare earth elements and transition metal elements.
`
`[0015] (6) The catalytic filter of the invention is characterised as a ceramic filter wherein the
`
`two ends of a honeycomb structure possessing a plurality of through-holes separated by cell
`
`walls are alternately closed with plugs and wherein catalyst
`
`is supported; wherein a
`
`predefined amount of NOX selective reduction catalyst component andfor N0): occlusion
`
`catalyst component aretis supported towards one end and relatively little of the N0x selective
`
`reduction catalyst component andfor NOx occlusion catalyst component arefis supported
`
`going towards the other end.
`
`[0016] {7} The catalytic filter of the invention is characterised as a ceramic filter wherein the
`
`two ends of a honeycomb structure possessing a plurality of through-holes separated by cell
`
`walls are alternately closed with plugs and wherein catalyst is supported; wherein a site
`
`supporting an NOx selective reduction catalyst component andfor NOX occlusion catalyst
`
`component is provided in a zone extending from one end face to a point displaced towards the
`
`other end face by a predefined length and a site not supporting NOx selective reduction
`
`catalyst component and’or NOx occlusion catalyst component is provided in a zone extending
`
`from the said point to the other end face.
`
`[0017] (8) The catalytic filter of the invention is characterised as a ceramic filter wherein the
`
`two ends of a honeycomb structure possessing a plurality of through-holes separated by cell
`
`walls are alternately closed with plugs and wherein catalyst is supported; wherein a site
`
`supporting an NOx selective reduction catalyst component and/or NOX occlusion catalyst
`
`component is provided in a zone extending from one end face to a point displaced towards the
`
`9
`
`

`
`other end face by U2-415 of the overall length of the filter and a site not supporting NOX
`
`selective reduction catalyst component andfor NOx occlusion catalyst component is provided
`
`in a zone extending from the said point to the other end face.
`
`[0018] {9} The catalytic filter in any of (6)-(8) above is characterised in that the aforesaid
`
`N0x occlusion catalyst component is constituted by a component comprising at least one
`
`element chosen from the group comprising alkali metals, alkaline earth metals, rare earths and
`transition metals in addition to noble metal elements.
`
`[0019] (10) The catalytic filter in any of (1)-(9) above is characterised in that a support
`
`material is supported on the cell wall surface of the aforesaid filter.
`
`[0020] (l 1) The catalytic filter in any of (1)-(9) above is characterised in that a predefined
`
`amount of support material is supported on the cell wall surface of the aforesaid filter towards
`
`one end and relatively little of the support material is supported going towards the other end.
`
`[002]] (12) The catalytic filter in any of(l )~(9) above is characterised in that a site supporting
`
`support material is provided on the cell wall surface of the aforesaid filter in a zone extending
`
`from one end face to a point displaced towards the other end face by a predefined length and a
`
`site not supporting support material is provided in a zone extending from the said point to the
`other end face.
`
`[0022] (13) The catalytic filter in any of(l }-(9) above is characterised in that a site supporting
`
`a support material
`
`is provided on the cell wall surface of the aforesaid filter in a zone
`
`extending from one end face to a point displaced towards the other end face by IE2-4E5 of the
`
`overall length of the filter and a site not supporting support material is provided in a zone
`
`extending from the said point to the other end face.
`
`[0023] (14) The catalytic filter in any of ( 10)-( l 3) above is characterised in that the aforesaid
`
`support material comprises at least one material chosen from the group comprising alumina,
`
`zirconia, titania and silica.
`
`[0024] (15) The catalytic filter in any of (l0)~(l4) above is characterised in that the aforesaid
`
`support material is constituted by acicular alumina.
`
`[0025] (16) The catalytic filter in any of(l)-(15) above is characterised in that the aforesaid
`
`filter is constituted by a ceramic porous body containing silicon.
`
`10
`
`

`
`[0026] (17) The catalytic filter in any of(1)-(15) above is characterised in that the aforesaid
`
`filter is constituted by a ceramic porous body comprising at least one ceramic chosen from the
`
`group comprising silicon carbide, silicon nitride, cordierite, mullite, sialon, and silica.
`
`[0027] (18) The catalytic filter in any of(l)-(15) above is characterised in that a predefined
`
`amount of catalyst promoter is supported on the cell wall surface of the aforesaid filter
`
`towards one end, and relatively little of the catalyst promoter is supported going towards the
`other end.
`
`[0028] (19) The catalytic filter in any of (1)-(17) above is characterised in that a catalyst
`
`promoter support site is provided on the cell wall surface of the aforesaid filter in a zone
`
`extending from one end face to a point displaced towards the other end face by a predefined
`
`length and a non-catalyst promoter supporting site is provided in a zone extending from the
`
`said point to the other end face.
`
`[0029] (20) The catalytic filter in any of (1)-(1?) above is characterised in that a catalyst
`
`promoter support site is provided on the cell wall surface of the aforesaid filter in a zone
`
`extending from one end face to a point displaced towards the other end face by U2-4E5 of the
`
`overall length of the filler and a non-catalyst promoter supporting site is provided in a zone
`
`extending from the said point to the other end face.
`
`[0030] (21) The catalytic filter in any of (18)-(20) above is characterised in that the aforesaid
`
`catalyst promoter is constituted by one comprising rare earth oxide.
`
`[003]] (22) The catalytic filter in any of (18)-(20) above is characterised in that the aforesaid
`
`catalyst promoter comprises at least one element chosen from the group comprising alkali
`
`metals, alkaline earth metals, rare earth elements and transition metal elements.
`
`[0032] (23) The catalytic filter in any of(l8)-(20) above is characterised in that the aforesaid
`
`catalyst comprises at least one entity or compound chosen from the group comprising cerium
`
`(Ce), lanthanum (La), barium (Ba), calcium (Ca) and potassium (K).
`
`[0033] (24) The catalytic filter in any of (1)»(23) above is characterised in that the zones
`
`wherein the support material, catalyst promoter and catalyst are supported on the cell wall
`
`surface of the aforesaid filter are of the same length from one end face towards the other end
`face.
`
`[0034] (25) The method of manufacturing the catalytic filter of the invention is characterised
`
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`in that a zone extending from one end face of the filter to a point displaced towards the other
`
`end face by a predefined length is impregnated with a solution of metal compounds
`
`containing noble metal and then dried.
`
`[0035] (26) The method of manufacturing the catalytic filter of the invention is characterised
`
`in that an alumina support material is applied to a filter by a process containing a solution
`
`impregnation step wherein a zone extending from one end face of the filter to a point
`
`dispiaced towards the other end face by a predefined length is impregnated in a solution of
`
`metal compounds containing aluminium, a drying step wherein the impregnated filter is dried,
`
`a precalcination step wherein an amorphous alumina film is formed by heating and calcining
`
`the dried filter at a temperature of not less than 300—500°C, a hydrothermal treatment step
`
`wherein the precalcined filter is treated by immersion in hot water and then dried, and a final
`
`calcination step wherein the hydrothennally treated filter is calcined at 500-1200°C.
`
`[0036] (2?) The method of manufacturing the catalytic filter of the invention is characterised
`
`in that a rare earth oxide is applied to a filter by a process comprising a solution impregnation
`
`step wherein a zone extending from one end face of the filter to a poi.nt displaced towards the
`
`other end face by a predefined length is impregnated in a solution of metal compounds
`
`containing rare earth elements, a drying step wherein the impregnated filter is dried, and a
`
`calcination step wherein the dried filter is heated and calcined in a nitrogen atmosphere at a
`
`temperature of 500-800°C, forming a rare earth oxide film.
`
`[0037] (28) The inventive gas cleaning system is characterised in that the filter in any of(l )-
`
`(24} above is installed in a diesel engine exhaust passage such that the end where a relatively
`
`large amount of catalyst is supported faces the exhaust gas inlet side and the end where
`
`relatively little or no catalyst is supported faces the discharge side.
`
`[0038] (29) The inventive exhaust gas cleaning system is characterised in that the filter in any
`
`of (1-){24} above is installed in a diesel engine exhaust passage such that the end where a
`
`relatively large amount of catalyst is supported faces the exhaust gas inlet side and the end
`
`where relatively little or no catalyst is supported faces the discharge side, a heater is installed
`
`on the exhaust gas inlet side of the aforesaid filter, and the filter is regenerated using the
`heater.
`
`[0039] (30) The inventive exhaust gas cleaning system is characterised in that the filter of any
`
`of Claims [-24 is installed in the exhaust passage ofa diesel engine with post-ignition, with
`
`the end where a relatively large amount of catalyst is supported facing the exhaust gas inlet
`
`side and the end where relatively little or no catalyst is supported facing the discharge side.
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`[0040] (31) The catalytic filter of the invention is characterised in that a specified amount of
`
`catalyst is supported towards one end and relatively little of the catalyst is supported going
`towards the other end.
`
`[0041] According to the invention in (1), by supporting little catalyst at the end reaching high
`
`temperature during regeneration, as at the exhaust gas discharge end of the filter, it is possible
`
`to reduce wastage of catalyst due to sintering. In addition, foul exhaust gas with the highest
`
`concentration of PM can be efficiently cleaned at the exhaust gas inlet end.
`
`[0042] According to the invention in (2), by supporting little catalyst at the end reaching high
`
`temperature during regeneration, as at the exhaust gas discharge end of the filter, it is possible
`
`to reduce wastage of catalyst due to sintering. In addition, foul exhaust gas with the highest
`
`concentration of PM can be efficiently cleaned at the exhaust gas inlet end. Furthermore, the
`
`pressure loss can be made smaller than when catalyst is uniformly supported on the cell wall
`
`surface as in the prior art.
`
`[0043] According to the invention in (3), by supporting little catalyst at the end reaching high
`
`temperature during regeneration, as at the exhaust gas discharge end of the filter, it is possible
`
`to reduce wastage of catalyst due to sintering, In addition, foul exhaust gas with the highest
`
`concentration of PM can be efficiently c