Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
  • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
  • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
  • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/02—Loose filtering material, e.g. loose fibres
  • B01D39/06—Inorganic material, e.g. asbestos fibres, glass beads or fibres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/66—Silver or gold
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/024—Multiple impregnation or coating
  • B01J37/0242—Coating followed by impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/04—Additives and treatments of the filtering material
  • B01D2239/0471—Surface coating material
  • B01D2239/0478—Surface coating material on a layer of the filter
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/10—Noble metals or compounds thereof
  • B01D2255/104—Silver
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/204—Alkaline earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/204—Alkaline earth metals
  • B01D2255/2042—Barium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/204—Alkaline earth metals
  • B01D2255/2045—Calcium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/204—Alkaline earth metals
  • B01D2255/2047—Magnesium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/206—Rare earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20715—Zirconium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/30—Silica
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/40—Mixed oxides
  • B01D2255/407—Zr-Ce mixed oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/01—Engine exhaust gases
  • B01D2258/012—Diesel engines and lean burn gasoline engines
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2510/00—Surface coverings
  • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
  • F01N2510/065—Surface coverings for exhaust purification, e.g. catalytic reaction for reducing soot ignition temperature

Definitions

• the present invention relates to a particulate combustion catalyst, to a particulate filter, and to an exhaust gas cleaning apparatus. More particularly, the present invention relates to a particulate combustion catalyst which realizes removal (through oxidation) of particulate matter discharged from a diesel internal combustion engine; to a particulate filter coated with the particulate combustion catalyst; and to an exhaust gas cleaning apparatus including the particulate filter coated with the particulate combustion catalyst.
• Exhaust gas discharged from diesel engines contains nitrogen oxides (NO x ) and particulate matter, and release of such substances into the atmosphere without any treatment is a main cause of air pollution. Therefore, demand has arisen for strict regulation for such substances.
• NO x nitrogen oxides
• SOFs soluble organic fractions
• Diesel exhaust gas trapping system employing a diesel particulate filter for trapping soot.
• particulate matter trapped therein must be continuously removed through oxidation.
• a variety of continuous regeneration systems have been proposed, and examples thereof include a system employing a catalyst including a carrier made of an inorganic oxide (e.g., zirconium oxide, vanadium oxide, or cerium oxide), and an expensive noble metal (e.g., Pt) supported on the carrier (see, for example, Patent Document 1, 2, or 3); and a continuous regeneration method involving NO 2 (see, for example, Patent Document 4).
• This continuous regeneration method requires provision, upstream of a particulate filter, of an oxidation catalyst (e.g., Pt) for oxidizing NO into NO 2 , and thus involves high cost.
• reaction involving NO 2 is affected by the ratio of NO x to C, and many restrictions are imposed on the employment of this method.
• Patent Document 1 Japanese Patent Application Laid-Open (kokai) No. H10-047035
• Patent Document 2 Japanese Patent Application Laid-Open (kokai) No. 2003-334443
• Patent Document 3 Japanese Patent Application Laid-Open (kokai) No. 2004-058013
• Patent Document 4 Japanese Patent No. 3012249
• An object of the present invention is to provide a particulate combustion catalyst which exhibits excellent heat resistance, which realizes removal of soot through oxidation at low temperature without employment of an expensive noble metal, and which enables oxidation reaction to proceed with the aid of only oxygen and thus realizes removal of soot through oxidation at low temperature regardless of the NO x concentration of exhaust gas.
• Another object of the present invention is to provide a particulate filter coated with the particulate combustion catalyst.
• Yet another object of the present invention is to provide an exhaust gas cleaning apparatus comprising the particulate filter coated with the particulate combustion catalyst.
• the present inventors have conducted extensive studies, and as a result have found that the objects can be achieved by employing, as a carrier of a particulate combustion catalyst, a specific oxide or a composite oxide having a specific composition; supporting, on the carrier, an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr; and supporting, on the carrier, metallic Ag or Ag oxide, which serves as a catalyst component.
• a specific oxide or a composite oxide having a specific composition supporting, on the carrier, an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr
• metallic Ag or Ag oxide which serves as a catalyst component.
• the present invention provides a particulate combustion catalyst characterized by comprising a carrier formed of zirconium oxide; an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr, the metal oxide being supported on the carrier in an amount, as reduced to metal, of 0.5 to 30 mass % with respect to the carrier; and metallic Ag or Ag oxide, which serves as a catalyst component and is supported on the carrier.
• the present invention also provides a particulate combustion catalyst characterized by comprising a carrier formed of a zirconium-cerium composite oxide; an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr, the metal oxide being supported on the carrier in an amount, as reduced to metal, of 0.5 to 30 mass % with respect to the carrier; and metallic Ag or Ag oxide, which serves as a catalyst component and is supported on the carrier.
• the present invention also provides a particulate combustion catalyst characterized by comprising a carrier formed of a composite oxide containing zirconium, cerium, and at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr; an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr, the metal oxide being supported on the carrier in an amount, as reduced to metal, of 0.5 to 30 mass % with respect to the carrier; and metallic Ag or Ag oxide, which serves as a catalyst component and is supported on the carrier.
• the present invention also provides a particulate filter characterized by being coated with any of the aforementioned particulate combustion catalysts.
• the present invention also provides an exhaust gas cleaning apparatus characterized by comprising a particulate filter coated with any of the aforementioned particulate combustion catalysts.
• the particulate combustion catalyst of the present invention exhibits excellent heat resistance. Employment of the particulate combustion catalyst of the present invention realizes removal of soot through oxidation at low temperature without use of an expensive noble metal. When the particulate combustion catalyst is employed, since oxidation reaction proceeds with the aid of only oxygen, soot can be removed through oxidation at low temperature regardless of the NO x concentration of exhaust gas. Even when a catalyst system including the particulate combustion catalyst is exposed to a high-temperature atmosphere for a long period of time, degradation of the system can be suppressed.
• the particulate combustion catalyst of the present invention employs a carrier formed of zirconium oxide, a carrier formed of a zirconium-cerium composite oxide, or a carrier formed of a composite oxide containing zirconium, cerium, and at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr.
• a catalyst including a carrier formed of a zirconium-cerium composite oxide tends to be higher in performance than a catalyst including a carrier formed of zirconium oxide, and a catalyst including a carrier formed of a composite oxide containing zirconium, cerium, and at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr tends to be higher in performance than a catalyst including a carrier formed of a zirconium-cerium composite oxide.
• the cerium oxide content of the composite oxide is preferably 5 to 50 mass %.
• the specific surface area of the carrier is reduced at a high temperature (e.g., 700° C. or higher), which may eventually cause thermal degradation of the catalyst.
• a high temperature e.g. 700° C. or higher
• an active species may fail to sufficiently exert its performance.
• the carrier exhibits poor heat resistance, which may eventually cause thermal degradation of the catalyst.
• the particulate combustion catalyst of the present invention employs, as a carrier, a composite oxide containing zirconium, cerium, and at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr
• the carrier contains an oxide of at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr
• the carrier exhibits improved thermal stability, and oxidation property at low temperature is improved.
• the amount of an oxide of at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr is preferably 1 mass % or more.
• the amount of an oxide of at least one metal selected from among Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn, and Sr is 1 to 35 mass % (i.e., when two or more metal oxides are employed, the total amount of the oxides is 1 to 35 mass %), and the cerium oxide content is 5 to 50 mass % (zirconium oxide content: balance).
• an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr must be supported on any of the aforementioned carriers.
• a conventionally known technique e.g., the impregnation method or the sol-gel method
• the resultant particulate combustion catalyst exhibits improved heat resistance.
• the amount (as reduced to metal) of an oxide of at least one metal selected from among Ba, Ca, Mg, and Sr is preferably 0.5 mass % or more with respect to the carrier.
• the amount (as reduced to metal) of such a metal oxide exceeds 30 mass % with respect to the carrier, accordingly, the relative amounts of zirconium oxide and cerium oxide are reduced, and characteristics of the carrier containing the zirconium-cerium composite oxide tend to be deteriorated. Therefore, preferably, the amount (as recued to metal) of an oxide of at least one metal selected from among Ba, Ca, Mg, and Sr is 0.5 to 30 mass % (i.e., when two or more metal oxides are employed, the total amount (as recued to metal) of the oxides is 0.5 to 30 mass %) with respect to the carrier (i.e., 0.5 to 30 parts by mass on the basis of 100 parts by mass of the carrier).
• metallic Ag or Ag oxide must be supported, as a catalyst component, on the carrier.
• a conventionally known technique e.g., the impregnation method or the sol-gel method
• Metallic Ag or Ag oxide which is employed in the present invention, is less expensive than, for example, Pt or Pd.
• metallic Ag or Ag oxide is employed in combination with a specific carrier used in the present invention, further excellent effects are obtained, as compared with the case where a Pt or Pd component is employed.
• the amount (as reduced to metal) of metallic Ag or Ag oxide supported on the carrier is 0.1 to 25 mass % on the basis of the total mass of the carrier and an oxide of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr.
• the amount of the catalyst component is less than 0.1 mass %, the catalyst component may fail to sufficiently exhibit its catalytic effects, whereas when the amount of the catalyst component exceeds 25 mass %, a specific combination employed in the present invention may fail to sufficiently exhibit a synergistic effect. Meanwhile, when the amount of the catalyst component is large, sintering of metal is likely to occur, and the catalyst component is not expected to exhibit its catalytic effects.
• the particulate filter of the present invention is produced by causing the particulate combustion catalyst of the present invention to be held on a base, preferably, the surface of the carrier is provided with a binder component such as SiO 2 , TiO 2 , ZrO 2 , or Al 2 O 3 .
• a binder component such as SiO 2 , TiO 2 , ZrO 2 , or Al 2 O 3 .
• the particulate filter of the present invention may assume any known form of particulate filter, but preferably has a three-dimensional structure.
• filters having a three-dimensional structure include a wall-through filter, a flow-through honeycomb filter, a wire mesh filter, a ceramic fiber filter, a metallic porous filter, a particle-charged filter, and a foam filter.
• the material of the base include ceramic materials such as cordierite and SiC; Fe—Cr—Al alloys; and stainless steel alloys.
• the exhaust gas cleaning apparatus of the present invention which includes therein the aforementioned particulate filter of the present invention, will be readily appreciated by those skilled in the art.
• any of the aforementioned types of carriers is mixed with a binder component (e.g., SiO 2 or alumina sol) and water, and the resultant mixture is finely milled by means of a milling apparatus (e.g., a ball mill).
• a particulate filter e.g., a wire mesh filter
• the slurry-coated filter is fired at a temperature of about 500° C. to about 700° C.
• the thus-formed wash-coating layer is impregnated with, for example, a nitrate of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr, and then drying and firing are carried out.
• the resultant product is impregnated with, for example, silver nitrate serving as a catalyst component, and then drying and firing are carried out.
• the wash-coating layer may be impregnated with, for example, a nitrate of at least one metal selected from the group consisting of Ba, Ca, Mg, and Sr, together with, for example, silver nitrate, followed by drying and firing.
• the total catalyst coating amount is preferably 10 to 100 g/L (for a wall-flow particulate filter) or about 50 to about 150 g/L (for a wire mesh particulate filter).
• the composite-oxide-coated filter was impregnated with an aqueous magnesium nitrate solution having a specific concentration and an aqueous silver nitrate solution having a specific concentration.
• the resultant product was dried at 120° C. for three hours, and then finally fired in air at 500° C. for one hour.
• the finally formed filter was found to have an Ag content of 5 g/L and an Mg content of 1 g/L.
• the Ag content as determined on the basis of the total mass of the aforementioned composite oxide and magnesium oxide was 12 mass %, and the Mg content as determined on the basis of the mass of the aforementioned composite oxide was 2.5 mass %.
• Example 2 The procedure of Example 1 was repeated, except that the aqueous magnesium nitrate solution was replaced with an aqueous calcium nitrate solution.
• the finally formed filter was found to have an Ag content of 5 g/L and a Ca content of 1 g/L.
• the Ag content as determined on the basis of the total mass of the aforementioned composite oxide and calcium oxide was 12.1 mass %, and the Ca content as determined on the basis of the mass of the aforementioned composite oxide was 2.5 mass %.
• Example 2 The procedure of Example 1 was repeated, except that the aqueous magnesium nitrate solution was replaced with an aqueous barium nitrate solution.
• the finally formed filter was found to have an Ag content of 5 g/L and a Ba content of 1 g/L.
• the Ag content as determined on the basis of the total mass of the aforementioned composite oxide and barium oxide was 12.2 mass %, and the Ba content as determined on the basis of the mass of the aforementioned composite oxide was 2.5 mass %.
• Example 2 The procedure of Example 1 was repeated, except that the aqueous magnesium nitrate solution was replaced with an aqueous strontium nitrate solution.
• the finally formed filter was found to have an Ag content of 5 g/L and an Sr content of 1 g/L.
• the Ag content as determined on the basis of the total mass of the aforementioned composite oxide and strontium oxide was 12.1 mass %, and the Sr content as determined on the basis of the mass of the aforementioned composite oxide was 2.5 mass %.
• Example 1 The procedure of Example 1 was repeated, except that the composite oxide of CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) was replaced with ZrO 2 , and the aqueous magnesium nitrate solution was replaced with an aqueous barium nitrate solution.
• the finally formed filter was found to have an Ag content of 5 g/L and a Ba content of 1 g/L.
• the Ag content as determined on the basis of the total mass of ZrO 2 and barium oxide was 12.2 mass %
• the Ba content as determined on the basis of the mass of ZrO 2 was 2.5 mass %.
• Example 2 The procedure of Example 1 was repeated, except that the composite oxide of CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) was replaced with a composite oxide of CeO 2 (30)ZrO 2 (70), and the aqueous magnesium nitrate solution was replaced with an aqueous barium nitrate solution.
• the finally formed filter was found to have an Ag content of 5 g/L and a Ba content of 1 g/L.
• the Ag content as determined on the basis of the total mass of the aforementioned composite oxide and barium oxide was 12.2 mass %
• the Ba content as determined on the basis of the mass of the aforementioned composite oxide was 2.5 mass %.
• the composite-oxide-coated filter was found to have a composite oxide content of 40 g/L.
• the composite-oxide-coated filter was impregnated with an aqueous barium nitrate solution having a specific concentration and an aqueous silver nitrate solution having a specific concentration.
• the resultant product was dried at 120° C. for three hours, and then finally fired in air at 500° C. for one hour.
• the finally formed filter was found to have an Ag content of 2 g/L and a Ba content of 2 g/L.
• the Ag content as determined on the basis of the total mass of the aforementioned composite oxide and barium oxide was 4.7 mass %
• the Ba content as determined on the basis of the mass of the aforementioned composite oxide was 5 mass %.
• Example 2 The procedure of Example 1 was repeated, except that the aqueous magnesium nitrate solution was not employed.
• the finally formed filter was found to have an Ag content of 5 g/L, and the Ag content as determined on the basis of the mass of the composite oxide was 12.5 mass %.
• Example 7 The procedure of Example 7 was repeated, except that the aqueous barium nitrate solution was not employed.
• the finally formed filter was found to have an Ag content of 2 g/L, and the Ag content as determined on the basis of the mass of the composite oxide was 5 mass %.
• the Tig (combustion initiation temperature) of soot corresponding to each of the catalyst-coated particulate filters produced in Examples 1 to 6 and Comparative Example 1 was measured through the following method.
• a specific amount of a dispersion prepared by dispersing carbon (Printex-V (toner carbon), product of Degussa) (20 mg) in ethyl alcohol was added dropwise to each of the catalyst-coated particulate filters produced in Examples 1 to 6 and Comparative Example 1 (25.4 mm in diameter ⁇ 60 mm in length) from above the filter, followed by drying at 100° C. for 10 minutes.
• carbon (20 mg) was deposited on one catalyst-coated particulate filter.
• the carbon-deposited filter was fixed at a center portion of a quartz-made simulated exhaust gas reaction tube.
• Table 1 shows the thus-measured Tig corresponding to the respective catalyst-coated particulate filters produced in Examples 1 to 6 and Comparative Example 1, as well as the compositions of the catalysts.
• Example 1 Ag + Mg/CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) 403° C.
• Example 2 Ag + Ca/CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) 409° C.
• Example 3 Ag + Ba/CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) 405° C.
• Example 4 Ag + Sr/CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) 417° C.
• Example 5 Ag + Ba/ZrO 2 415° C.
• Example 6 Ag + Ba/CeO 2 (30)ZrO 2 (70) 407° C. Comparative Ag/CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O 3 (4) 452° C.
• Example 1 Ag + Mg/CeO 2 (22)ZrO 2 (72)La 2 O 3 (2)Nd 2 O
• the balance point temperature of the filter was measured by use of actual exhaust gas.
• Each of the catalyst-coated particulate filters produced in Example 7 and Comparative Example 2, or each of the catalyst-coated particulate filters produced in Example 7 and Comparative Example 2 and then subjected to thermal treatment at 700° C. or 800° C. for 20 hours was placed in a stainless steel holder, and the holder was fixed in a quartz reaction tube. While a portion of exhaust gas discharged from a diesel generator engine (engine displacement: 0.2 L) (rotation speed: 3,000 rpm) was distributed to the quartz reaction tube at a flow rate of 30.8 L/min, the quartz reaction tube was heated from outside by means an electric furnace.
• the quartz reaction tube was heated in a stepwise manner at 20 degrees (° C.)/10 min.
• the difference in pressure between the inlet and the outlet of the reaction tube containing the particulate filter was measured, and the temperature at which the pressure difference is zero was determined.
• the thus-determined temperature was regarded as balance point temperature.
• Table 2 shows the balance point temperatures of the respective catalyst-coated particulate filters.
• the catalyst-coated particulate filter of Example 7 i.e., the particulate filter of the present invention
• exhibits excellent heat resistance i.e., an increase in balance point temperature is suppressed even after thermal treatment at a high temperature

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