Catalyst article and the use thereof for filtering fine particles

1. A catalyst article for treating an exhaust gas from a positive-ignition internal-combustion engine, the article comprising:

a substrate which is a wall-flow filter having an inlet end and an outlet end and an axial length L therebetween, a plurality of inlet channels extending from the inlet end and a plurality of outlet channels extending from the outlet end,

wherein the plurality of inlet channels comprise a first catalyst composition extending from the inlet or outlet end for at least 50% of L and the plurality of outlet channels comprise a second catalyst composition extending from the outlet or inlet end for at least 50% of L, wherein the first and second catalyst compositions overlap by at most 80% of L, and

wherein the first and second catalyst compositions each independently comprise a particulate oxygen storage component (OSC) having a first D90 and a particulate inorganic oxide having a second D90 and:

i) the first D90 is less than 1 micron and the second D90 is from 1 to 20 microns; or

ii) the second D90 is less than 1 micron and the first D90 is from 1 to 20 microns.

2. The catalyst article according to claim 1 , wherein the particulate OSC has a first D10and the particulate inorganic oxide has a second D10, wherein:

i) when the first D90 is less than 1 micron and the second D90 is from 1 to 20 microns, the first D10 is at least 100 nm and the second D10 is at least 500 nm; or

ii) when the second D90 is less than 1 micron and the first D90 is from 1 to 20 microns, the second D10 is at least 100 nm and the first D10 is at least 500 nm.

3. The catalyst article according to claim 1 , wherein:

i) the first D90 is less than 1 micron and the second D90 is from 5 to 20 microns, or ii) the second D90 is less than 1 micron and the first D90 is from 5 to 20 microns.

4. The catalyst article according to any of claim 1 , wherein the first and second catalyst compositions overlap by at most 20% of L.

5. The catalyst article according to claim 1 , wherein the particulate OSC is selected from the group consisting of cerium oxide, zirconium oxide, a ceria-zirconia mixed oxide, and an alumina-ceria-zirconia mixed oxide.

6. The catalyst article of claim 1 , wherein particulate inorganic oxide is selected from the group consisting of alumina, magnesia, silica, lanthanum, neodymium, praseodymium, yttrium oxides, and mixed oxides or composite oxides thereof.

7. The catalyst article of claim 1 , wherein the first and/or second catalyst composition further comprises a first platinum group metal (PGM) component selected from the group consisting of platinum, palladium, rhodium, and a mixture thereof.

8. The catalyst article of claim 1 , wherein the first and/or second catalyst composition further comprises barium or strontium.

9. The catalyst article according to claim 1 , wherein the first and second catalyst compositions are the same.

10. The catalyst article according to claim 1 , wherein the first and/or second catalyst composition have a ratio by weight of the particulate OSC to the particulate inorganic oxide of from 3:1 to 1:3.

11. The catalyst article of claim 1 , wherein the first and/or second catalyst compositions are provided directly on the substrate.

12. An exhaust gas treatment system comprising the catalyst article according to claim 1 in fluid communication with an exhaust manifold of a positive ignition engine.

13. A method of treating exhaust gas emitted from a positive ignition internal combustion engine, the method comprising contacting the exhaust gas with the catalyst article of claim 1 .

14. Use of the catalyst article according to claim 1 in an exhaust gas treatment system for reducing the emission of particles smaller than 23 nm.

15. The use according to claim 14 , wherein the use reduces the emission of particles smaller than 23 nm by at least 20% by number.