| abstract |
A catalysed filter for filtering particulate matter from exhaust gas comprising one or more catalyst poisons and emitted from a positive ignition internal combustion engine, which filter comprising a porous substrate having a total substrate length and having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure containing pores of a first mean pore size, wherein the porous substrate is coated with a washcoat comprising a plurality of solid particles, wherein the porous structure of the washcoated porous substrate contains pores of a second mean pore size, wherein the second mean pore size is less than the first mean pore size, which washcoat being axially arranged on the porous substrate as a first zone comprising the inlet surfaces of a first substrate length less than the total substrate length and a second zone comprising the outlet surfaces of a second substrate length less than the total substrate length, wherein the sum of the substrate length in the first zone and the substrate length in the second zoneā§100%, wherein the washcoat of at least the second zone is a three-way catalyst washcoat comprising one or more precious metal supported on a high surface area oxide, and an oxygen storage component and wherein:n (i) a specific surface area of washcoat in the first zone>second zone; or (ii) both a washcoat loading and a specific surface area of washcoat in the first zone>second zone. |