POSITIVE IGNITION ENGINE AND EXHAUST SYSTEM COMPRISING CATALYSED ZONE-COATED FILTER SUBSTRATE

A catalyzed filter for filtering particulate matter from exhaust gas emitted from a positive ignition internal combustion engine comprises a ceramic porous wall-flow filter substrate having a total substrate length and having inlet channels defined in part by ceramic inlet wall surfaces and outlet channels defined in part by ceramic outlet wall surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a first porous structure containing pores of a first mean pore size, wherein the porous substrate is coated in part with a catalyst washcoat composition, wherein a second porous structure of a washcoated part of the 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 catalyst washcoat composition being disposed in a first zone comprising the inlet surfaces of a first substrate length less than the total substrate length, wherein a second zone comprising the outlet surfaces of a second substrate length contains no washcoat and wherein the sum of the substrate length in the first zone and the substrate length in the second zone is >100%.