Patent ID: 7998424

Claim:
An exhaust system for a lean-burn internal combustion engine, comprising a catalyst for oxidising carbon monoxide (CO) and hydrocarbons (HC), which catalyst comprising a flow-through substrate monolith comprising: a first platinum group metal zone of substantially uniform length containing at least one platinum group metal (PGM) supported on a surface area-increasing washcoat component, which first platinum group metal zone being defined at an upstream end by an inlet end of the substrate monolith and at a downstream end by a point less than half way along a length of the substrate monolith measured from the inlet end; a second platinum group metal zone containing at least one PGM supported on a surface area-increasing washcoat component, which second platinum group metal zone being of substantially uniform length and comprising the point half way along the substrate monolith length measured from the inlet end; and a third platinum group metal zone containing at least one PGM supported on a surface area-increasing washcoat component of substantially uniform length, which third platinum group metal zone being defined at a downstream end by an outlet end of the substrate monolith and at an upstream end by a point at most three quarters of the way along the substrate monolith length measured from the inlet end, wherein both the PGM loading in the first platinum group metal zone and the PGM loading in the third platinum group metal zone is greater than the PGM loading in the second platinum group metal zone, and wherein the first platinum group metal zone comprises a washcoat loading that is less than a washcoat loading of the third platinum group metal zone.