Patent ID: 7832203

Claim:
An exhaust system for an internal combustion engine, which system comprising: a catalysed ceramic wall flow particulate filter coated throughout with a washcoat composition, the washcoat composition comprising an oxidation catalyst comprising a platinum group metal selected from the group consisting of platinum, palladium, and a mixture thereof, and a NO x absorbent comprising a metal selected from the group consisting of an alkali metal, an alkaline earth metal, a rare earth metal, and a mixture thereof for absorbing NO x contained in an exhaust gas when the composition of the exhaust gas is lambda>1, and for releasing the NO x absorbed in the NO x absorbent when the exhaust gas composition is 1≧lambda; and a platinum group metal catalyst coated onto a substrate upstream of the ceramic wall flow particulate filter for oxidising NO to NO 2 at least when the composition of the exhaust gas is lambda>1, wherein the uncoated ceramic wall flow particulate filter has a porosity of >40% and a mean pore size of 8-25 μm and the washcoat composition has a D50 less than or equal to 8 μm.