An exhaust system for a lean-burn internal combustion engine, which system comprises a catalysed substrate monolith, as a first catalysed substrate monolith, for use in treating exhaust gas emitted from the lean-burn internal combustion engine, a second catalysed substrate monolith comprising a selective catalytic reduction (SCR) catalyst, which second catalysed substrate monolith is disposed downstream from the first catalysed substrate monolith, and an injector for injecting a nitrogenous reductant into exhaust gas between the first catalysed substrate monolith and the second catalysed substrate monolith, wherein the first catalysed substrate monolith comprises: a first washcoat coating; a second washcoat coating; and a substrate monolith; wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal (PGM) and at least one support material for the at least one platinum group metal (PGM), wherein the at least one platinum group metal (PGM) in the first washcoat coating comprises platinum, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥ 700 °C; wherein the second washcoat coating comprises at least one metal oxide for trapping volatilised platinum group metal (PGM) and a catalyst composition comprising at least one metal selected from the group consisting of palladium, silver, gold and combinations of any two or more thereof, wherein the at least one metal oxide supports the at least one metal, and the only PGM that can be present in the second washcoat coating is palladium, and wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat coating; and wherein the substrate monolith is a filtering substrate monolith having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure. a first washcoat coating; a second washcoat coating; and a substrate monolith; wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal (PGM) and at least one support material for the at least one platinum group metal (PGM), wherein the at least one platinum group metal (PGM) in the first washcoat coating comprises platinum, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥ 700 °C; wherein the second washcoat coating comprises at least one metal oxide for trapping volatilised platinum group metal (PGM) and a catalyst composition comprising at least one metal selected from the group consisting of palladium, silver, gold and combinations of any two or more thereof, wherein the at least one metal oxide supports the at least one metal, and the only PGM that can be present in the second washcoat coating is palladium, and wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat coating; and wherein the substrate monolith is a filtering substrate monolith having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure. <EOS>