Diesel oxidation catalyst and exhaust system

An oxidation catalyst for treating an exhaust gas from a diesel engine, which oxidation catalyst comprises:

• a first washcoat zone for oxidising carbon monoxide (CO) and hydrocarbons (HCs), wherein the first washcoat zone comprises a first platinum group metal (PGM), which is a combination of platinum and palladium, a first support material and a hydrocarbon adsorbent material, which is a zeolite, and wherein the first washcoat zone does not comprise rhodium and is substantially free of manganese or an oxide thereof;
• a second washcoat zone for oxidising nitric oxide (NO), wherein the second washcoat zone comprises platinum (Pt) and manganese (Mn) disposed or supported on a second support material, wherein the second support material comprises a refractory metal oxide, wherein the refractory metal oxide is silica-alumina or alumina doped with silica, and wherein the second washcoat zone does not comprise a hydrocarbon adsorbent material, which is a zeolite;
• and
• a substrate having an inlet end and an outlet end, and
• wherein the second washcoat zone is disposed at an outlet end of the substrate, and the first washcoat zone is disposed at an inlet end of the substrate, wherein the first washcoat zone has a length of 10 to 45% of the length of the substrate or the second washcoat zone has a length of 10 to 45% of the length of the substrate and the first washcoat zone comprises a total amount of hydrocarbon adsorbent, which is a zeolite, of 0.2 to 3.00 g in−3.