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 region for oxidising carbon monoxide (CO) and hydrocarbons (HCs), wherein the first washcoat region comprises a first platinum group metal (PGM) and a first support material, and wherein the first washcoat region does not comprise manganese or an oxide thereof;
• a second washcoat region for oxidising nitric oxide (NO), wherein the second washcoat region comprises platinum (Pt), manganese (Mn) and a second support material comprising a refractory metal oxide, which is an alumina doped with silica in a total amount of 0.5 to 45% by weight of the alumina, wherein the platinum (Pt) is disposed or supported on the second support material and the manganese (Mn) is disposed or supported on the second support material;
• a third washcoat region comprising a zeolite catalyst, wherein the zeolite catalyst comprises Pd, a zeolite and optionally a base metal;
• a substrate having an inlet end and an outlet end, and
• wherein the first washcoat region is a first washcoat layer and the second washcoat region is a second washcoat layer, and the second washcoat layer is disposed on the first washcoat layer;
• wherein the third washcoat region is disclosed directly on to the substrate;
• and
• wherein the first washcoat region further comprises a hydrocarbon adsorbent which is a zeolite.