Diesel oxidation catalyst and exhaust system

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

• a first washcoat zone for oxidizing carbon monoxide (CO) and hydrocarbons (HCs), which comprises platinum (Pt) and manganese (Mn) disposed or supported on a first support material, wherein the first support material comprises a refractory oxide comprising silica-alumina or alumina doped with silica;
• a second washcoat zone for oxidizing nitric oxide (NO) to nitrogen dioxide (NO2), which comprises a platinum group metal (PGM), and manganese (Mn) disposed or supported on a second support material, wherein the second support material comprises a refractory oxide comprising alumina, and the platinum group metal (PGM) is selected from the group consisting of (i) platinum and (ii) a combination of platinum and palladium in a ratio of platinum to palladium by total weight of ≥2:1, and the second washcoat zone is substantially free of a zeolite;
• and
• a flow-through substrate monolith or a filtering substrate monolith having a length defined by an inlet end and an outlet end;
• wherein the first washcoat zone is compositionally different from the second washcoat zone, and wherein the second washcoat zone is disposed at an outlet end of the substrate monolith, and the first washcoat zone is disposed at an inlet end of the substrate monolith and wherein the first washcoat zone has a length of 10 to 90% of the length of the substrate monolith.