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 effective for NOx storage, which comprises a first platinum group metal (PGM), a first support material and a NOx storage component, wherein the first platinum group metal (PGM) is selected from platinum, palladium, a combination of platinum and palladium, a combination of platinum and rhodium, a combination of palladium and rhodium, and a combination of platinum, palladium and rhodium;
• a second washcoat region effective for oxidizing nitric oxide (NO) to nitrogen dioxide (NO2), which comprises a platinum group metal 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 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 wherein the second washcoat region does not comprise a hydrocarbon adsorbent material, which is a zeolite;
• and
• a substrate having an inlet end and an outlet end, wherein the first washcoat region is arranged or oriented to contact exhaust gas before the second washcoat region.