COMPOSITE, ZONED OXIDATION CATALYST FOR A COMPRESSION IGNITION INTERNAL COMBUSTION ENGINE

A composite oxidation catalyst (14, 16, 18, 20) for use in an exhaust system for treating an exhaust gas produced by a vehicular heavy-duty diesel vehicle, and upstream of a particulate matter filter (44, 50) in the exhaust system comprises: a substrate (5), optionally a honeycomb flow-through substrate monolith, having a total length L and a longitudinal axis and having a substrate surface extending axially between a first substrate end (I) and a second substrate end (O); and three or more catalyst washcoat zones (1, 2, 3; or 1, 2, 3, 4) arranged axially in series on and along the substrate surface, wherein a first catalyst washcoat zone (1) having a length Li, wherein Li < L, is defined at one end by the first substrate end and at a second end by a first end (19, 21) of a second catalyst washcoat zone (2) having a length L2, wherein L2 < L, wherein the first catalyst washcoat zone (1) comprises a first refractory metal oxide support material and two or more platinum group metal components supported thereon comprising both platinum and palladium at a weight ratio of platinum to palladium of