Composite, zoned oxidation catalyst for a compression ignition internal combustion engine

A composite oxidation catalyst for use in an exhaust system for treating an exhaust gas produced by a vehicular compression ignition internal combustion engine, preferably fora heavy-duty diesel vehicle, and upstream of a particulate matter filter in the exhaust system, which composite oxidation catalyst comprising:

• a substrate having a total length L and a longitudinal axis and having a substrate surface extending axially between a first substrate end and a second substrate end;
• and
• four or more catalyst washcoat zones arranged axially in series on and along the substrate surface, wherein a first catalyst washcoat zone having a length L1, wherein L1<L, is defined at one end by the first substrate end and at a second end by a first end of a second catalyst washcoat zone having a length L2, wherein L2<L, wherein the first catalyst washcoat zone 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 ≥1;
• the second catalyst washcoat zone comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon;
• a third catalyst washcoat zone comprising a third refractory metal oxide support material and one or more platinum group metal components supported thereon is defined at a second end thereof by the second substrate end;
• and a fourth catalyst washcoat zone located between the second catalyst washcoat zone and the third catalyst washcoat zone, which fourth catalyst washcoat zone comprises a fourth refractory metal oxide support material and one or more platinum group metal components supported thereon and is defined at a first end thereof by a second end of the second catalyst washcoat zone and at a second end thereof by a first end of the third catalyst washcoat zone;
• wherein a total platinum group metal loading in the first catalyst washcoat zone defined in grams of platinum group metal per litre of substrate volume (g/L) is greater than a total platinum group metal loading in the second catalyst washcoat zone, wherein a total platinum group metal loading in the third catalyst washcoat zone defined in grams of platinum group metal per litre of substrate volume (g/L) is less than the total platinum group metal loading in the second catalyst washcoat zone and wherein the first catalyst washcoat zone comprises one or more first alkaline-earth metal components supported on the first refractory metal oxide support material;
• and
• wherein a total platinum group metal loading in the fourth catalyst washcoat zone defined in grams of platinum group metal per litre of substrate volume (g/L) is greater than the total platinum group metal loading in each of the second catalyst washcoat zone and the third catalyst washcoat zone.