Composite, zone-coated, dual-use ammonia (AMOX) and nitric oxide oxidation catalyst

An exhaust system for a vehicular compression ignition engine for treating an exhaust gas comprising inter alia oxides of nitrogen (NOx), the exhaust system comprising:

• a composite oxidation catalyst comprising
• an oxidation catalyst substrate having a total length L and a longitudinal axis and having an oxidation catalyst substrate surface extending axially between a first oxidation catalyst substrate end and a second oxidation catalyst substrate end;
• two or more catalyst washcoat zones comprised of a first catalyst washcoat layer comprising a refractory metal oxide support material and one or more platinum group metal components supported thereon and a second catalyst washcoat layer different from the first catalyst washcoat layer and comprising a refractory metal oxide support material and one or more platinum group metal components supported thereon, which two or more catalyst washcoat zones being arranged axially in series on and along the oxidation catalyst substrate surface, wherein a first catalyst washcoat zone having a length L1, wherein L1<L, is defined at one end by the first oxidation catalyst 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 one or more platinum group metal components supported thereon;
• and the second catalyst washcoat zone comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon;
• and
• a washcoat overlayer extending axially from the first oxidation catalyst substrate end for up to 200% of the axial length of the underlying first catalyst washcoat layer, which washcoat overlayer comprising a particulate metal oxide loading of >48.8 g/l (>0.8g/in3), wherein the particulate metal oxide is an aluminosilicate zeolite including at least one of copper, iron and manganese, 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 different from the total platinum group metal loading in the second catalyst washcoat zone;
• a first injector for a nitrogenous reductant or a precursor thereof connected to a source of nitrogenous reductant or nitrogenous reductant precursor, which first injector being arranged to inject the nitrogenous reductant or nitrogenous reductant precursor into a flowing exhaust gas upstream from the composite oxidation catalyst;
• and,
• a selective catalytic reduction catalyst substrate comprising a selective catalytic reduction catalyst disposed between the first injector for a nitrogenous reductant or a precursor thereof and the composite oxidation catalyst,
• wherein the first oxidation catalyst substrate end of the composite oxidation catalyst is oriented to an upstream side.