Oxidation catalyst for internal combustion engine exhaust gas treatment

An oxidation catalyst for the oxidative treatment of a hydrocarbon (HC) and carbon monoxide (CO) in an exhaust gas, which is a catalysed substrate monolith, the oxidation catalyst comprising a supporting substrate and a plurality of catalyst layers supported on the supporting substrate, wherein the plurality of catalyst layers comprise a washcoat material, an active metal and a hydrocarbon adsorbent, and wherein one catalyst layer lies on the catalyst surface layer side and is a first washcoat coating, and one or more other catalyst layers lie on the side lower than the one catalyst layer, wherein one of the one or more other catalyst layers is a second washcoat coating;

• and wherein:
• (a) the amount of hydrocarbon adsorbent in the one catalyst layer is greater than the amount of hydrocarbon adsorbent in the one or more other catalyst layers, and the concentration of active metal in the one catalyst layer is the same as or less than the concentration of active metal in the one or more other catalyst layers;
• or
• (b) the amount of hydrocarbon adsorbent in the one catalyst layer is the same as the amount of hydrocarbon adsorbent in the one or more other catalyst layers, and the concentration of active metal in the one catalyst layer is less than the concentration of active metal in the one or more other catalyst layers;
• and
• wherein a Pt:Pd weight ratio of both the first washcoat coating and the second washcoat coating combined is ≧1:1, and wherein the supporting substrate is a substrate monolith.