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, the oxidation catalyst comprising a supporting substrate and a plurality of catalyst layers supported on the supporting substrate, wherein each catalyst layer in the plurality of catalyst layers comprises an active metal, a washcoat material for supporting the active metal and a zeolite hydrocarbon adsorbent, and wherein one catalyst layer lies on a catalyst surface layer side and one or more other catalyst layers lie on a side between the said one catalyst layer and the supporting substrate;

• and wherein:
• (a) the amount of zeolite hydrocarbon adsorbent in the said one catalyst layer is greater than the amount of zeolite hydrocarbon adsorbent in the said one or more other catalyst layers, and the concentration of active metal in the said one catalyst layer is the same as or less than the concentration of active metal in the said one or more other catalyst layers;
• or
• (b) the amount of zeolite hydrocarbon adsorbent in the said one catalyst layer is the same as the amount of zeolite hydrocarbon adsorbent in the said one or more other catalyst layers, and the concentration of active metal in the said one catalyst layer is less than the concentration of active metal in the said one or more other catalyst layers;
• and wherein:
• each washcoat material is selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, ceria, titania, optionally stabilised ceria-zirconia mixed oxide, a zeolite molecular sieve or a mixture of any two or more thereof;
• and
• each active metal is a base metal or a platinum group metal, wherein the base metal is copper, manganese, cobalt or zinc, and the platinum group metal is platinum, palladium or a mixture thereof;
• wherein the supporting substrate is a substrate monolith, the said one catalyst layer is a first washcoat coating and one of the said other catalyst layers is a second washcoat coating;
• and wherein the first washcoat coating comprises a catalyst composition comprising platinum and at least one support material for the platinum, and the second washcoat coating comprises a catalyst composition comprising both platinum and palladium and at least one support material for the platinum and the palladium and wherein a weight ratio of platinum to palladium in the second washcoat coating is ≤2.