Automotive catalytic aftertreatment system

A method of maintaining diesel oxidation catalyst (DOC) activity during active heat treatment of an aftertreatment device located downstream of a diesel oxidation catalyst (DOC) in a diesel engine exhaust gas aftertreatment system, at exhaust gas temperatures of 200 to 375° C., which method comprises:

• passing the exhaust gas at temperature of 200 to 375° C. over the diesel oxidation catalyst (DOC) to maintain the activity of the diesel oxidation catalyst (DOC) during active heat treatment of the aftertreatment device, wherein the diesel oxidation catalyst (DOC) has a diameter of from 4 to 15 inches and a length of from 2.5 to 10 inches and comprises (1) a catalyst composition supported on a substrate unit, wherein the catalyst composition comprises platinum, palladium and one or more support materials selected from the group consisting of alumina, silica-alumina, ceria, ceria-zirconia and titania and does not include a hydrocarbon adsorbent, which is a zeolite;
• (2) an upstream zone and (3) a remainder, wherein the upstream zone has a concentration of platinum (Pt) that is greater than the concentration of platinum (Pt) in the remainder and the upstream zone has a length from 0.5 to 1.5 inches, and is of higher oxidation activity for hydrocarbons (HC) than the remainder, the weight ratio of platinum (Pt) to palladium (Pd) in the remainder is 1:3 to 5:1.