Emission control device for internal combustion engine

Abstract

A plurality of catalysts (,), (,) are disposed in an engine exhaust passage (,). At least the catalyst disposed downstream of these catalysts comprises a multi-layered catalyst (,) which is covered in a catalyst layer (,) on the surface and an HC absorbent layer (,) on an inner layer with respect to a catalyst carrier (,). A ratio of the downstream multi-layered catalyst (,) (catalyst heat capacity/catalyst surface area) is set so that it is greater than the same ratio for the upstream catalyst (,). In this way, temperature increase in the upstream catalyst (,) is advanced, the temperature gradient in the downstream catalyst (,) is increased and temperature rises in the HC absorbent layer are reduced. As a result, the HC emission period approximates the activation period of the catalyst layer (,). In this way, during low temperature vehicle operation, it is possible to synchronize the timing of HC emission by the HC absorbent layer and catalyst activation and therefore to achieve extreme reductions in HC emitted to the outside atmosphere.