Exhaust gas purification device for internal combustion engine

Abstract

The invention relates to an exhaust control device of an engine () comprising a catalyst () in an exhaust passage (). In this invention, the active element transforms as a solid solution in the carrier when a catalyst temperature is higher than or equal to a predetermined solid solution temperature and an atmosphere in the catalyst is an oxidation atmosphere and the active element precipitates from the carrier when the catalyst temperature is higher than or equal to a predetermined precipitation temperature and the atmosphere in the catalyst is a reduction atmosphere. According to this invention, an air-fuel ratio of an exhaust gas flowing into the catalyst is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio when the active element solid solution degree is smaller than a target solid solution or a lower limit of a target solid solution degree range and the catalyst temperature is higher than or equal to the predetermined solid solution temperature, and the air-fuel ratio of the exhaust gas flowing into the catalyst is controlled to an air-fuel ratio richer than the stoichiometric air-fuel ratio when the active element solid solution degree is larger than the target solid solution degree or an upper limit of the target solid solution degree range and the catalyst temperature is higher than or equal to the predetermined precipitation temperature.