Exhaust gas purification device for an internal combustion engine

Abstract

In an exhaust gas purification device, a catalytic converter containing selective reduction catalysts is disposed in an exhaust gas passage of an internal combustion engine capable of being operated at a lean air-fuel ratio. The catalytic converter includes a plurality of the selective reduction catalysts disposed in series in the casing of the catalytic converter. Bypass passages which supply the exhaust gas to downstream selective reduction catalysts in the casing by bypassing the upstream catalysts are provided. When a reducing agent is supplied to the exhaust gas upstream of the converter, a part of the supplied reducing agent directly reaches the downstream selective reduction catalyst through the bypass passages without being oxidized by the upstream selective reduction catalysts. Therefore, the NO,purifying abilities of the downstream catalysts are improved and the formation of sulfates on the downstream catalysts is suppressed.