EXHAUST GAS PURIFYING DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

A hydrocarbon supplying valve (15) and an exhaust gas purifying catalyst (13) are arranged in the engine exhaust gas passage of an internal combustion engine. The exhaust gas purifying catalyst (13) comprises a mixture of a first catalyst in which platinum (51) and a basic layer (52) are supported on alumina (50) and a second catalyst in which rhodium (56) is supported on zirconia (55). The concentration of hydrocarbons that flow into the exhaust gas purifying catalyst (13) is oscillated with an amplitude within a predetermined range of 200 ppm or greater and with a period within a predetermined range of 5 seconds or less. Thus, NOx contained in the exhaust gas is reduced by the exhaust gas purifying catalyst (13).