EXHAUST PURIFYING SYSTEM OF AN INTERNAL COMBUSTION ENGINE

An internal combustion engine in an engine exhaust passage of which a hydrocarbon feed valve (15) and an exhaust purification catalyst (13) are arranged. On the exhaust purification catalyst (13), platinum Pt (51) is carried and a basic layer (53) is formed. A concentration of hydrocarbons flowing into the exhaust purification catalyst (13) is made so vibrate within a predetermined range of amplitude of 200 ppm or more and within a predetermined range of period of 5 seconds or less whereby NO x which is contained in the exhaust gas is reduced in the exhaust purification catalyst (13).