Exhaust purification system of internal combustion engine

An exhaust purification system of an internal combustion engine, the exhaust purification system comprising:

• an exhaust purification catalyst arranged in an engine exhaust passage for reacting NOx contained in exhaust gas and reformed hydrocarbons to produce a reducing intermediate containing nitrogen and hydrocarbons;
• a precious metal catalyst carried on an exhaust gas flow surface of the exhaust purification catalyst;
• a basic exhaust gas flow surface part formed around the precious metal catalyst;
• and
• an electronic control unit, wherein the electronic control unit is configured to control a vibration of a concentration of hydrocarbons flowing into the exhaust purification catalyst within a predetermined range of amplitude and within a predetermined range of period, and is configured to control the vibration period of the concentration of hydrocarbons longer than the predetermined range, wherein
• when the electronic control unit controls the vibration of the concentration of hydrocarbons flowing into the exhaust purification catalyst within the predetermined range of amplitude and within the predetermined range of period, the exhaust purification catalyst has a property of producing the reducing intermediate and chemically reducing the NOx contained in the exhaust gas by a reducing action of the produced reducing intermediate, and
• when the electronic control unit controls the vibration period of the concentration of hydrocarbons longer than the predetermined range, the catalyst has a property of being increased in a storage amount of NOx that is contained in the exhaust gas and,
• at the time of engine operation, a demanded produced amount of the reducing intermediate required for chemically reducing the NOx is calculated, and the amplitude and vibration period of the concentration of hydrocarbons flowing into the exhaust purification catalyst are controlled so that an amount of production of the reducing intermediate becomes said demanded produced amount.