| abstract |
A hydrocarbon supply 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) includes an upstream-side catalyst (14a) and a downstream-side catalyst (14b) arranged in series. The upstream-side catalyst (14a) is made of a three-way catalyst having oxygen storage capability. Precious-metal catalysts (55, 56) are loaded on the exhaust-gas circulation surface of the downstream-side catalyst (14b), and basic, exhaust-gas circulation surface sections (58) are formed around the precious-metal catalysts (55, 56). The concentration of hydrocarbons that flow into the upstream-side catalyst (14a) is made to oscillate with an amplitude within a predetermined range of 200 ppm or greater and a period within a predetermined range of 5 seconds or less. Thus, NO x contained in the exhaust gas is subjected to reduction by the exhaust-gas purifying catalyst (13). |