Patent ID: 6345496
Filing Date: 2002-02-12
Classification: B01D,F01N,F02B,F02D,Y02T

Abstract:
The method for purifying an exhaust gas of an engine, the method comprising the steps of:alternately and repeatedly controlling an exhaust gas air-fuel ratio between a lean exhaust gas air-fuel ratio and a rich exhaust gas air-fuel ratio; and introducing the exhaust gas to an NH3 synthesizing catalyst, the NH3 synthesizing catalyst being arranged in series with a NOx occluding and reducing (NOx-OR) catalyst in a common exhaust passage, the NH3 synthesizing catalyst synthesizing NH3 from NOx in the NH3 synthesizing catalyst when the exhaust gas air-fuel ratio is rich, and synthesizing almost no NH3 from NOx in the NH3 synthesizing catalyst when the exhaust gas air-fuel ratio is lean and wherein, when the exhaust gas air-fuel ratio is lean, the NOx-OR catalyst occludes NOx therein, and when the exhaust gas air-fuel ratio is rich, the NOR-OR catalyst releases the occluded NOx therefrom and reduces the NOx.