US 6,345,496 B1 · Method and device for purifying exhaust gas of an engine

Abstract

An exhaust manifold (7) of an engine (1) is connected to a three way (TW) catalyst (8a), and the TW catalyst (8a) is connected to an NH3 adsorbing and oxidizing (NH3-AO) catalyst (10a). The engine (1) performs the lean and the rich engine operations alternately and repeatedly. When the engine (1) performs the rich operation and thereby the exhaust gas air-fuel ratio of the exhaust gas flowing into the TW catalyst (8a) is made rich, NOx in the inflowing exhaust gas is converted to NH3 in the TW catalyst (8a). The NH3 is then adsorbed in the NH3-AO catalyst (10a). Next, when the engine (1) performs the lean operation and thereby the exhaust gas air-fuel ratio of the exhaust gas flowing into the TW catalyst (8a) is made lean, NOx in the exhausted gas passes through the TW catalyst (8a), and flows into the NH3-AO catalyst (10a). At this time, NH3 adsorbed in the catalyst (10a) is desorbed therefrom, and reduces the inflowing NOx.

Claims124

Dependent claims

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.

The device for purifying an exhaust gas of an engine having an exhaust passage, comprising:

exhaust gas air-fuel ratio controlling means arranged in one of the engine and the exhaust passage for 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;
an NH3 synthesizing catalyst arranged in the exhaust passage downstream of the exhaust gas air-fuel ratio controlling means, 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
a NOx occluding and reducing (NOx-OR) catalyst arranged in the exhaust passage downstream of the NH3 synthesizing catalyst, the NOx-OR catalyst occluding NOx in the exhaust gas therein when the exhaust gas air-fuel ratio is lean, and releasing the occluded NOx therefrom and reducing the NOx when the exhaust gas air-fuel ratio is rich.

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