| abstract |
(57) [Summary] The exhaust manifold (7) of the internal combustion engine (1) is connected to the three-way catalyst (8a), and the three-way catalyst (8a) is connected to the NH 3 deposition oxidation catalyst (10a). The engine (1) repeatedly performs the lean operation and the rich operation alternately. When the engine (1) performs the rich operation and the exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalyst (8a) is made rich, the three-way catalyst (8a) converts NO X in the exhaust gas into NH 3 . This NH 3 is then adsorbed on the NH 3 adsorption oxidation catalyst (10a). Next, when the engine (1) performs a lean operation and the exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalyst (8a) is made lean, the NO X in the exhaust passes through the three-way catalyst (8a), and NH 3 The adsorption oxidation catalyst (10a) is reached. At this time, the adsorbed NH 3 is desorbed from the NH 3 -adsorbing oxidation catalyst (10a), and NO X is reduced by the NH 3 . |