| 摘要 |
PURPOSE: To provide a device by which NOx in an exhaust gas discharged when the fuel-air ratio is deviated to the lean side can particularly efficiently be removed. CONSTITUTION: In this device, a lean NOx catalyst (B) obtained by depositing a catalytic noble metal and an NOx occlusion material on a porous carrier is disposed on the upstream side of an exhaust gas passage and a three dimensional catalyst (A) obtained by depositing a catalytic noble metal on a porous carrier is disposed on the downstream side of the exhaust gas passage. NO in the exhaust gas is allowed to react with a large amount of oxygen in the exhaust gas on the lean NOx catalyst (B) on the upstream side of the exhaust gas passage to convert NO into NO2 , which is then occluded in the NOx occlusion material. At this time, the larger the amount of oxygen, the more easily the oxidation reaction of NO is effected and even when the fuel-air ratio is greatly deviated to the lean side in a transition region, the reaction is satisfactorily effected. When the fuel-air ratio is on the rich side, NOx occluded in the NOx occlusion material is released, and then, reduced and removed not only on the lean NOx catalyst (B) but also on the three dimensional catalyst (A). |
