| 摘要 |
A catalyst for purifying exhaust gases which aims to efficiently purify NOx in exhaust gases in oxygen-rich atmospheres whose oxygen concentrations are more than required for oxidizing CO and HC, and to attain improved NOx purifying performance after used for a long time. The catalyst comprises, being arranged in an order from the upstream to the downstream of exhaust gas flow, a first catalyst 1 in which a noble metal catalyst 12 is loaded on a porous acidic support, a second catalyst 2 in which at least one kind of metal 22 selected from the group consisting of alkali metals, alkaline-earth metals, and rare earth metals is loaded on a porous support, and a third catalyst 3 in which a noble metal catalyst 32 is loaded on a porous support. Since SO2 is not adsorbed or oxidized by the first catalyst 1, SO2 is discharged downstream from the second catalyst 2 without generating sulfate. Therefore, since the NOx absorber is free from degradation even after used for a long time, the second catalyst 2 maintains high NOx adsorbing performance on the fuel-lean side, and the third catalyst 3 reduces NOx which are emitted from the second catalyst 2 on the stoichiometric point or on the fuel-rich side.
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