| 摘要 |
PURPOSE:To suppress the complete oxidation of small molecule HC and improve the purification factor of NOx by forming an exhaust gas pufifying device of more than two kinds of catalytic material of three-dimensionally framed crystal structure respectively different in super-cage diameter, and also forming this device in such a way that the distribution of the catalytic material with small super-cage diameter becomes large on the specific side. CONSTITUTION:An exhaust gas purifying device 2 is formed of three lean NOx catalysts in the order of catalysts A, B, C from the upstream side in the exhaust gas flow direction. The lean NOx catalysts A, B, C are placed in such a way that the one with a small super-cage diameter is disposed on the upstream side in the exhaust gas flow direction and the ones with larger super-cage diameters are disposed in due order onto the downstream side. Since the lean NOx catalyst with the small super-cage diameter efficiently attracting small molecule HC is distributed largely on the upstream side in the exhaust gas flow direction, the small molecule HC is attracted to the catalyst on the upstream side and used for the purifiction of NOx. The complete oxidation of the small molecule HC is thus suppressed, and the purification factor of NOx can be improved. |
