Selective Reduction of NO_x over Iridium Catalyst Supportedon MFI-type Metallosilicate for Lean Burn Gasoline Engine

摘要

Iridium catalyst supported on MFI-type metallosilicate with activation treatment in 10% H_2O-N_2 at 700 deg C was prepared and its catalytic activity for the selective reduction of NO_x with hdyrocarbons under oxgen reduce NO_x and the emission of hydrocarbons at a wide temperature range. The two stage catalysts with activated iridium catalyst and Pt-Ph/Al_2O_3 (Three-way catalyst), were prepared and showed NO_x reduction activity at a wide temperature range of 250-500 deg C. Hydrocarbons were completely removed at higher temperatures than 300 deg C. This system revealed high NO_x reduction activity both a lean and stoichiometry atmosphere, and showed superior transient NO_x reduction activity from lean to a stoichiometry atmoshpere. The activated iridium catalyst showed a maximum NO_x conversion of 70% at 400 deg C in the actual exhaust gas of a lean burn gasoline engine. It is inferred that the activated iridium catalyst had sufficient NO_x reduction activity and durability after aging treatment of a lean atmosphere at 600 deg C and rich atmoshpere at 800 deg C for a lean burn gasoline engine.