Selective Reduction of NOx over Iridium Catalyst Supported on MFI-type Metallosilicate for Lean Burn Gasoline Engine

Shigeru NOJIMA*, Kozo IIDA and Norihisa KOBAYASHI†

Hiroshima R & D Center, Mitsubishi Heavy Industries LTD; 4-6-22 Kanonshin-machi, Nishi-ku, Hiroshima-shi 733-8553 Japan
† Power Systems Headquarters, Mitsubishi Heavy Industries LTD; 3-3-1 Minatomirai, Nishi-ku, Yokohama-shi 220-0012 Japan

Iridium catalyst supported on MFI-type metallosilicate with activation treatment in 10% H2O-N2 at 700 °C was prepared and its catalytic activity for the selective reduction of NOx with hydrocarbons under oxgen rich conditions was investigated. The primary objective is the development of a catalyst system which reduce NOx and the emission of hydrocarbons at a wide temperature range. The two stage catalysts with activated iridium catalyst and Pt-Rh/Al2 O3 (Three-way catalyst), were prepared and showed NOx reduction activity at a wide temperature range of 250−500 °C. Hydrocarbons were completely removed at higher temperatures than 300 °C. This system revealed high NOx reduction activity both a lean and stoichiometry atmosphere, and showed superior transient NOx reduction activity from lean to a stoichiometry atmosphere. The activated iridium catalyst showed a maximum NOx conversion of 70% at 400 °C in the actual exhaust gas of a lean burn gasoline engine. It is inferred that the activated iridium catalyst had sufficient NOx reduction activity and durability after aging treatment of a lean atmosphere at 660 °C and a rich atmosphere at 800 °C for a lean burn gasoline engine.


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