Selective Reduction Mechanism of NOx with Hydrocarbons over Ir Catalyst with Activation Treatment

Shigeru NOJIMA*, Kozo IIDA, Shuji FUJII and Norihisa KOBAYASHI ††

Hiroshima R & D Center, Mitsubishi Heavy Industries LTD; 4-6-22 Kanonshin-machi, Nishi-ku, Hiroshima-shi 733-8553 Japan
Fundamental R & D Center, Mitsubishi Heavy Industries LTD; 1-8-1 Kouura, Kanagawa-ku, Yokohama-shi 236-8515 Japan
†† Power Systems Headquarters, Mitsubishi Heavy Industries LTD; 3-3-1 Minatomirai, Nishi-ku, Yokohama-shi 220-0012 Japan

Among the noble metal catalysts tested in the present study, iridium catalyst supported on MFI-type metallosilicate, which had been activated in 10% H2O-N2 at 700 °C, showed the highest catalytic activity for the selective reduction of NOx with hydrocarbon under oxygen rich condition. The conversion of NO into N2 on the activated iridium catalysts was not affected by the presence of water vapor. The characterization by XRD, XPS and TEM revealed that the agglomerated Ir metal was formed in the iridium catalysts showing the high NOx reduction activity. From FT-IR and TPD measurements, -NO2 or -ONO, and -CO formed on catalyst surface in NO+C3H6+O2 reaction were found to be intermediates of the selective reduction of NOxDOn the basis of these results, it is inferred that the high NOx reduction activity of the activated iridium catalyst resulted from the presence of the active oxygen species on activated iridium catalyst which might react with NO and hydrocarbons to form reactive oxygenated intermediates.

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