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

Abstract

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 NO_x 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 NO_x 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 NO_x.On the basis of these results, it is inferred that the high NO_x 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.