Bimetallic Pt-Au cluster-derived catalysts for the selective catalytic reduction of NO by propylene

The selective catalytic reduction of nitric oxide by propylene in the presence of excess oxygen has been investigated over a series of silica supported Pt and Pt-Au catalysts. Cluster-derived catalysts were prepared by wet impregnation using a Pt₂Au₄(C≡C ^tBu)₈ organometallic cluster precursor, and compared to catalysts obtained by incipient wetness impregnation using individual Pt and Au salts. The addition of Au by co-impregnation resulted only to a small shift (20-25°C) in the light-off of propylene towards higher temperatures. A markedly different catalytic behavior was observed in the case of cluster-derived catalysts, where a 150°C delay was observed both in the temperature of maximum NO reduction and the light-off of propylene in the presence and in the absence of NO. Most importantly, the selectivity towards N₂ increased by 50% compared to the monometallic Pt catalysts. The results of characterization studies indicate that the monometallic Pt/SiO ₂ and the co-impregnated Pt-Au/SiO₂ samples have similar metal particle sizes. A more narrow particle size distribution was observed with the cluster-derived bimetallic sample.