Synthesis and characterization of bimetallic platinum-gold catalysts

Supported bimetallic Pt-Au catalysts were prepared by wet impregnation using Pt2Au4(C≡CtBu)g and [Pt3Au(mu2-CO)3(PPh3) 5]NO3 bimetallic cluster precursors. The activities of these catalysts for the selective catalytic reduction of nitric oxide by propylene and the 16O/18O exchange reaction were investigated and were compared to those of catalysts of identical compositions obtained by incipient wetness impregnation from individual Pt and Au salt precursors. In addition, several characterization techniques, including FT-IR of adsorbed 12CO/13CO mixtures, H2 chemisorption, and transmission electron microscopy were employed to examine the catalysts before and after exposure to reaction conditions.; The kinetic results indicate that the addition of Au by co-impregnation results to only small differences in the behavior of the monometallic Pt catalysts. In contrast, significant differences are observed when the cluster route is used for the preparation of the bimetallic systems. In these cases, the presence of Au delays the oxidation of propylene, increases the selectivity towards N2 during HC-SCR, and inhibits the ability of Pt to activate oxygen during the 16O/18O exchange reaction. Results from the characterization studies indicate the presence of primarily segregated Pt and Au phases in the catalysts obtained by incipient wetness impregnation from individual Pt and Au salt precursors. The same results further suggest that the use of the organo-metallic cluster precursor results to the formation of intimately mixed Pt and Au in the form of small nanoparticles.