CATALYTIC PROPERTIES OF LAYERED GOLD-PALLADIUM COLLOIDS

Layered bimetallic gold-palladium colloids in the size range of 20-56 nm have been synthesized by the seed-growth method: gold seeds were co vered by palladium layers of various thickness and vice versa. The out er metal was coordinated by trisulfonated triphenylphosphine and sodiu m sulfanilate ligands to stabilize the bimetallic particles to such an extent that they could be isolated in the solid state. Owing to the h ydrophilic ligand shell, redispersion in water was possible in any con centration. High-resolution transmission electron microscopy and energ y-dispersive X-ray analysis was used to characterize the colloids. Sta bilized and nonstabilized gold-palladium and palladium-gold systems on a TiO2 support were used as heterogeneous catalysts for the hydrogena tion of hex-2-yne to cis-hex-2-ene. Both the palladium-plated gold see ds and the gold-plated palladium particles showed considerably increas ed activities compared with the pure metals. The ligand shell seems no t to influence the catalytic behavior because protected and unprotecte d colloids behave very similarly.