PREPARATION AND CHARACTERIZATION OF SUPPORTED PT-RU BIMETALLIC CLUSTERS - STRONG PRECURSOR SUPPORT INTERACTIONS

Highly dispersed PtRu bimetallic particles supported on silica were prepared from Pt(NH3)4(NO3)2 and Ru(NH3)6Cl3 precursors. Diffuse UV reflectance studies show that decomposition does not occur upon adsorption. Pretreatment of the pure metal precursors show that a sequential oxygen-hydrogen treatment leads to poor Ru dispersions but high Pt dispersions. Pretreatment in hydrogen leads to high Ru dispersions (∼70%) but rather poor Pt dispersion (∼40%). These observations are discussed by invoking a mobile Pt surface phase consisting of [Pt(NH3)2(H)2]0 in the case of reduction in hydrogen and the formation of RuO2 under O2 pretreatment. Individual particle analyses were performed using analytical electron microscopy. The small bimetallic particles prepared by coimpregnation were Ru rich while the larger particles were rich in Pt. All of the bimetallic particles analyzed were shown to be bimetallic. The sequential impregnation of Pt/SiO2 with Ru(NH3)6Cl3 resulted in the formation of segregated Pt and Ru metal phases. Pretreatment of the surface phases in oxygen prior to reduction also led to separate Pt and Ru metal phases. It was concluded that a requirement for the formation of bimetallic particles is that at least one of the surface phases should be mobile with respect to the other. © 1990.