STRUCTURE AND CHEMICAL-COMPOSITION OF SURFACTANT-STABILIZED PTRU ALLOY COLLOIDS

In situ XRD has been used to study both unsupported and silica-support ed clusters PtRu[N(Oct)(4)Cl](5) (Pt:Ru approximate to 1:1). Structura l information has been gained by Debye function analysis. For the unsu pported clusters, the best fit simulation gives a 50/50 mixture of col loid particles with fcc symmetry and multiply twinned decahedral parti cles. The narrow size distribution centers around 12 Angstrom. The nea r-neighbor distance is found to be 0.9% smaller than for the bulk PtRu . XANES data provide evidence for the metallic character of the Pt com ponent. The silica-supported colloid particles oxidize rapidly in air to form an amorphous state but can be rereduced in hydrogen at room te mperature. An ''open-slit'' XRD technique was used to study the partic le growth in H-2 and He. Particles annealed to 700 degrees C in He sho w a twinned fcc symmetry with an average size of 23 Angstrom. The CO o xidation of this catalyst was studied by in situ XRD. At 280 degrees C surface oxide species are formed that slowly coalesce to RuO2 particl es. After rereduction the catalyst consists of a pure hcp ruthenium ph ase and larger alloy particles enriched in platinum.