GENESIS OF COBALT OXIDE-INDUCED SURFACE-STRUCTURE IN PTCOX AL2O3 CATALYSTS/

Molecular approach to surface structure of the PtCox/Al2O3 (x = 0-0.67 ) samples prepared by co-impregnation with aqueous solution of H-2[PtC l6] and Co(NO3)(2) as precursors, has been investigated by means of X- ray photoelectron spectroscopy during the drying-calcination-reduction sequence of preparation. Ion exchange between the chloride ligands an d oxygen ions during calcination in oxygen of the samples containing c onstant loading of Pt and increasing amount of Co, was induced by coba lt oxide at high cobalt content. Simultaneously, CoO was anchored to a lumina surface, whereby, after subsequent reduction, a novel CoO-modif ied-support interface was developed and metallic platinum and intermet allic Pt-Co species were formed. As a result, the estimated dispersion of Pt, D-Pt passed through a shallow minimum over the various composi tion. Similar trend was observed for the reaction rate in the CO hydro genation suggesting that the catalytic activity of the PtCox/Al2O3 sam ples is related to platinum, while product selectivity is primarily co ntrolled in a complex manner by the platinum particles on the CoO-modi fied support. The present work represented how molecular approach in t he genesis of a bimetallic catalyst helps in understanding the mechani sm of the catalytic reaction.