Genesis of cobalt oxide-induced surface structure in PtCoxAl2O3 catalysts

Molecular approach to surface structure of the PtCoxAl2O3 (x = 0–0.67) samples prepared by co-impregnation with aqueous solution of H2[PtCl6] 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 and oxygen ions during calcination in oxygen of the samples containing constant loading of Pt and increasing amount of Co, was induced by cobalt oxide at high cobalt content. Simultaneously, CoO was anchored to alumina surface, whereby, after subsequent reduction, a novel CoO-modified-support interface was developed and metallic platinum and intermetallic PtCo species were formed. As a result, the estimated dispersion of Pt, DPt passed through a shallow minimum over the various composition. Similar trend was observed for the reaction rate in the CO hydrogenation suggesting that the catalytic activity of the PtCoxAl2O3 samples is related to platinum, while product selectivity is primarily controlled in a complex manner by the platinum particles on the CoO-modified support. The present work represented how molecular approach in the genesis of a bimetallic catalyst helps in understanding the mechanism of the catalytic reaction.