Photothermal synergisms in heterogeneous gas phase ethanol oxidation over TiO(2) and Pt/TiO(2)

Heterogeneous photocatalysis over TiO{dollar}sb2{dollar} has been the subject of intense study over the past twenty-seven years. The research has addressed the nature of TiO{dollar}sb2{dollar} surface properties, the role of electron-hole pairs generated by ultraviolet light, and the role of oxygen and organics that are adsorbed on the TiO{dollar}sb2{dollar} surface. In addition, much of the research has been driven by the potential for low or ambient temperature oxidation reactions to eliminate toxic organics from liquid or gas phase environments.; This research addresses the design of an improved heterogeneous photocatalyst for gas phase environment operation and explores the mechanisms responsible for improved activity. Improvement of TiO{dollar}sb2{dollar} photocatalysts for complete oxidation of organics to CO{dollar}sb2{dollar} and H{dollar}sb2{dollar}O is desirable, since TiO{dollar}sb2{dollar} has a high selectivity for partial oxidation products but few active sites for complete oxidation. Improved photocatalysts will allow for greater throughput of treated gas streams in more economically designed reactors. Presently, TiO{dollar}sb2{dollar} photocatalytic reactor systems are limited to designs that can treat relatively low (100 ppm) concentrations due to its low selectivity for complete oxidation and the absorption of all incident ultraviolet light ({dollar}<{dollar}385 nm) in about a 1{dollar}mu{dollar}m thick particulate film.; In these studies, a good oxidation catalyst, Pt, is coupled with TiO{dollar}sb2{dollar} by supporting nanometer size particles of Pt on TiO{dollar}sb2{dollar} and simultaneously subjecting the catalyst to thermal and photonic energy. A unique and significant synergistic effect was discovered where the activity for complete oxidation was greater than that of illuminated TiO{dollar}sb2{dollar} plus the thermal activity of Pt. The contours of this synergism were explored, and the effects of catalyst preparation were studied. The nature of the mechanism responsible for the synergism was investigated. A Schottky barrier effect was eliminated as a contributing mechanism since a physical mixture of Pt/SiO{dollar}sb2{dollar} and TiO{dollar}sb2{dollar} exhibited a similar synergistic effect. It was determined that spillover of photoactivated oxygen from TiO{dollar}sb2{dollar} to Pt and gas phase transport of intermediates produced from photo-oxidation on TiO{dollar}sb2{dollar} to Pt were the major contributing mechanisms in the synergism.