Surface composition, morphology, and catalytic activity of model polycrystalline Titania surfaces

XPS, UPS, STM, and TPR were used to characterize the oxidation state, morphology, and catalytic behavior of polycrystalline titania films grown by in situ oxidation of Ti metal. Depending on the conditions, either fully oxidized films (similar to6 Angstrom, stoichiometric TiO2, stable to similar to473 K) or partially reduced oxide films could be produced. The morphology of these films could also be varied by varying the pretreatment of the metal substrate: either coarse-grained or nanocrystalline material could be produced. Styrene adsorbs and desorbs reversibly from the fully oxidized titania surface in the absence of water. The hydroxylated, fully oxidized surface converts styrene to acetophenone, a partial oxidation product, with 100% selectivity. The water treated, partially reduced surface converts styrene to ethylbenzene, a partial hydrogenation product, with 100% selectivity. Reaction selectivity and the switch in selectivity are determined by the oxidation state of the surface and do not depend on its morphology. The relevance of these findings to an understanding of the properties of metal/titania catalysts is discussed.