Activation of gold on titania:: Adsorption and reaction of SO2 on Au/TiO2(110)

Synchrotron-based high-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of gold with titania and the chemistry of SO2 on Au/TiO2-(110) surfaces. The deposition of Au nanoparticles on TiO2-(1 10) produces a system with an extraordinary ability to adsorb and dissociate SO2. In this respect, Au/TiO2 is much more chemically active than metallic gold or stoichiometric titania. On Au(111) and rough polycrystalline surfaces of gold, SO2 bonds weakly and desorbs intact at temperatures below 200 K. For the adsorption Of SO2 on TiO2(1 10) at 300 K, SO4 is the only product (SO2 + O-oxide --> SO4,ads). In contrast, Au/TiO2(1 10) surfaces (theta(Au) less than or equal to 0.5 ML) fully dissociate the SO2 molecule under identical reaction conditions. Interactions with titania electronically perturb gold, making it more chemically active. Furthermore, our experimental and theoretical results show quite clearly that not only gold is perturbed when gold and titania interact. The adsorbed gold, on its part, enhances the reactivity of titania by facilitating the migration of O vacancies from the bulk to the surface of the oxide. In general, the complex coupling of these phenomena must be taken into consideration when trying to explain the unusual chemical and catalytic activity of Au/TiO2. In many situations, the oxide support can be much more than a simple spectator.