Pd nanoparticle enhanced re-oxidation of non-stoichiometric TiO2: STM imaging of spillover and a new form of SMSI

We have used STM imaging in situ to demonstrate two fundamental steps in ca talytic processes on model catalysts at elevated temperature. We show that Pd nanoparticles on sub-stoichiometric TiO2(110) dissociatively adsorb O-2 at 673 K which "spills over" onto the support where further reaction takes place. The spillover oxygen re-oxidises the surface by removing Tin+ inters titial ions trapped in the crystal lattice, preferentially re-growing TiO2 around and over the particles. The identification of the metal enhanced re- oxidation mechanism may have important and general consequences for the und erstanding of catalysis and gas sensing.