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 catalytic processes on model catalysts at elevated temperature. We show that Pd nanoparticles on sub-stoichiometric TiO₂(110) dissociatively adsorb O₂ at 673 K which spills over onto the support where further reaction takes place. The spillover oxygen re-oxidises the surface by removing Tiⁿ⁺ interstitial 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 understanding of catalysis and gas sensing.