Scanning tunnelling microscopy studies of the reactivity of the TiO2(110) surface: Re-oxidation and the thermal treatment of metal nanoparticles

We have employed variable temperature scanning tunnelling microscopy (STM) to probe the surface structure of the TiO2(110) surface with clean, adsorba te and metal covered terminations. The aim of the work is to understand the nature of catalysis on supported metal oxide catalysts for which a good mo del is an admetal on a single crystal oxide surface. For Pd overlayers, ann ealing in vacuum shows the formation of metal particles with nanometer size d dimensions, which are comparable to those seen in real catalysts. The cle an TiO2(110) surface has two commonly observed terminations, the (1x1) bulk truncation, the (1x2) reduced and reconstructed surface. Less commonly, fo r very reduced crystals, the formation of ordered defects occurs leading to crystallographic shear planes. We have explored all of these surfaces by l ow energy electron diffraction (LEED) and STM to provide structural informa tion, while we have employed dynamic imaging of the surface in reactive con ditions at elevated temperature to assess the chemistry. We find that oxyge n rich atmospheres promote a re-growth of the surface that has important co nsequences for the surface chemistry and morphology. The oxidation and redu ction of the support in this system has been shown to modify the reactive p roperties of the supported metal and we relate our observations to the stro ng metal support interaction (SMSI).