Modeling heterogeneous catalysts: metal clusters on planar oxide supports

Model catalysts consisting of Au and Ag clusters of varying size have been prepared on single crystal TiO₂(110) and ultra-thin films of TiO₂, SiO₂ and Al₂O₃. The morphology, electronic structure, and catalytic properties of these Au and Ag clusters have been investigated using low-energy ion scattering spectroscopy (LEIS), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) and spectroscopy (STS) with emphasis on the unique properties of clusters <5.0 nm in size. Motivating this work is the recent literature report that gold supported on TiO₂ is active for various reactions including low-temperature CO oxidation and the selective oxidation of propylene. These studies illustrate the novel and unique physical and chemical properties of nanosized supported metal clusters.