Chapter 4 Aun and Agn (n=1–8) nanocluster catalysts: gas-phase reactivity to deposited structures

Publisher Summary This chapter helps in understanding the size-dependent chemistry of metal clusters on two fronts: by probing the reactivity of mass-selected Au n + and Ag + n nanoclusters in the gas phase, and by studying the properties of mass-selected Au + n and Ag + n nanoclusters deposited on TiO 2 surfaces under ultrahigh vacuum (UHV) conditions. Detailed results on gas-phase clusters provide important thermodynamic information, both as data for testing theoretical models and to establish structural, energetic, and reactive properties for size-selected clusters. Depositing size selected clusters provides a platform for studying model nanocluster catalysts with a well-defined size. Surface structures, binding sites, and binding energies are determined by combining atomic-resolution scanning tunneling microscopy (STM) and density functional theory (DFT). In the event that a cluster should land in the immediate vicinity of a vacancy, interaction with a vacancy can occur, resulting in the appearance of a cluster over a bridging O atom row or between 5c-Ti atom and bridging O atom rows. Interestingly, Au7 are the first truly 3-D structures (according to DFT and supported by our STM data), often containing highly uncoordinated peak atoms, perhaps responsible for their relatively high catalytic activity in comparison to other cluster sizes.