Water-Gas --Shift Reaction on Gold Nanoparticles Supported on Iron Oxide Surfaces: A Scanning Tunneling Microscopy/Spectroscopy Study

We present a Scanning Tunneling Microscopy (STM)/Scanning Tunneling Spectroscopy (STS) study of the Water-Gas-Shift reaction on a model catalyst system consisting of supported gold nanoparticles on a reduced Fe$_{3}$O$_{4}$(111) surface in ultrahigh vacuum. Gold forms two electrically distinct nanoparticles on an iron oxide surface upon annealing multilayer Au/Fe$_{3}$O$_{4}$(111) at 500 $^{\circ}$C for 15 minutes. STS measurements show that large gold nanoparticles ($\sim $ 8 nm) exhibit a metallic electronic structure while single gold adatoms bonded to the oxygen sites of the Fe$_{3}$O$_{4}$(111) surface are likely positively charged. This Au/Fe$_{3}$O$_{4}$(111) system is dosed with CO and H$_{2}$O at various temperatures. The site specific adsorption and the interaction of CO with the Au nanoparticles will be presented and discussed along with the observation of the site specific dissociative adsorption of H$_{2}$O to elucidate the catalytic properties of Au nanoparticles on a reducible iron oxide surface.