Model inverse electro-catalyst investigations of metal support interactions

Gold supported titania nano-particle surfaces have been synthesised in order to understand supported electrochemical mechanisms through an inverse catalyst. The catalyst process investigated was the electro-oxidation of CO which is known to be promoted on Au nano-particles on a titania support. Synthesis proceeded via physical vapour deposition (PVD) of titanium onto a gold surface (both polycrystalline and 111 crystal), followed by alloying and oxidation to form discrete particles of titania on the surface, with variations in density of particles achieved by control of the initial titanium coverages.Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) measurements indicate these particles develop with consistent triangular and hexagonal shapes, with average diameters of 11.5 and 20 nm observed depending on alloying temperature. The procession of titanium deposition on the gold surface and subsequent alloy formation was followed by X-ray photoelectron spectroscopy (XPS) measurements, with the formation of pure TiO2 revealed once synthesis was complete, with minimal modification to the final electronic state of the underlying gold.Electrochemical testing in an acidic environment provides evidence for alteration of the electrooxidation of CO on these modified gold surfaces. A deactivation of the CO oxidation is observed with initial addition of titania, explained by the blocking of CO adsorption on the surface. This is followed by significant subsequent increases in activity with increasing densities of titania particles, with decreasing over-potential and increasing current density observed as the titania coverage increases.This observed effect on CO oxidation activity with titania coverage in the inverse system provides significant evidence for the action of either reactant spill-over or Ti-Au interface sites as being responsible for the changes in activity observed for titania modified gold systems, whether in the inverse or standard form