Low-Temperature Oxidation of Carbon Monoxide with Gold(III) Ions Supported on Titanium Oxide

Au/TiO2 catalysts prepared by a deposition-precipitation process and used for CO oxidation without previous calcination exhibited high, largely temperature-independent conversions at low temperatures, with apparent activation energies of about zero. Thermal treatments, such as He at 623K, changed the conversion-temperature characteristics to the well-known S-shape, with activation energies slightly below 30kJmol(-1). Sample characterization by XAFS and electron microscopy and a low-temperature IR study of CO adsorption and oxidation showed that CO can be oxidized by gas-phase O-2 at 90K already over the freeze-dried catalyst in the initial state that contained Au exclusively in the +3 oxidation state. CO conversion after activation in the feed at 303K is due to Au-III-containing sites at low temperatures, while Au-0 dominates conversion at higher temperatures. After thermal treatments, CO conversion in the whole investigated temperature range results from sites containing exclusively Au-0.