Gold/titania interfaces and their role in carbon monoxide oxidation

The chemisorption properties of differently prepared model gold/titania int erfaces have been compared with the aim of gaining a better understanding o f the synergistic interplay between the constituents in gold/titania cataly sts used in low-temperature CO oxidation. The structurally different gold/t itania interfaces were prepared using various techniques, including wet che mical deposition (dip coating) and physical vapor deposition of TiO2 on fla t and highly oriented Au(111)/mica films and immobilization of gold colloid s on TiO2/Au(111)/mica films as well as on TiO2 powders. The low-temperatur e activity of small gold colloids anchored on films was corroborated by DRI FTS measurements. CO, CO2, and O-2 adsorption/desorption studies were perfo rmed on the flat model catalysts with TDS, XPS, and ISS. All flat model sys tems did not show any significant CO adsorption. Oxygen desorption was evid enced by TDS. The adsorptive properties of powder model catalysts were inve stigated with DRIFTS, pulse thermal analysis, XPS, and ISS. CO adsorption o n gold was weak and reversible in all cases and not significantly influence d by the presence of TiO2. Temperature programmed desorption of CO2 indicat ed that CO2 was adsorbed if the systems were treated ex situ in oxygen at 6 73 K. The observed chemisorptive properties of the structurally different g old/titania interfaces support a mechanistic model for CO oxidation which i s based on oxygen adsorption on vacancy sites of titania and CO adsorption on gold.