Gold/titania interfaces and their role in carbon monoxide oxidation

The chemisorption properties of differently prepared model gold/titania interfaces have been compared with the aim of gaining a better understanding of the synergistic interplay between the constituents in gold/titania catalysts used in low-temperature CO oxidation. The structurally different gold/titania interfaces were prepared using various techniques, including wet chemical deposition (dip coating) and physical vapor deposition of TiO(2) on flat and highly oriented Au(111)/mica films and immobilization of gold colloids on TiO(2)/Au(111)/mica films as well as on TiO(2) powders. The low-temperature activity of small gold colloids anchored on films was corroborated by DRIFTS measurements. CO, CO(2), and O(2) adsorption/desorption studies were performed on the flat model catalysts with TDS, XPS, and ISS. All flat model systems did not show any significant CO adsorption. Oxygen desorption was evidenced by TDS. The adsorptive properties of powder model catalysts were investigated with DRIFTS, pulse thermal analysis, XPS, and ISS. CO adsorption on gold was weak and reversible in all cases and not significantly influenced by the presence of TiO(2). Temperature programmed desorption of CO(2) indicated that CO(2) was adsorbed if the systems were treated ex situ in oxygen at 673 K. The observed chemisorptive properties of the structurally different gold/titania interfaces support a mechanistic model for CO oxidation which is based on oxygen adsorption on vacancy sites of titania and CO adsorption on gold.