Adsorption and reaction of CO on RuO2(1 1 0) surfaces

RuO2(1 1 0) single crystal surfaces were prepared by exposing a Ru(0 0 0 1) surface to high doses of O2 at 700 K. This surface exhibits coordinatively unsaturated (cus) Ru atoms (Ru-cus) onto which CO may adsorb at 85 K. Actually, high resolution electron energy loss spectroscopy reveals an energy of 262 meV (2115 cm−1) for the C–O stretch vibration of adsorbed CO indicating relatively weak binding in terminal configuration on Ru-cus. Thermal desorption spectroscopy shows partial desorption for temperatures above 250 K and, in parallel, formation of CO2 through reaction with neighboring surface oxygen atoms called O-bridge. Thereby, underlying Ru atoms become accessible onto which CO adsorbs more strongly giving rise to CO stretch-mode energies of 235 (1895) and 245 (1975) meV (cm−1). Hence, above 250 K, Ru-cus is not able to stabilize CO but serves as transient source for CO (and presumably other adsorbates), thus enabling the remarkable catalytic activity of this surface.