Reaction of CO with O adatoms on rutile TiO2(1Â 1Â 0) surfaces

► O-rich TiO2(1 1 0) surface (O-TiO2) is obtained by exposing a reduced surface to an O2 gas. ► O adatoms (Oad) created on the O-rich surface is chemically active. ► The intensity of the defect state seen in UPS spectra increases, while the amount of 18O decreases with increasing CO dose onto 18O-TiO2(1 1 0). ► Clearly shows the reaction of Oad with CO to form CO2.