Off-Normal CO2 Desorption from the Photooxidation of CO on Reduced TiO2(110)

Abstract

Photoinduced reactions between O2 and CO on reduced rutile TiO2(110) are studied at low temperature (∼30 K). Photon-stimulated desorption (PSD) of O2, CO2, and CO is observed with comparable yields. Isotope labeling experiments indicate that O2 chemisorbed in a vacancy is more active for photooxidation than O2 chemisorbed on a Ti5c site. The angular distribution for the desorbing CO2 is peaked at ∼40° with respect to the surface normal in the [11̅0] azimuth (i.e., perpendicular to the bridging oxygen rows), suggesting that CO2 is produced from O2 occupying an oxygen vacancy and CO adsorbed on a Ti5c site next to it. The experimental results are consistent with CO2 being produced from a transition state that has been predicted theoretically. The CO PSD from TiO2(110) is enhanced dramatically by the presence of chemisorbed O2, suggesting that it is a byproduct of the CO photooxidation process.