Dynamics of CO photooxidation to CO2 on rutile (110)

Free-electron lasers (FELs) enable the study of the ultrafast dynamics of photocatalytic reactions by time-resolved X-ray photoelectron spectroscopy (tr-XPS) with femtosecond time resolution. In an optical pump - soft X-ray probe photoemission experiment conducted at the free-electron laser in Hamburg (FLASH), we observed the ultrafast oxidation of CO to CO₂ on rutile TiO₂(110) by monitoring the O 1s core level region. Within 800± 250 fs after laser excitation, CO₂ as a product of the photooxidation of CO is detected. Based on density functional theory calculations, we propose that the oxygen activation pathway for the CO oxidation is initiated via an O₂-TiO₂ charge transfer complex directly excited by the 770 nm pump laser. Our results give insight into the fundemental understanding of photocatalytic processes of TiO₂ polymorphs relevant for the design of more efficient photoctalaysts.