CO Photooxidation on TiO₂(110)

The photooxidation of chemisorbed CO on TiO2(110) was investigated. Molecular O2, chemisorbed at 105 K at anion vacancy defect sites on TiO2(110), is shown to undergo excitation leading to either photodesorption of O2 or photooxidation of coadsorbed CO to produce CO2. The yield of photoproduced CO2 and photodesorbed O2 follows the same excitation curve versus photon energy with a threshold at the TiO2 band gap, 3.1 eV. The decay time for photoproduced CO2 is essentially identical with the characteristic decay time for photodesorbed α-O2, corresponding to a photodesorption cross section = 8 × 10-17 cm2 for 3.94 eV photons. This indicates that both O2 photodesorption and CO2 photoproduction are related to the same α-O2 species. Compared to O2 photodesorption, CO2 photoproduction is a minor process. Lattice oxygen in TiO2 is not chemically involved in CO2 formation during ultraviolet irradiation.