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In-situ FTIR has been employed to investigate adsorption and photoassisted oxygen scrambling of CO, CO2, CO3, and HCOO on powdered TiO2 with 18O2. As clean TiO2 is exposed to CO at 35 °C, the IR frequencies of adsorbed CO shows that CO is bonded to Ti ions with an oxidation state +4 or less. The CO molecules that are bonded to two metal centers are more stable than those to only one center. In the case of CO2 adsorption, it produces adsorbed CO3 and CO2 with Ti−O−C−O bonding. Adsorbed CO does not exchange oxygen with 18O2, while adsorbed CO2, CO3, and HCOO do under UV irradiation. In the case of CO3 with bidentate configuration, only the oxygen bonded to the carbon with carbonyl character is involved in the exchange. Possible mechanisms for the oxygen scrambling of CO2, CO3, and HCOO are discussed.
Liao et al. (Tue,) studied this question.