FTIR study of adsorption and photoassisted oxygen isotopic exchange of carbon monoxide, carbon dioxide, carbonate, and formate on TiO₂

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.