FTIR Study of Adsorption and Photoassisted Oxygen Isotopic Exchange of Carbon Monoxide, Carbon Dioxide, Carbonate, and Formate on TiO₂

Abstract

In-situ FTIR has been employed to investigate adsorption and photoassisted oxygen scrambling of CO, CO 2, CO 3, and HCOO on powdered TiO 2 with 18 O 2 . As clean TiO 2 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 CO 2 adsorption, it produces adsorbed CO 3 and CO 2 with Ti−O−C−O bonding. Adsorbed CO does not exchange oxygen with 18 O 2, while adsorbed CO 2, CO 3, and HCOO do under UV irradiation. In the case of CO 3 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 CO 2, CO 3, and HCOO are discussed.