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.

No abstract

Comparison of photooxidation rates of formic acid and formate on TiO 2 as well as the effect of adsorbed water on formate and formic acid photodecomposition rates have been investigated by Fourier transformed infrared spectroscopy. Adsorbed formic acid and formate are all photooxidized to CO 2 in O 2 . Formic acid on TiO 2 shows a photoreaction rate that is roughly 53 times that of formate groups for a same surface concentration. The presence of H 2 O can increase formate and formic acid photooxidation rates by a factor close to 2. In addition, photochemistry of adsorbed ethanol and ethoxy is also compared. It is found that ethanol is important for the formation of acetaldehyde, while ethoxy groups are photooxidized to adsorbed acetate, formate, and water. Possible reasons for these differences are discussed.

No abstract

No abstract