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.

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The adsorption and photoreactions of CH 2 Cl 2 on powdered TiO 2 have been investigated by Fourier transform infrared spectroscopy. CH 2 Cl 2 is adsorbed molecularly or dissociatively to form chloromethoxy (CClH 2 O (a) ) at 35 °C. CClH 2 O (a) decomposes into CH 3 O (a) and HCOO (a) in a vacuum at temperatures higher than ∼100 °C. As TiO 2 in contact with gaseous CH 2 Cl 2 is heated in a closed cell, HCl from Cl (a) and OH (a) recombination, CH 2 O from CH 3 O (a) decomposition, and CO and CO 2 from HCOO (a) decomposition are detected. In the CH 2 Cl 2(a) photodecomposition in the absence of O 2 , CO (a) , CO 3(a) , and HCOO (a) are generated. The TiO 2mediated CH 2 Cl 2(a) photodecomposition is likely initiated by surface-active oxygen species instead of direct hole transfer. In the presence of O 2 , CH 2 Cl 2(a) photodecomposition is accelerated. In addition to CO (a) , CO 3(a) , and HCOO (a) , H 2 O (a) and CO 2(a) are generated as well. In the case of CO (a) formation, O 2 is also involved in addition to TiO 2 lattice oxygen. The O 2 participation may be via oxygen anion species.

Fourier‐transform infrared spectroscopy has been employed to investigate the adsorption and photo‐oxidation of CH4 over powdered TiO2. The interaction between the CH4 and TiO2 surface is weak. It is found that no CH4 molecules are adsorbed on the surface at 35 °C in a vacuum. Under UV irradiation, CH4 decomposes to form CO(a), CO2(g), H20(a), and HCOO(a) in the presence of O2. The photoreaction rate is retarded and only small amounts of CO(a) and HCOO(a) are formed in the absence of O2. It is observed that the oxygen atoms of O2 are incorporated into these photoproducts as 18O2 is used. The major 18O‐containing products are C18O(a), C18O2(g), H2 18O(a), HC16O18O(a), and HC18O18O(a) after 180 min UV irradiation. However, the extent of 18O incorporating into the adsorbed formate is dependent on UV irradiation time. In the early stage of UV irradiation HC16O16O(a) is the major formate form indicating the involvement of TiO2 lattice oxygens for its formation, but HC18O18O(a) becomes the major one after 180 min indicating the involvement of 18O2. Formate on TiO2 further photodecomposes to CO2(g), but not to CO(a). CO(a) formation is directly from CH4 photodecomposition with the participation of TiO2 lattice oxygens and O2.

The adsorption, thermal stability, and photochemical reactions of N(C2H5)3 on powdered TiO2 have been studied by Fourier transform infrared spectroscopy (FTIR). N(C2H5)3 molecules are adsorbed molecularly on TiO2 at 35 °C and can be removed from the surface at 300 °C in a vacuum. In the presence of O2, N(C2H5)3 starts to decompose on TiO2 at a temperature of ∼215 °C. N(C2H5)3 on TiO2 is desorbed from the surface upon photoirradiation. In the presence of O2, the photodesorption process is suppressed and photoreactions of N(C2H5)3 are promoted. CO2(g), H2O(a), NCO(a), HCOO(a), CH3COO(a), and surface species containing NH x , CO, C−N, or C−N−C groups are detected during N(C2H5)3 photodecomposition on TiO2. As H2O is added to the photoreaction system of N(C2H5)3 on TiO2 in O2, the amounts of NCO(a) and NH x detected during photoirradiation decrease, but with appearance of CN groups. Most importantly, it is found that H2O participates in the HCOO(a) and CH3COO(a) formation.