In-Situ FTIR Study of Adsorption and Photoreactions of CH2Cl2 on Powdered TiO2

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 2 -mediated 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.