Mechanism of Photooxidation of Trichloroethylene on TiO2: Detection of Intermediates by Infrared Spectroscopy

The photooxidation of trichloroethylene (TCE) on TiO 2 has been investigated using infrared spectroscopy for kinetic studies of the production of intermediate species and for investigation of the reaction mechanism. Trichloroethylene is oxidized by chemisorbed molecular O 2 when TiO 2 band gap radiation ( h ν > 3.1 ± 0.1 eV) is incident. An intermediate species, dichloroacetyl chloride, HCl 2 CCOCl, was identified. At 300 K, Cl 2 CO, CO, CO 2, HCl, and H 2 O are final photooxidation products. At 473 K, Cl 2 CO undergoes a thermal side reaction on TiO 2 to produce Cl 2 C CCl 2 . Studies in which oxygen-labeled H 2 O was present indicated no incorporation of the oxygen label into any of the intermediates, showing that the OH • driven oxidation mechanism proposed by others is not operative. At 150 K, TCE blocks TiO 2 sites, significantly retarding O 2 adsorption and slowing the photooxidation reaction.