MECHANISM OF PHOTOOXIDATION OF TRICHLOROETHYLENE ON TIO2 - DETECTION OF INTERMEDIATES BY INFRARED-SPECTROSCOPY

The photooxidation of trichloroethylene (TCE) on TiO2 has been investi gated using infrared spectroscopy for kinetic studies of the productio n of intermediate species and for investigation of the reaction mechan ism. Trichloroethylene is oxidized by chemisorbed molecular O-2 when T iO2 band gap radiation (hv > 3.1 +/- 0.1 eV) is incident. An intermedi ate species, dichloroacetyl chloride, HCl2CCOCl, was identified. At 30 0 K, Cl2CO, CO, CO2, HCl, and H2O are final photooxidation products. A t 473 K, Cl2CO undergoes a thermal side reaction on TiO2 to produce Cl 2C=CCl2. Studies in which oxygen-labeled H2O was present indicated no incorporation of the oxygen label into any of the intermediates, showi ng that the OH. driven oxidation mechanism proposed by others is not o perative. At 150 K, TCE blocks TiO2 sites, significantly retarding O-2 adsorption and slowing the photooxidation reaction.