Gas-phase photooxidation of trichloroethylene on TiO2 and ZnO:: Influence of trichloroethylene pressure, oxygen pressure, and the photocatalyst surface on the product distribution

Transmission Fourier transform infrared spectroscopy has been used to identify gas-phase and surface-bound products and intermediates formed during the gas-phase photooxidation of trichloroethylene (TCE) on TiO(2) and ZnO. Several factors are found to influence the gas-phase product distribution for this reaction. On clean TiO(2) and ZnO surfaces and at high TCE and O(2) pressures, gas-phase CO, CO(2), COCl(2), CCl(2)HCOCl, CHCl(3), C(2)HCl(5), and HCl are produced, whereas at low TCE and O(2) pressures, TCE is converted to gas-phase CO and CO(2) only. In addition to TCE and O(2) pressure, the product distribution of the photooxidation of TCE is strongly dependent upon the coverage of adsorbed species on the surface of the photocatalyst. It is shown here that the complete oxidation of adsorbed TCE can occur on clean photocatalytic surfaces whereas only partial oxidation of adsorbed TCE occurs on adsorbate-covered surfaces. The role of adsorbed surface products in TCE photooxidation is discussed.