The gas phase photocatalytic destruction of tetrachloroethylene (PCE) was investigated by using an in situ photocatalytic reactor with FF-IR analysis in batch mode. The main products of PCE degradation are CO2 and COCl2, with trichloroacetylchloride as an intermediate. It was found that the rate of PCE degradation and the appearance of products in the gas phase are highly dependent on their adsorption properties on the surface of the catalyst, besides other reaction conditions, such as the intensity of irradiation and the composition of the reaction mixture.