In this study, the deactivation behavior of TiO2 as a photocatalyst for benzene decomposition to carbon dioxide and water was investigated. The effect of space time on the benzene and carbon dioxide conversions were monitored. Benzene conversion and carbon dioxide production rates were not correlated, indicating accumulation of a carbon containing intermediate on the surface. This intermediate was blocking the active sites at a stiochiometry of 1 C:1 site. High space times favored the production of carbon dioxide therefore reduced the rate of accumulation of the surface poisoning intermediate.