Gas-solid heterogeneous photocatalytic oxidation (PCO) of heptane and toluene over UV-illuminated pure titania, titania-silica mixed oxides and sulfated titania was investigated at room temperature in a batch reactor. By comparing the photocatalytic activities of the different catalysts, we draw the following two conclusions: (1) there is no clear relationship between the crystalline phase and photocatalytic activity; (2) larger surface area is not always effective in the photocatalytic process and its effects on the photocatalytic activity strongly depend on the nature of the reactant used. In addition, the study on the behavior of catalyst deactivation and regeneration shows that titania-silica mixed oxide is deactivated More slowly than pure titania and sulfated titania, and for sulfated titania the regeneration temperature can be lowered due to the presence of SO42-. (C) 2004 Elsevier B.V. All rights reserved.