Since the relevance of deactivation phenomena in heterogeneous gas-solid photocatalytic processes, a study on the deactivation of MoOx/TiO2 catalysts in the oxidative photodehydrogenation of cyclohexane has been carried out in a fixed bed reactor and compared to the behaviour of catalysts used in a two-dimensional fluidized bed photoreactor. Superior photocatalytic performances were obtained in the fluidized bed reactor with respect to the fixed bed reactor both in terms of cyclohexane conversion and benzene yield. At the opposite of the fixed bed, in the fluidized bed reactor, catalyst did not deactivate. Characterization performed on catalysts after photocatalytic tests evidenced that the deactivation of the catalysts is correlated to the accumulation of carbonaceous species on catalyst surface and the sulphur disappearance. The catalysts used in fluidized conditions remained active as they maintained their initial sulphur content at the surface. (C) 2011 Elsevier B.V. All rights reserved.