In this work, the reactions of ethane and ethene in an oxidizing and non-oxidizing atmosphere over gamma-alumina were investigated under temperature-programmed conditions, in an attempt to estimate the possible contribution and functionality of the Support in the reaction pathway of ethane ODH over MoO3/Al2O3 catalysts. The results indicate that alumina contributes to the primary deep oxidation and dehydrogenation routes of ethane to COx and coke respectively, which proceed effectively over the acidic OH groups and the Al3+-O2- acidic centers. On the contrary, the formation of ethylene seems to be coupled to the presence of redox sites on the catalytic surface and requires the presence of the molybdena phase. Moreover, the redox sites of the MoOx, species were found to unselectively activate the further overoxidation of the olefin to carbon oxides. Therefore, Al2O3 catalyzes the unselective primary oxidation of ethane to carbon oxides, whereas the molybdena phase is involved in the selective oxidative dehydrogenation (ODH) of ethane to ethene and the secondary overoxidation of ethene to COx. (c) 2005 Elsevier B.V. All rights reserved.