Aspects of the Surface pathway of the ethane oxidative dehydrogenation (ODH) were investigated by in situ infrared spectroscopy. Adsorption and surface reactions were studied on MoO3/Al2O3 and Al2O3, in order to investigate contributions of the support as well as selective and unselective routes of the ODH reaction. The interaction of ethane with the oxides was investigated at isothermal conditions (50degreesC) in the absence and presence of oxygen by time resolved IR spectroscopy between 50 and 500degreesC. Catalytic testing of these materials in ethane oxidative dehydrogenation showed that the molybdena catalyst is highly selective (initial C2H4 selectivity was 96%), while mainly COx, was formed with alumina. The strong acid sites on alumina, detected by NH3-TPD, are speculated to be responsible for the unselective conversion of ethane to COx, while the moderate acid strength introduced by molybdena allows selective activation of ethane and inhibits the further oxidation of ethylene produced. The spectroscopic data indicate that the activation of the ethane C-H bond proceeds through the formation of alkoxides, which decompose to ethylene and a surface OH group or are oxidized to surface bound oxygenates. MoO3/Al2O3 favors the first route, while pure alumina favors formation of oxygenates and full oxidation. (C) 2004 Elsevier B.V. All rights reserved.