Mechanistic features of the ethane oxidative dehydrogenation by in situ FTIR spectroscopy over a MoO 3/Al 2O 3 catalyst

Abstract

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 MoO 3/Al 2O 3 and Al 2O 3, 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 (50 °C) in the absence and presence of oxygen by time resolved IR spectroscopy between 50 and 500 °C. Catalytic testing of these materials in ethane oxidative dehydrogenation showed that the molybdena catalyst is highly selective (initial C 2H 4 selectivity was 96%), while mainly CO x was formed with alumina. The strong acid sites on alumina, detected by NH 3-TPD, are speculated to be responsible for the unselective conversion of ethane to CO x , 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. MoO 3/Al 2O 3 favors the first route, while pure alumina favors formation of oxygenates and full oxidation.