Oxidative dehydrogenation of ethane over a lithium-promoted magnesium oxide catalyst

Abstract

Lithium-promoted magnesium oxide is an effective catalyst for the conversion of ethane to ethylene. A selectivity of 75% for ethylene was obtained at 40% ethane conversion over 6.5 g of 3 wt% Li + MgO catalyst at 600 °C. These results were obtained with initial pressures of 95 Torr C 2H 6 and 47 Torr O 2 at a space velocity of 260 h −1. An apparent activation energy of 37.3 kcal mol −1 was observed for this process. The carbon oxides are formed both by the direct oxidation of ethane and the secondary oxidation of ethylene. In the reactor employed in this study homogeneous reactions became dominant at temperatures greater than 675 °C. The catalytic system is believed to involve the generation of C 2H 5 · radicals on the surface, followed by the emanation of these radicals into the gas phase where they react with O 2 to form C 2H 4. The ability of this catalyst to generate alkyl radicals from CH 4 or C 2H 6 appears to be a general phenomenon [ J. Phys. Chem. 89, 4415 (1985)]. The subsequent reactions of these alkyl radicals (e.g., coupling or reaction with O 2) determines to a large extent the final product distribution. Ethylene also may be formed via surface ethoxide ions.