A kinetic study of the oxidative coupling of methane over a BaCO 3 / La 2O n(CO 3) 3-n catalyst : I. Determination of a global reaction scheme and the influence of heterogeneous and homogeneous reactions

Abstract

It is shown that ethane is a primary, while ethylene is a secondary OCM product. CO and CO 2 are primary products from each of these hydrocarbons. The surface of the BaCO 3/La 2O n(CO 3) 3-n catalyst initiates the reactions of both CH 4, C 2H 6 and C 2H 4 with oxygen, and is active for CO 2 and H 2O formation. However, at higher temperatures, gas phase reactions are of increasing importance for the product distribution, and at 800°C, the conversion of C 2H 6 and C 2H 4 with oxygen is equally rapid without a catalyst. C 2H 6 and, especially, C 2H 4 are more easily oxidized than CH 4. The catalyst surface is the main source for CO 2 formation, while CO is formed mainly in the gas phase. The kinetic parameters corresponding to each of the reactions in the OCM scheme have been determined. It has been shown that secondary reactions are of little importance when starting from a CH 4/O 2/Inert feed at 680°C. However, at 720°C a significant part of the oxidation products are formed via secondary oxidation of ethane and ethylene. The primary C 2 selectivity was found to increase with increasing temperature.