Kinetic and mechanistic study of the methane coupling reaction

Abstract

Detailed kinetic measurements have been made for the methane coupling reaction over a reducible and an irreducible oxide catalyst for a range of temperatures and methane and oxygen partial pressures. The results show a correlation with methane partial pressure which suggests that the reaction is close to second order with respect to methane. The results are analysed in terms of Rideal–redox and Langmuir–Hinshelwood models, and it is shown that the results can be explained by a Langmuir–Hinshelwood model in which the rate determining step is assumed to be surface coupling of adsorbed methyl moieties. However, the existence of a kinetic isotope effect in the formation of ethane from methane is not consistent with this model. An alternative model is presented in which the regeneration of the active centres on the surface of the oxide catalysts is included in the kinetic analysis. This model correctly predicts a ‘pseudo’-second-order reaction with respect to the methane partial pressure, but is also consistent with the observed kinetic isotope effect.