Catalytic oxidative coupling of methane and surface potential measurements over pure samarium oxide: evidence for a heterogeneous C2 yield limitation

Abstract

The oxidative coupling of methane has been studied over a pure samarium oxide catalyst by classical tests and surface potential measurements. This latter technique provides some interesting information on the nature of the oxygen species adsorbed over the catalytic surface and on the kinetic parameters of the reactions which take place on the solid. In our experimental conditions (P_CH4/P_O2= 2) the negatively adsorbed oxygen species involved in the catalytic process is O^– below 400°C and O^2– at higher temperature. The reactivities of the hydrocarbons follow the order C₂ methane, whatever the temperature. The activation energy obtained from classical tests (95 kJ mol^–1) is very close to that obtained from surface-potential experiments. The results lead us to propose that an important part of the C₂ yield limitation is due to the heterogeneous process.