Measurement of kinetic isotope effects over methane coupling catalysts in the presence of carbon dioxide

Abstract

Publisher Summary This chapter investigates the effects of kinetic isotope over methane coupling catalysts in the presence of carbon dioxide. The experiments were carried out using a new batch of catalyst made by the procedure described by Edwards. Methane coupling and oxygen exchange may occur on different types of surface sites; however, the greater effect of carbon dioxide on isotope mixing compared to methane coupling can be readily rationalized. The experimental results indicate that the oxygen species, which attacks methane in the coupling reaction is the same as that involved in the oxygen isotope mixing reaction. The greater effect of carbon dioxide on the latter reaction can be explained in terms of its larger site requirement. A substantial deuterium kinetic isotope effect occurs in the presence and absence of carbon dioxide indicating that C–H bond breaking is rate limiting in both situations—the coupling reaction and the oxygen isotope mixing reaction. There may be a slight reduction in the kinetic isotope effect when using both a methane/oxygen ratio and a large excess of carbon dioxide.