Investigations of Active Sites for Methane Activation in the Oxidative Coupling Reaction over Pure and Li-Promoted MgO Catalysts

Abstract

The oxidative coupling of methane to ethane over model MgO catalysts prepared under well-controlled, ultrahigh vacuum (UHV) conditions has been studied using a combination of surface science techniques and elevated-pressure kinetic measurements. The utilization of electron energy loss spectroscopy has allowed us to characterize a variety of defects and to identify the active sites which are responsible for the methane coupling reaction. The results indicate that [Li+O−] centers are not likely directly involved in the methane activation step, but rather promote the production of F-type centers in the near-surface region which are responsible for this key step in the methane coupling reaction. The origin of [Li+O−] and F-type defects and their densities and stabilities are discussed.