INVESTIGATIONS OF ACTIVE-SITES FOR METHANE ACTIVATION IN THE OXIDATIVE COUPLING REACTION OVER PURE AND LI-PROMOTED MGO CATALYSTS

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. © 1993 Academic Press, Inc.