Selective oxygen species for the oxidative coupling of methane

Abstract

Herein, we attempt to identify selective oxygen species for the oxidative coupling of methane using lanthanum-based perovskite catalysts (LaXO3, X=Al, Fe, or Ni), which are well-known not only as stoichiometric materials with simple and definite structures but also as materials with outstanding catalytic activities in various methane conversion reactions. The catalytic activities of LaXO3 in the presence or absence of oxygen clearly demonstrated that surface lattice oxygen species are responsible for the selective conversion of methane. More importantly, electrophilic (LaAlO3), moderate (LaFeO3), and nucleophilic (LaNiO3) lattice oxygen species selectively catalyze the oxidative coupling of methane to C2 hydrocarbons, the direct partial oxidation of methane to carbon monoxide, and the methane combustion to carbon dioxide, respectively. In addition, adsorbed oxygen species originating from gas-phase oxygen play roles both in converting methane to COx and in filling surface lattice oxygen vacancies, which are caused by the reaction of lattice oxygen and methane. Finally, we concluded that electrophilic lattice oxygen species and the facile filling of surface lattice oxygen vacancies by gas-phase oxygen are key factors for the systematic design of efficient catalysts for the oxidative coupling of methane.