Reactivity of the Fe2O3(0001) Surface for Methane Oxidation: A GGA + U Study

CH4 oxidation by an oxygen carrier, such as iron oxide, continues to be involved in many important valuable industrial catalytic processes, including chemical looping combustion. In this paper, reaction pathways of complete and partial oxidations of CH4 on thermodynamically stable hematite (α-Fe2O3) (0001) facets are investigated with periodic GGA + U calculations. Upon Fe–O3–Fe-termination, initial CH4 decomposition proceeds via C–H bond activation on the Fe site, with an energy barrier of 1.04 eV. Subsequent decomposition and oxidation of the CHx species (x = 1, 2, 3) exploit the lattice O species according to the Mars–van Krevelan mechanism, forming CHxO in more thermodynamically and kinetically favorable pathways. The reduced iron oxide can be reoxidized with O2 as the oxidant, allowing VO to greatly facilitate O2 dissociation, i.e., dramatically lowering the O2 dissociation barrier by 2.83 eV, for active site regeneration. Furthermore, CH4 oxidation chemistry involving the ferryl O (i.e., oxygen spec...