Oxidative coupling of methane in chemical looping design

The search for alternative non‑carbon-emitting uses of the huge reserves of natural gas has renewed the interest on direct conversion of methane to value added chemicals. Oxidative coupling of methane (OCM) is a key potential route to convert methane directly to ethylene and innumerous works have focused on the study and development of catalysis for such reaction. Despite these efforts, the limited yield and selectivity achieved still hinders the industrial deployment of such reactions. In this work, we provide a mini-review on studies that focus on OCM process based on the chemical looping (CL) concept, in which methane and oxygen are fed in two separated cyclic steps and a metal oxide catalyst is used as the oxygen source to activate the methane molecule. CL emerges as a promising design for viable methane conversion by improving selectivity due to the use lattice oxygen species for methane activation, avoiding undesired combustion gas phase reactions triggered by molecular oxygen. We review all classes of catalyst tested in this approach, including single oxides, doped and co-doped systems based on Mg-Mn oxides, rare earths, Mn-Na2WO4, and perovskites, and most recent optimization of reactor operation conditions.