Active-oxygen species on non-reducible rare-earth-oxide-based catalysts in oxidative coupling of methane

From supplementary in situ Raman spectroscopic studies of active-oxygen species on non-reducible rare-earth-oxide-based catalysts in the oxidative coupling of methane (OCM) and structural adaptability considerations, further support has been obtained for our proposal that there may be an active and elusive precursor (of (O) under bar (-)(2) and (O) under bar (2-)(2) adspecies), most probably (O) under bar (2-)(3) formed from reversible redox coupling of an (O) under bar (2) adspecies at an anionic vacancy with a neighboring O2- in the surface lattice. This active precursor may initiate H abstraction from CH4 and be itself converted to (O) under barH(-) + (O) under bar (-)(2), or it may abstract an electron from the oxide lattice and be converted to (O) under bar (2-)(2) + (O) under bar (-). The prospect of developing this type of OCM catalysts is discussed.