Exploring the Influence of AlOx Polyhedra on Reactive Oxygen Sites and Oxidative Coupling of Methane (OCM) Reaction Performance of LaAlO3 Perovskite

At present, there are still controversy viewpoints on the reactive oxygen sites in the OCM reaction on ABO₃ perovskites. Some researchers believe that electron-deficient chemisorbed oxygen species (O₂^-, O₂^2-, and O^-) contribute to C₂ product formation, and surface lattice oxygen (O^2-) promotes the deep oxidation of methane, while others hold an opposite viewpoint. In addition, the influence of BO_x polyhedra on the reactive sites and reaction performance has rarely been elucidated. Considering this, two types of LaAlO₃ perovskites, comprising different contents of surface and bulk coordinatively unsaturated sites (AlO₄ tetrahedra), were synthesized for the OCM reaction. Through a series of in situ and ex situ characterization techniques and combined with DFT calculations, a high oxygen vacancy concentration was revealed for the AlO₄-rich LaAlO₃ perovskite, leading to an abundance of reactive oxygen and promoting oxygen mobility. The study identified monatomic surface lattice oxygen O^2- as the active sites for the deep oxidation of methane at low temperatures. The O₂^2- species generated by oxygen vacancies promotes the formation of C₂ products at high temperatures.