Structure and catalysis of Li_xNi_2-xO₂ oxide systems for oxidative coupling of methane

Photoelectrom spectroscopy (XPS and UPS) studies have been applied to the investigation of active oxygen species of solid solution series Li_xNi_2-xO₂ with wide range of 0<x≤1 for understanding the origin of high activity and C₂-selectivity of the oxidative coupling of methane. From the comparison of these spectral features, the surface oxygen of Li_0.3Ni_1.7O₂ with a cubic structure was assigned to O^2- species, while that of LiNiO₂ with a hexagonal structure was attributed to O^- species associated with the catalytic activity for the oxidative coupling of methane. From the relationship between these structures and the catalytic activity, it was inferred that the anisotropic layered superstructure of LiNiO₂ largely affected the formation of the active oxygen species for the oxidative coupling reaction.