Structure and catalysis of LixNi2-xO2 oxide systems for oxidative coupling of methane

Photoelectron spectroscopy (XPS and UPS) studies have been applied to the investigation of active oxygen species of solid solution series LixNi2-xO2 with wide range of 0<x less than or equal to 1 for understanding the origin of high activity and C-2-selectivity of the oxidative coupling of methane. From the comparison of these spectral features, the surface oxygen of Li0.3Ni1.7O2 with a cubic structure was assigned to O2- 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.