Effects of the preparation method on the crystallinity and catalytic activity of LaAlO3 perovskites for oxidative coupling of methane

Abstract

Oxidative coupling of methane (OCM) was performed over three structurally different LaAlO3 perovskite catalysts prepared using the citrate sol-gel (LaAlO3_C), solid-state (LaAlO3_S), and hard-templating (LaAlO3_H) methods. Although three LaAlO3 perovskite catalysts were successfully prepared, the catalytic activity of the catalysts was significantly different depending on their preparation method. The preparation method, and thereby the crystallinity of the LaAlO3 perovskite catalysts, has a strong influence on the amount of surface lattice oxygen species, which play a key role in producing C2 compounds in OCM. Consequently, the C2 yield over LaAlO3 catalysts shows the same order as that shown by their relative crystallinity (LaAlO3_C > LaAlO3_S > LaAlO3_H). In other words, high crystallinity enabled LaAlO3 catalysts to retain a large amount of surface lattice oxygen species, resulting in a higher C2 yield. Among the tested catalysts, LaAlO3_C, prepared using the citrate sol-gel method, retained the highest amount of lattice oxygen species owing to its high crystallinity and exhibited the highest C2 yield (ca. 12% at 750°C) for OCM.