Applications of rare earth oxides in catalytic ammonia synthesis and decomposition

Abstract

Ammonia has gained increasing attention as a promising energy carrier because of its high capacity for hydrogen storage (17.6 wt%), facile liquefaction under mild conditions and easy liberation of H₂. Catalytic ammonia synthesis and decomposition under mild reaction conditions, two key techniques enabling ammonia as an energy carrier, are generally catalyzed by supported transition metal nanoparticles. In recent years, rare earth oxide materials have shown great potential to be employed as efficient catalyst supports in ammonia synthesis and decomposition reactions for improving the catalytic performance or decreasing the dosage of active transition metals. This review aims to summarize the recent progress with particular emphasis on the unique features of rare earth oxide materials in dispersing and stabilizing transition metal nanoparticles. Key factors that control the structures and catalytic performances of transition metal catalysts supported on the rare earth oxides and rare earth oxide-based composites are briefly discussed, aiming to gain insights for the development of more efficient supported catalysts. Additionally, investigations on rare earth oxides as catalyst promoters for ammonia synthesis and decomposition catalysts are also surveyed. Moreover, future research directions in developing highly efficient rare earth oxide supported catalysts for ammonia synthesis and decomposition reactions are discussed with emphasis on the possible approaches to improve their catalytic performances.