Catalytic Ammonia Synthesis over Non-noble Metals Supported on Nitrides

Abstract

Catalytic ammonia synthesis under mild conditions has been widely studied around the world since ammonia has great potential as a hydrogen energy carrier. Ammonia synthesis from N₂ and H₂ effectively proceeds on transition metal surfaces and the catalytic activity is governed by the metal-nitrogen interaction. Ruthenium catalyst shows the optimum activity. Here, we show that nitride-supported non-noble metal catalysts achieve ammonia synthesis via an anion vacancy-mediated Mars–van Krevelen type mechanism. We developed a novel perovskite oxynitride-hydride, BaCeO_3–xN_yH_z, that contains high density heteroanion sites such as N³⁻ and H⁻ ions. Furthermore, high ammonia synthesis activity can be achieved by combination of rare-earth nitride and Ni metal nanoparticles. These nitrides are unstable in air, but air-stable rare-earth nitrides can be formed by doping Al into the lattice. We can thus propose the development of non-noble metal catalysts that operate efficiently under mild conditions.