Photodriven Ammonia Synthesis from N2 and H2: Recycling of a Molecular Molybdenum Nitride

The synthesis of ammonia from its elements, N2 and H2, is the most atom-economical and thermodynamically preferred route but presents a high kinetic barrier and thus is rare using molecular compounds. Irradiation of a molecular molybdenum nitride prepared from N2 cleavage with visible light in the presence of an iridium photocatalyst and 1-4 atm of H2 produced high yields of ammonia along with the formation of a cationic, formally molybdenum(VI) pentahydride as the major molybdenum-containing product. Continued irradiation of the molybdenum hydride under an N2 atmosphere resulted in regeneration of the molybdenum nitride that was recycled and used for additional hydrogenation to generate more ammonia, demonstrating superstoichiometric batch ammonia synthesis using only N2 and H2 with molecular compounds under ambient conditions.