Ternary ruthenium complex hydrides for ammonia synthesis via the associative mechanism

Ammonia is the feedstock for nitrogen fertilizers and a potential carbon-free energy carrier; however, its production is highly energy intensive. Conventional heterogeneous catalysts based on metallic iron or ruthenium mediate dinitrogen dissociation and hydrogenation through a relatively energy-expensive pathway. Here we report the ternary ruthenium complex hydrides Li₄RuH₆ and Ba₂RuH₆ as an alternative class of catalysts, composed of electron- and hydrogen-rich [RuH₆] anionic centres, for non-dissociative dinitrogen reduction, where hydridic hydrogen transports electrons and protons between the centres, and the Li/Ba cations stabilize N_xH_y (x = 0–2, y = 0–3) intermediates. The dynamic and synergistic involvement of all the components of the ternary complex hydrides facilitates an associative reaction mechanism with a narrow energy span and perfectly balanced kinetic barriers for the multistep process, leading to ammonia production from N₂ + H₂ with superior kinetics under mild conditions.