Balanced nitrogen and hydrogen chemisorption by [RuH₆] catalytic center favors low-temperature NH₃ synthesis

Ammonia is a central vector in sustainable global growth, but the usage of fossil feedstocks and centralized Haber-Bosch synthesis conditions causes >1.4% of global anthropogenic CO₂ emissions. While nitrogenase enzymes convert atmospheric N₂ to ammonia at ambient conditions, even the most active manmade inorganic catalysts fail due to low activity and parasitic hydrogen evolution at low temperatures. Here, we show that the [RuH₆] catalytic center in ternary ruthenium complex hydrides (Li₄RuH₆) activates N₂ preferentially and avoids hydrogen over-saturation at low temperatures and near ambient pressure by delicately balancing H₂ chemisorption and N₂ activation. The active [RuH₆] catalytic center is capable of achieving high yield at low temperatures via a shift in the rate-determining reaction intermediates and transition states, where the reaction orders in hydrogen and ammonia change dramatically. Temperature-dependent atomic-scale understanding of this unique mechanism is obtained with synchronized experimental and density functional theory investigations.