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 N-2 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 N-2 preferentially and avoids hydrogen over-saturation at low temperatures and near ambient pressure by delicately balancing H-2 chemisorption and N-2 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.