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.