Insight into dynamic and steady-state active sites for nitrogen activation to ammonia by cobalt-based catalyst

The industrial synthesis of ammonia (NH₃) using iron-based Haber-Bosch catalyst requires harsh reaction conditions. Developing advanced catalysts that perform well at mild conditions (<400 °C, <2 MPa) for industrial application is a long-term goal. Here we report a Co-N-C catalyst with high NH₃ synthesis rate that simultaneously exhibits dynamic and steady-state active sites. Our studies demonstrate that the atomically dispersed cobalt weakly coordinated with pyridine N reacts with surface H₂ to produce NH₃ via a chemical looping pathway. Pyrrolic N serves as an anchor to stabilize the single cobalt atom in the form of Co₁-N_3.5 that facilitates N₂ adsorption and step-by-step hydrogenation of N₂ to *HNNH, *NH-NH₃ and *NH₂-NH₄. Finally, NH₃ is facilely generated via the breaking of the *NH₂-NH₄ bond. With the co-existence of dynamic and steady-state single atom active sites, the Co-N-C catalyst circumvents the bottleneck of N₂ dissociation, making the synthesis of NH₃ at mild conditions possible.