Insight into Dynamic and Steady-State Active Sites for Nitrogen Activation to Ammonia by Cobalt-Based Catalyst

The industrial synthesis of ammonia (NH 3 ) 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 NH 3 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 H 2 to produce NH 3 via a chemical looping pathway. Pyrrolic N serves as an anchor to stabilize the single cobalt atom in the form of Co 1 -N 3.5 that facilitates N 2 adsorption and step-by-step hydrogenation of N 2 to *HNNH, *NH-NH 3 and *NH 2 -NH 4 . Finally, NH 3 is facilely generated via the breaking of the *NH 2 -NH 4 bond. With the co-existence of dynamic and steady-state single atom active sites, the Co-N-C catalyst circumvents the bottleneck of N 2 dissociation, making the synthesis of NH 3 at mild conditions possible.