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.