Studies of a Highly Active Cobalt Atomic Cluster Catalyst for Ammonia Synthesis

Theoretical studies have demonstrated that metal atomic clusters are highly efficient in catalytic ammonia synthesis under mild conditions. However, activation of N 2 over atomic clusters from an experimental viewpoint has not been systematically investigated. Here, for the first time, cobalt atomic dimers on a nitrogen–carbon support were synthesized for NH 3 synthesis. It is disclosed that N 2 activation over Co 2 atomic clusters (Co 2 ACCs) is entirely different from that over Co single-atom catalysts (Co SACs) or Co nanoparticles (Co NPs). A suite of in situ spectroscopy studies reveal that Co 2 ACCs not only provide active sites to promote strong metal–support interactions but also initiate strong interclustering interactions, resulting in electron transfers from Co d-orbitals to antibonding orbitals of N 2 molecules. As such, the activation energy of the Co 2 ACC catalyst in NH 3 synthesis is small. Consequently, the catalytic activity of the developed Ba-promoted Co 2 ACC catalyst reached 19.42 mmol NH 3 g cat –1 h –1 at 400 °C and 1 MPa, which is much superior than that of other Co-based catalysts under such mild conditions. More importantly, the synthesis strategy of Co 2 ACCs has general applicability as demonstrated in the preparation of Fe 2 and Mn 2 atomic clusters.