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

Abstract

Theoretical studies have demonstrated that metal atomic clusters are highly efficient in catalytic ammonia synthesis under mild conditions. However, activation of N2 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 NH3 synthesis. It is disclosed that N2 activation over Co2 atomic clusters (Co2 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 Co2 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 N2 molecules. As such, the activation energy of the Co2 ACC catalyst in NH3 synthesis is small. Consequently, the catalytic activity of the developed Ba-promoted Co2 ACC catalyst reached 19.42 mmolNH3 gcat–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 Co2 ACCs has general applicability as demonstrated in the preparation of Fe2 and Mn2 atomic clusters.