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 NH3 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 NH3 synthesis is small. Consequently, the catalytic activity of the developed Ba-promoted Co-2 ACC catalyst reached 19.42 mmol(NH3) g(cat)(-1) h(-1) at 400 degrees 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.