Influence of Coordination Environment of Anchored Single‐Site Cobalt Catalyst on CO 2 Hydrogenation

Heterogeneous catalysts generally have a variety of active‐site structures due to the innate heterogeneity of the surface, resulting in complicated correlations between activity and active‐site structure. Single site heterogeneous cobalt catalysts with a uniform catalytic surface were utilized as a platform to probe surface sensitive reactions; in this case CO 2 hydrogenation. It was found that atomically isolated cobalt single sites, which exist solely in the tetrahedral Co 2+ coordination, exclusively form CO under typical CO 2 methanation conditions, while cobalt clusters yielded the highest rate of CO 2 reaction and began to form methane. Utilizing the principles of Ostwald Ripening to probe the ensemble effects for CO 2 hydrogenation, the transition from atomic isolation to small clusters of atoms to nanoparticles was explored. The chemical structure of the cobalt was elucidated primarily via X‐Ray Absorption Spectroscopy (XANES/EXAFS) and X‐Ray Photoelectron Spectroscopy (XPS).