Computational Screening of Supported Metal Oxide Nanoclusters for Methane Activation: Insights into Homolytic versus Heterolytic C-H Bond Dissociation

Since its discovery in zeolites,the [CuOCu](2+) motifhas played an important role in our understanding of selective methaneactivation over supported metal oxide nanoclusters. Although thereare two known C-H bond dissociation mechanisms, namely, homolyticand heterolytic cleavage, most computational studies on optimizingmetal oxide nanoclusters for improved methane activation reactivityhave focused only on the homolytic mechanism. In this work, both mechanismswere examined for a set of 21 mixed metal oxide complexes of the formof [M1OM2](2+) (M-1 and M-2 = Mn, Fe, Co, Ni, Cu, and Zn). Except for pure copper, heterolyticcleavage was found to be the dominant C-H bond activation pathwayfor all systems. Furthermore, mixed systems including [CuOMn](2+), [CuONi](2+), and [CuOZn](2+) are predictedto possess methane activation activity similar to pure [CuOCu](2+). These results suggest that both homolytic and heterolyticmechanisms should be considered in computing methane activation energieson supported metal oxide nanoclusters.