Exploring Metal–Support Interactions To Immobilize Subnanometer Co Clusters on γ–Mo2N: A Highly Selective and Stable Catalyst for CO2 Activation

Strong bonding interactions between a transition metal and a substrate or support is one of the most effective strategies to immobilize subnanometer scale clusters or atoms in heterogeneous catalysis. We show that such a type of phenomenon can take place on a Mo2N surface. Combined experimental and theoretical studies show that strong metal–support interactions between face-centered cubic-structured γ-Mo2N and cobalt have been confirmed to effectively anchor subnanometer Co clusters and prevent their aggregation. The results of X-ray absorption near edge structure, ambient pressure X-ray photoelectron spectroscopy, and density functional theory revealed electronic perturbations in the nitride-bonded cobalt not seen on a strongly active oxide such as CeO2. A charge transfer from Co to Mo2N was observed with a significant stabilization of the Co 3d levels, which prevents the full decomposition of CO2. The subnanometer Co loaded on γ-Mo2N catalysts exhibited very high selectivity to the product CO, whereas the undesirable methanation activity, typically inevitable on traditional Co/oxide catalysts, was successfully suppressed. As a consequence of the electronic perturbations induced by the nitride, the cobalt was not able to fully dissociate the CO2 molecule to generate C or CHx fragments necessary for methane production. Under reaction conditions, the strong bonding between Co and γ-Mo2N maintained the subnanometer geometry of Co, leading to a remarkable selectivity and stability.