Size-Selective CO2 Activation by Vanadium-Doped Cobalt Clusters

CO2 activation is the primary step for CO2 reduction to C2 products. To understand the reactivity of bimetallic catalysts toward CO2 and, in particular, the role of dopant elements, we experimentally studied CO2 adsorption on pure and vanadium-doped cationic cobalt clusters. Doped and pristine clusters are reacted with CO2 in a flow tube-like reaction channel, and resulting cluster-CO2 products are characterized by free-electron laser-based infrared (IR) spectroscopy. The spectra for CO2 adsorbed on pure Con+ clusters are highly similar for each cluster size studied, and they indicate that CO2 is mostly physisorbed on the cluster. However, substituting a Co atom with a single V atom results in strongly varying IR spectra for VCon-1+·CO2 adducts, indicative for size-selective activation, dissociation, and even cluster oxidation. An absolute localized molecular orbital-based energy-decomposition analysis and decomposition into complementary occupied-virtual pairs reveals that charge transfer from the cluster into the CO2 antibonding π* lowest unoccupied molecular orbital is the dominant factor in activation, combined with an overall more positive charge on the vanadium atom and a strong dative V-O bond in the dissociated product. The size selectivity demonstrates how a fine interplay between dopant element and cluster size could be made instrumental in tuning the reactivity of catalyst materials.