Adsorption and activation of CO2 molecule on subnanometer-sized anionic vanadium carbide clusters VnC4− (n = 1–6): A theoretical study

Abstract

Adsorption and activation of CO2 onto small-sized transition metal clusters is of practical importance for the conversion of this molecule to value-added products. We study the efficacy of small anionic vanadium carbide clusters, VnC4− with n = 1–6 towards the aforementioned key step by employing density functional theory based method. One of such clusters has been shown to perform very well in activating N2 molecule as revealed in a recent experiment. The results of our calculations suggest that the binding of CO2 molecule with the anionic vanadium carbide clusters becomes stronger with increase in number of vanadium atoms in the cluster. This adsorption energy trend can be properly rationalized by using the d-band center model. The strong adsorption of CO2 molecule is also accompanied with its high degree of activation. The high activation of CO2 is characterized by a significant amount of charge transfer from the anionic clusters to the molecule. We further find that the activation barrier heights for the dissociation of CO2 to CO and O fragments are considerably small for V4C4− and V5C4− clusters. In particular, V5C4− cluster with an activation barrier of 0.83 eV may serve as a good candidate for activation and dissociation of a CO2 molecule.