Activation of CO2 by supported Cu clusters

Abstract

Catalytic reduction of carbon dioxide to useful chemicals is a potent way to mitigate this greenhouse gas, but the challenge lies in finding active reduction catalysts. Using density functional theory we studied CO₂ activation over TiO₂-supported Cu clusters of size 1–4 atoms. The linear to bent transformation of CO₂ is necessary for activation, and we found that all the clusters stabilized bent CO₂, along with a significant gain of electrons on the CO₂ (indicative of activation). On all the TiO₂ supported Cu clusters, the interfacial sites were found to stabilize the bent CO₂ adsorption, where the active site of adsorption on Cu dimer, trimer and tetramer was on the Cu atom farthest away from the TiO₂ surface. Particularly, the Cu dimer stabilized bent CO₂ very strongly, although this species was found to be unstable on the surface. A synthesis technique that could stabilize the Cu dimer could therefore lead to a very active catalyst. Furthermore we found (using vibrational and charge analysis) that the active sites for the CO₂ activation predominantly had 0 and +1 oxidation states; the oxidation state of Cu is known to directly affect CO₂ reduction activity. Our study shows TiO₂-supported small Cu clusters can be active catalysts for CO₂ reduction and also provides further motivation for theoretical and experimental studies of metal clusters.