Theoretical study of the adsorption of carbon monoxide on small copper clusters

A theoretical study was carried out on the adsorption of carbon monoxide on small Cun (n ⩽ 8) clusters and its comparison with the adsorption of oxygen using density functional methods. The study of the CO-copper system is important for understanding the mechanism of synthesis of organic substances catalyzed by copper. Adsorption energies from 9.3 to 27.9 kcal/mol were found, which represented values very similar to those calculated for the adsorption of molecular oxygen in a previous study. Nevertheless, the reactivity of the CO molecule is independent of even-odd alternation with respect to the number of atoms of copper in the cluster, a result in contrast with previous results on the reactivity of the molecular oxygen with the same copper clusters. The CO molecule is adsorbed on a top site (1-fold coordination) approaches perpendicularly to the adsorption site, presenting a high degree of symmetry in the adsorption system. A high degree of symmetry of the adsorption system was also found for the adsorption of oxygen, both atomic and molecular, in previous studies. This showed that symmetry could be an important factor to consider for describing the adsorption process of elemental gases on copper clusters.