Theoretical investigation of the adsorption of oxygen on small copper clusters

A theoretical study of molecular oxygen adsorption on small Cun (n ⩽ 8) clusters and its comparison with the adsorption of atomic oxygen was carried out using density functional methods. The oxygen-copper system is important to understand the mechanism of the oxidation by oxygen catalyzed by copper. Here, we show that the molecular oxygen reactivity is dependent of even and odd alternation of the number of copper atoms in the cluster, finding that Cun with an odd n exhibit in general the highest reactivity. A similar behavior was found for the atomic oxygen adsorption on the same copper clusters. The molecular adsorption energy has values from 4.7 to 39.1 kcal/mol that are small in comparison with the atomic case. In all stable cases, the oxygen molecule approaches parallel to the copper cluster, adsorbing in simple or coordinated sites maintaining a high symmetry of the oxygen-copper-cluster system. In addition, an energy barrier in the dissociation of the molecular oxygen was not found.