Competition between Eley-Rideal and Langmuir-Hinshelwood Pathways of CO Oxidation on Cun and CunO (n=6, 7) Clusters

The competition between the Eley-Rideal (ER) and the Langmuir-Hinshelwood mechanisms of CO oxidation on Cu-n and CunO (n = 6, 7) clusters was explored by means of spin-polariied density functional theory calculations. The separate and successive adsorptions of CO and O-2 on the clusters were studied. CO and O-2 molecules exhibit different adsorption behaviors, and a cooperative effect was noted for their coadsorption. The reaction pathways of CO oxidization were then investigated by locating the transition state and intermediate structures. The ER mechanism was More favorable for the reactions on Cu-6,Cu-7 and Cu6O but was less favorable on Cu7O. The ER or LH preference of the CO + O-2 reaction on the clusters was further, rationalized. We found that activation of O-2 is the key issue that affects the ER-LH competition. The pathway, either ER or LH, in which O-2 is highly activated is always preferred, while, the O-2 activation depends on its adsorption pattern, site, and sequence in the presence of CO.