Adsorption mechanism of CO molecule on Al(111) surface: periodic DFT investigation

The adsorption mechanism of the CO molecule on Al(111) surface has been investigated systematically at the atommolecule level by the method of periodic density functional theory. The adsorption energies, adsorption structures, charge transfer, and density of states have been calculated in a wide range of coverage. It is found that the hcp-hollow site is the energetically favorable site. A significant positive correlation has been found between the adsorption energy (E-ads) and coverage. The adsorbed CO molecules are almost perpendicular on the surface with the C atom facing the surface. There is an obvious charge transfer from Al atoms to the C atom; the Al atoms that have interaction with the C atom offer the most charge. The 4 sigma, 1 pi, and 5 sigma molecular orbitals of CO are found to contribute to bonding with the Al. The charges filling in the 2 pi molecular orbital contribute to C-O bond activation. In conclusion, the passivation of aluminum surface and the activation of CO molecule occur simultaneously in the adsorption of CO on Al surface.