First-principles calculations based on density functional theory and the generalized

gradient approximation were used to study the adsorption of CO and NO molecules

on the Cu2O(111) surface in the presence of oxygen vacancies. The calculations

employ slab geometry and periodic boundary conditions with partial relaxation of

atom positions. Two molecular orientations, X- and O-down (X = C, N), at two

distinct sites, Cu1C and oxygen vacancy sites, were considered. Total energy

calculations indicated that the Cu1C position was relatively more favoured than the

oxygen vacancy site. The predicted binding energies were 144.5kJ/mol (CO) and

124.1kJ/mol (NO). The C–O and N–O stretching frequencies were unequally redshifted

upon adsorption. Upon adsorption at Cu1C site, CO molecule was found to

bind to Cu1C atoms in a vertical configuration whereas the NO molecule adsorbed

in a tilted mode. Upon adsorption at an oxygen vacancy site, the CO and NO

molecules were both vertical to the Cu2O(111) surface. Their adsorption properties

at oxygen vacancy sites were dependent upon the defect density. As the density of

defective sites increased, the adsorption energies of the defect-XO configuration

increased and the N–O bond was continuously weakened whereas the C–O bond remained constant. Therefore, such a process favoured the dissociation of the NO

molecule and had a small influence upon the adsorbed CO molecule.

Roles of Oxygen Vacancy in the Adsorption Properties of CO and NO on

Cu2O(111) Surface: Results of a First-Principles Study. B.Z.Sun, W.K.Chen,

J.D.Zheng, C.H.Lu: Applied Surface Science, 2008, 255[5], 3141-8