Carbon monoxide reaction with UO2(111) single crystal surfaces: A theoretical and experimental study

Abstract

The reaction of CO has been investigated on the surfaces of UO2(111) single crystal. Over the stoichiometric surface CO does not adsorb at 300K and no further reaction is noticed. Over UO2−x (prepared by Ar+ bombardment), CO molecules adsorb and in presence of traces of H2 they couple to form acetylene molecules that desorb in two temperature domains during temperature programmed desorption (TPD). In the presence of excess H2 the coupling product is found to be ethylene. X-ray photoelectron spectroscopy (XPS) of the core level shows the presence of an U4f line at 377eV on the UO2−x surface, attributed to U metal. This line disappears upon CO adsorption (5L and above) at 300K; indicating oxidation of U metal atoms by O from dissociatively adsorbed CO. XPS C1s shows that the only C containing species formed is carbide. Computation of a α-U metal 2d-periodic slab was also conducted using plane-wave pseudopotential in the density functional theoretical framework. Two modes of CO adsorption were considered: mo...