FACILE CARBON-MONOXIDE DISSOCIATION ON COPPER - PROMOTION BY ALUMINUM

High-resolution electron energy loss spectroscopy (HREELS) and Auger electron spectroscopy (AES) have been utilized to study CO adsorption and decomposition on copper supported on an Al(111) single crystal. CO adsorption sites are created upon the evaporation of copper onto an atomically clean Al(111) surface at 95 K. Exposing a Cu/Al(111) interface, possessing approximately one-half monolayer of copper, to CO produces a species which exhibits a weak vibrational mode with an unusually low CO stretching frequency of 1260 cm-1. The low-frequency of this CO mode indicates that this species possesses a severely weakened C-O bond. This is verified by its thermal decomposition upon heating to 348 K and the coincident formation of adsorbed carbon and oxygen on the surface, as observed spectroscopically. The thermal instability and the vibrational spectra of this CO species suggest that the CO is bound in a di-sigma structure, where both the C and O atoms are chemically bonded to metal atoms (i.e., Cu(x)-C-O-Al(y)). This structure is proposed to be a precursor state to CO dissociation on the Cu/Al(111) interface. Thus, aluminum atoms, as neighbors to copper atoms, can provide a route to CO dissociation which is not available to either copper or aluminum alone.