Precursor species of carbon monoxide before its dissociation on aluminium-promoted Ni and Cu surfaces

Carbon monoxide adsorbed on Al-promoted Ni and Cu surfaces undergoes facile dissociation at 300 K or below. CO adsorbed on an Al-promoted Ni surface shows a larger separation (3.5 eV) between the 5σ and 4σ levels compared to that on a clean Ni surface (3.0 eV), besides exhibiting a low C-O stretching frequency. CO adsorbed on an Al-promoted Cu surface shows a similar large 5σ-4σ separation; this is accompanied by the disappearance of the satellites in the valence band and O(1s) regions. These features of CO adsorbed on Al-promoted Ni and Cu surfaces characterize the precursor to dissociation. Molecular orbital calculations suggest that CO bonds parallel to the Al-promnoted Cu surface.