Carbon monoxide chemisorption on Cu covered Ni(111) surfaces

Abstract

The adsorption of carbon monoxide on copper covered Ni (111) surfaces has been studied by high resolution electron energy loss spectroscopy (HREELS). CO is used to titrate the various adsorption sites present, yielding information about the structure and composition of the two metal species at the surface. The results show that CO adsorbs at locations which resemble the top and bridge sites of pure Cu(111) and Ni(111) surfaces, and on a new mixed Cu–Ni bridge site. For a Cu coverage greater than one monolayer, the CO HREEL spectra are very similar to those observed on the clean Cu(111) surface. For Cu coverages less than one monolayer, and deposition at 80 K, small Cu clusters and Cu islands are observed. For submonolayer Cu deposition at temperatures >300 K, a mixed Cu–Ni layer can be formed. The HREELS results for the mixed surface with low Ni concentration show that CO adsorbs on the Ni top sites first (at T<400 K), Cu top sites next (at T<150 K), and then a mixed Cu–Ni bridge site (at T<120 K). Strong evidence suggests that the mixed CuNi bridge site is occupied by depopulating the Ni–CO top-site species.