Adsorption of carbon monoxide over the ‘on-top’ sites of Ni, Cu and Ni–Cu surfaces. An extended Hückel molecular orbital study

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Abstract
Results of extended Hückel molecular orbital (EHMO) calculations for the adsorption of carbon monoxide over Ni, Cu and Ni–Cu model clusters containing 32 atoms are reported. The ‘on-top’ mode of adsorption of CO over different sites such as terrace, step and corner sites is considered. In the bimetallic Ni–Cu system the effect of alloying Cu with Ni is studied with relevance to the chemisorption of CO. From the calculations, we infer the relative importance of the electronic structure and the geometry of metal atoms in different sites for dissociation and further reaction of CO. The orders of strength of adsorption of CO over terrace, step and corner sites on Ni, Cu and Cu–Ni surfaces are not the same. Indeed, the presence of copper attenuates the strength of CO adsorption.