Theoretical study of adsorption of SO2 on Ni(111) and Cu(111) surfaces

Surface structures and electronic properties of sulfur dioxide, SO2, molecularly adsorbed on Ni(111) and Cu(111) surfaces were investigated using B3LYP density functional theory. Geometry and orientation of SO2 were fully optimized on the metal clusters and three and two stable structures were obtained for Ni(111) and Cu(111) surfaces, respectively. For the Ni(111) surface, the most stable structure was that SO2 adsorbs with its molecular plane nearly parallel to the surface, with all the S and O atoms in bridge sites, and in good agreement with the observed structures on the Ni(111) surface. For the Cu(111) surface, the most stable structure in which SO2 adsorbs with its plane perpendicular to the surface and with O atoms in on-top sites, was also in accord with the observed one on the Cu(111) surface. The adsorption energy was much larger for the Ni surface than for the Cu surface. The result of a Mulliken population analysis showed that the σ donation from the SO2 σ orbital to the surface, and π back donation from the surface to the SO2 π* orbital, play important roles in the adsorption, and that the amounts of both σ donation and π back donation were larger for the Ni surface than for the Cu surface. Upon adsorption the S–O bond length was elongated and the O–S–O angle became contracted.