Density functional theory studies of the adsorption of ethylene and oxygen on Pt(111) and Pt3Sn(111)

Density functional theory, employing periodic slab calculations, was used to investigate the interactions of ethylene and oxygen with Pt(111) and Pt(3)Sn(111). The predicted energetics and structures of adsorbed species on Pt(111) are in good agreement with experimental data. The binding energies of pi -bonded ethylene, di-sigma -bonded ethylene, and ethylidyne species are weaker on Pt(3)Sn(111) than on Pt(111) by 21, 31, and 50 kJ/mol, respectively. Hence, the electronic effect of Sn on the adsorption of ethylene depends on the type of adsorption site, with adsorption on three-fold site weakened more than adsorption on two-fold and one-fold sites. Oxygen atoms bond as strongly on Pt(3)Sn(111) as on Pt(111), and these atoms prefer to adsorb near Sn atoms on the surface. The addition of Sn to Pt(111) leads to a surface heterogeneity, wherein ethylidyne species prefer to adsorb away from Sn atoms and oxygen atoms prefer to adsorb near Sn atoms. Implications of this surface heterogeneity on hydrocarbon reaction selectivity on Pt-based catalysts are discussed. (C) 2001 American Institute of Physics.