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

Density functional theory, employing periodic slab calculations, was used t o investigate the interactions of ethylene and oxygen with Pt(111) and Pt3S n(111). The predicted energetics and structures of adsorbed species on Pt(1 11) are in good agreement with experimental data. The binding energies of p i -bonded ethylene, di-sigma -bonded ethylene, and ethylidyne species are w eaker on Pt3Sn(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 o n 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 s trongly on Pt3Sn(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 h eterogeneity, wherein ethylidyne species prefer to adsorb away from Sn atom s and oxygen atoms prefer to adsorb near Sn atoms. Implications of this sur face heterogeneity on hydrocarbon reaction selectivity on Pt-based catalyst s are discussed. (C) 2001 American Institute of Physics.