Theoretical Study for the Pt_2Au- and PtAu_2-Ethylene Interaction

摘要

A theoretical study was done for the on-top coordination mode of the ethylene molecule chemisorbed over the Pt(100) surface, which was modeled by the Pt_2Au and PtAu_2 systems. In this on-top reaction mode, the C-C axis is parallel to the Pt-Pt, Pt-Au, or Au-Au axis, respectively. Calculations were done with the Turbomole program, which is a density functional theory based method. Relativistic energy corrections were included and electron-core potentials were used. orbital basis sets of DZP quality were employed for all the atomic species. The gradient-dependent BLYP functional was used for the description of the exchange-correlation energy. It was found that the ethylene moiety is severely perturbed by this metallic surfaces. We have found that in Pt_3-C_2H_4, which contains two Pt surface atoms and one Pt bulk atom, the moiety is chemisorbed with a binding energy (BE) of 50.3 kcal/mol. Substitution of the bulk Pt atom by an Au atom reduces the BE to 37.6 kcal/mol, but it also produces strong structural changes on ethylene. Substitution of one surface Pt atom by one Au atom produces a Pt-PtAu system, which is able to chemisorb the ethylene moiety with a BE of 13.31 kcal/mol. Similarly, replacement of one surface Pt atom and one bulk Pt atom by Au atoms, respectively, gives a Pt-Au_2 system where the BE is 14.2 kcal/mol. Finally, replacement of the two surface Pt atoms by Au atoms produces a Pt-Au_2 system which is unable to chemisorb the C_2H_4 molecule, since here there is an energy barrier of 12.72 kcal/mol. Thus, the substitution of the Pt bulk (surface) atoms by Au particles enhances (diminishes) the chemisorption of C_2H_4.