Theoretical study for the Pt2Au- and PtAu2- ethylene interaction

Abstract

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 Pt2Au and PtAu2 systems. In this on-top reaction mode, the CC axis is parallel to the PtPt, PtAu, or AuAu 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 Pt3C2H4, 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 PtPtAu 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–Au2 system where the BE is 14.2 kcal/mol. Finally, replacement of the two surface Pt atoms by Au atoms produces a PtAu2 system which is unable to chemisorb the C2H4 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 C2H4. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 699–707, 1999