Ethylene adsorption on the Pt-Cu bimetallic catalysts. Density functional theory cluster study

The vibrational frequencies of C2H4 adsorbed on the clusters of D4h and C3v symmetry have been calculated. The phonon vibrations occur below 250 cm−1. The intense bands around 200 cm−1 are attributed to stretching vibrations of the Pt-Cu bonds normal to the cluster surface. The stretching vibrations of the Pt-C bonds depend on the local structure of the active site: νs(Pt-C) = 268 cm−1 and νas(Pt-C) = 357 cm−1 for the cluster of the D4h symmetry; νs(Pt-C) = 335 cm−1 and νas(Pt-C) = 397 cm−1 for the cluster of the C3v symmetry. Bands in the range of 800-3100 cm−1 are attributed to vibrations of the adsorbed C2H4 molecule. The signature frequencies of the π-C2H4 adsorption complex are the δs(CH2) deformation vibration at ∼1200 cm−1 and the ν(C-C) stretching vibration at ∼1500 cm−1. These vibration are absent for di-σ-C2H4 adsorption complexes.