Fully optimized geometries and adsorption energies obtained from nonlocal density functional calculations are presented for Pd-n(C2H4) (n = 1-6) clusters. The adsorption mode can be pi or di-a according to the cluster size. The di-sigma adsorption mode is characterized by a strong distortion for both the ethylene and the metal cluster. The potential energy surfaces for the C-H activation show that the d(10) configuration of palladium is suitable for the formation of the it molecular complexes, whereas the d(9)s(1) configuration is suitable for the formation of the sigma bonds of the vinyl-hydride products.