The dehydrogenation of ethylene on Pd second-neighbor ensembles of both PdAu(1 0 0) and PdAu(1 1 1) surface alloys in presence of surface oxygen atoms (Os) and hydroxyl groups (OHs) was investigated at the density functional level with a cluster model approach. The calculated activation barriers for ethylene dehydrogenation to form vinyl on Os-and OHs-covered PdAu surfaces are significantly lower than those on clean surface alloys. Therefore, our outcomes suggest that a Langmuir-Hinshelwood-type mechanism involving a vinyl surface species cannot be excluded a priori when investigating the microscopic behaviour of the oxygen-assisted acetoxylation of ethylene on PdAu catalysts. (C) 2010 Published by Elsevier B.V.