Ethylene, sulphur, and chlorine coadsorption on Pd(111): a theoretical study of poisoning and promotion

First principles calculations for the coadsorption of C3H4 with S and Cl on Pd(111) are presented. Sulphur poisons adsorption, decreasing the strength of the ethylene-surface interaction. While low coverages of chlorine alone do not appear to affect ethylene adsorption on the otherwise clean palladi um surface, chlorine does act as a promoter on the sulphur poisoned surface , increasing the strength of the ethylene-surface interaction. The promotio nal effect is attributed to changes in the dative bonding of the molecule a nd the surface and cannot be explained solely in terms of changes in the me tal workfunction. (C) 1999 Published by Elsevier Science B.V. All rights re served.