THEORETICAL CHARACTERIZATION OF H-2 ADSORPTION ON AUPT CLUSTERS

Linear and triangular AuPtn cluster reactions with H-2 are studied the oretically, using ab initio multiconfiguration self-consistent field ( MC-SCF) calculations, followed by extensive multireference configurati on interaction (MR-CI) variational and perturbative. Both the linear d imer and the triangular trimers capture the hydrogen molecule by the P t cluster side and by the Au cluster side. Gold has an electronic effe ct on the Pt activity, more important than a geometrical one, poisonin g the Pt activity to dissociate H-2 and lowering the adsorption heats. This effect is stronger in the AuPt dimer, where the H-2 capture occu rs only at the molecular level, without showing hydrogen bond dissocia tion. The trimers look more active, relaxing the H-H bond until breaka ge. No activation barriers are observed in all the cases considered. T he hydrogen molecule is not able to cross the clusters due to the larg e barriers present. (C) 1998 John Wiley & Sons, Inc.