Interaction of H2 with gold–palladium binary clusters: Molecular and dissociative adsorption

We present density functional calculations of H2 molecular and dissociative adsorption on small bimetallic AunPdm clusters with n + m ⩽ 5. Molecular adsorption is found to be favorable for Au2, Au3 and Au2Pd clusters, while dissociative adsorption is favored for other clusters. The H atoms draw electrons from the metal clusters in dissociative adsorption while the H2 molecule donates electron density to metal clusters in molecular adsorption. The H2 molecule prefers binding to Pd atoms when both Au and Pd sites co-exist and the metal framework is related to the ground state of bare AunPdm cluster in molecular adsorption. In contrast, the geometries of metal framework are greatly changed upon H2 dissociative adsorption. The binding energy per atom and the HOMO–LUMO gaps for molecular and dissociative adsorptions were also compared and discussed. The Au4PdH2 cluster shows the relatively higher stability among the physisorbed structures.