Nitrogen Monoxide Adsorption on Pt₄ Clusters Coated on -Al₂O₃ (111) Surface

The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt₄) clusters supported on gamma alumina (-Al₂O₃) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt₄ geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt₄ on -Al₂O₃(111) surface in tetrahedron configuration is energetically more favorable as compared to that of the planar rhombus. However, it was found that NO molecule adheres strongly to Pt₄ with planar configuration on -Al₂O₃(111) surface. In addition, the NO adsorption calculation on the isolated Pt₄ clusters also shows similar preference to planar configuration. The local density of states (LDOS) reveals that the difference in reactivity comes from the different hybridization strengths between the electronic states of nitrogen atom and those of platinum tetramers. The results are in good agreement with the experiments which show similar tendency for CO and N₂O reactivity to gas-phase platinum clusters.