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

The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt-4) clusters supported on gamma alumina (gamma-Al2O3) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt-4 geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt-4 on gamma-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 Pt-4 with planar configuration on gamma-Al2O3(111) surface. In addition, the NO adsorption calculation on the isolated Pt-4 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.