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The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt4) clusters supported on gamma alumina (gamma-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 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 Pt4 with planar configuration on gamma-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.

Density-functional calculations were performed to study Pt-O bonding interaction on core-shell Ni@Pt and pure Pt clusters composed of 55 atoms each. Based on oxygen adsorption energy and ν(Pt-O) stretching frequency, the global trend of Pt-O bonding strength in the clusters accommodates the successive order of bridge (and/or hcp-like) > fcc-like > vertex site. Further analysis on oxygen-induced reconstruction effect using first nearest neighbor (1NN) analysis shows that 1NN Pt-Pt distribution pattern of surface atoms changes abruptly after oxygen adsorbed. The profiles of distorted 1NN distribution pattern are greatly determined by the position and the number of adsorbed oxygen on the clusters including whether the cluster type is core-shell or not. The broadening distribution pattern clearly indicates deviation of Pt-Pt bond length due to Pt-O bonds formation and the general trend is similar with the one observed in platinum-related spectroscopy studies.

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We investigated the reactivity of CeO 2 -supported Pt 4 cluster (denoted as Pt 4 /CeO 2 (111)) towards O 2 adsorption and dissociation as well as the geometry/electronic properties associated with such metal oxide supported cluster system using Density Functional Theory and on-site Coulomb interaction correction via the Hubbard-like term, U (DFT+U). It was found that Pt 4 binds strongly to CeO 2 (111) via Pt-O-Ce bonds which act as "anchors" between the surface and the cluster, confirming its non-sintering as found in experiments. The adsorption of the cluster involves net electron transfer to CeO 2 , however, charge redistribution also happens within the cluster (from Pt atom bonded to the surface to the Pt on top of the cluster). This charge couples to the top Pt leading to reduce its spin moment as compared to that of unsupported cluster. When O 2 adsorbs on Pt 4 /CeO 2 (111), while it prefers Pt vertex site near the CeO 2 surface, the O-O bond elongation is more profound at the Pt-Pt edges. The energy barrier for dissociating O 2 from this edge site precursor state is smallest. A correlation between the O-O bond length at the precursor state and the stability at the transition state is revealed. Finally, the barrier for dissociation in unsupported Pt 4 is lower, indicating suppression of the cluster's reactivity due to the support. We 2 attribute this to the hybridization of Pt-5d orbitals with O-2p orbitals in CeO 2 (111) leading to the broadening of Pt-5d states near the Fermi level.