Abstract
We investigated the reactivity of CeO2-supported Pt4 cluster (denoted as Pt4/CeO2(111)) toward O2 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 Pt4 binds strongly to CeO2(111) via PtOCe 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 CeO2, 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 O2 adsorbs on Pt4/CeO2(111), while it prefers Pt vertex site near the CeO2 surface, the OO bond elongation is more profound at the PtPt edges. The energy barrier for dissociating O2 from this edge site precursor state is smallest. A correlation between the OO bond length at the precursor state and the stability at the transition state is revealed. Finally, the barrier for dissociation in unsupported Pt4 is lower, indicating suppression of the cluster's reactivity due to the support. We attribute this to the hybridization of Pt-5d orbitals with O-2p orbitals in CeO2(111) leading to the broadening of Pt-5d states near the Fermi level.
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