Coordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on γ-Al2O3

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Science  25 Sep 2009:
Vol. 325, Issue 5948, pp. 1670-1673
DOI: 10.1126/science.1176745

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Bonding Oxides and Metals

The binding of noble metals that can act as catalysts to metal oxides that are reducible is assumed to occur at the exposed cation of the oxide. For nonreducable oxides such as aluminum oxide, it is not so obvious how the metal can bind strongly. Kwak et al. (p. 1670) used a combination of high-resolution transmission electron microscopy and solid-state magic-angle spinning nuclear magnetic resonance to study the anchoring of platinum at high and low loadings on alumina. At the surface, the Al3+ ions were penta-coordinated. Density functional calculations support a model in which the cation binds three oxygen atoms in the alumina and two from platinum oxide.


In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a critical role in determining particle morphology and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning nuclear magnetic resonance spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with density functional theory calculations to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a γ-Al2O3 catalyst support material. The results obtained show that coordinatively unsaturated pentacoordinate Al3+ (Al3+penta) centers present on the (100) facets of the γ-Al2O3 surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al3+penta = 1), whereas two-dimensional Pt rafts form at higher coverages.

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