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Nature of the Chemical Bond between Metal Atoms and Oxide Surfaces: New Evidences from Spin Density Studies of K Atoms on Alkaline Earth Oxides

2005; American Chemical Society; Volume: 127; Issue: 48 Linguagem: Inglês

10.1021/ja0542901

1943-2984

Mario Chiesa, Elio Giamello, Cristiana Di Valentin, Gianfranco Pacchioni, Zbigniew Sojka, Sabine Van Doorslaer,

Crystal Structures and Properties

We have studied the interaction of K atoms with the surface of polycrystalline alkaline-earth metal oxides (MgO, CaO, SrO) by means of CW- and Pulsed-EPR, UV−Vis−NIR spectroscopies and DFT cluster model calculations. The K adsorption site is proposed to be an anionic reverse corner formed at the intersection of two steps, where K binds by more than 1 eV, resulting in thermally stable species up to about 400 K. The bonding has small covalent and large polarization contributions, and the K atom remains neutral, with one unpaired electron in the valence shell. The interaction results in strong modifications of the K electronic wave function which are directly reflected by the hyperfine coupling constant, Kaiso. This is found to be a very efficient "probe" to measure the degree of metal-oxide interaction which directly depends on the substrate basicity. These results provide an original and general model of the early stages of the metal−support interaction in the case of ionic oxides.