Abstract
Hydrogen chemisorption on small silica-supported Pt clusters was investigated using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy. The clusters were found to exhibit a bulklike Pt first nearest neighbor (NN) distance (2.76 A) and low disorder while covered by chemisorbed hydrogen. In contrast, bare Pt clusters produced by heating in vacuo at 300 °C are characterized by a contracted Pt NN distance (2.66 A) and greater disorder. These effects are reversed by re-exposure of the bare Pt clusters to H2 at 25 °C. The metal−support interface is characterized by a short Pt−O distance, irrespective of the presence of chemisorbed hydrogen. An apparent L3 edge shift of 0.8 eV relative to bulk Pt is observed for the hydrogen-covered clusters. This shift is attributed to a decrease in the Pt L3 edge resonance (white line) intensity, as no corresponding shift is observed at the L2 edge. A hydrogen-related L2,3 XANES feature at 9 eV ap...
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