Investigation by X-Ray Absorption Spectroscopy of Platinum Clusters Supported on Zeolites

Dedicated to Professor G. M. Schwab on his 80. birthday The onset of the Lm edge of the X-ray absorption spectrum of platinum in F-zeolites involves an electronic transition from core to band levels producing a so-called white line. The spectral area of this increases and the edge position shifts to higher energies, first when the platinum particle size becomes small enough so that the clusters are in the supercages, second when the clusters are covered with oxygen, and third when multivalent cations are introduced in the zeolite. Both features of the absorption edge indicate that under the three above circumstances, platinum becomes more electron deficient. This conclusion had been inferred earlier from the enhanced catalytic activity of Pt clusters in Y zeolites.