Information on Metal-Support Interactions from Near Edge X-ray Absorption Spectroscopy and Multiple Scattering Calculations

Abstract

We have used the L edge resonances in the x-ray absorption spectrum to obtain information on changes in the electronic structure of supported catalysts, compared to the bulk metal. The areas of the L2 and L3 edge resonances in silica and alumina-supported Ir catalysts indicate that the catalyst metal particles have a lower d orbital occupancy than the bulk metal. An approximate quantitative measure of the d orbital occupancy has been obtained using a calibration for a series of compounds based on multiple-scattering Xα calculations. At 90K the L2 and L3 edge regions in a silica-supported Pt catalyst show increased absorption 5-10 eV above the edge, compared to the same region in the bulk metal. We attribute this increased absorption to a transition to an empty antibonding state arising from the bonding of the metal particles to the support anions. Multiple-scattering Xα calculations on a simple cluster model of the