Contribution of a Shape Resonance and Pt-H EXAFS in the Pt L2,3 X-ray Absorption Edges of Supported Pt Particles: Application and Consequences for Catalyst Characterization

The electronic and geometric effects induced by hydrogen chemisorption on small platinum particles supported on high surface-area saponite clay and zeolite LTL were studied by near edge X-ray absorption fine structure (XAFS) spectroscopy. A new subtraction procedure was developed to separate the electronic from geometric effects. A significant Pt-H extended X-ray absorption fine structure (EXAFS) scattering (structural effect) was found for energy values between 0 and 20 eV. In addition, the Pt-H antibonding state (electronic effect) was found to produce a shape-resonance and was isolated from the near edge of the L3 X-ray absorption spectrum. Moreover, for Pt/LTL the shape and energy of the shape-resonance was found to strongly depend on the acidity/alkalinity of the support material, implying a direct influence of the support on the electronic properties of the platinum particles. The results of the study of the resonance state and the Pt-H EXAFS scattering demonstrate the potential of these techniques for characterization of hydrogen chemisorption, metal-promoter, and metal-support effects in catalysis research.