The electronic and geometric e †ects 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 Ðne structure (XAFS) spectroscopy. A new subtraction procedure was developed to separate the electronic from geometric e †ects. A signiÐcant PtÈH extended X-ray absorption Ðne structure (EXAFS) scattering (structural e †ect) was found for energy values between 0 and 20 eV. In addition, the PtÈH antibonding state (electronic e †ect) was found to produce a shape-resonance and was isolated from the near edge of the X-ray L 3 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 inÑuence of the support on the electronic properties of the platinum particles. The results of the study of the resonance state and the PtÈH EXAFS scattering demonstrate the potential of these techniques for characterization of hydrogen chemisorption, metal-promoter, and metal-support e †ects in catalysis research.

The activity and selectivity of hydroisomerization of n-hexane over Pt/mordenite is strongly influenced by acid leaching. The activity increases and the selectivity changes to favor primary products. Leaching selectively modifies the mordenite structure, making more sites accessible for reaction and facilitating desorption of reaction products. It is argued that the activity of untreated mordenite is limited by mass transfer effects. These effects largely vanish after modification of the zeolite structure by generation of a 3-D micropore structure as well as mesopores. The alleviation of intracrystalline diffusion limitation is the major factor in activity enhancement after acid leaching of Pt/mordenite.

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