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The sections in this article are Introduction Physical Principles of X-Ray Adsorption and Electron Scattering Absorption of X-Rays Scattering of the Photoelectron Isolating the Oscillatory Part (χAX + χEX) from the Absorption Data Pre-Edge Subtraction and Determination of Eedge Post-Edge Background Removal and Normalization EXAFS The EXAFS Equation EXAFS Data Analysis Fourier Transformation Fourier Filtering Phase Shifts and Backscattering Amplitudes Derived from EXAFS Data Obtained from Reference Compounds Obtaining R, N and Δσ2, k-Space and R-Space Fitting The Use of Theoretical References Difference File Technique Structural Analysis with EXAFS of a Heterogeneous Single-Site Cr/SiO2 Ethylene Trimerization Catalyst. An Illustrative Example Introduction Raw XAS Data of New Cr/SiO2 Catalysts and CrCl3–TAC Reference Compound Fabrication and Calibration of Ab Initio Phase Shifts and Backscattering Amplitudes EXAFS Data Analysis Conclusions: EXAFS Data Analysis Atomic XAFS (AXAFS) Introduction Physical Principles of AXAFS The Field and Inductive Interactions Separation of AXAFS from EXAFS Data The Interatomic Potential Model for Metal–Support Interaction ΔXANES Technique Introduction Calculations of Pt L3 ΔXANES Using the FEFF8 Code Experimental ΔXANES Data from Pt/H-USY and Pt/NaY Experimental Information ΔXANES Spectra Relevance for Pt-Catalyzed Hydrogenolysis/Hydrogenation Reactions General Applicability of the ΔXANES Technique Acknowledgments Keywords: physical principles of XAS; EXAFS data-analysis; atomic XAFS; delta XANES

The adsorption site and the mode of ethylene bonding on Pt/Al2O3 catalysts have been determined. Theoretically obtained signatures using FEFF8 showed that the possible bonding modes of ethylene can be distinguished, which is experimentally shown for the room temperature adsorption of ethylene. This study shows that it is feasible to determine the structures of the adsorption sites and the modes of bonding of hydrocarbon molecules on the surfaces of supported metal catalysts.

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.

Two new techniques in X-ray absorption spectroscopy (XAS) have recently been developed which provide previously unobtainable information on supported noble metal catalysts. Atomic X-ray absorption fine structure (AXAFS) provides direct information on the average changes in interatomic potential of the metal particles induced by metal-support effects. Changes in the interatomic potential can now be directly related to changes in catalytic reactivity. Analysis of shape resonances near the X-ray absorption edge provides information on the changes in the nature of the bonding of adsorbates (like hydrogen) to the metal cluster as induced by the properties of the support. The strong decrease in activity of supported platinum clusters for neo-pentane hydrogenolysis with increasing alkalinity of the support can be ascribed to a decrease in ionization potential of the metal particles directly influenced by the alkalinity of the support.