Beam-size-related phenomena and effective normalization in energy-dispersive EXAFS for the study of heterogeneous catalysts, powder materials and the processes they mediate: observations and (some) solutions.
The effects of focal spot size and the nature of powder samples (such as heterogeneous catalysts) on the quality of data obtainable from a dispersive EXAFS experiment are characterized at ID24 of the ESRF. Using examples of supported Pd catalysts, it is shown that, for a given photon flux, massive improvements in data quality can be achieved by increasing the size of the dispersive beam in the vertical, whilst concurrently applying a methodology to account for scattering effects emanating from the samples under study. These improvements are demonstrated using progressively practical and demanding examples. Questions regarding optimal beam dimensions for the study of such materials, how to counter undesirable effects that arise from the coherence of the source, how to obtain similar results consistently across the 5-30 keV bandwidth of ID24, and whether a methodology for simultaneous normalization in dispersive EXAFS is of significant utility in such circumstances are discussed.
Newton
Mark A
MA
European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, BP 220, 38043 Grenoble, France. newton@esrf.fr