Site-selective XAFS Spectroscopy Tuned to Surface Active Sites of Copper Catalysts
To overcome the problem of X-ray absorption fine structure
(XAFS) spectroscopy in which the obtained information is the average for all
sites in sample, Rowland-type fluorescence spectrometer was designed to measure
site-selective XAFS spectra by utilizing the chemical shift of emission peak
for each site. Johansson-type cylindrically-bent Ge(111) crystal and scintillation
counter were mounted on the spectrometer. The improvement of energy resolution
of spectrometer was discussed when the primary beam size and two slit size
in the Rowland circle were varied. The energy resolution was ~1.1 eV, smaller
than the core-hole lifetime width for Cu K alpha1 (2.11 eV). The site selection
of the Cu(0) and Cu(I) site-tune spectra was experimentally measured for the
physical mixture of Cu metal + Cu(I) and for Cu/ZnO catalyst. Obtained experimental
site selection was compared to the theoretical estimations.
Site-selective XANES spectra for the physical mixture of copper metal and copper(I) iodide. The fluorescence spectrometer was tuned to 8046.6 eV (a) and 8049.1 eV (b). Conventional fluorescence XANES spectra for the physical mixture of Cu metal + CuI (c), Cu metal (d), and CuI (e). All the samples were diluted in boron nitride matrix to Cu 5% (w/w).