Site-selective X-ray absorption fine structure (XAFS) spectroscopy (2). XAFS spectra tuned to surface active sites of Cu/ZnO and Cr/SiO2 catalysts

Site-selective XAFS spectra were measured by tuning the Rowland-type fluore scence spectrometer to each site of Cu/ZnO and Cr/SiO2 catalysts. The chemi cal shifts between Cu-0 and Cu-I sites and between Cr-III and Cr-VI sites w ere relatively large for model compounds (Delta E = 1.6 eV), and were utili zed as the tune energies of site-selective XAFS. Site-selective XANES tuned to Cu-0, Cu-I, and Crm sites were successfully obtained. Based on the corr elation between the chemical shift and the peak width (energy resolution of the fluorescence spectrometer), site-selective XANES spectra were analyzed . The population ratio of Cu metal, Cu2O, and Cu-I atomically dispersed on ZnO was estimated to be 70(+/- 23) : 22(+/- 14) : 8(+/- 5). The contributio n of the Cr-III site to site-selective XANES tuned to the Cr-III site was 9 4(+/- 3)%.