A Development of EXAFS and XANES Measurements in the Laboratory An Application to Silica Supported Cu-Rh Bimetallic Catalyst

Abstract

An attempt was made to improve an extended X-ray absorption fine structure (EXAFS)facility by the use of higher-order reflections from dispersing crystals. A resolution good enough to observe X-ray absorption near edge structure (XANES) has been obtained in the lower energy region (5-10 keV), and EXAFS measurements have been extended to cover up to about 26 keV, including K absorption edges of Ru, Rh, Pd, and Ag, which are important in catalysis. Some examples of the performances of this spectrometer are presented. By making use of the spectrometer, local structures around Cu and Rh atoms in Cu-Rh/SiO2catalysts have been studied by the EXAFS of Cu and Rh and also by the XANES of Cu. The catalysts prepared by two kinds of preparation procedures, the impregnation method and the alkoxide method, have been examined. In the catalysts prepared by both methods, Rh atoms are in the metallic environment and surrounded by other Rh atoms, but Cu atoms are not. It is concluded that Cu atoms have both Cu and Rh neighbors and are concentrated on the surface. The tendency is more pronounced in the catalyst prepared by the alkoxide method, indicating a difference in the metal particle size of the two catalysts prepared by the different methods.