APPLICATION OF MOSSBAUER-SPECTROSCOPY FOR THE CHARACTERIZATION OF IRON-CONTAINING CATALYSTS

Work in our laboratory demonstrates the unique analytical power as wel l as the limits of Mossbauer Spectroscopy (MES) as a tool for characte rizing the size and phase of supported iron containing catalyst partic les, particularly carbon supported catalysts. The major challenge in e mploying MES to characterize catalytic particles is understanding the impact of the relaxation effects on the spectra. Proper methods yield particle size and phase information, whereas improper interpretation c an lead to the misidentification of phases. This is illustrated by fee ding ersatz ''relaxed'' spectra data, generated mathematically with a program which accounts for all aspects of relaxation, to a standard fi tting routine. The fitting routine misinterprets the data and provides false phase identification. Methods for recognizing relaxation phenom ena and strategies for extracting correct information from relaxed spe ctra are reviewed. Also reviewed are the major findings of studies on carbon supported catalysts. For example, MES studies, in conjunction w ith other techniques, demonstrate that bulk and surface structures whi ch are easily accessible for carbon supported bimetallics are generall y not found on refractory oxides.