Application of Mössbauer spectroscopy for the characterization of iron-containing catalysts

Abstract

Work in our laboratory demonstrates the unique analytical power as well as the limits of Mossbauer Spectroscopy (MES) as a tool for characterizing the size and phase of supported iron containing catalyst particles, particularly carbon supported catalysts. The major challenge in employing 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 can lead to the misidentification of phases. This is illustrated by feeding ersatz “relaxed” spectra data, generated mathematically with a program which accounts for all aspects of relaxation, to a standard fitting routine. The fitting routine misinterprets the data and provides false phase identification. Methods for recognizing relaxation phenomena and strategies for extracting correct information from relaxed spectra are reviewed. Also reviewed are the major findings of studies on carbon supported catalysts. For example, MES studies, in conjunction with other techniques, demonstrate that bulk and surface structures which are easily accessible for carbon supported bimetallics are generally not found on refractory oxides.