Characterization of industrial catalysts by EXAFS

Abstract
Industrial catalysts are designed to present very high specific surface areas and are thus in general poorly crystallised, being often amorphous to X-ray diffraction for instance. In addition the working conditions of these solids are severe, high temperatures and pressures of reactive gases are used during both use and preparation. The penetrating power of X-rays enables in-situ devices to be built so that the the processes involved in activation and deactivation of catalysts can be followed. Several families of industrial catalysts are easily amenable to X-ray absorption spectroscopy analysis. These include sulfide based catalysts, typically with over ten weight percent metal content. Problems are encountered in the study of precious metal systems, for example platinum based bimetallic catalysts supported on aluminium oxide,where metal loading is lower (less than one weight percent). Using in-situ conditions enables studies of the dynamics of reactions and of the state of working catalysts. The structural modifications observed indicate that this type of study is often necessary to obtain meaningful relationships between the state of the solid and its chemical behaviour.