Abstract
This chapter demonstrates the possibilities of using electron paramagnetic resonance (EPR) imaging as a useful tool for the characterization of diffusion and coking processes in zeolite powders and in pelletized zeolite catalysts. The measurements have been carried out by using a conventional EPR spectrometer ERS 221 and the accessory unit ZZG1 for tomography, produced by the Centre of Scientific Instruments of the Academy of Sciences of the German Democratic Republic. The EPR spectra and their temperature dependence demonstrate this motional behavior. The technique of spectrally resolved EPR imaging with multiple-stepped stationary gradient was used. EPR imaging is one of the powerful methods that are able to provide valuable information about coke formed in pellets. In most hydrocarbon reactions catalyzed by zeolites, the deactivation of the catalyst due to coke deposition is a serious problem. The spatial distribution of nitroxide molecules and of coke in zeolite powders and in zeolite catalyst pellets, respectively, was measured with the modulated-gradient technique.
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