Internal transport resistances and their influence on diffusion in zeolites as traced by microscopic measuring techniques

Interference microscopy (IFM) and FTIR microscopy (IRM) are applied to study intracrystalline concentration profiles in SAPO-5, CrAPO-5 and ZSM-5 zeolite crystals. By using both techniques, the high spatial resolution of interference microscopy is complemented by the ability of FTIR spectroscopy to pinpoint adsorbates by their characteristic IR bands. In this way the experimental results are shown to unveil a number of remarkable deviations in the real structure of zeolite crystals from their textbook patterns. The influence of structural defects on the equilibrium concentration profiles as well as on sorption dynamics of guest molecules is investigated. Owing to the ability to gain direct insight into the influence of surface defects and intracrystalline defects on molecular uptake, the applied techniques give more accurate information on the molecular transport in zeolite crystals than the classical uptake methods.