EXPERIENCES IN STUDYING ZEOLITES AND RELATED MICROPOROUS MATERIALS BY SYNCHROTRON X-RAY-DIFFRACTION

Synchrotron X-ray diffraction techniques can address a number of the challenges that zeolite materials present in attempts at atomic level structural characterization. With high-resolution powder diffraction, interpretations of complex patterns from multiphasic samples, as are often recovered from zeolite hydrothermal syntheses, are facilitated. Phase identifications and pattern indexings can be simplified and the possibilities for structure solution and for Rietveld refinements are extended. Additionally, there is broader scope for probing superlattice orderings, subtle symmetry distortions, anisotropic particle size broadening effects, and planar faulting behaviour (which is relatively common in zeolite systems, exemplified by the zeolites beta and ZSM-20). Single crystal diffraction techniques are less mature, but measurements on individual crystallites in the sub 5-mu-m regime, typical of most synthetic zeolites, are feasible. Additionally, the use of Laue geometry offers the promise of being able to make single crystal diffraction experiments on a time-scale appropriate for tracking the temporal evolution of processes such as ion exchange, sorption, or framework modification.