Techniques for the general study of inorganic compounds are used in the structural studies of zeolites:
- X-ray Diffraction (XRD) - plays a major role, but this is mainly as poder diffraction work as zeolite single crystals are extremely difficult to produce. With the development of Reitveld "profile" refinement in the early 1970's, came a technique to obtain high quality structural data from neutron diffraction methods. Neutron diffraction studies are becomming increasingly imortant, and have an advantage over X-ray diffraction in that neutron diffraction there is a significant difference between the scattering lengths for neutrons of alumnium and silicon, allowing for the Si-Al distribution over the tetrahedral sites to be studied. Increasing used is being made of X-ray methods, with high quality results obtained when synchrotron radiation is used as the X-ray source, giving narrow, well defined peaks in the spectra. High resolution electron microscopy can be used to image zeolite structures, and canbe used to study extended faults within the structure, which are not possible to see with diffraction methods.
- Magic Angle Spinning Nuclear Magnetic Resonance (MASNMR) - allows high resolution structural data to ne obtained for the zeolite solid, since spinning at the magic angle of 54°.44' effectively removes the line broadening influences in the slid state NMR spectrum. Most studies are centred upon 29Si NMR, with the observed chemical shift dependant on the nucleic environment. The shift will therefore be different if 0, 1, 2, 3 or 4 silicon atom are in the four surrounding tetrahedral sites.
Development of 2D-NMR techniques such as COSY and NOESY methods to zeolite systems is progressing, and is an excellent tool when combined with high resolution powder diffraction techniques.
- Extended X-ray Absorption Fine Structure (EXAFS) - is a technique widely used in materials and biological sciences and examines the oscillations in intensity caused by excitation of electrons from core levels to continuum levels. The oscillations are present due to photoelectron backscattering created by the excitation. EXAFS experiments are useful in the study of the structure of the local cage environment, and in extra-framework cations.