Identification of Molecular Sieve Structures

Abstract

When we ask what characterization techniques would constitute the “bare necessities” for identification of a molecular sieve structure, two techniques stand out over the rest: X-ray powder diffraction and adsorption capacity measurements. X-ray powder diffraction indicates uniqueness in structure, as the powder diffraction pattern is a fingerprint of individual zeolite structures. The powder pattern also can provide information on the degree of crystallinity as well as phase purity, which is used for quality control in preparing different batches of known zeolite materials. Unit cell volume, calculated from the diffraction data, is sensitive to the amount of aluminum in the structural sites, expanding with decreasing SiO2/Al2O3and providing compositional information about the structure. Cell volume changes also indicate the degree of incorporation of other framework elements. Table 5.1 summarizes the information obtainable from X-ray powder diffraction.