The Local Structure of Zeolites from X-Ray and Neutron Scattering Data

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CTS-0085036Raul F. LoboUniversity of Delaware"The Local Structure of Zeolites from X-Ray and Neutron Scattering Data"ABSTRACTLike many useful materials, zeolites are often idealized as perfect crystals, solids inwhich periodic long-range order is observed in all three directions in space. Yet, very frequently the useful properties of a material stem from a small amount of minority elements (or defects) incorporated within the structure that shift the local environment away from the average. In this project the Pair Distribution Function (PDF), as derived from X-ray and neutron diffraction patterns, is being measured to investigate the local atomic environment in an important group of industrially significant zeolites. The gas-adsorption behavior and the catalytic activity of these porous materials are intrinsically associated with minor amounts of aluminum substituted for silicon in the structure. Since both catalysis and adsorption are fundamentally local phenomena, the understanding of zeolite properties thus depends on a detailed knowledge of the geometry of the sites. The research objective is to determine in detail the atomic geometry of these sites using the PDF.The results will help to explain the properties of various zeolites in their roles as catalysts and adsorbents. More detailed structure-property information will guide the design and synthesis of new, more effective materials with enhanced properties. The experimental structural data will also be valuable as a guide in the molecular modeling of zeolite properities.