3-D Raman Spectroscopy of Large Zeolite ZSM-5 Crystals

Abstract

Hydrothermal treatment is a common method used to modify the physicochemical properties of zeolite-based catalyst materials. It alters the number and type of acid sites via dealumination and increases molecular diffusion via mesopore formation. Steaming also reduces the structural integrity of zeolite frameworks. In this study, we have used Raman microscopy to map large zeolite ZSM-5 crystals before and after steaming. 3-D elemental maps of T-O (T: Al or Si) sites of the zeolite were obtained. We have determined the Raman active vibrational bands, which are indicative of (non-) framework Al as well as of structural integrity. Zeolite steaming caused the introduction of additional heterogeneities within the zeolite framework. Al migration and the formation of extra-framework Al species were observed. The described experiments demonstrate the capability of 3-D Raman spectroscopy as a valuable tool to obtain information on the spatial distributions of framework elements as well as defects within a zeolite-based material.