Unit Cell Volume as a Measure of the Framework Composition of ZSM-5 Type Zeolites

Abstract

A simple X-ray powder diffraction procedure is proposed to determine the framework composition of ZSM-5 type zeolites. The procedure is based on a linear relation between the unit cell volume and the framework aluminum content found by analyzing two families of ZSM-5 zeolites with different SiO2/Al2O3 ratios. One family consisted of products synthesized in the presence of TPA+ cations while hydrogen forms were included in the second series of samples. Linear relationships between cell constants, cell volume (Vu.c.), and the framework aluminum content (NAl) were established. For the samples synthesized in the presence of an organic template and sodium cations, the relation between NAl and Vu.c. is given by NAl = (Vu.c. – 5332 Å3)/15.13. A similar equation was computed for H-ZSM-5 zeolites: NAl = (Vu.c. – 5330 Å3)/15.40. Equations derived can be used to evaluate the number of framework aluminum in the unit cell. In this way, the ratio of the framework and nonframework aluminum atoms in the samples of ZSM-5 type zeolites subjected to heat treatment can be estimated.