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 SiO 2 /Al 2 O 3 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 (V u.c. ), and the framework aluminum content (N Al ) were established. For the samples synthesized in the presence of an organic template and sodium cations, the relation between N Al and V u.c. is given by N Al = (V u.c. − 5332 Å 3 )/15.13. A similar equation was computed for H-ZSM-5 zeolites: N Al = (V u.c. − 5330 Å 3 )/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.

Zeolite Crystal Engineering

“…It has been known for some time, but is becoming increasingly more evident, that the ability to control the number and spatial arrangement of aluminum in zeolite frameworks can have a profound impact on materials properties and their performance in applications, particularly in the area of catalysis. Aluminum siting can be controlled by the judicious selection of one or more structure-directing agents or by the use of seeds or IZT synthesis methods. − Control of aluminum composition can impact physical properties, such as unit cell volume or hydrothermal stability, which can likewise influence their performance in applications spanning separations to catalysis.…”