Tracking deactivation of zeolite beta with and without a detailed structure model: XRD analysis and in situ studies

Abstract

This paper introduces two versatile new models for assessing the deactivation level of the industrially useful catalyst Beta zeolite. 1) a stacking disorder (SD) model: in which supercells built from stacked layers with refined faulting probability are generated, averaged and fitted to the powder pattern, and dummy carbon atoms in the pore system allow estimation of the degree of deactivation by coke; 2) a semi-empirical (SE) model: in which a reduced tetragonal unit cell is used to fit the sharp Bragg reflections in the PXRD pattern in a Le Bail-type fit and the broad, diffuse peaks are fitted individually to obtain intensities and positions. The reduced cell gives very precise lattice parameters, which can be determined quickly for a series of in situ data, while the ratio between the scale factor of the sharp reflection part in the model and the intensity of the first broad peak gives a measure of the degree of deactivation by coke. The models are validated, and their strengths and weaknesses compared by fitting of in situ PXRD data collected during temperature programmed oxidation of coke from two Beta zeolite samples fully deactivated in the MTH process. Analysis of such data from Beta zeolites has not been demonstrated before and could provide a convenient and useful tool for the chemical industry.