Aluminium distribution in the zeolites offretite and erionite

Abstract

In earlier interpretations of offretite and erionite 29Si n.m.r. spectra a random aluminium distribution is assumed; the best agreement between observed and calculated spectra is normally obtained with a lower Si Al ratio than expected from chemical analyses. In this work observed spectra from offretite and erionite with different Si Al ratios have been compared with calculated spectra assuming both a random and a non-random aluminium distribution. A non-random aluminium distribution with a preferred aluminium occupation on the T 2 sites, ( Si Al(T 1 site) in the range 0.43–0.55), results in an optimum fit between the observed and the calculated spectra with the Si Al ratios in agreement with that determined by other analytical methods. An aluminium displacement in this range is also to be expected from considerations of the cation filling in the structures.