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The study of 29Si MAS NMR spectra of zeolites of both low and high Si/Al ratios has provided insight on the factors affecting the residual 29Si line-widths of these materials. It is found that the residual linebroadening in low Si/Al ratio zeolites is due to the distribution of local environments of a particular Si(nAl) type, resulting from the distribution of aluminium atoms in second and further coordination spheres. This is complicated in some cases by a distribution of chemical shifts resulting from crystallographic inequivalence, each of which is subject to the above environmental broadening factors.

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