The nitration of toluene with nitric acid and acetic anhydride using zeolite H-beta as catalyst was studied with multi-nuclear solid-state NMR spectroscopy in order to investigate the causes for the observed enhanced para-selectivity. The reversible transformation of framework aluminium from a tetrahedral into an octahedral environment was observed by Al-27 NMR upon interaction of the zeolite with the different components of the nitrating system. The octahedral co-ordination complex between lattice aluminium and acetylnitrate might explain the surface-catalysed para-selective nitration reaction and suggests that the lattice flexibility plays an important role in determining the regio-selectivity of the nitration catalysed by zeolites.