29Si and 27Al MAS NMR characterization of non-hydrated zeolites Y upon adsorption of ammonia

Abstract

Solid-state NMR characterization of zeolite catalysts in the hydrated state is often accompanied by an uncontrolled hydrolysis of the framework. In the present work it is demonstrated that the limitations occurring for 29Si and 27Al MAS NMR spectroscopy of non-hydrated zeolites Y, such as strong decrease of resolution and significant line broadening, can be overcome by loading these materials with ammonia. In the 29Si MAS NMR spectra of non-hydrated and ammonia-loaded zeolites Y, no dehydration-induced high-field shift of Si( nAl) signals ( n = 3, 2, 1) occurs, which is generally responsible for the loss of resolution in the spectra of non-hydrated materials. The 27Al MAS NMR spectra of the non-hydrated and ammonia-loaded zeolites Y consist exclusively of signals of the tetrahedrally coordinated framework aluminum atoms with spectroscopic parameters similar to those of framework aluminum atoms in hydrated samples. The framework n Si/ n Al ratios of the non-hydrated zeolites Y obtained by both 29Si and 27Al MAS NMR spectroscopy upon ammonia-loading agree well with each other.