17O MQMAS NMR studies of zeolite HY

Abstract

High-resolution 17O multiple-quantum MAS (MQMAS) NMR spectra have been obtained for zeolite HY in order to study its local structure and Brønsted acidity. The 17O NMR signals due to all the different oxygen environments have been observed in one single experiment, including the readily-resolved signals arising from the two types of oxygen atoms of the zeolite framework (Si–O–Al and Si–O–Si), and oxygen atoms directly bound to Brønsted acid sites (Si–O(H)–Al). The 17O NMR parameters such as the isotropic chemical shift ( δ CS) and quadrupolar coupling parameters (quadrupolar coupling constant, QCC and asymmetry parameter, η) for these oxygen species have been extracted and found to be consistent with the results from previous NMR measurements. The NMR parameters of the framework sites reveal a greater distribution of T–O–T′ bond angles over those typically observed in hydrated zeolites.