High-field 1H MAS NMR investigations of acidic and non-acidic hydroxyl groups in zeolites H-Beta, H-ZSM-5, H-ZSM-58 and H-MCM-22

Abstract

Solid-state NMR investigations of acidic and non-acidic hydroxyl groups in dehydrated zeolites H-Beta, H-ZSM-5, H-ZSM-58 and H-MCM-22 have been carried out in an external magnetic field with a flux density of B o = 18.8 T. The variety of signals which have been found in the high-field 1H MAS NMR spectra indicate a heterogeneity of Brønsted sites in zeolites. 1H MAS NMR signals observed at chemical shifts between 1.2 ppm and 2.6 ppm are due to silanol and AlOH groups. Depending on the zeolite type, the spectra consist of up to four signals of bridging OH groups in the range of 3.6 ppm and 5.0 ppm. Signals at 6.3 to 8.7 ppm are explained by hydrogen bonded internal silanol groups.