ENHANCED RESOLUTION IN THE H-1-NMR SPECTRA OF ZEOLITE H-ZSM-5 BY HETERONUCLEAR DIPOLAR-DEPHASING SPIN-ECHO MAS

Dipolar-dephasing with high power Al-27 irradiation yields H-1 MAS NMR echo spectra of 'aluminium-unconnected' hydroxyl groups in dehydrated zeolites. The aluminium-connected SiOHal and AlOH hydroxyls can be ob served as the difference spectra. The technique increases the number o f OH lines in the 1H NMR spectra of dehydrated zeolite H-ZSM-5. Two ki nds of Bronsted sites can be distinguished and interpreted in terms of their mobility in the vicinity of framework aluminium atoms.