D. Freude, ENHANCED RESOLUTION IN THE H-1-NMR SPECTRA OF ZEOLITE H-ZSM-5 BY HETERONUCLEAR DIPOLAR-DEPHASING SPIN-ECHO MAS, Chemical physics letters, 235(1-2), 1995, pp. 69-75
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.