Enhanced resolution in the 1H NMR spectra of zeolite H-ZSM-5 by heteronuclear dipolar-dephasing spin-echo MAS

Dipolar-dephasing with high power 27Al irradiation yields 1H MAS NMR echo spectra of ‘aluminium-unconnected’ hydroxyl groups in dehydrated zeolites. The aluminium-connected SiOHAl and AlOH hydroxyls can be observed as the difference spectra. The technique increases the number of OH lines in the 1H NMR spectra of dehydrated zeolite H-ZSM-5. Two kinds of Brønsted sites can be distinguished and interpreted in terms of their mobility in the vicinity of framework aluminium atoms.