2D multiquantum MAS-NMR spectroscopy of 27Al in aluminophosphate molecular sieves

Two-dimensional multiquantum MAS-NMR spectroscopy (2D-MQ) has been applied to the discrimination of the different 27Al sites in several aluminophosphate molecular sieves. It is shown that a new quintuple-quantum MAS-NMR method (2D-5Q) gives an extraordinary improved resolution compared to the DOR or DAS technique. The pure-absorption 2D spectra allow the direct determination of the number of different species, the correct determination of their actual chemical shifts and quadrupolar parameters. In addition, the method gives incomparable information about the distributions of both the chemical shifts and quadrupolar coupling constants. These findings are demonstrated by the experimental spectra of the ALPO-11 and VPI-5 aluminophosphate molecular sieves.