DOUBLE-ROTATION AL-27 NMR IN MOLECULAR-SIEVES

Although high-resolution NMR spectra can be obtained in solids, the us e of Al-27 NMR to investigate the structure of aluminosilicate and alu minophosphate molecular sieves has been severely limited because aniso tropic second-order quadrupolar interactions, responsible for spectral broadening, cannot be eliminated by conventional magic angle spinning (MAS) or multiple pulse techniques. Here we give the principles of th e double rotation (DOR) NMR technique which can remove not only the fi rst-order broadenings but also the second-order broadenings in the NMR spectra of quadrupolar nuclei in solids. High-resolution Al-27 NMR us ing DOR is capable of resolving discrete framework aluminum sites in a luminophosphate molecular sieves, permitting quantitative investigatio n of site-specific adsorbate-host interactions, and of discriminating different aluminum species in zeolites.