NMR invisible aluminum species in dealuminated mordenite zeolite:: a 1H/27Al TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced H-1/Al-27 TRAPDOR method as well as Al-27 magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0 +/- 0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non-framework aluminum species Al(OH)(n), respectively. The source of the "invisible Al" is discussed on the basis of the NMR experimental results.