NMR INVISIBLE ALUMINUM SPECIES IN DEALUMINATED MORDENITE ZEOLITE - A H-1 AL-27 TRAPDOR NMR-STUDY/

Various kinds of aluminum species in dealuminated mordenite were inves tigated in detail, and the quadrupole coupling constants (QCCs) for al uminum atoms associated with these species were obtained by means of t he newly introduced H-1/Al-27 TRAPDOR method as well as Al-27 magic an gle 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 ki nds of non-framework aluminum species Al(OH)(n), respectively. The sou rce of the ''invisible Al'' is discussed on the basis of the NMR exper imental results.