NEW ASSIGNMENT OF THE SIGNALS IN NA-23 DOR NMR TO SODIUM SITES IN DEHYDRATED NAY ZEOLITE

A new assignment of the signals in the Na-23 DOR NMR spectra to the di fferent sodium sites in dehydrated NaY zeolite is presented. Na-23 DOR and MAS NMR measurements of dehydrated NaY, Ca2+-exchanged NaY sample s, and NaY samples in which Mo(CO)6 is adsorbed are used for this purp ose. Four distinct signals in the Na-23 DOR NMR spectra of dehydrated NaY are found: the first signal with an isotropic chemical shift of -6 ppm and a quadrupolar coupling constant of 0.4 MHz is assigned to the Na+ cations at site I. The second signal, with an isotropic chemical shift of -12 ppm and a quadrupolar coupling constant of 2.3 MHz, is as signed to the Na+ cations at sites I'/II'. The third and the fourth si gnals, with isotropic chemical shifts of -4 and 5 ppm and quadrupolar coupling constants of 4.2 and 4.7 MHz, respectively, are assigned to t he Na+ cations at sites II and III.