NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIC STUDY OF SPIN-LATTICE RELAXATION OF QUADRUPOLAR NUCLEI IN ZEOLITES

We have obtained the temperature-dependent nuclear magnetic resonance spin-lattice relaxation times of several nonintegral spin quadrupolar nuclei (O-17, Na-23, Al-27, and Ga-17) in a series of hydrated zeolites (NaA, NaX, NaY, NaGaY, and NH4-ZSM-5) at 8.45 T. There is no correlation between T1 and the static part of the electric field gradient, which gives rise to the observed nuclear quadrupole coupling constants (e2qQ/h). In all cases, however, we find that relaxation is overwhelmingly dominated by modulation of the time-dependent electric field gradient at the nuclear site due to motion of water molecules and hydrated cations in the zeolite pores. The relaxation times are a function of Si/Al ratio as well as hydration. Our results provide estimates of the Sternheimer antishielding factors (1 - gamma-infinity) in moderate agreement with generally accepted literature values and should be applicable to analysis of the relaxation behavior of other nonintegral spin quadrupolar nuclei in zeolites, e.g., Li-7, B-11, K-39, Rb-87, and Cs-133.