Diffusion of Water in Zeolites

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Abstract
The self-diffusion coefficient D of water occluded in samples of near-faujasite has been determined by pulsed field-gradient spin-echo nuclear magnetic resonance. The value of D in square centimeters per second × 10 5 at 30°C is 1.34, 1.65, and 1.88 in the following zeolites, respectively: Na X , Ca X , and Ca Y ( X and Y being an indication of ratio of silicon to aluminum in the zeolites). By comparison, the value of D in pure water at 30°C is 2.5 × 10 -5 cm 2 /sec. Arrhenius activation energies for D are 6.9, 6.8, and 5.6 kilocalories per mole, respectively, for the three faujasites and 5.0 kcal/mole for pure water. Thus, there appears to be little difference in diffusion behavior between free water and water occluded in faujasite.