Diffusion of Water in Zeolites
Carlo Parravano 1,
J. D. Baldeschwieler 1, and
Michel Boudart 1
1 John Stauffer Laboratories for Chemistry and Chemical Engineering, Stanford University, Stanford, California 94305
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 x 105 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 x 10-5 cm2/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.
