Localization of residual water in alkali-metal cation-exchanged X and Y type zeolites

The arrangements of residual water and alkali-metal cations in zeolites Y and X have been determined by Rietveld refinement in combination with Fourier analysis of X-ray powder patterns. The sodium forms NaY and NaX as well as partially cation exchanged forms MNaY and MNaX (M = K, Rb, Cs) were studied. It was shown that only sodium participates in the interaction with the water molecules, therewith causing the formation of distinctive sodium-water structures in the large cavity system of the hosts. Heavier alkali-metal ions that are also present affect the formation of these structures in an indirect way by blocking cation positions for sodium. The results, gleaned from X-ray diffraction, were put into relation to temperature-programmed desorption (TPD) measurements, obtained from previous investigation of these zeolites.