Crystal Structure of Zeolite Y as a Function of Ion Exchange

The crystal structures of a series of hydrated Na-, NH4-, Caand La-exchanged zeolite Y have been determined as a function of exchange conditions using synchrotron powder diffraction data. Four sieves were also studied in the dehydrated state in situ at 300°C. Only small differences in the framework structures were observed; the largest differences involve 02 and 03, to which the cations are coordinated. In hydrated NaY (LZ-Y52), sites I', II, and II' are occupied. In ammonium-exchanged sieves, the Na at sites I' and II are replaced by NH4 ions, with the residual sodium displaced to sites 11'. In uncalcined Ca-FAU, the Ca are distributed over sites I', II', and II. At 300°C, the Ca occupy sites I or I', depending on the cation concentration. On returning to room temperature and the hydrated state, the Ca return to their original positions. The La in uncalcined La-FAU preferentially occupy site V, near the center of the 12-ring windows. At 300°C, La exhibits a strong preference for site I', and remains at this site on return to room temperature. Ca and La occupy different sites, both at room temperature and at 300°C, and exhibit different mobility. The cation contents calculated from the refined site occupancies agree well with those determined by chemical analysis. The crystal structures of NH4and H-Y were studied as a function of framework aluminum concentration. The framework structure becomes more uniform as the Al concentration decreases. Significant changes in structure and property trends occur at cell dimensions of approximately 24.45 Å. Faujasite crystallinity decreases markedly with dealumination.