Crystallization Mechanism of Zeolite UZM-5

Abstract

A reliable formation pathway for UZM-5 zeolite crystals in the presence of tetraethylammonium, tetramethylammonium, and Na+ ions at 150 degrees C has been proposed based on the C-13 MAS NMR and IR spectra of a series of solid products recovered as a function of time during the crystallization process, as well as on the crystal structure of as-made UZM-5 determined using synchrotron powder X-ray diffraction and Rietveld analyses. The nucleation of this cage-based small-pore zeolite begins with the construction of the largest 26-hedral lta-cages among its four different structural units. The next step is the attachment of 14-hedral wbc-cages to the preorganized lta-cage at shared 6-rings in an appropriate orientation that will allow the growth of two wbc-cage layers linked by 8-hedral rth-cage formation along both a and b axes. The resulting interlayer space is readily converted to a layer of lta-cages by interconnecting two opposing wbc-cages, with the concomitant formation of interlayer d4r-cages and 8-rings. Over the outer surface of the resulting UZM-5 nuclei, which resembles one-half of an lta-cage, the crystal growth may take place in a self-assembled manner as described above.