An investigation into the crystallization of low-silica X zeolite

The crystallization of low-silica X (LSX) zeolite with FAU topology was examined under hydrothermal synthesis conditions. PXRD was employed to follow the evolution of the long-range ordering of the gel. Raman spectra provided information on various ring and cage species existing in the gel. 27Al and 29Si solid-state NMR spectroscopy was utilized to monitor the change in local environment of tetrahedral sites. The results indicate that an amorphous aluminosilicate phase was formed immediately upon mixing different reactive species. Hydrothermal treatment led to the formation of sodalite-cage like species and the species with larger cavities, joint four-member rings (4Rs) and branched 4Rs, which are the structural building units of the FAU framework. These units were assembled into the crystalline structure of LSX zeolite. 23Na and 39K solid-state NMR results show that the transformation process was accompanied by the changes of the local structure of hydrated Na+ and K+ ions. The two types of cations may work synergistically to template the crystallization of LSX zeolite.