Facile and selective synthesis of zeolites L and W from a single-source heptanuclear aluminosilicate precursor

Zeolites are usually synthesized by hydrothermal reactions using monomeric or polymeric Al- and Si-containing precursors, whereas simple and direct routes for the rational synthesis of zeolites remain elusive. In this work, we demonstrate the synthesis of the two zeolites L (LTL type) and W (MER type) from a single molecular precursor (MP), (PyH)[Al{Ph2Si(OSiPh2O)(2)}(2)] (AlSi6 ; PyH = pyridinium cation), under hydrothermal conditions using KOH as the only additive. Under acidic conditions, the heptanuclear structure of AlSi6 is hydrolyzed without cleavage of the Si-Ph bonds, while the hydrothermal reaction under basic conditions allows the crystallization of zeolites under concomitant Si-Ph cleavage. X-ray diffraction and scanning electron microscopy studies revealed that zeolite L, which exhibits a cylindrical morphology, was produced selectively by hydrothermal treatment of AlSi6 at 160-200 degrees C in the presence of KOH (3 eq.). In contrast, increasing the amount of KOH (from 6 to 12 eq.) resulted in the formation of zeolite W with a twin-ball morphology. The specific surface area and Si/Al ratios of the synthesized zeolites L and W are comparable to those previously reported. These experimental results suggest promising potential of structurally and compositionally well-defined MPs, including even those with organic functional groups, for the construction of zeolites.