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 °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.