Crystallisation of silicalite-1 precursors in the amine–(C3H7)4NBr–SiO2–H2O system

Abstract

The crystallisation of alkali-metal-free silicalite-1 precursors from the PIPZ–TPABr–SiO₂–H₂O (PIPZ = piperazine, TPA = tetrapropylammonium) system has been investigated under static and stirred conditions. In many cases large rod-like crystals of (TPA, PIPZ)-silicalite-1 were obtained. The crystallisations were accompanied by decreases in pH caused by the incorporation of base in the crystals. Smaller pH decreases were observed when the PIPZ/SiO₂ molar ratio was increased.