Crystallization of silicalite-1 from clear synthesis solutions: Effect of template concentration on crystallization rate and crystal size

Abstract

Synthesis of silicalite-1 powders and membranes from initially clear solutions with different tetrapropylammonium hydroxide or bromide concentrations was studied. While tetrapropylammonium bromide acts only as template, tetrapropylammonium hydroxide provides both the template and hydroxyl ions to the synthesis medium. The effects of template and hydroxyl ion concentration on the product yield, crystallization rate and crystal size were investigated. Pure and highly crystalline silicalite-1 was obtained with all compositions. The nucleation time decreases from 100 h to 20 h and the crystal size decreases from 3.5 μm to 0.35 μm as the template amount x is increased from 5 to 30 moles at a batch composition of 80SiO2.xTPAOH.1500H2O at 95 °C. Yield of silicalite-1 passes through a maximum at intermediate TPA concentration. ©2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.