Offretite zeolite templated by amphiphile and its catalytic performance in microwave-assisted Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate

Abstract

A detailed investigation on the crystallization of offretite (OFF) zeolite templated by non-toxic cetyltrimethylammonium bromide (CTABr) is reported. Various hydrothermal synthesis conditions are prepared by systematically adjusting the synthesis variables, namely crystallization time, heating temperature and amount of reactants (SiO2, Al2O3, K2O, M2O (M = Na+, Cs+), CTABr and H2O) to investigate their effects on the crystal growth of OFF zeolite. It is shown that each variable has its profound influences on the crystallization process, which further affect the properties of final zeolite products (e.g. phase purity, morphology, crystal size). Unlike classical synthesis pathway using tetramethylammonium (TMA+) as organic template, the CTABr-templating approach successfully produces large OFF single crystals (framework Si/Al ratio = 4.11) with hexagonal prism shape (ca. 9.4 × 1.8 μm2) and smooth surface. Besides that, the OFF zeolite (81.9% conversion) also shows comparable or even higher catalytic performance than other zeolites reported in this work and other works in microwave assisted-Knoevenagel reaction of benzaldehyde and ethyl cyanoacetate, offering a sustainable and facile pathway for preparing zeolitic materials for advanced applications.