Ultra Rapid Production of Silicalite-1 Nanocrystals by Microwave-Assisted Hydrothermal Synthesis

Zeolites are crystalline, microporous aluminosilicates with well-defined pores of molecular dimensions. In powder form they are used in a broad variety of applications such gas separation processes (molecular sieving), catalysis as well as adsorbents and ion exchangers with highcapacities and selectivities. When zeolites are grown as films, they offer the potential for continuous separation of industrially important gas/vapor mixtures, and can be used as for applications in membrane reactors, as sensitive chemical sensors, and in electronic and thermoelectric applications [1]. A large number of publications reports on the synthesis of silicalite-1 seeds by classical one step or two steps hydrothermal synthesis. In most studies the starting sol ageing time is an important parameter for obtaining the colloidal silicalite-1 seeds. The classical stirring time for the starting sol and the hydrothermal synthesis are typically 40 h to 13 months and the temperature used for the synthesis of silicalite-1 seeds typically varies from 34 °C to 230 °C [1, 2]. Microwave assisted hydrothermal synthesis is relatively new, first reported near 10 years ago for preparing zeolites: initially for NaA and ZSM-5, then for other alumino-silicates (ANA, FAU, sodalite, . . .), aluminophosphates, cloverites and MCM. The synthesis of silicalite-1 nanocrystals by microwave assisted hydrothermal synthesis has been also reported[3-5]. Because the optimization of time is also very important in the industrial manufacturing of zeolites, the objective of this work was to apply the two steps strategy to MW-assisted synthesis in order to define a methodology for a very rapid synthesis of small and homogeneous silicalite-1 nanocrystals