Rapid synthesis of silicalite-1 seeds by microwave assisted hydrothermal treatment

The objective of this work was to evaluate the use of microwave (MW) heating for the rapid synthesis of small and homogeneous silicalite-1 seeds. The influence of the chemical composition of the starting sol, the sol stirring time at room temperature and the hydrothermal synthesis conditions on the characteristics of the derived seeds have been studied. The silicalite-1 seeds were characterized by their size, shape, homogeneity, aggregation and yield. The TPAOH template concentration was an important parameter for the reaction yield, as well as particle size and aggregation. Starting from an optimized formulation (SiO2:0.4TPAOH:19.5H2O:4C2H5OH), we first demonstrated that MW heating drastically shortens the synthesis duration time because long sol ageing (maturation-nucleation) times are not required in this case. On the other hand the hydrothermal synthesis parameters (MW power, temperature, duration, number of synthesis steps) have been optimized in order to control the morphological characteristics and yield of the silicalite-1 crystals. Although an original fibrous morphology was obtained for very short MW assisted hydrothermal synthesis times (10-30 min), very small individual seed (size of ≈50-60 nm) were obtained after only 110-150 min, starting from sols aged for either 1 or 264 h.