Synthesis of large silicalite-1 single crystals from two different silica sources

Large silicalite-1 crystals were hydrothermally synthesized at 150–200 °C by using reaction mixtures of the system SiO2–TPABr (tetropropylammonium bromide)–NH4F–H2O. Fumed silica or a quartz glass plate was used as the silica source. Large crystals up to 1800 μm were obtained in reaction mixtures containing a quartz glass plate at 180 °C for 5 weeks; on the other hand, for fumed silica, the crystal sizes were lower than 690 μm. It was found that the use of a quartz glass plate was effective for obtaining large crystals than fumed silica, presumably due to the slow dissolution rate of the quartz glass plate in the presence of fluoride ion. In addition, the crystal sizes were largely dependent on the reaction mixture composition used as well as the reaction temperature employed.