Crystal growth of high silica ZSM-5 at low temperature synthesis conditions

Abstract

At the temperature of 90°C and under atmospheric pressure, growth kinetics of high silica ZSM-5 was investigated through a long induction, nucleation and crystal growth periods. It was found the entire crystallization mechanism of ZSM-5 seems to be the combined process of the nucleation via solid-solid transformation, intergrowth among seed crystals and the normal growth in the reaction mixture. Nuclei were initially formed on the Si-rich surface of the amorphous intermediates, indicating that the reaction of TPA with Si species was prior to that with Al species. As the reaction time proceeded, various types of intergrowth among the seed crystals were observed along with the crystals growing independently. The intergrowth seems to play a role for forming typical ZSM-5 crystal shapes. And then ZSM-5 crystals further grew in the reaction mixture, so that the bulk Si/Al2 ratio of crystals approached that of the initial reaction mixture.