Simple and facile one-step synthesis of bowl-like hollow ZSM-5 zeolites

Abstract

Hollow zeolites have been considered as promising materials due to their unique porosity. Although some progress has been made in the synthesis of hollow zeolites, there are still few reports on the one-step synthesis of high-quality hollow ZSM-5 zeolites. In this work, we used a simple one-step strategy to synthesize high-quality bowl-like hollow ZSM-5 zeolites without additional templates. The strategy involves two key factors including the hydrolysis temperature of TEOS (tetraethoxysilane) and the amount of NaOH. During the preparation of the synthesis gel, the hydrolysis temperature of TEOS was carefully controlled to tune the spatial distribution of Al and Si throughout the micelle/nucleus, creating Al-zoning and a Si-rich core for the formation of intracrystalline macropores. The amount of Na⁺ was adjusted to change the competitive electrostatic interactions with TPA⁺ for negatively charged groups on the surface of crystals, producing bowl-like macropores on the shell of crystals. Various characterizations were made and the formation mechanism of bowl-like hollow ZSM-5 zeolites was proposed.