An In Situ Carbonaceous Mesoporous Template for the Synthesis of Hierarchical ZSM-5 Zeolites by One-Pot Steam-Assisted Crystallization

摘要

Zeolites, which possess uniform micropores, large specific surface area, and intrinsic acidity, have been widely used in many industrial processes related to adsorption, separation, ion exchange, and catalysis. However, due to the inherent small pore sizes of conventional zeolites (<1.5 nm), the mass transfer in them is restricted, and consequently their performances need to be further improved, especially in processes involving bulky molecules. A reduction in particle size, for example in nanosized zeolite crystallites, could partially resolve the diffusion problem in microporous zeolites due to their larger external surfaces and the decreased diffusion path length in the micropore channels. However, the collection difficulty in the preparation or during applications limited their ever wider applications. Alternatively, hierarchical zeolites, which combine the strong acidity and high stability of crystalline microporous zeolites with the enhanced molecular diffusion resulting from additional mesoporosity, have become a research focus in recent years and have been developed through multistep post-synthesis demetallation or desilication treatments and templating synthesis with careful design of the synthesis procedure or the mesoscale templates.