Carbon nanotubes as transient inhibitors in steam-assisted crystallization of hierarchical ZSM-5 zeolites

Abstract

Carbon nanotubes (CNTs) can be well dispersed in an ethanol diluted zeolite precursor and thus encapsulated in the formed dry gel after solvent evaporation. This specially prepared dry gel allows small quantites of CNTs to effectively act as transient inhibitors in the subsequent steam-assisted crystallization of ZSM-5 nanocrystal aggregates with hierarchical porosity. Although finnally separated from zeolite, CNTs can still transiently inhibit the zeolite growth to avoid fusing into a large crystal. The inter-crystalline mesoporosity in hierarchical ZSM-5 is not created by the space occupied by CNTs, but preserved from the mesoporosity formed by nucleation and initial crystallization. Excessive quantities of CNTs are not recommended because their excessive inhibition induces the appearance of amorphous impurity in hierarchical ZSM-5.