A facile route to synthesize mesoporous ZSM-5 with hexagonal arrays using P123 triblock copolymer

Abstract

Mesoporous ZSM-5 samples were synthesized using Pluronic P123 triblock copolymer (EO20PO70EO20) as a supramolecular template through a pH adjusting method. The resulting materials were characterized using X-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption, scanning electron microscopy (SEM), solid-state nuclear magnetic resonance (MAS-NMR) and ammonia temperature programmed desorption (TPD) analyses. Adjusting the synthesis pH allowed obtaining a well-crystallized ZSM-5 material with meso-channels of size of 8–10 nm as calculated from non-local density functional theory (NLDFT) and also supported by TEM images. This strategy performs the growth of zeolite crystals with a mesostructured pore lattice in a cooperative manner, avoiding both a phase separation between the surfactant and zeolite units during crystallization and the formation of a separate amorphous mesoporous material. In addition, ammonia TPD studies revealed that the acidity of the mesoporous ZSM-5 material is comparable with the microporous conventional one. It was found from NH3-TPD profiles that in the case of the mesoporous ZSM-5 samples some of the strong acid sites have been transformed into weak acid sites which might be attributed to the acid sites present on the crystal external surface in mesopores.