One-step post-synthesis treatment for preparing hydrothermally stable hierarchically porous ZSM-5

Hierarchically porous ZSM-5 (SiO2/Al2O3 ≈ 120) containing phosphorus was prepared by a one-step post-synthesis treatment involving controlled desilication and phosphorous modification. The hierarchically porous ZSM-5 featured high thermal and hydrothermal stability. The obtained ZSM-5 zeolites were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, NH3 temperature-programmed desorption, and 27Al and 31P magic-angle spinning nuclear magnetic resonance spectroscopy. The prepared ZSM-5 displayed enhanced activity and prolonged lifetime toward hydrocarbon cracking. The high activity was attributed to improved coke tolerance owing to the presence of the highly stable mesoporous network of ZSM-5 and acid sites introduced upon phosphorus modification. Additionally a mechanism of the stabilization of the zeolites by phosphorus was proposed and discussed.