Direct oxidation of benzene to phenol by N2O over meso-Fe-ZSM-5 catalysts obtained via alkaline post-treatment

Abstract

Fe-ZSM-5 zeolites with uniform crystal size and shape were synthesized by a hydrothermal method, and these parent zeolites were desilicated by an alkaline-treatment method to obtain mesoporous Fe-ZSM-5 (meso-Fe-ZSM-5) zeolites. Both Fe-ZSM-5 and meso-Fe-ZSM-5 zeolites were characterized by XRD, N₂ adsorption–desorption, ICP-AES, SEM, TEM, UV-vis, and TGA techniques and as catalysts they were used in the direct oxidation of benzene to phenol (BTOP) by N₂O as oxidant. The meso-Fe-ZSM-5 catalysts show a much higher catalytic activity and stability, compared to the parent Fe-ZSM-5 catalysts. A comparison study on the uptakes of benzene in the parent and alkali-treated zeolites indicates that the internal mass-transfer limitations of the meso-Fe-ZSM-5 zeolites are significantly improved due to the introduction of intracrystalline mesoporosity, resulting in a better catalytic activity and stability in the BTOP reaction. Desilication in the alkaline medium of Fe-ZSM-5 crystals enables a more efficient utilization of the zeolite in the BTOP reaction that is strongly affected by diffusional limitations.