Dual Roles of Steam in the Dry Gel Synthesis of Mesoporous ZSM-5

Mesoporous HZSM-5 was synthesized with a SiO2/Al2O3 ratio of 100 using a steam-assisted crystallization method. The resulting material was characterized by N2 physisorption, powder X-ray diffraction, focused ion beam-scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectrometer (XPS) depth profiling, NH3-temperature programmed desorption (TPD), pyridine-TPD, and collidine-TPD. Crystallization time was varied to determine the effect on material physical properties, total acidity, accessible acid sites, and aluminum distribution within the zeolite particles. The Barrett, Joyner, and Halenda mesopore volumes, Brunauer, Emmett, and Teller surface areas, and total pore volumes decreased with longer crystallization times, while the mesopore sizes increased with time. At prolonged crystallization time, the material underwent dealumination via steam etching followed by reforming of material, thus blocking accessibility to the mesopores. The total acidity was optimized at 18 h of...