Abstract: The preparation of zeolite ZSM-5 without using a template was extensively investigated. Zeolite ZSM-5 small particle aggregates were synthesized in the absence of a template using sodium silicate as the silica source and by controlling the nucleation time at high temperature with a simple two-step method in a rotating autoclave on a spit within an oven. The first stage at higher temperature consisted of accelerating the nucleation and the second stage at lower temperature consisted of obtaining small crystals in the absence of a template. The resulting zeolites were characterized by X-ray powder diffraction, scanning electron microscopy, ammonia temperature-programmed desorption, and N₂ adsorption. Compared with the micron-sized zeolite crystals that are synthesized in the one-step method, zeolite ZSM-5 small particles prepared by the two-step method have a higher specific surface area and an equivalent acid site content. The sample synthesized by the two-step method mainly contains Brönsted acid sites and a few Lewis acid sites indicating that Al is incorporated into the framework of the zeolite.

Key words: ZSM-5 zeolite, template-free, aggregate, two-step synthesis, particle size