Hierarchical zeolite ZSM-58 as shape selective catalyst for methanol-to-olefins reaction
A hierarchical zeolite ZSM-58 architecture, with zeolitic DDR topology, was synthesized via postsynthetic desilication using sodium hydroxide solutions with varying concentration in presence of tetraethylammonium ions acting as pore growth moderator. Resulting ZSM-58 materials were analyzed by X-ray diffraction, argon physisorption, scanning electron microscopy and temperature-programmed desorption of ammonia. By varying the base concentration, intracrystalline mesopores with a volume up to 0.50 cm3 g−1 were introduced. Due to enhanced adsorption/desorption kinetics, all desilicated ZSM-58 samples exhibited longer catalytic lifetime and higher product yields in the methanol-to-olefins (MTO) reaction compared to purely microporous ZSM-58. All catalyst materials achieved a remarkably narrow product spectrum with yields around 80% for the C2-/C3-fraction and absence of products larger than C5.