A Nanostrips-Assemble Morphology of ZSM-5 Zeolite for Efficient Propylene Production from Methanol Conversion

Abstract

Turning the morphology and orientated growth of zeolite crystals is essential to alter their catalytic performances. MFI-type ZSM-5 nanostripes (named as D-Z5) with a sea-urchin-like overall morphology were directly synthesized with a commercially available and small-molecular organic structure-directing agent (OSDA) of 1-butyl-1-methylpyrrolidinium hydroxide. Their nanostrip crystals exhibited a unique dioriented morphology with thin thicknesses of ∼8 nm and ∼70 nm along the a-axis and b-axis, respectively. The dealuminated D-Z5 displayed higher propylene selectivity (∼57%), longer lifetime (60 h) and much higher propylene-to-ethylene ratio (>12) in methanol-to-propylene (MTP) reaction than those conventional ZSM-5 with known crystal morphologies. Computational simulation and experimental measurements provided solid proof that the diorientated crystals decreased the bulky molecular diffusion resistance, postponed the secondary reaction and then promoted propylene to diffuse rapidly out of two sets of micropores in zeolites. This unusual diorientation phenomenon is not only beneficial for improving the MTP catalytic performance of ZSM-5, but also expected to be versatile to develop other useful zeolite catalysts.