Catalyst optimization for enhanced propylene formation in the methanol-to-olefins reaction

ZSM-5 zeolites possessing different chemical compositions, acidities and crystal sizes, were synthesized and characterized by XRD, SEM and FTIR. Those as-prepared acid catalysts were tested in the conversion of methanol into light olefins at 673 K under atmospheric pressure. Propylene-to-ethylene ratios above 5 were achieved over ZSM-5 zeolite catalyst prepared via the fluoride route. This promising methanol-to-propylene (MTP) catalyst was designed both at the molecular scale, exhibiting low Brønsted acid site density, and at the microscopic level since large crystals (25 μm) with few defects were obtained. Aiming in a possible industrial application, the synthesis medium has to be seriously modified, thus avoiding harmful hydrofluoric acid use. Hydrochloric and phosphoric acids were therefore chosen as alternatives and resulted in the same ZSM-5 crystal morphologies and similar catalytic performance.