Slowing down the deactivation of H-ZSM-5 zeolite catalyst in the methanol-to-olefin (MTO) reaction by P or Zn modifications.

• Zn species exchange protons of HZSM-5 zeolite decreasing Brønsted acid sites. • P species interact with Al framework causing its dealumination and loss of silanols. • Zn slows down methanol transformation but above all, the deactivation. • Zn has a greater effect on slowing the formation of intermediates and coke species. • Zn increases the propylene-to-ethylene ratio. The benefits of H-ZSM-5 zeolite modification with H 3 PO 4 or ZnCl 2 have been analyzed during the methanol to olefins (MTO) reaction. The catalysts were prepared, characterized and tested using three different reactors: fixed-bed, operando FTIR and UV–vis. The spent catalysts were further characterized for analyzing the nature and location of the species trapped. The results show that the zeolite modified with H 3 PO 4 has suffered a simultaneous dealumination, leading to a decrease of number of acid sites and activity. However, the zeolite modified with ZnCl 2 shows the inclusion of Zn transforming Brønsted into Lewis acid sites, leading to reaction intermediates (hydrocarbon pool species) that decreases the rate of reaction but improves propylene selectivity (+10%), slows downs coke formation (-42%) and expands catalytic lifetime (+80%). The distinct effect of Zn modification, typically associated with the promotion of aromatics, is explained on the grounds of the severe transformation of the strong and Brønsted acid sites. [ABSTRACT FROM AUTHOR]