Highly Selective Methylation of Ethylene to Propylene within the Confined Side Pockets of Mordenite Zeolite.

Ethylene methylation with C1 reagents provides a viable route for propylene production and enables flexible adjustment of olefin output ratios in industrial processes (e.g., naphtha steam cracking and methanol-to-olefins). However, this process faces the long-standing challenges of low propylene selectivity and rapid catalyst deactivation. Herein, a highly selective and stable catalyst for ethylene methylation to propylene was developed by precisely regulating the acid site distribution in mordenite (MOR) zeolite, where the acid sites in the 12-membered ring (12-MR) channels were passivated using pyridine, while those located in the confined 8-membered ring (8-MR) side pockets remained accessible. This spatial control of acid site distribution allowed the exclusive occurrence of ethylene methylation within the sterically confined pockets, effectively suppressing the side reactions requiring larger space (e.g., methanol-to-hydrocarbons reaction and olefin oligomerization). Remarkably, the optimized pyridine-modified MOR catalyst achieved an unprecedented propylene selectivity of 97% and exhibited exceptional stability with no sign of deactivation during a 70 h test. In situ Fourier transform infrared (FT-IR) spectroscopy, theoretical calculations, and isotope labeling experiments were utilized to elucidate the mechanism of ethylene methylation and establish the reaction network within the confined pockets. It is anticipated that the side pockets of the MOR zeolite, which can be considered as an angstrom-scale reactor, would provide more opportunities for the precise assembly of small organic molecules.