Illuminating selectivity descriptors for the methanol-to-propylene process over Ca-modified and unmodified zeolite ZSM-5

There is a growing demand for propylene calls for effective carbon reduction methods. The methanol-to-propylene (MTP) process stands out as a promising solution for meeting global propylene demand sustainably. In this study, we identify the mechanistic factors responsible for enhanced reactivity, superior propylene selectivity, and durable catalyst lifespan in the MTP process catalyzed by both unmodified siliceous and Ca-modified ZSM-5 zeolites. By employing advanced characterization techniques like in situ UV-visible and solid-state NMR spectroscopy, along with well-designed control experiments, we highlight the importance of the alkene cycle within the zigzag channel of zeolite ZSM-5 for superior propylene selectivity. Furthermore, our work identifies oxymethylene species as a key intermediate that enhances the lifetime of the alkene cycle and governs MTP catalysis. We also explore the synergistic interaction between Lewis-Brønsted acids and their impact on hydrocarbon pool species to deepen our understanding of zeolite catalysis.