Methanol to Olefins Reaction Route Based on Methylcyclopentadienes as Critical Intermediates

Starting from C1 raw material, methanol conversion to hydrocarbons has been realized via a rather complicated pathway. In this contribution, we proposed an alternative methanol reaction route and provided a general understanding of such complex indirect mechanism. The methylcyclopentenyl cations and their deprotonated counterparts (methylcyclopentadienes) were validated to appear on the working H-SAPO-34 catalyst by in situ C-13 MAS NMR spectroscopy and the GC-MS technique, and their catalytic reactivity was revealed by the C-12/C-13-CH3OH isotopic switch experiment. In this context, a cyclopentadienes-based cycle was established, in which light olefins were formed with methylcyclopentadienes as critical intermediates. The feasibility of this alternative route was confirmed by density functional theory calculations. Notably, the cyclopentadienes-based cycle runs in parallel with the traditional alkenes-based and aromatics-based cycles; these three mechanistic cycles are interrelated through interconversion of the involved intermediates, including alkene, cyclopentadiene, and aromatic species. All these three cycles work together for the C-C bond assembly in the methanol-to-olefins reaction system. These findings help to build a more complete methanol conversion network and advance the in-depth understanding of indirect mechanism of methanol conversion.