Direct observation of methylcyclopentenyl cations (MCP+) and olefin generation in methanol conversion over TON zeolite

Abstract

The mechanism of the methanol to olefin (MTO) reaction over H-ZSM-22, a TON-type zeolite without cavities or channel intersections, has been investigated in the temperature range of 250–350 °C. For the first time, an induction period in low-temperature methanol conversion and the methylcyclopentenyl cation (MCP⁺) formed during this period have been observed directly and successfully. ¹³C magic angle spinning (MAS) NMR, ¹³C-labeling experiments and theoretical calculations have been employed to confirm the important active intermediates during methanol conversion at 300 °C. The reactions performed at different temperatures were comparatively studied and the differences in the reaction route for alkene formation from methanol conversion and the modes of H-ZSM-22 catalyst deactivation were revealed.