Methylcyclopentenyl cation mediated reaction route in methanol-to-olefins reaction over H-RUB-50 with small cavity

Abstract

Abstract Methylcyclopentenyl cations (MCP+) have been regarded as active intermediates during methanol conversion, however, their function mode in the reaction are still uncertain. In our recent report, trimethylcyclopentenyl cation (triMCP+) and its deprotonated counterpart (trimethylcyclopentadiene, triMCP) were directly captured on H-RUB-50 catalyst with small cavity by the aid of in situ 13C MAS NMR spectroscopy, and their higher catalytic reactivity were clarified by 12C/13C-CH3OH isotopic switch experiment. In this contribution, an alternative route—cyclopentadienes-based cycle was applied on methanol conversion catalyzed on the H-RUB-50, in which ethene was produced with the participation of triMCP+ as critical intermediate. Then the cyclopentadienes-based cycle was predicted to be energetically favorable for ethene formation by density functional theory (DFT) calculations. The energetic comparison of paring mechanism in the aromatics-based cycle and cyclopentadienes-based cycle with the involvements of trimethylcyclopentadienyl (triMCPdi+) and triMCP+ as the corresponding active intermediates suggests that cyclopentadienes-based cycle is a feasible route for ethene formation. Furthermore, this work highlights the importance of the steric constraint and the host-guest interaction induced by the zeolite with cavity structure in the formation of intermediates and reaction pathway.