Revealing the roles of hydrocarbon pool mechanism in ethanol-to-hydrocarbons reaction

Abstract

Ethanol-to-hydrocarbons (ETH) process, is investigated in this work due to the requirement of sustainable production route for light olefins such as ethene and propene. Majority of the mechanism insights of ETH process are principally proposed based on the methanol-to-hydrocarbons (MTH) process, which involves a homologous reaction system. The reaction intermediate species including cyclopentenyl cations and aromatics species, which are denoted as “hydrocarbon pool (HCP)” species in MTH process, were discovered and identified in the ETH process by in situ solid-state 13C NMR (ssNMR) experiments, advanced 2D 13C–13C INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) ssNMR experiment, 12C/13C-C2H5OH isotope switching experiments complemented by gas chromatography-mass spectroscopy (GC–MS). Especially, in the ETH reaction, ethylcyclopentenyl cations and their deprotonated form were first captured and exhibited relatively higher activity in the formation of ethene and propene. Multi-routes with the participation of these active intermediates were proposed and evaluated by density functional theory calculation (DFT), demonstrating that they can play important roles in the formation of olefins. Ethene formation are mainly formed from ethanol dehydration, whereas propene can be produced via multi-routes with the participation of the captured HCP species. Moreover, the detailed reaction routes may be modulated by the temperature. This work provides direct evidences of the critical function of HCP species in the ETH process and reveals the mechanism of olefin formation.