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New Insight into the Hydrocarbon-Pool Chemistry of the Methanol-to-Olefins Conversion |
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Release time:2014-11-9 Source:admin Reads:1112 | |
New Insight into the Hydrocarbon-Pool Chemistry of the Methanol-to-Olefins Conversion over Zeolite H-ZSM-5 from GC-MS, Solid-State NMR Spectroscopy, and DFT Calculations
Chao Wang, Yueying Chu, Anmin Zheng, Jun Xu,* Qiang Wang, Pan Gao, Guodong Qi, Yanjun Gong, and Feng Deng*
Over zeolite H-ZSM-5, the aromatics-based hydrocarbon-pool mechanism of methanol-to-olefins (MTO) reaction was studied by GC-MS, solid-state NMR spectroscopy, and theoretical calculations. Isotopic-labeling experimental results demonstrated that polymethylbenzenes (MBs) are intimately correlated with the formation of olefin products in the initial stage. More importantly, three types of cyclopentenyl cations (1,3-dimethylcyclopentenyl, 1,2,3-trimethylcyclopentenyl, and 1,3,4-trimethylcyclopentenyl cations) and a pentamethylbenzenium ion were for the first time identified by solid-state NMR spectroscopy and DFT calculations under both co-feeding ([13C6]benzene and methanol) conditions and typical MTO working (feeding [13C]methanol alone) conditions. The comparable reactivity of the MBs (from xylene to tetramethylbenzene) and the carbocations (trimethylcyclopentenyl and pentamethylbenzium ions) in the MTO reaction was revealed by 13C-labeling experiments, evidencing that they work together through a paring mechanism to produce propene. The paring route in a full aromatics-based catalytic cycle was also supported by theoretical DFT calculations.
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