title: 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.
abstract: 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 ([(13) C6 ]benzene and methanol) conditions and typical MTO working (feeding [(13) C]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 (13) C-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.
authors.affiliation: Wuhan Center for Magnetic Resonance, State Key Laboratory, Magnetic Resonance and Atomic Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (P.R. China), Fax: (+86) 27-87199291.
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.forename: Yueying
authors.initials: Y
authors.lastname: Chu
authors.forename: Anmin
authors.initials: A
authors.lastname: Zheng
authors.forename: Jun
authors.initials: J
authors.lastname: Xu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
authors.forename: Pan
authors.initials: P
authors.lastname: Gao
authors.forename: Guodong
authors.initials: G
authors.lastname: Qi
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Gong
authors.forename: Feng
authors.initials: F
authors.lastname: Deng
keywords: carbocations; olefins; reaction mechanisms; solid-state NMR spectroscopy; zeolites