Revealing Main Reaction Paths to Olefins and Aromatics in Methanol-to-Hydrocarbons over H-ZSM-5 by Isotope Labeling

The nature of hydrocarbon pool (HCP) intermediates in the methanol-to-hydrocarbons (MTH) process has been thoroughly investigated, especially for BEA- and CHA-type zeolite catalysts like H-β H-SAPO-34. Herein, we further reveal dynamic mechanistic details MTH over H-ZSM-5 catalyst at 400 °C, based on dual-cycle mechanism HCP this medium-pore zeolite. Application switching sequences 13C-labeled unlabeled methanol pulses a model combined with on-line MS analysis recently reported technique called “fast scanning-pulse GC analysis” provides direct quantitative insight into reactions under quasi-steady-state conditions. transient product responses showed almost instant formation hydrocarbons upon small pulse methanol, followed by secondary light aromatics via decomposition olefin alkylation–dealkylation, long bed when is quickly consumed initial reaction zone bed. isotopic typical aliphatic C3+ after 13C-methanol to fast isotope scrambling species. indicates complete consecutive but slower incorporation 12C 13C-aromatics. Results provide experimental confirmation kinetically preferred olefin-based cycle aromatic-based cycle. sequential strongly suggests that paring pathway through aromatic ring contraction re-expansion steps operative. In appearance pulsing larger beds, four processes are directly discerned, involving displacement adsorbed species formed water, yielding labeled products aromatization, conversion reactions.