Molecular elucidation of the deactivation mechanism of HZSM-22 zeolite-catalyzed methanol-to-hydrocarbons (MTH) reaction

Methanol-to-hydrocarbons (MTH) reaction comprises a set of crucial catalytic processes to produce light olefins, gasoline, or aromatics. MTH reaction is a classic example of reaction complexity in zeolite catalysis. The molecular understanding of reaction routes and deactivation mechanisms still encounters many challenges. Herein, we chose HZSM-22 zeolite with the simple one-dimensional 10-membered ring (10-MR) channel as a prototypical system, leveraging the spatial nanoconfinement effect of its unique pore architecture to minimize reaction complexity. The identification of the molecular structures of coke species with acene-, biphenyl-, or fluorene-typed structures was made possible through a combination of the advanced matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry (MALDI FT-ICR MS) with the gas chromatography-mass spectrometer (GC-MS) technique. With this, we uncovered two modes of growth mechanism of coke molecules, i.e., a stepwise route and a dehydrogenative coupling route. The findings deepen the mechanistic understanding of zeolite deactivation and provide a theoretical foundation for designing coke-resistant catalysts.