Direct Evidence on the Mechanism of Methane Conversion under Non‐oxidative Conditions over Iron‐modified Silica: The Role of Propargyl Radicals Unveiled

Abstract

Radical-mediated gas-phase reactions play an important role in the conversion of methane under non-oxidative conditions into olefins and aromatics over iron-modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C₂₊ radical intermediates participating in the complex gas-phase reaction network. Our experiments pinpoint different C₂ -C₅ radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H₂ C-C≡C-H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction-acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.