Demonstrates that molecular oxygen alters carbenium ion reactivity in methanol-to-hydrocarbon processes, suggesting new pathways for catalyst stability.
Carbenium ions are critical intermediates in zeolite-catalyzed hydrocarbon transformations; yet, their fundamental reactivity and mechanistic pathways remain incompletely understood, particularly under conditions relevant to practical catalysis. Here, we demonstrate that molecular oxygen─often present in catalytic systems but rarely mechanistically considered─profoundly alters carbenium ion chemistry. Through a combination of solid-state ¹³C NMR, operando UV-vis, and online mass spectrometry, we show that O₂ selectively promotes the oxidative transformation of cyclopentenyl cations via cyclopentenone-type intermediates on ZSM-5 zeolite. This oxygen-mediated pathway enhances the formation of methylated aromatics, modulates reaction selectivity, and accelerates the evolution of polyaromatic species, ultimately impacting the catalyst stability. These effects are consistently observed in both methanol-to-hydrocarbon and ethene conversion over zeolites.
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Cai et al. (2025) studied this question.
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