Unraveling the role of Zn species in catalyst deactivation and coke formation over Zn/ HZSM ‐5 during LDPE pyrolysis

Abstract Zn/HZSM‐5 enables selective LDPE pyrolysis to monocyclic aromatics with minimal light olefins, yet suffers from rapid coke‐induced deactivation. This study clarifies the dynamic evolution of Zn species governing this process. Isolated Zn sites drive deep dehydrogenation, generating acetylene and diene intermediates that accelerate polycyclic aromatic hydrocarbons (PAHs, coke precursors) formation. Crucially, oxygenated additives in LDPE degrade over acid sites to form intermediates that lower the energy barrier for PAH condensation, further exacerbating coking. Coke distribution is spatially heterogeneous: external surfaces accumulate long‐chain alkenes and oxygenates, while micropores foster condensed aromatics via sequential HACA and MAC mechanisms. Progressive coking encapsulates and sinters active [ZnOH] + into inert ZnO, triggering a switch from Zn‐driven aromatization to Brønsted acid‐dominated cracking. These findings reveal an intrinsic trade‐off where sites enabling high selectivity simultaneously dictate rapid deactivation, guiding the design of robust catalysts for plastic upcycling.