Boosting sustainable monocyclic aromatics yield from catalytic fast pyrolysis of cotton stalk via a novel ZnZrOx-ZSM-5 tandem catalysis

Biomass valorization plays a vital role in ecological conservation and the advancement of a circular economy, while posing significant scientific challenges. This work successfully constructed a novel tandem catalytic system (ZnZrOx-ZSM-5) for the efficient production of sustainable monocyclic aromatics (SMAs) via the ex-situ catalytic pyrolysis of cotton stalk. Compared to the sole ZSM-5, the tandem catalyst significantly enhanced the absolute yield of SMAs from 8.2 % to 26.8 %. Combined various structural characterization and carefully catalytic experiments, it was revealed that pyrolysis volatiles derived from cotton stalk first encounter the ZnZrOx bed-rich in oxygen vacancies and basic sites, where compounds such as AAAKs (alcohols, aldehydes, acetic acid, and ketone) and bulky alkoxy-phenols are preferentially pre-cracked into alkanes/alkenes and light phenols, respectively. Subsequently, within the ZSM-5 bed, these pre-cracked intermediates enhance the formation of SMAs by a series of reactions-including Diels-Alder condensation, dehydroxylation, and aromatization with hydrocarbon pool species. Simultaneously, GC‑MS analysis confirmed that the introduction of ZnZrOx effectively suppresses the formation of bulky polycyclic molecules (e.g., naphthalene, phenanthrene), thereby alleviating catalyst pore blockage and deactivation.