Oxygenated polycyclic aromatic hydrocarbons as key coke precursors in coke formation during zeolite-catalyzed furfural pyrolysis

Coke deposition and catalyst deactivation represent significant challenges in catalytic research, yet the mechanisms underlying their formation remain inadequately understood. Herein, we employed the HZSM-5 catalyzed conversion of furfural as a model reaction and, using a newly developed online high-resolution mass spectrometry (HRMS) technique, directly detected a broad spectrum of oxygenated polycyclic aromatic hydrocarbons (OPAHs) under reaction conditions. Solid-state NMR further revealed the functional group architectures of OPAH side chains in condensed-phase coke, while density functional theory (DFT) calculations elucidated plausible formation and transformation pathways. These complementary approaches establish that highly active OPAHs serve as crucial intermediates in the coke deposition process. We propose a novel mechanism in which light OPAHs, orginating from small-molecule products, undergo rapid polymerization at the active sites to yield larger polycyclic aromatic hydrocarbons, traditionally classified as coke. This newly identified mechanism highlights the unexpectedly rapid coking during the catalytic pyrolysis of biomass, and underscores the significant role of OPAHs in catalyst deactivation. By providing molecular-level insights into coke growth, this study lays a foundation for strategies to suppress coke formation, thereby improving the efficiency and sustainability of catalytic conversion technologies for biomass utilization.