Unveiling the Catalytic Pyrolysis Behavior and Kinetics of Epoxy Resin over Niobium Oxide-Tailored ZSM-5 Zeolites

Abstract The sustainable recycling of thermosetting epoxy resin (ER) waste remains a critical environmental challenge. While fast pyrolysis offers a viable upcycling route, the direct thermal degradation of ER predominantly yields low-value, oxygen-rich phenolic compounds. In this study, a series of hierarchical niobium oxide-tailored ZSM-5 zeolites (xNb-ZSM) were synthesized to promote the selective catalytic pyrolysis of ER into high-value aromatic hydrocarbons. Comprehensive characterizations (X-ray diffractometry (XRD), BET, TEM, and pyridine-adsorbed Fourier transform infrared spectroscopy (Py-IR)) revealed that the incorporation of amorphous niobium oxide species successfully generated a hierarchical mesoporous–microporous network and enriched the strong Lewis acid sites, thereby optimizing the Brønsted/Lewis (B/L) acid synergy without destroying the intrinsic zeolite framework. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) results demonstrated that the optimal 3Nb-ZSM catalyst achieved an exceptional aromatic selectivity of 65.5%, significantly outperforming the commercial HZSM-5 (45.9%). Furthermore, kinetic analysis utilizing the model-free Starink isoconversional method elucidated the underlying catalytic mechanism. The hierarchical pore architecture of 3Nb-ZSM drastically mitigated mass transfer limitations, reducing the average apparent activation energy (Ea) to 182.5 kJ/mol, compared to 241.5 kJ/mol for pure HZSM-5. Crucially, the Nb-modified catalyst effectively suppressed coke formation during the late stages of high conversion, avoiding the sharp Ea increase associated with catalyst deactivation. This work provides deep mechanistic and kinetic insights into the design of robust, coke-resistant catalysts for the highly selective upcycling of waste polymers into valuable petrochemicals.