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

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 (E a) 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 E a 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.