Mechanistic insight into the hydrogen transfer pathway for selective upcycling of PET to arenes

Abstract

Selective upcycling of waste plastics into value-added chemicals is of great significance for achieving the resource utilization. In the present study, the selective transformation of polyethylene terephthalate (PET) into arenes (benzene, toluene and p-xylene, labeled as BTX) via one-pot reaction in methanol without external hydrogen supply was put forward, which included methanol reforming, PET methanolysis and following in-situ hydrodeoxygenation. Mechanistic insight into the hydrogen transfer pathway in methanol-mediated PET upcycling into BTX over Pt/TiO2 was systematically elucidated. Remarkably, isotope labeling experiments revealed that hydrogen atoms from methanol could be transferred to the aromatic rings, owing to the formation of electron-deficient sites during conjugation. Density functional theory (DFT) calculations further confirmed that the cleavage of C–O bond in PET methanolysis derivatives took precedence over direct saturation of CO bond, followed by in-situ hydrodeoxygenation transformation for the production of BTX. Using Pt/TiO2 as catalyst for H-transfer upcycling of PET in methanol, desirable BTX yield of 77.96% could be achieved after 3 h reaction. The present research will supply a novel perspective for the high-value utilization of waste oxygen-rich plastics via hydrogen transfer manner.