Solvent- and metal-free upcycling of low-density polyethylene using a practical ZSM-5/Al₂O₃ bead catalyst

Upcycling plastic waste into valuable resources without solvents, precious metals, or additional H₂ under mild conditions is a formidable challenge that requires new innovations. Herein, we document a catalyst based on Al₂O₃ beads and zeolite ZSM-5 (ZSM-5#Al₂O₃(2 h)). It cracked polyethylene (PE) into gasoline-range C₄ - C₁₂ hydrocarbons with a selectivity of 98% and a yield of >71% within 1.5 h at 260 °C. Characterization of the catalysts revealed a mesoporous structure and suitable Brønsted acid sites, which promoted the diffusion and catalytic activation of PE. Adjusting the dosage of zeolite supported on Al₂O₃ beads enables regulation of both the number and strength of acidic sites. Theoretical calculations confirmed that the interfacial interaction between zeolite ZSM-5 and Al₂O₃ reduces the acid strength of the composite. This is beneficial for the formation of higher hydrocarbons. Remarkably, the process was performed in a 1 L CSTR unit. These results provide  instructive guidance for the design of high-performance catalytic materials used in PE waste recycling.