Hierarchical ZSM‐5 Catalysts With Engineered Surface Acid Sites for Selective and Efficient Upgradation of Waste Polyolefins

The accumulation of plastic waste poses severe environmental challenges, driving the need for efficient catalytic recycling technologies to enable a circular economy. High-density polyethylene (HDPE) is particularly challenging to catalytically upgrade due to its high crystallinity and the limited accessibility of its polymer chains. While zeolite catalysts offer shape selectivity advantages for product control, their practical application in polyolefin conversion has been constrained by low catalytic activity. Herein, we engineered a hierarchical ZSM-5 zeolite with a substantially enhanced external surface area and multilevel porosity to reduce mass-transfer limitations and improve catalytic efficiency. Pyridine and 2,6-di-tert-butylpyridine Fourier transform infrared spectroscopy studies confirmed that the synthesized ZSM-5 possesses significantly more external and macromolecule-accessible acid sites compared to commercial counterparts. The optimized ZSM-5 with a Si/Al ratio of 100 achieved an 86.8% HDPE conversion at a mild temperature of 250°C, exhibiting high selectivity toward C₄-C₁₂ unsaturated hydrocarbons. The mass-based activity was 1.5 times higher than that of the best-reported pure zeolite catalyst for polyethylene cracking. By engineering the external surface acidity and molecular transport pathways of zeolite catalysts, this work paves the way for efficient chemical valorization of waste polyolefins, demonstrating the power of rational catalyst design.