Understanding the Surface Acidity Mediated Reaction Pathway in CO₂ Assisted Aromatization of Polyolefin Waste

The upcycling of polyolefins into high-value aromatics remains a challenge due to the significant size mismatch between polymer chains and the micropores of zeolite catalysts. Here, we demonstrate that tailoring the surface acidity of ZSM-5 enables efficient coconversion of polyethylene (PE) and CO2, achieving over 93% selectivity for aromatics in the liquid products, with a yield of 64.5%. Notably, this process operates without noble metals or metal oxides. Systematic studies using model alkanes reveal that surface acid sites play a dual role: facilitating C–C bond cracking to generate reactive intermediates while promoting undesired isomerization and coking. Optimized ZSM-5 (Si/Al = 85) balances surface and internal acidity, promoting selective aromatization while maintaining high catalyst stability. CO2, though may not be directly involved in aromatic formation, enhances hydrogen transfer via the reverse water–gas shift reaction, suppressing overcracking reactions. This study highlights the critical role of surface acidity in bridging polymer cracking and aromatization, providing insights into designing advanced zeolite-based catalysts for plastic upcycling.