Dual-catalyst system without supported metals toward polyethylene waste upcycling

Abstract

The accumulation of polyolefin plastic wastes has emerged as a pressing global environmental challenge, driven by its inherent resistance to degradation and the limited efficiency of current recycling technologies. Hydroconversion methods, such as hydrocracking, offer a promising route for transforming polyolefins into high-value liquid alkanes under mild conditions. However, most current catalytic systems are heavily dependent on expensive noble metals, resulting in high management costs. Here, we report a cost-effective and scalable free of supported metals dual-catalyst system combining β zeolite and metal oxides (Nb₂O₅, CeO₂, TiO₂, or ZrO₂) for the tandem cracking-hydrogenation of polyolefins under mild conditions. The system exploits a strong synergistic effect between β zeolite and oxide, achieving a polyethylene (PE) conversion of up to 98.2 % and liquid alkane yields of 87.1 %, with a product distribution centered in the C₄–C₁₅ range. Mechanistic investigations, supported by in situ spectroscopy and DFT calculations, revealed that polymer chains are initially cracked at the Brønsted acid sites of β zeolite to form olefins, which are subsequently hydrogenated on oxides via heterolytic H₂ activation. Notably, the system demonstrated stability and versatility in processing PE-rich waste plastics. This study presents a practical and economically viable approach to converting plastic waste into valuable fuels, which is expected to advance sustainable chemical recycling strategies.