A new study published in Engineering demonstrates a tandem catalytic approach that converts waste polyethylene and carbon dioxide into separable liquid aromatics and carbon monoxide under atmospheric pressure, offering a practical route for the valorization of two waste carbon resources. Researchers from Sichuan University and Peking University developed a bifunctional oxide–zeolite catalyst system composed of CuFeO₂ and Ga-[Ga]/ZSM‑5, which operates at 400 °C to realize the one‑step conversion without high-pressure requirements.

Conventional chemical recycling of polyethylene often faces low selectivity for light aromatics and generates complex mixtures of linear and cyclic compounds that are difficult to separate, while CO₂ hydrogenation typically relies on external hydrogen supplies. In this design, the synergistic interaction between cationic gallium species and Brønsted acid sites in Ga-[Ga]/ZSM‑5 promotes dehydrogenation and suppresses common hydrogen‑transfer reactions, leading to noticeable hydrogen production. The CuFeO₂ component drives the reverse water–gas shift reaction, consuming in‑situ generated hydrogen to shift the reaction equilibrium and enhance aromatic formation with improved hydrogen utilization.

Under optimized conditions, the cascade catalytic system achieves 99% selectivity toward separable aromatics in liquid products and 91.9% selectivity toward C₁–C₂ aliphatic hydrocarbons in gaseous products. The aromatic yield reaches 75.3 wt%, with benzene, toluene, and xylene (BTX) accounting for 81.1% of this fraction, and CO₂ conversion reaches up to 10.9 mmol per gram of polyethylene. Isotope labeling experiments confirm that CO₂ participates exclusively in the reverse water–gas shift reaction without direct incorporation into aromatic hydrocarbon structures.

The catalyst system shows good stability and recyclability upon regeneration by calcination, and remains effective when tested with real‑world plastic feedstocks including high‑density polyethylene, low‑density polyethylene, polypropylene, and mixed plastic waste containing common impurities. By adopting a cascade reactor configuration, the process further optimizes product distribution, nearly eliminating C₃–C₄ alkane impurities and yielding easily separable aromatic products with high purity. This integrated strategy couples polyethylene upcycling with CO₂ utilization, providing a technically feasible pathway to transform waste plastics and greenhouse gas into valuable petrochemical intermediates and syngas precursors.

The paper “Upcycling Polyethylene into Separable Aromatics Through Tandem Catalysis with CO₂ at Atmospheric Pressure,” is authored by Wenjun Chen, Mingyu Chu, Yue Liu, Yiyi Fan, Meiqi Zhang, Meng Wang, Fan Zhang. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.12.006. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.