Angewandte Chemie International Edition
First Author: Ruiliang Gao Corresponding Author: Yong Wang
Article Title: Noble Metal-Free Low-Temperature Aromatization of Polyethylene Waste for High-Quality Fuel Production
Impact Factor: 16.9
Article Link: https://doi.org/10.1002/anie.202506815
Paper highlights/abstract
In 2019, global annual plastic production reached 368 million tons, and is expected to double in the next two decades. Due to the chemical stability of waste polyolefins (such as PE and PP), recycling is difficult, and most are landfilled or released into the natural environment, posing a serious threat to ecosystems and human health. Chemical recycling technology, which converts waste plastics into high-value fuels and chemicals, was listed by IUPAC as one of the top ten disruptive innovative technologies in 2019. Existing catalytic technologies (such as hydrocracking and pyrolysis) mainly convert polyolefins into alkanes below 400°C, and the resulting products are usually used as fuels, but their octane number and energy density are relatively low. High-end fuels, such as aviation kerosene, require high-energy-density components containing 30%-70% aromatics and naphthenes, which traditional low-temperature cracking technologies cannot meet. Although high-temperature thermal cracking (>500°C) can produce aromatics, it is accompanied by serious coking problems and the production of low-value byproducts; while low-temperature aromatization technology for recycling polyolefins is promising, it still faces challenges such as low aromatic selectivity and high costs. Therefore, developing a polyolefin upgrading and recycling technology that does not require precious metals, operates efficiently at lower temperatures, and can selectively produce light aromatics is of great significance for achieving the resource utilization of waste plastics and the production of high-end fuels.
Based on their previously published paper (Angew. Chem. Int. Ed., 2025, e202424334), Professor Wang Yong and Associate Researcher Mao Shanjun’s team at the Institute of Catalysis, Zhejiang University, replaced the precious metal catalyst and innovatively proposed a new reaction pathway: combining the traditional cracking of PE with CO hydrogenation and the Prins reaction in a syngas atmosphere, using a Zn-ZrO and ZSM-5 catalytic system. Under mild, precious-metal-free conditions as low as 280°C, the selectivity of aromatics in the organic products can reach 68%. The intermediate of CO hydrogenation—formaldehyde—is crucial, as it can undergo a Prins reaction with olefins produced from PE cracking, promoting the formation of active oxygen-containing compounds and diene intermediates, while precisely controlling the carbon chain length. This process not only lowers the energy barrier for subsequent aromatization reactions but also significantly improves the selectivity for aromatic hydrocarbons, enabling efficient, low-temperature upgrading and conversion of polyolefins.
Illustrated Analysis
This process innovatively couples CO hydrogenation and polymer cracking, achieving efficient catalytic upgrading of polyolefins at lower temperatures to produce high-quality fuels. The product quality can be flexibly controlled within a theoretical octane number range of 79 to 103 by adjusting the hydrogen partial pressure in the syngas or the ratio of the two catalysts. Temperature-programmed surface reaction (TPSR) and isotope labeling experiments confirmed that formaldehyde, an intermediate produced by CO hydrogenation, couples with olefins from polyolefin cracking and participates in subsequent aromatization reactions. Notably, directly adding formaldehyde or methanol to the reaction system instead of generating formaldehyde in situ from syngas did not yield ideal results, highlighting the importance of kinetic matching between the various reaction steps in this process.
The customized high-temperature photocatalytic vertical furnace used by Professor Feng Hao’s research group in the experiment was provided by KeMi Instruments. Anhui KeMi Instruments Co., Ltd. was also specifically mentioned in the paper. We would like to express our sincere gratitude to Professor Feng Hao for his choice and recognition of KeMi Instruments.
