Upcycling waste plastic into aromatics presents an attractive strategy to tackle both plastic pollution and energy challenges. However, previous studies often rely on high temperatures, precious metals, and have broad product distributions. In this study, we reported that a Ni/ZSM-5 bifunctional catalyst can directly convert polyethylene (PE) into methylated aromatics with high selectivity under mild conditions, while eliminating the requirement for hydrogen gas and solvents. The liquid yield could attain up to 70.3%, and the aromatics yield could achieve up to 51.7%. Over 78.4% of the aromatics were methylated aromatics including toluene, xylene, and mesitylene. Polymer chains underwent dehydrogenation over Ni and the acid sites in ZSM-5, forming C=C bonds. Certain of these bonds evolved into carbenium ions through the process of proton transfer at the acid sites. The optimization of Ni and acid sites enhanced the oligomerization, cyclization, and aromatization process. The extra mesopores created by Ni on the molecular sieve aid in the generation of aromatics. Furthermore, the Ni/ZSM-5 catalyst demonstrated the ability to convert typical commercial grades of PE plastic, such as gloves and bottles, into aromatics with a selectivity of up to 61.1%. It offers an economically feasible and environmentally friendly upcycling avenue for the circular economy of plastics.

中文翻译：

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在温和条件下，聚乙烯废料在 Ni/ZSM-5 上无氢升级回收为甲基化芳烃


将废塑料升级回收成芳烃是应对塑料污染和能源挑战的有吸引力的策略。然而，以前的研究通常依赖于高温、贵金属，并且具有广泛的产品分布。在这项研究中，我们报道了 Ni/ZSM-5 双功能催化剂可以在温和条件下直接将聚乙烯 （PE） 转化为具有高选择性的甲基化芳烃，同时无需氢气和溶剂。液体收率最高可达 70.3%，芳烃收率最高可达 51.7%。超过 78.4% 的芳烃是甲基化芳烃，包括甲苯、二甲苯和均三甲苯。聚合物链在 Ni 和 ZSM-5 中的酸位点上发生脱氢，形成 C=C 键。其中一些键通过酸位点的质子转移过程演变成钶离子。Ni 和酸位点的优化增强了低聚化、环化和芳构化过程。Ni 在分子筛上产生的额外介孔有助于芳烃的产生。此外，Ni/ZSM-5 催化剂能够将典型的商业等级的 PE 塑料（如手套和瓶子）转化为芳烃，选择性高达 61.1%。它为塑料循环经济提供了一种经济上可行且环保的升级再造途径。