Minhao Tang, Ji Shen, Zhimin Liu
The global plastic pollution issues demand transformative upcycling technologies. As a kind of advanced material, well-defined heterocatalysts (WDHCs), which encompass well-defined nanoparticles, sub-nanoclusters, and atomically dispersed single-atom catalysts, have been widely employed in the chemical transformation of various waste plastics, showing high performance due to their unique structures. This review article summarizes advances on WDHCs for plastic upcycling, focusing on the structure-activity relationship of WDHCs and catalytic mechanisms. A framework of rational design for various WDHCs is first established, concentrating on the strategic engineering of metal centers, coordination environments, and support interfaces. Subsequently, the applications of WDHCs in catalyzing degradation of plastics via thermo-, photo-, and thermo-electronic strategies are introduced in sequence, with emphasis on mechanistic insights and structure-activity relationships of WDHCs. A critical assessment of catalyst stability, deactivation pathways, and performance in realistic mixed-plastic feeds is integrated throughout. Finally, the challenges related to scalable synthesis of catalysts and their stability, together with process integration, are addressed, offering perspectives on the development of sustainable and industrially viable plastic upcycling technologies. This work aims to serve as a foundational reference and a design guide for the next generation of high-performance WDHCs in enabling a circular economy of post-consumer plastics.