Orchestrating Cluster-Level Atomic Assemblies for Hydrogen/Solvent-Free Plastic Upcycling

The size of supported metal species plays a critical role in catalytic activity, yet the atomic-scale structure sensitivity in hydrogen- and solvent-free thermal polymer upcycling has not been fully explored. This study investigated the relationship between the atomic configuration and upcycling efficiency, aiming to optimize the yield of valuable aromatics. High-order Ru atomic clusters (ACs) with optimal coordination incorporated into hydrogen-form Zeolite Socony Mobil-5-300H (HZSM-5-300H) showed superior low-density polyethylene (LDPE) conversion (62.93% vs 41.61%), better aromatic selectivity (70.43% vs 48.43%), and more favorable economic viability compared to low-order Ru ACs with isolated atomic sites on HZSM-5-300H. Structural and performance analysis revealed that the Ru assembly was a dominant factor in plastic upcycling, overshadowing the contributions of other components. The increased conversion was attributed to the optimal adsorption energy of intermediates and the enhanced dehydrogenation capacity of high-order Ru ACs, improving the feasibility of subsequent steps. Distinguished aromatic yield was achieved due to efficient dehydro-aromatization and hydrogen migration while minimizing rehydrogenation of aromatics and maintaining appropriate H* binding capacity. The metal–acid balance for 0.5 wt % Ru/300H (i.e., high-order Ru ACs) was better optimized for C–C cleavage compared to 0.2 wt % Ru/300H (i.e., low-order Ru ACs), leading to a significant increase in turnover frequency (TOF) for aromatic yield from cyclohexane dehydro-aromatization, rising from 296.56 μM·mg–1 Ru·h–1 to 544.34 μM·mg–1 Ru·h–1. The scalability of this approach can be extended to various systems, including different metals, supports, and acidities. Overall, this study highlights the advantages of high-order Ru ACs over low-order Ru ACs in hydrogen- and solvent-free waste plastic upcycling, offering insights into the development of efficient, cost-effective catalysts for polymer recycling.