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.