Size-dependent catalysis of Ru nanoparticles for selective reductive amination of PET plastic

Converting waste polyethylene terephthalate (PET) plastic into high-value p-xylylenediamine (PXDA) is a revolutionary solution to alleviate energy shortages and plastic pollution. However, current catalytic methods are often limited by poor chemoselectivity due to uncontrolled reductive amination and hydrodeoxygenation capabilities. Herein, we report a precision strategy to regulate the aggregation state of Ru on nitrogen-doped carbon, enabling size-dependent control of reaction pathways in the reductive amination of PET. Ultrasmall Ru nanoclusters (~1.3 nm) favor over-hydrogenation to 1,4-cyclohexanedimethanamine, whereas larger Ru nanoparticles (~4.6 nm) promote excessive hydrodeoxygenation to p-xylene. Notably, Ru/NC-SNPs (~2.4 nm) gives a high PXDA yield of 95.5% with a low apparent activation barrier (30.8 kJ/mol) under mild conditions. Mechanistic studies indicate that Ru/NC-SNPs achieve an optimal balance between hydrogen activation and amidation activity, thereby enabling selective amidation through the controlled dehydrogenation of the amide intermediate. The catalyst also demonstrates broad applicability for post-consumer PET, mixed plastics containing PET and other polyester plastics. Techno-economic analysis and life-cycle assessments further confirm the economic viability and environmental benefits of this process. This work establishes a size-governed selectivity paradigm for Ru-based catalysts and provides a general strategy for steering competing pathways in heterogeneous reductive amination toward sustainable PET valorization. Turning waste plastic into valuable chemicals requires precise control of competing reactions. This study shows that tuning ruthenium particle size enables selective conversion of polyethylene terephthalate into p-xylylenediamine.