Nuclearity-dependent design principles of ruthenium catalysts for selective hydroconversion of diverse polyolefins

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Polyolefin waste presents a major upcycling challenge because of its chemical inertness. Ruthenium catalysts are highly active for polyethylene hydrogenolysis, but often overproduce methane and linear alkanes and show limited substrate scope. Here we establish a mechanistic framework showing that the interplay between Ru nuclearity, valence, and support acidity governs the selectivity in Ru/NbOx-catalyzed polyolefin hydroconversion. Metallic Ru nanoparticles activate both C-H and C-C bonds and favor hydrogenolysis, whereas atomically dispersed Ru species, together with hydrogen spillover-generated Nb-OH sites, enable C-H activation and Brønsted acid-assisted hydrocracking. Methane originates primarily from hydrogenolysis on extended metallic Ru domains and is minimized by controlling Ru ensemble size or shifting the reaction toward hydrocracking. Accordingly, Ru/NbOx-600 fully converts polyethylene to 93.1% C5-35 linear alkanes, while Ru/NbOx-300 hydrocracks polypropylene at 1731 gPP·gRu-1·h-1 with 90.6% C5-20 branched liquid fuel selectivity. This work establishes design principles of Ru catalysts for selective, efficient plastic upcycling. Turning stubborn plastics into useful chemicals is hard because they resist reaction. This study shows how ruthenium form and support acidity steer their breakdown, enabling selective conversion of polyethylene and polypropylene into liquid fuels.