Selective Conversion of Polyolefin Waste to Branched Alkanes via Methane-Free Tandem Hydrocracking-Isomerization

In recent years, catalytic hydrocracking has emerged as a promising waste-to-feedstock solution for processing plastic waste. Although ruthenium nanoparticle catalysts exhibit high activity in converting polyolefins into small alkanes, they also tend to produce undesirable methane (CH₄) via terminal C─C bond hydrogenolysis. Herein, we report a Ru-supported sulfated zirconia (RuSZ₁) catalyst for the efficient isomerization and hydrocracking of polyolefins without generating CH₄. Various high-M_w polyethylene and polypropylene samples (up to 1 000 000 g/mol) were fully converted into branched alkanes (C₄-C₂₀). Control experiments using RuSZ₁ revealed negligible scission activity for alkanes with fewer than seven carbons, suggesting that isomerization precedes hydrocracking. Hydrogenolysis to form C₁ and C₂ products is likely inhibited by saturation of sulfate species at the Ru sites, and these products were not observed under any reaction conditions. Full conversion of polyolefins under solvent-free conditions was achieved, with up to 93% yield of C₃-C₁₂ alkanes.