Low-Temperature Upcycling of Polypropylene Waste into H₂ Fuel via a Novel Tandem Hydrothermal Process

Plastic waste is a promising and abundant resource for H₂ production. However, upcycling plastic waste into H₂ fuel via conventional thermochemical routes requires relatively considerable energy input and severe reaction conditions, particularly for polyolefin waste. Here, we report a tandem strategy for the selective upcycling of polypropylene (PP) waste into H₂ fuel in a mild and clean manner. PP waste was first oxidized into small-molecule organic acids using pure O₂ as oxidant at 190 °C, followed by the catalytic reforming of oxidation aqueous products over ZnO-modified Ru/NiAl₂ O₄ catalysts to produce H₂ at 300 °C. A high H₂ yield of 44.5 mol/kg_PP and a H₂ mole fraction of 60.5 % were obtained from this tandem process. The entire process operated with almost no solid residue remaining and equipment contamination, ensuring relative stability and cleanliness of the reaction system. This strategy provides a new route for low-temperature transforming PP and improving the sustainability of plastic waste disposal processes.