Upcycling of Waste Polyester Plastic to Carboxylic Acids and Hydrogen by a Ru^δ+–Ru⁰ Dual-Site Catalyst

Abstract

Chemical upcycling of plastic waste into high-value chemicals or fuels could mitigate environmental pollution and create a more sustainable society. Hydrolytic depolymerization is a viable method for polyester recycling but typically requires high temperature to drive this reaction and complete subsequent distillation operations to separate a diol from the aqueous phase. Here, through theoretical screening, we discover a Ruδ+–Ru0 dual-site catalyst can achieve the tandem PET (polyethylene terephthalate) depolymerization and in situ reforming of ethylene glycol (EG) under mild conditions. Mechanism studies reveal that the Ruδ+ site can selectively promote adsorption and C–H bond dissociation, yet C–C bond cleavage takes place on both Ruδ+ and Ru0 sites, which synergistically promotes PET and EG conversion and helps avoid excessive oxidation of intermediates to CO2 or CO. As a result, this catalyst delivers a conversion of 100% toward PET and EG into high-value organic acids, including terephthalic acid, and high-purity H2 with a generation rate of 1.03 m3 kgPET–1 d–1 gCat–1 at 90 °C. Besides, this catalyst is catalytically active toward a wide scope of substrates, including real-world waste PET products, PET-containing mixed plastics, and other polyester plastics. Techno-economic analysis and environmental assessment show that this integration process can significantly increase net profits and reduce carbon emissions.