Catalytic Hydrodeoxygenation of Mixed Plastic Wastes into Sustainable Naphthenes

Abstract

The chemical upcycling of plastic wastes by converting them into valuable fuels and chemicals represents a sustainable approach as opposed to landfilling and incineration. However, it encounters challenges in dealing with mixed plastic wastes due to their complex composition and sorting/cleaning costs. Here, we present a one-pot hydrodeoxygenation (HDO) method for converting mixed plastic wastes containing poly(ethylene terephthalate) (PET), polycarbonate (PC), and poly(phenylene oxide) (PPO) into sustainable naphthenes under mild reaction conditions. To facilitate this process, we developed a cost-effective, contaminant-tolerant, and reusable Ni/HZSM-5 bifunctional catalyst through an ethylene glycol-assisted impregnation method. The metallic Ni site plays a pivotal role in catalyzing C–O and C–C cleavages as well as hydrogenation reactions, while the acidic site of HZSM-5 facilitates dehydration and isomerization reactions. The collaboration between metal and acid dual sites on Ni/HZSM-5 enabled efficient HDO of a wide range of substrates, including bottles, textile fibers, pellets, sheets, CDs/DVDs, and plastics without cleaning or pigments removal and even their various mixtures, into naphthenes with a high yield up to 99% at 250 °C and 4 MPa H₂ within 4–6 h. Furthermore, the metal-acid balance of the Ni/HZSM-5 catalyst is crucial for determining both HDO activity and product distribution. This proposed one-pot HDO process utilizing earth-abundant metal catalysts provides a promising avenue toward practical valorization of mixed plastic wastes.