Water-assisted single-step catalytic hydrodeoxygenation of polyethylene terephthalate into gasoline- and jet fuel-range cycloalkanes over supported Ru catalysts in a biphasic system

Abstract

To resolve white plastic pollution and the human carbon footprint, we report an efficient green approach to quantitatively convert polyethylene terephthalate (PET) to high-density C₆–C₈ cyclic hydrocarbons via single-step water-assisted hydrodeoxygenation (HDO) over a Ru/TiO₂ catalyst in a biphasic system. To understand the structure–activity relationships of supported metal catalysts in PET HDO, acidic and neutral support-loaded Ru catalysts were prepared, characterized, and evaluated in mono- and biphasic systems. An experimental study revealed that Ru/TiO₂ effectively catalyzed the production of C₆–C₈ cyclic hydrocarbons from PET. Under mild conditions (220 °C, 50 bar H₂, 12 h), the catalyst completely converted PET into fuel-range C₆–C₈ cyclic hydrocarbons at a remarkably high selectivity of 96.8–99.2%. The catalyst successfully cleaved all C–O bonds in the aromatic plastic in a water–dodecane (O/W) biphasic system via the favorable effects of the metal-acid bifunction, hydrophilicity, and high dispersion of small Ru particles on the support. Due to its hydrophilic behavior, the nanosized catalyst formed stable Pickering emulsion droplets in the biphasic system. The presence of these droplets increased the selectivity towards C₆–C₈ hydrocarbons by forming a reaction interface with a large area between the oil and water layers. This improves accessibility to the active sites of the catalyst, stabilizes the intermediates, and enhances mass transfer and the separation of the target products. Furthermore, using a model compound study, we identified the pathway involved in the HDO reaction. Moreover, the addition of water to the biphasic system significantly increased the rate of proton transfer on the catalyst support. This study presents an excellent single-step catalytic pathway for application in synthesizing C₆–C₈ cyclic hydrocarbons using PET waste in a water-assisted biphasic system, providing a viable solution for plastic recycling.