Solvent- and Hydrogen-Free Upcycling of Polystyrene by Layered Double Oxides

Chemical upcycling of plastic waste into value-added feedstocks holds great promise for advancing the circular economy, while confronting formidable challenges. Herein, we report a cost-effective catalyst MgAl-layered double oxide (MgAl-LDO) for upcycling polystyrene (PS) into liquid fuel substitute components with rich styrene under solvent- and H₂-free conditions. The operando characterizations and theoretical simulations demonstrate that the MgAl-LDO, featuring rich basic sites (Mg─O), is favorable for efficient activation of C─H bonds and selective cleavage of C(sp³)-C(sp³) bonds. In particular, MgO in MgAl-LDO affords a low barrier for the rate-determining step for the formation of styrene while simultaneously suppressing the side reaction of further hydrogenation. As a result, the MgAl-LDO achieves a liquid fuel yield of 59.5% with a styrene selectivity of 70.9% at 280°C. Further, the obtained styrene monomer was copolymerized with methyl methacrylate (MMA) to prepare high value-added MMA-styrene copolymer, which offers pivotal insights into advanced chemical upcycling strategies, facilitating the transition to a sustainable plastics economy and the reduction of environmental impacts.