Tandem catalytic strategy enables selective upcycling of polystyrene waste into pure toluene

Polystyrene (PS) is one of the most difficult‑to‑recycle plastics, constituting about one‑third of landfill content worldwide. Its polymer backbone consists mainly of inert C–C bonds, making deconstruction into valuable chemicals particularly challenging. In a study published in ENG. Chem. Eng., researchers highlight a breakthrough recently reported in Nature Nanotechnology by Wang and colleagues, who developed a tandem depolymerization and hydrogenolysis strategy that upcycles polystyrene waste into single toluene via selective C–C bond cleavage.
The challenge lies in the thermodynamic incompatibility between depolymerization and hydrogenation. Depolymerization requires high temperatures, but high temperatures are incompatible with catalysts featuring high hydrogenolysis activity, resulting in low selectivity for C–C bond cleavage. Conventional approaches typically produce mixed aromatic hydrocarbons with both monocyclic and polycyclic motifs.
The new tandem design decouples these two processes. The first stage involves polystyrene hydropholysis at 475 °C to generate aromatic intermediates. The second stage is vapor‑phase hydrogenolysis of these intermediates at 275 °C and 0.4 MPa over a ruthenium single‑atom modified Co₃O₄ catalyst (RuSA/Co₃O₄). The ruthenium single atoms in Co₃O₄ reduce the energy barrier for Csp₂/Csp₃–Csp₃ bond cleavage in key intermediates while promoting toluene desorption, thereby steering selective toluene formation.
The system achieves 99 % selectivity for toluene with a yield of 83.5 wt%. Importantly, it is compatible with various disposable polystyrene‑based raw materials, delivering approximately 81 wt% yield and >99 % selectivity for toluene. The process also demonstrates high economic viability and a low carbon footprint.
The phenyl group accounts for 74 % of polystyrene’s total weight, making selective deconstruction into aromatic hydrocarbons an attractive but challenging goal. Toluene is one of the key chemical feedstocks, with global demand expected to increase from 37 to 77 million tons by 2035. Directed deconstruction of polystyrene into toluene with high selectivity is therefore of great significance for advancing carbon circulation and reducing petrochemical feedstock reliance.
Current challenges for industrial translation include plastics feeding continuity, feedstock flexibility (e.g., polyethylene, polypropylene, and polyvinyl chloride), mixed plastics processing, reaction sustainability, and process‑level energy integration. Future efforts must also address catalyst design (activity, selectivity, and structural integrity) and reaction pathway regulation.
This work demonstrates that selective deconstruction of plastic waste is achievable through rational catalyst design and process integration. By breaking the yield‑selectivity trade‑off, the tandem depolymerization and hydrogenolysis strategy provides a transformative paradigm for polystyrene valorization, moving from non‑selective deconstruction toward selective synthesis of single valuable products.