Breaking the yield–selectivity trade-off in polystyrene waste valorization via tandem depolymerization and hydrogenolysis

Abstract

Converting plastic waste into valuable products mitigates plastic pollution and lowers the carbon footprint of naphtha-derived aromatics. However, the difficulties of precisely controlling complex multiphase systems and the catalyst inefficiencies hinder process viability. Here we report a vapour-phase hydrogenolysis strategy catalysed by Ru single atoms on Co3O4 (RuSA/Co3O4), decoupling depolymerization from hydrogenolysis to overcome the toluene yield–selectivity trade-off. In a pressurized dual-stage fixed-bed reactor, polystyrene undergoes hydropyrolysis at 475 °C, followed by vapour-phase hydrogenolysis at 275 °C (0.4 MPa H2, 2.4 s), yielding toluene with 99% selectivity, 83.5 wt% yield and 1,320 mmol gcat.−1 h−1 rate. The RuSA/Co3O4 catalyst demonstrates excellent stability, maintaining >99% conversion and selectivity during 100 h continuous operation (turnover number 24,747), and effectively processes diverse real-world polystyrene wastes. Life-cycle assessment shows a 53% carbon footprint reduction over fossil-based methods, while techno-economic analysis estimates a competitive minimum selling price of US$0.61 kg−1, below the US$1 kg−1 industry benchmark. A tandem catalytic strategy is developed to convert polystyrene waste into a spectrum of aromatic intermediates and subsequently into a single dominant product, toluene. This tandem design enhances product selectivity to 99% and minimizes downstream separation costs.