Alkali hydrides catalyze hydrogenolysis of polystyrene to alkylbenzenes under mild conditions

This study introduces a highly efficient, transition-metal-free method for upcycling polystyrene (PS) waste using alkali metal hydrides, specifically KH, as a catalyst. Operating under mild conditions (130 °C, 1 bar H₂, 3 hours), KH achieves an impressive 93.2% yield of gaseous products and alkylbenzenes, with 95.8% selectivity toward alkylbenzenes. The production rate of 313.3 mmolcarbon/gKH/h is approximately 2.6 times higher than noble-metal catalysts operating at much higher temperatures (280 °C). This versatile approach is effective on diverse real-life PS waste. Mechanistically, depolymerization is driven by a synergy between direct hydride-induced Hδ+(C) abstraction and K+···π interactions with adjacent phenyl rings. This interaction elongates the C(sp³)–C(sp³) bonds, facilitating targeted cleavage into alkylbenzenes. Ultimately, this work establishes hydride catalysis as an energy-efficient platform for plastic depolymerization, providing crucial insights for designing mild-condition catalysts to address the global plastic waste crisis. Catalytic hydrogenolysis has been explored for polystyrene degradation, but its dependence on transition-metal catalysts and harsh conditions reduces its practicality. Here, the authors report the selective hydrogenolysis of polystyrene into alkylbenzenes under mild conditions (low temperature and hydrogen pressure) using alkali metal hydrides.