Supercritical CO₂-promoted degradation of polystyrene to aromatic oils with NiO@C catalyst

Exploring new system for chemical recycling of plastic is an effective way to convert plastic waste into energy. Herein, the use of supercritical CO₂ (ScCO₂) to promote the catalytic degradation of polystyrene (PS) with high yield of aromatic oils was proposed. ScCO₂ provided a homogeneous environment for the reaction, which not only facilitated the swelling of PS, but also inhibited the formation of coke, beneficial for the degradation of PS to aromatic oils. In addition, CO₂ as an oxidant reacted with PS or intermediates to generate new products. NiO@C catalyst prepared by doping carbon material in NiO had a simple preparation process, an abundance of porous structure and strong acidic sites, thus improving the catalytic activity. Under the co-action of ScCO₂ and NiO@C, the yield of aromatic oils produced from PS was up to 89.3 ± 0.6 wt% at 300 °C with a reaction time of 2 h and a catalyst loading amount of 10 wt%. Moreover, the NiO@C catalyst was used for three cycles without obvious change in the catalytic performance. The efficient catalytic degradation of PS to aromatic oils by ScCO₂ promoted NiO@C catalysis provides a potential route for simultaneously recycling plastic and sequestering carbon.