Solvent-Free Recycling of Polystyrene Waste into Valuable Monoaromatics over Ni/NbOx Catalyst

Abstract

The catalytic upcycling of polystyrene (PS) waste into valuable aromatic chemicals can mitigate plastic pollution and reduce dependence on fossil-derived aromatics; however, its hydroconversion into mono-aromatics remains challenging due to the intrinsic stability of C-C bonds in the polymer backbone and the competitive hydrogenation of aromatic rings under hydrogen atmospheres. Herein, we report a solvent-free catalytic strategy for the efficient upcycling of PS into monoaromatics over a bifunctional Ni/NbO_x catalyst. Under relatively mild conditions, i.e. 260 °C and 3 MPa H₂, a 1 wt% Ni/NbO_x catalyst achieves complete PS conversion within 3 h without solvent, delivering a liquid yield above 90% and a monoaromatics selectivity of 80.8%, corresponding to a mono-aromatics formation rate of 2.02 g _{mono-aromatics} g_cat^-1 h ^-1 . Comparison with physical mixture of Ni + NbOx indicates that a close contact between Ni and NbO_x in Ni/NbO_x enhance hydrogen spillover, thus resulting in a higher activity for the hydrocracking of polystyrene into mono-aromatics. The Ni/NbO_x catalyst exhibits good recyclability and applicability to real-world and mixed plastic wastes, providing a cost-effective and scalable catalytic approach for the sustainable upgrading of polystyrene waste into valuable aromatic chemicals.