Solvent-free recycling of polystyrene waste into valuable mono-aromatics over a 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 the 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 mono-aromatics 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 a solvent, delivering a liquid yield above 90% and a mono-aromatics selectivity of 60.7%, corresponding to a mono-aromatics formation rate of 2.02 g_{mono-aromatics} g_cat⁻¹ h⁻¹. Comparison with a physical mixture of Ni + NbO_x indicates that the close contact between Ni and NbO_x in Ni/NbO_x enhances 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.