Selective Hydrocracking of Polystyrene without Solvent to Alkylbenzenes over a Single-Atom Catalyst Co ₁ -Al ₂ O ₃

Polystyrene (PS) is one of the most widely used plastics yet scarcely recycled. Although hydrocracking catalysts with hydrogen can cleave the C−C bond in PS, they also tend to hydrogenate aromatic rings, reducing the value of the product derived from PS hydrocracking. Here, we report a single-atom catalyst Co1-Al2O3 that efficiently cleaves the PS backbone C−C bond while completely preserving the aromatic rings under solvent-free hydrocracking conditions. This catalyst produces a series of alkylbenzenes, including toluene, ethylbenzene, cumene, and diphenylalkanes, without forming cycloalkanes, achieving an alkylbenzene formation rate of 0.695 garomatic gcat−1 h−1. Control experiments with model substrates such as bicumyl (2,3-dimethyl-2,3-diphenylbutane) and with benchmark Al2O3-supported Co particles reveal that isolated Co2+ sites in Co1-Al2O3 prefer to selectively cleave the C−C bonds rather than hydrogenate aromatic rings, whereas metallic Co particles favor aromatic hydrogenation and shift hydrocracking toward hydrogenolysis. The effectiveness of the single-atom catalyst Co1-Al2O3 in postconsumer PS hydrocracking highlights its potential for practical PS upcycling to valuable alkylbenzenes.