The continuous increase in manufacturing coupled with the difficulty of recycling of plastic products has generated huge amounts of waste plastics. Most of the existing chemical recycling and upcycling methods suffer from harsh conditions and poor product selectivity. Here we demonstrate a photocatalytic method to oxidize polystyrene to aromatic oxygenates under visible light irradiation using heterogeneous graphitic carbon nitride catalysts. Benzoic acid, acetophenone, and benzaldehyde are the dominant products in the liquid phase when the conversion of polystyrene reaches >90% at 150 °C. For the transformation of 0.5 g polystyrene plastic waste, 0.36 g of the aromatic oxygenates is obtained. The reaction mechanism is also investigated with various characterization methods and procedes via polystyrene activation to form hydroxyl and carbonyl groups over its backbone via C–H bond oxidation which is followed by oxidative bond breakage via C–C activation and further oxidation processes to aromatic oxygenates.

Because of the structural complexity and inhomogeneity, the effect of the coordination environment on the catalytic properties is underexplored in heterogeneous catalytic systems. To address this challenge, the atomically dispersed Pt is anchored on two Mo-based supports with similar morphology and particle size, that is, face-centered cubic-structured α-MoC and MoN. Spectroscopic and computational investigations demonstrate that the Pt atoms are coordinated with N atoms in Pt/MoN but with Mo atoms in Pt/α-MoC, leading to an entirely different catalytic performance in the oxygen reduction reaction (ORR). The Pt mass activity for Pt/MoN reaches 0.71 A/mg Pt at 0.9 V [vs reversible hydrogen electrode (RHE)], which is 15 times higher Pt mass activity than that of Pt/α-MoC. Density functional theory calculations correlate the better ORR performance of Pt/MoN with the weaker adsorption of OH* because of the modulation of electronic properties of Pt by the coordination with N atoms. This study highlights the importance of controlling the coordination environment of metal atoms in heterogeneous (electro)catalysis and suggests that tuning the coordination environment could be an effective strategy in catalyst development.

Synthesis of atomically dispersed catalysts with high metal loading and thermal stability is challenging but particularly valuable for industrial applications in heterogeneous catalysis. Here, we report a facile synthesis of a thermally stable atomically dispersed Ir/α-MoC catalyst with metal loading as high as 4 wt%, an unusually high value for carbide supported metal catalysts. The strong interaction between Ir and the α-MoC substrate enables high dispersion of Ir on the α-MoC surface, and modulates the electronic structure of the supported Ir species. Using quinoline hydrogenation as a model reaction, we demonstrate that this atomically dispersed Ir/α-MoC catalyst exhibits remarkable reactivity, selectivity, and stability, for which the presence of high-density isolated Ir atoms is the key to achieve high metal-normalized activity and mass-specific activity. We also show that water-promoted quinoline hydrogenation mechanism is preferred over the Ir/α-MoC, which contributes to high selectivity towards 1,2,3,4-tetrahydroquinoline. The present work demonstrates a new strategy to construct high-loading atomically dispersed catalyst towards hydrogenation reaction.