Efficient upgrading of polystyrene plastics to nitriles through a catalytic oxidative amination process†

Abstract

The upcycling of C–C bond linked polyolefins has drawn wide attention in recent years and a lot of studies have been focused on the conversion of polyolefins to hydrocarbons, while the further valorization to more value-added products has barely been developed. In this work, we developed an efficient strategy to upgrade polystyrene (PS) plastics into a single N-containing product, benzonitrile, over a NiO/CeO₂ catalyst via a one-pot, two-step process. The first step is the oxidative-amination of PS to a mixture of benzamide and benzonitrile and the second step is the dehydration of benzamide to benzonitrile; finally, a single N-containing product, benzonitrile with a 50.3% yield, was achieved. Mechanism studies via control experiments in the first oxidative-amination step showed that benzaldehyde was the important intermediate, which can undergo two parallel pathways generating benzamide and benzonitrile, respectively. Following the dehydration of benzamide to benzonitrile in the second step, benzonitrile was produced as the only product. This strategy can also be extended to real-life PS plastics and a high yield of benzonitrile was achieved. This novel study provides an efficient approach for upgrading waste plastics to a single high-value product.