Catalysts Developed from Waste Plastics: A Versatile System For Biomass Conversion

The end-of-life treatment of post-consumer plastic waste constitutes one of modern society’s greatest problems, whereby highly unsustainable landfilling and incineration are the two main disposal routes. At present, the chemical upcycling of plastic waste is largely limited to its pyrolytic conversion into hydrocarbon fuels or nanomaterials. Herein, we demonstrate the upcycling of high-volume plastic waste by turning them into catalysts for biomass valorization. Many existing studies synthesise organocatalysts from a bottom-up approach using specialized monomers. Yet, transforming widely available waste polymers into functionalized materials for catalysis remains relatively unexplored. In this study, homogeneous and crosslinked heterogeneous catalysts derived from waste polystyrene food containers are shown to convert readily-available saccharide precursors from biomass into 5-hydroxymethylfurfural (5-HMF), a key biorefinery platform chemical, under short reaction times and mild conditions. In addition, the heterogeneous catalyst can be reused multiple times with little loss of yield between repeated runs. Other than 5-HMF, doping the reaction with water or halide salts also allowed the formation of valuable products such as formic acid and diformylfuran. Our work expands on existing upcycling options for post-consumer plastic waste by giving them a new lease of life as value-added catalysts.消费后塑料废弃物的生命周期末端处理是现代社会面临的重大挑战之一，当前不可持续的填埋与焚烧仍是两大主流处置途径。目前，塑料废弃物的化学升级回收（chemical upcycling）大多局限于将其热解转化为烃类燃料或纳米材料。本研究通过将大体积消费后塑料废弃物转化为用于生物质资源化利用（biomass valorization）的催化剂，实现了其升级回收。现有诸多研究均借助特种单体通过自下而上合成法（bottom-up approach）制备有机催化剂（organocatalysts），而将广泛可得的废弃聚合物转化为可用于催化的功能化材料的研究仍相对较少。本研究表明，以废弃聚苯乙烯餐盒制备得到的均相及交联型非均相催化剂，可在短反应时间与温和反应条件下，将易得的生物质糖类前驱体转化为关键生物炼制平台化合物5-羟甲基糠醛（5-hydroxymethylfurfural，5-HMF）。此外，该非均相催化剂可多次循环使用，且重复反应间的收率损失极小。除5-羟甲基糠醛外，在反应体系中添加水或卤化物盐，还可生成甲酸（formic acid）与二甲醛基呋喃（diformylfuran）等高价值产物。本研究拓展了消费后塑料废弃物的现有升级回收路径，使其得以作为高附加值催化剂重获新生。