Transition Metal Catalysts for Depolymerization

Abstract

Abstract The global production and use of plastics is ever increasing, and consequently, so is plastic waste. Chemical recycling or depolymerization offers a potentially sustainable solution to the crisis of plastic pollution, enabling the production of either valuable organic compounds or monomers for a closed‐loop system. A vast amount of such depolymerization processes involve transition‐metal‐based catalysts. This review article provides a synopsis of various methods used for the transition‐metal‐catalyzed depolymerization of plastics. Processes based on both hetero‐ and homogeneous catalysts have been reviewed along with details of commercialized processes where relevant. The content has been divided on the basis of the type of plastics—polyolefins (polyethenes, polystyrene, and polyvinyl chloride), polyesters, polycarbonates, polyamides, polyurethanes, and polyureas. Processes based on pyrolysis, hydrogenolysis, and solvolysis have been discussed throughout the article as promising tools for the depolymerization of plastics. Considering that there is a plethora of literature on plastic degradation, we have focused only on the processes where a transition metal is used as a catalyst under thermal conditions. Therefore, several other processes such as plastic degradation using enzyme, plasma, supercritical solvents, and ionic liquid or photodegradation have been deemed out of scope of this article.