Understanding the Structure–Activity Relationships in Catalytic Conversion of Polyolefin Plastics by Zeolite-Based Catalysts: A Critical Review

Polyolefins, the largest used commodity plastics in the world, find extensive application in many fields. However, most end up in landfills or incineration, leading to severe ecological crises, environmental pollution, and serious resource waste problems. As representatives on chemical upcycling of polyolefin plastics polyolefin waste to fuels and bulk/fine chemicals, polyolefin catalytic cracking and hydrocracking based on zeolite or metal/zeolite composite catalysts are considered the most effective paths due to their large capacity and strong adaptability to existing petrochemical equipment. After an overview of the reaction mechanisms of pyrolysis and catalytic cracking, this review aims to comprehensively discuss the influence of zeolite catalyst structure (acidity, pore structure, and morphology) on the catalytic activity, selectivity, and stability of polyolefin cracking, particularly emphasizing the importance for matching acidity and pore structure for target product formation. Subsequently, the structure–activity relationship between the metal site and zeolite's acid site in polyolefin hydrocracking is also discussed. In the end, emerging opportunities and challenges are proposed to promote a more efficient way for polyolefin chemical upcycling.