Catalytic Upcycling of Polyolefins and Polystyrene: Integrating Active Site Design With Mass Transfer Considerations.

Plastic waste accumulates globally due to its chemical inertness and resistance to degradation, creating both an escalating environmental burden and a squandered fossil-derived carbon resource. Catalytic upcycling provides a promising route to convert these materials into fuels and chemicals; however, development is constrained by the dual challenge of cleaving robust C-C bonds while processing macromolecular substrates subject to severe diffusion limitations. This review assesses the current landscape of catalytic conversion of polyolefins (PO) and polystyrene (PS), including hydrogenolysis, catalytic cracking, hydrocracking, and selective oxidation, and clarifies that catalytic performance cannot be rationalized or optimized solely based on intrinsic active site chemistry. Instead, the spatial distribution of metal and acid sites, catalyst porosity, susceptibility to deactivation and poisoning, and multiscale transport phenomena collectively dictate apparent activity, selectivity, and stability. By integrating active site design with mass-transfer considerations, from intrapore diffusion to reactor-level flow behavior, this review identifies design principles that reconcile high intrinsic activity with mass-transfer efficiency. Overall, tuning the interplay between catalytic functionality and transport properties emerges as a central requirement for advancing efficient, selective, and scalable plastic upcycling technologies.