An Investigation into Polyester Adsorption onto Alumina toward an Improved Understanding of Hydrogenolysis Catalysts.

Chemical recycling of end-of-life plastic wastes through hydrogenolysis is a promising pathway for achieving a circular plastics economy and reducing overall energy costs. Understanding molecular interactions at the inorganic-organic depolymerization interface is crucial for enhancing catalyst performance and overcoming challenges posed by mixed plastic waste streams. We investigated a fundamental step in the depolymerization process: physisorption of polymers onto the metal oxide support preceding diffusion to and reaction at the catalyst-support junction. Molecular dynamics simulations, augmented with well-tempered metadynamics, were conducted to explore the adsorption of polylactic acid (PLA) and polyethylene terephthalate (PET) oligomers onto a hydroxylated alumina support surface. Our findings revealed multiple layers of highly oriented solvent molecules (1,4-dioxane) above the surface, creating significant barriers to polyester adsorption. Disrupting and displacing these solvent layers led PET oligomers to adsorb closer to and interact stronger with the surface than PLA oligomers, possibly contributing to the higher reaction temperatures needed to achieve full conversion in PET versus PLA hydrogenolysis. We further suggest an experimental approach to validate our results of solvent layering behavior through predictions of X-ray reflectivity that are consistent with our initial experiments. The insights gained in this study can be leveraged to refine our understanding of catalytic mechanisms to predict depolymerization reactivity and selectivity and improve future hydrogenolysis catalyst designs.