(294c) Atomistic Simulations of Polymer/Alumina Catalyst Support Interfacial Interactions for Applications in Plastics Upcycling

Upcycling end-of-life plastics into alternative chemicals is critical to envisioning a waste-free and circular plastic economy. Hydrogenolysis, using supported metal catalysts, has shown promise as a viable catalytic pathway for transforming plastic wastes into new value-added chemicals in an economical manner. However, the complex chemical makeup of mixed plastic waste streams poses a major challenge to realizing this opportunity. Understanding the key molecular interactions that take place at the inorganic-organic depolymerization interface and directly affect catalytic performance, from a computational perspective, is thus paramount to improving the design of new catalysts for plastics hydrogenolysis.

We hypothesized that interactions between the polymers and the catalytic surface would be governed by the presence of the metal oxide support. As such, we performed physics-based, molecular dynamics simulations on the polymer-support interfacial system to elucidate these key interactions. Here, we report the interfacial molecular layering, orientational distribution, and free energies of interaction, of polyester polylactic acid and polyethylene terephthalate, as well as polyolefin polyethylene, at the alumina metal oxide support surface. Our simulation results identified variable effects of polymer chain length and functional groups on the interfacial molecular behavior of the polymers, which will be validated using X-Ray reflectivity experiments on analogous in vitro model systems. In this investigation, we applied state-of-the-art enhanced sampling techniques well-tempered metadynamics and parallel tempering metadynamics in the well-tempered ensemble. These methods rendered highly accurate descriptions of polymer-support interactions and near-surface polymer configurations over timescales not previously achievable using classical simulations. Molecular insights gained from this work can be leveraged to improve future catalyst designs and propose catalytic mechanisms that directly affect reactivity and selectivity. The general simulation workflow derived from this work can also be applied to elucidate interfacial phenomena at other inorganic-organic interfaces, such as that of lithium-ion battery electrodes and of organically-functionalized colloidal nanocrystals.