Theoretical determination of a model molecule for the catalytic upcycling of polyethylene and polypropylene

Abstract

Considering the severe environmental and humanitarian implications of global plastic waste accumulation, understanding polyolefin catalytic degradation is essential. Accordingly, a model compound would improve experiments' reproducibility and simplify theoretical models. Therefore, this study aimed to determine the minimum number of monomers necessary to represent the degradation and upcycling of polyethylene and polypropylene over metal catalysts. Using density functional theory (DFT) calculations, we evaluated how polymer's chain length affects reaction energies and energy barriers for C-H and C-C cleavage over stepped transition metal surfaces. We found that chain length does not significantly affect the C-H and C-C cleavage reaction energies and the C-H cleavage energy barriers. Our findings suggest that molecules as small as ethane may be suitable as a model to study polyethylene's catalytic C-H and C-C cleavage. Although such a simple molecule cannot capture complex transport and entanglement phenomena in full polymers, it may prove useful for determining reaction energetics in complex systems.