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

Considering the severe environmental and humanitarian implications of global plastic waste accumulation, understanding polyolefin catalytic breakdown is essential. Accordingly, a model compound would improve the reproducibility of experiments and simplify theoretical models. This study aimed to determine the minimum number of monomers necessary to represent the breakdown of polyethylene and polypropylene over metal catalysts. Using density functional theory (DFT) calculations, we evaluated how the 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 a small oligomer (less than 10 carbons) could 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, entanglement phenomena, and product selectivity observed in full polymers, it may prove useful for determining reaction energetics in complex systems and accelerating catalyst screening.