Shape-Dependent Reactivity of Ru/CeO2 Catalysts in the Chemical Recycling of Polypropylene to Liquid Hydrocarbons via Hydrogenolysis

The t ransformation of polyolefin waste to liquid hydrocarbons via hydrogenolysis offers a promising pathway for the chemical recycling of waste polymers. This work describes the importance of shaped CeO2 supports (nanorods and nanocubes) in governing metal-support interactions and facilitating the production of highly dispersed Ru species, for application in the hydrogenolysis of various pristine and post-consumer polypropylene (Mw = 11975-250,000 Da). The shaped 2 wt.% Ru/CeO2 exhibit high liquid alkane yields (58-81%) when compared to the non-shaped 2 wt.% Ru/CeO2 catalysts (liquid yield: 34-58%) under optimized mild reaction conditions (220 °C, 16 h, 30 bar H2). The formation of small Ru clusters and adatoms on the shaped CeO2 are key to control the regioselectivity by favoring greater hydrogen adsorption and facilitating the scission of internal C-C bonds to produce high liquid alkane yields with increased catalytic activity. This was further confirmed mechanistically using a computational density functional theory study on the hydrogenolysis of pentane (C5) to determine the favorable formation of methane over larger Ru particles (≥1.5 nm) that are present in the non-shaped Ru/CeO2 catalyst.