(638a) Ru/C Property Insights for Polypropylene Waste Hydrogenolysis

Plastic waste accumulation is a global environmental issue, posing severe ramifications for the natural world. The current management of plastic waste is unsustainable, resulting in an estimated 79% of all plastic being disposed of in landfills, while only 9% is recycled. Plastic upcycling via hydrogenolysis is an attractive solution to redirect common polyolefin waste from the landfill and into value-added products such as lubricants. Ruthenium (Ru) supported catalysts are highly active for polyolefin hydrogenolysis. However, high catalyst activity and selectivity require high Ru loadings (>4 wt. %) and high catalyst/polymer ratios, increasing overall costs. Thus, this work aims to provide insights that will improve a fundamental understanding of structure-activity relationships governing catalytic behavior, as this is necessary for the development of tunable catalysts and can ultimately be leveraged to enable rational design.

One of the objectives is to correlate particle size, structure, and metal support interactions (MSI) with product selectivity in polypropylene (PP) hydrogenolysis. Previous work in the field has shown that Ru’s performance is dependent on particle size with high activity for ultra-small clusters. MSI in reducible supports also play a key role in stabilizing small Ru clusters and creating active Ru^δ+ species but details regarding their impact remain unclear. Our work focuses on investigating Ru particle size effect on an inert carbon support utilizing various characterization methods including HRTEM, H₂-TPR/TPD, XPS, NMR and GPC. Using an activated carbon support and systematic variation of Ru particle size (by changing Ru loadings and different pretreatment protocols), we reveal basic site requirements for PP hydrogenolysis and demonstrate the influence of small Ru nanoclusters on product selectivity.