Elucidating the Effect of Nanocube Support Morphology on the Hydrogenolysis of Polypropylene over Ni/CeO2 Catalysts

The catalytic hydrogenolysis process offers the selective production of high-value liquid alkanes from waste polymers. Herein, through normalisation of Ni structure, Ni mass and density, and CeO2 crystallite size, the importance of CeO2 nanocube morphology in the hydrogenolysis of polypropylene (Mw = 12000 g mol-1; Mn = 5000 g mol-1) over Ni/CeO2 catalysts was determined. High liquid productivities (65.9-70.9 gliquid gNi-1 h-1) and low methane yields (10%) were achieved over two different Ni/CeO2 catalysts after 16 h reaction due to the high activity and internal scission selectivity of the supported ultrafine Ni particles (<1.3 nm). However, the Ni/CeO2 nanocube catalyst exhibited higher C-C scission rates (838.1 mmol gNi-1 h-1) than a standard benchmark mixed shape Ni/CeO2 catalyst (480.3 mmol gNi-1 h-1) and represents a 75% increase in depolymerisation activity. This led to shorter hydrocarbon chains achieved by the nanocube catalyst (Mw = 2786 g mol-1; Mn = 1442 g mol-1) when compared to the mixed shape catalyst (Mw = 4599 g mol-1; Mn = 2530 g mol-1). The enhanced C-C scission rate of the nanocube catalyst was determined to arise from a combination of improved H-spillover, reducibility, and favourable basic properties that tune the adsorption of hydrocarbon chains.