Polypropylene Plastic Waste Conversion to Lubricants over Ru/TiO2 Catalysts

Plastic recycling and upcycling are required to combat the environmental crisis from landfilling consumer products. Chemocatalytic technologies are the most promising approach to achieve this. Here, we show that ruthenium deposited on titania is an active and selective catalyst in polypropylene breakdown into valuable lubricant-range hydrocarbons with narrow molecular weight distribution and a low methane formation at low temperatures of 250 °C with a modest H2 pressure. Amorphous polypropylene and everyday bags and bottles were also effectively converted to lubricants with yields up to 80+%. Quantification of critical properties, including pour point, kinematic viscosity, and viscosity index, indicates that the products are promising alternatives to currently used base or synthetic oils. The reaction network involves the sequential conversion of polymer into the oil with a gradual decrease of molecular weight until ∼700–800 g/mol and slow liquid gasification to methane and ethane. NMR, ATR-IR, GCMS, and isotopic labeling experiments expose the complexity of structure and reaction evolution whereby hydrogenolysis involves intermediate dehydrogenation with synchronous loss of polypropylene stereoregularity.