Single-use plastics impose an enormous environmental threat, but their recycling, especially of polyolefins, has been proven challenging. We report a direct method to selectively convert polyolefins to branched, liquid fuels including diesel, jet, and gasoline-range hydrocarbons, with high yield up to 85% over Pt/WO3/ZrO2 and HY zeolite in hydrogen at temperatures as low as 225°C. The process proceeds via tandem catalysis with initial activation of the polymer primarily over Pt, with subsequent cracking over the acid sites of WO3/ZrO2 and HY zeolite, isomerization over WO3/ZrO2 sites, and hydrogenation of olefin intermediates over Pt. The process can be tuned to convert different common plastic wastes, including low- and high-density polyethylene, polypropylene, polystyrene, everyday polyethylene bottles and bags, and composite plastics to desirable fuels and light lubricants.

Plastics waste has become a major environmental threat, with polyethylene being one of the most produced and hardest to recycle plastics. Hydrogenolysis is potentially the most viable catalytic technology for recycling. Ruthenium (Ru) is one of the most active hydrogenolysis catalysts but yields too much methane. Here we introduce ruthenium supported on tungstated zirconia (Ru-WZr) for hydrogenolysis of low-density polyethylene (LDPE). We show that the Ru-WZr catalysts suppress methane formation and produce a product distribution in the diesel and wax/lubricant base-oil range unattainable by Ru-Zr and other Ru-supported catalysts. Importantly, the enhanced performance is showcased for real-world, single-use LDPE consumables. Reactivity studies combined with characterization and density functional theory calculations reveal that highly dispersed (WO x ) n clusters store H as surface hydroxyls by spillover. We correlate this hydrogen storage mechanism with hydrogenation and desorption of long alkyl intermediates that would otherwise undergo further C–C scission to produce methane.

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 H 2 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.

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A direct comparison of the recent advancements in the hydrogenolysis and hydrocracking of polyolefins is lacking. This perspective aims to address this gap while providing insights from model alkane studies to guide future research.

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Transformation of the Sn-BEA site structure during the interaction with water has been investigated by means of Fourier transform infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and catalytic experiments. It is shown that the Lewis and Brønsted acid properties of Sn-BEA zeolite before and after the adsorption of water change significantly. New surface OH groups exhibiting different structures are observed after adsorption, whereas tin oxide supported on Si-BEA is inactive in this transformation. It is demonstrated that the formed bridged OH groups possess strong Brønsted acidity, thus enabling the protonation of pyridine. It is suggested that the adsorption of water occurred over tin Lewis acid sites followed by the hydrolysis of the Si–O–Sn bonds and the formation of Si–OH and Sn–OH surface species. In this process, the tin atoms change their coordination number from 4 to 6, possessing different kinetics for the different types of Sn sites observed by NMR spectroscopy. The formation of additional catalytically active acid sites through water adsorption on Sn-BEA is demonstrated in situ in the course of isobutene dimerization reaction.