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.

No abstract

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.

One-pot conversion of cellulose to n-hexane was carried out over the Ir-ReO x /SiO 2 (Re/Ir = 2) catalyst combined with HZSM-5 as cocatalyst in a biphasic reaction system (n-dodecane + H 2 O). The yield of n-hexane reached 83% from ball-milled cellulose and 78% from microcrystalline cellulose. Even using a high weight ratio of cellulose to water (1:1), a 71% yield of n-hexane could be obtained from ball-milled cellulose. The yield of n-hexane was almost maintained during three repeated tests when the catalyst was calcined again. The transformation of cellulose to n-hexane consists of the hydrolysis of cellulose to glucose via water-soluble oligosaccharides, hydrogenation of glucose to sorbitol, and successive hydrogenolysis of sorbitol to n-hexane. The Ir-ReO x / SiO 2 catalyst promotes a hydrogenation and hydrogenolysis step. HZSM-5 enhanced the hydrolysis of cellulose in hot water and C−O bond hydrogenolysis activity of the Ir-ReO x /SiO 2 catalyst.

Rh–Ir–ReOx/SiO2 catalyst with ReOx-modified Ir–Rh alloy particles can convert furfural to 1,5-PeD in high yield.

Renewable jet-fuel-range alkanes are synthesized by hydrodeoxygenation of lignocellulose-derived high-carbon furylmethanes over ReO -modified Ir/SiO catalysts under mild reaction conditions. Ir-ReO /SiO with a Re/Ir molar ratio of 2:1 exhibits the best performance, achieving a combined alkanes yield of 82-99 % from C -C furylmethanes. The catalyst can be regenerated in three consecutive cycles with only about 12 % loss in the combined alkanes yield. Mechanistically, the furan moieties of furylmethanes undergo simultaneous ring saturation and ring opening to form a mixture of complex oxygenates consisting of saturated furan rings, mono-keto groups, and mono-hydroxy groups. Then, these oxygenates undergo a cascade of hydrogenolysis reactions to alkanes. The high activity of Ir-ReO /SiO arises from a synergy between Ir and ReO , whereby the acidic sites of partially reduced ReO activate the C-O bonds of the saturated furans and alcoholic groups while the Ir sites are responsible for hydrogenation with H .

A physical mixture of ReOx–Au/CeO2 and carbon-supported rhenium catalysts effectively converted 1,4-anhydroerythritol to 1,4-butanediol with H2 as a reductant.