6 Minutes
A simple metal addresses a complex recycling problem
A team of chemists at Northwestern University has developed an inexpensive, nickel-based catalyst that could make mixed plastic recycling far more practical. The new catalyst selectively converts polyolefin plastics — mainly polyethylenes and polypropylenes, which dominate single-use packaging — into liquid hydrocarbons such as oils and waxes. These products can be upgraded into lubricants, fuels and other higher-value materials, potentially eliminating labor-intensive pre-sorting and reducing landfill waste.
A new nickel-based catalyst could revolutionize recycling by turning everyday single-use plastics into useful products—without tedious sorting. Credit: Shutterstock
Scientific background and motivation
Polyolefins are the most widely produced plastics globally, found in milk jugs, squeeze bottles, plastic wrap, trash bags and many disposable items. Industry production exceeds 200 million tons per year, yet recycling rates for these materials remain low — often below 10% worldwide — because their carbon-carbon backbone is chemically inert and hard to cleave. Current mechanical recycling typically requires meticulous sorting and yields downcycled, lower-quality pellets. Thermal processes such as pyrolysis or gasification work but demand high temperatures (400–700 °C) and are energy intensive.
To overcome those limits, the Northwestern group turned to hydrogenolysis, a catalytic process that uses hydrogen to cleave carbon-carbon bonds, producing smaller hydrocarbon molecules. Existing hydrogenolysis methods often rely on rare noble metals (platinum, palladium) and high operating conditions that make scale-up costly and unsustainable. The Northwestern team instead designed a single-site organo-nickel catalyst derived from commercially available nickel compounds — an Earth-abundant, low-cost alternative.
How the single-site nickel catalyst differs
Unlike nanoparticle catalysts that present multiple, poorly defined active centers, the single-site design provides a well-defined catalytic center analogous to a precise scalpel. That structural control enables selective hydrogenolysis: the catalyst preferentially breaks certain carbon-carbon bonds in branched polyolefins (for example, isotactic polypropylene) while leaving unbranched chains largely intact. This selective chemistry achieves a form of chemical separation inside mixed waste streams, reducing the need for manual pre-sorting and lowering energy requirements compared with existing methods.
Experiment details and performance metrics
In laboratory experiments the organo-nickel catalyst operated at temperatures about 100 °C lower and at roughly half the hydrogen pressure reported for comparable nickel-based systems. The researchers report using an order of magnitude less catalyst loading while obtaining roughly tenfold greater activity. The process converts solid polyolefin feedstocks into liquid oils and waxes that can be fractionated and upgraded.
The catalyst also shows exceptional thermal and chemical stability. A typical barrier for mixed-plastic processing is contamination by polyvinyl chloride (PVC), which decomposes to release hydrogen chloride (HCl) and other corrosive species that deactivate many catalysts. Surprisingly, the Northwestern catalyst not only tolerates PVC contamination but showed improved activity in experiments where PVC composed up to 25% of the waste weight. The team also demonstrated simple regeneration of the catalyst using inexpensive alkylaluminium treatment, enabling repeated reuse.
Why PVC tolerance matters
PVC contamination is a leading cause of batch rejection in recycling. Even trace PVC in an otherwise recyclable load can produce corrosive byproducts during thermal recycling and force entire batches to the landfill. A catalyst that operates effectively in the presence of PVC could open the door to processing mixed municipal plastic waste streams that are currently uneconomical or classed as unrecyclable.
Key discoveries and implications
- Selective hydrogenolysis with a single-site organo-nickel catalyst enables chemical upcycling of mixed polyolefin waste without painstaking sorting.
- The catalyst operates under milder conditions than many alternatives: lower temperature, lower H2 pressure, less catalyst loading, and higher activity.
- It transforms low-value, solid polyolefin waste into liquid oils and waxes that can be refined into higher-value chemicals and fuels, creating new value streams for waste materials.
- Unexpected acceleration of catalytic activity in presence of PVC suggests robust performance even with contaminated feedstocks, addressing a major logistical and economic barrier to large-scale recycling.
Researchers published these findings in Nature Chemistry (Sept. 2, 2025). The work was led by Tobin Marks and Yosi Kratish at Northwestern, with Qingheng Lai as first author, and included collaborators at Purdue University and Ames National Laboratory. Funding came from the U.S. Department of Energy and The Dow Chemical Company.
Related technologies and future prospects
This nickel-based approach complements other chemical recycling strategies — hydrocracking, pyrolysis, and catalytic depolymerization — by offering a lower-cost, lower-energy pathway specifically tailored to polyolefins. Scaling the process to industrial throughput will require pilot demonstrations to validate catalyst lifetime, product separation logistics, hydrogen sourcing, and life-cycle greenhouse gas impacts. Integration with existing recycling infrastructure or refinery/upgrader facilities could accelerate deployment. Additionally, pairing the process with green hydrogen could improve the climate profile of the produced fuels and chemicals.
Expert Insight
Dr. Elena Ruiz, materials chemist and recycling technologist (fictional commentary), notes: 'The key advance here is precision: a single-site catalyst tuned to cut polyolefin chains selectively. That allows chemists to convert messy, mixed waste into streams that chemical engineers can refine. The PVC tolerance is particularly important — it removes a frequent bottleneck for municipal and industrial feedstocks. If pilot tests confirm longevity and economics, this could be a game-changer for circular plastics.'
Conclusion
The Northwestern nickel catalyst demonstrates that Earth-abundant metals, when precisely engineered at the molecular scale, can deliver selective, energy-efficient chemical recycling of the most common single-use plastics. By converting mixed polyolefin waste into valuable oils and waxes and tolerating contaminants like PVC, this approach could reduce sorting costs, lower landfill input, and create new revenue from waste streams. Next steps include scale-up demonstrations, lifecycle assessments, and integration planning to test economic viability and environmental benefits at commercial scale. The innovation marks an important step toward practical, large-scale mixed plastic recycling and circular-materials strategies.
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