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Nickel Catalyst Could Reduce Sorting in Polyolefin Recycling
Northwestern University researchers developed a single-site nickel catalyst that selectively breaks down common polyolefin plastics, works under milder conditions than comparable nickel systems and remains active in PVC-contaminated mixtures. The research is promising, but it remains a laboratory-scale demonstration rather than a commercial recycling process.
By Paul Ploumis
Published September 19, 2025
Key Points
- The catalyst targets polyolefins, especially polyethylene and polypropylene, rather than all mixed plastics.
- Compared with other nickel-based systems, Northwestern reported operation at a temperature 100°C lower and at half the hydrogen pressure.
- The system used 10 times less catalyst loading while showing 10 times greater activity in the researchers' comparison.
- PVC contamination did not deactivate the catalyst; mixtures containing up to 25% PVC showed improved performance in laboratory tests.
- The catalyst can be regenerated, but commercial-scale throughput and economics were not demonstrated in the published study.
SCRAPMONSTER EDGE
PVC contamination did the opposite of what recyclers would normally expect. PVC can release corrosive hydrogen chloride that deactivates many catalysts, yet Northwestern's nickel catalyst remained active and actually performed better in lab mixtures containing up to 25% PVC by weight. In other words, one-quarter of the test mixture could be PVC without shutting the catalyst down.
MONTREAL (Scrap Monster): Researchers at Northwestern University have developed a nickel-based catalyst that could reduce one of the costliest steps in polyolefin recycling: separating different plastics before chemical processing.
The study, published September 2, 2025 in Nature Chemistry, focuses on polyolefins, the family of plastics that includes polyethylene and polypropylene. These materials are widely used in packaging and other short-lived products and account for a large share of global plastics consumption.
Northwestern estimates that more than 220 million tonnes of polyolefin products are produced globally each year, while reported recycling rates range from less than 1% to 10%.
Catalyst Targets Branched Polyolefins Selectively
The catalyst does not simply dissolve an indiscriminate mixture of plastics. Its main advantage is selectivity.
The single-site nickel system preferentially cleaves carbon-carbon bonds in branched polyolefins such as isotactic polypropylene while leaving more linear polyethylene less affected. That allows chemically different polyolefins in the same waste stream to be separated through the reaction itself.
The process converts low-value solid polyolefin material into liquid oils and waxes that can potentially be upgraded into products such as lubricants, fuels and candles.
Lower Temperature, Lower Hydrogen Pressure
Polyolefin hydrogenolysis already exists, but many systems rely on high temperatures, elevated hydrogen pressure or expensive noble-metal catalysts such as platinum and palladium.
Northwestern's researchers instead designed a single-site catalyst based on nickel, a more abundant and less expensive metal.
According to co-corresponding author Yosi Kratish, the system operated at a temperature 100°C lower and at half the hydrogen pressure used by comparable nickel-based approaches.
The researchers also reported using 10 times less catalyst loading while achieving 10 times greater activity in their comparison.
PVC Contamination Produced an Unexpected Result
Polyvinyl chloride is normally difficult to accommodate in thermal and catalytic recycling because it can release hydrogen chloride as it decomposes. That corrosive byproduct can deactivate catalysts and complicate mixed-plastic processing.
In Northwestern's experiments, however, the nickel catalyst remained active in the presence of PVC.
More surprisingly, performance improved when PVC was present. The researchers reported enhanced activity even when PVC accounted for as much as 25% of the total waste mixture by weight.
The catalyst could also be regenerated over multiple cycles using an inexpensive alkylaluminium treatment.
Why This Matters for Mixed-Plastic Recycling
Sorting is one of the major economic and operational barriers in plastics recycling. Different polymers melt, react and degrade differently, and contaminants can reduce the quality of recycled material or make a batch unsuitable for processing.
A catalyst that can selectively process one polymer family in a mixed stream could reduce some of that sorting burden.
That does not mean all mixed plastic waste can now be fed directly into a commercial plant. The research specifically concerns polyolefin hydrogenolysis and selected contaminants, not every polymer found in municipal recycling streams.
Commercial Scale Has Not Yet Been Demonstrated
The published work is a laboratory-scale study. Nature Chemistry's extended data describe polymer experiments using quantities on the order of hundreds of milligrams, including PVC-contaminated tests with roughly 500 milligrams of polymer.
That is scientifically useful for understanding catalyst performance, but it is very different from operating continuously on tonnes of mixed post-consumer material.
Before the technology could be assessed as a commercial recycling route, industry would need evidence on catalyst lifetime, hydrogen consumption, feedstock preparation, chlorine management, product recovery, continuous throughput and overall economics at much larger scale.
Market Read
The most important result is not that sorting has been eliminated. That has not yet been demonstrated commercially.
The significance is that the researchers showed a low-cost nickel system can selectively process difficult polyolefins under milder conditions while remaining active in the presence of a contaminant that normally creates major recycling problems.
For plastics recyclers, that moves the research in an interesting direction: using chemistry to perform part of the separation work that facilities currently try to accomplish mechanically before processing.
