Recycling plastic could soon become drastically easier and more efficient. A research team at Northwestern University has developed a novel plastic upcycling method that eliminates one of the biggest challenges in plastic recycling: the need to pre-sort different types of plastics.
At the core of this breakthrough is a low-cost, nickel-based catalyst that selectively targets polyolefin plastics including polyethylene and polypropylene. These plastics make up nearly two-thirds of global single-use plastic consumption. Because the catalyst works directly on unsorted waste, it could be applied to large volumes of mixed plastic without any separation process.
Transforming Trash into Valuable Products
Once activated, the catalyst converts solid polyolefin plastics into liquid oils and waxes, which can be repurposed into higher-value products such as fuels, lubricants, and candles. Notably, this catalyst is reusable and remains stable even when the plastic waste contains polyvinyl chloride (PVC), a toxic and traditionally unrecyclable material.
As reported by SciTechDaily, the study published in Nature Chemistry highlights how this new catalyst can simplify recycling, reduce waste, and increase the economic feasibility of plastic recovery.
Addressing the Sorting Challenge
“For decades, one of the biggest hurdles in recycling has been the meticulous sorting of plastic waste by type,” said Tobin Marks, senior author of the study and a renowned expert in catalysis. “Our new catalyst could bypass this costly and time-consuming step for polyolefins.”
Co-author Yosi Kratish added, “Most household plastics are polyolefins—everything from milk jugs to trash bags. These products are often used once and then discarded. Without a better recycling method, they end up in landfills or the environment, breaking down into harmful microplastics.”
Why Polyolefins Are So Difficult to Recycle
Polyolefins are incredibly durable due to their strong carbon-carbon bonds, which resist most chemical breakdown methods. This structural resilience makes them hard to degrade using traditional recycling methods.
“When we design catalysts, we look for weak points,” explained Kratish. “But polyolefins don’t have any. Every bond is strong and chemically inert.”
Current Methods Fall Short
Existing recycling methods offer limited solutions. Mechanical recycling, which involves shredding and melting plastics, requires strict sorting due to different melting points and material properties. Even slight contamination can ruin entire batches.
Thermal methods involve heating plastics to extremely high temperatures—between 400 and 700°C—to break them down. While effective, this approach is energy-intensive and often economically unsustainable.
A Precision Catalyst with Lower Energy Demands
Seeking a better solution, the researchers turned to hydrogenolysis, a process that uses hydrogen gas and a catalyst to break down plastics. While traditional hydrogenolysis methods require expensive noble metals and high heat, the Northwestern team identified a cationic nickel catalyst that operates at significantly lower temperatures.
“Compared to other nickel-based catalysts, ours operates at 100 degrees lower temperature and half the hydrogen pressure,” said Kratish. “We also use 10 times less catalyst, yet achieve 10 times the activity. So, we’re winning across all parameters.”
Smart Design Enables Selective Breakdown
The catalyst’s single-site molecular design allows it to selectively cleave specific bonds in branched polyolefins, such as isotactic polypropylene, without affecting unbranched ones. This makes it function more like a surgical tool than a blunt-force method, enabling a targeted chemical breakdown of mixed plastics.
Contamination? No Problem—It’s a Benefit
Most recycling catalysts fail in the presence of PVC, which releases corrosive hydrogen chloride gas when heated. But this new nickel-based catalyst is so chemically stable that not only does it survive PVC contamination—it performs even better.
Incredibly, when the waste mixture included up to 25% PVC, the catalyst’s activity actually improved. This surprising outcome suggests that the system could process waste previously deemed “unrecyclable” due to contamination.
“Adding PVC has always been forbidden,” said Kratish. “But now, it makes our process better. That’s just crazy. Nobody expected that.”
Sustainable and Scalable
The catalyst can be regenerated multiple times using a simple, low-cost treatment with alkylaluminium, ensuring long-term usability and low operational cost.
“Using Earth-abundant metals like nickel, instead of rare and expensive ones, is essential for scalability,” noted Qingheng Lai, the study’s lead author. “We’re thinking not just about science, but also about how to apply it at a global scale.”
