The new catalyst could make plastic recycling much less complicated

A new catalyst can allow mixed plastic recycling

The future of plastic recycling could soon become much simpler and more efficient.

Researchers at Northwest University have developed a new method of plastic upcycling that reduces considerably – and can even eliminate – the need for pre -sort of mixed plastic waste.

At the heart of the process is a low -cost catalyst based on nickel which selectively targets polyolefin plastics, including polyethylenes and polypropylenes, which constitute almost two thirds of the overall consumption of single -use plastic. This means that the catalyst could be applied to large volumes of non -sorted polyolefin waste.

When activated, the catalyst converts these solid plastics with low value into liquid and waxes which can be reused in larger products such as fuels, lubricants and candles. The catalyst can be reused several times and, in particular, is also able to decompose plastics contaminated by polyvinyl chloride (PVC), a toxic material for a long time considered as “non -recyclable” plastics.

Key challenges and potential for breakthroughs

The study was recently published in the journal Chemistry of nature.

“One of the largest obstacles in plastic recycling has always been the need to meticulously sort plastic waste by type,” said Tobin Marks in Northwestern, the main author of the study. “Our new catalyst could bypass this costly and highly intensity of labor for current polyolefin plastics, which makes recycling more efficient, practical and economically viable than current strategies.”

“When people think of plastic, they probably think of polyolefins,” said Yosi Kratish of Northwestern, an author of co-corners on the newspaper. “Basically, almost everything in your refrigerator is based on polyolefin – compressed bottles for condiments and flashes, milk jugs, plastic film, garbage bags, disposable utensils, juice boxes and much more. in harmful microplastics. »»

An expert in world renowned catalysis, Marks is the Catalytic Chemistry Professor of Vladimir N. Ipatieff at the Weinberg College of Arts and Sciences of Northwestern and chemical and biological genius teacher at McCormick School of Engineering in Northwestern. He is also affiliated with the faculty at the Paula M. Triens Institute for Sustainability and Energy. Kratish is an assistant research professor in the Marks group and member of the faculty affiliated to the Triens Institute. Qingheng Lai, a research partner in the Marks group, is the first author of the study. Marks, Kratistish and Lai co-a co-led the study with Jeffrey Miller, professor of chemical engineering at Purdue University; Michael Wasielewski, professor of chemistry from Clare Hamilton Hall in Weinberg; And in Takeshi Kobayashi a researcher at the National Laboratory Ames.

The situation of polyolefin

Cups of yogurt and snacks of snacks with shampoo bottles and medical masks, polyolefin plastics are part of daily life. These are the most used plastics in the world, produced in enormous quantities. According to some estimates, more than 220 million tonnes of polyolefin products are manufactured worldwide each year. However, according to a 2023 report in the review NatureThe recycling rates of these plastics remain wrongly, lowering between 1% and 10% worldwide.

This bad recycling file is largely due to the sustainability of polyolefins. Their structure is made up of small molecules connected by carbon-carbon links, which are notoriously strong and difficult to separate.

“When we design catalysts, we target weak points,” said Kratish. “But polyolefins have no low links. Each link is incredibly strong and chemically unrealed.”

Problems with current processes

Currently, only a few processes, less than Ideaux, which can recycle polyolefin. It can be shredded in flakes, which are then melted and descendants to form low quality plastic pellets. But because different types of plastics have different properties and melting points, the process requires workers to scrupulously separate various types of plastics. Even small amounts of other plastics, food residues or non -plastic materials can compromise an entire lot. And these compromise lots go directly to the discharge.

Another option is to heat plastics at incredibly high temperatures, reaching 400 to 700 degrees Celsius. Although this process degrades polyolefin plastics in a useful mixture of gas and liquids, it is extremely at high energy intensity.

“Everything can be burned, of course,” said Kratish. “If you apply enough energy, you can convert anything into carbon dioxide and water. But we wanted to find an elegant way to add the minimum amount of energy to derive the maximum value product.”

Precision engineering

To discover this elegant solution, brands, kratish and their team turned to hydrogenolysis, a process that uses gas hydrogen and a catalyst to decompose polyolefin plastics with smaller and useful hydrocarbons. Although there are already hydrogenolysis approaches, they generally require extremely high temperatures and expensive catalysts made from noble metals such as platinum and palladium.

“The production scale of polyolefins is enormous, but the world’s reserves of noble metals are very limited,” said Lai. “We cannot use the entire metal supply for chemistry. And, even if we did, there would still not be enough to solve the problem of plastic. This is why we are interested in the abundant metals of the earth. ”

For its polyolefin recycling catalyst, the northwest team has identified cationic nickel, which is synthesized from an abundant nickel compound, inexpensive and commercially available. While other catalysts based on nickel nanoparticles have several reaction sites, the team has designed a single -site molecular catalyst.

The design of a single site allows the catalyst to act as a highly specialized scalpel – preferentially cuts carbon -carbon links – rather than less controlled blunt instrument which decomposes without discrimination the entire structure of the plastic. Consequently, the catalyst allows the selective degradation of branched polyolefins (such as isotactic polypropylene) when mixed with unmanned polyolefins – effectively separating them chemically.

“Compared to other nickel -based catalysts, our process uses a single site catalyst that works at a temperature of 100 degrees lower and half the hydrogen pressure,” Kratish said. “We also use 10 times less catalyst loads, and our activity is 10 times higher. So we gain in all categories. ”

Accelerated by contamination

With its unique active site, precisely defined and isolated, the nickel catalyst has unprecedented activity and stability. The catalyst is so thermally and chemically stable, in fact, that it maintains control even when exposed to contaminants such as PVC. Used in pipes, floor coverings and medical devices, PVC is visually similar to other types of plastics but much less stable during heating. During decomposition, PVC releases hydrogen chloride, a highly corrosive by-product which generally deactivates catalysts and disrupts the recycling process.

Surprisingly, not only has Northwestern’s catalyst resisted PVC contamination, but PVC has actually accelerated its activity. Even when the total weight of the waste mixture is made up of 25% PVC, scientists have found that their catalyst was still working with improved performance. This unexpected result suggests that the team’s method could overcome one of the largest obstacles in mixed plastic recycling – the rupture of waste currently deemed “non -recyclable” due to PVC contamination. The catalyst can also be regenerated on several cycles thanks to simple treatment with cheap alkylaluminium.

“Adding PVC to a mixture of recycling has always been prohibited,” said Kratish. “But apparently, it makes our process even better. It’s crazy. It’s certainly not something that someone expected.”

Reference: “Stable organickel catalyst with unique site with monomonickels of polyolefine links C – C preferably” by Qingheng Lai, Xinrui Zhang, Shan Jiang, Matthew D. Krzyaniak, Selim Alayoglu, Amol Agarwal, Yukun Liu, Vinay Dravid, Michael R. Wasielewski, Jeffery T. Miller, Yosi Kratish and Tobin J. Marks, September 2, 2025, Nature chemistry.
DOI: 10.1038 / S41557-025-01892-Y

Supported by the American Department of Energy (Reward number of-SC0024448) and the DOW Chemical Company.

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