Latest Research: New Nickel Catalyst Emerges, Potentially Ending Plastic Recycling Pre-Sorting Challenges

The era of pre-sorting mixed plastic waste may soon come to an end, and the "secret weapon" behind this is a low-cost catalyst made from nickel as the raw material, which can precisely "tackle" one of the most challenging plastic polymers we face. The related research findings were published on September 2nd in the journal Nature Chemistry.

Despite decades of global efforts in plastic recycling, the work remains at the stage of "easier said than done." A frustrating reality is largely attributed to a class of polymers known as polyolefins. Humans produce approximately 220 million tons of polyolefin-based products annually, most of which are single-use items such as condiment bottles, milk jugs, cling films, garbage bags, and juice boxes.

"Basically, almost everything in your refrigerator is made of polyolefin-based materials," said Northwestern University chemist and co-author of the study, Yossi Klatzkin, in a statement.

Normally, the decomposition of plastics requires the use of catalysts—these compounds can exploit the weaker chemical bonds within plastic molecules to initiate the decomposition process; otherwise, plastics might take hundreds or even thousands of years to degrade naturally.

Currently, we recycle less than 10% of polyolefin products each year, while the rest accumulate into mountains, ultimately being landfilled or sent to industrial furnaces. This is because, although other plastics can typically be broken down using catalysts, polyolefins are an exception. These tough polymers are difficult to degrade due to their small molecules being linked by extremely stubborn carbon-carbon bonds.

"Polyolefins have no weak links. Every chemical bond is very strong, and their chemical properties are stable." Klatish said.

Our current "solution" is more of a stopgap measure than a real solution. Polyolefin products can be crushed, melted, and then downgraded to recycled low-quality plastic pellets, but even this process has many limitations. Manual sorting is still a necessary step, and even the slightest trace of food residue or non-plastic materials can ruin an entire batch of recyclables. Additionally, burning polyolefins requires a temperature as high as 1292 degrees Fahrenheit.

“Of course, everything can be burned,” Kratish said. “If you put in enough energy, you can turn anything into carbon dioxide and water. But what we want is to find an elegant way to do it—with the least energy input and the highest-value output.”

A potential solution might be hydrogenolysis, which involves using a combination of hydrogen and catalysts to decompose polyolefin plastics into truly useful hydrocarbons. Existing hydrogenolysis methods also require high temperatures and expensive catalysts made from precious metals like palladium and platinum, but Kratish's team has found a workaround.

Unlike rare metals such as palladium and platinum, engineers have discovered that a synthetic alternative called cationic nickel is inexpensive, abundant, and easy to obtain. Other nickel-based catalysts contain multiple reactive sites, while the single-site variant of cationic nickel allows it to function more like a precise laser or a sharp blade. Instead of breaking down all the structures in plastics, it specifically targets those stubborn carbon–carbon bonds, decomposing them at lower temperatures and with half the hydrogen pressure. This new type of catalyst is highly stable and can even process plastics notorious for their high pollutant content, such as polyvinyl chloride.

"Previously, adding PVC to the recycling mixture was always prohibited. But apparently, this has instead made our process better," said Kratish. "It's crazy and completely unexpected for everyone."

If this new type of catalyst proves to be scalable and efficient, it is expected to greatly reduce the need for cumbersome pre-sorting of plastics, while significantly decreasing the amount of microplastics released into the environment each day.