Turning high-emissions waste into fertiliser: study

UNSW engineers have tackled the problem of how to make urea for fertiliser without the intensity of emissions associated with fossil fuel-powered factories.

Corresponding author Associate Professor and Scientia Fellow Dr Rahman Daiyan from UNSW Sydney’s School of Minerals and Energy Resources Engineering said the work is part of a broader push to go beyond the global move to green ammonia, focusing instead on decarbonising the entire fertiliser chain.

“Urea is the fertiliser used to feed the crops for more than half of the world’s population,” Daiyan said. “But currently, it’s made from natural gas or coal. It’s a very fossil fuel-intensive, high-temperature, high-pressure technology with huge emissions.”

Two problems, one solution

Industrial activities release enormous amounts of carbon dioxide (CO₂) into the atmosphere each year, with around 40 billion tonnes released in 2024 alone. At the same time, nitrogen pollutants such as nitrate and nitrite — collectively referred to as NO_x species — contaminate waterways and ecosystems.

The UNSW study brought these two problems together. Using renewable electricity to trigger an electrochemical reaction, the researchers could directly couple CO₂ with nitrogen pollutants to form urea.

“Making carbon and nitrogen bond together in a controlled and reliable way is extremely difficult,” said the study’s first author, UNSW PhD student Putri Ramadhany. “To overcome this challenge, we designed a catalyst that works at an atomic scale and can hold carbon- and nitrogen-based molecules together long enough for them to react.”

The UNSW-developed catalyst — made of copper and cobalt — demonstrated a strong synergy between the two metals, and improved urea production when compared with existing systems.

Daiyan said it’s a promising foundation for a circular process that, in future, could convert captured carbon dioxide and nitrogen pollutants into urea. This, he said, is a route that removes pollution, creates valuable chemicals and runs on renewable electricity.

“We’ve been trying to look into pathways for decarbonising urea production,” Daiyan said. “The vision is zero-carbon urea where we directly couple waste carbon dioxide with nitrogen pollutants using renewable electricity, rather than relying on ammonia as an intermediate.

“That allows us to run the system on solar and wind, avoid high temperatures and pressures and reduce emissions.”

The groundwork for industrial scale-up

While most fundamental research ends at benchtop experiments, the UNSW team has taken these findings and scaled them up using urea electrolysers, which is the equipment considered a benchmark for industrial translation.

To understand how the material behaved under real-world conditions, the team used advanced electron-beam characterisation at the Australian Synchrotron. Here, they could watch the chemical reactions take place in real time, laying the groundwork for future scale-up.

The solution is outlined in a study published in Nature Communications.

The technology is still under development, but early results show promising selectivity under laboratory conditions. Rather than relying on direct air capture, the approach is designed to use carbon dioxide that is already generated from these industrial and biogenic emission streams.

Ultimately, Daiyan sees this research as part of a bigger shift towards circularity — using waste carbon for materials that require carbon dioxide for production: fuels, chemicals, plastics and other manufacturing.

He said getting technologies like this from lab to industry typically takes more than a decade — but this project may move faster.

“Hopefully it will take us another two or three years to get to the stage where we can get an industry partner on board,” he said.

“Our work highlights how thoughtful catalyst engineering paired with real-time characterisation can turn environmental problems into opportunities.”

Image credit: iStock.com/fcafotodigital. Image used for illustrative purposes only.