Australian researchers use liquid metal catalysts to develop low-carbon ammonia

Michael Quin/RMIT University

RESEARCHERS from a Melbourne university have developed a low-carbon method of making ammonia using liquid metal catalysts.

Ammonia is a major CO2 emitter, with global production accounting for more than 2% of global energy and 2% of global CO2 emissions.

Ammonia is traditionally made using the Haber-Bosch process where gaseous nitrogen and hydrogen react with an iron catalyst at temperatures of around 450^oC to make ammonia.

A team from RMIT University developed a method which they say uses 20% less heat and 98% less pressure than the traditional process of ammonia production.

Torben Daeneke, a professor at RMIT’s School of Engineering, said: “Conventional catalysts require 200 bar and above and tend to work at roughly 500oC. Our catalyst works at 4 bar and 400oC, achieving an excellent rate.

“Having said that, increasing the pressure for our catalyst will likely result in even further enhanced activity.”

Nano planets

The new method involves a liquid metal catalyst made of copper and gallium, called “nano planets” as they are formed into droplets that have a hard crust, liquid outer core, and solid inner core structure.

Daeneke said: “Copper and gallium separately had both been discounted as famously bad catalysts for ammonia production, yet together they do the job extremely well.”  

The team found that gallium can split nitrogen and copper can split hydrogen just as effectively as traditional processing.

Commercialisation and hydrogen storage

The researchers say this new method is suitable for both ammonia production at large-scale facilities and decentralised production sites due to the flexibility in pressure needed for the process.

RMIT says the method could be a “key enabler” for the hydrogen industry as it provides a safer, easier way to transport the energy source.

Daeneke said: “Ammonia is stable and can be exported easily as a liquid. Once it reaches its destination the ammonia can be broken down into hydrogen and nitrogen again. The nitrogen taken from air would therefore be used as a carrier in the process.”

The team is currently speaking to potential partners about scaling the technology and researching the possibility of the method working at lower pressures.
Daeneke added: “Our vision is to combine our green ammonia production technology with hydrogen technologies, allowing green energy to be shipped safely around the world without huge losses on the way.”