Liquid metal could be key to greener ammonia
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An RMIT-led study relying on liquid metal catalysts has demonstrated a low-energy approach for producing ammonia that is as effective as the current gold standard, which relies on the force of pressure. This new process could lead to significant cuts in carbon emissions caused by production of the widely used chemical.
Ammonia is used in fertiliser to grow much of the world’s food; it also plays a role in clean energy as a carrier to safely transport hydrogen. However, the global production of ammonia presents a huge environmental problem, with the gas consuming over 2% of global energy and producing up to 2% of global carbon emissions.
Dr Karma Zuraiqi, RMIT Research Fellow and lead author of the study, said the team’s greener alternative used 20% less heat and 98% less pressure than the century-old Haber-Bosch process used today for splitting nitrogen and hydrogen into ammonia.
“Ammonia production worldwide is currently responsible for twice the emissions of Australia. If we can improve this process and make it less energy-intensive, we can make a large dent in carbon emissions,” said Zuraiqi, from RMIT’s School of Engineering.
“The copper and gallium we use is also much cheaper and more abundant than the precious metal ruthenium used as a catalyst in current approaches,” Zuraiqi added.
“These advantages all make it an exciting new development that we’re keen to take further and test outside the lab.”
Liquid metal as a catalyst
The team is at the forefront of harnessing the special properties of liquid metal catalysts for ammonia production, carbon capture and energy production.
A catalyst is a substance that makes chemical reactions occur faster and more easily without itself being consumed.
This latest study showcased the RMIT-proprietary technique by creating tiny liquid metal droplets containing copper and gallium — named ‘nano planets’ for their hard crust, liquid outer core and solid inner core structure — as the catalyst to break apart the raw ingredients of nitrogen and hydrogen.
“Liquid metals allow us to move the chemical elements around in a more dynamic way that gets everything to the interface and enables more efficient reactions, ideal for catalysis,” said RMIT’s Professor Torben Daeneke.
“Copper and gallium separately had both been discounted as famously bad catalysts for ammonia production, yet together they do the job extremely well.”
Tests revealed gallium broke apart the nitrogen, while the presence of copper helped the splitting of hydrogen, combining to work as effectively as current approaches at a fraction of the cost, according to the scientists.
“We essentially found a way to take advantage of the synergy between the two metals, lifting their individual activity,” Daeneke said.
RMIT is now leading commercialisation of the technology, which is co-owned by RMIT and Queensland University of Technology (QUT).
The next challenge: upscaling for industry
While ammonia produced via the traditional Haber-Bosch process is only viable at huge facilities, the team’s alternative approach could suit both large-scale and smaller, decentralised production, where small amounts are made cheaply at solar farms. This in turn would slash transport costs and emissions.
Currently, the technology is yet to be proven beyond lab conditions, but the team plans to upscale their system and design it to operate at even lower pressures, making it more practical as a decentralised tool for a broader range of industries.
As well as producing ammonia for fertiliser, the technology could be a key enabler for the hydrogen industry, supporting the move away from fossil fuels.
“One good way to make hydrogen safer and easier to transport is to turn it into ammonia,” Daeneke explained.
“But if we use ammonia produced through current techniques as a hydrogen carrier, then emissions from the hydrogen industry could significantly increase global emissions.
“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,” he said.
“At this stage, we are really excited by the results and are keen to speak with potential partners interested in scaling this up for their industry.”
The research was supported by the Australian Research Council and the Australian Synchrotron (ANSTO). Analysis of molecular interactions was carried out at RMIT’s Microscopy and Microanalysis Facility, as well as QUT’s Central Analytical Research Facility, the Australian Synchrotron and via the NCI Australia supercomputing facility.
‘Unveiling metal mobility in liquid metal catalysts for ammonia synthesis’ has been published in Nature Catalysis.
