Chemists Manage to Make Green Ammonia ‘More Naturally’ Using Water and Light, Plus Two Key Ingredients
Ammonia is a chemical that helps agriculture and industry but the way it is produced is usually very costly energy-wise. A more natural approach appears much less costly this way.
Almost 80 per cent of all ammonia produced (just under 200 million tonnes) are used for fertiliser. Its production is usually from using the Haber-Bosch Process. Ammonia production accounts for about 2% of the globe’s energy consumption, and 2% of the global carbon dioxide emissions.
Researchers have been developing a catalytic system for producing ammonia from abundant molecules on Earth, including atmospheric nitrogen and water.
Chemists and researchers from The University of Tokyo, Japan, have tried to produce ammonia more efficiently. For the first time the group simply combined atmospheric nitrogen, water and sunlight. Using two catalysts, they produced large amounts of ammonia but without using excessive energy. The process is more similar to natural processes in nature, found in plants utilising symbiotic bacteria.
The key lies in two catalyst types combined, offering great potential to reduce the energy production cost through a reaction driven by sunlight.
“This is the first successful example of photocatalytic ammonia production using atmospheric dinitrogen as a nitrogen source and water as a proton source, that also uses visible light energy and two kinds of molecular catalysts,” clarified co-author Dr. Nishibayashi.
“We used an iridium photocatalyst and another chemical called a tertiary phosphine which enabled photochemical activation of water molecules. The reaction efficiencies were higher than expected, compared to previous reports of visible light-driven photocatalytic ammonia formation.”
Controlling the Chemistry With Catalysts
Chemical reactions do not always happen as fast as desired or in the required result. Controlling the outcome depends on efficiency and timing and catalysts can help.
The transition metal molybdenum was used for activating dinitrogen and the metal iridium for the light-driven activation of water with tertiary phosphines - used to help protons get out of water molecules.
“When the iridium photocatalyst absorbs sunlight, its excited state can oxidise the tertiary phosphines. The oxidised tertiary phosphines then activate water molecules via formation of a chemical bond between the phosphine’s phosphorous atom and the water, yielding protons,” said Nishibayashi.
“The molybdenum catalyst then enables nitrogen to bond with these protons to become ammonia. The use of water for producing dihydrogen or hydrogen atoms is one of the most important processes for achieving green ammonia production.”
This small scale experiment could next be replicated at much larger scales, while trying to improve safety and effectiveness of the process even more. For instance, solar power could stimulate the process or recycled phosphine oxides could be useful components.
Is simpler better, like in nature?
Ammonia is formed in nature like in plants when fixing nitrogen, with connection to photosynthesis. Electrons of this reaction are given by light and protons from water - mimicking nature in a way (almost like biomimicry).
The simplicity of using water and incorporating a more natural based process could result in cleaner outcomes for ammonia production - which is somewhat limited at present as a viable clean fuel.
Source of the news
Yasuomi Yamazaki, Yoshiki Endo, Yoshiaki Nishibayashi, Catalytic ammonia formation from dinitrogen, water, and visible light energy, Nature Communications. 2025.