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THERE could finally be a way to make fertiliser without releasing huge amounts of greenhouse gases. If the new method can work on an industrial scale, it could help feed the world鈥檚 growing population, while also limiting climate change.

Farmers rely on fertilisers to feed their crops. Many of these contain ammonia, but the only way to make it on a large scale is the Haber-Bosch process. The method, which was developed in the 1900s, makes the chemical by combining nitrogen from the air with hydrogen.

The process requires temperatures of around 425掳C and pressures of up to 200 times normal atmospheric pressure. The energy required to achieve this typically comes from fossil fuels, and the ammonia industry accounts for over 1 per cent of our annual greenhouse gas emissions.

To solve this problem, Yoshiaki Nishibayashi at the University of Tokyo, Japan, and his colleagues have developed a way of making ammonia that not only works at room temperature but also at standard atmospheric pressure.

Chemists have been searching for a replacement for the Haber-Bosch process for years. In 2003, a team converted nitrogen into ammonia, using a molybdenum-based catalyst to speed up the reaction 鈥� the first method without added heat or pressure that worked.

In 2011, Nishibayashi鈥檚 team succeeded in making ammonia from nitrogen using a catalyst based on molybdenum iodide, which worked at room temperature and standard atmospheric pressure.

However, there was still a major problem. As well as a catalyst, this method needed expensive chemicals to react with nitrogen and provide protons for the reaction. This pushed up costs and limited the usefulness of this and some other new methods.

Nishibayashi鈥檚 team has now found a way to use cheap, readily available substances instead. The researchers鈥� chosen reagent is the strongly reactive samarium diiodide, and their proton sources are either simple alcohols or water. When combined with a molybdenum-based catalyst, the team was able

鈥淭he ammonia production rate is 500 times faster than that of the Haber-Bosch process,鈥� says Nishibayashi. It is also one or two orders of magnitude faster than the other reactions developed so far, and is approaching the speed of the enzyme nitrogenase, which some bacteria use to capture nitrogen from the air.

Nishibayashi has patented the new process and is working with the Nissan Chemical Corporation on scaling the method up for industrial production. The sticking point will probably be that huge volumes of samarium would be needed for large-scale ammonia production, pushing up costs. It may be possible to tweak how samarium behaves to reduce the amount that is needed.

But Polly Arnold at the University of Edinburgh, UK, says it would be better to stick with the Haber-Bosch process, which has already been 鈥渂rilliantly optimised鈥�, and instead find ways to cut its greenhouse gas emissions.