A new process of creating ammonia from nitrogen and water eliminates the use of hydrogen or solid metal catalysts.
The low temperature, low pressure electrolytic process developed at Ohio's Case Western Reserve University uses plasma, an ionized cloud of gas. This gives it the ability to activate chemical bonds, including the nitrogen molecule, at room temperature.
Mohan Sankaran, Goodrich Professor of Engineering Innovation at the university's School of Engineering, said: “Our approach – an electrolytic process with a plasma – is completely new. Perhaps most significantly, our process does not produce hydrogen gas. This has been the major bottleneck of other electrolytic approaches to forming ammonia from water and nitrogen.”
The ammonia is formed at the interface of a gas plasma and liquid water surface and forms freely in the solution. Sankaran and his research partner Julie Renner have used an element from the Norway-developed Birkeland-Eyde process, which reacts nitrogen and oxygen to produce nitrates, another chemical that can be used in agriculture.
Birkeland-Eyde uses more energy in the form of electricity than the Haber-Bosch process, from which virtually all commercial ammonia is made. Haber-Bosch uses nitrogen and hydrogen, with an iron catalyst at high temperature and pressure.
Sankaran said: “Our approach is similar to electrolytic synthesis of ammonia, which has gained interest as an alternative to Haber-Bosch because it can be integrated with renewable energy. However, like Birkeland-Eyde process, we can use a plasma, which is energy intensive. Electricity is still a barrier, but less so now, and with the increase in renewables, it may not be a barrier at all in the future."
Ammonia is one of the most energy-intensive of the large-volume chemicals and traditional ammonia-making processes in chemical plants require massive amounts of hydrogen gas from fossil fuels. The new process doesn't need high pressure, high temperature or hydrogen, and is ideal for a smaller plant. It also has a high potential to be powered by renewable energy.
The energy efficiency of the new process is still less than the Haber-Bosch, but its discovery could lead to smaller, more localised ammonia plants that use green energy.
Results of the study were published in the journal Science Advances.