University of Notre Dame researchers have developed a renewable energy approach for synthesizing ammonia. Ammonia is crucial for the world’s agricultural production because its an essential nitrogen component of fertilizers that support the world’s food and fuel production needs.

The industrial Haber-Bosch process developed in the early 1900s for producing ammonia relies on non-renewable fossil fuels and has limited applications for only large centralized chemical plants.

The new process, reported with publication in Nature Catalysis, utilizes a plasma – an ionized gas – in combination with non-noble metal catalysts to generate ammonia at much milder conditions than is possible with Haber-Bosch. The energy in the plasma excites nitrogen molecules, one of the two components that go into making ammonia, allowing them to react more readily on the catalysts. Because the energy for the reaction comes from the plasma rather than high heat and intense pressure, the process can be carried out at small scale. This makes the new process well-suited for use with intermittent renewable energy sources and for distributed ammonia production.

Experimental set-up consisting of an L-shaped quartz tube DBD plasma reactor with 5 mm inner diameter tube and an optical fiber coupled to a spectrometer. The bottom part of the L-bend has a quartz window for easy optical access to the catalyst bed. Image Credit: University of Notre Dame. Click image for the largest view.

William Schneider, H. Clifford and Evelyn A. Brosey Professor of Engineering, affiliated member of ND Energy and co-author of the study explained, “Plasmas have been considered by many as a way to make ammonia that is not dependent on fossil fuels and had the potential to be applied in a less centralized way. The real challenge has been to find the right combination of plasma and catalyst. By combining molecular models with results in the laboratory, we were able to focus in on combinations that had never been considered before.”

The research team led by Schneider; David Go, Rooney Family Associate Professor of Engineering in aerospace and mechanical engineering; and Jason Hicks, associate professor of chemical and biomolecular engineering, discovered that because the nitrogen molecules are activated by the plasma, the requirements on the metal catalysts are less stringent, allowing less expensive materials to be used throughout the process. This approach overcomes fundamental limits on the heat-driven Haber-Bosch process, allowing the reaction to be carried out at Haber-Bosch rates at much milder conditions.

Professor Hicks said, “The goal of our work was to develop an alternative approach to making ammonia, but the insights that have come from this collaboration between our research groups can be applied to other difficult chemical processes, such as converting carbon dioxide into a less harmful and more useful product. As we continue studying plasma-ammonia synthesis, we will also consider how else plasma and catalysts could benefit other chemical transformations.”

This technology could very well have a great effect on food and fuel production worldwide. The basics of nitrogen and hydrogen formed up in ammonia is a key to sustainable populations that occupy the planet now. Driving to more fertilizer thus more and better food and fuel stocks are key to improving living standards and thus getting the population growth rate down.

One almost overlooks the reduction in huge amount of natural gas used in the commercial Haber-Bosch process. There remains the question of the new process’s source for the hydrogen. There remains a way to go with this technology.


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