Ammonia is a crucial component of global food production needed to feed a growing population, but its production contributes about 2% of global energy consumption and 1.4% of carbon dioxide emissions.

Engineers at Rice University have developed an innovative reactor design that could revolutionize ammonia production. This new system not only decarbonizes the production process but also helps reduce water pollution by converting nitrates, common pollutants, into valuable ammonia. This breakthrough has the potential to positively impact various industries, from agriculture to manufacturing.

Ammonia is one of the most widely produced chemicals in the world, with demand exceeding 180 million tonnes per year. The main production method is the Haber-Bosch process, which requires high temperatures and pressures for the reaction between hydrogen and nitrogen and relies on a large-scale centralised infrastructure. An alternative approach is electrochemical synthesis, which uses electricity to facilitate chemical reactions.

“Electrochemistry can take place at room temperature, is better suited to scalable formats for different infrastructure systems and can be powered by decentralized renewable energy,” said Feng-Yang Chen, a doctoral student at Rice University and lead author of the study. “However, the current challenge of this technology is that large amounts of additional chemicals are required during the electrochemical conversion process. The reactor we developed uses recyclable ions and a three-chamber system to improve the efficiency of the reaction.”

The use of a porous solid electrolyte represents a significant advance as it eliminates the need for high concentrations of supporting electrolytes, a persistent problem in previous sustainable attempts to convert nitrates to ammonia. In addition, by using renewable energy to power the conversion process, ammonia production can become carbon neutral.

“We conducted experiments in which we passed nitrate-contaminated water through this reactor and measured the amount of ammonia produced and the purity of the treated water,” said Chen, who is pursuing a doctorate in chemical and biomolecular engineering under Wang’s supervision. “We discovered that our novel reactor system can very efficiently convert nitrate-contaminated water into pure ammonia and clean water without the need for additional chemicals. Simply put, you put wastewater in and get pure ammonia and purified water out.”

The newly developed reactor system enables electrochemical conversion of nitrate into ammonia, making denitrification unnecessary. This process bypasses the conventional denitrification and Haber-Bosch processes and offers not only sustainable ammonia production but also an efficient method for water detoxification.

“Nitrate is one of the pollutants that most frequently violates drinking water standards, and it is a significant problem in growing cities as farmland with nitrate-contaminated groundwater supplies is converted to urban development,” said Pedro Alvarez, George R. Brown Professor of Civil and Environmental Engineering, director of the Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) and the Water Technologies Entrepreneurship and Research (WaTER) Institute at Rice University.

According to Alvarez, “Conventional nitrate removal in drinking water treatment is done via ion exchange or membrane filtration using reverse osmosis, which creates brines and transfers the nitrate problem from one phase to the other.”

“Professor Wang’s innovation comes at just the right time and is important as it provides a solution that eliminates nitrate toxicity and the associated burden without the need to add treatment chemicals,” Alvarez said.

The impact of this research extends far beyond ammonia production. The innovative reactor design and comprehensive techno-economic evaluation provide valuable insights for the further development of environmentally friendly chemical processes. This could potentially revolutionize the way industries deal with environmental problems.

“Our results suggest a new, more environmentally friendly way to combat water pollution and ammonia production that could influence how industry and communities address these challenges,” said Wang, associate professor of chemical and biomolecular engineering, materials science and nanoengineering, and chemistry at Rice University. “If we are to decarbonise the electricity grid and achieve net zero targets by 2050, we urgently need to develop alternative routes to sustainable ammonia production.”

Journal reference:

1. Feng-Yang Chen, Ahmad Elgazzar, Stephanie Pecaut, Chang Qiu, Yuge Feng, Sushanth Ashokkumar, Zhou Yu, Chase Sellers, Shaoyun Hao, Peng Zhu & Haotian Wang. Electrochemical nitrate reduction to ammonia with cation transport in a solid electrolyte reactor. Nature Catalysis, 2024; DOI: 10.1038/s41929-024-01200-w