Envision a realm where industrial byproducts are not merely diminished but transformed into valuable resources. This form of a circular economy is already underway for carbon. Now, scholars in energy, environmental, and chemical engineering at Washington University in St. Louis have crafted an encouraging pathway to convert toxic nitric oxide, a significant contributor to acid rain, into useful nitric acid, which serves day-to-day purposes from fertilizer fabrication to metal refinement.
Feng Jiao, the Lauren and Lee Fixel Distinguished Professor at the McKelvey School of Engineering at WashU, along with colleagues, devised a technique to transform nitric oxide (NO) emissions into high-purity, concentrated nitric acid (HNO₃). This innovative process functions under near-ambient conditions with minimal infrastructure requirements, providing a cost-effective resolution to industrial nitrogen waste while delivering economic and ecological advantages. The findings were published on April 3 in Nature Catalysis.
“We’ve created an electrochemical method for converting NO, a hazardous waste gas, into useful nitric acid,” Jiao explained. “Our main aim is to tackle NO emissions from mining operations, where substantial quantities of nitric acid are utilized to process metal ores, resulting in significant releases. Our technology allows for on-site conversion of NO back into nitric acid for immediate reuse, fostering a more sustainable and circular system.”
The groundbreaking electrochemical mechanism employs an affordable carbon-based catalyst for NO oxidation. When paired with a single-metal oxygen reduction catalyst pioneered by Gang Wu, a professor of energy, environmental, and chemical engineering at McKelvey Engineering, the system operates with diminished energy expenditure to convert NO into HNO₃ without the necessity for chemical additives or additional purification processes.
The electrochemical oxidation apparatus is intentionally designed to be “plug and play,” Jiao stated, assembled on-site without substantial financial investments in infrastructure or costly raw materials, such as precious metals. It is adaptable and modifiable for small to medium-scale operations, functioning at room temperature, which significantly decreases energy consumption, costs, and ecological effects compared to traditional NO processing methods that necessitate elevated working temperatures.
The system achieves over 90% faradaic efficiency when utilizing pure NO. Even at reduced concentrations of NO, the system maintains more than 70% faradaic efficiency, making it versatile for various industrial waste streams. The direct synthesis of concentrated high-purity HNO3 – up to 32% by weight – from NO and water without electrolyte additives or subsequent purification establishes an electrochemical pathway to convert NO waste gases into valuable substances, promoting sustainable pollution reduction and chemical production.
Apart from mining, Jiao remarked that this method might possess wider industrial implications as well as notable commercial potential, which he and his collaborators illustrated through an extensive techno-economic evaluation demonstrating that their process features reduced energy consumption and operating costs relative to conventional HNO₃ production techniques. Converting industrial pollutants into advantageous chemical goods is both a smart business strategy and beneficial for the planet, Jiao affirmed.
“The nitric acid produced by our system can be directly utilized in mining operations or other chemical processes,” Jiao highlighted. “We’ve already attained impressive efficiency and purity levels in our output. Moving forward, we aim to enhance those figures even further while scaling up for real-world applications. We’re exploring how to integrate this technology into a nitrogen circular economy that will pave the way for more efficient and sustainable agricultural, manufacturing, and various other sectors.”
Xia R, Dronsfield S, Lee A, Crandall BS, Liang J, Hasa B, Redder A, Wu G, Goncalves TJ, Siahrostami S, Jiao F. Electrochemical oxidation of nitric oxide to concentrated nitric acid with carbon-based catalysts at near-ambient conditions. Nature Catalysis, online April 3. DOI: https://www.nature.com/articles/s41929-025-01315-8
This research was funded by Washington University in St. Louis, the University of Calgary’s Canada First Research Excellence Fund Program, and the Global Research Initiative in Sustainable Low Carbon Unconventional Resources. It was also partially supported by computational resources at the University of Calgary and Compute Canada.
Initially published on the McKelvey Engineering website
The article Electrochemical method supports nitrogen circular economy was first featured on The Source.