Stanford researchers have found an environmentally friendly method of producing ammonia using small droplets of water and nitrogen sourced from the air.
Ammonia (NH3) serves as the foundation for the creation of chemical fertilizers used for agricultural crops. For over 100 years, the global production of ammonia in large quantities has relied on the Haber-Bosch process. This industrial breakthrough has had a major impact on agriculture, enabling the feeding of a rapidly growing human population. However, the Haber-Bosch process is extremely energy-intensive, requiring high pressure levels of 80-300 atmospheres and temperatures ranging from 572-1000 F (300-500 C) to break nitrogen’s strong bonds. Additionally, the steam-treatment of natural gas involved in the process contributes significantly to the release of carbon dioxide, a key contributor to climate change.
All told, to satisfy the current annual worldwide demand for 150 million metric tons of ammonia, the Haber-Bosch process gobbles up more than 2% of global energy and accounts for about 1% of the carbon dioxide emitted into the atmosphere.
In contrast, the innovative method debuted by the Stanford researchers requires less specialized circumstances.
“We were shocked to see that we could generate ammonia in benign, everyday temperature-and-pressure environments with just air and water and using something as basic as a sprayer,” said study senior author Richard Zare, the Marguerite Blake Wilbur Professor in Natural Science and a professor of chemistry in the Stanford School of Humanities and Sciences. “If this process can be scaled up, it would represent an eco-friendly new way of making ammonia, which is one of the most important chemical processes that takes place in the world.”
The new method also uses little energy and at a low cost, thus pointing a way forward to potentially producing the valuable chemical in a sustainable manner. Xiaowei Song, a postdoctoral scholar in chemistry at Stanford, is the lead author of the study, which was recently published in the Proceedings of the National Academy of Sciences.
New chemistry from blue-sky study
The new chemistry discovered follows in the footsteps of pioneering work by Zare’s lab in recent years examining the long-overlooked and surprisingly high reactivity of water microdroplets. In a 2019 study, Zare and colleagues novelly demonstrated that caustic hydrogen peroxide spontaneously forms in microdroplets in contact with surfaces. Experiments since have borne out a mechanism of electric charge jumping between the liquid and solid materials and generating molecular fragments, known as reactive oxygen DOI: 10.1073/pnas.2301206120
The study was funded in part by the U.S. Air Force Office of Scientific Research through the Multidisciplinary University Research Initiative.