A team of researchers at MIT has developed an innovative way of making ammonia without the usual fossil-fuel-powered chemical plants that require high heat and pressure. Instead, they have found a way to use the Earth itself as a geochemical reactor, producing ammonia underground. The processes uses Earth’s naturally occurring heat and pressure as well as the reactivity of minerals already present in the ground.

The team proposes injecting water underground into an area of iron-rich subsurface rock. The water carries with it a source of nitrogen and particles of a metal catalyst, allowing the water to react with the iron to generate clean hydrogen, which in turn reacts with the nitrogen to make ammonia. A second well would then be used to pump that ammonia up to the surface.

The process, which has been demonstrated in the lab but not yet in a natural setting, is described in an open-access paper in the journal Joule. The paper’s co-authors are MIT professors of materials science and engineering Iwnetim Abate and Ju Li, graduate student Yifan Gao, and five others at MIT.

Although ammonia production is crucial for global agriculture, it comes with substantial carbon footprints. Here, for the first time, we propose and demonstrate a different method for stimulated (proactive) and in situ geological ammonia (Geo-NH₃) production directly from rocks. Our approach demonstrated that NH₃ can be efficiently generated by reacting natural (Fe,Mg)₂SiO₄ (olivine) minerals with nitrate-source water at 130°C–300°C and 0.25–8.5 MPa, and even at ambient temperature and pressure. Using both actual rocks and synthetic mineral Fe(OH)₂, we investigated mechanisms and optimized conditions through experiments and theoretical calculations. We revealed the basic chemistry enabling Geo-NH₃ production: Fe²⁺ contained in rocks reduces the nitrate source to NH₃. Our approach, involving only the injection of nitrate-source water into the subsurface to utilize in situ subsurface heat and pressure, requires no external H₂ or electric current and emits no direct CO₂, offering a feasible alternative to sustainable NH₃ production at scale.

—Gao et al.

Schematic and configuration of the abate cycle, the subsurface thermochemical redox reaction for ammonia synthesis. (A) It comprises several components, including an injection well, fluid delivery apparatus, flow passages (boreholes), and a production well. These components are interconnected for fluid communication. Additional elements, like pumps, may be employed to regulate compound flow. Water, nitrate (NO₃⁻), and additives (e.g., catalyst, pH agent, etc.) flowtoward the ultramafic rock bed through the first borehole (blue arrows). After redox reactions on the rock surface, NH₃ exits the subsurface through the second borehole (green arrow) to be collected at the surface (can be collected either in a gas form or as NH₃ dissolved in water). (B) Schematic of reaction at the rock-fluid interface where the Fe²⁺ in the rock is oxidized while reducing NO₃⁻ into NH₃. Gao et al.

The standard method for making ammonia is the Haber-Bosch process, which was developed in Germany in the early 20^th century to replace natural sources of nitrogen fertilizer such as mined deposits of bat guano, which were becoming depleted. The Haber-Bosch process is very energy intensive—it requires temperatures of 400 degrees Celsius and pressures of 200 atmospheres, and this means it needs huge installations in order to be efficient. Some areas of the world, such as sub-Saharan Africa and Southeast Asia, have few or no such plants in operation. As a result, the shortage or extremely high cost of fertilizer in these regions has limited their agricultural production.

The Haber-Bosch process “is good. It works,” Abate says. “Without it, we wouldn’t have been able to feed 2 out of the total 8 billion people in the world right now, he says, referring to the portion of the world’s population whose food is grown with ammonia-based fertilizers. But because of the emissions and energy demands, a better process is needed, he says.

Burning fuel to generate heat is responsible for about 20% of the greenhouse gases emitted from plants using the Haber-Bosch process. Making hydrogen accounts for the remaining 80%. But ammonia, the molecule NH₃, is made up only of nitrogen and hydrogen. There’s no carbon in the formula, so where do the carbon emissions come from? The standard way of producing the needed hydrogen is by processing methane gas with steam, breaking down the gas into pure hydrogen, which gets used, and carbon dioxide gas that gets released into the air.

Other processes exist for making low- or no-emissions hydrogen, such as by using solar or wind-generated electricity to split water into oxygen and hydrogen, but that process can be expensive. That’s why Abate and his team worked on developing a system to produce what they call geological hydrogen. Some places in the world, including some in Africa, have been found to naturally generate hydrogen underground through chemical reactions between water and iron-rich rocks. These pockets of naturally occurring hydrogen can be mined, just like natural methane reservoirs, but the extent and locations of such deposits are still relatively unexplored.

Abate realized this process could be created or enhanced by pumping water, laced with copper and nickel catalyst particles to speed up the process, into the ground in places where such iron-rich rocks were already present. “We can use the Earth as a factory to produce clean flows of hydrogen,” he says.

He recalls thinking about the problem of the emissions from hydrogen production for ammonia: “The ‘aha!’ moment for me was thinking, how about we link this process of geological hydrogen production with the process of making Haber-Bosch ammonia?”

That would solve the biggest problem of the underground hydrogen production process, which is how to capture and store the gas once it’s produced. By implementing the entire Haber-Bosch process underground, the only material that would need to be sent to the surface would be the ammonia itself, which is easy to capture, store, and transport.

The only extra ingredient needed to complete the process was the addition of a source of nitrogen, such as nitrate or nitrogen gas, into the water-catalyst mixture being injected into the ground. Then, as the hydrogen gets released from water molecules after interacting with the iron-rich rocks, it can immediately bond with the nitrogen atoms also carried in the water, with the deep underground environment providing the high temperatures and pressures required by the Haber-Bosch process. A second well near the injection well then pumps the ammonia out and into tanks on the surface.

We call this geological ammonia because we are using subsurface temperature, pressure, chemistry, and geologically existing rocks to produce ammonia directly. —Iwnetim Abate

Whereas transporting hydrogen requires expensive equipment to cool and liquefy it, and virtually no pipelines exist for its transport (except near oil refinery sites), transporting ammonia is easier and cheaper. It’s about one-sixth the cost of transporting hydrogen, and there are already more than 5,000 miles of ammonia pipelines and 10,000 terminals in place in the U.S. alone.

Ammonia can be burned directly in gas turbines, engines, and industrial furnaces, providing a carbon-free alternative to fossil fuels. It is being explored for maritime shipping and aviation as an alternative fuel, and as a possible space propellant.

Another upside to geological ammonia is that untreated wastewater, including agricultural runoff, which tends to be rich in nitrogen already, could serve as the water source and be treated in the process.

The initial work on the process has been done in the laboratory, so the next step will be to prove the process using a real underground site. The team has applied for a patent and aims to work towards bringing the process to market.

Resources

• Yifan Gao, Ming Lei, Bachu Sravan Kumar, Hugh Barrett Smith, Seok Hee Han, Lokesh Sangabattula, Ju Li, Iwnetim I. Abate, Geological ammonia: Stimulated NH3 production from rocks, Joule, 2025, doi: 10.1016/j.joule.2024.12.006