Low-Emission NH3 Method Boosts Yield 5.6-Fold

Abstract

By enabling ammonia synthesis under near ambient conditions, mechanochemistry provides a paradigm shift, a new decentralized production method that avoids the high temperature (above 400 °C) and high pressure (above 200 bar) requirements of the centralized Haber-Bosch process. Leveraging the principles of mechanochemistry and its dynamic reaction environment, we hypothesize that inducing high-density defects on iron (Fe) catalyst can amplify catalytic activity by increasing initial state and adsorption capacity. In this study, we introduce a novel mechanochemical ammonia synthesis method utilizing silicon nitride (Si3N4) as a defect-inducing physical promoter. The physical properties of Si3N4 make it an ideal candidate to more efficiently generate active surfaces on Fe catalyst via mechanochemical actions. The Fe catalyst with Si3N4 (3.0 at%) promoter achieves an ammonia concentration 5.6-fold higher than unpromoted Fe, while maintaining substantial stability. This research not only establishes a promising pathway for low-energy ammonia production but also provides insights into dynamic defect engineering strategies for catalytic systems.

A groundbreaking new method for ammonia synthesis has demonstrated a 5.6-fold increase in yield, offering a promising alternative to traditional, carbon-intensive production processes. This advancement leverages silicon nitride (Si₃N₄), a material that can be sourced from recycled solar panel waste, highlighting its potential to transcend the limitations of fossil fuel-based methods and contribute to sustainable resource management.

Led by Professor Jong-Beom Baek from the School of Energy and Chemical Engineering at UNIST, the research team announced that they successfully enhanced the efficiency of mechanochemical ammonia synthesis through the addition of silicon nitride.

Ammonia is a vital compound in global agriculture, underpinning fertilizer production that feeds approximately half of the world's population. Beyond its agricultural importance, ammonia is increasingly recognized as a clean fuel carrier, especially for hydrogen storage and transportation, raising its future demand.

However, current ammonia production relies on the century-old Haber-Bosch process, which requires high temperatures above 400°C and pressures over 200 atmospheres-conditions that consume vast amounts of energy and contribute over 2% of global carbon dioxide emissions.

In response, researchers are turning to mechanochemical ammonia synthesis as a sustainable alternative. This process involves rolling steel balls in a sealed container to induce collisions between nitrogen (N₂) and hydrogen (H₂) molecules on catalytic surfaces, promoting reactions at significantly lower temperatures and pressures. This method not only reduces energy consumption and greenhouse gas emissions but is also well-suited for decentralized, small-scale production-allowing direct manufacturing of ammonia at farms and local sites where it's needed most.

In their latest study, the team incorporated a small amount of silicon nitride into the process, resulting in a 5.6-fold increase in ammonia yield compared to conventional methods. Analyses revealed that silicon nitride induces high-density defects on the iron catalyst surface, effectively facilitating the dissociation of nitrogen molecules into atomic nitrogen and their subsequent hydrogenation.

Silicon nitride is known for its exceptional resistance to impact, chemical corrosion, and heat, enabling long-term catalytic performance. Importantly, it can be produced from recycled silicon materials recovered from end-of-life solar panels-aligning with sustainable energy and resource recycling goals. According to the International Energy Agency, over 49 million tons of solar panel waste are expected globally by 2050, emphasizing the importance of resource recovery from renewable energy waste.

Professor Baek commented, "This technology significantly enhances ammonia production efficiency under low-temperature and low-pressure conditions, contributing to decentralized manufacturing. Moreover, since it utilizes recycled solar panel waste, it addresses both decarbonization and resource circularity, making it a comprehensive solution for sustainable ammonia production."

The findings were published online in Nature Communications on July 1, 2025. This research was supported by the Ministry of Science and ICT (MSIT) and the National Research Foundation of Korea (NRF), among other institutions.

Journal Reference

Jae Seong Lee, Sooyeon Kim, Seung-Hyeon Kim, et al., "Mechanochemical ammonia synthesis enhanced by silicon nitride as a defect-inducing physical promoter," Nature Commun., (2025).