Researchers at Science Tokyo have developed a groundbreaking iron-based catalyst that significantly outperforms the century-old conventional catalyst used for ammonia (NH3) production. This innovative catalyst, designed with an inverse structure, has shown a dramatic increase in NH3 generation rates per catalyst volume, offering the potential to greatly improve the efficiency of ammonia production—an essential process in agriculture and chemicals.

For nearly 100 years, the production of ammonia, which is crucial for fertilizers that support global agricultural demands, has relied on the Haber-Bosch (HB) process. This process combines nitrogen (N2) and hydrogen with a catalyst to generate ammonia. Despite numerous advancements in catalyst design, the iron-based "Promoted-Fe" catalyst developed over a century ago remains the standard for large-scale ammonia production. This catalyst has been considered the most effective for achieving high NH3 generation rates per volume across various temperatures and pressures.

However, the efficiency of the HB process has been constrained by the fact that ammonia production is limited by the rate of generation per catalyst volume, not just the catalyst's weight. While much academic research has focused on increasing NH3 production rates per catalyst weight, this metric is less relevant when optimizing the actual production process. To overcome this limitation, the research team at Science Tokyo, led by Professor Michikazu Hara, developed a catalyst with a revolutionary inverse structure. This new design leverages existing iron-based catalyst principles to significantly enhance performance.

Traditional catalysts for NH3 synthesis typically consist of small transition metal particles supported by low-density, high-surface-area materials. While this configuration boosts NH3 production rates per catalyst weight, the low density limits the ammonia generation rate per catalyst volume. In contrast, Science Tokyo's inverse structure catalyst uses larger iron particles combined with potassium and aluminum hydride (AlH), a combination that dramatically increases the NH3 generation rate per unit volume.

This newly developed AlH-K+/Fe catalyst has demonstrated remarkable performance, achieving NH3 generation rates per volume nearly three times higher than the Promoted-Fe catalyst. Furthermore, it operates effectively at temperatures as low as 50°C, a range where the traditional catalyst is inefficient, and remains stable for over 2,000 hours without a decline in activity.

Mechanistic studies revealed that the inverse structure increases the density of active sites and enhances electron donation on the iron surface, improving the efficiency of N2 cleavage during the reaction's rate-limiting step. This breakthrough holds promise for more sustainable, energy-efficient ammonia production, as the AlH-K+/Fe catalyst is made from abundant earth materials. It offers the potential to contribute to climate change mitigation efforts by advancing NH3 production in a more sustainable way.

This revolutionary catalyst design could transform the future of ammonia synthesis, making it more efficient and environmentally friendly, which is crucial for global agricultural production and sustainability.