Is There Ongoing Progress in the Development of Ammonia Synthesis Catalysts?

After the industrialization of sulfur dioxide oxidation and ammonia oxidation processes, the traditional synthesis of ammonia method adopted by BASF in Germany in 1910 is considered one of the pioneering catalytic processes applied on a large scale. 

For over 80 years, this crucial yet simple multiphase catalytic reaction for synthesizing ammonia and the highly profitable catalysts used have been among the most important research topics in the fields of catalysis and industry. Extensive research by many scholars has made significant contributions to the development of catalytic science and related disciplines, particularly in clarifying the three major factors in catalysis: structural effects, electronic effects, and synergistic effects. 

Despite variations in catalyst formulations and continuous improvements in industrial production processes and equipment, the essence of the process has remained largely unchanged. The harsh conditions, including high temperature and pressure, have not been overcome. The basic composition of the catalysts, primarily iron-based with alkali metals as electron promoters and other oxides as structure promoters, remains consistent. An example of such a catalyst is the ICI3524 catalyst from the UK, which contains approximately 0.8% KO, 2.5% AlO, 2.0% CaO, 0.3% MgO, 0.4% SiO, and trace amounts of TiO, ZrO, and VO.

In the 1960s, interdisciplinary collaborations led researchers to think beyond the constraints of iron-based catalysts and explore new methods and catalysts for ammonia synthesis. Through simulation, reasoning, experimentation, and analysis, some novel ammonia synthesis catalysts were developed. For instance, the Transition Metal Electron Donor-Acceptor (EDA) type ammonia synthesis catalyst proposed by Tamaru and Ozaki between 1968 and 1971, although it could synthesize ammonia under normal pressure conditions at 100°C lower than traditional molten iron catalysts and exhibited 2-3 times higher catalytic activity, it was never industrialized. 

In the 1970s, the global energy crisis escalated, leading to increased ammonia production costs. To reduce costs, countries worldwide focused on developing high-activity ammonia synthesis catalysts under low-temperature and low-pressure conditions. For example, British Petroleum and KLG Corporation in the USA jointly developed ruthenium-based ammonia synthesis catalysts. This can be considered the second generation of ammonia synthesis catalysts after iron-based catalysts. Notably, there is still no consensus on the mechanism of this typical catalytic reaction.

After more than a century of development, ammonia synthesis technology has become mature. However, the ammonia synthesis industry remains energy-intensive. Therefore, improvements in the ammonia synthesis process and catalysts will have a significant impact on reducing energy consumption and enhancing economic benefits. Developing new catalysts with high activity at low temperatures, reducing reaction temperatures, improving ammonia equilibrium conversion rates and single-pass conversion rates, or achieving low-pressure ammonia synthesis have always been the pursuit of the ammonia synthesis industry. From the invention of ruthenium-based catalysts to the establishment of iron-based catalyst systems and the introduction of ternary nitride catalysts, these efforts demonstrate the relentless pursuit of exploring the path to ammonia synthesis.