Haber-Bosch Process: List of Catalysts

The Haber-Bosch process is an important industrial process for the production of ammonia, which is used as a fertilizer and a key raw material for the production of various chemicals. The process involves the reaction of nitrogen gas and hydrogen gas in the presence of a catalyst to produce ammonia. Over the years, several catalysts have been developed for the Haber-Bosch process. In this article, we will discuss some of the most widely used catalysts for this process.

• Iron-Based Catalysts: Iron-based catalysts were the first catalysts used in the Haber-Bosch process and remain the most widely used today. These catalysts are typically composed of iron oxide (Fe₂O₃) or iron carbide (Fe₃C) supported on a high surface area material such as alumina. These catalysts typically operates at temperatures between 400°C and 550°C and pressures ranging from 150-300 bar. The feed gas, which consists of nitrogen and hydrogen, is introduced to the catalyst bed at a ratio of 1:3.  Iron-based catalysts are relatively cheap and readily available, making them ideal for large-scale industrial processes. However, they have a low activity and selectivity, which can lead to the formation of by-products and waste.

• Cobalt-Based Catalysts: Cobalt-based catalysts have been developed as an alternative to iron-based catalysts. These catalysts are typically composed of cobalt oxide (CoO) or cobalt carbide (Co₂C) supported on a high surface area material such as alumina. Cobalt-based catalysts have a higher activity and selectivity than iron-based catalysts, meaning that they can produce more ammonia with fewer by-products and waste. However, cobalt-based catalysts are more expensive than iron-based catalysts and are less stable under the high pressure and temperature conditions of the Haber-Bosch process. The reaction for cobalt-based catalysts  typically occurs at temperatures between 450°C and 500°C and pressures ranging from 150-250 bar. The feed gas, consisting of nitrogen and hydrogen, is introduced at a ratio of 1:3 or 1:4.

• Nickel-Based Catalysts: Nickel-based catalysts have also been developed as an alternative to iron-based catalysts. These catalysts are typically composed of nickel oxide (NiO) or nickel carbide (Ni₃C) supported on a high surface area material such as alumina. Nickel-based catalysts have a higher activity and selectivity than iron-based catalysts, similar to cobalt-based catalysts. However, nickel-based catalysts are also more expensive than iron-based catalysts and are less stable under the high pressure and temperature conditions of the Haber-Bosch process.

• Molybdenum-Based Catalysts: Molybdenum-based catalysts have been developed as an alternative to iron-based catalysts, with promising results. These catalysts are typically composed of molybdenum oxide (MoO₃) or molybdenum carbide (Mo₂C) supported on a high surface area material such as alumina. Molybdenum-based catalysts have a higher activity and selectivity than iron-based catalysts, and are less sensitive to poisoning by impurities in the feed gas.

• Ruthenium-Based Catalysts: Ruthenium-based catalysts have also been developed as an alternative to iron-based catalysts, with promising results. These catalysts are typically composed of ruthenium oxide (RuO₂) or ruthenium carbide (Ru₂C) supported on a high surface area material such as alumina. Ruthenium-based catalysts have a higher activity and selectivity than iron-based catalysts, and can operate at lower temperatures and pressures than iron-based catalysts, which can reduce the energy requirements and cost of the process. 

Despite the promising results obtained with molybdenum and ruthenium-based catalysts, there are still significant challenges that need to be addressed before they can be widely adopted in the Haber-Bosch process. One of the main challenges is the cost of these catalysts, which are significantly more expensive than iron-based catalysts. In addition, the long-term stability of these catalysts under the harsh conditions of the Haber-Bosch process is still a matter of investigation.

The development of efficient and effective catalysts for the Haber-Bosch process has been a key factor in the success of this process. While iron-based catalysts remain the most widely used catalysts, there is growing interest in developing alternative catalysts based on molybdenum and ruthenium. These catalysts have shown promising results in terms of activity, selectivity, and resistance to poisoning, but significant challenges still need to be addressed before they can be widely adopted in the Haber-Bosch process.