What is the Role of Alkali and Alkaline Earth Metals and Their Oxides in Ammonia Catalysts?

Potassium (K) a Crucial Promoter is in Iron-Based Catalysts for Ammonia Synthesis

Research indicates that K does not impact the crossover frequency of iron melt ammonia synthesis. However, it does influence the crossover frequency of ammonia decomposition, with the degree of impact increasing with the concentration of ammonia in the gas phase. How does the addition of alkaline CaO mitigate the effects of KO, AlO, and SiO?

Catalyst Support, Specifically Al₂O₃, Contribute to Iron Surface Stability and Porosity?

The Al₂O₃ support increases the surface area of iron, maintaining its porous structure, preventing sintering-induced enlargement of iron grains, and ensuring surface stability. What is the suitable Al₂O₃ content, and how does it affect catalyst activity, particularly under high-temperature and high-hydrogen-to-nitrogen ratio conditions? How does SiO stabilize iron grains and enhance water and heat resistance?

Compounds Lead to Catalyst Poisoning, and How Can Their Presence Be Minimized

The presence of chlorine, sulfur, phosphorus, oxygen, and other compounds (CO, CO₂, H₂O, etc.) in the catalyst can lead to poisoning, with higher activity catalysts being more sensitive. How does oxygen, even in ppm levels, significantly influence iron catalysts for ammonia synthesis? Why is the removal of oxygen from the synthesis gas necessary? How does the poisoning effect vary when alkali metals act as promoters?

In summary, this exploration delves into the nuanced impacts of alkali and alkaline earth metals, their oxides, catalyst support, and poisoning factors on the activity and performance of iron catalysts in ammonia synthesis.