Precipitated Ammonia Synthesis Catalysts

Ammonia synthesis catalysts were prepared by co-precipitation from mixed solutions of ferric and aluminium nitrates at an approximate weight ratio of 97(Fe2O3):3(Al2O3). After drying and calcination in air, these catalysts had a greater surface area than the conventional fused catalysts, but even when the potassium promoter was added, they did not show any improvement in activity. However, when cobalt nitrate was included up to approximately 10% in the mixed metal nitrate solution, the catalytic activity was greatly increased to the extent that it was much more active than either the conventional fused or speculative catalysts prepared by sintering at high temperature the appropriate mixture of metal oxides. Addition of potassium as the ferrocyanide increased activity even further so that double the normal activity could be achieved. The activity of the cobalt-containing catalysts declined at a similar rate to that of conventional catalysts, but even after repeated accelerated aging procedures, it retained a large advantage over the fused catalyst. On a large scale using whole pellets, the activity advantage was maintained but on discharge it was apparent that the pellets had shrunk and were very weak.