The effect of the iron oxidation degree on distribution of promotors in the fused catalyst precursors and their activity in the ammonia synthesis reaction

The effect of the oxidation degree of iron on the distribution of promotors has been determined utilizing a method for the determination of quantitative distribution of promotors in the respective crystallographic phases of the catalyst precursors. The content of calcium, aluminum, potassium and silicon in the intergranular spaces of iron oxides increases with a decrease of the iron oxidation degree. In the catalyst precursors containing the wustite phase in addition to the magnetite phase, potassium is located in 90% in the forms readily undergoing dissolution which are not bound with iron. About only 45% potassium incorporated to the catalyst precursors containing gamma-Fe2O3, was found in the forms, not bound with iron. The activity of the catalysts with various degrees of iron oxidation in the ammonia synthesis reaction and their thermal stability has been studied. Two maxima of activity were found in the studied region of iron oxidation degree: the first one corresponding to conventional catalysts based on magnetite and the second one, flat, about 10% lower, within the degree of oxidation from 4 to 6. A very large decrease of the activity of examined catalysts with an increase of the degree of oxidation of iron was found after performing the thermal stability test. (C) 2002 Elsevier Science B.V. All rights reserved.