INFLUENCE OF ALUMINUM AND POTASSIUM ON ACTIVITY AND TEXTURE OF FUSED IRON CATALYSTS FOR AMMONIA-SYNTHESIS

BET, scanning electron microscopy and X-ray diffraction were used to investigate the texture of fused iron catalysts which had been previously reduced and passivated, and into which potassium hydroxide was introduced by impregnation or aluminium removed by extraction. Activity tests were carried out under 10.0 MPa in the 400-520-degrees-C temperature range. Investigations were performed on the doubly promoted (Al, Ca) and industrial, triply promoted (K, Al, Ca) catalysts. Introduction of potassium hydroxide into the doubly promoted catalyst increases the process rate by about 15-20 times per unit surface area. Sintering and recrystallization are observed in the catalyst, proving that interaction takes place during the process between the potassium hydroxide introduced and the alumina present on the iron surface. Partial removal of aluminium from the surface of the doubly and triply promoted catalysts also leads to sintering and recrystallization under ammonia synthesis conditions. This shows that the presence of alumina on the surface, and not within the iron, is responsible for textural promotion. Loss of catalysts activity is proportional to reduction in total surface area.