Sulfidation of alumina-supported iron and iron-molybdenum oxide catalysts

The transition of alumina-supported iron and iron-molybdenum catalysts from the oxidic precursor to the sulfided catalysts was systematically studied by means of in-situ Mössbauer spectroscopy at room temperature. This enabled the adjudgement of various sulfidic phases in the sulfided catalysts. The alumina support material prevents complete sulfidation of the iron phase. Some of the iron diffuses into the support material at temperatures of 573 K and higher. The relative amount of iron diffused into the alumina was reduced at higher iron content and in the presence of molybdenum. Together with the formation of elemental sulfur and a lower intrinsic activity, the incomplete sulfidation accounts for the poor HDS activity of alumina-supported iron and iron molybdenum sulfide catalysts.