IRON-OXIDE DEHYDROGENATION CATALYSTS SUPPORTED ON MAGNESIUM-OXIDE .2. REDUCTION BEHAVIOR

The reduction behaviour of iron oxide supported on magnesium oxide has been studied using temperature-programmed reduction (TPR), X-ray diffraction (XRD), and high-field magnetic measurements. The catalysts, containing 1-6 wt.% Fe, were prepared by incipient-wetness impregnation of a preshaped magnesium oxide support with organometallic complexes, such as, ammonium iron(III) citrate and ammonium iron(III) EDTA. In the fresh calcined catalyst the iron oxide is present as magnesium ferrite, MgFe2O4. With TPR two broad reduction peaks, reflecting the sequential reduction of Fe3+ via Fe2+ to Fe0, were observed. High-field magnetic measurements enabled us to describe the reduction behaviour in detail. In the first reduction step, proceeding at ca. 630 K, MgFe2O4 is reduced to FeO partly via Fe3O4. A second reduction step at 750 K results in the formation of metallic iron. Part of the metallic iron has been found to be present in the form of superparamagnetic particles within the MgO support.