Iron oxide dehydrogenation catalysts supported on magnesium oxide. Part 2.—Reduction behaviour

Abstract

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.