Oxidation and reduction properties of iron-containing oxides

Ayub, Ibrar (2002). Oxidation and reduction properties of iron-containing oxides. PhD thesis The Open University.

Abstract

Iron oxides and their metal- doped variants of formulation M/Fe3O4, M/y-Fe2O3, M/a-Fe2O3 have been prepared by the calcination of solids formed by the boiling of precipitates under reflux and by hydrothermal processing.

Titanium-, tin-, ruthenium- and magnesium- doped variants of y-Fe2O3 have been subjected to special investigation and the influence of the dopants on the surface area, particle size, reduction properties, stability to conversion to a-Fe2O3- related structures, and oxidation- reduction cycling has been examined. Titanium- doped y-Fe2O3 prepared by the calcination of a solid formed by the addition of base to salt and boiling the precipitate under reflux was formed with a smaller particle size and higher surface area than the other counterparts. These properties remained superior to those of the other materials when Ti/y-Fe2O3 was subjected to a three-fold reductionoxidation cycle. The stabilisation of a spinel- related y-Fe2O3 structure with respect to thermally induced conversion to a corundum- related a-Fe2O3 phase was related to the presence of titanium as opposed to particle size or surface area effects.

Impregnation of Ti/y-Fe2O3 with palladium lowered the temperatures at which the iron oxide was reduced as a result of the adsorption and dissociation of hydrogen on palladium which facilitates more facile reduction of iron in iron oxide. The oxygen storage capacity and the performance of palladium- impregnated Ti/y-Fe2O3 for the oxidation of carbon monoxide to carbon dioxide was good. Although generally similar behaviour was observed in y-Fe2O3 doped with tin, ruthenium and magnesium, and in palladium impregnated variants, Ti/y-Fe2O3 and palladium impregnated Ti/y-Fe2O3 showed the most favourable properties in terms of their potential use as oxygen-storage components in automobile exhaust catalysts.

A comparison of the results with those recorded from materials derived from Fe3O4 and a-Fe2O3 confirmed the superior properties of Ti/y-Fe2O3 and palladium impregnated Ti/y-Fe2O3 for use as catalysts in automobile exhaust systems.

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