Iron oxides and their metal- doped variants of formulation M/Fe<sub>3</sub>O<sub>4</sub>, M/y-Fe<sub>2</sub>O<sub>3</sub>, M/a-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub>- related structures, and oxidation- reduction cycling has been examined. Titanium- doped y-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub> was subjected to a three-fold reductionoxidation cycle. The stabilisation of a spinel- related y-Fe<sub>2</sub>O<sub>3</sub> structure with respect to thermally induced conversion to a corundum- related a-Fe<sub>2</sub>O<sub>3</sub> phase was related to the presence of titanium as opposed to particle size or surface area effects. Impregnation of Ti/y-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub> for the oxidation of carbon monoxide to carbon dioxide was good. Although generally similar behaviour was observed in y-Fe<sub>2</sub>O<sub>3</sub> doped with tin, ruthenium and magnesium, and in palladium impregnated variants, Ti/y-Fe<sub>2</sub>O<sub>3</sub> and palladium impregnated Ti/y-Fe<sub>2</sub>O<sub>3</sub> 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 Fe<sub>3</sub>O<sub>4</sub> and a-Fe<sub>2</sub>O<sub>3</sub> confirmed the superior properties of Ti/y-Fe<sub>2</sub>O<sub>3</sub> and palladium impregnated Ti/y-Fe<sub>2</sub>O<sub>3</sub> for use as catalysts in automobile exhaust systems.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:390781 |
| Date | January 2001 |
| Creators | Ayub, Ibrar |
| Publisher | Open University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oro.open.ac.uk/58145/ |
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