Decomposition of N2O on Fe2O3/Al2O3 catalysts. Relationships between physicochemical and catalytic properties

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Abstract
The influence of the iron(III) content and the calcination temperature on the dispersion of supported Fe3+ species on alumina, on the semiconducting properties and on the catalytic activity of Fe2O3/Al2O3 catalysts has been studied, with the decomposition of N2O into N2 into N2 and O2 being used as a probe reaction. Above 250 °C iron(III) is located on the surface of the carrier as α-Fe2O3 and ‘strongly associated iron(III)’(denoted by Fe3+–S). The ratio of the amounts of these species remains constant from X= 0.172 to X= 0.615 mmol Fe3+ per g of alumina and then changes favouring Fe3+–S. The transformation of α-Fe2O3 into Fe3+–S is not accompanied by any detectable change in the Fe3+ dispersion but causes an increase in the activation energy of conduction. A rise in the calcination temperature and iron(III) content brings about an increase in the size of supported α-Fe2O3 crystals shown by a decrease in the dispersion of Fe+. It has been demonstrated that α-Fe2O3 and Fe3+–S exhibit similar activity. This increases linearly with the dispersion of the Fe3+ ions. Moreover, no relationship was found to exist between the semiconducting properties of the catalysts estimated by the activation energy of conduction and the catalytic activity. X-ray photoelectron spectroscopy was used to estimate the dispersion of the supported iron(III), conductivity experiments were performed to determine the activation energy of conduction and catalytic tests were carried out to determine catalytic activity.

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