Polymorphous transformation of rod-shaped iron oxides and their catalytic properties in selective reduction of NO by NH3

Abstract

Polymorphous transformation of rod-shaped γ-Fe₂O₃ was applied to fabricate Fe₃O₄/Fe₂O₃ nanorods. Hydrogen reduction of γ-Fe₂O₃ nanorods at 350 °C yielded Fe₃O₄ nanorods with similar size; re-oxidation of the resulting Fe₃O₄ nanorods produced γ-Fe₂O₃ at 500 °C and α-Fe₂O₃ nanorods at 600 °C. When applied to catalyze selective reduction of NO with NH₃, the activity followed the order γ-Fe₂O₃ > γ-Fe₂O₃-500 > α-Fe₂O₃ > Fe₃O₄, which was well correlated with their crystalline structures. The superior performance of γ-Fe₂O₃ nanorods was attributed to the simultaneous exposure of Fe³⁺ and O²⁻, which favoured the adsorption and activation of NH₃ and NO molecules.