γ-Fe2O3 and a-Fe2O3 catalysts were prepared respectively via a novel microwave pyrolysis method using FeSO4·7H2O and Fe(NO3)3·9H2O as ferrous source. Crystalline phase and microstructure of catalysts were characterized by X-ray diffraction(XRD)

mercury intrusion porosimetry(MIP)

N2 adsorption-desorption and NH3-SCR activity of different catalysts were investigated. SCR reaction rates over the catalysts at different temperatures were obtained by unitary processing

and SCR activities over γ-Fe2O3 and vanadium-based catalysts were compared. The effects of O2 concentration

molar ratio of NH3/NO

SO2

and H2O on SCR activity of γ-Fe2O3 catalyst were also studied. Pure γ-Fe2O3 catalyst could be obtained via this novel microwave pyrolysis method

and showed higher crystallinity than a-Fe2O3 catalyst. γ-Fe2O3 catalyst had broader pore size distribution as well as appropriate ratios of mesopores and macropores. Meanwhile

γ-Fe2O3 catalyst exhibited better SCR activity than a-Fe2O3 catalyst. The highest NOx conversion of γ-Fe2O3 catalyst was up to 96% at 400℃ and SCR reaction rates normalized by surface area were three times higher than that of a-Fe2O3 catalyst at 300

325 and 350℃

respectively. The optimum molar ratio of NH3/NO and O2 concentration for selective catalytic reduction over γ-Fe2O3 catalyst were recommended to be 1 and 3.5% (vol)

respectively.