[Preparation of -FeO Catalyst by Heat Treatment of Natural Limonite for Selective Catalytic Reduction of NO by NH].

Natural limonite was used as a precursor to prepare -FeO via thermal treatment. The influences of reaction temperature, manganese oxides existing in limonite and coexisting SO and HO on the catalytic reduction activity of the prepared-FeO were evaluated, and the activity of SCR was compared with that of -FeO, by means of XRD, XRF, XPS, NH-TPD, FT-IR and so on. The results showed that because the surface acidity of -FeO is stronger, the SCR temperature window of -FeO was 200-350℃ being broader than that of -FeO (200-300℃), and in the active temperature window, the NO removal reached over 99%. The existence of MnO in the newly formed -FeO slightly decreased the SCR reactivity at lower temperature (100-200℃), while it decreased the SCR reactivity at higher temperature (400-450℃). The existence of SO led to the shifting of temperature window by 100℃ from 200-350℃ to 300-450℃, and the volume fraction of 5%HO only had a tiny negative effect on the SCR reactivity of -FeO. However, the coexisting SO and HO, especially when the volume fraction of SO reached 0.12%, significantly decreased the SCR reactivity due to the generation of ammonium sulfate. Besides, although the magnetic susceptibility of reacted -FeO experienced a slight decrease compared with the newly prepared -FeO, the catalysts could still be used repeatedly by magnetic recycling.