Influence of the addition of transition metals (Cr, Zr, Mo) on the properties of MnOx–FeOx catalysts for low-temperature selective catalytic reduction of NOx by Ammonia

Abstract

The co-precipitation and citric acid methods were employed to prepare MnOx–FeOx catalysts for the low-temperature selective catalytic reduction (SCR) of NOx by ammonia. It was found that the Mn–Fe (CP) sample obtained from the co-precipitation method, which exhibited low crystalline of manganese oxides on the surface, high specific surface area and abundant acid sites at the surface, had better catalytic activity. The effects of doping different transition metals (Mo, Zr, Cr) in the Mn–Fe (CP) catalysts were further investigated. The study suggested that the addition of Cr can obviously reduce the take-off temperature of Mn–Fe catalyst to 90°C, while the impregnation of Zr and Mo raised that remarkably. The texture and micro-structure analysis revealed that for the Cr-doped Mn–Fe catalysts, the active components had better dispersion with less agglomeration and sintering and the largest BET surface specific area. In situ FTIR study indicated that the addition of Cr can increase significantly the surface acidity, especially, the Lewis acid sites, and promote the formation of the intermediate –NH3+. H2-TPR results confirmed the better low-temperature redox properties of Mn–Fe–Cr.