Selective Catalytic Reduction of NOx with NH3 on a Cr-Mn Mixed Oxide at Low Temperature

A series of Cr-Mn mixed oxide catalysts were prepared by the citric acid method and characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The effect of Cr/(Cr + Mn) molar ratio on activity for the selective catalytic reduction (SCR) of NOx with ammonia in the presence of excess oxygen at low temperature (80-220 degrees C) was studied. A 98.5% NOx conversion with 100% selectivity for N-2 was obtained with Cr(0.4)-MnOx(Cr/(Cr + Mn) molar ratio = 0.4) at 120 degrees C and 30 000 h(-1). The addition of chromium to MnOx produced a CrMn1.5O4 crystal phase, which played an important role in low-temperature SCR.