Investigation and characterization on MnO_x/TiO₂ for low-temperature selective catalytic reduction of NO_x with NH₃

A series of catalysts of manganese oxides supported on TiO₂ with various loadings of manganese and calcination temperatures were prepared. The catalytic activity in low temperature selective catalytic reduction of NO_x with NH₃ was investigated. With the aid of such characteristics as X-ray diffraction (XRD), surface area (BET), temperature programmed reduction (TPR), Fourier transform infrared (FT-IR) and NH₃ temperature programmed desorption (NH₃-TPD), the optimum condition for MnO_x/TiO₂ catalysts preparation was found. The NO_x conversion increases with the loading of manganese, while the N₂ selectivity decreases. The calcination temperature also has an impact on the activity and selectivity. Both of the catalytic activity and the N₂ selectivity of MnO₂ are higher than those of the mixture of MnO₂ and Mn₂O₃. At a space velocity of 12 600 h^-1, MnO₂ yields 97% NO_x conversion at 80°C and nearly 100% conversion and 100% N₂ selectivity at 120°C. With the presence of 6% H₂O, the conversion reaches 99.0% at 120°C. This suggests that MnO₂ is the most promising catalytic species for low temperature selective catalytic reduction of NO with NH₃.