Performance and kinetics study for low-temperature SCR of NO with NH3 over MnOx–CeO2 catalyst

A series of manganese–cerium oxide catalysts were prepared by different methods and used for low-temperature selective catalytic reduction (SCR) of NOx with ammonia in the presence of excess O2. The Mn–Ce–Ox catalysts showed high activities. The experimental results showed that the best Mn–Ce mixed-oxide catalyst yielded nearly 100% NO conversion at 120 °C at a high space velocity of 42,000 h−1. As the manganese content was increased from zero to 30% (i.e., the molar ratio of Mn/(Mn+Ce)), NO conversion increased significantly, but decreased at higher manganese contents. The most active catalyst was obtained with a molar Mn/(Mn+Ce) ratio of 0.3. The effect of the calcination temperature was also investigated and the optimum calcination temperature was 650 °C. These catalysts are substantially more active than all other catalysts reported in the literature. SO2 and H2O (at high concentrations) have slight effects on the SCR activity. From a steady-state kinetics study, it was found that the low-temperature SCR reaction was zero order with respect to NH3 and first order with respect to NO. Compared with the other catalysts reported for low-temperature SCR of NO with ammonia, based on the first-order rate constants, the MnOx–CeO2 catalyst was several times more active than other catalysts reported in the literature. Only N2 rather than N2O was found in the product when the temperature was below 150 °C. At higher temperatures, trace amounts of N2O were detected.