Low-temperature selective catalytic reduction of NO with NH3 over MnCe oxides supported on TiO2 and Al2O3: A comparative study

MnCe oxides were supported on TiO2 and Al2O3 by an ultrasonic impregnation method and used for selective catalytic reduction (SCR) of NO with NH3 at low-temperature (80–220 °C). MnCe/TiO2 showed a relatively higher SCR activity than MnCe/Al2O3 at the temperature range of 80–150 °C. When the reaction temperature was higher than 150 °C, MnCe/Al2O3 exhibited superior SCR activity to MnCe/TiO2. NH3 temperature programmed desorption study proved that MnCe/TiO2 was mainly Lewis acidic, while MnCe/Al2O3 could provide more Brönsted acid sites. These acid sites play an important role in SCR according to in situ diffuse reflectance infrared transform spectroscopy (DRIFT) analysis. The main SCR reaction was a typical Eley–Rideal mechanism on MnCe/TiO2, which took place between coordinated NH3/NH4+ and gas-phase NO. For MnCe/Al2O3, the reaction mainly occurred via another pathway when the temperature exceeded 150 °C, which commenced with the adsorption and oxidation of NO and was followed by reaction between NO2 or NO2-containing compounds and NH3 adspecies. This reaction pathway makes a significant contribution to the improved NO conversion for MnCe/Al2O3 at higher temperature.