Low-temperature selective catalytic reduction of NO with NH(3) over Mn-Ce oxides supported on TiO2 and Al2O3: a comparative study.

MnCe oxides were supported on TiO(2) and Al(2)O(3) by an ultrasonic impregnation method and used for selective catalytic reduction (SCR) of NO with NH(3) at low-temperature (80-220 degrees C). MnCe/TiO(2) showed a relatively higher SCR activity than MnCe/Al(2)O(3) at the temperature range of 80-150 degrees C. When the reaction temperature was higher than 150 degrees C, MnCe/Al(2)O(3) exhibited superior SCR activity to MnCe/TiO(2). NH(3) temperature programmed desorption study proved that MnCe/TiO(2) was mainly Lewis acidic, while MnCe/Al(2)O(3) 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/TiO(2), which took place between coordinated NH(3)/NH(4)(+) and gas-phase NO. For MnCe/Al(2)O(3), the reaction mainly occurred via another pathway when the temperature exceeded 150 degrees C, which commenced with the adsorption and oxidation of NO and was followed by reaction between NO(2) or NO(2)-containing compounds and NH(3) adspecies. This reaction pathway makes a significant contribution to the improved NO conversion for MnCe/Al(2)O(3) at higher temperature.