Ruiben Jin

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 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.

Photocatalytic reduction of NO with NH3 using Si-doped TiO2 prepared by hydrothermal method.

A series of Si-doped TiO2 (Si/TiO2) photocatalysts supported on woven glass fabric were prepared by hydrothermal method for photocatalytic reduction of NO with NH3. The photocatalytic activity tests were carried out in a continuous Pyrex reactor with the flow rate of 2000mL/min under UV irradiation (luminous flux: 1.1x10(4)lm, irradiated catalyst area: 160cm2). The photocatalysts were characterized by X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrophotometer, transmission electron microscopy (TEM), photoluminescence (PL) and temperature-programmed desorption (TPD). The experiment results showed that NO conversion on Si/TiO2 at 323K could exceed 60%, which was about 50% higher than that on Degussa P25 and pure TiO2. With the doping of Si, photocatalysts with smaller crystal size, larger surface area and larger pore volume were obtained. It was also found that Ti-O-Si bands were formed on the surface of Si/TiO2 and that the surface hydroxyl concentration was greatly increased. As a result, total acidity and NH3 chemisorption amount were enhanced for Si/TiO2 leading to its photocatalytic activity improvement.