Water and temperature effects on photo-selective catalytic reduction of nitric oxide on Pd-loaded TiO2 photocatalyst.

Photo-selective catalytic reduction (photo-SCR) of nitric oxide (NO) was studied in the presence of water. The incipient wetness impregnation was applied to prepare 1 wt% PdO/TiO2 photocatalyst. Steady-state photoreaction was carried out in a continuous-flow photoreactor with 0.55-1.6 v% water at 30-120 degrees C under UV-light intensity of approximately 200mW/cm(2). The C3H8/NO molar ratio in the feed ranged from 0.8 - 16.8 at a volume hourly space velocity (VHSV) from 330-1090 h(-1). The result indicates that the increase of temperature has played an important role in inhibiting NO transformation to NO2 under the humid condition. Another important factor for maximizing denitrification (reduction of nitrogen oxides, DeNOx) efficiency was C3H8/NO ratio. An increase of temperature at a suitable C3H8/NO ratio can minimize NO2 formation, which can lead to high NO removal efficiency of more than 90% at a temperature of 70-100 degrees C. In addition, the mechanism of palladium transformation during photoreaction is proposed, to explain the influence of Pd on the improvement of NO removal.