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

Abstract

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°C under UV-light intensity of ∼ 200 mW/cm². 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, DeNO_x) 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°C. In addition, the mechanism of palladium transformation during photoreaction is proposed, to explain the influence of Pd on the improvement of NO removal.

Keywords:

• nitric oxide
• photocatalysis
• selective catalytic reduction
• Pd
• TiO₂

Acknowledgements

This work was financially supported by the National Science Council of Taiwan under project No. NSC98-2911-I-002-002. We would also like to thank Raymond Liao for checking the grammar.