Photocatalytic NO reduction with C3H8 using a monolith photoreactor

Photocatalytic reduction of nitric oxide was studied on a PtOxPdOy/TiO2-coated monolith photoreactor using propane as the reducing agent. The performance of NO reduction was compared under three reaction conditions including NO/propane, NO/propane/O2 and NO/propane/H2O at three reaction temperatures, 25, 70 and 120 °C. The NO/propane system showed the best performance of near 90% conversion at 25 °C. The NO conversion decreased slightly as temperature increased in NO/propane system, however, NO/propane/O2 and NO/propane/H2O systems showed an opposite trend. Oxygen and water significantly inhibited the reduction of NO because oxygen competed with NO as oxidant, and water interfered the adsorption of both NO and propane. TiO2 became super-hydrophilic under UV-light irradiation thus the catalyst surface was easily covered by water in moisture condition. By increasing the reaction temperature, water tended to desorb from the catalyst surface thus released more active sites for NO photoreduction. An in situ FTIR was also performed to study the intermediate species of the NO/propane and NO/propane/O2 systems under UV-light irradiation. The results indicated that NO went through both oxidation and reduction with C3H8 on PtOxPdOy/TiO2. The reaction path of NO might change with increasing temperature.