Selective Catalytic Reduction Of Nitrogen Oxides Under Lean-Burn Condition Over Fe-Mo/ZSM-5 Catalysts

The nitrogen oxides from automobile exhaust emissions have become the main sources of air pollution in cities and roads. And now the techniques used for the removal of NO_x is three-way-catalyst (TWC), under suitable conditions, it can reduce more than 90% of engine-out CO, HC and NO_X. However, there is a significant problem associated with the use of TWC converters, the conversion efficiency of the converter is high only when the engine is operated within a narrow band of air-fuel ratios, thus it is required to maintain sufficiently accurate control of the mixture ratio. But, during the lean operation(A/F > 15), TWCs are not effective in reducing nitrogen oxides. Consequently, TWC converters cannot be used under lean burn condition. On the other hand, in order to meet the need of improvement of fuel efficiency and reducing the emissions of CO₂, the application of diesel engines and lean-burn gasoline engines will be increased. Hence, for controlling NO_x for diesel engines and lean-burn gasoline engines where the exhaust contains excess amount of O₂, the special treatment, selective catalytic reduction (SCR) of NO_x. is necessary. The study of catalysts for SCR has received much interest in...