Fast Lean-Rich Cycling for Enhanced NOx Conversion on Storage and Reduction Catalysts

Lean NOx (NO + NO2) reduction was carried out using rapid periodic injection of C3H6 over a NOx storage and reduction (NSR) monolith catalyst containing Pt/Rh/BaO/CeO2/Al2O3. The effects of injection speed, feed temperature, rich phase composition, lean phase duration, and feed concentration of CO2 were systematically studied to highlight distinct performance characteristics at faster injection frequencies. Increased NOx and C3H6 conversions were achieved using high frequency injection. The detrimental effects of barium nitrate decomposition at high temperatures and barium carbonate formation were also found to be less significant using rapid pulsing. In addition, a prolonged approach to cyclic steady state was observed for high frequency operation. The results are indicative of a qualitative mechanistic change and suggest the generation of reactive “HCxNyOz” intermediate species that enable improved performance over traditional NSR cycling.