Study of NO _x Reduction Efficiency in NSR and NSR-SCR Combined Systems

The present study was carried out to analyze the catalytic action of K₂O-Al₂O₃ in NO_x Storage and Reduction (NSR) monolith catalyst and Fe₂O₃-TiO₂ in Selective Catalytic Reduction (SCR) monolith catalyst. The core objective of this investigation is to determine the maximum percentage of Oxides of Nitrogen (NO_x) reduction in NSR and NSR-SCR combined system with respect to engine exhaust gas temperature and compares the results with the results of the conventional mode of operation. To accomplish this task monolith ceramic bricks were coated with K₂O-Al₂O₃ (NSR) and Fe₂O₃-TiO₂ (SCR) catalyst and were placed in different configurations inside the catalytic chamber. Several trials were attempted to get the optimal operating temperature that has a maximum NO_x removal efficiency when successively connecting a single NSR catalyst and the combined NSR-SCR double bed catalyst. Single NSR monolith at 320 °C, showed the best NO_x conversion rate of 74%. The double NSR-SCR configuration permitted the SCR catalyst storing ammonia to respond with NO_x leaving from the NSR. The SCR reaction between ammonia which leaves from NSR, later adsorbed by SCR and the NO that is not reacted in NSR which enters SCR bring about a total NO_x reduction efficiency of 93%. Double bed NSR - SCR is better than single stage NSR by 20%. The study also revealed that the given system is not applicable for engines having exhaust temperature range less than 250 °C as they are unable to provide sufficient activation energy.