Control of NOx storage and reduction in NSR bed for designing combined NSR–SCR systems

A detailed analysis of the catalytic behavior in the storage and reduction of NOx of a homemade Pt–BaO/Al2O3 NSR monolith catalyst determining the N2/NH3 production surface in response to operational variables, namely temperature and hydrogen concentration during rich conditions was obtained. The production response curves are used to design the optimal operation, with high NOx removal efficiency and maximum production of nitrogen, when running the single NSR catalyst and the combined NSR–SCR configuration with Fe-beta zeolite catalyst placed downstream the Pt–BaO/Al2O3 monolith. Optimal operation of the single NSR monolith was attained at 300 °C and 1% H2, which showed NOx removal of 74% with 64% of nitrogen production (both related to the total amount of NO in the feedstream, difference was mainly ammonia). The double NSR–SCR configuration allowed the Fe-beta catalyst storing ammonia to react with NOx leaving the NSR during the subsequent lean phase. This has a benefit on both the NOx removal efficiency and the N2 production. The amount of ammonia needed for total NOx removal efficiency and N2 production can be supplied by tuning temperature and H2 concentration. Temperature of 300 °C and 3% H2 during rich conditions, produced 23% of ammonia at the exit of NSR. The SCR reaction between this amount of ammonia adsorbed on Fe-beta and the untrapped NO in NSR, resulted in practical total NOx removal efficiency (98%) and N2 production of 97% when the double NSR–SCR system is operated.