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.