Improving high-temperature NOx conversion in the combined NSR-SCR system with an SCR catalyst mixed with an NH3 adsorbent

Abstract The growing worldwide interest in environmental protection and the strong demand to decrease the emission of pollutants from automotive exhaust require the development of catalysts and post-cleaning systems that are very efficient and stable. To that end, we investigated ways of improving the high-temperature NH 3 selective catalytic reduction (SCR) activity in the NO x storage reduction (NSR) and SCR combined system, and found that NH 3 oxidation is promoted under high-temperature NSR-SCR reaction conditions. To suppress NH 3 oxidation and improve the NH 3 -SCR reaction in the NSR-SCR system, we examined mixing an NH 3 adsorbent with the SCR catalyst (NSR-SCR + NH 3 adsorbent system). The H-type mordenite zeolite (H-MOR) adsorbent demonstrated superior performance for retaining NH 3 without oxidation under high-temperature transient conditions than the other NH 3 adsorbents examined. NO x conversion under high-temperature transient conditions was improved in going from the single NSR system (71% at 450 °C) to NSR-SCR (75% at 450 °C), and NSR-SCR+H-MOR (85% at 450 °C). We confirmed that N 2 formed over long times, from the commencement to the end of the lean phase, in the NSR-SCR+H-MOR system. This phenomenon, in which the NH 3 adsorbed on H-MOR is gradually released to the SCR up to the end of the lean phase, enhances NO x reduction in the NSR-SCR system.