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Emission control systems combining NOx Adsorber catalysts with Selective Catalytic Reduction catalysts (NAC + SCR) offer potential performance advantages for NOx control under lean conditions compared to systems consisting of only one of these technologies. The combined systems, however, also present new catalyst design challenges. In contrast to NAC-only systems, formation of NH₃ over the NAC component under NOx regeneration conditions is a desirable feature in the combined (NAC + SCR) system. The SCR component in the combined system needs to be as thermally durable as the stand-alone SCR technology and also has to withstand repeated high-temperature lean/rich transients encountered during periodic desulfation of the upstream NAC component. In this study, advanced NAC and SCR components were developed specifically for the combination system. The advanced NAC component exhibited a wider operating temperature window and higher NH₃ generation activity at reduced PGM loading.

Since early 2010, most new medium- and heavy-duty diesel vehicles in the US rely on urea-based Selective Catalytic Reduction (SCR) technology for meeting the most stringent regulations on nitrogen oxides (NOx) emissions in the world today. Catalyst technologies of choice include Copper (Cu)- and Iron (Fe)-based SCR. In this work, the performances of Fe-SCR and Cu-SCR were investigated in the most commonly used DOC + CSF + SCR system configuration. Cu-SCR offered advantages over Fe-SCR in terms of low temperature conversion, NO₂:NOx ratio tolerance and NH₃ slip, while Fe-SCR demonstrated superior performance under optimized NO₂:NOx ratio and at higher temperatures. The Cu-SCR catalyst displayed less tolerance to sulfur (S) exposure. Reactor testing has shown that Cu-SCR catalysts deactivate at low temperature when poisoned by sulfur.