Oxygen Storage and NO Traps

In the most direct application, the TWC is placed upstream from the NO trap, providing for both the usual means of emissions control under start-up and stoichiometric conditions and a cooler environment for the trap, which has a relatively narrow, low-temperature window of efficient operation under lean conditions. If the TWC stores oxygen, the shift from lean to stoichiometric conditions, initiating the release of NO from the trap, will precede the breakthrough of reductants, allowing some of the NOx to escape. Limiting the OSC of the TWC mitigates this effect, but it also compromises TWC performance. 

Poisoning of the NOx trap by fuel sulfur, which as a relatively stable sulfate impedes the formation of the nitrate, presents another problem, but in this case, oxygen storage may be useful. The accumulation of sulfates can be diminished 

On the other hand, incorporation of an oxygen storage component into the NOx trap also leads to the generation of an exotherm during normal NOx regeneration, which has the effect of lowering the upper temperature limit of operation. 

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