Abstract – The NOx trap monolithic catalytic reactor is emerging as a promising technology for meeting the increasingly stringent restrictions on vehicular emissions from lean burn and diesel engines. The NOx trap is a multi-functional catalytic (Pt/BaO/Al2O3) reactor operated periodically between lean and rich conditions. During the lean operation, the NOx is stored on an alkali earth oxide as nitrites/nitrates and reduced during the rich operation period, which is usually much shorter than the lean period. Successful design and operation of the NOx trap requires understanding the fundamental mechanisms and kinetics of storage and reduction and their coupling with the transport processes. The influence of hydrogen on NOx trap performance is of interest because H2, produced by water gas shift reaction, presents an important component in the exhaust and is an efficient reductant for NO, especially, at lower temperatures. In this study, a short monolith model has been developed to validate the hypothetical reaction pathway of NO reduction by H2. The short monolith model allows us to include both mass transfer and detailed chemistry describing the adsorption, desorption, storage and surface reaction steps for the various species. The calculated selectivities to N2O, N2, and NH3 as functions of feed composition and temperature at steady state are compared with experimental findings. Transient study for cycling NOx trap operation will also be discussed.

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