ABSTRACT
Pt), an adsorbent (e.g., barium oxide, BaO), and a reduction
catalyst (e.g., Rh).
The adsorption process involves two steps, as repre-
sented by Eqs. 6 and 7, which occur during normal lean
engine operation. NOx emissions from the diesel engine are
typically composed of 90-95% nitric oxide (NO). In the
first step, the nitric oxide reacts with oxygen on active
oxidation catalyst sites to form NO2. The second step
involves adsorption of NO2 by the storage material in the
form of an inorganic nitrate.[5] When the engine runs under
excessive fuel conditions or at elevated temperatures, the
nitrate species become thermodynamically unstable and
decompose, producing NO or NO2, according to Eqs. 8
and 9. Under rich conditions, the released NOx is converted
to N2 by the reductant, such as CO, H2, or HC, over the
reduction catalyst (e.g., Rh), represented by Eq. 10.
