As an important approach to improve the fuel economy of lean-burn engines, cutting down the thermal loss will lower the exhaust temperature. In response to this technical challenge, the enhancement of the low temperature performance turns out to be an imperative issue with the NO
x storage and reduction (NSR) catalysts. Targeted at gaining technical information on upgrading practical NSR catalysts, NO
x storage reactions over a model NSR catalyst under a series of lean-burn exhaust atmospheres and a corresponding thermodynamic analysis were conducted in this research. It was found that, below 400°C, the residual reducing agents of CO and C
3H
6 in the lean gas reduced NO
2 to NO over the NSR catalyst; hence, the outlet NO
2 concentration fell lower than the value derived merely from thermodynamic equilibrium with NO oxidation reaction. With CO and C
3H
6 existing in the reaction atmosphere, it did not matter if NO
2 or NO was used as the inlet NO
x species; the outlet NO
2 concentration would turn out the same. Thus, the NO
x storage amount with NO
2 as an inlet NO
x species is approximately the same as that with NO. If no CO and C
3H
6 are present in the reaction atmosphere, the outlet NO
2 concentration equaled the thermodynamic equilibrium value with NO oxidation reaction, while an increase in the NO
x storage amount with NO
2 as an inlet NO
x species had been observed. These results indicated that the enhancement of NO oxidation to NO
2 and the removal of the residual reducing agents from the exhaust gas are both necessary for improving the NO
x storage performance at low temperatures.
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