Understanding the role of C3H6, CO and H2 on efficiency and selectivity of NOx storage reduction (NSR) process

The NOx storage reduction (NSR) process is commonly envisaged for the NOx treatment of exhaust gas from lean-burn engine vehicles. NOx are firstly stored on the catalyst, which is periodically submitted to a reducing mixture for few seconds in order to reduce the stored NOx into N2. The on-board reducer is coming from the gasoline/diesel fuel and, in fact, the NSR catalyst is submitted to a mixture of hydrocarbons, CO and H2 with various compositions depending on the lean/rich step. In this study, the influence of each reducer (C3H6, CO and H2) is evaluated separately, with a special consideration to the N2O selectivity. It is demonstrated that the N2O can be emitted during both lean and rich periods, with varying ratio depending on the considered reducer and the temperature of gas. For instance, at 300 °C, a high N2O selectivity is observed when C3H6 is used, and near half of the N2O emission occurs during the storage phase in lean condition.

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► N2O emission during the NSR process depends on the used reducer(s) (C3H6, CO, H2) and the temperature.
► Using complex mixtures, near half of N2O can be produce during the lean periods over a Pt/CZ catalyst.
► At 300 °C, the N2O is attributed to (i) CO ≥ C3H6 > H2 for the rich periods, and (ii) C3H6 > H2 > CO (≈0) for the lean periods.
► Finally, most of the N2O at 300 °C is attributed to C3H6, whereas the role of H2 is predominant at 200 °C.