Simultaneous removal of NOx and soot particulate from diesel exhaust by in situ catalytic generation and utilisation of N2O

One of the outstanding challenges in diesel exhaust catalysis is to integrate oxidation chemistry, soot filtration and NOx reduction in a single aftertreatment unit, while avoiding the need for fuel injection to regenerate the filter. Here we show that destruction of trapped soot can be initiated catalytically at 200 degrees C when its oxidation is coupled with non-selective NOx reduction (using NH3 as reductant), which acts as an in-situ source of N2O. In laboratory tests over an extended temperature range (up to 800 degrees C), using supported silver as a catalyst for both non-selective NOx-reduction and soot oxidation, the conversion of immobilised soot to CO2 can be resolved into four consecutive steps as the temperature rises: catalysed oxidation by N2O; non-catalysed oxidation by NO2; catalysed oxidation by O-2; non-catalysed oxidation by O-2. Initial engine tests indicate that the critical first step (C + N2O) can be replicated in a diesel exhaust.