Interaction between soot and stored NOx during operation of LNT Pt–Ba/Al2O3 catalysts

The interaction of soot with nitrates stored on a model PtBa/Al2O3 LNT catalyst sample is here investigated under realistic conditions, i.e. upon lean/rich cycling in the presence of water and CO2. The presence of soot inhibits the NOx storage capacity of the catalyst during the lean phase at different temperatures, in the range 200–350 °C, but does not affect significantly the regeneration process of the stored nitrates. Simultaneously with the NOx storage, soot is converted to CO2 at temperatures above 300 °C. Soot is oxidized by NO2 formed by NO oxidation on Pt sites, but the participation of the stored nitrates in the soot oxidation is also likely, as pointed out by TPD/TPO experiments showing the occurrence of a surface reaction involving soot and the stored nitrates.