Non-isothermal NOx storage/release over manganese based traps: mechanistic considerations

The NO storage properties of MnOx/support materials (5–50 wt% MnOx loading) was experimentally investigated in the presence of O2 and H2O between 50 and 700 °C applying a non-isothermal temperature-programmed method. In dependence on MnOx loading and NO supply, the materials show an intermediate decrease of NO storage capacity between 200 and 300 °C. This effect is caused by decomposition of surface nitrites with release of NO into the gas phase as proved by in situ DRIFT measurement. The interpretation is corroborated by modelling of the underlying adsorption/desorption reaction steps, considering the different thermal stability of nitrite/nitrate surface species.