Effect of soot on the storage-reduction performances of PtBa/Al2O3 LNT catalyst

The effect of soot on the storage-reduction performances of a PtBa/Al2O3 catalyst is investigated in this work. It is found that the presence of soot reduces the NOx storage capacity of the catalyst, evaluated in presence of water and CO2 in the feed stream in the range 200–350 °C and with different values of the NO inlet concentration. Besides the presence of soot favors the decomposition and the reduction of the stored nitrates, while soot is being oxidized. A direct reaction between the stored nitrates and soot is suggested, that has been explained on the basis of the surface mobility of the adsorbed nitrates. This soot oxidation pathway involves surface species and parallels the NO2-soot oxidation that occurs in the presence of gas-phase NO2. Finally, the presence of soot does not influence appreciably the behavior of the PtBa/Al2O3 catalyst in the reduction by H2 of the stored nitrates: in all cases N2 is the main reaction product and ammonia is observed in minor amounts.