The effect of C(s) on the trapping of NOx onto Pt/Ba/Al2O3 catalysts

Pt/BaO/Al2O3 catalysts react with NO/O2 mixtures to form barium nitrites and nitrates. In the presence of small amounts of C(s) admixed with the catalyst the concentrations of NOx adsorbed is considerably reduced and the stability of the stored NOx is decreased. These results suggest that there are important implications for any attempts to combine NSR and particulate combustion systems within a single catalytic system. Furthermore, it is clear that there are significant concentrations of mobile NOx species present in the environs of the NOx trap prior to fixation on BaO, i.e. the transfer between NO2 formed on the Pt component of the trap and the “fixed” NOx in Ba(NO3)2 involves significant concentrations of gaseous or surface mobile NO2.

Research highlights▶ Soot prevents NSR traps from performing optimally. ▶ Less NOx is trapped. ▶ Stored NOx is less stable. ▶ The effect is seen at very low levels of soot. ▶ NO2 is mobile before being trapped on an NSR trap.