In this paper, the effect of CO2 and H2O on NOx storage and reduction over a Pt–Ba/¿-Al2O3 (1 wt.% Pt and 30 wt.% Ba) catalyst is shown. The experimental results reveal that in the presence of CO2 and H2O, NOx is stored on BaCO3 sites only. Moreover, H2O inhibits the NO oxidation capability of the catalyst and no NO2 formation is observed. Only 16% of the total barium is utilized in NO storage. The rich phase shows 95% selectivity towards N2 as well as complete regeneration of stored NO. In the presence of CO2, NO is oxidized into NO2 and more NOx is stored as in the presence of H2O, resulting in 30% barium utilization. Bulk barium sites are inactive in NOx trapping in the presence of CO2·NH3 formation is seen in the rich phase and the selectivity towards N2 is 83%. Ba(NO3)2 is always completely regenerated during the subsequent rich phase. In the absence of CO2 and H2O, both surface and bulk barium sites are active in NOx storage. As lean/rich cycling proceeds, the selectivity towards N2 in the rich phase decreases from 82% to 47% and the N balance for successive lean/rich cycles shows incomplete regeneration of the catalyst. This incomplete regeneration along with a 40% decrease in the Pt dispersion and BET surface area, explains the observed decrease in NOx storage.