An experimental study describes fast cycling NOx storage and reduction on a Pt/Rh/BaO/CeO2/Al2O3 monolith catalyst for emission control of lean burn vehicles. Comparison of the temporal dependence of the effluent composition when using H-2 and C3H6 as reductants enables an assessment of the mechanism. Involvement of a surface N-containing oxygenate pathway is indicated by the appearance of peaks of N2O, N-2, and CO2 during the rich to lean switch. Adsorbed intermediate reactivity measurements provide further evidence. m/e = 28 signal indicating thermal decomposition and oxidation of HC-intermediates under lean/rich/blank cycle of different durations. [GRAPHICS] .