A focused experimental study describes fast cycling NOx storage and reduction (NSR) with H-2 and C3H6 as reductants on a Pt/BaO/CeO2/Al2O3 lean NOx trap (LNT) catalyst for emission control of lean burn vehicles. The results provide insight and deeper understanding of the impact of cycle frequency on the LNT performance and underlying NSR mechanism, with particular focus on whether a new NOx reduction pathway emerges when hydrocarbon reductant is used. Differentiation is made between two NOx conversion enhancement mechanisms-the conventional NSR mechanism with improved NOx storage utilization and a hydrocarbon-intermediate mechanism. A comparison of cycle-average NOx conversion using H-2 and C3H6 as reductants at the same lean/rich stoichiometry level provides revealing information. Both aerobic + anhydrous and anaerobic + anhydrous propylene-containing feeds enable an estimate of the contribution of H-2-generating water-gas shift and propylene steam reforming. The observed NOx conversion enhancement of up to 45% (absolute) with 10 x faster cycling is nearly independent of reductant type and is attributed to improved NOx storage utilization. Exothermic heat effects with temperature rise as high as 275 degrees C and significant temperature spatial gradients are encountered with H-2 during slow cycling, which makes H-2 an unexpectedly less effective reductant than C3H6. The hydrocarbon-intermediate pathway is shown to be responsible for a smaller fraction of the NOx conversion enhancement encountered during fast cycling. (C) 2018 Elsevier Ltd. All rights reserved.