NOx Storage and Reduction (NSR) conducted at higher cycling frequency enables enhanced conversion of NOx emitted by lean burn gasoline and diesel vehicles. Ting et al. (2018) reported data using a Pt/Rh/BaO/CeO2/Al2O3 showing that stored NOx utilization is primarily responsible for enhanced NOx conversion during fast cycling. In this study a low-dimensional, two-phase monolith reactor model comprising a network of reactions with global kinetics using C3H6 as the reductant is developed. Kinetic parameters not available from the literature are estimated through a fit of NSR with conventional cycling and anaerobic rich feed devoid of CO2 and H2O, while the model is validated for NSR spanning a range of cycle times for a rich feed containing CO2 H2O, and O-2. The model predicts most of the data features, including transient and cycle-averaged species concentrations and temperature. The model elucidates differences between C3H6 and H-2 during both conventional and fast cycling. For example, the higher NOx conversion obtained with C3H6 during conventional cycling is a result of a higher temperature rise with H-2 which adversely impacts NOx storage, while the higher conversion obtained during fast cycling is attributed to the faster diffusional flux of H-2, which results in a larger fraction of NOx released during the rich feed ("NOx puff"). The reaction network includes a two-step HC-intermediate pathway involving vinyl isocyanate (C2H3NCO) as the proposed surface intermediate. This pathway predicts the observed double peaks of N-2, while requiring substantially more C3H6 to reduce stored NOx to N-2. As a result, the vinyl isocyanate pathway is shown to be less efficient than the conventional NSR pathway.