NO x storage and NO oxidation experiments have been carried out on a model Pt/BaO/Al 2 O 3 catalyst powder in order to elucidate kinetic and thermodynamic limitations. Uptake of NO on a pre-oxidized catalyst reveals the existence of multiple regimes. The short-term storage is a sensitive function of storage time, but is nearly independent of temperature whereas the long-time storage has much slower kinetics and is a non-monotonic function of temperature. A simple steady-state reactor model is developed that predicts NO oxidation conversion and the limiting NO x storage. The model predicts that full barium utilization is thermodynamically feasible even under kinetically limiting conditions of incomplete NO oxidation. However, apparent NO x diffusion limitations prevent complete utilization. Storage and reduction (with propylene) experiments indicate that less than 10% of the barium is needed to achieve high NO x conversion (>85%) at moderate space velocity. At higher temperature both NO oxidation and barium nitrate formation are thermodynamically limited, both of which adversely impact the NO x reduction. Thermogravimetric measurements corroborate a physical picture in which only a small fraction of barium is utilized during lean/rich cycling protocols giving high NO x conversion.