The effects of temperature and amount of stored NOX on the performance of Rh/Ba/Al2O3 for a NOX storage and reduction catalyst were studied by spatially and temporally resolved operando X-ray absorption spectroscopy. By simultaneously analyzing the spatial distribution of the oxidation state of Rh in the catalytic reactor, and the concentration profile of the outlet gas, it was found that the NOX conversion rate was reduced by three factors: 1) an inadequate number of vacant NOX storage sites in the catalyst when the amount of stored NOX was too high, 2) a lower reduction rate for Rh oxide at lower temperature and 3) a higher decomposition rate for stored NOX at higher temperature. Therefore, the NSR catalyst should be employed at a moderate temperature, at which the reduction rate for Rh oxide is sufficiently high and the decomposition rate for stored NOX is sufficiently low. In addition, the amount of stored NOX should be controlled in order to maintain vacant storage sites in the catalyst.