An intensive in situ and operando IR study on NOx adsorption over potassium (K) loaded zirconia-titania NSR catalyst in comparison to a barium (Ba) loaded one is reported. Based on in situ IR experiments, NOx adsorption under heated environment was confirmed to favor potassium bidentate nitrate species rather than ionic nitrate species observed for Ba-loaded NSR catalyst (previously published). Complementary operando IR experiments revealed different mechanisms for NO adsorption over the two NO storage materials (NSMs): initial simultaneous NO3- and NO3- formation over K loaded catalyst while over Ba-loaded one, NO2- is first accumulated before being converted to NO3-. Isotopic labelling in combination with operando experiments identified distinct dynamic behaviors regarding the exchange between nitrogen containing species on surface and in gas phase. This work provides beneficial inputs for advanced catalyst converter design, for example with zone-coated washcoat that contains more than one catalyst formulations.