Effects of periodic switching between lean and rich combustion conditions on CO, HC and NOx conversion on a monolithic catalyst with NOx storage were simulated by mathematical model. The model includes description of oxygen and NOx storage on the washcoat. Parametric study showed possibility to reach much improved time-averaged NOx conversion on a single monolith in comparison with steady-state operation, but lower CO and HCs conversions under reducing (rich) conditions. Sequence of monoliths, the first one with NOx storage catalyst and the second one with oxidizing catalyst, then enables to obtain satisfactory conversions of all pollutants.