The NOx storage and reduction functions of a Pt-Ba/Al2O3 "NOx storage-reduction" catalyst has been investigated in the present work by applying the transient response and the temperature programmed reaction methods, by using propylene as the reducing agent. It is found that: (i) the storage of NOx occurs first at BaO and then at BaCO3, which are the most abundant sites following regeneration of catalyst with propylene; (ii) the overall storage process at BaCO3 is slower than at BaO; (iii) CO2 inhibits the NOx storage at low temperatures; (iv) the amount of NOx stored up to catalyst saturation at 350degreesC corresponds to 17.6% of Ba; (v) the reduction of stored NOx groups is fast and is limited by the concentration of propylene in the investigated T range (250-400degreesC); (vi) selectivity to N-2 is almost complete at 400degreesC but is significantly lower at 300degreesC due to the formation of NO which can be tentatively ascribed to the presence of unselective Pt-O species.