Calcination of a Pt/Ba/CeO2 catalyst at 700 degrees C and subsequent reduction in hydrogen, carbon monoxide or propene at 350-550 degrees C resulted in a considerable improvement of its NO (x) storage-reduction (NSR) properties compared to those of a freshly prepared Pt/Ba/CeO2 catalyst. This behavior is traced back to the temporary formation of BaPtO3 perovskite which leads after reduction to well-distributed Pt particles in intimate contact with the barium-containing phases. The oxidation and reduction of platinum is reversible which can be exploited for the design of "self-regenerating" NSR-catalysts under lean (> 600 degrees C) and rich (> 400 degrees C) reaction conditions. The formation of the BaPtO3-perovskite may not only be interesting for NSR-catalysis, but generally for Pt-based catalysts where a high dispersion of Pt is important.