CeO2 promoted with either 1 wt% Pt or 1 wt% Pd was evaluated as a model system for passive NO (x) adsorber applications. According to NO (x) storage experiments conducted over the temperature range 80-160 A degrees C, promotion with Pt resulted in higher NO (x) storage efficiencies than for the Pd-promoted material. However, for NO (x) storage at 80 and 120 A degrees C, the latter released more NO (x) below 350 A degrees C during temperature-programmed desorption in relative and absolute terms, the Pt analog releasing most of its stored NO (x) above 350 A degrees C. DRIFT spectra showed that the use of Pd leads to preferential adsorption of NO (x) in the form of nitrites, while predominately nitrate formation is observed over the Pt promoted material. Overall, the use of Pd promoted CeO2 is preferred for low temperature NO (x) storage and release due to its ability to store NO (x) as thermally labile nitrites.