Room temperature adsorption and temperature programmed desorption (TPD) of NO, NO with O2, and NO after NO2 saturation were investigated for Na/Y, Na/ZSM5, Cu/ZSM5 and SiO2 gel. The adsorbates were characterized by TPD, using mass spectrometry to identify the desorbed molecules. In the presence of O2, the adsorption of NO and NO2 is non-additive; co-desorption of nearly equal amounts of NO and NO2 takes place suggesting the formation of a complex with an overall composition N2O3 within the zeolite. Since SiO2 gel does not adsorb NO nor NO2, the adsorption capacity of the zeolites is a function of their specific structure. The oxidation of NO to NO2 is catalyzed by Na/Y and Na/ZSM5.