One approach to the remediation of NOx generated under lean automotive engine conditions is its controlled storage and then periodic release and reaction under enriched conditions. This process is being considered for automotive exhaust systems that will be operated pre–dominantly lean for reasons of fuel economy. Because of the special characteristics of alkali and alkaline earth elements in the presence of NOx, they are being considered for use, in conjunction with γ–alumina–based washcoats and precious metal catalysts, as NOx catalyst coatings on cellular supports.It is known that alumino–silicates will react with alkali and alkaline earth elements to form stable ceramic phases when mixtures of the components are held in direct contact at elevated temperatures. While reactions do occur both between the NOx adsorber components and the washcoat and between the NOx adsorber components and the substrate, their effect on the thermal–mechanical properties of actual NOx adsorber/catalyst systems were unknown. One of the purposes of this study was to age such systems under various conditions and measure the resulting change in properties.This study confirms that reactions do occur between cordierite and candidate NOx catalysts at moderate to high temperatures. However, the physical properties of strength, stiffness, and thermal expansion exhibit only modest changes even after very severe thermal treatments, suggesting such systems are thermal–mechanically durable for automotive applications.