The thermal decomposition of bulk Ba(NO
3)
2, Ba(NO
3)
2 impregnated on γ-Al
2O
3, and the release of NO
2 stored on BaO/γ-Al
2O
3 are investigated by thermogravimetric analysis (TGA) and infrared spectroscopy (IR) as a function of baria loading. Two distinct weight loss events at
434 °C and ≥545 °C are observed on the γ-Al
2O
3 supported samples, corresponding to the decomposition of dispersed and bulk-like Ba(NO
3)
2 to BaO, respectively. Decomposition of dispersed phase having a temperature of 150 °C lower than bulk Ba(NO
3)
2 is attributed to a strong interaction between dispersed BaO and alumina. Bulk-like phase shows a similar decomposition characteristics to bulk Ba(NO
3)
2 as BaO loading increases to 31.8%. The decomposition products vary from predominantly NO
2 at low temperature (≤434 °C) to NO at high temperature (≥545 °C), consistent with the trend expected from the NO
2 ↔ NO + 1/2O
2 thermal equilibrium. As the total baria loading is increased, the amount of dispersed phase saturates at a baria loading of 14%(w/w) while the bulk-like phase increases without reaching saturation. Both phases can be regenerated on 15 min exposure of corresponding BaO/Al
2O
3 to NO
2 at room temperature. The release of these regenerated nitrates mimics the decomposition characteristics of impregnated Ba(NO
3)
2 on γ-Al
2O
3. X-ray powder diffraction and IR spectra show that the stored NO
2 species gradually convert to a crystalline, bulk-like Ba(NO
3)
2 phase when aged at room temperature. These results are useful for optimizing BaO loading strategies for lean NO
x trap catalyst.