An in-situ DRIFTS study was conducted on a 2.13%Pt/20%Ba/Al2O3 monolith and it was found that NOx is mainly stored in the form of bulk barium nitrates at 300°C. Very little of the NOx was stored on the alumina support due to the high surface coverage of barium. While saturating the catalyst at 150, 225, and 300°C with a mixture of 376 ppm NO2 and 12% O2, an apparent activation energy for the formation of barium nitrates was calculated to be 28 kJ mol-1. After completing storage/reduction cycles with NO2/O2 and NO2, it was found that the amount of NOx stored was 5% lower in the absence of oxygen. The same change was found through reactor experiments on the monolith. At 300°C, a gas mixture of 376 ppm NO/12% O2 forms barium nitrates and nitrites at the beginning of capture. However, the nitrites are oxidized to nitrates at later capture times. As the temperature is decreased, nitrites become a more prevalent surface species until at 150°C they are the main storage species. It was found that the DRIFTS response factor for barium nitrates was 1.4 times larger than for barium nitrites. When 5% CO2 was added to the storage/reduction cycles from 150°C to 300°C, barium carbonates were formed with their stabilities dependent on temperature. The addition of 5% H2O lowered the amount of NOx stored by forming hydroxyl groups on barium at all temperatures. More specifically, the addition of 5% H2O at 300°C to a lean phase with 376 ppm NO2/12% O2 lowered storage by 11% calculated from DRIFTS experiments and 5% calculated from reactor experiments. Similar results will also be presented on monoliths with varying barium loadings. More specifically, 1.87%Pt/8%Ba/Al2O3 and 1.79%Pt/4%Ba/Al2O3 monoliths will be studied.