In this study, fresh and laboratory-aged (rapid ageing hot in laboratory (RAHLAB)) Pd-Ba-OSC/Al 2O 3 and Pd-OSC/Al 2O 3-La 2O 3 catalysts were investigated. The effect of low barium content on the behaviour of the OSC material (Ce 1− x Zr x O 2 mixed oxides) was studied. The influence of the addition order of Ba, Pd, and OSC material in the catalyst washcoat was also examined. In a model reaction NO + CO, the catalytic activities and selectivities to N 2 and N 2O were analysed by the FT-IR technique. In addition, the effect of thermal ageing treatment on catalytic behaviour was investigated. The addition of barium was found to have several positive effects on the fresh Pd-Ba-OSC/Al 2O 3 catalysts. The catalytic activity (NO reduction by CO) was improved below the light-off temperature when barium was added into the catalyst. At 500 °C, the fresh catalysts were fully selective to N 2. The barium-containing catalysts had a bit higher dispersion values compared to the sample without barium. The high surface area over the fresh barium-containing catalysts could explain partly the improvements in the dynamic oxygen storage capacity (OSC). Besides, that the barium-containing catalysts were more active than the Pd/(OSC-La 2O 3-Al 2O 3) catalyst, it was also observed that the addition order of barium has an effect on the catalytic activity of fresh catalysts. The fresh (Pd-Ba-OSC)/Al 2O 3 and (Ba-Pd-OSC)/Al 2O 3 catalysts were more active than the Pd/(OSC-La 2O 3-Al 2O 3) catalyst. This indicates that the interaction of Pd, Ba, and OSC was better on these catalysts. For the aged catalysts, the addition order of Pd, Ba, and OSC had no obvious effect on differences in catalytic properties between Ba-containing samples. All the aged catalysts had high selectivities to N 2 at 500 °C. Characterisation results by XRD, chemisorption, and BET revealed that catalytic deactivation was occurring during the ageing process. This thermal deactivation was observed as a lower catalytic activity and a lower OSC compared to the fresh catalysts. The deactivation is due to the collapse of the surface area, sintering of Pd particles and solid–solid phase transitions observed in the bulk material. Therefore, Ba content (only ∼3 wt.%) in the catalyst was probably too small to stabilise the catalyst against sintering.