This work investigated the nitrous oxide (NOx) storage process using alumina-based catalysts (K2O/Al2O3, CaO/Al2O3, and BaO/Al2O3). The feed was a synthetic exhaust gas containing 1,000 ppm of nitrogen monoxide (NO), 1,000 ppm i-C4H10, and an 8% O2 and N2 balance. The catalyst was carried out at temperatures between 250–450°C and a contact time of 20 minutes. It was found that NOx was effectively adsorbed in the presence of oxygen. The NOx storage capacity of K2O/Al2O3 was higher than that of BaO/Al2O3. The NOx storage capacity for K2O/Al2O3 decreased with increasing temperature and achieved a maximum at 250°C. Potassium loading higher than 15% in the catalyst negatively affected the morphological properties. The combination of Ba and K loading in the catalyst led to an improvement in the catalytic activity compared to its single metal catalysts. As a conclusion, mixed metal oxide was a potential catalyst for de-NOx process in meeting the stringent diesel engine exhaust emissions regulations. The catalysts were characterized by a number of techniques and measurements, such as X-ray diffraction (XRD), electron affinity (EA), a scanning electron microscope (SEM), Brunner-Emmett-Teller (BET) to measure surface area, and pore volume and pore size distribution assessments.