Barium oxide-based NO, storage and reduction (NSR) catalysts with different amounts of potassium oxide were prepared to investigate the role of potassium oxide in the aspects of amount and strength of NO2 storage. The dispersion of barium and potassium oxides on alumina, the amount and state of NO2 stored on them, and the desorption profiles of NO2 from them were examined by XRD, N-2 adsorption, electrical conductivity measurement, XPS, Fr-IR and TPD techniques. Barium and potassium oxides were mainly loaded in the mesopores of the alumina and the NO2 was stored by being converted to nitrates. The alumina itself had a small capacity for NO2 storage, but the impregnation with potassium oxide increased the capacity. The co-loading of potassium oxide and barium oxide enhances the strength of the interaction between the storage material and NO2, shifting the desorption peak of NO2 to a elevated temperature. (C) 2007 Elsevier B.V. All rights reserved.