MnO (x) -Y2O3 binary metal oxide catalysts are synthesized by a constant-pH co-precipitation method, their ability of NO (x) storage capacity and absorbing process were investigated. The pure MnO (x) and Y2O3 calcined at 500 A degrees C for 4 h in static air are both of body-centre structure, while the binary metal oxides containing Mn and Y are mainly of amorphous phase. The adulteration of Y2O3 can remarkably improve the specific surface areas of the catalysts, which probably result of the enhancement on NO storage capacity and catalytic oxidation ability of NO at 100 A degrees C. The XPS results indicate that both Mn and Y have 3+ chemical states in the binary oxides. FT-IR spectra could be beneficial to explain the NO storage process on the binary metal oxide: NO can be adsorbed on the MnO (x) and Y2O3 sites as nitrates and nitrites, respectively, and then the nitrites on Y2O3 site are shifted to Mn2O3 site and then is oxidized to nitrates. As a result, the NO storage capacity is enhanced due to the adulteration of Y2O3, finally the NO (x) are adsorbed on the Mn2O3 site as nitrate species.