Novel Y₂O₃ Doped MnO _x Binary Metal Oxides for NO _x Storage at Low Temperature in Lean Burn Condition

Abstract

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 °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 °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.