Rare earth-doped copper-manganese mixed oxide catalysts were prepared by coprecipitation and mechanical mixing using copper sulfate,manganese sulfate,and rare-earth oxides REO(REO indicates La2O3,CeO2,Y2O3,or Pr6O11) as raw materials.The samples were characterized by X-ray diffraction(XRD),temperature-programmed reduction(TPR),temperature-programmed reduction of oxidized surfaces(s-TPR),and temperature-programmed desorption(TPD).Catalytic activities were tested for a water-gas shift reaction.Doping rare earth oxides did not alter the crystal structure of the original copper-manganese mixed oxides but changed the interplanar spacing,adsorption performance and reaction performance.Doping with La2O3 enhanced the activity and stability of Cu-Mn mixed oxides because of high copper distribution and fine reduction.Doping with CeO2 and Y2O3 also decreased the reduction temperatures of the samples to different degrees while improving the dispersion of Cu on the surface,thus,catalytic activity was better than that of undoped Cu-Mn sample.The Pr6O11-doped sample was difficult to reduce,the dispersion of surface coppers was lowered,resulting in poor activity.
The Cu-Mn catalysts doped with different amounts of lanthanum(La) for water-gas shift reaction(WGSR) were prepared, and characterized by X-ray diffraction(XRD), temperature-programmed reduction(TPR), temperature-programmed reduction of oxidized surfaces(s-TPR), temperature-programmed desorption of CO_2(CO_2-TPD), infrared spectrum(FT-IR) and X-ray photoelectron spectroscopy(XPS). Catalytic activities were tested for a water-gas shift reaction. The results showed that the introduction of 0.5 mol.% La could significantly improve the catalyst activity for low-temperature shift reaction compared with the undoped catalyst, which might be from the introduction of La making the Cu and Mn components distribute uniformly and the synergistic effect between Cu and Mn increasing the dispersion of Cu on the surface of the catalyst. The apparent CuO phases besides Cu_(1.5)Mn_(1.5)O_4 were found in the samples with at least 3.0 mol.% La content, and the basic sites increased with the increasing of La contents at a decreased rate. With excessive La doping, La particles would aggregate and cover some active sites, resulting in that Mn could not effectively inhibit the gathering together and growing up of Cu crystalline grain, and decreased the dispersion of Cu on the surface, which resulted in the poor activity of the catalyst for WGSR.
