The Study Of Preparation, Characterization And Catalytic Activity For Ce_xPr_1-xO_2-δ Mixed Oxides

1, A series of Ce_xPr_1-xO_2-δ solid solutions calcined at 500 ℃ were synthesized by a sol-gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO and CH₄ over these mixed oxides was investigated. When the x value was changed from 1.0 to 0.8, only a cubic phase CeO₂ was observed. The samples were very well crystallized in the x range from 0.99 to 0.80. This is due to the formation of solid solutions caused by the insertion of Pr completely into the CeO₂ crystal lattices. Raman bands at 465 cm^-1 and 1150 cm^-1 in Ce_xPr_1-xO_2-δ samples are attributed to the Raman active F_2g mode of CeO₂. The broad band around 570 cm^-1 in the region 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at about 195 cm^-1 may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies.. The TPR profile of Pr₆O₁₁ shows two reduction peaks and the reduction process is followed:PrO_1.83→|(530℃) PrO_1.61 →|(650℃)PrO_1.5. The reduction peak temperature forCe_xPr_1-xO_2-δ mixed oxides is lower than that for either Pr₆O₁₁ or CeO₂. TPR results indicate that Ce_xPr(1-x)O_2-δ mixed oxides have higher redox properties because of the formation of Ce_xPr_1-xO_2-δ solid solutions. The presence of the oxygen vacancies favors CO and methanol oxiidation, while the activity of CH4 oxidation is mostly related to reduction temperatures and redox properties.2, A series of Ce_xPr_1-xO_2-δ mixed oxides calcined at 900 ℃ were synthesized by sol-gel method and characterized by XRD, Raman, XPS, O2-TPD techniques. When x value was changed from 1.0 to 0.5, only a cubic phase CeO₂ was observed. The samples were very well crystallizedon decreasing x from 0.50 to 0.99. For CexPri_xO2-5 samples 465 cm'1 and 1150 cm"1 Raman peaks are attributed to the Raman active F2g mode of CeO2. The broad peak at about 570 cm"1 in the region 0.3 < x < 0.99 can be linked to lattice defects resulting in oxygen vacancies. The new band at about 195 cm"1 may be attributed to the asymmetric vibration caused by the formation of oxygen vacancies. The results of XPS experiment reveal that the Pr atom is richer in the surface of the solid solutions. On the basis of the changes of I570/I465 intensity from the content of Ce atom, it can be presume that the mixed oxide is composed of a richer Pr solid solution layer in the surface and a richer Ce solid solution layer in the bulk. As the increasing of the Ce content the thickness of the surface layer decreases. The result of O2-TPD and TPR experiment indicates that the formation of solid solution have elevation the stabilization and redox capability. Calcination temperatures had great effect on the peak intensityfor CeO2 but less effect on Ceo.8Pro.202.5 in Raman spectra. It might be due to the transformation of the colors for the mixed oxides, the insertion of Pr atom into the ceria lattice could enhance the sintering resistance and thermal stability of the mixed oxides.3 n Ceo.8Zr0.202 supported Ag-Pd catalysts have been prepared by the impregnation method and characterized by ethanol-TPD, CO-TPD and XRD. The effect of different impregnation sequences on catalytic activity for ethanol and CO oxidation has been investigated. The experimental...