Characterization and Preparation of Ce_xPr_(1-x)O_(2-δ) Mixed Oxides and the Catalytic Activity for CO and CH_4

A series of CexPr1-xO2-δ mixed oxides were synthesized by the sol-gel method and characterized by Raman and XRD techniques. The results show that when x value is changed from 1:0 to 0.5, only a cubic phase CeO2 appears. The samples are very well crystallized on decreasing x from 0.50 to 0.99. It can be explained to form an ordered array of O vacancies caused by the insertion of Pr atom completely into the CeO2 crystal lattice. For CexPr1-x02-δ samples 465cm-1 and 1150cm-1 Raman peaks are attributed to the Raman active F2g mode of CeO2. The broad peak at about 570cm-1 in the region 0.3≤x≤0.99 can be linked to lattice defects resulting in oxygen vacancies. The new band at about 195cm-1 may be attributed to the asymmetric vibration that is caused by the formation of oxygen vacancies. TPR profiles of Pr6O11 and CeO2 have two reduction peaks respectively. The reduction process of Pr6O11 is: PrO1.83 PrO1.83→αPrO1.61 →β PrO1.5; For CeO2, the peak of low temperature attributed to the reduction of the surface oxygen of CeO2, the peak of high temperature attributed to the reduction of bulk CeO2. The reduction peak temperature of CexPr1-xO2-δ mixed oxides is lower than that of Pr6O11 and CeO2, which indicates that the formation of CexPr1-xO2-δ solid solutions improves the reductionoxidation behavior. The activity of CexPr1-xO2-δ for CO oxidation indicates that the existing of the oxygen vacancies favors CO oxidation; while the activity of CH4 oxidation is related to the temperature and the area of the reduction-oxidation peak.