Structure and redox properties of CexPr1-xO2-δ mixed oxides and their catalytic activities for CO, CH3OH and CH4 combustion

A series of CexPr1-xO2-sigma mixed oxides were synthesized by a sol-gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH3OH and CH4 on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO2 was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO2 crystal lattices. Raman bands at 465 and 1150cm(-1) in CexPr1-xO2-sigma samples are attributed to the Raman active F-2g Mode of CeO2. The broad band at around 570 cm(-1) in the region of 0.3 <= x <= 0.99 can be linked to oxygen vacancies. The new band at 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: PrO1.83 ->(530 degrees C)PrO1.61 ->(PrO1.5)-Pr-650 degrees C. The reduction temperature of CexPr1-xO2-sigma mixed oxides is lower than those of Pr6O11 or CeO2. TPR results indicate that Ce(x)Pri(1-x)O(2-sigma) mixed oxides have higher redox properties because of the formation of CexPr1-xO2-sigma solid solutions. The presence of the oxygen vacancies favors CO and CH3OH oxidation, while the activity of CH4 oxidation is mostly related to reduction temperatures and redox properties. (c) 2006 Elsevier B.V. All rights reserved.