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−δ 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 1150 cm−1 in CexPr1−xO2−δ samples are attributed to the Raman active F2g 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 °CPrO1.61⟶650 °CPrO1.5. The reduction temperature of CexPr1−xO2−δ mixed oxides is lower than those of Pr6O11 or CeO2. TPR results indicate that CexPr1−xO2−δ mixed oxides have higher redox properties because of the formation of CexPr1−xO2−δ 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.

Pr3+ can be introduced into the CeO2 crystal lattices to form solid solutions with lattice defects. The band around 570 cm−1 in CexPr1−xO2−δ mixed oxides can be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The presence of the oxygen vacancies favors CO oxidation and CH3OH, while the activity of CH4 oxidation is mostly related to reduction temperatures and redox properties. Figure optionsDownload as PowerPoint slide