Study of the redox behaviour of high surface area CeO 2–SnO 2 solid solutions

Abstract

Molten alkali metal nitrites or nitrates and co-precipitation methods were used to prepare CeO 2, SnO 2 and Ce 0.5Sn 0.5O 2 solid solutions with high surface areas. In the case of the single oxides prepared by the molten salt method, the use of KNO 3 leads to better crystallised solids than with KNO 2, but on the opposite with higher particle sizes and lower BET surface areas. The same effect was observed for the preparation of the mixed oxides with different resulting structures. With KNO 3, the mixed oxide appears as a mechanical mixture of the single oxides, whereas with KNO 2, a mixture of amorphous SnO 2 and of solid solution with a specific surface area (SSA) of 100 m 2 g −1 has been synthesised, but without evidence of Ce 2Sn 2O 8 pyrochlore formation. The solid prepared by co-precipitation is also well dispersed. Its amorphous structure by X-ray diffraction (XRD) analysis does not allow to conclude to the formation of a solid solution. TPR experiments with hydrogen have shown a beginning of reduction at lower temperature in presence of the solid solution compared to the mechanical mixture of the single oxides. An improved reducibility was also observed with the oxide prepared by co-precipitation, which is in favour of a solid solution formation also in this case. Therefore, the resulting hydrogen consumption obtained when reducing the solid solutions at 450 °C is very high and the oxygen storage capacities (OSCs) reach about 1 mmol O 2 g −1, value higher than those obtained with ceria-zirconia solid solutions. The OSC values were confirmed by oxygen chemisorption on the reduced solid between 25 and 450 °C. The full recovery of the initial solid solution was shown by XRD analysis and a second redox cycle has demonstrated the reversibility of the redox properties at this temperature.