Ce0.4IIICe0.6IVAlO3.3 – an unexpected product of a solid state reaction in the CeO2–Al2O3 system†
Abstract
Phase transformations in the highly dispersed CeO2–Al2O3 system subjected to heating under reducing and oxidizing atmospheres were studied by HRTEM, EDX, XRD, ICP, TPR and magnetic susceptibility measurements. It has been found that the nanocrystalline CeIIIAlO3 phase with a hexagonal structure appearing in the system during reduction in H2 at 850 °C transforms upon oxidation at 175–200 °C into a similar hexagonal phase with structural formula Ce0.4IIICe0.6IVAlO3.3. The Ce0.4IIICe0.6IVAlO3.3 phase is unstable in air above 600 °C and decomposes to nanocrystalline CeO2 and alumina. Reduction in hydrogen at 700 °C transforms the Ce0.4IIICe0.6IVAlO3.3 back to hexagonal CeIIIAlO3, which at 1000 °C (in hydrogen flow) recrystallizes into the well-known, tetragonal CeAlO3. The red–ox behaviour of the hexagonal CeAlO3 is compared with that of CeO2 and the possible implications for catalysis are discussed.