DFT Study The Effect Of Alkaline Earth Doping On The Oxygen Storage-Release Properties Of Ceria

The effects of alkaline-earth doped ceria-based oxides on the oxygen migration and structure is studied by density functional theory (DFT) and dynamic oxygen storage capacity (DOSC).Theoretical study using Density Function Theory (DFT) and Linear Synchronous Transit (LST) methods shows that the dopants could introduce large effects on the structure in the bulk and the activation energy for oxygen migration. The calculation indicates the larger activate energy for Ce3MgO6 and the smaller activate energy for Ce3CaO6 and Ce3SrO6, compared to that of Ce4O7. The experiment of Dynamic OSC also gives the similar results. Ce0.67Zr0.33M0.01O2.01 (M=Ca, Sr) compounds improve the performance of Dynamic OSC (DOSC) compared with Ce0.67Zr0.33O2. In contrast, Mg-doped material presents an abnormal decline of DOSC after the deep reduction/mild oxidation treatment. The surface structures identified by Raman spectroscopy is also used to explain the observed DOSC performance. The results imply that bulk oxygen play a major role in influencing DOSC as well.The DFT calculation certificates that the MgO doped ceria induces the smaller lattice parameter and the contraction of crystal cell which narrowed the oxygen migration channel. The oxygen migration will more difficult during the reduced MgO-CeO2 mixed oxide. The doping of CaO and SrO facilitates the oxygen migration, because the ion radiuses approach the doping radius for ceria. The slightly expansion of crystal cell of reduced CaO-CeO2 and SrO-CeO2 weaken the stress which inhibit the transition betweenγ-Ceria andα-Ceria.The electronic properties of Alkaline-earth doped ceria are also groped for. The CaO and SrO doping increases the iconicity and decrease the covalent properties for ceria. The 5p band of cerium cation is broadened and the electronic density is thinned because of the interaction among cerium cation, oxygen ion and alkaline-earth cation. The alteration of electronic properties makes the redistribution of electronic more easily which favored the oxygen ion migration during the ceria-based oxides.