The effect of calcination temperature on the oxygen storage and release properties of CeO2 and Ce-Zr-O metal oxides modified by phosphorus incorporation

The present work reports on the effects of calcination temperature (Tc) on the oxygen storage and release properties of CeO2 and Ce0.8Zr0.2O2 solids deliberately contaminated with CePO4. Pulsed-feed and stepped-feed dynamic OSC, 18O2 temperature programmed isotopic exchange (TPIE), and 18O2 transient isothermal isotopic exchange experiments were conducted in order to investigate the alteration of the OSC process by the applied Tc. The characterisation of the solids calcined at a low temperature (ca. 873 K) by XRD, Raman and XPS confirms the presence of CePO4 crystallites covering to a large extent the surface of the solid metal oxides. However, calcination at a higher temperature (ca. 1273 K) results in the sintering of the crystallites of the metal oxides and CePO4, the sintering of the latter being more intense. This sintering effect causes the rearrangement of the surface of CeO2 and Ce0.8Zr0.2O2 solids giving rise to the partial uncovering of it from CePO4. The OSC properties of all P-contaminated solids were found to be largely worse than the corresponding ones of P-free solids due to the presence of CePO4 in the surface/subsurface region of the former solids. However, the OSC properties of the phosphated Ce0.8Zr0.2O2 solid were partially recovered after calcination in air at 1273 K. This effect was not observed in the case of CeO2 and it must be related to the surface/subsurface reorganization of the solid driven by calcination at 1273 K, and also to the intrinsic OSC properties of Ce0.8Zr0.2O2 solid. Therefore, CexZr1−xO2 solid solutions appear to be excellent oxygen storage materials for commercial TWC applications and their OSC properties display an enhanced resistance against P-deterioration compared to those of pure CeO2.