Flame-made nanocrystalline ceria/zirconia doped with alumina or silica: structural properties and enhanced oxygen exchange capacity

Silica- and alumina-doped nanocrystalline ceria/zirconia (Ce0.5Zr0.5O2) were prepared in one step by flame-spray pyrolysis. Structural and textural properties were characterized using high-resolution electron microscopy, nitrogen adsorption and X-ray diffraction. Oxygen exchange capacity was studied by pulse thermal analysis using H-2 as reducing agent. Adding silica (up to 20 wt%) or alumina (up to 16 wt%) altered the particle morphology from polyhedral to spherical particles. In doped ceria/zirconia, the oxygen exchange capacity (OEC) was affected by the silica content but very little by the alumina content. The highest OEC (450 mmol O-2 kg(-1)) was measured for ceria/zirconia doped with 3 wt% silica, whereas for flame-made ceria/zirconia (360 mmol O-2 kg(-1)) and corresponding precipitated silica-or alumina-doped materials the OEC was considerably lower. For high dopant contents (20 wt% silica) an amorphous layer was formed on top of a crystalline core. This layer acted as a diffusion barrier, so that the OEC dropped to about 76 mmol O-2 kg(-1).