Structural and Textural Modifications of ZrO2 Induced By La2O3 Addition, Thermal Treatment and Reducing Process

• Published in: Journal of structural chemistry 2018-03, Vol.59 (2), p.474-481
• Main Authors: Aribi, K., Ghelamallah, M., Bellifa, A., Granger, P., Choukchou-Braham, A.
• Format: Article
• Language: English
• Subjects: Atomic; Atomic structure; Atomic/Molecular Structure and Spectra; Catalysis; Chemical Sciences; Chemistry; Chemistry and Materials Science; Heat treatment; Inorganic Chemistry; Lanthanum; Lanthanum oxides; Mixed oxides; Molecular; Optical and Plasma Physics; Physical Chemistry; Reduction; Roasting; Scanning electron microscopy; Sintering; Solid State Physics; Specific surface; Surface area; X-ray diffraction; Zirconium dioxide; Zirconium oxides
• ISSN: 0022-4766; 1573-8779
• DOI: 10.1134/S0022476618020312

Lanthana-doped zirconium oxide may strongly influence the solid state reaction. A series of samples denoted Zr x La 1– x (where x = atomic percentage of the element) are prepared by hydrolysis in the neutral medium from ZrO 2 and La 2 O 3 . These samples are calcined under air at 450 °C, 900 °C, and 1200 °C, then characterized by specific surface area (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermoreductions programmed under H 2 (TPR–H 2 ). The results show that after calcination at 450 °C, the lanthanum addition increases slightly the zirconia surface area and the XRD analysis does not reveal any interaction between two oxides. After calcination at 900 °C, sintering appears and oxides lose half of their surface area. Lanthanum is not inserted into the structure of ZrO 2 , while some interaction occurs between lanthanum and zirconium oxide. At 1200 °C, the sintering of the samples is very important; the specific surface is about 1 m 2 /g –1 ; XRD results show that Zr x La 1– x are formed basically by three mixed oxides: La 2 Zr 2 O 7 , La 0.5 Zr 0.5 O 1.75 , La 0.46 Zr 0.54 O 1.77 , which is confirmed by the SEM method. H 2 -TPR experiments confirm that changes in the reducibility can reflect some alterations of the nature of interactions between ZrO 2 and La 2 O 3 . Preliminary experiments on zirconia do not reveal the occurrence of significant reduction processes. On the other hand, extensive reduction of La 2 O 3 is much more accentuated for lanthana samples. At high temperatures, a significant lessening in the H 2 consumption suggests that ZrO 2 would likely interact with La 2 O 3 , which is confirmed in the results indicating the presence of the pyrochlore type of oxides mentioned above.