Textural-structural Properties And Reactivity Under Inert And Reducing Conditions Of La2o3-modified Α-al2o3

Résumé: A series of samples, noted Al1–x La x (where x = weight composition of La) has been prepared by hydrolysis, in neutral medium from Al2O3 and La2O3. These samples were calcined under air at 700 °C then characterized by specific surface area (BET), X-ray diffraction (XRD), thermoreduction programmed under H2 (TPR-H2), thermogravimetry (TG) and differential thermal analysis (DTA). For Al1La0, the surface specific area shows a very light increase of 6–7% which could be due from water molecule physisorbed, after calcination and degasification during measurement. XRD patterns recorded on Al1La0 shows that Al2O3 is in alpha form. For α-Al2O3 modified with lanthana, spectra revealed the change of La2O3 to La(OH)3 during its hydrolysis. These results are in perfect agreement with those of thermogravimetry and thermoreduction. The overall hydrogen consumption appears greater for samples modified with lanthana. For lanthana-alumina samples, a weak and broad signal appears near 425–432 °C likely reflecting La(OH)3 surface reduction process. A broad and intense signal arises above 600 °C increasing in intensity with the lanthana content with a sharp shift to higher temperature ascribed to the bulky reduction La(OH)3. The TG-DTA analysis under argon shows that volatile specie as water of hydration is eliminated at 100 °C, dehydroxylation of La(OH)3 to LaO(OH) in the range of 300–350 °C and formation of La2O3 around 500 °C.

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