Preparation and Characterization of Me₂O₃−CeO₂ (Me = B, Al, Ga, In) Mixed Oxide Catalysts. 2. Preparation by Sol−Gel Method

The present work focuses on the combination of ceria mixed with another oxide from group III, using the sol–gel method. B 2 O 3 − Al 2 O 3 − Ga 2 O 3 − or In 2 O 3 −CeO 2 mixed oxides have been prepared in order to improve the catalytic properties of these materials. The structural, textural, and surface properties of these catalysts have been fully characterized by means of a variety of techniques (Brunauer−Emmett−Teller, BET; X-ray diffraction analysis, XRD; Raman; scanning electron microscopy, SEM; thermogravimetric analysis, TG; and temperature-programmed reduction/oxidation, TPR-TPO). The highest surface area was achieved for the Al 2 O 3 −CeO 2 mixed oxide. Only the fluorite structure of CeO 2 was observed by XRD for all prepared mixed oxides; the presence of oxygen vacancies was proven by Raman spectroscopy. The acid–base properties were estimated by the adsorption of probe molecules (NH 3 and SO 2 ); two methods, microcalorimetry and X-ray photoelectron spectroscopy (XPS), have been employed for that purpose. All investigated mixed oxides express surface amphoteric character; however, it seems that surface basicity is more pronounced than surface acidity. The surface bacisity, which is mainly of the Brönsted type, has been found as dependent on the character of the group III metal. Red-ox properties were investigated for the In 2 O 3 −CeO 2 sample, the achieved degree of reduction being 34%. TPR/TPO experiments performed up to 830 °C irreversibly changed the morphology and the structure of the samples, leading to the crystallization of In 2 O 3 .