STRUCTURAL AND ACID-BASE PROPERTIES OF SUPPORTED EUROPIUM OXIDES

Microcalorimetric and infrared spectroscopy studies of ammonia and car bon dioxide adsorption were carried out to investigate the number, str ength, and type of acid/base sites of europium oxide supported on gamm a-Al2O3 and SiO2. X-ray diffraction, luminescence spectroscopy, and Mo ssbauer spectroscopy were used to characterize the structure, bonding, and valence of the europium atoms. Europium oxide neutralizes acid si tes on gamma-Al2O3, lowering the initial heat of ammonia adsorption fr om 155 to 120 kJ/mol. Both Lewis and Bronsted acid sites exist on Eu2O 3/Al2O3 samples, with Lewis acid sites in dominance. Europium oxide in creases the number and strength of base sites on gamma-Al2O3, with the initial heat of carbon dioxide adsorption increasing from 145 to 160 kJ/mol. Surface hydroxyl groups and oxygen anions are responsible for base sites on the Eu2O3/ Al2O3 samples. The addition of europium oxide to SiO2 increases the number and strength of acid sites, with the ini tial heat for ammonia adsorption increasing from 85 to 125 kJ/mol. Eur opium oxide on silica shows few basic sites. Luminescence spectra show that EU(3+) ions OCCUPY a range of dissimilar bonding sites on both s upports, particularly at low concentrations. At the higher concentrati ons, EU(3+) ions occupy more well-defined sites, having a weaker inter action with the support. The acid/base properties of these supported e uropium oxides can be related to the electronegativities of these samp les, with higher electronegativity enhancing acidic properties and sup pressing basic properties.