Structural and Acid/Base Properties of Supported Europium Oxides

Abstract

Microcalorimetric and infrared spectroscopy studies of ammonia and carbon dioxide adsorption were carried out to investigate the number, strength, and type of acid/base sites of europium oxide supported on [gamma]-Al[sub 2]O[sub 3] and SiO[sub 2]. X-ray diffraction, luminescence spectroscopy, and Mossbauer spectroscopy were used to characterize the structure, bonding, and valence of the europium atoms. Europium oxide neutralizes acid sites on [gamma]-Al[sub 2]O[sub 3], lowering the initial heat of ammonia adsorption from 155 to 120 kJ/mol. Both Lewis and Bronsted acid sites exist on Eu[sub 2]O[sub 3]/Al[sub 2]O[sub 3] samples, with Lewis acid sites in dominance. Europium oxide increases the number and strength of base sites on [gamma]-Al[sub 2]O[sub 3], 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 Eu[sub 2]O[sub 3]/[gamma]-Al[sub 2]O[sub 3] samples. The addition of europium oxide to SiO[sub 2] increases the number and strength of acid sites, with the initial heat for ammonia adsorption increasing from 85 to 125 kJ/mol. Europium oxide on silica shows few basic sites. Luminescence spectra show that Eu[sup 3+] ions occupy a range of dissimilar bonding sites on both supports. 31 refs., 13more » figs., 1 tab.« less