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 acidhase sites of europium oxide supported on y-Alz03 and SiO2. 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 y-AlzOs, lowering the initial heat of ammonia adsorption from 155 to 120 kJ/mol. Both Lewis and Bransted acid sites exist on Eu203/A1203 samples, with Lewis acid sites in dominance. Europium oxide increases the number and strength of base sites on y-AlzO3, 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 Eu203/ A1203 samples. The addition of europium oxide to Si02 increases the number and strength of acid sites, with the initial heat for ammonia adsorption increasing from 85 to 125 kl/mol. Europium oxide on silica shows few basic sites. Luminescence spectra show that Eu3+ ions occupy a range of dissimilar bonding sites on both supports, particularly at low concentrations. At the higher concentrations, Eu3+ ions occupy more welldefined sites, having a weaker interaction with the support. The acidhase properties of these supported europium oxides can be related to the electronegativities of these samples, with higher electronegativity enhancing acidic properties and suppressing basic properties.

Characterization of Mordenite-Supported Pd, Pt, and Ir Determined by CO Adsorption Microcalorimetry and the Dehydrogenation Reaction of C3 Alkanes

“…However, adsorption studies using the microcalorimetry of chemisorption on Pt catalyst systems are very few, in spite on the fact that this kind of investigation with appropriate probe molecules can lead to an understanding of the nature of gas-solid interactions and provide insight into the properties of the adsorbent surface [12][13][14]. Recently, studies on catalyst properties with calorimetry have increased, probably because of the rapid development of the calorimetry technique [12][13][14][15][16][17][18][19][20][21][22][23]. These studies mainly concentrate on the adsorption of NH 3 , C 6 H 5 , and CO 2 on an acid-base catalyst [12][13][14][15].…”

NMR and Mössbauer Study of Al2O3–Eu2O3

“…It has been observed that Eu 2 O 3 is stable towards H 2 reduction below 1473 K, however in some works it has been reported [2] it can be reduced to Eu +2 in H 2 at 673-773 K when supported on g-Al 2 O 3 . However, according to our Mössbauer spectra at 40 mm/s, no evidence of Eu +2 or Eu 0 was obtained.…”

“…Rare earth oxides (REO) have been studied as catalytic promoters due to the generation of reactive sites, improvement of thermal stability and promoting the generation of basic sites [1,2]. Alumina-based mixed oxides have been widely studied with different types of elements (Si, Zr, Ti, etc.)…”

“…Alumina-based mixed oxides have been widely studied with different types of elements (Si, Zr, Ti, etc.) forming several solid solutions at certain concentrations; in the case of europium-promoted oxides prepared by impregnation method, Eu 2 O 3 neutralizes acid sites on Al 2 O 3 due to presence of hydroxyl groups and oxygen anion acting as base sites on the Eu 2 O 3 / Al 2 O 3 supports [2]. These properties make appropriate these supports for oxidation reactions, hydrogenation-dehydrogenation of hydrocarbons, dehydration and dehydrogenation of alcohols, olefin isomerizations, paraffin cracking, and NO x elimination [3].…”

“…The latter is a unique technique for investigating structural and dynamics aspects of solids on atomic scale [2,5,6]. …”