RESUMO
Two series of manganese-based oxygen storage materials, BaLnMn(2)O(5+δ) (Ln = Y, Gd, Nd, and La) and Ca(2)Al(1-x)GaxMnO(5+δ) (0 ≤x≤ 1), were synthesized and characterized to clarify cationic substitution effects on the oxygen intake/release behaviors of these materials. The thermogravimetric data revealed that the isovalent substitutions neighboring the active sites for oxygen intake/release are very effective. For BaLnMn(2)O(5+δ), fully-reduced δ≈ 0 products with larger Ln ions showed oxygen intake starting at lower temperatures in flowing O(2) gas, resulting in a systematic relationship between the onset temperature and the ionic radius of Ln(3+). Furthermore, the δ vs. P(O(2)) plots at 700 °C indicated a systematic trend: the larger the ionic size of Ln(3+) is, the larger oxygen contents the Ln-products exhibit. For Ca(2)Al(1-x)GaxMnO(5+δ), on the other hand, the temperature-induced oxygen intake/release characteristics appeared to be influenced by Ga-for-Al substitution, where the onset temperatures of oxygen release (upon heating) and oxygen intake (upon cooling) are decreased with the increasing Ga content (x).
