Basic properties of rare earth oxides

l Basic properties of rare earth oxides (REOs) calcined at different temperatures were investigated. During the calcination process, the crystal structures of Lu, Yb, Tm, Er, Y, Ho, and Dy oxides transformed from monoclinic to cubic with increasing calcination temperature, while those of Sc Ce La Pr Nd Sm Eu Gd, and Tb oxides showed no change at temperatures below 1100 degrees C No acidic sites were observed in the. measurement of NH(3) adsorbed on the REOs at 25 degrees C. CO(2) was adsorbed on the REOs: CO(2) desorption peaks were observed depending on the strength of the basic sites. Light REOs, such as La(2)O(3) Pr(6)O(11), Nd(2)O(3), and Sm(2)O(3), had surface basic sites from which CO(2) desorbed at temperatures below 500 degrees C, as well as structural carbonate that decomposed above 500 degrees C. Heavy REOs, such as Dy(2)O(3), Ho(2)O(3), Y(2)O(3), Er(2)O(3), Tm(2)O(3), Yb(2)O(3), and Lu(2)O(3), had weak basic sites. The basic properties of REOs are attributed to lanthanide contraction: the strength of the basic sites decreases with decreasing radius of the rare earth cation. (C) 2008 Elsevier B.V. All rights reserved.