Basic properties of rare earth oxides Original Research Article

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 °C. No acidic sites were observed in the measurement of NH3 adsorbed on the REOs at 25 °C. CO2 was adsorbed on the REOs: CO2 desorption peaks were observed depending on the strength of the basic sites. Light REOs, such as La2O3, Pr6O11, Nd2O3, and Sm2O3, had surface basic sites from which CO2 desorbed at temperatures below 500 °C, as well as structural carbonate that decomposed above 500 °C. Heavy REOs, such as Dy2O3, Ho2O3, Y2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3, 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.