Catalytic Properties of Rare Earth Oxides

Abstract The rare earth (lanthanide) oxides, although constituting a closely related group of compounds, exhibit a rich variety of characteristic behaviors and solid-state properties, including several features that make them interesting subjects for Catalytic studies. Abundances and costs of these materials parallel those of the rare earth metals themselves, and range from common and fairly inexpensive (e.g. La2O3 and CeO2) to scarce and relatively costly (e.g., Tm2O3 and Lu2O3). All are quite refractory and nonvolatile, having melting points in excess of 2000° C, and some display a complex array of nonstoichiometric compositions. Most of the oxides are paramagnetic, with stable cationic electron configurations containing as many as seven unpaired 4f-electrons, and, as escheated from their periodic location, all are quite strongly basic. However, although the catalytic and surface properties of alkali, alkaline-earth, and other basic oxides have been extensively studied and documented 1, equivalent information about the series of basic rare earth oxides has only begun accumulating during the last 10 to 15 years. The increased attention that is currently being focused on these substances has paralleled both a developing realization of some of their unique catalytic properties and their increasing availabilities in purities high enough to warrant fundamental investigations.