Preparation and characterization of the catalytically active forms of rare earth oxides

Abstract

Catalytically active forms of the rare earth oxides Ln 2O 3(Ln = La, Sm, Eu, Dy, Ho, and Yb), Pr 6O 11, and CeO 2 have been prepared. The dehydration behavior of the precursors of these oxides has been studied by XRD, TG, DTA, TPD-MS, IR, and adsorption-desorption isotherms of N 2 at −196°C. Thermal analyses show that in most cases the dehydration takes place through an intermediate oxyhydroxide LnO (OH) that decomposes to the respective oxide at around 400°C. Strongly held difficult to remove carbonates were present on the surface, e.g., for Yb 2O 3 it was necessary raise the outgassing temperature to 700°C to achieve carbonate decomposition. At temperatures around 500°C these oxides are well crystallized and have moderate specific surface areas (10–40 m 2g −1). As a representative of the series, a detailed study of the dehydration and surface decarbonation of Yb 2O 3 was carried out by means of TPD-MS and infrared spectroscopy.