FORMATION, CHARACTERIZATION, AND CATALYTIC ACTIVITY OF GADOLINIUM OXIDE - INFRARED SPECTROSCOPIC STUDIES

Gd2O3 was obtained as a final product of the thermal decomposition of Gd(CH3COO)(3).4H(2)O. The decomposition processes up to 800 degrees C were characterized by Td, DTA, XRD, and IR spectroscopy of the gas and solid phase products. Activation energies were determined nonisothermally for thermal events during decomposition. Gd(CH3COO)(3).4H(2)O is completely decomposed to Gd2O3 at 650 degrees C through two different intermediates: GdO(CH3COO) at 325 degrees C and Gd2O2CO3 (in two different crystalline phases) at 365 and 405 degrees C. Oxide samples obtained at 800 and 1000 degrees C were Subjected to texture analysis,pyridine adsorption, and qualitative and quantitative activity tests for the decomposition of 2-propanol vapor at 100-400 OC. The results revealed that (i) Gd2O3 at 800 degrees C has higher surface area (27 m(2)/g) and is mainly mesoporous in comparison to that of Gd2O3 at 1000 degrees C (12 m(2)/g), which is mainly-microporous in nature. (ii) Gd2O3 at 800 degrees C is a basic surface and contains two different Lewis acid sites. At greater than or equal to 100 OC, pyridine interacts with the surface, forming carboxylate and nitrite surface species, which decomposed at 300 degrees C, yielding a carbonate surface species. (iii) Gd2O3 catalyzes 2-propanol dehydrogenation (forming acetone) at greater than or equal to 150 degrees C and dehydration (forming propene) at greater than or equal to 250 degrees C. At greater than or equal to 350 degrees C, acetone was involved;in a secondary surface reaction, presumably with surface hydroxyl groups created from the water vapor (dehydration product), to give rise to CH4, CO2, and isobutene. Gd2O3 at 1000 degrees C shows more dehydrogenation activity than does the 800 degrees C material. 2-Propanol is irreversibly adsorbed at 25 degrees C on Gd2O3 in the form of coordinated molecules and two different types of 2-propoxide ions (terminal and bridge bonded).