Characterization of supported ruthenium catalysts derived from reaction of Ru3(CO)12 with rare earth oxides

The surface chemistry of supported ruthenium on high surface area (>50 m(2) g(-1)) rare earth oxides (La, Ce, Pr, Tb, Ho, and Yb) has been studied by temperature-programmed reduction, temperature-programmed oxidation, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and hydrogen chemisorption. Reduction of carbonyl ligands and surface carbonate by H-2 takes place in the range 255C < T < 300 degrees C, with evolution of CH4 and formation of nanometer-sized Ru particles. The Ru nanocrystallites were readily oxidized to RuO2, which strongly interacted with the support. Prolonged heating (6 h) in 1% O-2/He at 350 degrees C led to loss of free RuO2 from the support, but shorter term heating resulted in rearrangement of RuO2 on the support, as revealed by alteration in the reduction profile with varying oxidation conditions. Hydrogen adsorption-desorption experiments showed that dispersion of Ru metal was increased by the reduction-oxidation-reduction cycle for La and Yb but not the other oxides. Facile reduction of Ce, Pr, and Tb oxides was attributed to the dissociative chemisorption of H-2 on Ru metal nanocrystallites, and spillover of atomic species to the support. Reducible oxides such as CeO2 and Pr6O11 have been found to be effective support for the production of lower alkene from synthesis gas. (C) 1998 Academic Press.