CHARACTERIZATION OF SUPPORTED RUTHENIUM CATALYSTS DERIVED FROM REACTION OF RU-3(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 s tudied by temperature-programmed reduction, temperature-programmed oxi dation, X-ray photoelectron spectroscopy, Fourier transform infrared s pectroscopy, 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 p articles. 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 oxida tion conditions. Hydrogen adsorption-desorption experiments showed tha t dispersion of Ru metal was increased by the reduction-oxidation-redu ction cycle for La and Yb but not the other oxides. Facile reduction o f Ce, Pr, and Tb oxides was attributed to the dissociative chemisorpti on of H-2 on Ru metal nanocrystallites, and spillover of atomic specie s to the support. Reducible oxides such as CeO2 and Pr6O11 have been f ound to be effective support for the production of lower alkene from s ynthesis gas. (C) 1998 Academic Press.