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 m² 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 H₂ takes place in the range 255°C < T < 300°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% O₂/He at 350°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 H₂ 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.