FTIR studies of CO adsorption on Al2O3- and SiO2-supported Ru catalysts.

The adsorption of CO on Al2O3- and SiO2-supported Ru catalysts has been investigated through FTIR spectroscopy. Deconvolution of the spectra obtained reveals the presence of 11 distinct bands in the case of Ru/Al2O3 and 10 bands in the case of Ru/SiO2, which were assigned to different carbonyl species adsorbed on reduced as well as partially oxidized Ru sites. Although most of these bands on both supports are similar, they exhibit substantial differences in terms of stability. In general, the analogous CO species on Ru/Al2O3 are adsorbed stronger than those on Ru/SiO2, with the most stable species observed being a dicarbonyl adsorbed on metallic Ru (i.e., Ru0(CO)2). Following sintering of the Ru, the ratio of multicarbonyl to monocarbonyl adsorption is reduced substantially because of the lack of isolated sites or small Ru clusters that enable the formation of multicarbonyl species via oxidative disruption. Finally, in the presence of O2, the main features observed correspond to monocarbonyl, dicarbonyl, and tricarbonyl species adsorbed on partially oxidized Run+. The intensities of all bands decrease drastically at temperatures above 210 degrees C because of the onset of CO oxidation, which results in substantially reduced surface coverage.