FTIR Studies of CO Adsorption on Al₂O₃- and SiO₂-Supported Ru Catalysts

Abstract

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.

Operando Spectroscopic Evidence of the Induced Effect of Residual Species in the Reaction Intermediates during CO2 Hydrogenation over Ruthenium Nanoparticles

“…This is consistent with our results in which the formation of methane is associated to the formation of adsorbed CO species. Regarding the bands of the ruthenium carbonyl species in more detail (Figure b), the stretching vibration modes are typical of dicarbonyl CO species on Ru 0 sites with relative large average particle size . When the temperature is increased, a displacement of the wavenumber from 1992 to 1962 cm −1 is obvious, which could be associated to the gradual reduction of the dipole coupling interaction among close CO species.…”

Insight into the nature of active redox sites in Ru-containing hydroxyapatite by DRIFT spectroscopy

“…Although the infrared spectra were rather complex due to changes in the oxidation state of Ru induced by CO adsorption at room temperature and the concomitant evolution of CO 2 , interpretation of the spectra is supported by the abundant information available in the literature on various supported Ru-containing catalysts [20,[40][41][42]44,51] in all catalysts. The oxidation state of the Ru in the Ru n+ -oxide phase should be 3+, because the Ru + and Ru 2+ oxides are unstable, and the presence of Ru 4+ in the as-prepared material could be excluded.…”

“…Similarly, a set of three bands at 2144 (HF 1 ), 2082 (HF 2 ), and 2047 (LF) cm −1 was found on CO adsorption on reduced Ru/SiO 2 and the set changed into bands at 2136, 2080, and 2032 cm −1 on the partially oxidized sample [51]. Similarly, two different tricarbonyl species absorbed at 2140-2080 cm −1 and 2130-2070 cm −1 on Ru/Al 2 O 3 [44]. Therefore, in analogy to the literature data, we tentatively assign the HF 1 and HF 2 bands observed in Fig.…”

Structure sensitivity in the ruthenium nanoparticle catalyzed aqueous-phase Fischer–Tropsch reaction

“…Fig. 3 shows the experimental and fitted Fourier transformed k 3 -weighted EXAFS and χ(k)·k 3 functions for four Ru nanoparticle catalysts of increasing size (fit parameters in 32 Therefore, the shift is best explained by stronger adsorption of CO. It is also seen that a shoulder appears at 2050 cm −1 with decreasing particle size, which is due to Ru-dicarbonyl species.…”