Abstract
The catalytic performance in CO hydrogenation over Ru, RuCo, and Co carbonyl cluster-derived catalysts has been investigated, and it was found that the activity and selectivity for oxygenated products on a series of RuCo/SiO 2 catalysts are much higher than those on Ru 3/SiO 2 and Co 4/SiO 2 catalysts. The mechanism of oxygenated formation on these RuCo/SiO 2 catalysts has been investigated by in situ infrared, mass, and X-ray photoelectron spectroscopies. The IR spectra of reaction of CO + H 2 with RuCO/SiO 2 catalysts show a band appearing at 1584 cm −1 which has a good relationship to the activity and selectivity for oxygenates in CO hydrogenation. The adsorption of CO on reduced RuCo/SiO 2 catalysts prepared from RuCo bimetallic carbonyl clusters exhibits a band at 1680 cm −1 shifting to 1640 cm −1 with 13CO, which is assigned to the C- and O-ended CO chemisorbed on RuCo/SiO 2 catalysts. The chemical trapping of 1584 cm −1 adspecies shows that the 1584 cm −1 species reacts with H 2 to produce CH 4 and CH 3OH, and the addition of D 2 to 1584 cm −1 species results in the formation of CHD 3 and CHD 2OD. With the increase of reaction time and temperature, we find the bands at 1555 and 1440–1470 cm −1, while the 1584 cm −1 band gradually decreases on RuCo/SiO 2 catalysts. XPS spectra demonstrate that the Ru and Co sites on the surface of RuCo/SiO 2 catalysts are in the chemical state of Ru 0 and Co 2+, respectively, and it is suggested that the bimetallic Ru 0-Co 2+ sites are very active centers for the formation of oxygenates in CO hydrogenation. Considering the product distribution at various reaction temperatures, it is suggested that the 1584 and 1555 cm −1 species possibly assigned to formyl and acyl are precursors to methanol and higher C 2-oxygenates, respectively, and the 1584 cm −1 species can be converted into 1555 cm −1 species by reaction with an alkyl group.
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