Abstract
Infrared spectra are reported of Ru/SiO2 at 473, 503 or 553 K and exposed to CO/H2 mixtures at 3, 15, or 30 bar and CO:H2 ratios of 14:1, 1:2, and 1:14. A band due to linearly adsorbed CO, which shifted to lower wavenumbers with increasing temperature and was both shifted and weakened with increasing time, was influenced by the dissociative adsorption of CO, structural reorganisation and sintering of Ru, and the build-up of surface hydrocarbon in situ during reaction. Both linear RuCO and a μ-bonded Ru carbonyl were precursors of active intermediates in reactions leading to methane and higher hydrocarbon products. Three types of surface hydrocarbon were present in situ during reaction: these were ethoxy groups on the silica support, probably derived from reaction of ethene with silanol groups. methylene chains (with methyl end groups) possibly bonded to Ru via a single CH2 end group, and CH2 groups specifically bonded to Ru. The formation of methylene-containing adsorbed species was favoured by increasing pressure, but the effect of temperature depended on the total reaction pressure. Increasing the CO:H2 ratio favoured CC chain growth. The infrared results support the proposal that hydrocarbonaceous species may be further hydrogenated on the Ru surface to give methane.
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