Abstract
Abstract The hydrogenation of carbon monoxide to produce hydrocarbons (Fischer–Tropsch synthesis) has been studied over Ru/SiO2 catalysts to which alkali metals (Li, Na, K, and Cs) were added. The effects of alkalis were compared by varying the amounts added and by varying the support to Al2O3. By the alkali addition, the CO conversion and the selectivity to methane decreased but the propagation probability as well as the olefin/paraffin ratio increased. Among the alkali metals, Li least depressed the catalytic activity of Ru/SiO2, but was most effective for the suppression of methane formation. In contrast to a K-added catalyst, the infrared band of adsorbed carbon monoxide shifted only slightly upon Li addition, showing its small electronic effect. The results in electron microscopy and X-ray diffraction suggested that the Ru particle size remained almost unchanged upon Li addition, although the amounts of adsorbed carbon monoxide and hydrogen significantly decreased. This indicates that Ru particles were partially covered by a compound of Li. On the basis of these results, it was concluded that the suppression of methane formation by Li was due to a geometric or ensemble effect.
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