Ru-Sn-B/TiO 2 catalysts for methyl oleate selective hydrogenation. Influence of the preparation method and the chlorine content

Abstract

Background: Fatty alcohols are produced commercially by selective hydrogenation of fattyacid esters using copper and chromium catalysts. To reduce drastic reaction conditions, Ru-Sn catalysts reduced with NaBH4 have been proposed. Chlorine negatively affects the selectivity and activity of this catalytic system. To get further information on why Cl influences the selectivity negatively, we studied the influence of the preparation method on titania-supported catalysts, which leads to catalysts with different chlorine contents.Results: The activity and selectivity were greatly affected by the chlorine content whichdepends on the metal impregnation method (coimpregnation in excess of solution orcoimpregnation by incipient wetness) and the support precalcination. Chlorine affects the Ru-Sn metal interaction modifying the activity and selectivity. Catalysts with high Ru-Sninteraction are more selective to oleyl alcohol. Catalyst prepared by coimpregnation methodexhibits bigger particles than by incipient wetness method, with agglomerated Ru3Sn7 cubicphase of 50 nm surrounded by amorphous Ru-Sn.Conclusion: High interaction between Ru and Sn is preferred because segregated Ru speciesare not selective for the formation of oleyl alcohol. The electronic state of Ru° is veryimportant because small variations in the electron density leads to a decrease in the adsorption of the hydrogen, or because Ru°-H species do not have the adequate binding energy to produce the necessary ?hydride form?. Ru electronic state is modified by the chlorine that surrounds it, decreasing its ability to adsorb hydrogen.