Ru-Sn-B/TiO2 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 fatty acid esters using copper-chromium catalysts. To reduce drastic reaction conditions, ruthenium-tin (Ru-Sn) catalysts reduced with sodium borohydride (NaBH4) have been proposed. Chlorine (Cl) negatively affects the selectivity and activity of this catalytic system. To get further information on why Cl influences the selectivity negatively, this study investigated the influence of the preparation method on titania (TiO2)-supported catalysts, which leads to catalysts with different Cl contents.RESULTS: The activity and selectivitywere greatly affected by the Cl content, which depends on themetal impregnation method (co-impregnation in excess of solution or co-impregnation by incipient wetness) and the support pre-calcination. Chlorine affects the Ru?Sn metal interaction, modifying the activity and selectivity. Catalysts with high Ru?Sn interaction are more selective to oleyl alcohol. Catalysts prepared by the co-impregnation method exhibit bigger particles than catalysts prepared by the incipient wetness method, with agglomerated Ru3Sn7 cubic phase of 50nm surrounded by amorphous Ru-Sn.CONCLUSION:High interaction betweenRuand Snispreferred because segregated Ru species arenot selective for the formation of oleyl alcohol. The electronic state of Ru0 is very important because small variations in the electron density lead to a decrease in the adsorption of hydrogen, or because Ru0-H species do not have the adequate binding energy to produce the necessary ?hydride form?. The Ru electronic state ismodified by the Cl that surrounds it, decreasing its ability to adsorb hydrogen.