Palladium supported catalysts for the selective hydrogenation of sunflower oil

Selective hydrogenation of ethyl esters of traditional sunflower oil (SOEE) was carried out at low temperature (40degreesC) in ethanol as solvent in the presence of supported palladium catalysts. In the range of studied dispersions (12-55%), the SOEE hydrogenation reaction is insensitive to the size of the palladium particles deposited on silica, but the largest metallic particles enhance the C18:1 cis-trans isomerization. The use of various oxide supports (alpha-Al2O3, gamma(c)-Al2O3, TiO2, MgO, ZnO, CeO2, CeZrO2) to deposit palladium does not allow to improve the selectivity of the reaction toward the cis C18:1 compared to Pd/SiO2 catalysts. On the other hand, the modification of palladium by lead, introduced by surface redox reaction (catalytic reduction), promotes the selectivity in cis C18:1. In addition, this technique of preparation involves a moderate decrease of the palladium activity compared to a traditional method of successive impregnations. The introduction of amines in the reaction medium modifies the hydrogenating properties of the Pd/SiO2 catalyst. According to the quantity and the nature of the added amine (aliphatic with linear or ramified chain and cyclic compounds), the catalytic activity can either be unchanged or inhibited. These evolutions result from a promoter electronic effect generated by the presence of the amine and from a poison geometric effect related to the adsorption of this nitrogen-containing compound on the palladium surface. Whatever the nature of the amine, it induces an increase of the selectivity toward the cis C18:1. (C) 2004 Elsevier B.V. All rights reserved.