The solvent effect in the hydrogenation of citral over Ir and Ir-Fe/TiO2 catalysis

Abstract

The solvent effect in the citral hydrogenation over iridium catalysts has been studied. The catalysts used in this research were, the monometallic Ir/ TiO2 reduced at low or high temperature (LT y HT) and the bimetallic Ir-Fe/TiO2 (LT y HT) catalysts. As solvent n-heptane, an equimolar mixture n-heptane-1-propanol and 1-propanol were used. The reactions were carried out at a hydrogen pressure of 8.27 bar and at 363 K. In the LT catalyst, the catalytic activity increases upon the addition of Fe3+. This positive effect was obtained keeping constant the selectivity to the unsaturated alcohol, being 100% selective to the products obtained by hydrogenation of the C=O bond. In the HT catalysts, both the addition of Fe and the presence of TiOx moieties generated by the strong metal support interaction (SMSI) effect, lead to an increase of surface acidity. In LT and HT catalysts, an increase in the polarity of the solvent increases the catalytic activity, however the reaction pathway is modified by the presence of acid sites which in polar solvents allow the formation of acetals, mainly in the HT catalysts.