Selective hydrogenation of citral toward unsaturated alcohols on PdSn catalysts supported on mesoporous silica

Abstract

The selective hydrogenation of citral to unsaturated alcohols was studied on x%Sn–Pd/CMI-1 catalysts (x in the range 0–3 wt%) synthesized by co-impregnation on an organized mesoporous silica of high specific surface area. The characteristics of the prepared catalysts were evaluated by chemical analysis, X-ray diffraction, nitrogen physisorption, transmission electron microscopy and temperature-programmed reduction, and from the activity for the model reaction of cyclohexane dehydrogenation. The existence of an interaction between Pd and Sn on the bimetallic catalysts was deduced, with the formation of a hexagonal Pd₃Sn₂ alloy. The catalytic performances were evaluated for the citral hydrogenation performed at 130 °C, under 76 bar hydrogen pressure, in liquid phase (isopropanol as solvent). The addition of Sn to Pd led to a decrease in the citral conversion accompanied by an increase in the selectivity to unsaturated alcohols, this phenomenon being explained by the decrease in the number of active Pd species on the surface of the catalysts and the presence of Pd₃Sn₂ alloy which activates the C=O bond of citral. A maximum value of 72% for the unsaturated alcohols selectivity was reached with the bimetallic 2%SnPd/CMI-1 catalyst with a citral conversion around 75% at the end of reaction time.

Graphical abstract