Hydrogenation of citral over ruthenium-tin catalysts Original Research Article

Citral was chosen to probe the kinetic behavior of the hydrogenation of α,β-unsaturated aldehydes over HTR and LTR titania-supported Ru-Sn catalysts. The catalysts were prepared by coimpregnation with ethanolic solutions of RuCl3 and SnCl2 and characterized using temperature-programmed reduction (TPR). The reaction was studied in a liquid phase semi-batch reactor at 399 K and a hydrogen pressure of 5 MPa. The global activity for the citral hydrogenation of HTR Ru-Sn/TiO2 catalysts as well as the selectivity to the unsaturated alcohols of both LTR and HTR Ru-Sn/TiO2 increased with the Sn/Ru atomic ratio, reaching a maximum at a value of Sn/Ru∼0.2. This suggested a promotion of the CO bond hydrogenation by particular bimetallic Sn-Ru ensembles. Besides, while for Sn/Ru≤0.1 the support effect of titania dominated, for higher values of the atomic ratio the performance of the catalysts was controlled by the promoter effect of tin. A combined effect of the support titania with the promoter tin was clearly detected.