Hydrogenation of citral over ruthenium-tin catalysts

Citral was chosen to probe the kinetic behavior of the hydrogenation of alpha,beta-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 similar to 0.2. This suggested a promotion of the CO bond hydrogenation by particular bimetallic Sn-Ru ensembles. Besides, while for Sn/Ru less than or equal to 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. (C) 2002 Elsevier Science B.V. All rights reserved.