Influence of Mg and Ce addition to ruthenium based catalysts used in the selective hydrogenation of alpha,beta-unsaturated aldehydes

Ce and Mg were used as promoters in two series of Ru based catalysts suppor ted on alumina (Al2O3) and activated carbon (AC). The catalysts were charac terized by H-2 chemisorption and temperature-programmed reduction (TPR), an d studied in the crotonaldehyde (gas phase) and the citral (liquid phase) h ydrogenations. Addition of MgO and CeO2 decreased the catalytic activity in crotonaldehyde and citral hydrogenations. With regard to the selectivity t owards unsaturated alcohols. similar trends were observed for the two react ions. MgO did not influence the selectivity, but CeO2 increased the selecti vity to unsaturated alcohols, especially on carbon supported catalyst. Bulk CeO2 and Ce/AC catalyst showed low activity but very high selectivity (93 and 100%, respectively) to the unsaturated alcohols. Based on these results and the calorimetric experiments of CO adsorption it was suggested that de fect sites on the surface of the promoter are the active and highly selecti ve sites for unsaturated aldehydes due to their influence on the C=O bond a ctivation. (C) 2001 Elsevier Science B.V. All rights reserved.