The partial hydrogenation of benzene is an interesting chemical reaction mostly because of cyclohexene, a compound that can be part of the production chain of many other chemicals. In the present work, it was investigated the effects of additives in the reaction medium on the performance of Ru/Al2O3 and Ru/CeO2 catalysts for the partial hydrogenation of benzene in liquid phase. The Ru catalysts were prepared by incipient impregnation or wet impregnation, both from aqueous solution of the precursor RuCl3 center dot xH(2)O. The catalysts prepared by incipient impregnation were reduced at 573 K under H-2 flow, whereas formaldehyde was used to reduce the catalysts prepared by wet impregnation. The solids were characterized by potentiometric titration, N-2 physisorption, SEM, TEM, EDX, XPS and TPR. The catalytic performance in the liquid phase was evaluated using a slurry Parr reactor at 373 K and under 5 MPa of H-2 pressure. The additives studied were the following: ethylenediamine, ethyl acetate, n-methyl-2-pyrrolidone, monoethyleneglycol and monoethanolamine. The results indicate that the Ru/Al2O3 catalyst, prepared by wet impregnation, leads to the highest values of activity and selectivity. The yield of cyclohexene follows the order: monoethanolamine > monoethyleneglycol > n-methyl-2-pyrrolidone >> ethyl acetate > without additive >> ethylenediamine. (c) 2012 Elsevier B.V. All rights reserved.