When 1% v/v solution of cinnamaldehyde/toluene was hydrogenated at 25 C and 47 psi hydrogen pressure over sol-gel Pd/SiO2 catalysts, a modification effect was observed. Sn and Ir were found to noticeably enhance the selectivity of Pd catalysts with respect to the hydrogenation of the C=O bond relative to the favored hydrogenation of the C=C bond. The produced cinnamyl alcohol, however, converts readily to phenylpropanol. On the other hand, Cu has caused a decrease in activity without any significant improvement on selectivity under the above conditions. The reaction kinetics were studied for the unmodified Pd catalysts, and the orders were determined to be first with respect to hydrogen, and zero with respect to cinnamaldehyde. The apparent activation energy was calculated and found to have a value of 30.1 kJ/mol. Also, the effects of metal loading and catalyst mass were studied. (C) 2002 Elsevier Science B.V. All rights reserved.