The liquid phase kinetics for the selective hydrogenation of mesityl oxide (MO) to methyl isobutyl ketone (MIBK) in acetone over a 0.52wt% Pd/Al2O3 catalyst was studied in a 300mL Parr autoclave operating in semibatch mode at 100 degrees C, initial MO concentrations ranging from 0.1 to 1.0 M and hydrogen partial pressures ranging from 1.50 to 4.23 MPa. The reaction was found to be first order in hydrogen partial pressure and a non-linear dependence on MO concentration was observed. An average MIBK selectivity of about 94.5% between 0.2 and 1.0 M initial MO concentration was obtained due to a competitive hydrogenation of acetone to 2-propanol. A mechanistic kinetic model was developed following the Langnmir-Hinshelwood approach from the assumptions that only diadsorbed MO participates in the hydrogenation reaction while MO adsorbed at a single site acts as an adsorbing inert, The addition of adsorbed hydrogen atoms is stepwise with the second addition of the adsorbed hydrogen atom being the rate-determining step. The proposed kinetic model was validated using initial rate data obtained from the kinetic experiments and showed the strongest statistical significance when compared to other models reported in the literature, suggesting that the proposed mechanism is reasonable. (c) 2005 Elsevier Ltd. All rights reserved.