The kinetics of liquid-phase selective hydrogenation of pyrolysis gasoline over a commercial egg-shell catalyst was investigated in a stirred semi-batch reactor in the absence of external transport limitations. Experimental observations showed that competitive hydrogenation between monoolefins and diolefins was noticeable, and that the reaction rates of diolefins were much faster than those of monoolefins. A Langmuir-Hinshelwood-type reaction mechanism was proposed for the reaction system, and then a rigorous diffusion-reaction mathematical model was developed. For the egg-shell catalyst particle, the diffusion and reaction of species were described separately in two distinct regions, i.e., the outer active region, where both diffusion and reaction occurred, and the inner inertia region, where only diffusion happened. The kinetic and adsorption parameters were estimated from the diffusion-reaction model with the experimental data. The model was able to describe the experimental observations very well. The simulation results showed that significant concentration gradients existed inside the egg-shell catalyst, which revealed that the influence of the internal diffusion resistances on the reaction kinetics was considerable. (C) 2009 Elsevier Ltd. All rights reserved.