The hydrogenation kinetics of some natural sugars to corresponding sugar alcohols in aqueous solutions was investigated on Ru/C catalysts in a pressurized slurry reactor. The kinetic data were well described by a Langmuir-Hinshelwood model assuming that the hydrogenation step on the catalyst surface is rate determining. The density, viscosity and hydrogen solubility of the reacting liquid were measured. This information was used to estimate the liquid-phase diffusion coefficients, which were utilized in a reaction-diffusion-catalyst deactivation model for porous catalyst layers. The model indicated that diffusional resistance becomes severe for rather small catalyst particles and the model described the movement of the reactive front inside the particle during the reaction. The simulation results indicate that structured reactors would provide a better approach than the conventional fixed bed technology, if continuous operation is desired.