Kinetics and mass transfer for supported ionic liquid catalysts (SILCAs) were studied for complex catalytic hydrogenations of unsaturated aldehydes. The system can be characterized as a gas−liquid−liquid−solid system, where gaseous hydrogen and an unsaturated aldehyde, citral, diffuse from molecular solvent to a thin layer of ionic liquid containing the catalytically active species, metallic palladium nanoparticles. The intrinsic kinetics was determined at 353−423 K (80−150 °C) and pressures ranging from 10 to 50 bar. A kinetic model was proposed that was able to predict the experimental concentration data successfully. In order to obtain more understanding about the importance of mass-transfer and diffusion limitations for these kinds of processes, a number of models describing the concentration profiles of the reactants in the catalysts were developed. The developed reaction-diffusion models revealed important insight into the potential limiting phenomena for this type of reaction systems.