The study concerns experimental and theoretical investigations of forced unsteady-state operations in comparison to the steady-state operation. Changes in the control variables influence the regime and the performance of a trickle-bed reactor. As an example for a periodically operated reactor, a determined forced unsteady-state technique was used in which the catalyst is contacted periodically with different liquid flow rates. Therefore the aims of the study were to look for such periodic operation conditions in which a periodical variation of the liquid stream leads to an improvement in reactor performance and to a mathematical model for the simulation and explanation of the observed effects. The hydrogenation of alpha-methylstyrene to cumene with surface-deposited palladium catalyst, C6H5C(CH3) = CH2 + H-2 --> C6H5CH(CH3)(2), was taken as, a model reaction. It will be shown that under liquid Bow interruption the time-average conversion is higher than under steady state operating conditions. The reason for such a result will be offered with a dynamic heterogeneous mathematical model.