A one-dimensional reactor and catalyst pellet scale flow-transport-reaction model utilizing the multicomponent Stefan-Maxwell formulation for inter- and intraphase transport is developed to simulate unsteady state operation in trickle bed reactors. The governing equations and method of solution are discussed. Results are presented for a model reaction system (hydrogenation of alpha-methylstyrene) under gas reactant limiting conditions, for liquid flow modulation as a test case of unsteady state operation. Model simulations predict that periodic liquid flow modulation can alter the supply of liquid and gaseous reactants to the catalyst and result in reactor performance enhancement above that achieved in steady state operation. The effects of key modulation parameters such as the total cycle period, cycle split, and liquid mass velocity are simulated, and model predictions are found to be in agreement with experimentally observed trends in the literature.