The hydrogenation of 2,4-dinitro-toluene on a Pd/C catalyst was employed as a test reaction to simulate, by the time-dependent Monte Carlo method, processes occurring in a three-phase batch reactor working at isobar and isotherm conditions. A new time-dependent Monte Carlo algorithm, including an original subroutine useful to reduce the time of the simulations, was developed and implemented in Fortran language. The paper describes the flowchart of the code together with the main technical details and the involved physical and chemical models. Computational characteristics, such as the simulated time to reach surface steady state conditions and the effects of the catalyst morphology are presented. Correlations between simulated and experimental data are summarized and current mechanistic hypotheses criticized.