We have studied hydrogen dissociation on a CO-precovered Ru(0001) surface, by means of six-dimensional (6D) quasi-classical and quantum dynamics. The 6D potential energy surface has been built by applying a modified Shepard interpolation method to a set of density functional theory (DFT) data, for a coverage of 1/3 monolayer CO. We compared our theoretical results to the experimental ones obtained by Ueta et al. [ChemPhysChem, 2008, 9, 2372]. In order to do so, we have simulated the supersonic molecular beam used in the experiments by taking into account the energy distribution and rovibrational states population in the molecular beam. We find that both the energy and rovibrational states distributions of the molecular beam influence the reactivity, with the largest effect being caused by the energy distribution. However, a significant discrepancy between theory and experiment persists. We argue that this discrepancy could be due to the RPBE functional used in the DFT calculations and/or the neglect of CO-motion in the calculations.