Platinum is one of the most valuable catalysts that have been used in the catalytic fields of hydrogenation, fuel-cell technologies, and photocatalytic water splitting. In this work, the dissociative chemisorption of hydrogen in a molecular form on a Pt13H24 cluster with cuboctahedral symmetry (Oh), which has one center Pt atom and side 12 Pt atoms (each bonded by two hydrogen), is investigated by using first-principles density functional theory calculation. After computing geometry optimization on the Pt13H24 cluster, the equilibrium distances of PtPt and PtH are inspected. Two nonequilibrium modifications, for example, addition of electrons and heat treatment were applied on the cluster, with the aim to simulate the experimental reaction of hydrogen on the Pt13 H24 cluster. An ab initio molecular dynamics (MD) is simulated after the cluster is charged and heat treated at high temperature to compute the trajectory for the positions of all the atoms. The computation results reveal that H2 desorption is observed during the MD simulation, and higher temperature is beneficial to the H2 desorption. An elementary hydrogen evolution mechanism on the charged Pt cluster can be established as 2Hads+ + 2e− + Ptads→ [PtadsHadsHads] → H2↑ + Pt. A rate (fs−1) of hydrogen desorption from different cluster models is determined, together with the hydrogen dissociative activation energy as a function of total charge. © 2012 Wiley Periodicals, Inc.