Pd-based sorbents have been considered as potential promising sorbents for Hg capture because of their regeneration and high activity over long times. First-principles calculations based on the density functional theory and the periodic slab models were used to gain a fundamental understanding of mercury oxidation mechanism on Pd(100) surface. The adsorptions of Hg-0, HCl, HgCl, and HgCl2 on the Pd(100) surface were studied. The electronic structural changes of surface system before and after adsorption were investigated to better understand the surface reactivity. The energy profile of the oxidation reaction and the structures of related transition states and intermediates were examined. The results show that Hg-0 is strongly adsorbed on hollow site of the surface with a chemisorption mechanism. HCl is chemisorbed on Pd(100) surface by side-on orientation, and its dissociation occurs with a low energy barrier, and this process is exothermic. The adsorptions of HgCl and HgCl2 are mainly chemisorption. The mercury oxidation reaction on Pd(100) surface occurs through a Langmuir-Hinshelwood mechanism in which Hg adsorbs and then reacts with HCl that has previously been adsorbed and dissociated on the Pd(100) surface. (C) 2013 Elsevier B.V. All rights reserved.