Theory Study Of H Adsorption On Pd And Pt Surfaces

The interaction of gaseous molecules with transition-metallic surfaces is very important to many technological processes such as oxidation, corrosion, heterogeneous catalysis and so on. Theoretical study on the atomistic level can not only help understand the interaction mechanism between the adsorbent and the metallic atoms, but also obtain the kinetic information of surface adsorption and diffusion. In the present paper, the embedded-atom method (EAM) many-body potentials are used to describe the interaction of H-H, Pt-Pt and Pd-Pd, the Morse potentials are used to describe the interaction between H and metal atoms.With those potentials, the adsorption and diffusion properties of hydrogen atom are calculated systematically on Pd and Pt low-index surface (100), (111) and (110). The calculation results show that on the low-index the stable sites exist at the ones with more coordinate atoms. The hydrogen atom prefers to be adsorbed at the 4-fold hollow site on the (100) surface, 3-fold Hf hollow site on the (111) surface, while the most favorable adsorption site on (110) surface is the 4-fold long bridge one. The 4-fold site H5 which locates on the step edge is the most preferable one for hydrogen atom on Pd (211) and Pt (211) surfaces. It's reported experimentally that the H/Pt (533) system has the similar result. On Pd (311) and Pt (311) surfaces, hydrogen atom gain the lowest adsorption energy on the 4-fold H4 site that locates on the step edge, there are two 3-fold adsorption sites Hf and Hh on the terrace surface, the adsorption energy of those are a little higher than that of H4; thus, we deduce that H4 is the first adsorption site to be occupied at low hydrogen exposure, and when hydrogen exposure is high, Hf and Hh will coexist with H4. The calculation results of H/Pd (311) are in reasonable agreement with the HREELS experiment results. According to our calculation results, the most adsorption sites on Pd (511) are two 4-fold hollow sites H1 and H2 on the (100) terrace surface, for the H/Pt (410) system, the 2-fold step edge site locates on the outmost and it gains the lowest binding energy, thus we believe that it will be the favorite site for hydrogen atom.We also calculate the adsorption properties of hydrogen atom on Palladium and Platinum nanoclusters, it's found that the adsorption energy of hydrogen on nanoclusters are lower than that of flat surfaces, the corresponding adsorption heights are also lower.