Theoretical Study Of Hydrogen Adsorption Properties On Pd Stepped Surfaces And Nanoparticle Facets

In the research domain of modern physics and chemistry, reaction between gas and transition metal is one of the most famous systems due to its importance in a variety of technological application, such as heterogeneous catalysis, oxidation of metal and organic synthesize. Consider research in microstructure is very important because it could help us to investigate these reactions in details. In present paper, modified analysis embedded-atom method (MAEAM) and MORSE potential are used to describe the interactions between Pd-Pd, H-H, and H-Pd. We investigate detailedly the adsorption properties of hydrogen on Pd (211), (311) and (533) stepped surfaces, adsorption geometries, binding energies and potential energy surface (PES) have been calculated. It is found that steps play an important role for adsorption properties of hydrogen atoms. The adsorption characters of metal surfaces with some steps are different comparing with low index surfaces. Moreover, hydrogen atoms tend to adsorb on four-fold hollow sites near precipitous steps. The lengthes of step has little affect on the most stable adsorption sites, however, the order of step and terrace give much infection of hydrogen adsorption properties. Finally, The adsorption properties of hydrogen on Pd nano-sized particle facets were obtained by taking into account the size effect and the coverage of hydrogen atoms. The properties of H-Pd systems with small size show significant changes compared to that of bulk-system's behavior. Adsorption energies of hydrogen near the boundary of every facet were bit little lower than that of the sites in the center. With the particle size growing shell-by-shell, most adsorption energies of these uniform adsorption sites upraise until the particle size reach 3.2nm, adsorption energies and bond lengths of hydrogen in the center adsorption sites approach to data of flat surfaces when particle size is bigger than 3.2nm. For 3.2nm particle, adsorption energy gap is about 0.6eV for (111) facet and 0.3eV for (100) facet as the coverage of H reach the coverage of 1.0 ML. H-Pd bond length reduces a little when coverage and particle size changes, these effects exhibit that bond length is less sensitive to particle size and coverage. We calculate the temperature effect of hydrogen adsorption, results show that adsorption energies increase linearly with the increasing of temperature, we also find two desorption phases of Pd(100) surface. Our data are in reasonable agreement with experimental and theoretical results.