Hydrogen Adsorption And Sulfur Binding On Pd, Cu, Au And Their Alloys By Density Functional Theory

Palladium and Palladium alloys membranes have attracted wide attention in membranes reactor, separateness and purification of hydrogen and so on because of their excellent permeability, perm-selectivity, as well as chemical and thermal stabilities. Hydrogen is an important intermediate in many catalysis reactions and sulfur is a common poison for palladium-based hydrogenation catalysts. The investigation of hydrogen adsorption and sulfur binding on Pd, Cu, Au and their alloys is significant for surface science, expecially, for heterogeneous catalysis.The density functional theory calculations are presented on the adsorption of atoms on metal surfaces in the field of surface science. The thesis mainly contains two parts. One is hydrogen atom adsorption on Pd(111), Cu(111), Au(111) and their alloys surfaces, the other is sulfur atom adsorbs on Pd(111), Cu(111), Au(111) and their alloys surfaces.The adsorption of both hydrogen and sulfur on pure Pd (111), Cu (111) and Au (111) surfaces, as well as on PdM₃ (111), Pd₂M₂ (111) and PdM₃ (111) surfaces is investigated. The most favorable adsorption sites, binding energies and the relaxation during adsorption are obtained with coverage of 0.25. The Pd surface exhibits the strongest adsorption of both hydrogen and sulfur atoms. Cu is the next and Au has the weakest affinity with them. The binding energies of adsorption of hydrogen and sulfur on Pd-M alloys decrease with the increase of the concentration of metal M, except Pd₃Au, in which case, the adsorption of hydrogen on Pd₃Au (111) surface is even stronger than that on pure Pd, due to the larger lattice constant.According to the values of binding energy, it is found that the binding energies of both hydrogen and sulfur on Pd-Au decrease slower than that on Pd-Cu, when the concentration of Au as low as 0.25 mol/mol. However, they decrease quickly when the concentration of Au exceeds 0.5 mol/mol. Pd-Au alloy with 0.25～0.5 mol/mol Au is a promising candidate to resist sulfur and also with high performance in hydrogen permeation.