Density Functional Theory Investigation on the Dissociation and Adsorption Processes of N2 on Pd(111) and Pd3Ag(111) Surfaces

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The dissociation and adsorption processes of N2 on Pd(111) and Pd3Ag(111) surfaces are investigated using density functional theory (DFT). The dissociation of N2 molecule on Pd(111) is most efficient if its center-of-mass (CM) is fixed on top of Pd atom while allowing the N atoms to dissociate on the hollow sites [hcp hollow--top--fcc hollow (h--t--f) configuration] with an activation barrier of 5.94 eV. In Pd3Ag(111), N2 also prefers dissociating along the h--t--f configuration but the activation barrier is higher, 6.01 eV, and is attributed to the presence of Ag atom. The local density of states (LDOS) of the d-orbital of surface atoms shows that the presence of Ag had reduced the density of states in the region around the Fermi level which causes the higher activation barrier observed towards N2. Charge difference distribution also shows that there is a greater gain of charges of N2 from the surface atoms of Pd(111) surface which induces repulsion and resulting to the dissociation to individual N atoms. This further explains the easier dissociation and adsorption of N2 on Pd(111) as compared to Pd3Ag(111) surface.
2011-04-25