First principles study of N and H atoms adsorption and NH formation on Pd(111) and Pd3Ag(111) surfaces

The role of the presence of Ag atom in Pd3Ag(111) surface on the adsorption of N and H atoms and NH species was studied by using first principles calculations based on density functional theory (DFT). The adsorption energies of N and NH species are weakened by at least 0.50 eV when Ag atom is one of the nearest neighbors, in contrast to the case of H, in which the adsorption energies are weakened by at most 0.15 eV. Local density of states (LDOS) profiles show that for N and NH adsorption near the silver alloy atom, the derived anti-bonding states are shifted below the Fermi level and hence the adsorption energy is weakened on the alloyed surface. In the presence of adsorbed N, the adsorption energies of H on the nearby sites are also reduced. Nonetheless, this reductions in H adsorption energies on the most stable sites are lower in Pd3Ag(111) surface. NH formations with H moving across the Pd atom on both surfaces show comparable activation barriers but the barrier is increased by 0.2-0.3 eV when the formation happens across Ag atom.