The First Principle Study On NO Interaction With Ir(111)

Nitric oxide (NO) is widely known as one of the most harmful materials on Earth,it harms not only the environment but also human health, people have been trying to reduce the content of NO molecules in the air for years. It had been widely studied in the field of surface science on the interaction of NO with transition metal surfaces. Studies have shown that, for NO or the mixed environment of O2and NO, Ir plays an important role for NO reducing as a catalyst. However, till now studies for the interaction of NO and Ir(111) surface is not complete, and there is no theoretical investigation for the interaction of NO dimer and Ir(111) surface.In this work, we report the first principle study on NO interaction with Ir(lll) surface. The atomic and electronic structures and other properties for NO molecule and NO dimer on Ir(111) are investigated systematically and the mechanism of NO interaction with Ir(111) is revealed.For NO/Ir(111) system, p(2×2) and p(1×1) adsorption structures are adopted and the coverage of ΘNO=0.25,0.5,0.75,1.0monolayer(ML) are considered. A seven layers slab model is used. It is demonstrated that the model describes NO/Ir(111) system better than a four layers model, especially for adsorption energy. Our calculations show that the weakest adsorption site is in Fcc-hollow site and the adsorption energies for other adsorption sites are similar at a coverage of ΘNO=0.25ML. The most favorable adsorption structures for ΘNO=0.5ML and ΘNO=0.75ML are Top+Hcp sites and Top+Fcc+Hcp sites respectively. For ΘNO=0.5ML, the adsorption energy of Top+Fcc adsorption structure is0.18eV higher than that of Fcc+Hcp adsorption structure. At a coverage of ΘNO=1.0ML, a top site is the most stable adsorption site. The adsorbed NO molecules are basically perpendicular to the substrate surface in different sites. And we find that the change of the bond length of NO (dN-O) upon adsorption in top sites is negligible. However, dN-O is elongated for NO in the Hollow sites and bridge site.For NO dimer/Ir(111) system, p(2×2) adsorption structure is adopted. Our calculations elucidate that there are three stable adsorption models for NO dimer on Ir(111). NO dimer is adsorbed on two hollow sites and a bridge site through one of N atoms with the N-N bond tilted away from surface normal about40°and its flat is perpendicular to the substrate surface. The N-N bond of adsorption NO dimer is shorter while its N-N bond near surface is elongated which may lead to NO dimer dissociated into O atom and N2O. The interaction between NO dimer and the substrate leads to N-N bond broken and NO dimer dissociated into two NO moleculars if the N-N bond of NO dimer is parallel to the substrate surface.