Density Functional Theory Study of Ag Chemisorption on Hematite

C E ZUBIETA; LEANDRO FORTUNATO; PATRICIA BELELLI; RICARDO M. FERULLO

Santiago

Congreso; 10 th Triennial Congress of the World Association of Theoretical and Computational Chemists; 2014

Iron oxides are materials of technological importance in different areas like corrosion and catalysis. They are widely found in earth sediments, as well as in mineral deposits. A. Biabani et al. study the effect of impregnated Ag nanoparticles into Fe2O3 support in catalytic low temperature CO oxidation [1]. The iron oxides have an important function as adsorbent of organic and inorganic species, which makes them of great potential for industrial applications. In this work we evaluate the geometric and electronic structure of Ag nanoparticles from 1 to 5 atoms deposited on (0001) hematite surface, considering their different anchoring with O or Fe exposed atoms. The calculations were carried out in the framework of the Density Functional Theory (DFT) using the Vienna Ab-initio Simulation Package (VASP). For materials such as hematite, α-Fe2O3, where ?d? electrons are strongly correlated, an effective on-site repulsion term (U=6 eV) of a Coulombic-type to the LDA Hamiltonian was applied. The adsorption energies of Ag1 and Ag2 are -1.35 and -1.40 eV, respectively, while the values significantly increase between -2.65 and -2.72 eV for Ag3, Ag4 and Ag5. For the pentamer, Bader charges resulted to be positive for the Ag atoms which are directly linked to surface O ions (0.34e, 0.28e and 0.43e); of the other two Ag atoms, one is neutral and the other acquires a negative charge of -0.15e. Results indicate that Ag3, Ag4 and Ag5 nanoparticles are polarized, with the negative charge accumulated toward the external metal atoms and moving away from the metal/oxide interface, as it was observed for the cases of Au/FeOOH and for Ag/MgO [2]. This behavior can be the reason of the stronger interaction of the bigger Ag nanoparticles in comparison with the smaller ones (Ag1 and Ag2), where the polarization effects produce an electrostatic attraction with the surface oxygen ions.